Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

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.

Synergistic effect of Zr and Mo on precipitation and high-temperature properties of Al-Si-Cu-Mg alloys

This study focuses on finding a solution to the sharp decline in mechanical properties of Al-Si-Cu-Mg alloys due to rapid coarsening of traditional intermediate phases at high temperature.A new type of modified al oy,to be used in automobile engines at high temperatures,was prepared by adding Zr and Mo into Al-Si-Cu-Mg alloy.The synergistic effects of Zr and Mo on the microstructure evolution and high-temperature mechanical properties were studied.Results show that the addition of Zr and Mo generates a series of intermetallic phases dispersed in the alloy.They can improve the strength of the alloy by hindering dislocation movement and crack propagation.In addition,some nano-strengthened phases show coherent interfaces with the matrix and improve grain refinement.The addition of Mo greatly improves the heat resistance of the alloy.The extremely low diffusivity of Mo enables it to improve the thermal stability of the intermetallic phases,inhibit precipitation during aging,reduce the size of the precipitates,and improve the heat resistance of the alloy.

Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

Microstructure and high-temperature tensile property of TiAl alloy produced by selective electron beam melting

The microstructure and high-temperature tensile property of a Ti-47Al-2Cr-2 Nb alloy fabricated via selective electron beam melting(SEBM) with hatch spacings of 85,100,and 115 μm were systematically investigated.When the hatch spacing increased from 85 to 115 μm,the microstructure comprising the horizontal cross section changed from coarse lamellar(y/B2) colonies to an inhomogeneous structure and the grain morphology transformed from elongated grains to inhomogeneous and equiaxed grains along the building direction of the vertical cross section.The boundary population of the SEBMproduced TiAl alloy samples was dominated by high-angle grain boundaries(≥ 15°),and the volume fraction of these boundaries decreased with hatch spacing increasing.Additionally,the as-built TiAl alloy sample produced under a spacing of 100 μm exhibited the highest room-and elevated-temperature tensile strengths,with the ultimate tensile strength at room temperature(642 MPa) increasing to 674 MPa at 700 ℃.Furthermore,the mechanism of anomalous strengthening at 700 ℃ was discussed in detail.

Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

Aluminum high pressure die casting(HPDC)technology has evolved in the past decades,enabling stronger and larger one-piece casting with significant part consolidation.It also offers a higher design freedom for more mass-efficient thin-walled body structures.For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting(for instance,shock towers and hinge pillars,etc.),a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures(450℃-500℃)followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement.To enable cost-efficient mass production of HPDC body structures,it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties.Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components.The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy(registered as A379 with The Aluminum Association,USA)to achieve the desired tensile properties without using T7 heat treatment.It was found that Cu addition should be avoided,as it is not effective in enhancing strength while degrades tensile ductility.Mg addition is very effective in improving strength and has minor impact on tensile ductility.The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

Effect of Cooling Rates on Solidification Microstructures and Tensile Property of a Novel Wrought Superalloy

The effects of cooling rates on solidification behaviors,segregation characteristics and tensile property of GH4151 alloy were investigated using microstructure characterization and tensile test.Firstly,a relationship between the secondary dendrite arm spacing and cooling rate was determined and it was confirmed to be valid.Secondly,it can be found from microstructure observations that the morphology of(Nb,Ti)C carbides transits from blocky and script type to fine script type and spotty type,and the refinedγ'phase was observed due to decrease of segregation with increasing cooling rates.Thirdly,the solidification microstructures of the industrial-scale samples were analyzed.The morphology ofηphase changes from indistinguishable shape,fine needle-like shape to large block-like shape with increasing ingot diameter.As a result,the mechanical properties of alloy decrease due to increase of brittle precipitations.The experimental results show that the precipitation behavior of GH4151 is affected by segregation degree of elements,and the segregation degree is determined by solute distribution process and solid back-diffusion process.

The Research for Surface Properties of Steel Slag Powder and High-Temperature Rheological Properties of Asphalt Mortar

In order to evaluate the feasibility of steel slag powder as filler,the coating properties of steel slag and limestone aggregate were compared by water boiling test,the micro morphology difierences between steel slag powder and mineral powder(limestone powder)were compared by scanning electron microscope(SEM),and the high-temperature rheological properties of asphalt mortar with difierent ratio of filler quality to asphalt quality(F/A)and difierent substitution rates of mineral powder(S/F)were studied by dynamic shear rheological test.The results show that the surface microstructure of steel slag powder is more abundant than that of mineral powder,and the adhesion of steel slag to asphalt is better than that of limestone.At the same temperature,the lower the ratio of S/F is,the greater the rutting factor and complex modulus will be.In addition,the complex modulus and rutting factor of the asphalt mortar increase with the increase of F/A,and the filler type and F/A have a negligible efiect on the phase angle.

Multiscale tensegrity model for the tensile properties of DNA nanotubes

DNA nanotubes(DNTs)with user-defined shapes and functionalities have potential applications in many fields.So far,compared with numerous experimental studies,there have been only a handful of models on the mechanical properties of such DNTs.This paper aims at presenting a multiscale model to quantify the correlations among the pre-tension states,tensile properties,encapsulation structures of DNTs,and the surrounding factors.First,by combining a statistical worm-like-chain(WLC)model of single DNA deformation and Parsegian's mesoscopic model of DNA liquid crystal free energy,a multiscale tensegrity model is established,and the pre-tension state of DNTs is characterized theoretically for the first time.Then,by using the minimum potential energy principle,the force-extension curve and tensile rigidity of pre-tension DNTs are predicted.Finally,the effects of the encapsulation structure and surrounding factors on the tensile properties of DNTs are studied.The predictions for the tensile behaviors of DNTs can not only reproduce the existing experimental results,but also reveal that the competition of DNA intrachain and interchain interactions in the encapsulation structures determines the pre-tension states of DNTs and their tensile properties.The changes in the pre-tension states and environmental factors make the monotonic or non-monotonic changes in the tensile properties of DNTs under longitudinal loads.

Improved continuous precipitation kinetics and tensile properties of extruded AZ80 alloy through {10-12} twin formation

This study investigates the effect of{10-12}deformation twins on the continuous precipitation behavior of an extruded Mg-8.0Al-0.5Zn-0.2Mn(AZ80)alloy during aging.The extruded AZ80 alloy is compressed along the transverse direction to introduce{10-12}twins,followed by an aging treatment at 300℃.The extruded material exhibits a twin-free microstructure with low internal strain energy,whereas the pre-twinned material possesses abundant{10-12}twins and has high internal strain energy.The aging results reveal that the peak-aging time of the pre-twinned material(1 h)is one-eighth of that of the extruded material(8 h).Although Mg_(17)Al_(12)continuous precipitates(CPs)are observed in both the peak-aged materials,these CPs are much smaller and more densely distributed in the pre-twinned material despite the significantly shorter aging time.The CPs size in the peak-aged materials increases in the following order:twinned region in the pre-twinned material(0.47μm)<residual matrix region in the pre-twinned material(1.71μm)<matrix region in the extruded material(2.55μm).Moreover,the CPs number density in the twinned region of the pre-twinned material is approximately 11 times higher than that in the matrix region of the extruded material.The peak-aged pre-twinned material exhibits significantly higher tensile strength and ductility than the peak-aged extruded material.These results demonstrate that the formation of{10-12}twins in the extruded AZ80 alloy substantially accelerates the static precipitation of CPs during aging at 300℃and improves the tensile properties of the peak-aged material.

Effect of Curing Age on Tensile Properties of Fly Ash Based Engineered Geopolymer Composites(FA-EGC)by Uniaxial Tensile Test and Ultrasonic Pulse Velocity Method

Tensile properties of fly ash based engineered geopolymer composites(FA-EGC)at different curing ages were studied by uniaxial tensile test and ultrasonic pulse velocity(UPV)methods,which included uniaxial tensile properties,the correlation between ultrasonic pulse velocity and tensile properties,and characteristic parameters of microcracks.The experimental results show that obvious strain hardening behavior can be found in FA-EGC at different curing ages.With the increase of curing age,the tensile strength increases,the tensile strain decreases and the toughness becomes worse.The UPV of FA-EGC increases with curing age,and a strong correlation can be found between tensile strength and UPV.With the increase of curing age,the average crack width of FA-EGC decreases and the total number of cracks increases.This is because the strength of geopolymer increases fast at early age,thus the later strength development of FA-EGC tend to be stable.At the same time,the bond strength between fiber and matrix,and the friction of fiber/matrix interface continue to increase with curing age,thus the bridging effect of fiber is gradually strengthened.In conclusion,the increase of curing age is beneficial to the development of tensile properties of FA-EGC.

High-temperature Tensile Behavior of Laser Welded Ti-22Al-25Nb Joints at Different Temperatures

The high-temperature tensile behavior of laser welded Ti-22Al-25Nb (at%) joints was investigated at 500,650,800,and 1 000 ℃.The temperatures for tensile tests were selected according to the phase transformation sequence of Ti2AlNb-based alloys.At temperatures lower than the B2+O phase field (500 ℃) and higher than the B2+O phase field (1 000 ℃),the joints fracture in the base metal in ductile fracture mode.By contrast,the joints exhibit obvious high-temperature brittleness in the B2+O phase field (650 °C and 800 ℃).Heat treatments were conducted with respect to the thermal history of tensile specimens.Intergranular microcracks along the grain boundary of B2 phase are found in the fusion zone after the heat treatments at 650 ℃ and 800 ℃.The high-temperature brittleness at 650 ℃ and 800 ℃ is attributed to the B2→O transformation along the grain boundary.The stress concentration caused by the volume change of B2→O transformation also contributes to the high-temperature brittleness of laser welded Ti-22Al-25Nb joints.

Effect of heat treatment on microstructure and tensile properties of A356 alloys

Two heat treatments of A356 alloys with combined addition of rare earth and strontium were conducted.T6 treatment is a long time treatment（solution at 535 ℃ for 4 h ＋ aging at 150 ℃ for 15 h）.The other treatment is a short time treatment（solution at 550 ℃ for 2 h ＋ aging at 170 ℃ for 2 h）.The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy,scanning electronic microscopy and tension test.It is found that a 2 h solution at 550 ℃ is sufficient to make homogenization and saturation of magnesium and silicon in α（Al） phase,spheroid of eutectic Si phase.Followed by solution,a 2 h artificial aging at 170 ℃ is almost enough to produce hardening precipitates.Those samples treated with T6 achieve the maximum tensile strength and fracture elongation.With short time treatment（ST）,samples can reach 90% of the maximum yield strength,95% of the maximum strength,and 80% of the maximum elongation.

Microstructure and tensile properties of containerless near-isothermally forged TiAl alloys

Ti-47Al-2Nb-2Cr-0.4（W, Mo） （mole fraction, %） alloy ingot fabricated using vacuum consumable melting was containerless near-isothermally forged, and the high temperature forgeability, microstructure and tensile properties were investigated. The results show that the TiAl ingot exhibits good heat workability during containerless near-isothermally forging process, and there are not evident cracks on the surface of as-forged TiAl pancake with a total deformation degree of 60%. The microstructure of the TiAl ingot appears to be typical nearly-lamellar（NL）, comprising a great amount of lamellar colonies （α2＋γ） and a few equiaxed γ grains. After near-isothermally forging, the as-forged pancake shows primarily fine equiaxed γ grains with an average grain size of 20 μm and some broken lamellar pieces, and some bent lamellas still exist in the hard-deformation zone. Tensile tests at room temperature show that ultimate tensile strength increases from 433 MPa to 573 MPa after forging due to grain refinement effect.

Effect of extrusion process on microstructure and mechanical properties of Ni_3Al-B-Cr alloy during self-propagation high-temperature synthesis

The well-densified Ni3Al-0.5B-5Cr alloy was fabricated by self-propagation high-temperature synthesis and extrusion technique. Microstructure examination shows that the synthesized alloy has fine microstructure and contains Ni3Al, Al2O3, Ni3B and Cr3Ni2 phases. Moreover, the self-propagation high-temperature synthesis and extrusion lead to great deformation and recrystallization in the alloy, which helps to refine the microstructure and weaken the misorientation. In addition, the subsequent extrusion procedure redistributes the Al2O3 particles and eliminates the γ-Ni phase. Compared with the alloy synthesized without extrusion, the Ni3Al-0.5B-5Cr alloy fabricated by self-propagation high-temperature synthesis and extrusion has better room temperature mechanical properties, which should be ascribed to the microstructure evolution.

Microstructure and tensile properties of AE42-based magnesium alloys with calcium addition

The as-cast microstructure of AE42 was of typical dendritic and composed of the a matrix and some needle-shaped interphases Al11RE3. A small mount of Ca addition results in significant microstructural refinement and formation of a Al2Ca phase, which showed two kinds of morphologies, lamellar and tiny granular. The former distributes on grain boundaries and the later is within the matrix grains. With the increase of Ca addition the volume fraction of Al-RE compound (Al11RE3) decreases, but Al2Ca increases. Addition of Ca causes a significant increase of yield strength of the alloy both at ambient and elevated temperatures, but a little decrease of the ductility. With calcium addition the ultimate strength decreases at ambient temperature and 150°t, but increases at 175°C and 200°C.

Tensile and wear properties of TiC reinforced 420 stainless steel fabricated by in situ synthesis

TiC particle reinforced 420 stainless steel matrix composites were fabricated, and the microstructure, tensile properties and wear resistance of the composites were studied. The experimental results indicate that the distribution of TiC particles with size of 5 to 10 μm in diameter is uniform if the volume fraction of TiC is lower than 6%. However, slight agglomeration can be observed when the TiC content exceeds 6%. With the increase of TiC content the tensile and yield strength of the composites prepared increases and reaches the maximum when the volume fraction of TiC increases to 5%. Further increase of TiC content causes reductions of yield and tensile strength. The ductility of the composites shows a monotone decrease with the increase of TiC addition. The introduction of TiC into 420 stainless steel results in significant improvement on wear resistance, which reaches a steady level when the volume fraction of TiC increases to 11% and does not show obvious variation if the TiC content is further increased.

Effects of Sn element on microstructure and properties of Zn-Cu-Bi-Sn high-temperature solder

The microstructures and properties of the Zn-Cu-Bi-Sn(ZCBS) high-temperature solders with various Sn contents were studied using differential scanning calorimetry(DSC),scanning electron microscopy(SEM) and X-ray diffraction(XRD).The results indicate that the increase of Sn content can both decrease the melting temperature and melting range of ZCBS solders and it can also effectively improve the wettability on Cu substrate.The shear strength of solder joints reaches a maximum value with the Sn addition of 5%(mass fraction),which is attributed to the formation of refined β-Sn and primary ε-CuZn_5 phases in η-Zn matrix.However,when the content of Sn exceeds 5%,the shear strength decreases due to the formation of coarse β-Sn phase,which is net-shaped presented at the grain boundary.

Molecular dynamics study on temperature and strain rate dependences of mechanical tensile properties of ultrathin nickel nanowires

Based on the EAM potential, a molecular dynamics study on the tensile properties of ultrathin nickel nanowires in the （100〉 orientation with diameters of 3.94, 4.95 and 5.99 nm was presented at different temperatures and strain rates. The temperature and strain rate dependences of tensile properties were investigated. The simulation results show that the elastic modulus and the yield strength are gradually decreasing with the increase of temperature, while with the increase of the strain rate, the stress--strain curves fluctuate more intensely and the ultrathin nickel nanowires rupture at one smaller and smaller strain. At an ideal temperature of 0.01 K, the yield strength of the nanowires drops rapidly with the increase of strain rate, and at other temperatures the strain rate has a little influence on the elastic modulus and the yield strength. Finally, the effects of size on the tensile properties of ultrathin nickel nanowires were briefly discussed.

Tensile properties and microstructure of Ti14 alloy after semi-solid forging

Tensile properties of a new α＋Ti2Cu alloy after solid forging at 950 °C and semi-solid forging at 1 000 °C and 1 050 °C were investigated over the temperature range of 20-600 °C. The results reveal that high strength and low ductility are obtained in all semi-solid forged alloys. Tensile properties decrease as the semi-solid forging temperature increases, and cleavage fractures are observed after semi-solid forging at 1 050 °C. The variations in tensile properties are attributed to the coarse microstructures obtained in the semi-solid alloys. It is found that the elevated semi-solid temperatures lead to more liquid precipitates along the prior grain boundaries, which increases the peritectic precipitation and formation of Ti2Cu precipitation zones during re-solidification. Recrystallization heat treatment leads to fine microstructure of semi-solid forged alloys, resulting in improvement of tensile properties.

Biaxial tensile properties and elastic constants evaluation of envelope material for airship

This paper presents an experimental study to determine the tensile properties of the envelope fabric Uretek3216L under biaxial cyclic loading.First the biaxial cyclic tests were carefully carried out on the envelope material to obtain the stress-strain data and the corresponding nonlinearity and orthotropy of the material were analyzed. Then for some determination options with different stress ratios the least squares method minimizing the strain terms was used to calculate the elastic constants from the experimental data.Finally the influences of the determination options with different stress ratios and the reciprocal relationship on the elastic constants were discussed.Results show that the orthotropy of the envelope material can be attributed to the unbalanced crimp of their constitutive yarns in warp and weft directions and the elastic constants vary noticeably with the determination options as well as the normalized stress ratios.In real design practice it is more reasonable to use constants determined for specific stress states in particular stress ratios depending on the project＆#39;s needs.Also calculating the structures with two limitative sets of elastic constants instead of using only one set is recommendable in light of the great variety of the constant＆#39;s values.