Papers by Keyword: Hot Isostatic Pressing (HIP)

Abstract: The aim of this research is to investigate the combined effects of CeO₂ additions and hot-isostatic pressing sintering (HIPping) technique on the densification of ZTA ceramics. Addition of CeO₂ to ZTA ceramics leads to formation of a secondary phase (CeAl₁₁O₁₈) which played a vital role in affecting the density and porosity. Microstructure investigations showed that HIPping had a significant role in the removal of pores. The sample with 5 wt.% of CeO₂ addition showed the optimum value. The highest bulk density is 4.46 g/cm³ and the lowest percentage of porosity is 0.35%.

Abstract: This research investigated the effect of hot extrusion on the flow behaviour of nickel-based superalloy FGH4096 by hot compression experiments in the temperature range from 1020 to 1110 °C and strain rates ranging from 0.1 to 0.001 s^-1. The influence of the hot extrusion on the initial microstructures, work hardening rate, strain rate sensitivity, and activation energy of deformation were discussed. The results show that the extruded microstructure is constituted by the fine dynamic recrystallisation of grains. The true strain-true stress curves show that the as-HIPed and as-HEXed FGH4096 superalloy present double flow stress peaks and discontinuous flow softening. The as-HEXed FGH4096 is easily dynamically softened at high temperatures and high strain rates compared with as-HIPed microstructures. As for the work hardening rate, the as-HEXed FGH4096 exhibits higher θ values than that of as-HIPed. It is beneficial to the homogenous deformation and grain refinement during subsequent turbine disk forging. Comparing to as-HIPed FGH4096, the highest strain rate sensitivity value of as-HEXed is 0.306 at 1110 °C. The isothermal superplastic forging of a P/M turbine disk may be carried out at this temperature. The deformation activation energy value of the as-HIPed FGH4096 is lower which means that dislocation sliding and climbing can be easily initiated in the as-HIPed alloy.

Abstract: An investigation of HIP parameters for EBM Ti-6Al-4V has been performed with the aim to maximize the strength of the HIPed material. A lower HIP temperature of 800 °C and a higher pressure of 200 MPa gives the highest strength and is also enough to eliminate all internal defects. By printing material with intentionally induced porosity combined with an optimized HIP cycle the highest strength can be obtained.

Abstract: MgO ceramics with the purity higher than 99.99% have been fabricated by a hot-isostatic press (HIP) technique of hot-pressed MgO compacts using nanometer MgO powder with an average particle size of 300 nm. The densification and grain growth behavior of MgO compacts during HIP process were investigated. The results indicate that the high-purity MgO ceramic with an average grain size of 9.76 μm and a density approximately to the theoretical density can be obtained by HIP method at 1350°C and 150 MPa for 60 min. HIP can significantly enhance the densification process of MgO compacts and cause a slightly change of grain size distribution.

Abstract: Pre-alloyed gamma titanium aluminide powders were fabricated by argon gas atomization. The powder was hot isostatic pressed (HIP) at 1200°Cand 150MPa for 3h to obtain full density compact. The properties of the powders and the HIP’ed compacts were investigated in this work. The microstructure of the powder exhibited dendrite and cellular mixed image, resulted from rapid solidification and independent of particle size. The microstructural transition from cell to dendrite could be readily represented in a droplet or the droplets of different size. The transition was the result of the decrease of undercooling. XRD analysis result showed that the powder consisted of α₂ phase and γ phase, coarse powder was mostly γ phase, while fine powder mostly α₂ phase. After HIP, the near gamma microstructure showed an average γ-TiAl grains of approximately 6μm.

Abstract: The microstructures and mechanical properties of IN738LC superalloy made by investment castings followed by Hot Isostatic Pressing (HIP) treatment have been investigated. The results revealed that after HIP treatment, the microporosities have been almost removed and the density rose by 0.21%. The eutectic size became smaller and the fraction decreased. The γ' phase was more regular and also increased in size, while a large number of secondary γ' phase appeared. With HIP treatment, the impact toughness increased from 5.0J ~ 7.0J to 8J ~ 9J and tensile strength at 200°C ~ 800°C was improved by approximately 3.2%~19.7%. In addition, the ductility and the stress rupture life have also been greatly improved as well.

Abstract: Ti-47Al-2Cr-2Nb-0.15B alloy is a typical γ-TiAl alloy, and powder metallurgy (PM) as a near-net shape method was used to prepare it in this article. Clean pre-alloyed powders were prepared by argon gas atomization, and TiAl alloy was prepared by hot isostatic pressing (HIP) at 1150 °C and 1230 °C. However, surface contamination is inevitable due to chemical reactions with the residual O₂ in the vacuum chamber during gas atomization, or due to physical adsorption of O₂ and H₂O during storage of the powder at room temperature. Infrared spectrometry was used to study this process. We found that the adsorption of gases is mainly H₂O. The adsorbed gas in powders would deteriorate the performance of PM alloy, so a gas protection environment is suggested. Tensile properties of PM TiAl alloy were compared with as-cast alloy. Results showed that PM TiAl alloy had better strength which also had more fine and uniform microstructure.

Abstract: The present study focused on the effect of hot isostatic pressing (HIP) treatment on the microstructure of K417G superalloy. The experimental results showed that after the HIP treatment the size and volume fraction of the porosities significantly decreased. In addition, the dendritic structure and γ/γ' eutectics in the as-cast specimens became obscure after the HIP treatment due to the improvement of segregation. The γ′ phases in the dendrite core were smaller than those in the interdendritic region, whether in the as-cast or HIP specimens. The slow cooling at the end of the HIP treatment leads to the irregular morphology of the γ′ phases.

Abstract: The CuCr25 alloys were prepared by spray forming technology, and effect of process parameters on the deposit was studied. The microstructure of CuCr25 alloy prepared by spray forming was studied, and the size of chromium particles was 3-10μm. It is fond that spray-deposited CuCr25 alloys were hot forged and hot isostatically pressed to full densification,and the size of chromium particles was increased little after being hold at 1070°C for 60mins. Conclusions were drawn from the researching results that spray forming was an ideal method to prepare CuCr25 alloys with fine chromium precipitates and homogeneous dispersion. After hot forging and hot isostatic pressing, the size of chromium particles was increased to 10-15μm. the density of the CuCr25 alloy could be 99%.

Abstract: The purpose of present study was to increase productivity and to reduce the polution of dust for making of endmill by conventional method such as grinding process. The micro scale endmill manufactured by powder injection molding, the molding (green part) was debinded and sintered. After that decreasing the porosities of the parts sintered, HIP process was adapted. After HIP process the relative density was shown more than 99% of the tools sintered. Finally, the micro cutting experiment using manufactured tool by PIM and HIP were implemented for verifying the feasibility of the tool. The ware of zirconia micro tool was observed very small, but the concentricity is less than the conventional tool made by grinding process. This type of tool is adequate to use in rough milling.