Hot Isostatic Pressing Pressure Research Articles

The formation mechanism of void in thin-walled capsule welding joint induced by HIP

Thin-walled capsule significantly impacts the overall quality of hot isostatic pressing (HIP）products, with capsule reliability being a crucial factor in determining the success or failure of the HIP process. High-temperature creep is essential for the densification of HIP powder. However, the capsule, made of dense metal, undergoes its own creep process. High temperature and high pressure may induce void formation in the capsule due to diffusion and creep. The integrity of the capsule typically relies on the welding process, and void formation at welded joints poses a significant challenge to the capsule’s reliability, increasing the likelihood of failure. This study investigates the mechanisms of void formation in welded joints during the HIP process. Results indicate that high temperature and high pressure during HIP promote the formation of two types of voids in mild steel: Kirkendall voids and creep voids. Kirkendall voids are driven by diffusion and influenced by the HIP insulation temperature, which affects their state but not their formation. Creep voids, however, originate from stress concentration at grain boundaries during creep deformation. Their distribution density is positively correlated with the degree of creep deformation, which is primarily controlled by HIP pressure and temperature.

Martensite Transformation in Tool Steels under Isostatic Pressure–Implementation of In-Situ Electrical Resistivity Measurements into a Hot Isostatic Press with Rapid Quenching Technology

Powder metallurgical (PM) parts usually benefit from more homogenous and finer microstructures as opposed to conventionally processed material. In particular, hot isostatic pressing (HIP) combined with near-net-shape technologies can produce almost defect free PM tools with complex geometries. Recent advances in the plant technology of smaller HIP units allow the integration of hardening heat treatments in HIP processes. Thus, additional processing steps, transportation, energy consumption and cost are reduced. However, it is known that high pressure influences phase stability and transformation temperatures. Still, knowledge of the martensite start temperature (MS) is crucial for the design of hardening heat treatment. Since the influence of pressure on MS in HIP heat treatment is insufficiently investigated, it is the aim of this study to deploy a measurement method that allows to record MS as a function of pressure, temperature and cooling rate. Taking the hot working tool steel AISI H11 (X37CrMoV5-1, 1.2343) as the reference material, in this study for the first time the method of an in-situ electrical resistivity measurement was used to measure MS within a HIP. To investigate the influence of HIP pressure on Ms, resulting microstructures and hardness, specimens were austenitized at a temperature of TAUS = 1050 °C for tAUS = 30 min at pAUS = 25, 50, 100 or 150 MPa. Additionally, the MS temperature of the same material was determined by quenching dilatometry at ambient pressure for comparison purposes. Characterization of microstructures was conducted by scanning electron microscopy while hardness as an important technological property of tool steels was measured according to the Vickers method. Furthermore, the CALPHAD method was used to compute the thermodynamic influence of pressure on phase stabilities. The experimental results indicate that the method of in-situ resistivity measurement can be used to measure MS during an integrated HIP heat-treatment process. Besides, a stabilizing effect of pressure on the close packed crystal structure of the austenitic fcc phase is clearly detected, resulting in a reducing influence on the MS temperature of AISI H11 by up to 90 K.

A multi-scale study of Inconel 625 powders HIP process and construction of HIP maps

A multi-scale analysis of Inconel 625 powders hot isostatic pressing (HIP) has been carried out numerically by finite element method base on the modified Shima model. Numerical results have indicated the capsule deformation and powders movement at different HIP parameters. Furthermore, five interrupted experiments have given a vivid description about the powder densification process in the micro level. Results have shown that at the initial stage of HIP, densification process is caused by the movement, arrangement, and aggregation of powders. When the coordinate number reaches to the maximum, plastic deformation plays the leading role in densification. When the applied pressure is bigger than the yield stress of powders, parts of the particles will be squeezed into the voids and all the powders particles are linked into a whole unit. At the last stage, plastic flows are relatively small; diffusion and power law creep mechanisms play the leading role in densification. Powder atoms are squeezed into the residual porosity slowly with the help of isostatic temperature and pressure. Based on the above micro analysis, coupled with the original empirical densification model, the HIP maps of Inconel 625 powders have been constructed. And the HIP maps have depicted how the relative density changes with HIP temperature, pressure, and duration time. Effects of particle size on the densification have also been considered in the HIP maps.

Interaction of hot isostatic pressing temperature and hydrostatic pressure on the healing of creep cavities in a nickel-based superalloy

The interaction of soaking temperature and hydrostatic pressure on the evolution of creep cavities under hot isostatic pressing (HIP) for a nickel-based superalloy is investigated. The concentrically-oriented γ′ rafting structure occurs around the cylindrical creep cavity under 1453K/150MPa/1h. The cylindrical cavity also tends to break into a row of spherical voids due to the classical Rayleigh instability. HIP temperature and pressure, acting as two driving factors for solute diffusion, interact and influence the healing behavior of creep cavities.

Modification of Sintered Titanium Alloys by Hot Isostatic Pressing

Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures close to ingot metallurgy products. However, residual porosity is normally present in the products produced by the PM route of powder pressing and sintering (P&S)\, and this needs to be reduced by using post-sintering process step such as hot isostatic pressing (HIP) and forging. In this study, the microstructural and mechanical property changes caused by HIP of samples of two alloys, near-α Ti-3Al-2.5V alloy and α+β Ti-6Al-4V, produced by P&S route were investigated. Two types of powders were utilised: prealloyed powders and blend of elemental titanium powder and master alloy powder. Four conditions defined by HIP temperature, pressure and time were used to HIP the sintered samples with two geometries. The results show that, independent of the HIP conditions used, HIP increased the relative density of the samples to approximately 97.5% and their hardness by 30-50 HV depending on the HIP condition. However, HIP at 1000°C changes the fracture mode of the sintered samples from ductile to brittle.

Effects of temperature of HIP process on characteristics of Inconel 718 superalloy

The present study focuses on the effects of the temperature of the hot isostatic pressing (HIP) procedure on Inconel 718 superalloy. HIP temperatures used were 1150, 1175, 1180 and 1205°C. HIP pressure was maintained at 1000 bar (98·6 MPa) and the soaking time was 2 h. Both room and high temperature tensile and bending tests were used to evaluate the effects of HIP temperature on Inconel 718 superalloy. Porosity tests and microstructural examination were performed. The results showed that the optimum HIP process temperature for 718 superalloy is 1180°C. Processing at this temperature can significantly reduce porosity and improve the microstructure segregation of Inconel 718 superalloy. Under these conditions, the superalloy showed an 18·28% increase in tensile strength at room temperature, a 7·38% increase at 540°C, and a 3·84% increase at 650°C. The elongation increased by 55·6% at room temperature, 109·71% at 540°C, and 19·91% at 650°C. Finally, the results of three-point bending tests showed that hipping at 1180°C can enhance the bending strength by 39·5% at room temperature and 13·83% at 540°C.

Evaluation of HIP pressure on Inconel 718 superalloy

In the companion study 'Effects of temperature of HIP process on characteristics of Inconel 718 superalloy' in the present issue, the temperature parameters for hot isostatic pressing (HIP) of Inconel 718 superalloy were discussed. That study showed that a HIP temperature of 1180°C for Inconel 718 superalloy was optimum. The present study continues to discuss the effects of processing pressure of HIP for Inconel 718 superalloy. Four different HIP pressures were used: 1000, 1500, 1750 and 2000 bar (1 bar = 0·0986 MPa). Meanwhile the HIP temperature was maintained at 1180°C and soaking time was 2 h. To evaluate the effects of HIP pressure for Inconel 718 superalloy, tensile and bending tests at room and high temperature were evaluated. Porosity tests and microstructure inspection were also performed. The results show that 1750 bar of HIP treatment was optimum for Inconel 718 superalloy. It reduced the porosity by 78·5% and decreased the δ phase precipitation for Inconel 718 superalloy. It also increased the tensile strength by 18·48% at room temperature, 13·02% at 540°C, and 20·11% at 650°C. The elongation increased by 33·2% at room temperature, 124·82% at 540°C, and 53·24% at 650°C in tension tests. Finally, the results of three-point bending tests showed that the optimum processing pressure of HIP can enhance the bending strength by 32·45% at room temperature and 17·84% at 540°C.

Evaluation of Hot Pressing and Hot Isostastic Pressing Parameters on the Optical Properties of Spinel

The effect of different hot pressing and hot isostatic pressing (HIP) temperatures and pressures on the optical properties of spinel was studied. Extinction coefficients of spinel samples were estimated by comparing the measured transmittance with the theoretical transmittance as calculated via a Sellmeier model. Results showed that the relative size of the scattering sites was large compared with the wavelengths of light (0.35–5.5 μm). Overall, increasing HIP temperature and pressure resulted in decreasing the optical extinction. The lower of two hot pressing temperatures (1620° vs 1650°C) prior to HIPing resulted in lower scatter coefficients after HIPing; this effect was most significant in the infrared.

Ferroelectric Properties and Memory Characteristics of Pb(Zr0.52 Ti0.48)O3 Thin Films Crystallized by Hot Isostatic Pressing

Pb(Zr0.52Ti0.48)O3 films with highly uniform c-axis orientation were fabricated on PbTiO3 (PT)/ Pt(111)/SiO2/Si(100) substrates by hot isostatic pressing (HIP) from the amorphous state. All the PZT samples HIP-treated 500°C for 1 h under gas pressures of 1.0–2.0 MPa showed the preferred (001) orientation with c-axis orientation, α > 0.80. The relative permittivity tended to decrease gently with increasing HIP pressure, whereas the dielectric loss increased almost linearly in the 1.5–100 MPa. The PZT sample treated at 1.5 MPa had a symmetric and slim hysteresis loop shape with a remanent polarization, P r = 15 μ C/cm2 and coercive field, E c = 60 kV/cm. Both samples treated at 10 and 100 MPa exhibited almost the fatigue-free behavior that resisted degradation even after 3 × 1010 cycles.

Effects of Hot Isostatic Pressing on Polarization Fatigue Characteristics of Lead-Based Ferroelectric Thin Films Crystallized from the Amorphous State

Ferroelectric properties and memory characteristics of Pt/0.24Pb(Zn1/3Nb2/3)O3⋅0.384PbZrO3⋅0.376PbTiO3 (PZNZT)/PbTiO3/Pt capacitors fabricated by crystallizing amorphous PZNZT films at 500°C for 1 h under high pressures of 1.0-176.5 MPa using hot isostatic pressing (HIP) are investigated. The relative permittivity decreased linearly with increasing HIP pressure. All the samples treated at pressures greater than 17.7 MPa completely showed fatigue-free characteristics even after up to 3×1010 cycles. From dielectric measurements and cross-sectional highresolution TEM images, these fatigue-free behaviors may be caused by that several elongated amorphous areas oriented parallel to the substrate formed near the interface between the crystallized PZNZT layer and the PbTiO3 (PT) seed layer, which would play an important role in restraining the diffusion of lead from the crystallized layer toward the PT seed layer.

Characteristic evaluation of HIP bonded SS/DSCu joints for surface roughness

Bonding technologies of SS/DSCu, SS/SS and DSCu/DSCu using HIP method have been developed for the fabrication of the ITER shielding blanket first wall. In this study, the effect of the roughness of the HIP bonding surface has been studied for the 1–40 μm roughness from the view points of bondability of surfaces by HIPping and simplification of fabrication procedure. For the tensile properties, it has been found that the effect of the roughness within above range is negligibly small. On the other hand, it has been confirmed that the finer the surface roughness, the higher impact properties for the DSCu/DSCu joints. Significant differences are not found in the SS316L/DSCu and SS316L/SS316L joints with 1–40 μm, though the finer the surface roughness, the slightly higher the impact energy value. Also, it has been found that the HIP bonded joint with good bondability is obtained by using higher HIP pressure, i.e. 200 MPa even with coarser surface roughness, i.e. ∼10 μm, to reduce the machining requirement in the fabrication procedure. In the fabrication of the International Thermo-nuclear Experimental Reactor (ITER) shielding blanket, conditions of the surface roughness and the Hot Isostatic Pressing (HIP) pressure will be selected by taking into account the machining cost for surface preparation and the HIP process cost based on dimensions of the part to be HIP bonded.

HIP sintering and magnetic saturation of iron nitride

In this study a hot isostatic pressing (HIP) furnace under high temperature and high nitrogen pressure is used to perform nitrogen diffusion in mechanically processed iron powders. After hipping, the γ′-Fe4N phase is formed while unreacted b.c.c. iron also remains in the powder. The amount of γ′-Fe4N is estimated by calculating the relative X-ray diffraction peak intensity. The latter amount increases with increasing milling time because of new surface formation and defect creation. The nitrogen diffusion into grains occurs for a minimum value of the HIP pressure, then the alloying of nitrogen with iron appears for a minimum temperature. Mössbauer and EXAFS analyses indicate that the iron nitride is mainly located at the surface of the powder grains.

A study of iron nitrogenation by hot isostatic pressing

In this study a hot isostatic pressing (HIP) furnace under high temperature and high nitrogen pressure is used to perform nitrogen diffusion in mechanically processed iron powders. After hipping, the γ′-Fe 4N phase is formed while unreacted b.c.c. iron also remains in the powder. The amount of γ′-Fe 4N is estimated by calculating the relative X-ray diffraction peak intensity. The latter amount increases with increasing milling time because of new surface formation and defect creation. The nitrogen diffusion into grains occurs for a minimum value of the HIP pressure, then the alloying of nitrogen with iron appears for a minimum temperature. Mössbauer and EXAFS analyses indicate that the iron nitride is mainly located at the surface of the powder grains.

Properties of silicon-based ceramics produced by hot isostatic pressing ultrafine powders

Abstract The densification of ultrafine laser-synthesized SiC (below 20 nm) and of mixtures of ultrafine SiSiC with conventional carbon powders has been performed by encapsulated hot isostatic pressing (HIP). Density and grain size as functions of temperature, HIP pressure, additive content and porosity distribution of the green body are discussed for the case of poor SiC samples. The results of measurements of thermomechanical properties and the influence of the grain size are presented. Hardness shows a significant increase with decreasing grain size, especially in specimens with a high density. Hot hardness measurements up to 1100°C on a specimen with a grain size of about 300nm revealed a relatively high hardness level compared with conventional SiC ceramics in the intermediate temperature range. Indentation fracture toughness slightly decreased with decreasing grain size. Thermal conductivity of the fine-grained SiC-based samples are lower than the values of conventional SiC ceramics, indicating the influence of the fine grain size on the phonon scattering. Measurements at temperatures up to 1500°C reveal that the reduction in the thermal conductivity in fine-grained SiC is significantly reduced at higher temperatures.

Hot isostatic pressing of cast SiCp-reinforced aluminium-based composites

Two as-cast SiC particulate reinforced composites were treated by hot isostatic pressing (HIP) under different pressures and temperatures. The microstructures and tensile properties of the composites were characterized in the as-cast and HIPped conditions to study the effects of the HIP treatment. It was found that ductility of the as-cast composites was increased greatly by the HIP treatment but the yield stress was reduced drastically. The reduction of internal defects was identified to be the major factor for the improvement of the ductility. After the T6 treatment, the HIPped specimens were better than the as-cast specimens in strength as well as in ductility. The effects of the HIP temperature and pressure were also studied, and it was found that in the chosen temperature range of 450–550°C and pressure range of 100–150 MPa, increasing the temperature tended to improve the tensile properties, whilst increasing the pressure had little effect on the strength and ductility.

New beryllium materials

Totally isotropic beryllium materials are first obtained by hot isostatic pressing (HIP) of atomized powders with spherically shaped particles. The process parameters for different size fractions of the spherical powder are optimized by the use of the mathematical model of beryllium compaction, developed by the authors with due consideration of different mechanisms of pressurized sintering, and also the patterns of hot-isostatic pressing. By the mathematical simulation the densification rates during hot isostatic pressing of the beryllium powder with a berylline oxide content up to 1.5% were calculated. The HIP maps were constructed for different temperatures, pressures and sizes of powders. The quantitative contributions from different mechanisms of preform densification are determined and calculated in relation to HIP temperature and pressure. All-round studies of new beryllium materials have been made to determine their structure, physical—mechanical and special properties. Isotropic beryllium prepared from atomized powders is promising for applications in nuclear materials science.

Hot Isostatic Pressing of MgAl2O4Spinel Infrared Windows

Abstract Optically transparent MgAl2O2 spinels have been produced by hot isostatic pressing (HIP). The spinel samples were prepared by hot pressing and subjected to capsule-free HIPing. The hot-pressed samples were made at 1500°C with a pressure from 14 to 41 MPa for 2 to 4 hours. In the HIP process, the pressure ranged from 14 to 207 MPa at 1500°C. The effect of hot isostatic pressure on the bulk density, microstructure and optical properties of the spinel sample were investigated here. The bulk density of the sample increased with HIP pressure and the sample HIPed at 207 MPa resulted in a bulk density of 3·576 g/cm3, about 99·94% of the theoretical density. A bimodal grain size distribution exists in samples HIPed at pressures ≤ 138 MPa. The extent of the abnormal grain growth decreased with pressure. The transparent spinel with uniform and fine grain size of 2 μn was obtained at 207 MPa. The transmission at short wavelength increased significantly with HIPing pressure. The transmittance of the sample HIPed at 207 MPa at a wavelength of 0·7 μn was 72%.

Modeling of the consolidation of continuous- fiber metal matrix composites via foil- fiber- foil techniques

The consolidation of metal-matrix composites (MMC) via hot isostatic pressing (HIP) of foil-fiber-foil layups has been investigated using finite element method (FEM) metal flow analysis. For this purpose, the deformation pattern for various fiber arrangements was determined using representative unit cells to describe extremes in behavior. For a given fiber architecture, the consolidation time was found to be heavily dependent on the ratio of the HIP pressure to average flow stress and the friction conditions at the matrix-fiber interface. The specific influence of material properties such as the rate sensitivity of the flow stress appears to enter only as a second order effect. The FEM solutions were used to construct HIP diagrams delineating temperature-time-pressure combinations for full composite consolidation. Laboratory trials on subscale foil-fiber coupons were used to validate the FEM predictions.

Parametric studies of the hot isostatic pressing of rapidly solidified 304 stainless steel powder

The increasing importance of powder materials fabrication by use of hot isostatic pressing (HIP) has led to recent emphasis on analytical techniques for describing and understanding the process. Understanding of particle consolidation during the HIP process has been attempted through the modelling of densification behavior by considering the deformation of a representative particle due to forces transmitted through the particle contacts. However, the properties of HIPed material have not been thoroughly investigated in terms of their deformation maps and HIP parameters. Mechanical properties of a compact can be quite different depending on the location of various deformation map boundaries. Diffusional creep is involved not only in densification but also in bonding at particle contacts. HIP pressure increases mechanical contact and enhances density but not particle bonding per se. Discrepancies between experimental and calculated data points for shorter HIP times may have been affected by oxide film layer on the original powder.

Diffusion bonding reactions between a SiC/SiC composite and two superalloys during joining by hot isostatic pressing

Diffusion reactions during solid state joining of a ceramic SiC/SiC composite to two superalloys, Hastelloy X and Incology 909, by hot isostatic pressing (HIP) have been investigated. The HIP pressure was 200 MPa in all joining cycles, and the temperature/dwell time were either 800°C/15 min, 900°C/1 h or 1000°C/ 1 h. The reaction zones formed consisted of a thin layer of carbides surrounded by several layers containing silicides and free carbon. The thickness of the reaction layers increased with increasing temperature, but were more affected by the composition of the alloy. With more carbide formers in the alloy, the thickness of the reaction layer decreased. The SiC composite was found to be considerably more prone to reactions with these superallys during HIP as compared to Si 3N 4 under similar conditions.