Effect of the capsule on deformation and densification behavior of nickel-based superalloy compact during hot isostatic pressing

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.

Mechanical densification synthesis of single-crystalline Ni-rich cathode for high-energy lithium-ion batteries

The intergranular microcracking in polycrystalline Ni-rich cathode particle is led by anisotropic volume change and stress corrosion along grain boundary,accelerating battery performance decay.Herein,we have suggested a simple but advanced solid-state method that ensures both uniform transition metal distribution and single-crystalline morphology for Ni-rich cathode synthesis without sophisticated coprecipitation.Pelletization-assisted mechanical densification(PAMD)process on solid-state precursor mixture enables the dynamic mass transfer through the increased solid-solid contact area which facilitates the grain growth during sintering process,readily forming micro-sized single-crystalline particle.Furthermore,the improved chemical reactivity by a combination of capillary effect and vacancyassisted diffusion provides homogeneous element distribution within each primary particle.As a result,single-crystalline Ni-rich cathode with PAMD process has eliminated a potential evolution of intergranular cracking,thus achieving superior energy retention capability of 85%over 150 cycles compared to polycrystalline Ni-rich particle even after high-pressure calendering process(corresponding to electrode density of~3.6 g cm^(-3))and high cut-off voltage cycling.This work provides a concrete perspective on developing facile synthetic route of micron-sized single-crystalline Ni-rich cathode materials for high energy density lithium-ion batteries(LIBs).

Preparation of B_(2)O_(3)-ZnO-SiO_(2)Glass and Sintering Densification of Copper Terminal Electrode Applied in Multilayer Ceramic Capacitors

B_(2)O_(3)-Zn O-SiO_(2)(BZS)glass containing Cu O with excellent acid resistance,wetting properties,and high-temperature sintering density was prepared by high temperature melting method and then applied in copper terminal electrode for multilayer ceramic capacitors(MLCC)applications.The structure and property characterization of B_(2)O_(3)-Zn O-SiO_(2)glass,including X-ray diffraction,FTIR,scanning electron microscopy,high-temperature microscopy,and differential scanning calorimetry,indicated that the addition of CuO improved the glass’s acid resistance and glass-forming ability.The wettability and acid resistance of this glass were found to be excellent when CuO content was 1.50 wt%.Compared to BZS glass,the CuO-added glass exhibited excellent wettability to copper powder and corrosion resistance to the plating solution.The sintered copper electrode films prepared using the glass with CuO addition had better densification and lower sintering temperature of 750℃.Further analysis of the sintering mechanism reveals that the flowability and wettability of the glass significantly impact the sintering densification of the copper terminal electrodes.

Sintering Densification of Boron Carbide Materials and Their Research Progress

Boron carbide(B_(4)C)has excellent high-temperature oxidation resistance,high hardness,low relative density,high melting point and excellent abrasive resistance,which is widely used in fields such as refractories,wear-resistant materials and lightweight protective materials.The research progress and application of B_(4)C materials in China and overseas in recent years were summarized.The influences of sintering processes(pressureless sintering,hot-pressing sintering,hot isostatic pressing sintering,spark plasma sintering and microwave sintering)and sintering additives(simple substances,oxides and carbides)on the B_(4)C densification were analyzed.The development of B_(4)C materials was prospected.

Densification Mechanism of Warm Compaction and Powder Mixture Designing Rules

By phenomenological analysis of warm compaction, it is found that, compared with the contribution of particle plastical deformation to densification of powder compact,the particle rearrangement is a dominant densification mechanism for powder warm compaction, and the plastical deformation of particles plays an important role in offering accommodating deformation for particle rearrangement and densifying powder compact at the final stage of pressing.In order to attain density gain as high as possible during warm compaction, six rules for designing warm compacting powder mixtures were proposed in detail.

Initial densification strain point's determination of honeycomb structure subjected to out-of-plane compression

Compression ratio is significant for cellular structures on energy absorption.In the present work,theoretical formulas to determine the initial densification strain of honeycomb structure were put forward by means of minimum energy principle.Detailed densification strain points were identified,with full fold model for kinds of specimens.To validate,corresponding numerical simulations were carried out with explicit finite element method.Excellent agreement in terms of initial densification stain point has been observed between the theoretical calculation and numerical simulation.The results show that:(1) different honeycomb structure has different initial densification strain point,and its geometric configuration of cells plays an evident role on densification;(2)half-wave length of the wrinkle of honeycomb in folding process significantly influences on the densification strain point;(3) the initial densification point is an decreasing power function of the ratio of foil thickness to cell length,with the exponent 2/3.These achievements provide important references for design in cellular energy absorption devices.

PLASTIC DEFORMATION AND DENSIFICATION FOR SINTERED POWDER MATERIALS

Equivalent yield strength of sintered powder materials is determined by experiments,and the following yield condition is constructed based on it.Experiments on uniaxial compression,and plane strain,closed die upsetting have been done using sintered copper,and the relation between the deformation resistance and compactness of the prefabricated preform is analysed.A design principle for the prefabricated preform density is proposed,and the effectiveness of shear plastic deformation to densifleation is pointed out.

Effects of hot isostatic pressing temperature on casting shrinkage densification and microstructure of Ti6Al4V alloy

The Ti6Al4V alloy castings were produced by the investment casting process, and the hot isostatic pressing(HIP) was used to remove shrinkage from castings. The processing pressure and holding time for HIP were 150 MPa and 20 min, respectively. Four different HIP temperatures were tested, including 750 ℃, 850 ℃, 920 ℃ and 950 ℃. To evaluate the effects of temperature on densification and microstructure of Ti6Al4V alloy treated by HIP, non-destructive testing and metallographic observation was performed. The experimental results show that the shrinkage was completely closed at 920 ℃ and 950 ℃. The densification of Ti6Al4V alloy increased as the HIP temperature increased below 920 ℃. The lamel ae were more uniform, the thickness of lamel ae was obviously broadened and the structure was coarsen. Besides, the Norton creep equation was used to simulate the effect of different temperatures on the densification of Ti6Al4V alloy during HIP. The simulation results were in good agreement with the experimental results. It was also found that 920 ℃ is a suitable temperature for HIP for Ti6Al4V alloy.

Densification of W-Ni-Cu and W-Fe-Cu Alloys at 1573 K

The tungsten alloys with Ni-Cu and Fe-Cu additives were sintered at 1573 K for 1 h by hot-pressing method. It was found that the alloy relative density can be improved with the additionof Cu when Cu content is not very high, and W95Ni3Cu2 alloy with full density can be obtainedon the sintering condition. However, with the Cu content further increasing, the relative densitychange of W-Ni-Cu alloy and W-Fe-Cu alloy shows difFerent trends: the former tends to decreaseobviously, but the latter shows little change. According to the analysis results, the element Cuhas different effects on the activation capability of Ni and Fe during sintering of the tungstenalloys.

A Numerical Study of Densification Behavior of Silicon Carbide Matrix Composites in Isothermal Chemical Vapor Infiltration

We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the reaction. Thereby, we established mathematical models on two scales, respectively, preform and reactor. These models were used for the numerical simulation of the process of ceramic matrix composites densified by isothermal chemical vapor infiltration(ICVI). The models were used to carry out a systematic study on the influence of process conditions and the preform structure on the densification behaviors. The most important findings of our study are that the processing time could be reduced by about 50% without compromising the quality of the material, if the processing temperature is 950-1 000 ℃ for the first 70 hours and then raised to 1 100 ℃.

Effects of carrier gas on densification of porous carbon-carbon composites during chemical vapor infiltration

The densification rate of C/C composites fabricated by directional flow thermal gradient chemical vapor infiltration process from C 3H 6, C 3H 6 N 2 and C 3H 6 H 2 was investigated respectively. The mechanism on the role of carrier gas in chemical vapor infiltration was also discussed. The results shows that whether or not adding N 2 as carrier gas has little influences on the densification behavior of C/C composites with the controlled temperature, the partial pressure of hydrocarbon and the effective residence time of the gas phase remain constant. When the controlled temperature is not less than 1 173 K,using N 2 or H 2 as carrier gas makes pronounced differences in densifying of C/C composites. The average bulk density of C/C composites from C 3H 6 H 2 is eight to ten percent higher than that from C 3H 6 N 2. However, when the controlled temperature is not higher than 1 123 K,the densification rate of C/C composites from C 3H 6 H 2 is much lower than that from C 3H 6 N 2, which implies that effects of carrier gas on densification of C/C composites are closely related to the type of carrier gas and infiltration temperature. At higher temperature, using H 2 as carrier gas is favorable to the densification of C/C composites, while at lower temperature, hydrogen, acting as reactive gas, can inhibit the formation of pyrolytic carbon.

High-pressure Sintering of Boron Carbide-Titanium Diboride Composites and Its Densification Mechanism

A high-pressure hot-pressing process was applied to densify a commercial boron carbide-titanium diboride (B4C-TiB2) powder mixture.Nearly fully dense (98.6%) materials were obtained at 1700℃ under a pressure of 100MPa.Compared to the sintering temperature required to achieve similar results when a pressure of only 30MPa was applied,the sintering temperature was found to decrease by about 200℃ under pressure of 100 MPa.Analysis of the thermodynamics and microstructure showed that the plastic deformation of the B4C grains induced by high pressure dominated the densification mechanism when high pressure was applied.Furthermore,higher pressure resulted in remarkably improved mechanical properties of the composites,which could be traced back to the generation of stacking faults in the B4C grains and aggregation of TiB2.

Temperature Fluctuation Synthesis/Simultaneous Densification and Microstructure Control of Titanium Silicon Carbide (Ti_3SiC_2) Ceramics

A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process. Si is used as an in-situ liquid forming phase and it is favorable for both the solid-liquid synthesis and the densification of Ti3SiC2 rainies. The present work demonstrated that the temperature fluctuation synthesis/simultaneous densification process is one of the most effective and simple methods for the preparation of Ti3SiC2 bulk materials providing relatively low synthesis temperature. short reaction time; and simultaneous synthesis and densification. This work also showed the capability to control the microstructure, e.g., the preferred orientation, of the bulk Ti3SiC2 materials simply by applying the hot pressing pressure at different Stages of the temperature fluctuation process. And textured Ti3SiC2 bulk materials with {002} faces of laminated Ti3SiC2 grains normal to the hot pressing axis were prepared.

Densification of the Tungsten Heavy Alloys at 1473 K and Fabrication of W-Mo System FGM with Density Gradient

The tungsten heavy alloys with Ni-Al and Fe-Al additives were sintered by hot-press method at 1473 K for 1 h. It was found that the relativedensity of the W-Fe alloy could be increased evidently by addition of Al. However, the relative density of W- Ni-Al alloy with low content of Al was conversely decreased considerably compared with that of W-Ni alloy. The causes have been studied. The sinter ing experiments of Mo aloy and W-Mo alloys with 3 wt pct Fe-1.5 wt pct Al additives were also carried out under the same sintering condition of low temperature.Finally, W-Mo system FGM with density gradient was successfully fabricated.Its density changed gradually from 17.0x103 kg/m3 to 9.5x103 kg/m3 within the middfe 1.1 mm thickness

Effect of LiF on Densification and Mechanical Properties of Dy-α-Sialon Ceramics

The effect of LiF on the densification and mechanical properties of hot-pressed Dy-α-sialon ceramics was studied. Comparatively, without LiF as sintering additive, the pure Dy-α-sialon ceramic should be sintered at 1750 ℃. When LiF is used, the sintering temperature of the Dy-α-sialon is greatly lowered to 1500～1650 ℃. Obviously, the addition of LiF has a strong effect on the improvement in densification. Meanwhile, the resultant Dy-α-sialon has no significant changes in the mechanical properties.

Densification abnormality in reactive hot pressing of Ti and Al elemental powders

The densification behavior of a TiAl base alloy prepared by elemental powder metallurgy has been studied. It is found that a densification abnormality occurs at 1 400 ℃, i.e. the compact density decreases with the increase of hot pressing temperature. By microstructural observation, including optical microscopy and TEM, it has been concluded that the densification abnormality can be attributed to the different high temperature creep mechanisms induced by microstructure coarsening in the late period of densification.

Densification Model for Porous Metallic Powder Materials

A new mechanical model for powder metallurgy compaction is presented. In this model, various amount of voids can be introduced into a continuous solid, therefore porosity can be conveniently controlled. The elastic-plastic finite element method was used to analyze the sintered powder material. The model was used to simulate compressing of a sintered cylinder. MSC.Marc of MSC. Software Corporation was applied here, and the sintered powder model was built in MSC.Mentat. The sintered cylindrical powder metallurgy part is treated as a piece of normal metal with pores in the model. The metal block is considered as cylinder with a radius of 6.0 mm and a total height of 10.0 mm. Young’s module was assumed to be 4 000 MPa. Poisson’s ratio was 0.269. The initial yield stress is 210 MPa. Friction coefficient used for the upper and lower contact surfaces is 0.3. Coulomb principle is adopted. Considering axisymmetricity, just half a section is analyzed. Totally there are 1 240 elements. Experiment was carried out by a computer controlled a universal tensile testing machine. During the experiment, the sample was prepared from highly compressible water atomized iron powder with 0.6wt% polymeric lubricant. Particle size is about 100～150 μm. The comparison was performed using a sintered cylindrical sample. The green compact was sintered at 1 140 ℃ for 2 hours. Initially, H0 is 10.20 mm, Φ0 is 12.01 mm and the initial relative density is 0.789. After pressing, H is 7.30 mm, Φ1 is 13.10 mm, Φ2 is 14.64 mm and relative density is 0.88. The load-displacement curves agree with the experimental results very well. Plastic deformation of metallic material is mostly caused by the slipping of crystal lattice. Although very small, a metal powder particle is composed of metallic crystal. Mechanical properties of a powder particle should be very close to their as solid metal counterpart.

Densification and Structure Evolution of ZrB_(2)-ZrO_(2) Composites Prepared by Plasma Activated Sintering using ZrB2@ZrO2 Powder

The densification and the structure evolution of the plasma activated sintered(PAS sintered)ZrB_(2)-ZrO_(2) composite via the ZrO_(2)-coated ZrB_(2) powder(ZrB_(2)@ZrO_(2))prepared by in situ passivation method were investigated.The composition and microstructure were characterized by XRD,Raman,SEM,and EDS techniques.The coated powder has excellent sintering performance.The relative density of the composite reaches above 90%at 1200℃,and the main sintering process occurs between ZrO_(2) particles.While at above 1500℃,the relative density reaches above 95%and the main sintering process occurs between ZrB_(2) and ZrO_(2) particles.With the increase of ZrO_(2) coating content,the structure of the sintered body changes from ZrB_(2) continuous network structure to island structure.When the content is 20%,an island structure is formed.Increasing the ZrO_(2) content further causes the overheating of ZrO_(2).Thus,the best sintering performance reaches when the coating content is 20wt%.

Investigation of Loss Weight and Densification of SiC-Al_2O_3-Y_2O_3 Ceramic Composite on Sintering

α-SiC, Al2O3 and Y2O3 powders were all used as raw materials. The SiC-Al2O3-Y2O3 ceramic composites were made by pressureless liquid phase sintering technology. The effects of sintering temperature, loss weight and coordination number on sintering densification were studied. The reason for producing loss weight on sintering was analysed. The results show that the primary reason for producing loss weight on sintering in SiC-Al2O3-Y2O3 ceramic composite was that chemical reactions between SiC and Al2O3 are happened during sintering, and given out volatile gases. If sintering temperature is excessively lower, grain size would be finer, and coordination number would be higher, well then material would be on no sintering densification. If sintering temperature is excessively higher, grains would grow up, though small coordination number would benefit to make pore eliminate and shrink, but coarse microstructure would also block gliding and resetting of grains, together affected by expansion stress from volatile gas, the material densification would instead go down. Only under the sintering process of 1850 ℃ for 30 min, material densification is better, and the mechanical property of ceramic composites is also improved.

Thermodynamics of Molten Pool Predicted by Computational Fluid Dynamics in Selective Laser Melting of Ti6Al4V:Surface Morphology Evolution and Densification Behavior

The three-dimensional physical model of the randomly packed powder material irradiated by the laser beam was established,taking into account the transformation of the material phase,the melt spreading and the interaction of the free surface of the molten pool and the recoiling pressure caused by the material evaporation during the selective laser melting.Influence of the processing parameters on the thermal behavior,the material evaporation,the surface morphology and the densification behavior in the connection region of the molten pool and the substrate was studied.It was shown that the powder material underwent the transformation from the partial melting state to the complete melting state and finally to the overheating state with the applied laser energy density increasing from 167 J/mm^(3) to 417 J/mm^(3).Therefore,the solidified track ranged from the discontinuous tracks with the rough surface to the continuous tracks with residual porosities,then to the continuous and dense tracks and terminally to the fluctuated tracks with the increase in the laser energy density.Meanwhile,the laser energy effect depth was maintained the positive relationship with the laser energy density.The vortex velocity obtained in the free surface of the molten pool towards to the rear region in the opposite laser scan direction promoted the melt convection to the edge region of the molten pool as the laser energy density was higher than 277 J/mm^(3),demonstrating the efficient energy dissipation from the center of the irradiation region to the whole part of the molten pool and the attendant production of the sufficient melt volume.Therefore,the efficient spreading of the molten pool and the metallurgical bonding ability of the melt with the substrate was obtained at the optimized laser energy density of 277 J/mm^(3).However,the severe material evaporation would take place as the melt was overheated,resulting in the formation of the residual pores and poor surface quality.