Hot Isostatic Pressing Treatment Research Articles

Effects of hot isostatic pressing treatment on the microstructure and tensile properties of Ni-based superalloy CM247LC manufactured by selective laser melting

This study manufactured CM247LC Ni-based superalloy, which has outstanding mechanical properties, using the laser powder bed fusion (L-PBF) method and selective laser melting (SLM). Furthermore, the effect of hot isostatic pressing (HIP) post treatment on the microstructure and mechanical properties of SLM-built CM247LC was investigated. The defect characteristics of SLM-built superalloy changed significantly according to scan speed and hatch space, and it achieved the optimal microstructure at an intermediate scan speed (600 mm/s). SEM, EBSD, and ECCI analyses of the as-built alloy identified grains that developed in the build direction, sub-grains consisting of dislocation networks and MC carbides. In addition, γ’ phase formed evenly throughout the sample after HIP post treatment. The as-built CM247LC showed a yield strength of 933.5 MPa and tensile strength of 1144.0 MPa. In the case of the HIP alloy, the yield strength remained at a similar level, but tensile strength increased significantly up to 1457.1 MPa, and tensile elongation increased four times compared to the as-built alloy. Based on the above findings, this study discussed the correlations between microstructure, improved tensile properties and deformation mechanism.

Multistep low-to-high-temperature heating as a suitable alternative to hot isostatic pressing for improving laser powder-bed fusion-fabricated Ti-6Al-2Zr-1Mo-1V microstructural and mechanical properties

Laser-powder-bed-fusion (L-PBF) is a subset of additive manufacturing (AM) that has been increasingly used to manufacture titanium components for aerospace applications. However, titanium components fabricated by L-PBF exhibit high mechanical strength and poor ductility because of refined αʹ martensite. Postheating is frequently used to transform the martensitic microstructure into equilibrium α phase for achieving the desired mechanical properties. In this study, superior strength and ductility were achieved by applying low-to high-temperature (LHT) multistep heating to Ti-6Al-2Zr-1Mo-1V (TA15) samples that were as-fabricated (AF) through L-PBF. For comparison, TA15 samples were subjected to one-step annealing and hot isostatic pressing (HIP). The L-PBF AF microstructure mainly comprised acicular αʹ martensite and exhibited high strength (1383 ± 9 MPa) and low ductility (6.3 ± 0.2%). Conventional one-step annealing formed lamellar α+β microstructures that exhibited decreased strength (896–1182 MPa) and improved ductility (12.0–14.3%) compared to AF. Hot isostatic pressing (HIP) treatment formed a lamellar α+β microstructure that exhibited a strength of 1015 ± 30 MPa and ductility of 15.9 ± 0.8%. LHT formed a trimodal microstructure comprising lamellar, equiaxed, and short-rod α and provided well-balanced strength (1033 ± 4 MPa) and ductility (16.6 ± 0.5%), which are superior than those of the samples prepared by using one-step annealing or HIP. Therefore, LHT is a suitable replacement for HIP to prepare L-PBF TA15 exhibiting superior mechanical properties for aerospace applications.

Microstructural and mechanical optimization of selective laser melted Ti6Al4V lattices: Effect of hot isostatic pressing

Ti6Al4V triply periodic minimal surface (TPMS) and Trabecular (Trab.) lattices were manufactured by selective laser melting (SLM). The defect distribution, phase composition, microstructural evolution and mechanical properties after hot isostatic pressing (HIPing) treatment were investigated. For both lattices, only micro-sized pores could be observed without any other defects. HIPing treatment had limited influence on pore elimination when the pore diameters were larger than 30 μm. The as-fabricated acicular martensites were in-situ decomposed into the homogeneous basket-weave α + β structure during HIPing process, and the microstructural anisotropy was effectively eliminated after HIPing. The two lattices had similar α/β phase fraction, but the average grain size of the TPMS lattice (2.206 μm) was much smaller than that of the Trab. One, which was attributed to the original microstructural difference in their as-fabricated counterparts. The compressive strength of the two lattices had no significant change after HIPing treatment, but the energy absorption capacity significantly improved due to the transformation induced plasticity effect of α + β laths formation. The fracture mechanism was altered from the brittle-dominated quasi-cleavage mode to ductility-dominated mode. The findings in this work provide an approach for microstructure and compression ductility improvement of SLM Ti6Al4V porous structure by specific heating treatments.

On the hot isostatic pressing of Inconel 625 structures built using laser powder bed fusion at higher layer thickness

This paper reports the effect of hot isostatic pressing (HIP) on the porosity, microstructure and mechanical properties of laser powder bed fusion (LPBF) IN625 structures built at a higher layer thickness of 100 µm. It is observed that the process-induced pores/voids of volume fraction (Vf) 0.43% in as-built IN625 structures are reduced significantly to ~ 0.01% after HIP treatment. The microstructure is changed from fine columnar dendrites to coarse equiaxed dendrites. The microstructural analysis of as-built structures reveals the presence of cellular/dendritic growth along with elemental segregation of Nb, Si and C and precipitation of Nb-rich carbides, whereas coarse recrystallized microstructure along with elemental segregation of Si and precipitation of Nb, Mo and Cr rich carbides is observed in hot isostatic pressed (HIP) samples. HIP structures exhibit lower tensile strength, higher ductility and lower anisotropy as compared to LPBF built structures. There is a reduction in the Vickers micro-hardness of IN625 samples after HIP, and the values are observed to be similar to their conventional counterparts. Further, an increase in the energy storage capacity of the material is observed after HIP treatment through Automated Ball Indentation (ABI®) studies. The study paves a way to develop ~ 100% dense, defect-free and isotropic engineering components using LPBF.

Effect of Oxygen Diffusion During the Post-Processing of Ti6Al4V Lattice Structures Fabricated by the Selective Laser Melting Process

Abstract Post-processing of Ti6Al4V lattice structures fabricated using selective laser melting (SLM) was performed using hot isostatic pressing (HIPing) and heat treatment (HT) to mitigate the undesired effect of rapid cooling during SLM. Oxygen diffusion during post-processing had a significant influence on the microstructure and subsequently the mechanical properties of the lattices. Oxygen content analysis was conducted to confirm the oxygen diffusion through the strurts’ peripheries. The effect of oxygen diffusion during the HIPing and sub-transus HT (600–800 °C) regimes on the phase transformation, failure mechanisms, and mechanical properties of the lattices was investigated. Results revealed that the transformation of the originally formed α′ martensite was dependent on the post-processing temperature. This transformation resulted in a decrease in yield strength. The decrease in failure strain (ductility) for all treated conditions was related to oxygen diffusion, forming near-surface α-case.

Mechanical responses of additively manufactured MoSiBTiC alloy under tensile and compressive loadings

The present study characterizes the tensile and compressive behaviors of a TiC-added Mo–Si–B alloy (MoSiBTiC alloy) fabricated by the laser powder bed fusion (L-PBF) method of additive manufacturing. Four-point bending tests were conducted at room temperature on MoSiBTiC alloy specimens prepared from L-PBF builds, before and after hot isostatic pressing (HIP) treatments. The elastic and strength properties in tension and compression were determined based on the bending test data, by considering nonlinear stress–strain relations. Microstructural observations, elemental composition analyses, and phase identifications were performed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The HIP treatments reduced process-induced defects in the L-PBF-processed MoSiBTiC alloy and resulted in improvements in their elastic and strength properties. A distinct difference was observed in the macroscale responses of the alloy under tension and compression, which was attributed to the defect behavior at microscale.

Improved quality and functional properties of Ti-6Al-4V ELI alloy for personalized orthopedic implants fabrication with EBM process

Understanding the manufacturing process parameters and their correlation with final product functional properties is needed to ensure performance in critical applications in the medical industry. This article presents the holistic procedure for verifying the quality of manufactured products, including the determination of basic material characteristics and strength parameters based on EBM (Electron Beam Melting) technology for the titanium alloy Ti-6Al-4V ELI. The aim of this study was to investigate the effects of the manufacturing and post-processing methods used, on the geometric accuracy, microstructure, mechanical and cytotoxic properties of additively manufactured parts, especially in the form of personalized jaw implants. The effect of Hot Isostatic Pressing (HIP) treatment on microstructure and properties is also taken into account. The EBM manufacturing process was developed and samples were built using three different orientations: 0° (horizontally), 45° (diagonally), and 90° (vertically). The novel results are systematically presented and discussed beginning from the selection of process parameters, sample manufacturing, wide microstructural characterization, determination of static mechanical properties as well as geometric accuracy, and quality control verification depending on the manufacturing process and the post-processing methods used. The conducted research allowed for the presentation of the entire process chain of the EBM manufactured medical implant made of high-purity titanium alloy (Ti-6Al-4V ELI), thus filling the scientific gaps related to the selective presentation and discussion of research results published in the literature on the subject.

The limit of hot isostatic pressing for healing cracks present in an additively manufactured nickel superalloy

Inconel 738LC (IN738LC) is a nickel-based superalloy specially used in the hot section components of turbine engines due to its outstanding hot corrosion resistance and mechanical properties under high temperatures. However, one of the main drawbacks of this superalloy is its susceptibility to cracking when it is manufactured by Laser Powder Bed Fusion (LPBF). This paper describes the effect of 400 W laser power and 90° rotation strategy on the formation of cracks and the capability of Hot Isostatic Pressing (HIP) post-treatment to substantially reduce them in the LPBF manufactured IN738LC samples. Based on the characterization of the cracks, the most important finding from this research work was the identification of the limit of crack width at 6 μm, beyond which the HIP treatment is unable to effect crack healing. Furthermore, this research shows that the HIP treatment leads to microstructural changes in the IN738LC samples with a massive precipitation of γ´ phase. Indeed, the formation of precipitates implied an increase in the microhardness of up to 23 %, which demonstrates that the HIP treatment also affects the mechanical properties of the IN738LC superalloy. It was therefore shown that the HIP treatment could be a crucial process to substantially reduce the defects of the additively manufactured parts.

Laser powder bed fusion and post processing of alloy 22

A nickel-based superalloy (Alloy 22) powder was gas atomized to be used as a feedstock in the Laser Powder Bed Fusion (L-PBF) process. In this study, laser power and scanning speed were optimized to manufacture parts with the highest density. Samples manufactured with power of 150 W and scanning speed of 200 mm/s showed the highest relative density of 99.6%. Additionally, for a higher production rate, samples were manufactured with power of 225 W and scanning speed of 1200 mm/s. Additively manufactured parts were post processed by conducting solution heat treatment, hot isostatic pressing (HIP), and HIP+solution heat treatments. HIP effectively eliminated most of the defects in the as-printed samples, but Mo-rich ultrafine precipitates were observed in HIP processed samples. Solution heat treatment led to full recrystallization and the total dissolution of the Mo-rich second phases into the Ni matrix. The role of solution treatment on enhancing ductility of HIPPed sample was found significant. Sample manufactured at 150 W and 200 mm/s followed by HIP and solution treatment showed similar mechanical properties to wrought Alloy 22.

Effect of Solution Treatment and Cooling Rate on the Microstructure and Hardness of Ti-6Al-4V Alloy Manufactured by Selective Laser Melting Before and After Hot Isostatic Pressing Treatment

This paper extends our previous work to investigate the effect of heat treatment on the microstructure of Ti-6Al-4V fabricated by selective laser melting. A post-heat treatment at 930 °C for 15 min followed by three cooling rates before and after hot isostatic pressing (HIP) treatment was applied. The findings illustrated that the microstructure of the quenched samples before the HIP treatment was characterized by a mixture of α + α′ phase with a microhardness value of 336 ± 6 HV0.3. Air cooling produced a structure dominated by the α phase, with ~ 7.5% of the β phase and a microhardness value of about 330 ± 4 HV0.3. Furnace cooling led to a mixture of α phase and ~ 17% of the β phase and hardness of 327 ± 6 HV0.3. After HIP followed by post-heat treatment, acicular α′ martensite with microhardness value 377 ± 2 HV0.3 dominated the quenched specimen microstructure. Following air cooling, the microstructure consisted of a mixture of α-lamella and β with some needles of the α with a microhardness value of 336 ± 3 HV0.3. In the case of the furnace cooling, a complete transformation of β to a mixture of α + β phase was observed. The β volume fraction formed in the microstructure was estimated at ~ 8.5%, having microhardness 322 ± 4 HV0.3. Reasons for such behaviors are discussed.

Excellent high-temperature strength and ductility of graphene oxide reinforced high-temperature titanium alloy matrix composite fabricated by hot isostatic pressing and heat treatment

GO reinforced high-temperature titanium alloy matrix composite with excellent high-temperature strength and ductility was successfully fabricated by hot isostatic pressing and heat treatment. After solution and aging treatment, the high-temperature strength of the composite was significantly improved because the increase of in-situ TiC at the interface enhanced interface bonding and the microstructure changed from equiaxed structure to bimodal structure. At the same time, the dissolution of silicides increased the high-temperature ductility. After solution at 1075 °C and aging at 700 °C, the tensile strength, yield strength and elongation at 600 °C of the high-temperature titanium alloy with 0.3 wt% GO reached 749 MPa, 571 MPa and 18.5%, respectively.

Dynamic Tensile Extrusion Behavior of Fine-Grained Copper Fabricated by Powder Injection Molding

The dynamic tensile extrusion (DTE) behavior and microstructural evolution of fine-grained (FG, ~1 μm < d < ~10 μm) Cu fabricated by powder injection molding (PIM) were investigated. The FGM Cu was fabricated by PIM with commercial micro-sized Cu powder sintering at 850 °C for 2 h, while the FGH Cu was developed by the hot isostatic pressing (HIP) of the FGM at 780 °C for 2 h under a pressure of 1000 bar. In order to compare the DTE behavior of the FG Cu manufactured using different methods, the ultrafine-grained-B (UFG, d < ~1 μm) Cu was developed by performing 16 passes of equal-channel angular pressing with route Bc, and the FG-150 Cu was fabricated by annealing the UFG-B Cu bar at 150 °C for 1 h. The DTE tests were performed with identical flyer velocities using an all-vacuum gas gun. The fragments and remnants were carefully recovered after the DTE tests and examined by electron backscattered diffraction measurement and a micro-Vickers hardness test. A strong dual <001> + <111> texture was developed during the DTE for both FGM and FGH Cu. In contrast to the outcome of the UFG-B and FG-150, little evidence of dynamic recrystallization taking place during the DTE in the FGM and FGH was found during analysis of the grain morphology and grain orientation spread. Premature failure based on void coalescence was induced at the vertex region of the FGM fragments due to pre-existing pores. The HIP treatment on the FGM Cu increased the relative density by reducing the pre-existing pores and, as a result, increased the DTE ductility of the FGH Cu.

Ultrafine-grained microstructure and controllable magnetic domains in Fe-based nanocrystalline alloys with excellent magnetic properties induced by hot isostatic pressing

The coarsening and inhomogeneous distribution of nano-grains caused by traditional heat treatment processes are the biggest obstacles for obtaining ultrahigh permeability and excellent comprehensive soft magnetic properties in Fe-based nanocrystalline alloys. Here, we propose a new strategy to control grain growth and magnetic anisotropy, by introducing isotropic compressive stress field in the annealing process to optimize the magnetic properties. Compared with conventional isothermal annealing, the coupling of stress-temperature field generated by hot isostatic pressing (HIP) induced the microstructure, magnetic domain evolution and magnetic properties in Si-rich Fe73.5Si15.5B7Nb3Cu1 amorphous ribbons have been systematically investigated. We demonstrate that HIP treatment promotes more Si atoms to dissolve in Fe unit cell to form Fe(Si) solid solution causing an increase in interplanar spacing. Also, the high-density Cu clusters precipitate in the amorphous matrix upon HIP serving as nucleation sites for α-Fe(Si) grains, which facilitate a high volume fraction, uniform and ultrafine-grained microstructure. Moreover, the existence of stress field introduces induced anisotropy effectively controls the magnetization mechanism and magnetic structure evolution. Furthermore, the Fe73.5Si15.5B7Nb3Cu1 nanocrystalline alloy treated by HIP exhibit excellent comprehensive magnetic properties, such as high Ms, high μe, low Pcv, low AC Hc and high Br/Bm.

Rejuvenation of Nickel-Based Superalloy Experiencing Creep via Use of Hot Isostatic Pressing and Heat Treatment

Rejuvenation of Nickel-Based Superalloy Experiencing Creep via Use of Hot Isostatic Pressing and Heat Treatment

Effect of post-processing heat treatment on cyclic plastic behaviour of AlSi10Mg aluminium alloy processed by LPBF

Recent studies have reached some antagonist conclusions regarding the benefits of post-processing treatments on fatigue performance of AlSi10Mg aluminium alloy processed by laser powder bed fusion (LPBF). Thus, this paper aims to explore the triangular relationship between post-processing routes, microstructure, and cyclic properties. In order to reach this goal, uniaxial strain-controlled fatigue tests are conducted on smooth specimens in low-cycle and high-cycle fatigue regimes for five different material states, encompassing the as-built condition, T6 condition, stress relief at a standard temperature, stress relief at a non-standard temperature, and stress relief at a non-standard temperature followed by hot isostatic pressure. It has been found that the microstructural transformations associated with the stress relief at both the standard and non-standard temperatures had a beneficial effect on fatigue strength of AlSi10Mg aluminium alloy processed by LPBF. Furthermore, the hot isostatic pressure treatment did not alter the fatigue performance.

Effect of Hot Isostatic Pressing on Microstructures and Stress-Rupture Properties of CM 939 Weldable Alloy

Effect of hot isostatic pressing (HIP) treatment on the microstructure and the stress rupture properties of CM 939 Weldable alloy have been investigated. The results shown that the HIP has the function of densification and homogenization, all of the microporosity have been almost removed, the segregation of the alloy have been reduced, the microstructure became better, the stress rupture life of CM 939 Weldable alloy have been obviously improved, Meanwhile, the data dispersion of stress rupture properties have been reduced for the alloy after HIP.

Integration of Hot Isostatic Pressing and Heat Treatment for Advanced Modified Γ-Tial Tnm Alloys

Integration of Hot Isostatic Pressing and Heat Treatment for Advanced Modified Γ-Tial Tnm Alloys

Effect of solution heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Hastelloy X manufactured by electron beam powder bed fusion

• As-built PBF-EB Hastelloy X has anisotropic microstructure and mechanical behavior. • Grain coarsening from solution heat treatment and HIP reduced the yield strength. • Crystallographic texture along 〈100〉 remained unaffected even after post-treatment. • Anisotropy in yield strength and ductility weakened following post-treatment. • Solid solution strengthening is the main contributor towards overall yield strength. Prior to the application of AM components for critical applications, it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts. In this study, efforts were made to achieve an in-depth understanding of the effect of post-fabrication Solution Heat Treatment (SHT) and Hot Isostatic Pressing (HIP) on the microstructure and mechanical properties of Hastelloy X parts built by electron beam powder bed fusion (PBF-EB) process. The effects of SHT and HIP on porosity, microstructure, texture and mechanical properties have been investigated and compared with that of as-built PBF-EB Hastelloy X. Post-fabrication HIP treatment led to a significant reduction in the porosity content, whereas no notable difference in porosity was observed between SHT and as-built parts. There was no evidence of any recrystallization occurring following the post-fabrication treatments as elongated columnar grain structures observed within as-built part were found to be maintained even after SHT and HIP process alongside the strong 〈100〉 crystallographic texture. Emphasis was laid upon understanding the influence of SHT and HIP on mechanical properties through stress-strain curves and work-hardening behaviour.

Ultraviolet Nanosecond Laser Treatment to Reduce the Friction Coefficient of Silicon Carbide Ceramics

The determination of the possibility for the reduction of the friction coefficient of ceramic parts from silicon carbide by pulse-periodic treatment with an ultraviolet nanosecond laser was carried out in the framework of this research. The gas-dynamic seal of the compressor rotor of the gas-turbine engine after hot isostatic pressing and mechanical treatment was exposed to surface microstructuring in a pulse-periodic mode. For experimental investigations, a laser with a maximum energy of the pulse of 50 µJ, a wavelength of 355 nm, and a pulse duration below 10 ns was used. It was determined that the surface quality was improved, and the surface roughness was reduced as a consequence of the realized laser polishing modes in the beam exposure area. The average value of the friction coefficient of the ceramic material surface decreased by 15% as result of pulse-periodic laser processing.

Effect of hot isostatic pressing on the cast Ti6Al4V alloy with shrinkage cavities inside: Healing behavior, microstructure evolution and tensile property

Healing behavior, microstructure evolution and tensile properties of cast Ti6Al4V alloy with the millimeter-scale shrinkage cavities inside during hot isostatic pressing (HIP) were investigated. X-ray computed tomography (CT) has been used to track pore closure process during a standard HIP cycle. The comparison of the CT scans before and after HIP indicates that HIP has the potential to close the millimeter-sized shrinkage cavities and the main closure mechanism of shrinkage cavity is plastic deformation which can be deduced by the rapid closure of the shrinkage cavity. The microstructure in the closure region was characterized in detail using scanning electron microscope (SEM) and electron backscattered diffraction (EBSD). It is inferred that closure interface can be partially healed by HIP-1 while can be totally healed by HIP-2. In addition, it was found that as the HIP duration became longer, the Burgers orientation relationship between α and β phases gradually deviated, and the misorientation along and across the single α colony gradually became larger, which could be attributed to the rotation of the crystalline lattice after hot deformation. In the individual α lamella, the rotation axis changed where the point-to-point misorientation was not continuous, thus the low-angle boundaries were formed. With the accumulation of strain energy, the low-angle boundaries transformed into high-angle boundaries, which resulted into the breakdown of α lamellae. The sub-division of α lamellae and recrystallized grain growth are determined to be the main spheroidization mechanisms of α lamellae during HIP. After HIP treatment and with the increase of HIP duration, the yield strength and tensile strength increased first and then slightly decreased, but the elongation was progressively increased due to the enhanced metallurgical bonding.