Effect Of Hot Isostatic Pressing Treatment Research Articles

Effect of hot isostatic pressing on the mechanical and corrosive properties of Ti–Ni alloy fabricated by selective laser melting

Hot isostatic pressing (HIP) is capable of mitigating the internal defects of materials, such as pores and cracks, resulting in improved mechanical properties and corrosion resistance, so it is particularly suitable as a post-treatment technology for the Ti–Ni alloys fabricated by selective laser melting (SLM), which display a broad application prospect in the biomedical field. Herein, the effect of HIP treatment on the mechanical and corrosion-resistant properties of SLM Ti–Ni alloys was systematically investigated. It was demonstrated that HIP treatment did not substantially affect the phase transformation behavior of the SLM Ti–Ni alloy, only showing a slight decrease in the values of As and Ms. However, HIP treatment improved the ultimate tensile strength and the elongation to fracture of the SLM Ti–Ni alloy by 67.3% and 23.2%, respectively. Meanwhile, the corrosion current density was reduced by two orders of magnitude after HIP treatment, indicating the significantly increased corrosion resistance. The enhanced mechanical properties and corrosion resistance of SLM Ti–Ni alloy were credited with the elevated temperature and pressure applied during the HIP process, which significantly eliminated the porosity defects and made the microstructure more uniform. These findings highlight the importance of performing HIP to enhance the comprehensive properties of SLM Ti–Ni alloys, which can expand the application prospects of SLM Ti–Ni alloys in the biomedical field.

Low-cycle fatigue behavior of a solution-treated and HIPped nickel-based single-crystal superalloy at 760 °C

Micropores have a substantial impact on the fatigue behaviors of nickel-based single-crystal (SX) superalloys. Nonetheless, Hot Isostatic Pressing (HIP) treatment is an available approach to effectively reduce defects and enhance fatigue lives. In this work, the HIP treatment was applied to a solution-treated second-generation nickel-based SX superalloy and then subjected to low-cycle fatigue (LCF) tests at 760 °C. The effects of HIP treatment on fatigue crack initiation and propagation at intermediate-temperature LCF were studied by analyzing the development of micropores and fatigue behaviors. The results show that HIP treatment can remarkably reduce the micropores and residual eutectics in the interdendritic regions of the solution-treated alloy, changing the crack initiation site from the sub-surface micropore to the surface microcrack and transforming the crack propagation from mode I (i.e., perpendicular to the load direction) to mode II (i.e., parallel to the crystallographic {111} planes). Consequently, HIP treatment can increase the fatigue lives of this SX superalloy by about three times. Due to the reduction of micropores and residual eutectics by HIP treatment, on the one hand, the surface microcrack can propagate through the oxide layer and recrystallization zone to form the crack initiation, effectively prolonging the time of the crack initiation stage. On the other hand, the elimination of stress concentration areas inhibits rapid crack propagation in the direction perpendicular to the stress axis, extending the life of the crack propagation. This research provides a method for controlling micropores and residual eutectics to improve the intermediate-temperature fatigue properties of the second-generation nickel-based SX superalloys.

Effect of HIP treatment on mechanical properties of TiAl4822 alloy additively manufactured by electron beam melting

One of the lightweight heat-resistant alloys, Ti-48Al-2Cr-2Nb (TiAl4822), has already been adopted to turbine blades for jet engines, but is manufactured by casting which requires expensive post process. Aerospace industry is intensively studying the additive manufacturing (AM) process for the engine parts. In this research, tensile and creep properties of additively manufactured TiAl4822 by electron beam melting (EBM) were studied. The mechanical tests were performed at 750 ℃ which is similar to the actual condition in low pressure turbine module. The effect of hot isostatic pressing (HIP) treatment on these properties was investigated because such information is very limited, even though HIP treatment is required in many aerospace parts. Near net shape specimens were prepared for both tensile and creep tests. The effect of the HIP treatment on the microstructure in the specimens was observed by scanning electron microscope (SEM). Electron back scatter diffraction (EBSD) was used to analyze the effect of the HIP treatment on microstructure such as area fraction of each phase and grain size in the specimen. The results showed that the benefit of sintering during the HIP treatment decreased the voids with a size of up to 40 μm and the defects with a size of millimeter order due to lack of fusion in the specimens. The HIP treatment improved both tensile and creep properties at 750 ℃. It was found that the HIP treatment improved creep life by 15% and elongation by 60%, and delayed the starting point of tertiary creep. This is mainly because the HIP treatment eliminated the defects caused by lack of fusion and made the material more ductile than as-built specimen. On the other hand, the microscopic analysis by EBSD revealed that the HIP treatment increased the average diameter of the grain and widened the distribution of grain size, with the increase of the area fraction of Ti3Al(α2). The increase of grain diameter could decrease the strength according to the Hall-Petch Law. In this research, however, the elimination of the defects such as the voids and the defects due to lack of fusion improved the tensile and creep properties. The results suggested that the post heat treatment including cooling process after HIP treatment to control the microstructure is important.

Effect of HIP treatment on the microstructure and mechanical properties of a Ni-based superalloy fabricated by selective laser melted method

Selective laser melting (SLM) is one of the most emerging additive manufacturing (AM) method through the melting of metal powder to manufacture the full density parts, which will lead to an orientation microstructure and anisotropy mechanical properties. Thus, corresponding post-processing treatments, such as solution treatment (ST) and hot isostatic pressing (HIP), were subjected to the specimens before tests. The effect of the HIP on the microstructure and mechanical properties of SLM Inconel 625 was investigated through uniaxial tension tests at room and elevated temperature. The fracture mechanism was systematically characterized and analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). It was found that the microstructure after the HIP process is composed of equiaxed austenite, and the annealing twins are reduced. The tensile test results reveal that the HIP has a significant impact on the plastic behavior of the alloy at high-temperature, and is the main reason for the greatly improved elongation, compared to the ST process.

Effect of HIP Treatment on Fatigue Notch Sensitivity of Ti–6Al–4V Alloy Fabricated by Electron Beam Melting

The effect of hot isostatic pressing (HIP) treatment on the fatigue notch sensitivity of Ti–6Al–4V alloy fabricated by electron beam melting (EBM) was investigated. The results indicate that the fatigue notch sensitivity of the as-fabricated samples is much lower than that of HIPed samples. The variation of $$\alpha$$ lamella thickness and the distribution of pore defects have an effect on the fatigue strength in smooth and notched EBM Ti–6Al–4V samples, resulting in the divergence of the as-fabricated and HIPed samples on fatigue notch sensitivity.

Study on SiO2 thin film modified by post hot isostatic pressing

SiO2 thin film is one of the important low refractive index films commonly used in the field of optical thin films. In this paper, the Hot Isostatic Pressing (HIP) technique is applied to the post-treatment of SiO2 thin film materials for the first time. The thin film samples were prepared by ion beam sputtering deposition technique. The samples were heated at 300 °C for 50 MPa under vacuum argon atmosphere for 24 h. The samples were analyzed by the spectra in the visible and infrared bands and surface deformation. The effects of HIP treatment on the refractive index, physical thickness, stress, Si-O-Si bond angle and relative density of films were obtained. The results show that the refractive index decreases from 1.4685 to 1.4591, the physical thickness increases 0.6%, the stress changes from −493 MPa to −226 MPa, and the Si-O-Si bond angle increases from 129.85° to 131.32°. The fundamental physical mechanism of the change for all the characteristics is the film stress. The release of film stress leads to the decrease of the density of the film, and the variation of the thin film density is proved by the change of asymmetric stretching vibration frequency of SiO2 thin film. In addition, the HIP treatment can reduce the OH-group chemical defects in the SiO2 thin film.

Effects of Hot Isostatic-Pressing Treatment on Properties of PbMg0.047Nb0.095Zr0.416Ti0.442O3 Thin Films

c-axis-oriented epitaxial 1.2-μm PbMg0.047Nb0.095Zr0.416Ti0.442O3 (PMNZT) films with a comparatively large piezoelectric coefficient d 33 (=90 pC/N) fabricated on Pt(100)/MgO(100) substrates by metalorganic decomposition were treated by hot isostatic pressing (HIP). The HIP-pressure dependence on d 33 of the 1.2-μm PMNZT samples treated at 850°C for 1 h under Ar/O2 mixed gas pressures of 49–196 MPa was investigated. The d 33 value of the HIP-treated samples was almost constant (=60 pC/N), independently of the amplitude in pressure. Although the HIP treatment hardly contributes to an improvement on d 33, it can be expected to minimize the deviation of d 33 and provide highly-reliable piezoelectric elements.

Effects of HIP Treatment on the Microstructure of Cr50-Si50 Target

Hot Isostatic Pressing (HIP) is a process that uniquely combines higher pressure and temperature to produce materials and parts with substantially better properties than those fabricated by other methods. Commercial as-hp (hot pressing) treated Cr50-Si50 targets are used throughout this study. The aim of this paper is to discuss the methods and to find a suitable HIP treatment for the as-hp treated Cr50-Si50 target. Otherwise, we also to find the effects of microstructure on the mechanical properties of HIP treated Cr50-Si50 target. To evaluate the effects on microstructure and properties of the Cr50-Si50 target by HIP process, SEM, TEM and porosity, density inspections were performed. The experiment results show that HIP treatment at 1373 K under the pressure of 175 MPa and 4 hours for Cr50-Si50 target is the optimum condition. In this study, HIP treatment reduced the porosity of the target about 60%.

Effect of HIP Treatment on the Fracture Strength of Reaction-Sintered SiC

Three reaction-sintered silicon carbides (RS-SiC) with different free Si contents and different porosities were heat-treated at 1780°C for 2h in Ar under a pressure of 200MPa by hot isostatic pressing (HIP) and 0.1MPa by usual heat-treatment. The capsule-free HIP-treated specimen lost 4% free Si by evaporation and exhibited a strength of 130MPa, about 72% lower than that of the as-received specimen. Nevertheless, the capsule HIP-treated specimen was free from pores, and exhibited a strength of 346MPa, about 25% lower than that of the as-received specimen. The HIP-treatment of the Si-free specimen in a capsule did not change the strength. However, the strength of the Ar-heated (0.1MPa) specimen without free Si was 270MPa, 32% higher than that before Ar-heating, showing an increase of the bonding area between grains due to mass transport by surface diffusion and/or evaportion-condensation. For the HIP-treated specimen, the decrease in the strength of the specimen with free Si may be attributed to the decrease in the bonding area resulting from penetration of liquid Si into SiC grain boundaries at elevated temperature; the unchanged strength of porous specimens without free Si may be due to the constant bonding area between grains because of no mass transport by surface diffusion and/or evaporation-condensation.