Hot Isostatic Pressing Process Research Articles

Interfacial characteristics and thermal stability of polymer-derived SiCf/Ti composite fabricated by powder hot isostatic pressing

The novel SiCf/Ti composite is prepared by hot isostatic pressing (HIP) with polymer-derived (PD) SiC fiber and powder titanium alloy as raw materials in this work. The interfacial characteristics and thermal stability of the PD SiCf/Ti composite have been systematically investigated. The interfacial properties of the PD SiCf/Ti composites are quantified to discuss the interfacial reaction mechanisms and kinetics. The results show that with the proposed HIP process, the powder matrix can be near-fully dense, and the matrix and SiC fiber are well bonded with a uniform interfacial layer. The major interfacial products are C-Ti compounds and Si-Ti compounds, which are formed by atomic diffusion reaction. During subsequent thermal exposure conditions, the interfacial layer growth is temperature-dependent and diffusion-controlled, following the parabolic relation and Arrhenius law. The frequency factor k0 is 102–103 times lower than that in the chemical vapor deposition (CVD) SiCf/Ti composites, showing better interfacial thermal stability. After thermal exposure, the element diffusion becomes significant, and the microhardness of the near-interface zone is noticeably greater than the matrix microhardness because of the atomic diffusion of C. The microhardness of both the matrix and near-interface zone reaches the highest value after 900 °C/9 h thermal exposure. It is concluded that the PD SiCf/Ti composites with good thermal stability can be successfully fabricated by powder HIP.

Atomistic simulations to reveal HIP-bonding mechanisms of Al6061/Al6061

Molecular dynamics simulations were employed to understand the diffusion bonding process during hot isostatic pressing (HIP) of Al6061/Al6061 alloy. Simulations of the HIP process reveal atomistic phenomena that are difficult or unlikely to be observed experimentally and provide useful insights into the mechanism of diffusion and bonding. The results reveal that at the start of the HIP process, a massive incursion of oxygen atoms occurs from the pre-existing γ-Al2O3 to the 6061 region across the interphase interface. These oxygen atoms interact with the enriched Mg atom layer present at the existing γ-Al2O3 and 6061 matrix to form a secondary complex Mg2Al2O5 phase. Diffusion calculations also show that transport of atoms due to the applied pressure is 4–5 orders of magnitude higher than would occur in the absence of HIP conditions. The Mg2Al2O5 phase also provides efficient pathways for the rapid transport of Mg atoms. Because of the higher diffusion coefficients observed for Mg within the phase, Mg atoms can move more swiftly compared to their diffusion within other phases such as γ-Al2O3. This accelerated mobility facilitates the rapid movement of Mg atoms across the interface, leading to changes in the local composition and the potential growth of the Mg2Al2O5 phase.

Suppression of the sausaging effect in (Ba,Na)Fe2As2 round wires by using Ag1−zSnz/Cu double sheath

We report the fabrication of (Ba,Na)Fe2As2 round wires that are processed using the hot isostatic pressing (HIP) technique. We employed double sheaths composed of Cu and Ag1−zSnz alloy because they offer superior mechanical strength compared to pure Ag. The cross-sectional area of the wire core was measured using X-ray computed tomography. The findings of this study demonstrate that utilizing Ag1−zSnz alloy as the inner sheath material helps reduce the degree of the sausaging effect in the wire, resulting in a more uniform cross-sectional area of the wire core. However, transport critical current density (Jc) of the wires with the Ag1−zSnz alloy decreased gradually as the Sn content, z, increased, which may be attributed to the nonoptimized sintering temperatures during the HIP process. These results suggest that when heat-treated at an appropriate temperature during the HIP process, the use of Ag1−zSnz alloy holds great potential for use in high-performance applications.

Numerical Simulation Study on Coupled Heat Transfer During the Heating Process of Hot Isostatic Pressing Equipment

Abstract Hot isostatic pressing (HIP) technology is currently the primary process for manufacturing high-performance advanced materials, powder metallurgy, and diffusion bonding. With the increasing demand for enhanced material performance and a wider range of materials, the HIP process now requires reaching temperatures of up to 2000 °C and pressures of 200 MPa, with a temperature range of less than ±5 °C. This presents significant challenges in equipment design. This article utilizes engineering data inversion methods to accurately determine material parameters under high temperatures and establishes a visual simulation model for the core area of HIP equipment. By comparing the calculated temperatures with actual equipment temperature uniformity during experimental processes, the study found that after 120 min of heating, the simulated temperature in the working area closely matched the actual engineering temperature of 2105.36 K, with an error of less than 5%. Under empty furnace conditions, the minimum temperature difference in the working area is 12 K, and effective temperature uniformity can be easily achieved through insulation. Simulation results indicated that the processed product may decrease temperature uniformity in the furnace, suggesting that adding bottom insulation could increase temperature uniformity in the effective heat zone by 25%. This research provides a theoretical foundation for HIP equipment design and process optimization through simulation, ultimately enhancing process quality in a cost-effective and cost-efficient manner.

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.

Defect recrystallization in subtransus hot isostatic pressing of electron beam powder bed fusion Ti-6Al-4V

Post-build hot isostatic pressing (HIP) is a widely used method to close as-built defects (gas or lack-of-fusion porosity) in additively manufactured (AM) metal parts. Pore closure during this process often creates clusters of equiaxed grains, in contrast to coarse and directional as-built microstructures widely seen in AM metals. Understanding the mechanisms behind the formation of such microstructures is desirable for controlling anisotropy and improving mechanical properties of AM parts. Prior work has attributed defect-induced equiaxed grains to recrystallization during the HIP process; however the specifics of this recrystallization process have not been explored. This work systematically analyzes the grain structure, orientation, and misorientations of electron beam powder bed fusion (PBF-EB) Ti-6Al-4V to identify the mechanisms by which clusters of equiaxed grains can form during HIP of as-built microstructures. A combination of two mechanisms, dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), explains the phenomena. Evidence for both these processes is found in small rotations in crystallographic orientation, localized strains around prior pore defects, and specific misorientation distributions. Only subtransus HIP of Ti-6Al-4V was explored in this work. However, the mechanisms presented here are thought to contribute to recrystallization in other HIP processes whether for super-transus Ti-6Al-4V, β-Ti alloys, other alloy systems, or non PBF-EB build processes. These results build upon prior efforts to identify specific mechanisms by which refined microstructures can be achieved in as-HIPed AM metals, improving microstructural control and providing another pathway for microstructural tailoring via AM of metals.

Mechanical and Fatigue Properties of Ti-6Al-4V Alloy Fabricated Using Binder Jetting Process and Subjected to Hot Isostatic Pressing.

Binder jetting 3D printing is an additive manufacturing technique based on the creation of a part through the selective bonding of powder with an adhesive, followed by a sintering process at high temperature to densify the material and produce parts with acceptable properties. Due to the high initial porosity in the material after sintering, which is typically around 5%, post-sintering treatments are often required to increase the material density and enhance the mechanical and fatigue properties of the final component. This paper focuses on the study of the benefits of hot isostatic pressing (HIP) after sintering on the mechanical and fatigue properties of a binder jetting Ti-6Al-4V alloy. Two different HIP processes were considered in this study: one at 920 °C/100 MPa for 4 h, and a second at a higher pressure but lower temperature (HIP-HPLT) at 850 °C/200 MPa for 2 h. The effects of the HIP on the densification, microstructure, mechanical behavior, and fatigue properties were investigated. The results show that the HIP-HPLT process produced a significant increase in the mechanical and fatigue properties of the material compared with the as-sintered parts and even with the conventional HIP process. However, the fatigue and fracture micromechanisms suggest that the oxygen content, which resulted from the decomposition of the binder during the sintering process, played a critical role in the final mechanical properties. Oxygen could reduce the ductility and fatigue life, which deviated from the behavior observed in other additive manufacturing techniques, such as powder bed fusion (PBF).

Effect of Heat Treatment and Hot Isostatic Pressing on the Corrosion Behavior of Ti6Al4 V Parts Produced by Electron Beam Melting Additive Manufacturing Technology.

In this study, we investigated the effect of heat treatment (HT) and hot isostatic press (HIP) on the corrosion behavior of Ti6Al4 V, manufactured by electron beam melting (EBM) additive manufacturing. The preliminary results showed that the thermal process makes the columnar structure more pronounced and the α-lathe coarser compared to EBM. The β phase disappeared with the aging treatment and when increasing the HIP temperature treatment. According the open circuit potential (E ocp) behavior of samples, the HIP3 sample had performed more positive corrosion potential than rivals after 2 h of immersion probably due to equiaxed grain with coarser α-late and the absence of the β phase. In adverse, inferior corrosion behavior was observed for HIP1 because of a higher quantity of the β phase causing probably galvanic corrosion. The HIP process leads to a lower corrosion potential than EBM. At least one protective oxide layer formation was observed for all samples at the anodic branch, and the current density was lower for the HT3 sample. The microstructure analysis revealed the presence of the β-phase in the form of needle-like for the HT1 sample and HIP1 in the corroded area. Furthermore, the EDS line analysis showed the presence of aluminum with oxygen at the edge of the corrosion area for HIP1 suggesting aluminum plays a barrier against degradation. On the other hand, the HT1 showed higher impedance resistance due to the coarser α-lathe microstructure and well-defined β phase.

Microstructural control of LPBF Inconel 718 through post processing of intentionally placed AM discontinuity distributions

A major untapped potential of laser powder bed fusion (LPBF) is the ability to additively manufacture (AM) parts with site-specific properties. However, robust methods of improving performance and manufacturing efficiency via spatial variations in microstructure are underexplored.This work investigates a method of creating several distinctive multi-modal microstructures in the nickel superalloy, Inconel 718, by performing a Hot Isostatic Pressing (HIP) procedure on characteristic LPBF discontinuities such as keyhole and lack of fusion (LOF) porosity, as well as large powder filled voids. Observed using electron backscattered diffraction, this approach leads to the formation of site-specific variations in microstructure and extreme bi-modal microstructures. Processing AM parts via this method facilitates the production of fully dense, equiaxed, and strain free material culminating in a substantial time saving per layer. Further optimisation is required in order to achieve an optimum volume fraction and distribution of γ″ precipitates in each heat treated microstructure.

Microstructure evolution of interface and matrix during the preparation of SiCf/Ti60 composites

In this paper, continuous SiC fiber-reinforced Ti60 (SiCf/Ti60) composites were fabricated by preparing SiCf/Ti60 precursor wires from matrix-coated fibers and hot isostatic pressing (HIP) consolidation. The microstructures of the precursor wires and composites were investigated using XRD, SEM, EPMA, EBSD, and TEM, which led to the microstructure evolution of the composites. The conclusions of this study are as follows. 1. A reaction layer (RL) with a thickness of approximately 0.1 μm already exists at the interface of the precursor wires during the preparation. The HIP process accelerates the diffusion of the carbon coating with the Ti60 matrix, resulting in an increase in the thickness of the RL to approximately 0.5 μm. This layer is primarily composed of fine-grained TiC layer || discontinuous silicides || coarse-grained TiC layer. 2. The matrix of SiCf/Ti60 precursor wires contains α-Ti (∼ 1.9 μm), S2 (∼ 50 nm), and β-Ti (∼ 50 nm), in the matrix, β-Ti is precipitated from α-Ti, and HIP makes α-Ti, S2, and β-Ti grow to ∼ 2.4 μm, ∼ 200 nm, and ∼ 300 nm, respectively. 3. There are 〈0001〉//axial direction (AD) and 〈10−10〉//AD fiber textures in the matrix of the precursor wires, and HIP makes the matrix undergo a plastic deformation dominated by dislocation slip, and the pole density of the two kinds of textures are both increased.

Experimental investigation on the deformation behavior of an isotropic 304L austenitic steel manufactured by laser powder bed fusion with hot isostatic pressing

Post-heat treatment, such as hot isostatic pressing (HIP), is increasingly employed in laser powder bed fused (L-PBF) metallic materials to release residual stress, alleviate microstructural anisotropy, and tailor mechanical properties. Here, we systematically investigate the initial and deformed microstructures of as-received and HIPed L-PBF 304L austenitic steel using various microstructural characterizations. The results indicate that the HIP procedure can decrease the porosity and generate the columnar-to-equiaxed transition (CET), resulting in an isotropic microstructural morphology better suitable for practice applications. Additionally, the HIP samples have exceptional ductility when compared to as-received samples, which is associated with the sustained strain hardening rate arising from the notable deformation twinning behavior. The majority of deformation twins are preferentially emitted from the straight annealing twin boundaries and then grow within the 〈111〉 − oriented annealing twins. The principle twinning mechanism involved is the twinning partial emission from the annealing twin boundaries or high-angle grain boundaries (HAGBs). Moreover, the inclusions distributed near/on the annealing twin boundaries can emit partials with multiple Burgers vectors during straining, resulting in the extra random activation of partials (RAP) twinning mechanism that sustains the deformation process. These findings give helpful suggestions for HIP process designs of L-PBF austenitic steels, as well as a solid foundation for future theoretical modeling research.

Development of high superconductor fraction (Ba, K)Fe2As2 wires with improved uniformity by two-axial rolling

Iron-based superconductors are regarded as prospective candidates for high magnetic field applications since they have very high upper critical field and low anisotropy. For practical applications, it is important to develop superconducting wires with strong current carrying capability. In this work, Cu/Ag composite sheathed (Ba, K)Fe2As2 (Ba-122) iron-based superconducting wires were fabricated by a two-axial rolling deformation process and a subsequent hot isostatic pressing (HIP) heat treatment. Compared with the previously reported Cu/Ag/Ba-122 wires prepared by groove rolling, the two-axial rolling allowed to use much thinner Cu/Ag composite sheath for wire fabrication, thus greatly increasing the filling factor of superconducting materials by about 5 times to 24 %, and lowering the volume fraction of silver down to 16 % in wires. By a comparative study on the microstructure and superconducting properties between the wires made by two-axial rolling and groove rolling processes, it is found that besides the significantly increased engineering critical current density, the former also exhibits improved homogeneity of mass distribution and uniformity of Ba-122/Ag interfaces, resulting in significantly enhanced n-values over 40 in magnetic fields up to 14 T. Our work suggests that two-axial rolling, combined with HIP processes, presents a promising approach to prepare iron-based superconducting wires with high filling factor, high uniformity and low cost for practical applications.

Insight into the interfacial microstructure and chemistry of hot isostatically pressed AA6061-AA6061 bonds for U-10Mo fuel cladding application

Hot isostatic pressing (HIP) is performed on AA6061-AA6061 plates for U-10Mo monolithic fuel cladding application and this process allows us to bond multiple plates and large surface areas in a single run. In the current work, we HIP'd several plates of AA6061 with different HIP can dimensions at 560 °C and 103 MPa for 90 min to gain insight into the interfacial microstructure, chemistry and eventually bond strength. Interfacial microstructure characterizations were performed using scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD) in conjunction with Transmission electron microscopy (TEM) to quantify precipitate fractions and study recrystallization, grain growth, and orientation relationships across the interface. Microstructural analyses revealed the precipitation of a large fraction of Mg2Si particles and a ∼50 nm thick Al-Mg oxide layer at the interface. Further TEM analysis confirmed that the oxide layer was not continuous, and Mg2Al2O5 oxide particles with an average size of 18 nm were present in the oxide layer. The bond strength of HIP-processed samples was correlated with peel testing and the bond strength was determined to be a direct function of the Mg2Si particle size at the interface. Finite element modeling analysis was performed to study the HIP can cooldown rate after HIP processing and was correlated with the interface precipitation.

Improved structure and enhanced properties of detonation sprayed W coating via hot isostatic pressing

Tungsten has garnered significant attention for its superior performance as a plasma-facing material in tokamak devices. However, its hardness and high ductile-to-brittle transition temperature present challenges for its application in plasma-facing components. To address these issues, this study employs the detonation spraying (DS) technique to prepare tungsten coatings on a TZM alloy substrate and further optimizes their properties through hot isostatic pressing (HIP) treatment. Advanced characterization techniques were utilized to conduct a detailed microstructural and compositional analysis of the coatings. The results indicated that the HIP treatment significantly reduced the porosity of the coatings, improving their density and overall quality. Additionally, HIP treatment led to a decrease in internal stress, a reduction in dislocations, and the grain growth within the coatings. The study also discussed how the HIP process improved the microstructure of the DS tungsten coatings through these mechanisms, thereby enhancing the coatings' thermodynamic properties. Mechanical property tests revealed that the coatings treated with HIP exhibited higher bonding strength and lower hardness, attributed to the increase in grain size and the reduction in dislocation density within the coatings. Thermal property tests demonstrated that the HIP-treated coatings possessed higher thermal diffusivity and specific heat capacity in the temperature range of 100 to 500 °C. Furthermore, the performance of the coatings under transient high heat flux conditions was significantly improved after the HIP treatment, showing better resistance to the thermal shock and cracking. These findings are of great importance for understanding the performance enhancement of DS tungsten coatings in nuclear fusion reactor applications via HIP, especially as candidate materials for the first wall of tokamak devices.

Surface reactivity during a hot isostatic pressing treatment of Ni-based superalloy René 77 specimens manufactured by laser powder bed fusion and metal inject molding

Additive manufactured alloys are generally affected by porosity. To solve this issue, Hot Isostatic Pressing (HIP) is a mandatory step. This work focuses on the reactivity of Ni-based superalloy René 77 during HIP at 1200 °C, in argon atmosphere. René 77 is chromia-forming in air at this temperature, but during HIP treatment, it formed α-Al2O3, Al-Ti mixed oxides and TiX (X= nitrogen/oxygen/carbon). The relative quantities of these phases depend on the specimen position inside the furnace, suggesting a gradient of impurity partial pressures. By combining experiments with thermodynamic calculations, this work contributes to a better understanding of HIP processes and suggests ways of improving them.

Generation and propagation mechanism of cracks in welded joints of thin-walled capsules during hot isostatic pressing

The quality of the capsule has an important effect on the quality of hot isostatic pressing (HIP) products. The reliability of the capsule is a key factor in determining the success or failure of HIP. The capsule is mainly formed through a sheet welding process. In order to ensure the reliability of the weld in HIP, stainless steel with better high-temperature and high-pressure performance than Q235 steel needs to be used. In this case, the fusion line becomes a dissimilar-material interface, which is more prone to fusion-line failure. This paper focuses on examining and studying the formation mechanism of fusion line cracks in welded joints during HIP. The results show that, first, the increase of the HIP temperature weakens the strength near the fusion line significantly. Second, the higher the HIP temperature, the more severe the grain coarsening, and the grain size along the radial direction of the capsule exhibits a monotonic change. Third, since the HIP process changes the micro-zone grain orientation of mild steel, the distribution characteristics of ferrite and pearlite change as well. when the temperature and pressure are higher, the texture still exhibits a strong and complex distribution.

Ballistic performance of titanium-based layered composites made using blended elemental powder metallurgy and hot isostatic pressing

Metal matrix composites tiles based on Ti–6Al–4V (Ti64) alloy, reinforced with 10, 20, and 40 (vol%) of either TiC or TiB particles were made using press-and-sinter blended elemental powder metallurgy (BEPM) and then bonded together into 3-layer laminated plates using hot isostatic pressing (HIP). The laminates were ballistically tested and demonstrated superior performance. The microstructure and properties of the laminates were analyzed to determine the effect of the BEPM and HIP processing on the ballistic properties of the layered plates. The effect of porosity in sintered composites on further diffusion bonding of the plates during HIP is analyzed to understand the bonding features at the interfaces between different adjacent layers in the laminate. Exceptional ballistic performance of fabricated structures was explained by a significant reduction in the residual porosity of the BEPM products by their additional processing using HIP, which provides an unprecedented increase in the hardness of the layered composites. It is argued that the combination of the used two technologies, BEPM and HIP is principally complimentary for the materials in question with the abilities to solve the essential problems of each used individually.

Structure and properties of samples made from XH50BMTJuB-VI (EP648-VI) alloy produced by using selective laser melting process

The paper presented examines the composition, the structure and properties of samples made from the XH50VMTJuB-VI (hereinafter EP648-VI) alloy obtained by using the selective laser melting process (the SLM-process) in relation to manufacturing parts for aviation purposes. The authors carried out a comparative study of the samples’ structure and properties upon conducting such operations as depositing in two directions (horizontal and vertical), separate heat treatment and after hot isostatic pressing (HIP) followed by a standard heat treatment process applied for deformable semi-finished products made from the XH50VMTJuB-VI(EP648-VI) alloy. The authors inform that the manufacturing of samples by means of the SLM-process involved powders obtained through the technology of the vacuum-induction spraying of the molten metal jet with an inert gas (argon). The paper has established that samples obtained by using the HIP process with the application of the heat treatment (a vacuum high-temperature homogenization followed by a long-term aging) demonstrated the best set of mechanical properties, since the implemented complex process ensured the “healing” of pores and discontinuities in the structure, and strengthening by means of the intermetallic g¢-phase, while separations of the excess, needle-shaped a -Cr phase are fine and evenly distributed in the material structure. The authors noted that mechanical properties of samples under analysis were generally in compliance with the requirements set forth in the regulatory documentation for deformable semi-finished products made from the XH50VMTJuB-VI (EP648-VI) alloy, while underlining the increase in the level of impact strength of samples that underwent the HIP process, and the long-term strength of samples manufactured in the vertical direction compared to other options studied. Following the results of the analysis, the authors established that the SLM-process made it possible to manufacture products whose level of mechanical properties was close to the level of the deformable material, and even exceeded it in some cases.

Matrix microstructure evolution during the fabrication of SiCf/Ti60 composites

Microstructure evolution during the hot isostatic pressing (HIP) of continuous silicon carbide fiber-reinforced Ti (SiCf/Ti) composites has not been investigated. In this study, SiCf/Ti60 composites were prepared via the HIP solidification method of Ti60 precursor wires. The evolution of the microstructure of the Ti60 precursor wires and SiCf/Ti60 composites was characterized using electron backscatter diffraction microscopy and transmission electron microscopy techniques. The results showed that the deformation of α-Ti was mainly accomplished by basal <a> dislocations and prismatic <a> dislocations slip during the HIP process. After the completion of HIP, the low-angle grain boundaries (LAGBs) were reduced to 24.6%, and the average grain size of α-Ti was increased to 7.47 μm2. Two fiber textures, <0001>//axial direction (AD) and <10-10>//AD strength, were present in α-Ti, with a 38% increase in <10-10>//AD strength. The phase contents of 1.0% β-Ti and 0.6% (Ti, Zr)6Si3 precipitated from different locations in the Ti60 matrix and induced changes in misorientation.

Comparison of the Microstructural, Mechanical and Corrosion Resistance Properties of Ti6Al4V Samples Manufactured by LENS and Subjected to Various Heat Treatments.

In this paper, the influences of two post-heat treatments on the structural, mechanical and corrosion resistance properties of additively manufactured Ti6Al4V alloys were discussed in detail. The materials were produced using the laser engineering net shaping (LENS) technique, and they were subjected to annealing without pressure and hot isostatic pressing (HIP) under a pressure of 300 MPa for 30 min at temperatures of 950 °C and 1050 °C. Annealing without pressure led to the formation of a thin plate structure, which was accompanied by decreasing mechanical properties and increasing elongation and corrosion resistance values. For the HIP process, the formation of a thick plate structure could be observed, resulting in the material exhibiting optimal mechanical properties and unusually high elongation. The best mechanical and corrosion resistance properties were obtained for the material subjected to HIP at 950 °C.