Hot Isostatic Pressing Process Research Articles

Influences of a Hot-Working Process on the Microstructural Evolution and Creep Performance of a Spray-Formed Nickel-Based Superalloy

A new third generation nickel-based powder metallurgy (PM) superalloy, designated as FGH100L, was prepared by spray forming. The effects of hot isostatic pressing (HIP) and isothermal forging (IF) processes on the creep performance, microstructure, fracture, and creep deformation mechanism of the alloy were studied. The microstructure and fracture were characterized by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The coupled HIP and IF process improved the creep performance of the alloy under the creep condition of 705 °C/897 MPa. As for both the HIPed and IFed alloys, the creep process was dominated by the accumulation of dislocations and stacking faults, cutting through γ′ precipitates. The microstructural evolution was the main factor affecting the creep performance, which mainly manifested as coarsening, splitting, and morphology change of γ′ precipitates. Both the creep fractures of the HIPed and IFed alloys indicated intergranular fracture characteristics. In the former, wedge-shaped cracks usually initiated at the trigeminal intersection of the grain boundaries, while in the latter, cavity cracks generate more easily around the serrated curved grain boundary and carbides.

The effect of hot isostatic pressure on the corrosion performance of Ti-6Al-4 V produced by an electron-beam melting additive manufacturing process

Additive manufacturing (AM) is a rapidly growing technology that enables the fast production of complex and near-net-shaped (NNS) components. Among the many applicable AM methods (particularly powder bed technologies), electron-beam melting (EBM) is gaining increased interest mainly in aerospace and medical industries, due to its inherent advantages for the printing of Ti-6Al-4V alloy. Although major strides have been made towards understanding the effect of hot isostatic pressure (HIP) on the mechanical properties of Ti-6Al-4V produced by AM, its effect on corrosion performance remains relatively unexplored. To date, the reported corrosion studies remain essentially limited to the selective laser melting (SLM) process, while the corrosion behavior of EBM Ti-6Al-4V and particularly HIPed EBM Ti-6Al-4V have not been fully realized. This paper provides a detailed analysis of this corrosion performance, including the stress-corrosion susceptibility of EBM Ti-6Al-4V in as-build condition and after HIP heat treatment. Microstructure and phase identifications were examined by scanning electron microscopy (SEM) and X-ray diffraction analysis. Corrosion performance was evaluated by electrochemical measurements, including open-circuit potential (OCP), potentiodynamic polarization analysis and impedance spectroscopy (EIS), as well as stress-corrosion examination in terms of slow strain-rate testing (SSRT). All of the corrosion tests were carried out in a 3.5 wt.% NaCl solution at ambient temperature. Owing to the natural excellent corrosion resistance of Ti-6Al-4V, the obtained results revealed that the HIP process has only a slight positive effect on the corrosion resistance of Ti-6Al-4V produced by EBM. This minor improvement may be related to the improved efficiency of the passivation layer that was attributed to the increased β-phase content and the reduction of α/β interfaces. In terms of stress corrosion sensitivity, the HIPed specimens exhibited extended time-to-failure (TTF) at the low strain rate at 2.5•10-7 1/sec, where the effect of the corrosive environment was more dominant.

Nanostructured NiTi Shape Memory Alloy Via Ni/Ti Nanolamination

Ultrafine grained NiTi shape memory alloy was consolidated from Ni/Ti laminates via accumulative roll bonding (ARB) followed by hot isostatic pressing (HIP). Due to the extensive plastic deformation arising from ARB and the attainment of ultra-thin layers of both Ti and Ni laminates, the subsequent HIP processing time was significantly reduced. Differential scanning calorimetry (DSC) analysis confirms that the shape memory effect was obtained in the consolidated NiTi alloy.

Study on effects of hot isostatic pressing process on microstructure and properties of CNTs/Al2009 composites

The CNTs/Al2009 composite powders were prepared by cryogenic milling method and then the CNTs/Al2009 matrix composites were fabricated by hot extrusion process or hot isostatic pressing (HIP)/hot extrusion process. The effects of HIP process on microstructure and interface structure of CNTs/Al2009 composites were studied by X-ray diffraction, raman spectroscopy, scanning electron microscopy and transmission electron microscope. Finally, the effects of HIP process on the CNTs/2009Al composites were characterized by tensile strength at room temperature. The results showed that the cryogenic milling process could disperse 1.0 wt. % of CNTs into the aluminum matrix, and the composites prepared by HIP and hot extrusion process had uniform microstructure and excellent tensile properties at room temperature. The tensile strength, yield strength and elongation of the 1.0 wt.% CNTs/Al2009 composites prepared by HIP and hot extrusion process were 560 MPa, 443.3 MPa and 10.2%, respectively. Hot isostatic pressing process had an important influence on the interfacial bonding strength of CNTs/Al2009 composites. The strength of the composite prepared by HIP and hot extrusion process was 20 MPa higher than that of direct hot extrusion process, and the elongation was basically the same. The main reason was that the high temperature and high pressure conditions of hot isostatic pressing process could promote the reaction of carbon and aluminum at the interface between CNTs and aluminum matrix, so that a few CNTs with severe damage and defects in some CNTs formed Al4C3 phase with aluminum, thereby improving two compatibility, and enhanced interface bonding.

Study on Microstructure and Mechanical Properties of Powder Metallurgy TA15 Titanium Alloy

TA15 pre-alloyed powder chosen in this paper is made by plasma rotating electrode method. The powders were used to prepare fully dense TA15 alloy ingots by the means of hot isostatic pressing(HIP) forming technology. The optimum parameter of the HIP process is 900°C /120MPa/3h. After the process of hot isostatic pressing, the powders were pressed into a fully dense ingot. An optital microscope was used to observe the microstructure of the ingot specimen and its formation mechanism was analysized. The microstructure of the TA15 alloy prepared by hot isostatic pressing of pre-alloyed powder is composed of fine α-equiaxed grains along lamellar colony boundaries. The mechanical properties exceed that of the casting level, which is close to the forging level. A typical TA15 alloy component was finally produced by HIP-PM process.

Влияние предварительной лазерной обработки поверхности на механические свойства диффузионного сварного соединения железоникелевого сплава

The experimental studies of the effect of preliminary laser pulsed surface treatment on mechanical properties of the diffusion welding joints of Fe-Ni alloy were carried out. The alloy surfaces was treated in inert gas (Ar) environment by scanning beam of nanosecond laser pulses with a wavelength 355 nm, repetition rate 100 Hz and scanning speed 1 mm/s. Laser spot was 220 µm, the energy density 2 and 3 J/cm2. Treated samples as well as the control untreated ones were placed at the same container and were diffusion bonded by hot isostatic pressing (HIP) at the temperatures of 1000 and 1160°С. Ultimate strength and elongation of weld joint materials were determined by tensile testing. It is shown that laser pulse treatment leads to improvement both the ultimate strength and relative elongation of the weld joints. Mechanical properties of the weld joints depends on the laser energy density. Weld joint properties can be increased by optimization of the laser treatment parameters. The best results were achieved at laser energy density 2 J/cm2. Ultimate strength was increased by 12% and 29% for HIP temperatures 1160 and 1000°С respectively. The elongation values also increased from 42% for non-treated samples up to 51% for samples treated at 2 J/cm2 energy density. Preliminary laser treatment of welded surfaces permits to reduce the HIP temperature by 160°С and thereby reduce power consumption during HIP process.

Characterization of Bi-Te p-Type Thermoelectric Materials Produced by Uniaxial and Hydrostatic Sintering Technologies.

The anisotropic structure of Bi₂Te₃-type thermoelectric materials makes them prone to mechanical vulnerabilities and inconsistent electrical and thermal properties according to microstructural orientation. In this study, sintered BiSbTe bodies were synthesized by spark plasma sintering (SPS), hot pressing (HP), and hot isostatic pressing (HIP) using p-type thermoelectric powders produced through oxide reduction. Changes in the microstructure and thermoelectric properties were investigated according to the sintering process. The thermoelectric properties of the samples produced by uniaxial methods (SPS and HP) were affected by the direction of pressing during sintering; the electrical and thermal conductivities differed by up to 30% depending on the orientation. In contrast, the hydrostatic HIP process did not impart such directionality; the difference in thermoelectric properties according to orientation was significantly reduced to less than 4%. Moreover, the sintered Bi₂Te₃ body produced by HIP showed outstanding thermoelectric performance at a much lower temperature than the samples produced by SPS or HP, with a maximum figure-of-merit (ZT) of 1.42 at 373 K.

Effect of post-treatments on microstructure and mechanical properties of a novel nickel-based powder metallurgy superalloy processed by selective laser melting

A newly developed third generation nickel-based powder metallurgy (PM) superalloy, designated as FGH100L, was produced through Selective Laser Melting (SLM). Post-treatments, including Heat Treatment (HT), Hot Isostatic Pressing (HIP) and combined HIP + HT treatment, were carried out on the as-SLMed alloy to improve its mechanical properties by controlling the microstructure and/or reducing the defects in the alloy. Both HT and HIP treatments facilitated the recovery and recrystallization of the superalloy, especially when the solution temperature reached 1150 °C, thereby homogenizing the microstructure and refining the grains. During the post-treatment, the number density of γ′ precipitates increased obviously with the process varying from SLM, SLM + HIP, SLM + HT to SLM + HIP + HT, and both yield strength and ultimate strength increased accordingly, indicating that the precipitation strengthening played a major role in improving the alloy strength. During the HIP process, the size and quantity of the pores were greatly reduced, which contributed greatly to a much higher elongation of the SLM + HIP alloy than that of the SLM and SLM + HT alloys. The fracture surfaces of the SLM alloys after different post-treatments showed transgranular fracture features, while the intergranular fracture was the main fracture mode of the as-SLM alloy.

Simultaneously enhanced strength and ductility of FGH4097 nickel-based alloy via a novel hot isostatic pressing strategy

Hot isostatic pressing (HIP) of nickel-based superalloys still suffer from some detrimental carbides precipitated along the prior particle boundaries (PPBs), resulting in the degradation of mechanical properties of superalloy parts. In this study, a novel asynchronous loading HIP strategy, elevating temperature to the highest value first and then raising pressure, was proposed for FGH4097 to overcome this industrial challenge. The results manifest this novel strategy paves the way for fabricating nickel-based superalloys with both significantly enhanced strength and ductility by in-situ eliminating carbides precipitated along PPBs during HIP process, further boosting HIP process as a potential technology for the near-net manufacturing of key components in aerospace field.

Enhanced tensile properties in a Mg-6Gd-3Y-0.5Zr alloy due to hot isostatic pressing (HIP)

Hot isostatic pressing (HIP) was applied to Mg-6Gd-3Y-0.5Zr (GW63) alloy to reduce shrinkage porosity, thus, to enhance the integrity and reliability of castings. During HIP process, shrinkage porosity was closed by grain compatible deformation and subsequent diffusion across the bonding interface. The amount of initial shrinkage porosity was the key factor for shrinkage porosity closure. HIP was testified to be effective on shrinkage porosity reduction in GW63 alloy due to its relatively narrow solidification range and resultant low content of initial shrinkage porosity in most sections, leading to higher tensile properties both in as-cast and cast-T6 condition. The improvement in tensile properties was mainly because of shrinkage porosity reduction and resultant effective rare-earth (RE) elements homogenization and precipitation strengthening.

Room-temperature lasing on Fe2+:ZnSe with meniscus inner doped layer fabricated by solid-state diffusion bonding

An Fe2+:ZnSe laser on a polycrystalline active element with an inner doped layer in the form of a meniscus operating at room temperature was investigated. The active element was manufactured using the solid-state diffusion bonding (SSDB) technique. The billets, in the form of plano-concave and plano-convex ZnSe lenses with a radius of curvature of 200 mm, were subjected to diffusion bonding. Before bonding, zinc selenide was doped with Fe2+ ions by diffusion through spherical lens surfaces by the process of hot isostatic pressing (HIP). After the SSDB procedure, the prepared sample was subjected to an additional HIP treatment. An Fe2+:ZnSe polycrystal was pumped by an electric-discharge hydrogen fluoride (HF) laser. The use of the active element with an inner doped layer in the form of the meniscus permitted an increase in the pump spot diameter, at which there was not yet any reduction in laser output energy associated with the development of transverse parasitic oscillation. This increase was ~19% (compared to samples with a single flat doped layer). The output energy of 480 mJ was achieved at a total efficiency (with respect to absorbed energy) of 38% on the 20 mm diameter Fe2+:ZnSe sample with the meniscus inner doped layer.

Recrystallization mechanism of abnormal large grains during long growth of CVD-ZnS

Abnormal large grains influencing highly the optical and electrical properties are commonly observed in the bottom part of CVD-ZnS layers. We have analyzed the films using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and infrared transmittance tests. Compared to normal grains, more homogeneous and simpler structures have been observed in abnormal large grains in CVD-ZnS. In addition to the obvious difference in sizes, the crystalline outline and interior structure of normal and abnormal large grains are found to be markedly different. Distorted structures and stacking faults, such as wurtzite phase and polytypes of ZnS, are not detected in the large grain areas. Preferred orientation of abnormal large grains is found to be sphalerite (1 1 1). These results could be explained as due to the recrystallization mechanism of abnormal large grains. Samples with large grains show lower infrared absorption band (at 6.2 µm wavelength) compared to samples with normal size grains. However, the infrared transmittance is found to be lower for the samples with large grains. Microstructure patterns show the presence of plenty of microdefects in boundaries between large grains, which indicates that the recrystallization in the volume with large grains is not as perfect as the recrystallization in hot isostatic pressure process (HIP).

Varied heat treatments and properties of laser powder bed printed Inconel 718

The effects of post-build heat-treatments on the microstructure, phase formation, recrystallization behavior, and mechanical properties of laser powder bed additively manufactured Inconel 718 superalloy were investigated. Several heat-treatment schedules were used, including simulated hot isostatic pressing (HIP), and variations of the standard double aging treatment with various soaking times and quench procedures. Their effects on the precipitation, grain morphology, grain size, texture sharpness and mechanical properties were all documented. For the as-built coupons, columnar grains with inter-dendritic micro-segregation were formed along the build direction (xz-plane) with equiaxed grains forming on perpendicular sections to the build direction (xy-plane). After prolonged soaking times during the simulated HIP process, the microstructure transitioned from heterogeneous columnar grains to homogenous recrystallized grains with MC-type carbide precipitates. This leads to changes of microhardness (281 HV2.0 to 171 HV2.0), Young's modulus (209 GPa–229 GPa) and texture intensity. However, aging treatments increased both hardness and Young's modulus possibly because of formation of γ″ and γ′ precipitates in the Ni-matrix and the small effective grain size. Phase analysis using XRD confirmed the evolution of the precipitate formation. The combination of additive manufacturing and post-build heat-treatments can result in optimized microstructures and mechanical properties for specific applications depending on part requirements and operating conditions.

A new and efficient thermo-elasto-viscoplastic numerical implementation for implicit finite element simulations of powder metals: An application to hot isostatic pressing

Hot isostatic pressing (HIP) combines high temperatures and pressures to consolidate powder metals (PM) to form exotic parts that cannot be obtained from traditional manufacturing processes. Manufacturers need to utilize mathematical tools, such as the finite element (FE) method, to simulate the HIP process to avoid the trial and error method in product and process development. FE simulations of the HIP process require constitutive models that simultaneously capture the various deformation mechanisms, such as plasticity and creep, during powder densification. Since the HIP process can occur over several hours, these numerical implementations need to be both accurate and efficient for manufacturers to exploit the HIP process fully. This paper presents a new and efficient numerical scheme that accelerates FE calculations of PM that undergoes the HIP process. This work couples the constitutive models presented in Van Nguyen et al. (2017) for thermal, creep, plasticity, and density changes into a seamless integration scheme. The proposed numerical scheme is implemented a user-defined material subroutine (UMAT) for mechanical calculations in an implicit formulation of the commercial finite element software LS-DYNA. A thermal user-defined material subroutine (ThuMAT) is also implemented to account for the porosity effect on thermal properties in thermal calculations. FE simulations of a stainless steel 304/316 L capsule that undergo the HIP process are performed to highlight the efficiency of the proposed model. The predicted deformed shape of the capsule using the proposed integration scheme showed excellent agreement with previous implementations. Furthermore, the proposed integration scheme can provide a computational speedup of up to 1,100% without a loss of accuracy compared to previous implementations.

Effect of HIP Treatment on Microstructure and Fatigue Strength of Selectively Laser Melted AlSi10Mg

This study shows the effect of hot isostatic pressing (HIP) on the porosity and the microstructure, as well as the corresponding fatigue strength of selectively-laser-melted (SLM) AlSi10Mg structures. To eliminate the influence of the as-built surface, all specimens are machined and exhibit a polished surface. To highlight the effect of the HIP treatment, the HIP specimens are compared to a test series without any post-treatment. The fatigue characteristic is evaluated by tension-compression high cycle fatigue tests under a load stress ratio of R = −1. The influence of HIP on the microstructural characteristics is investigated by utilizing scanning electron microscopy of micrographs of selected samples. In order to study the failure mechanism and the fatigue crack origin, a fracture surface analysis is carried out. It is found that, due to the HIP process and subsequent annealing, there is a beneficial effect on the microstructure regarding the fatigue crack propagation, such as Fe-rich precipitates and silicon agglomerations. This leads, combined with a significant reduction of global porosity and a decrease of micro pore sizes, to an improved fatigue resistance for the HIPed condition compared to the other test series within this study.

Estimation of fatigue parameters in total strain life equation for powder metallurgy superalloy FGH96 and other metallic materials

Monotonic tensile and low cycle fatigue (LCF) tests of powder metallurgy (PM) superalloy FGH96 were conducted at 480 °C and 650 °C. The alloy was widely used to manufacture the aero-engine turbine disk by a process of hot isostatic pressing (HIP). An analysis method was proposed to obtain the fatigue parameters of the total strain equation with clearly physical meaning. The proposed method offered satisfied results for FGH96. Fractography analysis was conducted to determine the material fatigue failure mechanisms. Comparing to the given parameters of total strain life equation of the handbook, the predicted fatigue lives of GH4169 alloy at 500 °C and 650 °C, FGH95 alloy at 500 °C and TC4 alloy at 200 °C by the proposed method agreed better with the experimental results.

Manufacturing and testing of flat type W/Cu/CuCrZr mock-ups by HIP process with PVD coating

The development of W/Cu/CuCrZr mock-ups by hot isostatic pressing (HIP) bonding technology is in progress for the application to tungsten divertor. In HIP process, physical vapor deposition (PVD) method was applied for interlayer coating of high purity nickel (Ni) and copper (Cu). Interlayer coatings were selected to enhance diffusion between tungsten (W) and oxygen free high conductivity copper (OFHC-Cu) interlayer during the HIP bonding process. The Ni and Cu were deposited by different thicknesses on tungsten surface with roughness of 6Z and 0.8Z. HIP technology is employed with two kinds of processing conditions: 60 MPa, 600 ℃ and 70 MPa, 700 ℃. The interlayer of samples are observed by FE-SEM and EDS and subjected to shear test and heat flux test. There is no significant difference in shear strength due to PVD coating thickness. But the shear strength of samples fabricated by 70 MPa and 700 ℃ HIP condition is higher than those fabricated by 60 MPa and 600 ℃ condition. Heat flux tests were performed to compare the thermal conductance through the bonded layer and thermal fatigue behavior of the samples as a preliminary test of bonding quality. All these results were analyzed systematically to find the optimum fabrication conditions in the HIP bonding of W/Cu/CuCrZr.

Numerical simulation and optimization of the hot isostatic pressure process of a part of aircraft structure

Hot isostatic pressure process (HIP) has been widely used in aviation and aerospace fields to produce high-performance components with requirements of lightweight, high-reliability, and high-load requirement. During the HIP process, components are produced by powders arrangement, deformation, and bound diffusion. However, the limitation of the HIP process is the non-uniform density distribution of the product, which should be eliminated by appropriate design of the process. In this study, the HIP process of a part of aircraft structure is numerically studied. An improved Shima model for the HIP is introduced to investigate the deformation and densification process of the component. Two schemes of the HIP process are designed and compared by analyzing the relative density distribution at the selected sections of the component. Based on the optimized scheme, the component with uniform density distribution and high density is produced. The results indicated that the proposed model can predict the density distribution of the component produced by the HIP process and is helpful for process optimization.

Assessment of the fatigue performance of heat-treated addictive manufactured TiAl6V4 specimens

Titanium Ti6Al4V alloy has excellent mechanical properties and corrosion resistance combined with low specific weight, and is commonly used in biomedical applications, automotive and aerospace components, involving fatigue loadings. Current work studies the fatigue behavior under strain amplitude control of titanium TiAl6V4 specimens, intending to characterize fatigue strength from low to high life range after different heat treatments. Fatigue tests were carried out at room temperature, using round dog bone specimens produced by selective laser melting (SLM), where laser powder deposition occurred in layers perpendicular to the loading direction. Two batches of specimens were tested: one subjected to a stress relieve treatment and a second one treated by the hot isostatic pressing process (HIP). The material was characterized in terms of the tensile mechanical properties, cycle curve, Basquin and Coffin equations. Additional analysis of the hardness and scanning electron microscopy was carried out to complement the discussion of the results. The obtained dada showed that the stress relieved specimens exhibits significantly cyclic softening, increasing with applied strain, while HIP specimens show a practically stable cyclic behavior in relation to the monotonic curve. Material response for both treatments is well fitted by Basquin and Coffin-Manson formulations. The transition life was 187 reversals and 326 reversals, for stress relieved and HIP specimens, respectively. Fatigue life for a given strain is governed by the strain value, independently of the post manufacturing heat treatment.

Effect of hot isostatic pressing on microstructure and mechanical properties of CLAM steel produced by selective laser melting

Blanket is the key energy conversion component of a fusion reactor, it is designed with a large number of complex embedded cooling channels to remove the high nuclear heat deposition. Due to the complex inner-channeled structure, the fabrication of the blanket components has been one of the key issues of the blanket technical development. In this study, the selective laser melting (SLM) additive manufacturing (AM) processing was employed to fabricate small scale test blanket module with China low activation martensitic (CLAM) steel, and the hot isostatic pressing (HIP) was applied to improve the microstructure and mechanical properties. The microstructure and mechanical properties of the SLM built CLAM at the as-built, standard heat treatment (SHT) and HIP&SHT status were investigated and evaluated. The results showed that the relative density at the as-built status compared to the hot-rolled CLAM steel reached 99.7%. The tensile strength of the as-built status was 966.2 MPa and 829.1 MPa in the directions vertical and parallel to the building direction, respectively. After the HIP&SHT, the orientation of the microstructure and the difference in strength in different directions decreased. The strength values in the directions vertical and parallel to the building direction were similar, which were equivalent to that of the hot-rolled CLAM steel with SHT. Moreover, the impact absorbed energy in the directions vertical and parallel to the building direction was increased from 21.02 J to 9.18 J at the as-built status to 54.48 J and 18.83 J at the HIP&SHT status, respectively. Meanwhile, micro-defects were drastically decreased with the help of HIP. It could be concluded that the dislocation migration and recrystallization in HIP process is effective to improve the microstructure and mechanical properties of the SLM built CLAM steel.