Effect Of Hot Isostatic Pressing Research Articles

Hot isostatic pressing of differently sintered binder jetted 316 L stainless steel: microstructure evolution and mechanical properties

In binder-jetted components, the typical sintered relative density can reach up to 99%, where remaining pores may degrade mechanical properties, including tensile strength, ductility, and fatigue performance. To enhance manufacturing efficiency in terms of cost and energy, it is crucial to develop post-printing heat treatments to optimize the sintering profile, providing both relative densities of >99% and dimensional accuracy. This study investigates the effect of hot isostatic pressing (HIP) on the microstructure evolution, pore elimination, and mechanical properties of binder-jetted 316L SS powder. Sintering at temperatures ranging from 1325 ℃ to 1430 ℃ resulted in relative density between 87-99.5%, while HIPed specimens revealed that a minimum relative density of 99.5% could be achieved on any samples sintered at 1370 ℃ or higher temperatures. Microstructure and grain analysis through electron backscattered diffraction (EBSD) showed grain coarsening after HIP treatment, with the highest grain growth occurring in the HIPed specimen sintered at 1400 ℃ (207.4±5.4 μm). However, a slight change in grain size was observed in the HIPed specimen sintered at 1430 ℃ due to a noticeable amount of delta-ferrite at the grain boundaries. Mechanical behavior and fractography were compared in sintered and HIPed specimens, and related discussions were leveraged.

Comparison of fatigue life behavior between 4-point and uniaxial loading for L-PBF Ti–6Al–4V after HIP treatments

The present study investigated the effects of Hot Isostatic Pressing (HIP) on the fatigue performance of Laser Powder Bed Fusion (L-PBF) Ti–6Al–4V alloy under both 4-point bending and uniaxial testing. Three HIP-cycles were examined: standard, low temperature/high pressure (LTHP), and super beta. Moreover, an annealed heat treatment group was incorporated to compare against the HIP groups. The material microstructure was analyzed and compared across the heat treatments during the study, which showed the presence of α′ martensites, α+β Widmanstätten, and coarse equiaxed grains. Similarly, tensile and hardness testing were implemented to study the mechanical properties, where due to the effects of the HIP treatments, higher ductility but lower hardness values were recorded. Furthermore, fracture morphologies and stress-life (cycles-to-failure) (S–N) curves of the Ti–6Al–4V specimens concerning the fatigue behavior were analyzed. The HIP treatment groups behaved similarly during 4-point bending and uniaxial testing, with the LTHP obtaining a superior fatigue life behavior, followed by the standard and super beta HIP groups. In addition, the efficacy of HIP to reduce pores showed better results in the 4-point bending specimens, leading to few defects as fatigue initiators in contrast to the uniaxial specimens. Fractography results suggested that defects and microstructural features acting as fatigue crack initiators (FCI) govern the fracture behavior of uniaxial specimens. In contrast, only the presence of microstructural features controls the 4-point bending failure behavior.

New insights into the stress rupture life enhancement mechanisms of a nickel-based superalloy

In this paper, the effects of hot isostatic pressing (HIP) and heat treatment (HT) on the stress rupture properties of nickel-based superalloy K417G were investigated. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were employed to analyze the microstructure, fracture morphology, determination of crack source and dislocation evolution after stress rupture fracture. The results indicate that, HIP specimens demonstrate a 19.5% reduction in stress rupture life compared to as-cast specimens, whereas HIP + HT specimens exhibit a 41% increase in stress rupture life, reaching a value of 63.04 h. The fracture mechanism of the samples under different heat treatment conditions is different. There are a large number of pores in the as-cast specimen, which leads to the initiation and propagation of cracks and eventually result in fracture. The pores in the HIP specimen are almost eliminated. However, the coarsening and uneven distribution of γ′ phase led to the weakening of the hindrance to dislocation movement. Additionally, the increase in elongated carbides at grain boundaries accelerates crack initiation and propagation. Under HIP and HT, the cubic γ′ phase is uniformly precipitated, which effectively hinders the movement of dislocation lines. Granular M23C6 carbides precipitate at grain boundaries, acting as pinning points to retard grain boundary sliding and crack propagation, thus improving the stress rupture life.

Effect of hot isostatic pressing and heat treatment on the evolution of precipitated phase and mechanical properties of GH3230 superalloy fabricated via selective laser melting

In this paper, the microstructure and mechanical properties of SLM-GH3230 superalloy treated by different post treatments (single hot isostatic pressing and heat treatments after hot isostatic pressing) were studied. The micro-morphologies show that the grains along building direction after HIP + HT are mainly columnar grains, which is consistent to that after single HIP. The granular precipitates distribute intergranularly and intragranularly after HIP, but gradually re-dissolve into matrix with the increase of the temperature of the post HT processes. XRD and EDS analyses results indicate that the matrix mainly consists of austenitic γ phase and the granular precipitates are mainly M6C carbides enriched in W element. The average grain size decreases after HT compared to that after HIP, and the crystallographic orientation of grains tends to be more uniform. The Vickers hardness decreases after HIP and HIP + HT processes within a certain degree. According to tensile test results, the sample shows a better combination of strength and plastic performance under HIP+1250 °C/30 min processing, which can also be verified by the characteristic of the fracture morphology with more tearing dimples.

Fused deposition modeling of Inconel 625 alloy: Effect of hot isostatic pressing on the microstructure and tensile properties

Inconel 625 alloy was fabricated using fused deposition modeling (FDM), an emerging advanced additive manufacturing (AM) technique. Subsequently, the effects of hot isostatic pressing (HIP) on its microstructure and mechanical properties were investigated. Notably, HIP treatment significantly reduced the defect density, resulting in enhanced tensile ductility.

Microstructural Evolution and Mechanical Properties of Ti-6Al-4V Alloy through Selective Laser Melting: Comprehensive Study on the Effect of Hot Isostatic Pressing (HIP)

This study explores the profound impact of varying oxygen content on microstructural and mechanical properties in specimens HO and LO. The higher oxygen concentration in specimen HO is found to significantly influence alpha lath sizes, resulting in a size of 0.5-1 μm, contrasting with the 1-1.5 μm size observed in specimen LO. Pore fraction, governed by oxygen concentration, is high in specimen HO, registering a value of 0.11%, whereas specimen LO exhibits a lower pore fraction (0.02%). Varied pore types in each specimen further underscore the role of oxygen concentration in shaping microstructural morphology. Despite these microstructural variations, the average hardness remains consistent at ~370 HV. This study emphasizes the pivotal role of oxygen content in influencing microstructural features, contributing to a comprehensive understanding of the intricate interplay between elemental composition and material properties.

The Impact of HIP Process and Heat Treatment on the Mechanical Behaviour of an Al–Si–Mg Alloy Component

AbstractThis study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.

Enhancing corrosion resistance of additive manufactured heterogeneous martensite stainless steel by hot isostatic pressing

The effect of hot isostatic pressing (HIP) on microstructure, corrosion resistance and passive film characteristics for heterogeneous martensite stainless steel (MSS) manufactured by laser powder bed fusion (LPBF) was studied. The microstructure was mainly typical original austenite grains and martensite laths and the high content of austenite disappeared after HIP. The average grain size (about 14.09 μm) was larger than that of sample before HIP (about 4.33 μm). When the laser power was 170 W and the scanning speed was 550 mm·s−1, the density of the samples after HIP increased to >99.99%. When the scanning speed increased to 1250 mm·s−1, the density of samples increased from 97.82% to 99.89%. After HIP treatment, the passivation trend of low density (97.8%) samples was more obvious and the pitting potential increased from −44 mVSCE to 179 mVSCE. The pitting potential of high density (99.77%) samples increased from 265 mVSCE to 291 mVSCE and the electrochemical impedance value increased. The sensitivity of the samples to chloride ions significantly decreases after HIP. The donor density for sample before HIP was 2.5546 × 1020 cm−3, which was higher than that of sample after HIP (2.001 × 1020 cm−3). Therefore, the corrosion resistance of LPBF high strength stainless steel was enhanced after HIP.

Effects of HIP Process Parameters on Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated by SLM

Ti-6Al-4V titanium alloy products formed by selective laser melting (SLM) are characterized by high strength and low plasticity. In addition, there may be pores inside the material, which may become a fracture sprouting point and accelerate the failure of the parts. Using an optical microscope (OM), scanning electron microscope (SEM), and electronic universal testing machine, the effects of hot isostatic pressing (HIP) parameters on the microstructure and tensile property of SLM-formed Ti-6Al-4V titanium alloy were investigated. The results show that HIP performed below the β-phase transition temperature, and the structure of the Ti-6Al-4V titanium alloy is composed of an α phase and β phase. With the increase in the HIP temperature, the α lath coarsens into a short rod, the content of the β phase increases and coarsens, and the tensile strength and yield strength of Ti-6Al-4V show a decreasing trend. With an HIP process performed at a temperature of 910 °C and pressure of 130 MPa for 2 h, the Ti-6Al-4V titanium alloy obtains the best matching of strength and plasticity.

Effects of heat treatments on the microstructure and tensile properties of IN738 superalloy with high carbon content fabricated via laser powder bed fusion

Heat treatment is a key process governing the final microstructure and mechanical properties of precipitation-hardened superalloys. However, traditional heat treatments are typically designed for cast or wrought superalloys. Therefore, this study investigates the effects of hot isostatic pressing (HIP) and a two-step heat treatment (THT) process that combines HIP with solution heat treatment (SHT) process. Heat treatments were conducted on a crack-free high carbon content IN738 alloy (IN738–0.3 C) fabricated via laser powder bed fusion (LPBF). HIP significantly reduced the porosity and residual stress of the LPBF IN738–0.3C samples. The HIP samples exhibited a large number of well-developed cuboidal γ′ precipitates (∼800 nm) and a few fine near-spherical γ′ precipitates (∼40 nm), whereas the THT samples had uniformly distributed γ′ precipitates with an average size of ∼80 nm. Therefore, the HIP and THT methods have potential to improve the properties of additive manufactured (AM) IN738 alloy. A superior combination of yield strength (1050 MPa), ultimate tensile strength (1295 MPa), and elongation (16.5 %) was achieved through THT. Additionally, the study revealed the detailed relationship between the microstructure and the mechanical properties. These results can serve as a reference for exploring suitable heat treatments for other AM precipitation-hardened Ni-based superalloys.

Impact behavior of gravity cast AlSi10Mg alloy: Effect of hot isostatic pressing and innovative high pressure T6 heat treatment

In the present study the impact behavior of gravity casting AlSi10Mg alloy was evaluated with an instrumented Charpy pendulum. The effect of hot isostatic pressing, also followed by a T6 treatment, was analyzed in comparison with samples in the as-cast, annealed and T6 conditions. Furthermore, the effect of the innovative high-pressure T6 was investigated. It was found that the hot isostatic pressing is able to ensure densification of the alloy with an increase in both hardness and energy absorbed during impact. The T6 treatment performed at atmospheric pressure after the hot isostatic pressing is able to increase hardness and peak force. At the same time, the innovative high-pressure T6 is able to ensure similar results than those of hot isostatic pressing followed by T6, leading to a significant decrease in the treatment duration and costs and reducing the carbon footprint of the manufacturing process.

Microstructure and Stress Rupture Properties of K417G Superalloy at Different Hot Isostatic Pressing Temperatures

The effect of hot isostatic pressing (HIP) on the stress rupture property of K417G nickel-based superalloy is studied experimentally. The results show that the stress rupture property of the alloy is improved by the appropriate HIP process. After HIP, the average microporosity of alloy after HIP is 0.04%, which is reduced by nearly 90% compared with the as-cast microstructure. The cubic γ′ precipitates grow up, accompanied by the precipitation of the fine γ′ phase in the matrix. In addition, the area fraction of (γ + γ′) eutectic decreases, dendritic segregation is improved, and the element distribution is homogenized. As the HIP temperature increased from 1175°C to 1195°C, the microporosity and eutectic are further reduced slightly. The stress rupture life at 760°C and 645 MPa of alloys after HIP at 1175°C and 1185°C increased by 90 h and 20 h, respectively, compared with the as-cast alloy, but it is not the case for HIP at 1195°C. In addition, the elongation after HIP is increased by about 60% compared to the as-cast alloy, with an average of 4.7%. The changes in the γ′ phase and the deformation mechanism after HIP are discussed.

Effect of Hot Isostatic Pressing of Water Atomized AISI 316L Manufactured by Laser Powder Bed Fusion

The objective of this work is to study the possibility of obtaining dense parts using water atomized AISI 316L steel powder in the L-PBF process. Despite its irregular, non-spherical, particle morphology, it has a significantly lower cost. 25 samples were produced varying the laser power and the scanning speeds to determine the optimal processing conditions. Additionally, hot isostatic pressing (HIP) was performed after the L-PBF process to further increase densification. Selected samples were subjected to microstructural characterization. The best densification results obtained were for the sample produced with the laser power of 173 W and scanning speed of 600 mm/s, where densifications close to 98% were obtained. HIP post-processing promoted increased densification of samples with closed porosity, allowing samples with densification above 95% to reach values close to 100%. HIP did not promote the closure of open pores. The results indicate that the use of water atomized AISI 316L in the L-PBF process combined with post-processing by HIP can produce dense engineering components and at the same time reduce the production costs of the manufactured components, mainly because it is a lower cost raw material when compared to the commonly used feedstock obtained by gas atomization.

Effect of Hot Isostatic Pressing Process Parameters on Properties and Fracture Behavior of Tungsten Alloy Powders and Sintered Bars

In order to investigate the effect of hot isostatic pressing (HIP) process parameters on the properties and fracture behavior of tungsten alloy, HIP experiments with different process parameters were carried out, and the relative density, Rockwell hardness, tensile properties, and tensile fracture behavior were analyzed. The results show that after HIP, the tungsten alloy samples obtained further densification, higher relative density and hardness, and lower dispersity. At 1300 °C and 140 MPa, the sintered bar achieved excellent mechanical properties: yield strength increased by 16.5%, tensile strength increased by 16.1%, and fracture strength increased by 85.3%. Comparing the two processes, the mechanical properties of tungsten alloy powders formed directly via HIP were not as good as those of the sintered bars. In addition, after HIP, the fracture mode of the tungsten alloy sintered bar samples was mainly ductile tear, and that of the tungsten alloy powder samples was mainly a full brittle fracture.

Effect of Hot Isostatic Pressing and heat treatments on porosity of Wire Arc Additive Manufactured Al 2319

Porosity and lack of fusion defects that can occur during additive manufacturing are often managed with Hot Isostatic Pressing (HIP). However, the thermal conditions experienced during the HIP cycle may create undesirable phases in some alloys and post HIP heat treatments including solution treatment + ageing may be necessary to achieve the desired final properties. It is currently unknown whether post-HIP heat treatments at standard atmospheric pressures promote the re-emergence of previously closed porosity in aluminium alloys produced by Wire Arc Additive Manufacturing (WAAM). Using micro 3D computed tomography, this work quantitatively investigates the extent of pore regrowth during post-HIP solution treatment and ageing of Al 2319 produced by WAAM. It is found that large porosity (diameters > 35 µm) that is closed during HIP mostly remain closed during subsequent heat treatment but almost a 3-fold increase in the frequency of fine gas porosity occurs during post HIP heat treatment. However, the overall porosity distribution after post HIP heat treatment remains up to 95 % lower than in the original as-built condition, indicating that HIP + heat treatments remain a viable pathway for defect reduction in industrial products.

Influence of Two‐Step Heat Treatments on Microstructure and Mechanical Properties of a β‐Solidifying Titanium Aluminide Alloy Fabricated via Electron Beam Powder Bed Fusion

Additive manufacturing technologies, particularly electron beam powder bed fusion (PBF‐EB/M), are becoming increasingly important for the processing of intermetallic titanium aluminides. This study presents the effects of hot isostatic pressing (HIP) and subsequent two‐step heat treatments on the microstructure and mechanical properties of the TNM‐B1 alloy (Ti–43.5Al–4Nb–1Mo–0.1B) fabricated via PBF‐EB/M. Adequate solution heat treatment temperatures allow the adjustment of fully lamellar (FL) and nearly lamellar (NL‐β) microstructures. The specimens are characterized by optical microscopy and scanning electron microscopy (SEM), X‐ray computed tomography (CT), X‐ray diffraction (XRD), and electron backscatter diffraction (EBSD). The mechanical properties at ambient temperatures are evaluated via tensile testing and subsequent fractography. While lack‐of‐fusion defects are the main causes of failure in the as‐built condition, the mechanical properties in the heat‐treated conditions are predominantly controlled by the microstructure. The highest ultimate tensile strength is achieved after HIP due to the elimination of lack‐of‐fusion defects. The results reveal challenges originating from the PBF‐EB/M process, for example, local variations in chemical composition due to aluminum evaporation, which in turn affect the microstructures after heat treatment. For designing suitable heat treatment strategies, particular attention should therefore be paid to the microstructural characteristics associated with additive manufacturing.

Effect of hot isostatic pressing on microstructural and micromechanical properties of additively manufactured 17–4PH steel

Microstructural and mechanical characterization techniques were utilized to establish the effect of the combined hot isostatic pressing (HIP) and standard H1025 heat treatment schedule on the properties of 17–4PH steel manufactured by means of laser powder bed fusion (LPBF). The as-printed (AP) sample initially consists of a dual-phase microstructure, with 78% martensite and 22% retained austenite. Then, the combined HIP and H1025 applied to the AP sample resulted in lower retained austenite of 7%. The microstructural analysis indicates that the post-processing after printing alleviated the process-induced defects reducing the overall defect content from 0.37% to 0.01%. Moreover, it is observed that the characteristic melt pools are dissolved, resulting in a homogeneous microstructure with reduced grain sizes. A room-temperature compression testing was then applied to the sample before and after post-processing treatment. It has been identified that, in both samples, the retained austenite transforms into martensite, a characteristic of the transformation-induced plasticity effect. The critical stress to initiate the dynamic transformation was then determined to be lower in the HIP sample than that of the AP sample. Based on the results, it can be concluded that the combined HIP+H1025 processing employed in this work effectively increased the mechanical properties of LPBF-fabricated 17–4PH steel. • 17–4Ph steel was fabricated via laser powder bed fusion. • Characterization of the samples was done by the means of EBSD analysis. • Using double differential method, the critical stresses for initiation of dynamic transformation of HIP sample was higher.

Processing, Microstructure, and Mechanical Properties of Laser Additive Manufactured Ti2AlNb-Based Alloy with Carbon, Boron, and Yttrium Microalloying

In this work, Ti-22Al-23Nb-0.8Mo-0.3Si-0.4C-0.1B-0.2Y (at. %) alloy powder was used to fabricate the Ti2AlNb-based alloy samples using Laser powder bed fusion (L-PBF) Additive Manufacturing with a high-temperature substrate preheating. L-PBF process parameters, including laser power, scan speed, hatching distance, and preheating temperature, allowing for obtaining fully dense (99.9% relative density) crack-free samples, were determined. The effects of substrate preheating temperature during the L-PBF process on microstructure, phase composition, and properties of the obtained Ti2AlNb-based alloy were investigated using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction analysis, and microhardness testing. The results obtained for the material with C, B, and Y microalloying were compared to the Ti2AlNb-based alloy fabricated by L-PBF from the powder not alloyed with C, B, and Y. The results revealed that the microalloying reduced the number of solidification cracks; however, no significant microstructural changes were observed, and high-temperature substrate preheating was still necessary to suppress cold cracking of the alloy. The microstructure of the alloy varied from fully-β/B2, B2 + O, to fully-O depending on the preheating temperature. Effects of hot isostatic pressing and heat treatment conditions on microstructure and mechanical properties were investigated.

Correlation between Interface Microstructure and Bond Strength of Al6061/Al6061 HIP-Bonded Plates for Fuel Cladding Application

The effects of hot isostatic pressing (HIP) processing parameters on microstructure and bond strength of Al6061/Al6061 plate interfaces were systemically investigated at the micro- and nanoscale. The HIP bonding of the two aluminum plates was performed at four temperatures: 350°C, 400°C, 450°C, and 560°C. The results reveal the formation of micron scaled Mg2Si precipitate and uniform nano scaled Mg2Al2O5 oxide at the interface. The formation of Mg2Al2O5 is closely associated with the fast bulk diffusion of Mg from the Al matrix to the amorphous Al2O3/Al interface and subsequent reaction between Mg and Al2O3. The highest and lowest bond strengths were observed in samples HIP bonded at 450°C and 350°C, respectively.

Effect of hot isostatic pressing on fatigue behavior and fracture mechanism of A319 aluminum alloy under uniaxial and nonproportional multiaxial loading conditions

AbstractThe effect of hot isostatic pressing (HIPing)‐induced porosity difference on the fatigue behavior and fracture mechanism of A319 aluminum alloy under uniaxial and nonproportional multiaxial loading is investigated. Non‐HIPed alloy exhibits weaker nonproportional additional hardening capacity than HIPed alloy, which is ascribed to the nonproportional multiaxial loads that enhance the cyclic softening induced by casting pores. Additional plastic damage caused by nonproportional multiaxial loads is highly susceptible to HIPing. Torsional loads trigger the tension‐compression asymmetry of the axial stress response during nonproportional multiaxial fatigue. Multiaxial fatigue life is more sensitive to HIPing at minor total strain amplitudes. The rapid bridging among adjacent pores serves as the preferred channel for fatigue crack propagation. Nonproportional multiaxial loads improve the probability of encountering pores during fatigue crack initiation and propagation.