Powder Metallurgy Hot Isostatic Pressing Research Articles

Phase-field modeling of interdiffusion between dissimilar Fe-Cr-Ni alloys during non-isothermal hot isostatic pressing

Powder metallurgy hot isostatic pressing (PM-HIP) has emerged as a promising alternative to welding for joining dissimilar metals. During HIP, interfacial bonding is mediated by solid state diffusion. The interdiffusion zone across the interface depends on processing conditions, calling for the need for accurate numerical tools capable of simulating interdiffusion and possible phase transformation in order to optimize processing parameters. Here, a phase-field (PF) model based on CALPHAD-based free energy functionals is developed to simulate the interdiffusion and phase evolution between dissimilar Fe–Cr–Ni based steels undergoing HIP and is demonstrated using the interface between 316L and SA508 steels. To overcome the numerical challenges caused by the singular magnetic and entropy terms in the CALPHAD free energy models in the Fe–Cr-Ni system, polynomial functions are fitted with temperature dependent coefficients represented by Fourier series to accurately describe the phase stability of both fcc and bcc phases in the composition and temperature space. This enables simulations of non-isothermal HIP cycles. Diffusivity data from commercial software and literature are taken to parameterize the kinetic parameters. A discrete nucleation model is incorporated for possible phase transformation. The modified thermodynamic models are validated against previous experiments at 923 K and 1273 K. The interdiffusion kinetics are benchmarked against new HIP experiments joining powder and bulk 316L to bulk SA508 with three different HIP cycles. The good agreement between simulations and experiments on both phase stability and interdiffusion indicate that the model is suitable for simulating interdiffusion between Fe–Cr–Ni alloys during HIP cycles. It is also found that using powder and bulk 316L gives similar interdiffusion profiles at elevated temperature when a dense interface forms during HIP.

Comparison study of creep constitutive laws in compaction of porous stainless steel 316 L

Modeling Powder Metallurgy Hot Isostatic Pressing (PM-HIP) is of paramount importance due to its critical role in modern manufacturing. Accurate modeling of PM-HIP and understanding the associated deformation behavior are essential for optimizing the process and advancing the design and production of high-performance materials in critical applications. To accurately simulate the deformation behavior during PM-HIP, this paper presents a comprehensive investigation of modeling PM-HIP processes using various creep models incorporating rate-dependent plasticity embedded into Finite Element Analysis (FEA). This study experimentally and computationally compares four distinct creep models: Kuhn McMeeking, power law creep, unified creep law, the rate-dependent creep that was modified by Abouaf et al. and with modification of Van Nguyen et al. for density dependency. The results showed the modified Abouaf's Model, uniquely designed to account for both primary and secondary creep, consistently exhibits the closest alignment with experimental outcomes compared to the other three creep models tested.

Identification of the Mechanism Resulting in Regions of Degraded Toughness in A508 Grade 4N Manufactured Using Powder Metallurgy–Hot Isostatic Pressing

Powder metallurgy–hot isostatic pressing (PM-HIP) is a form of advanced manufacturing that offers the ability to produce near-net shape components that are otherwise not achievable via conventional forging or wrought manufacturing. Accessing the design space of PM-HIP is dependent upon the ability to achieve uniform or known properties in finalized components, which has resulted in a number of programs aimed at identifying properties achievable via PM-HIP manufacturing. One result of these programs has been the consistent observation of a variation in toughness observed for the low-alloy steel ASTM A508 Grades 3 and 4N. While observed, the degree of variability and the mechanism resulting in the variability have not yet been fully defined. Thus, a systematic approach to evaluate the variation observed in impact toughness in PM-HIP ASTM A508 Grade 4N was proposed to elucidate the responsible metallurgical mechanism. Four unique billets manufactured from two heats of powder with different particle size distributions (PSDs) were fabricated and tested for impact toughness and tensile properties. The degradation in impact toughness was confirmed to be location-specific where the near-can region of all billets had reduced impact toughness relative to the interior of each billet. The mechanism driving the location-specific property development was identified to be mobile oxygen that follows the thermal gradient that develops during the HIP cycle and leads to a redistribution of mobile oxygen where oxygen is concentrated ~1” inboard of the original canister/billet interface. Redistributed oxygen then forms stable oxides along coincident prior particle and prior austenite grain boundaries, effectively reducing the impact toughness. With the mechanism now addressed, necessary actions can be taken to mitigate the effect of the oxygen redistribution, allowing for use in PM-HIP A508 Grade 4N in commercial industry.

Optimization of the grain boundary network and tensile properties of powder metallurgy-hot isostatic pressed Ni-based alloy Inconel 625

Powder metallurgy-hot isostatic pressing (PM-HIPing) is an advanced manufacturing technology for large-sized and complex-shaped components for nuclear applications. In the present study, a novel PM-HIPing strategy was proposed to optimize the grain boundary network and tensile properties of Ni-based alloy Inconel 625, and it was verified by a series of experiments. Samples with 69 % and 74 % of coincidence site lattice (CSL) grain boundaries were obtained when the narrow-size ranged powder was consolidated at 1140 °C and 1180 °C, respectively. The fraction of CSL grain boundaries was further increased to ∼78.5 % after a high temperature solution treatment. Room temperature yield strength and ultimate tensile strength of PM-HIPed alloy 625 were comparable to that of the wrought specimens, elongation of the specimens was ∼56–60 %, the samples all featured with dimple ductile dominant fracture mode.

Corrosion of 316L stainless steel produced by laser powder bed fusion and powder metallurgy in pressurized water reactor primary coolant

Corrosion mechanism of 316 L stainless steel produced by laser powder bed fusion-hot isostatic pressing (LPBF-HIP) and powder metallurgy-hot isostatic pressing (PM-HIP) is studied with in-situ electrochemical impedance measurements coupled to detailed oxide film characterization. Quantitative analysis of impedance spectra using the Mixed-Conduction Model and estimation of local kinetic and transport parameters by interpretation of in-depth elemental composition profiles indicated lower corrosion and oxidation rates of LPBF-HIP and PM-HIP materials in comparison to conventional wrought 316 L. This owes to a higher fraction of low-angle grain boundaries, smaller grain size, the presence of nano-sized oxide particles and elevated Cr and Ni contents.

Review on High-Energy Beam Based Processing Technologies for Fabrication of Small Modular Reactor

The development of small modular reactors (SMRs) has attracted significant attention owing to the increasing interest in energy security and carbon neutrality worldwide. An SMR is an advanced nuclear reactor with a power capacity of up to 300 MWe per unit. To fabricate the SMR, innovative manufacturing technologies such as powder metallurgy hot isostatic pressing (PM-HIP), electron beam welding (EBW), and diode laser cladding (DLC) were introduced to reduce the fabrication cost and time. Particularly, this replaced arc-based welding and cladding with high-energy beam-based EBW and DLC. The EBW could provide one pass welding for extremely thick specimens. In addition, in the case of using the DLC, only one layer cladding was acceptable for corrosion protection owing to its low dilution rate. However, studies on the innovative manufacturing technologies were less reported because of technology security. In this study, recently reported research articles regarding the EBW and DLC were reviewed. In particular, local vacuum and reduced pressure electron beam studies were discussed by comparing their the arc welding results. Process parameter studies on the DLC were also reviewed to introduce appropriate optimized conditions for the industry application.

Helium ion irradiation-induced damage of powder metallurgy-hot isostatic pressed Ni-based alloy GH3535 for molten salt reactor applications

Powder metallurgy-hot isostatic pressing (PM-HIPing) is a promising technology for the manufacturing of components for nuclear reactors. In this study, Ni-based alloy GH3535 for molten salt reactor applications, was processed via PM-HIPing, and irradiation damage behaviors of the PM-HIPed GH3535 along with its forged counterparts were studied with He+ ions irradiation and microstructural characterization. The irradiation-induced defects in the samples, such as helium bubbles and dislocation loops, were characterized using transmission electron microscope (TEM). The mechanical responses of irradiated specimens were studied by nano-indentation. The results show that the PM-HIPed GH3535 exhibits a comparable irradiation resistance to its forged counterparts. Size of the helium bubbles and dislocation loops are larger for samples irradiated at high temperature than those irradiated at room temperature, irrespective of processing methods. However, number density of these defects is smaller for the high temperature irradiated samples than those irradiated at room temperature, which is particularly evident for the forged sample. The samples show significant hardening after irradiation, evidenced by the nano-indentation hardness test results. The experimental results and the calculations based on dispersed barrier hardening (DBH) model are in general agreement. This study will provide important data to support the application of the PM-HIPed materials or components in the nuclear reactors.

SA508 low alloy steel to 316L stainless steel dissimilar metal joint made by powder metallurgy hot isostatic pressing

Joining ferritic SA508 low alloy steel (LAS) and austenitic 316 L stainless steel (SS) via powder metallurgy hot isostatic pressing (PM-HIP) was evaluated as an alternative method to welding. This study investigated the mechanical and microstructural evolutions of the bimetallic interface under different joint designs and heat treatments. The direct joining of dissimilar metal alloys by PM-HIP method resulted in two designs: 1) powder SA508 to solid bar 316 L (P508–B316L) and 2) powder 316 L solid bar SA508 (P316L-B508). In both cases, P508–B316L and P316L-demonstrated satisfactory tensile strength, however, high hardness and severe depreciation in toughness were located on the bimetallic interface. The mechanisms responsible for the detrimental mechanical properties were verified. Large oxides were observed in P508–B316L due to the prior powder boundary (PPB) oxides present in SA508 powder. The intense sensitization occurred from the formation of M23C6 carbides, consequently from the slow cooling after PM-HIP in P316L-B508. Post-HIP heat treatments were explored to reduce the distance of carbide formation; however, the heat treatment could not eliminate the carbides. The experimental results were compared to the diffusion couple simulation as a function of carbide formation with distance. The analysis also showed the high hardness at the bimetallic interface was primarily contributed by solid solution strengthening. In conclusion, the direct joining of P316L-B508 and P508–B316L via PM-HIP was deemed to be unfeasible, and a transitional material is necessary to impede the diffusion of carbon.

Oxidation Resistance in 1200\xb0C Steam of a FeCrAl Alloy Fabricated by Three Metallurgical Processes

FeCrAl alloys are a leading candidate material for accident tolerant fuel cladding due to their good performance in both normal light-water reactor operating conditions as well as their resilience to high-temperature accident scenarios. For commercial-scale production, new fabrication techniques need to be investigated. In this study, the effects of fabrication methods on the high-temperature steam oxidation performance of C26M (Fe12Cr6Al2Mo in wt.%) were investigated. Three variants of C26M were manufactured: wrought (cast and forged) (WC26M), powder metallurgy hot isostatic pressing (PMC26M), and laser powder bed fusion additive manufacturing (AMC26M). All three variants were exposed to steam at 1200°C for 2 h. Results showed no significant variation in mass change between the variants after steam exposure. All three variants effectively formed stable protective alumina films with ~0.6–1.3 µm thickness. This study suggests FeCrAl alloys have excellent resilience to high-temperature steam in nuclear reactor accident scenarios regardless of the fabrication method.

Comparison Between Hot Rolled and Powder Metallurgy–Hot Isostatic Pressing (PM-HIP) Processed Duplex Stainless Steel UNS S32205

Comparison Between Hot Rolled and Powder Metallurgy–Hot Isostatic Pressing (PM-HIP) Processed Duplex Stainless Steel UNS S32205

Powder HIP of pure Nb and C-103 alloy: The influence of powder characteristics on mechanical properties

In this work, pure Nb processed by Powder Metallurgy Hot Isostatic Pressing (PM HIP) was investigated as a potential alternative to C-103 Nb-based alloy for the manufacture of near-net-shape thruster combustion chambers. Three Nb powders with varied particle size range (fine, mid-range and coarse) and C-103 powder were investigated to understand the differences in particle size distribution (PSD), morphology and oxygen (O) content present in the alloy chemistry. The as-HIPed microstructures of pure Nb and C-103 are characterised by a near to fully dense microstructure and the absence of PPBs. Microstructural analyses performed on pure Nb highlighted the influence of particle size on the average as-HIPed grain size. Additionally, it was observed that O content plays a crucial role in the microhardness of pure Nb. Tensile tests performed on Nb mid-range and on Nb mid-range sieved showed that a simple sieve operation was effective in increasing the strength of the material while maintaining good levels of elongation. Alternatively, it was also demonstrated that pure Nb powder heat treatment can be regarded as an effective way to increase the O levels in pure Nb powders as witnessed by the high hardness levels. On the other hand, as-HIPed C-103 powder showed superior tensile properties if compared to the minimum specifications for wrought C-103. Finally, to summarise, the work performed on pure Nb, a simple structure-property relation model was developed to predict the YS of pure Nb based on the O levels and grain size of the as-HIPed microstructure.

Development of Ni-base metal matrix composites by powder metallurgy hot isostatic pressing for space applications

In this work, near-net-shape powder metallurgy hot isostatic pressing (NNS PM HIP) of Ni-base metal matrix composite (Ni-MMC) was developed to improve the hardness and wear properties of turbopumps mechanical seals. Silicon carbide (SiC) and titanium diboride (TiB2) fine powders were used as reinforcements with different ratios to improve the hardness and consequently the tribological properties of the developed Ni-MMC material. Powder characterisation was performed on the blended powders to check the homogeneity of the mixed powders. The hot isostatically pressed (HIPed) Ni-MMC microstructures were analysed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The HIPed material showed a fully dense microstructure with a continuous network of ceramic reinforcement particles at the prior particle boundaries (PPBs). Furthermore, microhardness tests were performed on IN625, IN625-SiC and IN625-TiB2 to understand the impact of the reinforcement on the microhardness. It was demonstrated that the volume percentage of ceramic reinforcement in the IN625 matrix plays a crucial role in achieving higher hardness by increasing the fraction of hard phases appearing in the microstructure of the developed Ni-MMC material. The final part of the work focuses on the canister design and manufacture of a near-net-shape (NNS) mechanical gas seal using IN625 based MMC to demonstrate the feasibility of manufacturing mechanical seals through the NNS PM HIP technique. Overall, IN625 based MMCs resulted in a drastic improvement in tribological properties if compared to the base material. Furthermore, the employment of the PM HIP consolidation technique resulted in a fully dense and homogeneous microstructure, highlighting the potentials of PM HIP in the generation of novel composite materials.

The role of powder atomisation route on the microstructure and mechanical properties of hot isostatically pressed Inconel 625

Abstract The powder's characteristics and its purity can greatly influence the properties of nickel (Ni)-base superalloys parts produced by near net-shape powder metallurgy hot isostatic pressing (NNS PM HIP) manufacturing process. In this study, Inconel 625 (IN625) powders produced using four different atomisation routes, argon, nitrogen, plasma and water atomisation (AGA, NGA, PA, WA, respectively) were investigated. The first section of this study is focused on the determination of powder characteristics which includes chemical composition, particle size distribution (PSD), tap density and powder's cross-section analysis, whereas the second section is about hot isostatic pressing (HIPping) of the four powder types and to assess the impact of the powder characteristics on the microstructure-property development after HIPping. To gain an understanding of the surface chemistry of the powders, X-ray photoelectron spectroscopy (XPS) analysis were carried out on the surface of the four powders. The latter analysis highlighted fundamental differences on the powder's surface, especially the differences in the surface and near-surface distribution of the alloying elements i.e. C, O, Cr, Mo and Nb present in the alloy chemistry. The micrographs of the four IN625 hot isostatically pressed (HIPped) powders revealed a fully dense microstructure with the presence of prior particle boundaries (PPBs). The atomisation route greatly impacted the nature and amount of PPBs, as well as on the fractions and sizes of oxides, carbides, oxycarbides and oxycarbonitrides precipitates. WA showed the most severe presence of PPBs, followed by NGA, AGA and lastly PA. The powder quality has a greater impact on the mechanical properties of as-HIPped materials, especially on ductility. Overall, PA HIPped IN625 possessed the optimum balance between tensile strength, ductility and Charpy impact properties once compared to the others and match the properties to wrought IN625 material.

Microstructure characterization and tensile properties of hot isostatic pressed China ultrahigh strength steel

Powder metallurgy hot isostatic pressing (HIP) is a promising technology for producing complex ultrahigh strength steel (UHSS) components. In the present study, a kind of China UHSS, 30CrMnSiNi2A steel, was prepared by HIP with different processing temperatures. The microstructure and tensile properties of HIPed compacts were analyzed in depth via scanning electron microscopy, X–ray diffraction, electron back–scattered diffraction, transmission electron microscopy, tensile testing and nanoindentation experiment. Results show that all HIPed compacts are granular bainitic structure composed of bainitic ferrite matrix and M–A islands. With the HIP temperature increasing, the volume fraction of M–A islands decreases, and the average grain size increases. Besides, a harmful structure (that is prior particle boundaries, PPBs), which is composed of a great number of Mn–rich and Si–rich oxide inclusions, is formed in the HIPed compacts. Notably, increasing HIP temperature is beneficial to eliminate PPBs. The volume fraction of M–A islands, grain size and the state of PPBs together determine the tensile properties of HIPed compacts, in which the state of PPBs has a most significant impact. With the HIP temperature rising, the tensile fracture mode changes from inter–particle debonding to transgranular quasi–cleavage, which benefits from the elimination of PPBs.

Inclusion of initial powder distribution in FEM modelling of near net shape PM hot isostatic pressed components

The final shape of powder metallurgy hot isostatic pressing (HIP) components is determined by many factors, including the shape and size of the capsule, the initial density distribution of the powder before HIP, and HIP process parameters. Current HIP simulation, which usually assumes that the powder inside the capsule is homogeneous, cannot predict non-uniform shrinkage. Therefore, the purpose of this work is to develop a methodology to quantitatively determine the initial powder density distribution inside HIP capsules, which were precompacted by different techniques. The relative density distribution obtained from experimental work is used as the initial condition for numerical simulations. The final shapes of the capsules produced by HIP are compared to simulation results. The paper shows the sensitivity of the final shape on the initial powder density distribution and illustrates the need to implement the initial powder distribution into the finite element model to improve the quality of the near net shape HIP simulation.

Manufacturing of the ITER TF coils radial plates by means of P/M HIP and a hybrid machining center

The fabrication of the ITER radial plates (RPs) is a demanding task, which includes machining and welding. It requires high accuracy with respect to its large size. There are two issues remained: (i) the productivity reduced by the large amount of machining and welding work; and (ii) the tight tolerance. A conventional machining center can be used only when segments and blocks are small. As a solution, this paper presents a method, which improves the final accuracy and increases the productivity. The method combines the powder metallurgy hot isostatic pressing (P/M HIP) technology and the mobile parallel kinematics machine system for fabricating the RPs. This paper first introduces the P/M HIP technology and describes the benefits of using the technology in the fabrication of the RPs, and then introduces the mobile machining/welding unit developed (ad hoc) and describes the possible manufacturing process to be used for the production of the radial plates.