High-entropy Alloy Powders Research Articles

Microstructure evolution and tensile property of high entropy alloy particle reinforced 316 L stainless steel matrix composites fabricated by laser powder bed fusion

316 L stainless steel is prone to failure under high-strength conditions due to low strength and poor wear resistance, which limits its further application severely. In this study, 2 wt% FeCoNiAlTi high entropy alloy (HEA) powders and 316 L stainless steel powders were mixed to fabricate HEA reinforced 316 L stainless steel matrix composites (MMCs) via laser powder bed fusion (LPBF). The influence of scanning speed on microstructure evolution, the mechanical properties and the strengthening mechanisms have been investigated systematically. The LPBF-fabricated HEA/316 L MMCs consists of both γ-Fe and α-Fe phases. For HEA/316 L MMCs, the grains are refined with the increase of scanning speed and the minimum size is around 0.64 µm. The precipitation of nanoparticles is observed, and the nanoparticles form a strong interfacial bounding with matrix, which indicates the good metallurgical bonding between HEA and 316 L stainless steel. The tensile strength of the LPBF-fabricated composites increases from 1164 MPa to 1276 MPa with increased scanning speed, which is approximately twice as high as the strength of LPBF processed 316 L stainless steel matrix. The contribution of each strengthening mechanism is calculated, and the contribution of particle strengthening is the largest (from 241 MPa to 300 MPa, changing with scanning speed). This work demonstrates the feasibility of using HEA as potential reinforcement in metallic systems and can further enlarge the application field of metallic materials.

High Entropy Alloy CoCrFeNiMo Reinforced Electrocatalytic Performance for High-Efficient Electrocatalytic Water Splitting.

The development of efficient, durable, and affordable electrocatalysts is critical for the advancement of a hydrogen economy, particularly in alkaline media. In this study, we propose CoCrFeNi and CoCrFeNiMo high entropy alloys (HEAs) powders as bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). While there is a performance gap compared to Pt/C, the prepared samples exhibit relatively good electrocatalytic activity with overpotentials of 156.7 mV and 160.5 mV for HER at 10 mA cm-2 in a 1.0 M KOH solution, respectively. Notably, the CoCrFeNiMo catalyst demonstrates significantly higher OER activity than commercial RuO2 with an overpotential of 390 mV at 50 mA cm-2 , and delivers a cell voltage of 1.86 V at a current density of 10 mA cm-2 for water splitting.

Ball milling process variables optimization for high-entropy alloy development using design of experiment and genetic algorithm

Besides developing new high-entropy alloys (HEAs) from vast compositional space, developing HEA powders with good control of grain- and- particle sizes (GPS) for improved flowability/sinterability in additive-manufacturing and sintering processes are of growing interest. Using a mechanical alloying process, the effect of parameters—process control agent (PCA) type and amount, and milling speed and time—on solid-solution onset and GPS of a model HEA (AlCoCrFe) is systematically investigated. The optimum PCA-type is first experimentally determined; followed by: a Taguchi design of experiment to plan and study the effect of parameters on the response variables—GPS, regression model to develop predictive process models, and model multi-objective optimization using genetic algorithm. Milling speed and PCA amount have the most effect on the grain- and particle- sizes, respectively. Two mathematical models for predicting mechanically-alloyed HEA GPS are developed. This work develops a framework for appropriate processing parameter selection for HEA powder development.

Study on mechanical alloying behavior and thermal stability of HfMoNbTaTi refractory high-entropy alloy

The present study prepared HfMoNbTaTi refractory high-entropy alloy powders with uniform distribution of components by mechanical alloying (MA). Six scenarios were designed to investigate the effects of rotational speed, milling duration, ball-to-powder weight ratio (BPR), and process control agent (PCA) on the alloy powder to achieve complete alloying, controlled morphology, and refined grain size. Results showed that the alloying efficiency and lattice strain increased significantly while the grain size decreased with increased rotational speed and BPR. In addition, the content of impurity elements (e.g., C, O, and Fe) also increased. Stearic acid added as PCA effectively prevented cold-welding and refined the particle/grain size but led to the appearance of unknown carbides. Excellent thermal stability was provided by the mechanically alloyed powders when annealed below 1000 °C. In contrast, the single body centered cubic (BCC) solid solution structure decomposed at 1200 °C annealing, and the decomposition temperature range was 942.5 °C–1041.2 °C based on the DSC curve. Finally, the dissolution pattern of components, the size mismatches effect, impact energy, and the optimal range of mechanical alloying process parameters were discussed in detail.

Correlation between the nanomechanical characteristic and the phase transformation of BCC-based high entropy alloys produced via powder metallurgy

ABSTRACT In this study, the effects of Cu addition on AlFeMnTiSi0.75Cu x (x = 0, 0.25, 0.5, 0.75, 1.00; in molar ratios) high entropy alloys (HEAs) prepared via mechanical alloying and spark plasma sintering were investigated. The structure, phase, morphology and composition of HEA powders were analysed and the results revealed that the AlFeMnTiSi0.75Cu x HEAs exhibited a multiphase structure. Additionally, after sintering at 900 °C, the formation of BCC, µ and L21 phases in the densified HEAs was enhanced. The investigation of the hardness, nanoindentation and compressive properties revealed that the microstructural and mechanical properties of AlFeMnTiSi0.75Cu x HEAs were improved at the optimal Cu fraction (0.25 molar ratio). The nanoindentation results revealed that the AlFeMnTiSi0.75Cu x HEAs exhibited the highest hardness and elastic modulus (HIT = 19.2 GPa, EIT = 336 GPa). These results improve the current understanding of multiphase HEAs and may pave way for the development of advanced HEAs with superior mechanical properties.

Phase evolution and high-temperature wear behavior of non-equiatomic metastable CoCrNiTiMox HEA coatings fabricated by high-velocity oxy-fuel technique

The current research aims to enhance the tribological performance of maraging steels at high temperatures by surface modification techniques. CoCrNiTiMox (x; molar fraction, x = 0.5, 1.5) high-entropy alloy (HEA) coatings with dense lamellar microstructures were deposited onto maraging steels using high-velocity oxy-fuel spray (HVOF). In order to achieve a uniform distribution of constituent elements for thermal spray deposition, mechanical alloying was employed to synthesize the HEA feedstock. The phases and microstructure of the synthesized HEA powder, as-sprayed coatings, and worn surfaces were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-sprayed HEA coatings exhibited metastability, with a BCC phase solid solution, NiTiO3 spinel, and an intermetallic MoNi phase for CoCrNiTiMo0.5 and Co2Mo3 phase for CoCrNiTiMo1.5. The average microhardness of CoCrNiTiMo0.5 and CoCrNiTiMo1.5 HEA coatings were 841 ± 62 HV0.3 and 952 ± 23 HV0.3, respectively. The specific wear rate and friction coefficients of CoCrNiTiMox HEA coatings exhibited a decreasing trend with an increase in temperature, owing to the formation of tribofilms on the worn surface. X-ray diffraction studies revealed the formation of NiMoO4 spinel for CoCrNiTiMo0.5 and MoO2, Co3O4 phases for CoCrNiTiMo1.5 HEA at a wear temperature of 600 °C. The investigation of worn surfaces showed a transformation in wear mechanisms from abrasive wear at room temperature to oxidative wear with mild fatigue at elevated temperatures.

Effect of Cr-Doping on the Structural and Magnetic Properties of Mechanically Alloyed FeCoNiAlMn1-xCrx High-Entropy Alloy Powder.

In this work, the new compositions of FeCoNiAlMn1-xCrx, (0.0 ≤ x ≤ 1.0), a high-entropy alloy powder (HEAP), are prepared by mechanical alloying (MA). The influence of Cr doping on the phase structure, microstructure, and magnetic properties is thoroughly investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry. It is found that this alloy has formed a simple body-centered cubic structure with a minute face-centered cubic structure for Mn to Cr replacement with heat treatment. The lattice parameter, average crystallite size, and grain size decrease by replacing Cr with Mn. The SEM analysis of FeCoNiAlMn showed no grain boundary formation, depicting a single-phase microstructure after MA, similar to XRD. The saturation magnetization first increases (68 emu/g) up to x = 0.6 and then decreases with complete substitution of Cr. Magnetic properties are related to crystallite size. FeCoNiAlMn0.4Cr0.6 HEAP has shown optimum results with better saturation magnetization and coercivity as a soft magnet.

Single-Phase High-Entropy Carbides Synthesized from a Mixture of Pre-Mechanically Alloyed TiZrHfTaNb HEA Powders and Carbon

In this paper, single-phase chemically homogeneous high-entropy ceramics (HEC) were synthesized from a mixture of pre-mechanically alloyed TiZrHfTaNb high-entropy alloy (HEA) powders and carbon. Mechanical alloying (MA) of a TiZrHfTaNb alloy with different process times made it possible to obtain a powder with uniform distribution of chemical elements and with the main phase in the form of a body-centered cubic (BCC) solid solution. HEC with the chemical formula MeC and space group Fm-3m begins to form at temperatures of about 1600 °C in the process of sintering a mixture of pre-mechanically alloyed HEA powders and carbon. A detailed study of the diffraction patterns revealed peaks of mixed zirconium-hafnium oxide (ZrHf)O2, which is also confirmed by the microstructure analysis results and distribution elements. Increasing the process temperature to 2000 °C leads to the formation of a single-phase and chemically homogeneous (TiZrHfTaNb)C HEC.

Microstructure evolution and tribological behavior of laser cladded Al1.8CrCuFeNi2/WC composite coatings on Ti-6Al-4 V

Al1.8CrCuFeNi2/WC composite coatings – prepared on Ti-6Al-4 V alloy by laser cladding of a high entropy alloy (HEA) Al1.8CrCuFeNi2 powder with the addition of either 0, 10, 20, 30, 50, or 70 wt% WC – were studied in detail for their structure, morphology, phase composition, mechanical and tribological properties. The WC-free Al1.8CrCuFeNi2 coating is composed of a dendritic-shaped bcc matrix phase with ∼14.6 vol% fcc phases between these dendrites. With increasing WC addition, the fcc phase-fraction decreases and several carbide phases are formed leading to the formation of a more complex microstructure. For example, the HEA/WC composite coating prepared with the addition of 30 wt% WC to the HEA powder is composed of an Al-Ti-Ni-rich bcc phase, eutectic, equiaxed Ti-rich carbides, W-rich carbides, and fishbone-like Ti-rich carbides. This coating exhibits a very high hardness of 1372.6 HV0.2 across the outermost 1.1 mm of the 1.5 mm coating thickness and allows for the highest hardness values among the coatings studied within the initial 0.4 mm directly at the interface to the substrate. This coating further provides the lowest mean-coefficient of friction of 0.49 and lowest wear rate, which is with 6.52·10−7 mm3/Nm only 7% of that provided by the WC-free HEA coating. Thus, by the addition of WC to the HEA powder and the thereby initiated formation of various carbides during the laser cladding process of the Ti-6Al-4 V alloy, composite coatings are accessible, which easily outperform those prepared without WC.

Environmentally friendly molten salt synthesis of high-entropy AlCoCrFeNi alloy powder with high catalytic hydrogenation activity

A molten salt synthesis method was used to prepare high-entropy AlCoCrFeNi alloy powder with a high specific surface area of 67.5 m2/g, exhibiting remarkable catalytic activity in the hydrogenation of p-nitrophenol by NaBH4. The life cycle assessment of the proposed method indicated that AlCoCrFeNi production was associated with greenhouse gas emission of 125 kgCO2e/kg-product, whose main contributors were CaH2 and citric acid used during the precursor's reduction and formation, respectively. On the other hand, that for a previously reported dealloying method was 277 kg CO2e/kg-product. Thus, a minimum of 54% greenhouse gas emission reduction compared to the conventional dealloying method is achievable in the proposed molten salt method. The results indicated the possible environmentally friendly production of high-surface-area, high-entropy alloy powders suitable for industrial applications.

Electrochemical oxidation of methylene blue dye in wastewater using mechanically alloyed high entropy alloy modified carbon paste electrode using cyclic voltammetry

Mechanical alloying is one of the popular, simple, and easy powder metallurgy methods to prepare nanostructured high entropy alloys (HEA). HEAs are modern-day alloys that exhibit significantly improved properties and are used in many unique applications. One such application is using HEA powders for determining the methylene blue dye in wastewater using cyclic voltammetry. We have successfully synthesized the HEA powder of composition 25Fe-19Cr-19Ni-18Ti-19Mn by planetary ball mill and studied their phases, surface morphology, and particle sizes by x-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) respectively. We have fabricated the HEA-modified carbon paste electrode (HEA-MCPE) to study the electrochemical oxidation of methylene blue (MB) dye present in the wastewater. MB is a cationic dye that is toxic, and carcinogenic in high doses; generally used in textile, paper, and leather industries for coloring purposes and discharged into the water sources and thus creating a threat to aquatic animals and humans. Therefore, we must determine the MB dye in waste water regularly. Our fabricated electrode can detect MB dye in wastewater over a pH range of 6 to 7.6 with a significant current response. We have found that, the 4 mg HEA-MCPE and pH 6 are the optimal experimental conditions for achieving a higher rate of electro-oxidation of MB dye. The calculated active surface area for bare and HEA-MCPE is found to be 0.180 and 0.918 cm2 respectively. We have found out that, increase in the concentration of MB from 1 mM to 5 mM increases the anodic peak current linearly due to the increased molecular interaction and the mobility of electrons between the analyte and the electrode surface.

Synthesis and properties of high-entropy CoCrFeNiMnWx alloys

Compact samples and coatings from CoCrFeNiMnWx high entropy alloys (HEAs) powders synthesized by mechanical alloying followed by plasma spheroidization (PS) were obtained by directed energy dssssseposition (DED). The microstructure of CoCrFeNiMnWx samples obtained by DED represents a cast dendritic structure. The phase composition of all samples represents a solid solution with FCC lattice. The increase in the lattice parameter in the samples by 0.33–0.47% compared to the spheroidized powder is characteristic of all obtained alloys after DED. The lattice parameter of CoCrFeNiMnWx samples increases with increasing W content, which is associated with the formation of a highly entropic solid replacement solution. The hardness of the samples increased by 4.6% and 12.9% with the addition of W in amounts of 0.125 and 0.25 at. % to the CoCrFeNiMn HEA, respectively. Tungsten-doped alloy coatings have a higher bending strength than the CoCrFeNiMn alloy. With relatively similar ductility values, the CoCrFeNiMn alloy has a lower strength, which is insufficient to resist cracking when bent to an angle above 20–45°, depending on the bending direction.

Physical models for vacuum-induced multistage atomization of high-entropy FeCoCrNiMo alloy powder for 3D printing

The atomization process of high-entropy FeCoCrNiMo alloy was tested using electrode induction gas atomization (EIGA) at different powers, pressures and rotary speeds. The modelization about the physical essence in the metal drop atomization was studied. A surface tension model, a specific surface energy model, a cooling rate model, and a solidification kinetic model of the alloy drop atomization process were built. Based on these models, the quantitative relationships between the powder particle size and process parameters during the alloy atomization were determined. Together with the results of particle size and scanning electron microscopy-based morphology of the powder obtained from EIGA under different process systems, the accuracy of the above physical models was validated.

Mechanical Alloying Behavior and Thermal Stability of CoCrCuFeMnNix High-Entropy Alloy Powders Prepared via MA.

CoCrCuFeMnNix (x = 0, 0.5, 1.0, 1.5, 2.0 mol, named as Ni0, Ni0.5, Ni1.0, Ni1.5, and Ni2.0, respectively) high-entropy alloy powders (HEAPs) were prepared via mechanical alloying (MA), and XRD, SEM, EDS, and vacuum annealing were used to study the alloying behavior, phase transition, and thermal stability. The results indicated that the Ni0, Ni0.5, and Ni1.0 HEAPs were alloyed at the initial stage (5-15 h), the metastable BCC + FCC two-phase solid solution structure was formed, and the BCC phase disappeared gradually with the prolonging of ball milling time. Finally, a single FCC structure was formed. Both Ni1.5 and Ni2.0 alloys with high nickel content formed a single FCC structure during the whole mechanical alloying process. The five kinds of HEAPs showed equiaxed particles in dry milling, and the particle size increased with an increase in milling time. After wet milling, they changed into lamellar morphology with thickness less than 1 μm and maximum size less than 20 μm. The composition of each component was close to its nominal composition, and the alloying sequence during ball milling was Cu→Mn→Co→Ni→Fe→Cr. After vacuum annealing at 700~900 °C, the FCC phase in the HEAPs with low Ni content transformed into FCC2 secondary phase, FCC1 primary phase, and a minor σ phase. The thermal stability of HEAPs can be improved by increasing Ni content.

Characterisation and property evaluation of High Entropy Alloy coating on 316L steel via thermal spray synthesis

The advancement in the alloys led the development of High Entropy Alloys (HEA) that possess improved performance and characteristics. In the current study, AlCoCrFeNi HEA powder was synthesised using gas atomisation and coated onto SS316L stainless steel substrate using the atmospheric plasma spraying process. The microstructural characterisation of the synthesised HEA powder exhibited spherical morphology with a mean particle size of 20 µm. The crystal structure is observed to be BCC phase. The coated samples displayed uniform coating with homogenous distribution of HEA over the coating thickness of 150 µm. The microhardness of the coated samples had an increment of 2.46 times against the uncoated samples due to the excellent bonding and fine dispersion of HEA. The subsequent wear test performed by varying the process parameters revealed improved wear resistance on the coated samples than the uncoated samples. The lower range of load, sliding velocity and sliding distance of coated samples offered 83.92 %, 76.56 % and 74.59 % increments in wear resistance respectively and the characterisation of the worn surface revealed the mechanism to be plastic delamination and adhesive wear. The corrosion test conducted in 3.5 wt% NaCl electrolytic solution also exhibited better corrosion resistance for the coated samples due to the formation of an oxide layer along the coating acting as a protective layer for the enhanced resistance to corrosion.

Microstructural mechanical and corrosion properties of SS304/HEA surface layer produced by Friction Stir Processing

Stainless steel SS304 is employed in great many domestic and industrial applications. The material's ability to tolerate extremely corrosive environments is hampered by harsh condition applications, and the mechanical qualities are also reduced that demanding the need for surface modification techniques to alter the surface at the microstructural level. In this study, CoCrFeCuTi High Entropy Alloys (HEA) powder was reinforced on an SS304 steel substrate employing a Friction Stir Processing (FSP) approach to achieving a high degree of grain size refinement and which leads to improving mechanical properties. The microstructural characterisation of the milled powder and the processed specimen followed by mechanical and corrosive properties are analysed. The morphology of the milled powder was irregular fragments and 17 µm as the mean particle size with the presence of BCC phase. The microstructural analysis of the processed substrate with HEA exhibited better grain refinement and neat dispersion of HEA reinforcement. The Vickers microhardness and tensile strength of the FSP-processed substrate with HEA were improved when compared with the FSP-processed substrate with no HEA. The electrochemical corrosion analysis affirms that the FSP-processed substrate with HEA is better resistant to corrosion.

Design of a novel CoCrFeNiCu0.3 high entropy alloy with desirable mechanical, corrosion and anti-bacterial properties via adjusting Cu distribution

Cu-containing high-entropy alloys (HEAs) with good antibacterial properties have application potential in the field of marine engineering. However, Cu tends to segregate in HEAs, which deteriorates the mechanical properties and corrosion resistance. This work proposed a feasible strategy to eliminate Cu segregation in FCC-structured HEAs by ball milling and spark plasma sintering using HEA powders and Cu powders. It was found that, with the increase of sintering temperature, the Cu-rich phase gradually dissolved-into the CoCrFeNiCu0.3 HEA and finally disappeared. Meanwhile, the distribution of Cu elements in HEAs gradually became uniformed. CoCrFeNiCu0.3 HEA with uniform distribution of Cu was successfully fabricated by sintering at 1400 °C. The dissolution of Cu-rich phase synergistically improved the strength and plasticity of CoCrFeNiCu0.3 HEAs. Meanwhile, the galvanic corrosion caused by Cu-rich phases was effectively restrained by the uniform distribution of Cu. Furthermore, the sintered CoCrFeNiCu0.3 HEAs preserved good antibacterial properties with an antibacterial rate above 95% due to the combined action of toxic sterilization of Cu ions and contact sterilization of Cu atoms. The CoCrFeNiCu0.3 HEAs with uniform distribution of Cu not only displayed good mechanical properties and corrosion resistance, but also exhibited outstanding antibacterial properties. This work provided a design concept for the development of marine structural materials.

Microstructure and Properties of NiCoCrAlTi High Entropy Alloy Prepared Using MA-SPS Technique

In this study, Ni35Co35Cr12.6Al7.5Ti5Mo1.68W1.39Nb0.95Ta0.47 high entropy alloy (HEA) was prepared using mechanical alloying (MA) and spark plasma sintering (SPS) based on the unique design concept of HEAs and third-generation powder superalloys. The HEA phase formation rules of the alloy system were predicted but need to be verified empirically. The microstructure and phase structure of the HEA powder were investigated at different milling times and speeds, with different process control agents, and with an HEA block sintered at different temperatures. The milling time and speed do not affect the alloying process of the powder and increasing the milling speed reduces the powder particle size. After 50 h of milling with ethanol as PCA, the powder has a dual-phase FCC+BCC structure, and stearic acid as PCA inhibits the powder alloying. When the SPS temperature reaches 950 °C, the HEA transitions from a dual-phase to a single FCC phase structure and, with increasing temperature, the mechanical properties of the alloy gradually improve. When the temperature reaches 1150 °C, the HEA has a density of 7.92 g cm-3, a relative density of 98.7%, and a hardness of 1050 HV. The fracture mechanism is one with a typical cleavage, a brittle fracture with a maximum compressive strength of 2363 MPa and no yield point.

Effects of milling time on the microstructure and properties of FeCoNiMnAl magnetic high-entropy alloys

FeCoNiMnAl magnetic high-entropy alloys (HEAs) were prepared by mechanical alloying and spark plasma sintering (SPS). The effects of milling time on the microstructure evolution, hardness, compressive strength, and magnetic properties of FeCoNiMnAl HEAs including powders and sintered bodies were investigated. After 30 h of milling, the HEA powders formed a solid solution with predominately face-centered cubic (FCC) phase structure and a small amount of body-centered cubic (BCC) phase. With a further increase in milling time, the BCC phase was transformed into the FCC phase. In the course of the BCC-to-FCC transformation, the hardness and compressive strength noticeably increased, while the magnetic properties of the alloys slightly decreased. Moreover, the decrease in lattice parameter of the FCC phase was shown to be an important factor enhancing the magnetic properties of HEAs. Besides, the high saturation magnetization of 84.7 emug was achieved in HEA-4. The maximum hardness and compressive strength of the samples were found to be 577 HV and 2099 MPa, respectively.

Effects of dispersoid preforming via multistep sintering of oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy

• A newly designed ODS manufacturing process, multi-step sintering process, consisting of a dispersoid preforming heat treatment followed by sintering to achieve the dispersoid refinement in HEA matrix was suggested. • An atypical form of Y 2 O 3 , FCC-Y 2 O 3 , formed adjacent to the dislocation inside the matrix grain during the dispersoid preforming heat treatment of multi-step sintering process with a cube-on-cube orientation relationship with the matrix. • The FCC-Y 2 O 3 formed in the multi-step sintered bulk acts as an effective obstacle to grain boundary and dislocation movement resulting in a microstructure refinement and the increment of mechanical strength. • In the bulk prepared by the conventional ODS manufacturing process, coarsened dispersoids consisting of a complex structured oxide with BCC-Y 2 O 3 as the core were predominantly formed along the grain boundary. • Cr-C-O region with a crystal structure of Cr 23 C 6 formed in the HEA matrix serves as an oxygen-supplying reservoir for dispersoids, promoting coarsening of the dispersoids. Dispersoid formation and microstructural evolution in an oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy (HEA) using a newly designed multistep sintering process are investigated. The proposed multistep sintering consists of a dispersoid preforming heat treatment of as-milled 0.1wt% Y 2 O 3 -CoCrFeMnNi high-entropy alloy powders at 800°C, followed by sintering at 800–1000°C under uniaxial pressure. In the conventional single-step sintered bulk, the coarsened BCC Y 2 O 3 dispersoids mainly form with an incoherent interface with the HEA matrix. In contrast, finer FCC Y 2 O 3 dispersoids, an atypical form of Y 2 O 3 , are formed in the matrix region after multistep sintering. Nucleation of FCC Y 2 O 3 dispersoids is initiated on the favorable facet, the {111} plane of the austenitic matrix, with the formation of a semi-coherent interface with the matrix during the dispersoid preforming heat treatment and it maintains its refined size even after sintering. It is found that dispersoid preforming prior to sintering appears promising to control the finer dispersoid formation and refined grain structure.