The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing(HIP) was modified through uniaxial compression experiments. The influence of cylindric...The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing(HIP) was modified through uniaxial compression experiments. The influence of cylindrical capsule characteristics on FGH4096M superalloy powder compact deformation and densification behavior during HIP was investigated through simulations and experiments. Results revealed the simulation shrinkage prediction fitted well with the experimental shrinkage including a maximum shrinkage error of 1.5%. It was shown that the axial shrinkage was 1.7% higher than radial shrinkage for a cylindrical capsule with the size of ∮50 mm × 100 mm due to the force arm difference along the axial and radial direction of the capsule. The stress deviated from the isostatic state in the capsule led to the uneven shrinkage and non-uniform densification of the powder compact. The ratio of the maximum radial displacement to axial displacement increased from0.47 to 0.75 with the capsule thickness increasing from 2 to 4 mm. The pressure transmission is related to the capsule thickness, the capsule material performance, and physical parameters in the HIP process.展开更多
Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. Howev...Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. However, there are few reports about the microstructure characteristics on the strengthening and toughening mechanisms of powder hot isostatic pressed(HIPed) titanium alloys. Therefore, TA15powder was prepared into alloy by HIP approach, which was used to explore the microstructure characteristics at different HIP temperatures and the corresponding tensile properties and fracture toughness. Results show that the fabricated alloy has a “basket-like structure” when the HIP temperature is below 950℃, consisting of lath clusters and surrounding small equiaxed grains belts. When the HIP temperature is higher than 950℃, the microstructure gradually transforms into the Widmanstatten structure, accompanied by a significant increase in grain size. The tensile strength and elongation are reduced from 948 MPa and 17.3% for the 910℃ specimen to 861 MPa and 10% for the 970℃ specimen.The corresponding tensile fracture mode changes from transcrystalline plastic fracture to mixed fracture including intercrystalline cleavage.The fracture toughness of the specimens increases from 82.64 MPa·m^(1/2)for the 910℃ specimen to 140.18 MPa·m^(1/2)for the 970℃ specimen.Specimens below 950℃ tend to form holes due to the prior particle boundaries(PPBs), which is not conducive to toughening. Specimens above 950℃ have high fracture toughness due to the crack deflection, crack branching, and shear plastic deformation of the Widmanstatten structure. This study provides a valid reference for the development of powder HIPed titanium alloy.展开更多
Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace.In order to obtain optimal processing parameters,the effects of hot ...Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace.In order to obtain optimal processing parameters,the effects of hot isostatic pressing parameters on defects,composition uniformity,microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail.Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects,especially,the internal defects are substantially eliminated when the temperature exceeds 920℃or the pressure exceeds 125 MPa.The higher temperature and pressure can improve the microstructure uniformity.Besides,the higher pressure can promote the composition uniformity.With the temperature increases from 880℃to 960℃,α-laths are coarsened.But with increasing pressure,the grain size of prior-βphase,the widths ofα-laths andα-colony are reduced.The tensile strength of Ti60 alloy is 949 MPa,yield strength is 827 MPa,and the elongation is 11%when the hot isostatic pressing parameters are 960℃/125 MPa/2 h,which exhibits the best match between the strength and plasticity.展开更多
The influence of different hot isostatic pressing regimes on microstructure,phase constitution,microhardness,tensile properties and deformability of TC4 alloy fabricated by selective laser melting(SLM)technology was s...The influence of different hot isostatic pressing regimes on microstructure,phase constitution,microhardness,tensile properties and deformability of TC4 alloy fabricated by selective laser melting(SLM)technology was studied.The results show that the microstructure of SLM TC4 alloy is composed of acicular martensiteα’phase,and the sample exhibits high microhardness and strength,but low plasticity.After hot isostatic pressing,acicular martensiteα’phase transforms intoα+βphase,and with the increase of hot isostatic pressing temperature and duration,αphase with coarse lath is gradually refined,and the proportion ofαphase is gradually reduced.Because of the change of phase constitution in SLM TC4 alloy after hot isostatic pressing,the grain refinement strengthening is weakened,the density of dislocation is reduced,so that both microhardness and tensile strength are decreased by around 20%,the elongation is increased by more than about 70%,even over 100%,compared with as-deposited TC4 alloy.When the hot isostatic pressing regime is 940°C/3 h/150 MPa,the tensile strength and the elongation achieve optimal match,which are about890 MPa and around 14.0%in both directions.The fracture mechanism of alloy after 940 oC/3 h/150 MPa HIP is dultile fracture.Hot isostatic pressing causes concave deformation of SLM TC4 alloy thin-walled frames,and the deformation degree increases with the increase of temperature.展开更多
The roles of hot isostatic pressing (HIP) temperatures (490 ℃/100 MPa/2 h,510 ℃/100 MPa/2 h,530 ℃/100 MPa/2 h) in the microstructure and properties of AlSi7Cu2Mg alloy step castings with three types wall thicknesse...The roles of hot isostatic pressing (HIP) temperatures (490 ℃/100 MPa/2 h,510 ℃/100 MPa/2 h,530 ℃/100 MPa/2 h) in the microstructure and properties of AlSi7Cu2Mg alloy step castings with three types wall thicknesses were studied.The experimental results show that HIP at 490 ℃ could effectively eliminate the internal closed porosity of the castings with a wall thickness of ≤40 mm,but for heavy castings (70 mm),even HIP at 530 ℃,a few loose defects remained inside the castings.Two types of incipient eutectics containing Al5Mg8Si6Cu2 and Al2Cu were observed in the samples that HIP at 530 ℃,which was responsible for the decrease of the tensile strength of the castings within the medium wall thickness (40 mm) compared with that HIP at 490 ℃.HIP could greatly reduce the difference of the tensile strength values of castings with wall thicknesses 17 mm and 70 mm from 117.93 MPa (without HIP) to 25.7 MPa (with HIP at 530 ℃).展开更多
The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing tests.The X-ray micro computed tomography ...The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing tests.The X-ray micro computed tomography was used to record the morphology changes before and after hot isostatic pressing.The two-dimensional geometry obtained by the microCT scan was used in simulation to study the evolution of the real shrinkage cavity during hot isostatic pressing.Shrinkage cavities,shrinkage porosity and small gas pores can be effectively eliminated under proper HIP conditions.The two-dimensional morphology in the simulation results agrees well with the experimental results.This study reveals that plastic deformation,creep and diffusion are the main mechanisms of cavity closure during hot isostatic pressing.In addition,the simplified elliptical pores with aspect ratios at different positions were used to replace the real pores to further study the factors affecting the position of dimples after HIP by simulation.It is found that the position of the dimples mainly depends on the aspect ratio of the elliptical pore and the distance between the pore surface and the external surface of the geometric model.展开更多
The high-temperature, high-pressure hot isostatic pressing technology was used for depositing hard coatings on Ti(C, N)-based cermets. The rnicrostructure and properties of the sample were investigated using optical...The high-temperature, high-pressure hot isostatic pressing technology was used for depositing hard coatings on Ti(C, N)-based cermets. The rnicrostructure and properties of the sample were investigated using optical microscopy, scan- ning electron microscopy, X-ray diffraction, electron probe microanalysis, and microhardness tester. The results showed that the rich titanium and nitrogen in surface zone were induced by the heat treatment. The high nitrogen activity of the surface region was the driving force for outward transport of titanium and inward transport of tungsten in the cobalt binder. The toughness and hardness were improved and a hardness gradient was formed. It is the high-temperature, high-pressure N2 that enables closure of holes, thereby alleviating defects and prolonging tool life.展开更多
The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples...The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.展开更多
The effects of temperature and pressure on density, microstructure and mechanical properties of powder compacts during hot isostatic pressing(HIPping) were investigated. Optimized HIPping parameters of temperature r...The effects of temperature and pressure on density, microstructure and mechanical properties of powder compacts during hot isostatic pressing(HIPping) were investigated. Optimized HIPping parameters of temperature range from 900 to 940℃, pressure over 100 MPa and holding time of 3 h, were obtained. Tensile properties after different heat treatments show that both the geometry of samples and cooling rate have a significant influence on mechanical properties. Finite element method was used to predict the temperature field distribution during HIPped sample cooling, and the experimental results are in agreement with simulation prediction. The interaction of HIPping parameters was analyzed based on the response surface methodology(RSM) in this study.展开更多
In this work, hot isostatic pressing (HIPing) technique was used to densify the Ti2AINb pre-alloyed powder. The influence of HIPing loading route parameters (temperature and rates of heating and pressurizing) on m...In this work, hot isostatic pressing (HIPing) technique was used to densify the Ti2AINb pre-alloyed powder. The influence of HIPing loading route parameters (temperature and rates of heating and pressurizing) on microstructure and properties of PM Ti2AINb alloys was studied. The results showed that HIPing loading route parameters affected the densification process and mechanical properties (especially high temper- ature rupture lifetime) of PM Ti2AINb alloys in the present work. A finite element method (FEM) model for predicting the final densification was developed and was used to optimize the HIPing procedure.展开更多
The ultra-high strength steel AerMetl00 was fabricated .by laser melting deposition (LMD) process. The effect of hot isostatic pressing (HIP) on high-cycle fatigue properties of the LMD AerMet100 steel was investi...The ultra-high strength steel AerMetl00 was fabricated .by laser melting deposition (LMD) process. The effect of hot isostatic pressing (HIP) on high-cycle fatigue properties of the LMD AerMet100 steel was investigated, and the influence of defects on fatigue behavior was discussed. Results showed that the LMD AerMetl00 steel had fine directionally solidified cellular dendrite structure and coarse columnar prior austenite grains. Metallurgical de fects such as gas pore and lack-of-fusion porosity were produced during the laser deposition process. After HIP treat- ment, the number and size of metallurgical defects had remarkably decreased. Moreover, high-cycle fatigue proper ties of the alloys after HIP treatment were superior to the as-deposited alloys.展开更多
Prior to the application of AM components for critical applications,it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties...Prior to the application of AM components for critical applications,it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts.In this study,efforts were made to achieve an in-depth understanding of the effect of post-fabrication Solution Heat Treatment(SHT)and Hot Isostatic Pressing(HIP)on the microstructure and mechanical properties of Hastelloy X parts built by electron beam powder bed fusion(PBF-EB)process.The effects of SHT and HIP on porosity,microstructure,texture and mechanical properties have been investigated and compared with that of as-built PBF-EB Hastelloy X.Post-fabrication HIP treatment led to a significant reduction in the porosity content,whereas no notable difference in porosity was observed between SHT and as-built parts.There was no evidence of any recrystallization occurring following the post-fabrication treatments as elongated columnar grain structures observed within as-built part were found to be maintained even after SHT and HIP process alongside the strong<100>crystallographic texture.Emphasis was laid upon understanding the influence of SHT and HIP on mechanical properties through stress-strain curves and work-hardening behaviour.展开更多
Hot isostatic pressing (HIP) with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy (Mgl) turbocharger blade to explore the healing process of casting pores...Hot isostatic pressing (HIP) with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy (Mgl) turbocharger blade to explore the healing process of casting pores generated during investment casting. Optical micrograph and scanning electron naicroscopy (SEM) observations indicate that eutectic pores are the main cast defects in the as-cast blade before HIP. These pores normally locate at the solidification front of γ/γ' eutectic with a size of a few micrometers to a few tens of micrometers. After HIP for 4 h, most of the pores were closed. Based on phase characteristics, these pores were healed by the formation of γ matrix with finer and irregular-shaped γ' precipitates. Healing interface can be easily distinguished by SEM. Line scan by using energy dispersive X-ray spectroscopy (EDS) reveals a much higher Ti and Al concentration in the healing interface. It is proposed that solute diffusion toward the casting pores during HIP results in the formation of γ, and the much higher concentration of γ'-forming elements Al and Ti near the healing interface contributes to the precipitation of γ' in the healed region in the succeeding cooling process after HIP.展开更多
The microstructural evolution of casting porosities and creep-induced cavities for a damaged nickel-based superalloy under different hot isostatic pressing (HIP) conditions was investigated in order to understand th...The microstructural evolution of casting porosities and creep-induced cavities for a damaged nickel-based superalloy under different hot isostatic pressing (HIP) conditions was investigated in order to understand the effects of HIP parameters on the healing behavior of micropores. A number of small-sized creep cavities formed during long-term service and large-sized porosities formed during the casting process were observed. These microdefects were partially healed after treated at high temperature of 1100 ℃ combined with 150 MPa pressure for 2 h, together with the formation of the so- called concentrically oriented γ rafting structure. When HIP temperature was increased to 1150 and 1175 ℃, both the amount and the size of the microdefects were decreased. The concentrically oriented γ rafting around creep cavities became more remarkable, and the primary γ denuded zone was also formed between the raft structure and the cavity. Energy-dispersive X-ray spectroscopy analysis revealed that the γ matrix solute atoms diffused toward the cavity under the concentration gradient, whereas the γ-forming elements diffused in a negative direction. When increasing HIP temperature up to 1200 ℃, the micropores were hardly observed, indicating that both casting porosities and creep-induced cavities had almost been healed. Meanwhile, theγ rafting structure disappeared since HIP temperature was beyond theγ solvus temperature. It is revealed by the experimental results that the atomic diffusion could mainly dominate the healing process of micropores.展开更多
This work reported the Ar-induced porosity in powder metallurgy Ti-5 Al-2.5 Sn alloy prepared by hot isostatic pressing(HIPing).The obtained microstructures of powder compacts were studied through optical and scanning...This work reported the Ar-induced porosity in powder metallurgy Ti-5 Al-2.5 Sn alloy prepared by hot isostatic pressing(HIPing).The obtained microstructures of powder compacts were studied through optical and scanning electron microscopes,X-ray tomography,and the mechanical properties evaluated through tensile and impact tests.The results showed that the Ar-induced porosity is related to the hollow powder with gas bubble and the Ar leakage of sealed container during the powder densification.The hollow powder with gas bubble shows no obvious effects on mechanical properties of as-HIPed powder compacts.The Ar content decreases with the increasing shrinkage of encapsulated powder.0.7%Ar-induced porosity degrades the impact toughness,but no reductions of tensile properties were obtained.Ar content test is an effective method to detect the powder compacts with Ar concentration.展开更多
Observation of dislocation configurations was conducted for aged and compressive deformed (Ni64A136) FeMoB alloy after hot isostatic pressing (HIP). It isshown that short and straight parallel dislocations are present...Observation of dislocation configurations was conducted for aged and compressive deformed (Ni64A136) FeMoB alloy after hot isostatic pressing (HIP). It isshown that short and straight parallel dislocations are present in the matrix of NiAI alloy.Long and tortuous dislocations and superdislocations appear in the 1%-deformed specimen. As the compressive strain increases to 2. 6%, high-densities dislocations appear inand between the deformation bands. The dislocations become tangled up in the specimencompressed to a strain of 6. 2 %.展开更多
To increase the adhesion strength between the coating and the substrate, sintered Ti(C,N)-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isosta...To increase the adhesion strength between the coating and the substrate, sintered Ti(C,N)-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isostatic pressing (HIPhag) treatment was performed at 1000℃ using nitrogen pressure up to 110 MPa. The mechanical properties of cermets after a coating process and subsequent HIPing treatment have been evaluated with respect to the hardness, the residual stress, and the coating adhesion. The results show that atter the HIPing process, there was a higher increase ha critical load ha the TiN-coated cermets with lower surface roughness compared with those with higher surface roughness. In all cases, the residual stress was found to be compressive. The effects of substrate surface roughness and posttreatment on the adhesion strength of the coatings were thus investigated. It was also fotmd that the HIPing posttreatment process is well suited for hacreasing the adhesion strength between the coating and the substrate.展开更多
Diffusion behavior of Nb in elemental powder metallurgy high Nb containing TiAl alloys was investigated. The results show that Nb element dissolves into the matrix by diffusion. Pore nests are formed in situ after Nb ...Diffusion behavior of Nb in elemental powder metallurgy high Nb containing TiAl alloys was investigated. The results show that Nb element dissolves into the matrix by diffusion. Pore nests are formed in situ after Nb diffusion. With the increase in hot pressing temperature, the diffusion of Nb will be more sufficient, and the microstructure is more homogeneous. Nb element diffuses completely at 1400℃. Meanwhile, compression deformation and agglomeration phenomena of pores are observed in some pore nests. Hot isostatic pressing (HIP) treatment can only efficiently decrease but not eliminate porosity completely.展开更多
Mechanical alloying (MA), a solid-state powder processing method, is a 'far from equilibrium' synthesis technique which allows development of novel crystal structures and microstructures, leading to enhanced p...Mechanical alloying (MA), a solid-state powder processing method, is a 'far from equilibrium' synthesis technique which allows development of novel crystal structures and microstructures, leading to enhanced physical and mechanical properties. The ability to synthesize a variety of alloy phases including supersaturated solid solutions, nanocrystalline structures, amorphous phases and intermetallic compounds themselves is discussed. No extension of solubility using MA has been observed in the intermetallics studied. Nanostructured grains were observed in all compositions. Long time milling generally resulted in amorphous phase formation in large part because of the increase in grain boundary energy/mole with reduced grain size; good agreement with the Miedema model for amorphization was obtained in the Al-Fe system. Generally an anneal was required to form the intermetallic after MA; however,intermetallics with a large negative enthalpy of formation were detected in the MA condition. A study of the hot isostatic pressing of γ-TiAl powders produced by MA demonstrated that full density can be achieved at least 400℃ below the normal temperature required for conventional powder, that is 725℃ or below. Nanometered sized grains (≤100nm)were observed after HIP'ing up to 850℃.展开更多
The present work reports the effect of thermal induced porosity(TIP)on the high-cycle fatigue(HCF)and very high-cycle fatigue(VHCF)behaviors of hot-isostatic-pressed(HIPed)Ti-6Al-4V alloy from gasatomized powder.The r...The present work reports the effect of thermal induced porosity(TIP)on the high-cycle fatigue(HCF)and very high-cycle fatigue(VHCF)behaviors of hot-isostatic-pressed(HIPed)Ti-6Al-4V alloy from gasatomized powder.The results show that the residual pores in the as-HIPed powder compacts present no obvious effect on the HCF life.The regrowth of the residual pores can be observed after solution heat treatment.The pore location ranks the most harmful for the fatigue life compared with the other initiating defects.The maximum stress intensity factors were calculated.The plastic zone size of fine granular area(FGA)is much less than the characteristic size of the microstructure,and the crucial size of the internal pores in this study is about 40μm.The failure types of fatigue specimens in the VHCF regime were classified,and the competition of different failure types was described based on the modified Poisson distribution.展开更多
基金financially supported by Guangdong Province Key Field R&D Program, China (No. 2019B01 0935001)the National Nature Science Foundation of China (No. 51905192)the Fundamental Research Funds for the Central Universities (No. FRT-TP-20-006A2)
文摘The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing(HIP) was modified through uniaxial compression experiments. The influence of cylindrical capsule characteristics on FGH4096M superalloy powder compact deformation and densification behavior during HIP was investigated through simulations and experiments. Results revealed the simulation shrinkage prediction fitted well with the experimental shrinkage including a maximum shrinkage error of 1.5%. It was shown that the axial shrinkage was 1.7% higher than radial shrinkage for a cylindrical capsule with the size of ∮50 mm × 100 mm due to the force arm difference along the axial and radial direction of the capsule. The stress deviated from the isostatic state in the capsule led to the uneven shrinkage and non-uniform densification of the powder compact. The ratio of the maximum radial displacement to axial displacement increased from0.47 to 0.75 with the capsule thickness increasing from 2 to 4 mm. The pressure transmission is related to the capsule thickness, the capsule material performance, and physical parameters in the HIP process.
基金financially supported by the National Natural Science Foundation of China (Nos. 51874037 and 51922004)the Beijing Natural Science Foundation (No. 2212035)+1 种基金the Fundamental Research Funds for the Central Universities (No. FRF-TP-19005C1Z)the National Defense Basic Research Project (No. JCKY2017213004)。
文摘Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. However, there are few reports about the microstructure characteristics on the strengthening and toughening mechanisms of powder hot isostatic pressed(HIPed) titanium alloys. Therefore, TA15powder was prepared into alloy by HIP approach, which was used to explore the microstructure characteristics at different HIP temperatures and the corresponding tensile properties and fracture toughness. Results show that the fabricated alloy has a “basket-like structure” when the HIP temperature is below 950℃, consisting of lath clusters and surrounding small equiaxed grains belts. When the HIP temperature is higher than 950℃, the microstructure gradually transforms into the Widmanstatten structure, accompanied by a significant increase in grain size. The tensile strength and elongation are reduced from 948 MPa and 17.3% for the 910℃ specimen to 861 MPa and 10% for the 970℃ specimen.The corresponding tensile fracture mode changes from transcrystalline plastic fracture to mixed fracture including intercrystalline cleavage.The fracture toughness of the specimens increases from 82.64 MPa·m^(1/2)for the 910℃ specimen to 140.18 MPa·m^(1/2)for the 970℃ specimen.Specimens below 950℃ tend to form holes due to the prior particle boundaries(PPBs), which is not conducive to toughening. Specimens above 950℃ have high fracture toughness due to the crack deflection, crack branching, and shear plastic deformation of the Widmanstatten structure. This study provides a valid reference for the development of powder HIPed titanium alloy.
基金financially supported by the National Key Research and Development Program of China(Grant No.2020YFB2008300)。
文摘Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace.In order to obtain optimal processing parameters,the effects of hot isostatic pressing parameters on defects,composition uniformity,microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail.Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects,especially,the internal defects are substantially eliminated when the temperature exceeds 920℃or the pressure exceeds 125 MPa.The higher temperature and pressure can improve the microstructure uniformity.Besides,the higher pressure can promote the composition uniformity.With the temperature increases from 880℃to 960℃,α-laths are coarsened.But with increasing pressure,the grain size of prior-βphase,the widths ofα-laths andα-colony are reduced.The tensile strength of Ti60 alloy is 949 MPa,yield strength is 827 MPa,and the elongation is 11%when the hot isostatic pressing parameters are 960℃/125 MPa/2 h,which exhibits the best match between the strength and plasticity.
文摘The influence of different hot isostatic pressing regimes on microstructure,phase constitution,microhardness,tensile properties and deformability of TC4 alloy fabricated by selective laser melting(SLM)technology was studied.The results show that the microstructure of SLM TC4 alloy is composed of acicular martensiteα’phase,and the sample exhibits high microhardness and strength,but low plasticity.After hot isostatic pressing,acicular martensiteα’phase transforms intoα+βphase,and with the increase of hot isostatic pressing temperature and duration,αphase with coarse lath is gradually refined,and the proportion ofαphase is gradually reduced.Because of the change of phase constitution in SLM TC4 alloy after hot isostatic pressing,the grain refinement strengthening is weakened,the density of dislocation is reduced,so that both microhardness and tensile strength are decreased by around 20%,the elongation is increased by more than about 70%,even over 100%,compared with as-deposited TC4 alloy.When the hot isostatic pressing regime is 940°C/3 h/150 MPa,the tensile strength and the elongation achieve optimal match,which are about890 MPa and around 14.0%in both directions.The fracture mechanism of alloy after 940 oC/3 h/150 MPa HIP is dultile fracture.Hot isostatic pressing causes concave deformation of SLM TC4 alloy thin-walled frames,and the deformation degree increases with the increase of temperature.
基金Funded by the Natural Science Foundation of Shanxi Province,China(No.201801D121108)the Project by Zhaoqing Xijiang Innovation and Entrepreneurship Team Project Funding of China(No.2017A0109004)。
文摘The roles of hot isostatic pressing (HIP) temperatures (490 ℃/100 MPa/2 h,510 ℃/100 MPa/2 h,530 ℃/100 MPa/2 h) in the microstructure and properties of AlSi7Cu2Mg alloy step castings with three types wall thicknesses were studied.The experimental results show that HIP at 490 ℃ could effectively eliminate the internal closed porosity of the castings with a wall thickness of ≤40 mm,but for heavy castings (70 mm),even HIP at 530 ℃,a few loose defects remained inside the castings.Two types of incipient eutectics containing Al5Mg8Si6Cu2 and Al2Cu were observed in the samples that HIP at 530 ℃,which was responsible for the decrease of the tensile strength of the castings within the medium wall thickness (40 mm) compared with that HIP at 490 ℃.HIP could greatly reduce the difference of the tensile strength values of castings with wall thicknesses 17 mm and 70 mm from 117.93 MPa (without HIP) to 25.7 MPa (with HIP at 530 ℃).
基金financially supportedby the National Key Research and Development Program of China(No.2020YFB1710100)the State Key Laboratory of Special Rare Metal Materials(Contract No.SKL2018K004)+1 种基金the Northwest Rare Metal Materials Research Institute Ningxia Co.,Ltd.,the National Natural Science Foundation of China(Grant No.51475181 and 51775205)the AECC Beijing Institute of Aeronautical Materials。
文摘The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing tests.The X-ray micro computed tomography was used to record the morphology changes before and after hot isostatic pressing.The two-dimensional geometry obtained by the microCT scan was used in simulation to study the evolution of the real shrinkage cavity during hot isostatic pressing.Shrinkage cavities,shrinkage porosity and small gas pores can be effectively eliminated under proper HIP conditions.The two-dimensional morphology in the simulation results agrees well with the experimental results.This study reveals that plastic deformation,creep and diffusion are the main mechanisms of cavity closure during hot isostatic pressing.In addition,the simplified elliptical pores with aspect ratios at different positions were used to replace the real pores to further study the factors affecting the position of dimples after HIP by simulation.It is found that the position of the dimples mainly depends on the aspect ratio of the elliptical pore and the distance between the pore surface and the external surface of the geometric model.
基金This work was financially supported by the Natural Science Foundation of Hubei Province (No. 2003ABA092) and the Natural Science Foundation of China (No.50074014).
文摘The high-temperature, high-pressure hot isostatic pressing technology was used for depositing hard coatings on Ti(C, N)-based cermets. The rnicrostructure and properties of the sample were investigated using optical microscopy, scan- ning electron microscopy, X-ray diffraction, electron probe microanalysis, and microhardness tester. The results showed that the rich titanium and nitrogen in surface zone were induced by the heat treatment. The high nitrogen activity of the surface region was the driving force for outward transport of titanium and inward transport of tungsten in the cobalt binder. The toughness and hardness were improved and a hardness gradient was formed. It is the high-temperature, high-pressure N2 that enables closure of holes, thereby alleviating defects and prolonging tool life.
基金financial support of the National Natural Science Foundation of China(Nos.52130110 and U22A20189)the Research Fund of the State Key Laboratory of Solidification Processing(No.2023-TS-10)。
文摘The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.
文摘The effects of temperature and pressure on density, microstructure and mechanical properties of powder compacts during hot isostatic pressing(HIPping) were investigated. Optimized HIPping parameters of temperature range from 900 to 940℃, pressure over 100 MPa and holding time of 3 h, were obtained. Tensile properties after different heat treatments show that both the geometry of samples and cooling rate have a significant influence on mechanical properties. Finite element method was used to predict the temperature field distribution during HIPped sample cooling, and the experimental results are in agreement with simulation prediction. The interaction of HIPping parameters was analyzed based on the response surface methodology(RSM) in this study.
文摘In this work, hot isostatic pressing (HIPing) technique was used to densify the Ti2AINb pre-alloyed powder. The influence of HIPing loading route parameters (temperature and rates of heating and pressurizing) on microstructure and properties of PM Ti2AINb alloys was studied. The results showed that HIPing loading route parameters affected the densification process and mechanical properties (especially high temper- ature rupture lifetime) of PM Ti2AINb alloys in the present work. A finite element method (FEM) model for predicting the final densification was developed and was used to optimize the HIPing procedure.
基金Sponsored by State Key Development Program for Basic Research of China(2011CB606305)Cheung Kong Scholars Innovation Research Team Program of Ministry of Education of China(IRT0805)
文摘The ultra-high strength steel AerMetl00 was fabricated .by laser melting deposition (LMD) process. The effect of hot isostatic pressing (HIP) on high-cycle fatigue properties of the LMD AerMet100 steel was investigated, and the influence of defects on fatigue behavior was discussed. Results showed that the LMD AerMetl00 steel had fine directionally solidified cellular dendrite structure and coarse columnar prior austenite grains. Metallurgical de fects such as gas pore and lack-of-fusion porosity were produced during the laser deposition process. After HIP treat- ment, the number and size of metallurgical defects had remarkably decreased. Moreover, high-cycle fatigue proper ties of the alloys after HIP treatment were superior to the as-deposited alloys.
文摘Prior to the application of AM components for critical applications,it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts.In this study,efforts were made to achieve an in-depth understanding of the effect of post-fabrication Solution Heat Treatment(SHT)and Hot Isostatic Pressing(HIP)on the microstructure and mechanical properties of Hastelloy X parts built by electron beam powder bed fusion(PBF-EB)process.The effects of SHT and HIP on porosity,microstructure,texture and mechanical properties have been investigated and compared with that of as-built PBF-EB Hastelloy X.Post-fabrication HIP treatment led to a significant reduction in the porosity content,whereas no notable difference in porosity was observed between SHT and as-built parts.There was no evidence of any recrystallization occurring following the post-fabrication treatments as elongated columnar grain structures observed within as-built part were found to be maintained even after SHT and HIP process alongside the strong<100>crystallographic texture.Emphasis was laid upon understanding the influence of SHT and HIP on mechanical properties through stress-strain curves and work-hardening behaviour.
基金financial support from the Ministry of Science and Technology of the People’s Republic of China(No.2012CB932201)the National Natural Science Foundation of China(No.51231006)+1 种基金the International Cooperation Program funded by National Natural Science Foundation of China(No.51261130091)the Key Research Program of Chinese Academy of Sciences(No.KGZD-EW-T06)
文摘Hot isostatic pressing (HIP) with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy (Mgl) turbocharger blade to explore the healing process of casting pores generated during investment casting. Optical micrograph and scanning electron naicroscopy (SEM) observations indicate that eutectic pores are the main cast defects in the as-cast blade before HIP. These pores normally locate at the solidification front of γ/γ' eutectic with a size of a few micrometers to a few tens of micrometers. After HIP for 4 h, most of the pores were closed. Based on phase characteristics, these pores were healed by the formation of γ matrix with finer and irregular-shaped γ' precipitates. Healing interface can be easily distinguished by SEM. Line scan by using energy dispersive X-ray spectroscopy (EDS) reveals a much higher Ti and Al concentration in the healing interface. It is proposed that solute diffusion toward the casting pores during HIP results in the formation of γ, and the much higher concentration of γ'-forming elements Al and Ti near the healing interface contributes to the precipitation of γ' in the healed region in the succeeding cooling process after HIP.
基金financially supported by the University–Industry cooperation project sponsored by Aviation Industry Corporation of China(No.cxy2010BH06)the National Natural Science Foundation of China(No.51301001)
文摘The microstructural evolution of casting porosities and creep-induced cavities for a damaged nickel-based superalloy under different hot isostatic pressing (HIP) conditions was investigated in order to understand the effects of HIP parameters on the healing behavior of micropores. A number of small-sized creep cavities formed during long-term service and large-sized porosities formed during the casting process were observed. These microdefects were partially healed after treated at high temperature of 1100 ℃ combined with 150 MPa pressure for 2 h, together with the formation of the so- called concentrically oriented γ rafting structure. When HIP temperature was increased to 1150 and 1175 ℃, both the amount and the size of the microdefects were decreased. The concentrically oriented γ rafting around creep cavities became more remarkable, and the primary γ denuded zone was also formed between the raft structure and the cavity. Energy-dispersive X-ray spectroscopy analysis revealed that the γ matrix solute atoms diffused toward the cavity under the concentration gradient, whereas the γ-forming elements diffused in a negative direction. When increasing HIP temperature up to 1200 ℃, the micropores were hardly observed, indicating that both casting porosities and creep-induced cavities had almost been healed. Meanwhile, theγ rafting structure disappeared since HIP temperature was beyond theγ solvus temperature. It is revealed by the experimental results that the atomic diffusion could mainly dominate the healing process of micropores.
基金the Natural Science Foundation of Shanxi Province,China(No.201901D211085)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(STIP)。
文摘This work reported the Ar-induced porosity in powder metallurgy Ti-5 Al-2.5 Sn alloy prepared by hot isostatic pressing(HIPing).The obtained microstructures of powder compacts were studied through optical and scanning electron microscopes,X-ray tomography,and the mechanical properties evaluated through tensile and impact tests.The results showed that the Ar-induced porosity is related to the hollow powder with gas bubble and the Ar leakage of sealed container during the powder densification.The hollow powder with gas bubble shows no obvious effects on mechanical properties of as-HIPed powder compacts.The Ar content decreases with the increasing shrinkage of encapsulated powder.0.7%Ar-induced porosity degrades the impact toughness,but no reductions of tensile properties were obtained.Ar content test is an effective method to detect the powder compacts with Ar concentration.
文摘Observation of dislocation configurations was conducted for aged and compressive deformed (Ni64A136) FeMoB alloy after hot isostatic pressing (HIP). It isshown that short and straight parallel dislocations are present in the matrix of NiAI alloy.Long and tortuous dislocations and superdislocations appear in the 1%-deformed specimen. As the compressive strain increases to 2. 6%, high-densities dislocations appear inand between the deformation bands. The dislocations become tangled up in the specimencompressed to a strain of 6. 2 %.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50074017).
文摘To increase the adhesion strength between the coating and the substrate, sintered Ti(C,N)-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isostatic pressing (HIPhag) treatment was performed at 1000℃ using nitrogen pressure up to 110 MPa. The mechanical properties of cermets after a coating process and subsequent HIPing treatment have been evaluated with respect to the hardness, the residual stress, and the coating adhesion. The results show that atter the HIPing process, there was a higher increase ha critical load ha the TiN-coated cermets with lower surface roughness compared with those with higher surface roughness. In all cases, the residual stress was found to be compressive. The effects of substrate surface roughness and posttreatment on the adhesion strength of the coatings were thus investigated. It was also fotmd that the HIPing posttreatment process is well suited for hacreasing the adhesion strength between the coating and the substrate.
基金This work is financially supported by the Key Grant Project of Chinese Ministry of Education (No. 704008) and by the Program from New Century Excellent Talents in University, China (No. NCET-04-01017).
文摘Diffusion behavior of Nb in elemental powder metallurgy high Nb containing TiAl alloys was investigated. The results show that Nb element dissolves into the matrix by diffusion. Pore nests are formed in situ after Nb diffusion. With the increase in hot pressing temperature, the diffusion of Nb will be more sufficient, and the microstructure is more homogeneous. Nb element diffuses completely at 1400℃. Meanwhile, compression deformation and agglomeration phenomena of pores are observed in some pore nests. Hot isostatic pressing (HIP) treatment can only efficiently decrease but not eliminate porosity completely.
文摘Mechanical alloying (MA), a solid-state powder processing method, is a 'far from equilibrium' synthesis technique which allows development of novel crystal structures and microstructures, leading to enhanced physical and mechanical properties. The ability to synthesize a variety of alloy phases including supersaturated solid solutions, nanocrystalline structures, amorphous phases and intermetallic compounds themselves is discussed. No extension of solubility using MA has been observed in the intermetallics studied. Nanostructured grains were observed in all compositions. Long time milling generally resulted in amorphous phase formation in large part because of the increase in grain boundary energy/mole with reduced grain size; good agreement with the Miedema model for amorphization was obtained in the Al-Fe system. Generally an anneal was required to form the intermetallic after MA; however,intermetallics with a large negative enthalpy of formation were detected in the MA condition. A study of the hot isostatic pressing of γ-TiAl powders produced by MA demonstrated that full density can be achieved at least 400℃ below the normal temperature required for conventional powder, that is 725℃ or below. Nanometered sized grains (≤100nm)were observed after HIP'ing up to 850℃.
基金financially supported by the Natural Science Foundation of Shanxi Province,China(No.201901D211085)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(STIP)
文摘The present work reports the effect of thermal induced porosity(TIP)on the high-cycle fatigue(HCF)and very high-cycle fatigue(VHCF)behaviors of hot-isostatic-pressed(HIPed)Ti-6Al-4V alloy from gasatomized powder.The results show that the residual pores in the as-HIPed powder compacts present no obvious effect on the HCF life.The regrowth of the residual pores can be observed after solution heat treatment.The pore location ranks the most harmful for the fatigue life compared with the other initiating defects.The maximum stress intensity factors were calculated.The plastic zone size of fine granular area(FGA)is much less than the characteristic size of the microstructure,and the crucial size of the internal pores in this study is about 40μm.The failure types of fatigue specimens in the VHCF regime were classified,and the competition of different failure types was described based on the modified Poisson distribution.