Pre-alloyed Powder Research Articles

Diffusion behavior of Ta and Re in tungsten alloy with different addition methods

The addition of Ta or Re alone can improve the performance of tungsten alloys, but the combined addition of Ta and Re results in complex diffusion behavior and the formation of new phases. In this work, W-Ta-Re-Ni-Fe alloys with different Re contents were prepared by two methods (direct mixed powder sintering and pre-alloyed powder sintering), the compositions and structures of the precipitated phase through two preparation methods were analyzed, and the diffusion paths of Ta and Re were summarized. The addition of Re contributed to refining the grain size of tungsten alloys, but excessive Re addition led to the formation of hexagonal and tetragonal solid solution mesophases. Mechanical alloying not only strengthened the W particles substantially but also inhibited the growth of mesophases. In-situ Ni3Ta coherent nano-reinforced phase was generated by the diffusion reaction of Ta and Ni, which substantially increased the strength of the matrix phase. These findings suggest that the composite addition of Ta and Re is expected to further improve the toughness of tungsten alloys by adjusting the addition amounts of Ta and Re and improving the powder pretreatment.

Influence of technological synthesis conditions on corrosion behaviour and mechanical properties for NiTi alloys

PurposeThis study aims to investigate NiTi alloys’ characterization and corrosion behaviour produced by two different powder metallurgy (PM) methods.Design/methodology/approachIt was pre-formed under a protective atmosphere at 900 °C under a force of 45 MPa and sintered for 1 h under 10–6 Mbar in an atmosphere-controlled heat treatment furnace at 1,100 °C. The relationship between microstructural properties, SEM, XRD, density, microhardness and corrosion behaviour of pre-alloyed NiTi alloys produced by two different methods with the production method was investigated.FindingsAs a result of the studies, TiO, NiTi, NiTi2 and Ni3Ti intermetallics were determined in XRD examinations. The best surface roughness was observed in the mechanically milled (MM’ed) pre-alloyed NiTi alloy compared to the pre-alloyed NiTi alloy mixed with turbula. The corrosion tests performed in 3.5% NaCl solution determined that the MM’ed pre-alloyed NiTi alloy had better corrosion resistance than the pre-alloyed NiTi alloy mixed with turbula. Pitting corrosion was visualized in the SEM images taken from the corrosion surfaces.Originality/valueTwo different PM methods produced pre-alloyed NiTi powders, and the effects of these methods on the mechanical and corrosion resistance of NiTi alloys were systematically investigated for the first time.

Design of a low Young’s modulus Ti-Zr-Nb-Sn biocompatible alloy by in situ laser powder bed fusion additive manufacturing process

A new metastable β Ti-22Zr-11 Nb-2Sn (at%) biomedical titanium alloy was elaborated from elemental powders by in situ laser powder bed fusion technique (L-PBF). Iterative design of experiments was used to identify optimized manufacturing parameters to obtain dense and homogeneous parts (>99.3%) with low unmolten niobium fraction (<0.05%). The microstructural and mechanical properties of this alloy were investigated in its as-fabricated state and after two heat-treatments at 400 °C and 700 °C, respectively. The alloy, showing a β-type microstructure, possesses a very low Young’s modulus (∼50 GPa) combined with a high tensile strength reaching about 1100 MPa after heat-treatment. These properties are very suitable for medical devices in osseous site such as hip prostheses or dental implants and the results were compared to the Ti-6Al-4 V ELI (wt%) medical grade fabricated from pre-alloyed powders. Thus, the present work demonstrates the significant potential of the in situ L-PBF technique to elaborate highly biocompatible titanium alloys with tailored chemical compositions.

Characterization of a 2205 Duplex Steel Modified with Boron Obtained via Powder Metallurgy

Stainless steels are commonly used when a good balance between mechanical properties and corrosion resistance is required. Usually, to increase wear resistance, hard particles are added (carbides, borides, nitrides, and others) to the more ductile matrix (ferrite or austenite). The addition of boron to steels leads to the formation of primary and eutectic borides, which harden the material as solidified. Therefore, herein, the viability to prepare a modified 2205 duplex steel with 2.5 wt% of boron through powder metallurgy is investigated. The boron addition is performed in the atomization step. In addition, the effect of temperature in the sintering process is investigated, as well as the characterization of microstructure formation, phase transformations, and mechanical properties. The specimens are prepared from a prealloyed metal powder with three different granulometries: thick (250–500 μm), medium (106–180 μm), and thin powders (&lt;45 μm). Shaping is conducted by cold uniaxial compaction with sintering in a controlled Ar atmosphere. An optimal sintering temperature of 1200 °C is identified for all granulometries studied. However, the highest densification of &gt;85% is observed with medium powder with an increase of nearly 40% in microhardness in comparison to the reference 2205 steel.

Corrosion-resistant thermal spray coatings for low-alloy steel in contact with molten nitrate salts in solar power plants

The longevity and the cost of thermal energy storage (TES) components in solar power plants is a matter of great concern. To address this issue, three kinds of thermal spray coatings (Ni-5Al, NiCoCrAlY, and CoNiCrAlY) were successfully deposited on the low-alloy steel (P91) substrate by high velocity oxygen fuel (HVOF) spraying process. The corrosion performance of the prepared coatings in Solar Salt (at 565 °C for 15 days) was evaluated in detail by gravimetric analysis, field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD). Results revealed that all three coatings were quite dense and the substrates were generally well protected by the coatings. Compared with Ni-5Al and NiCoCrAlY coatings, the CoNiCrAlY coating exhibited the best corrosion performance owing to the formation of a dense oxide layer on the surface. Further, it was revealed that despite containing corrosion-resistant composition in NiCoCrAlY coating, the presence of a large number of phase interfaces could be the vulnerable regions that may result in local corrosion failure. Moreover, increasing the content of aluminum and using pre-alloyed powder may be an excellent solution to improve the performance of Ni-5Al coating.

Assessment of Microstructural, Mechanical and Electrochemical Properties of Ti-42Nb Alloy Manufactured by Electron Beam Melting.

The β-type Ti-42Nb alloy has been successfully manufactured from pre-alloyed powder using the E-PBF method for the first time. This study presents thorough microstructural investigations employing diverse methodologies such as EDS, XRD, TEM, and EBSD, while mechanical properties are assessed using UPT, nanoindentation, and compression tests. Microstructural analysis reveals that Ti-42Nb alloy primarily consisted of the β phase with the presence of a small amount of nano-sized α″-martensite formed upon fast cooling. The bimodal-grained microstructure of Ti-42Nb alloy comprising epitaxially grown fine equiaxed and elongated equiaxed β-grains with an average grain size of 40 ± 28 µm exhibited a weak texture. The study shows that the obtained microstructure leads to improved mechanical properties. Young's modulus of 78.69 GPa is significantly lower than that of cp-Ti and Ti-6Al-4V alloys. The yield strength (379 MPa) and hardness (3.2 ± 0.5 GPa) also meet the criteria and closely approximate the values typical of cortical bone. UPT offers a reliable opportunity to study the nature of the ductility of the Ti-42Nb alloy by calculating its elastic constants. XPS surface analysis and electrochemical experiments demonstrate that the better corrosion resistance of the alloy in SBF is maintained by the dominant presence of TiO2 and Nb2O5. The results provide valuable insights into the development of novel low-modulus Ti-Nb alloys, which are interesting materials for additive-manufactured implants with the desired properties required for their biomedical applications.

Effect of spark plasma sintering temperature on the multi-scale microstructure evolution and mechanical properties of Ti2AlC/TiAl composites with network architecture

In the present work, Ti2AlC/TiAl composites with network architecture were fabricated by the method of spark plasma sintering (SPS) at different temperature using Ti–48Al–2Cr–2Nb pre-alloyed powders and graphene nanosheets (GNSs) as raw materials. The effect of sintering temperature on the multi-scale microstructure evolution and mechanical properties of Ti2AlC/TiAl composites with network architecture was investigated. The results showed that equiaxed γ-TiAl matrix composite reinforced with the continuous network structured micro-Ti2AlC phases could be in-situ fabricated at the sintering temperature of 1200 °C. With the increase of sintering temperature from 1200 °C to 1320 °C, the micro-Ti2AlC continuous network structure gradually transforms into the nearly continuous, quasi-continuous and semi-continuous network. While the equiaxed γ-TiAl matrix gradually transforms into duplex, nearly lamellar, fully lamellar TiAl. Meanwhile, the micro-nano Ti2AlC precipitates would be formed in the TiAl matrix when the sintering temperature exceeds 1200 °C. When the sintering temperature is 1310 °C, the near lamellar TiAl matrix composite reinforced with the quasi-continuous network structured micro-Ti2AlC phases and micro-nano Ti2AlC precipitates is obtained, and the as-prepared composite possesses the best mechanical properties at both room and high temperature due to the synthetic effect of quasi-continuous network structure, intrinsic properties of Ti2AlC and lamellar TiAl.

Microstructure of an additively manufactured Ti-Ta-Al alloy using novel pre-alloyed powder feedstock material

Microstructure of an additively manufactured Ti-Ta-Al alloy using novel pre-alloyed powder feedstock material

Microstructural Characterization and Prior Particle Boundary (PPB) of PM Nickel-Based Superalloys by Spark Plasma Sintering (SPS).

This research investigates the microstructure and defects of powder metallurgy (PM) nickel-based superalloys prepared by spark plasma sintering (SPS). The densification, microstructural evolution, and precipitate phase evolution processes of FGH96 superalloy after powder heat treatment (PHT) and sintering via SPS are specifically analyzed. Experimental results demonstrate that SPS technology, when applied to sinter at the sub-solidus temperature of the γ' phase, effectively mitigates the formation of a prior particle boundary (PPB). Based on experimental and computational findings, it has been determined that the presence of elemental segregation and Al2O3 oxides on the surface of pre-alloyed powders leads to the preferential precipitation of MC-type carbides and Al2O3 and ZrO2 oxides in the sintering necks during the hot consolidation process, resulting in the formation of PPB. This study contributes to the understanding of microstructural modifications achieved through SPS technology, providing crucial information for optimizing sintering conditions and reducing the widespread occurrence of PPB, ultimately enhancing the material performance of PM nickel-based superalloys.

Laves phase and equiaxed grains formation in directed energy deposited AlCuFeNiTi high entropy alloy

In this study, an equiatomic AlCuFeNiTi high entropy alloy (HEA) was successfully fabricated for the first time using pre-alloyed powder with the directed energy deposition method on a Ti-6Al-4V substrate. The alloy was characterized using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and nanoindentation to provide insight into the relationship between its microstructural and nanoscale mechanical properties. The microstructure has three distinct regions, resulting from variation in the alloy's local elemental and crystallographic composition that influences its mechanical properties. The alloy was found to be multiphase with a mostly ordered Heusler structure (L21) and a small amount of FCC structure with traces of C14 Laves in them. Needle-like and spherical-shaped Cu-rich precipitates were also observed in the dendrites. During the solidification process, evidence of dendritic fragmentation was observed, contributing to the alloy having mostly equiaxed grains rather than the commonly observed columnar grains in previously reported additively manufactured (HEAs). Nanoindentation results showed that the dendrites constitute a hard zone, whereas the inter-dendritic regions typify a continuous soft zone, with the dispersed Laves phase having the highest hardness. The presence of Laves phase inside the grain boundaries and its distribution as small-size grains strengthens the grain boundaries. Results highlight the synthesis of an equiaxed HEA with multiple distinct regions that influence its overall mechanical properties.

A novel and sustainable method to develop non-equiatomic CoCrFeNiMox high entropy alloys via spark plasma sintering using commercial commodity powders and evaluation of its mechanical behaviour

A novel approach to developing high entropy alloys (HEAs) using spark plasma sintering (SPS) was explored in this work where a mix of commercial commodity powders like Ni625, CoCrF75, and 316L was used instead of pre-alloyed powders avoiding the expensive pre-alloying steps like mechanical alloying or gas atomizing. Three non-equiatomic HEAs, based on Co, Cr, Fe, Ni, and Mo were designed and developed by blending the powders which were sintered via SPS and resulted in a single FCC phase after homogenization. The HEAs were microstructurally and mechanically characterized with tensile and hot compression tests up to a temperature of 750 °C showing excellent properties. The maximum room temperature tensile strength and ductility demonstrated was 712 MPa and 62% respectively, by the alloy Co23.28Cr28.57Fe25.03Ni21.01Mo2.1. Moreover, the same alloy exhibited a compression strength greater than 640 MPa with a ductility above 45% at a temperature of 750 °C. Also, this study paves the way for a novel fabrication route that offers more flexibility to develop new HEAs cost-effectively and efficiently which is crucial for the discovery of new materials over high-throughput techniques. Using such commodity alloys also opens the possibility of developing ingot casting from recycled scraps avoiding the direct use of critical metals.

In-vitro corrosion and biocompatibility properties of heat treated Mg-4Y-2.25Nd-0.5Zr alloy

In this study, corrosion and biocompatibility behaviour of Mg-4Y-2.25Nd-0.5Zr alloy (Mg-Y-Nd-Zr) was investigated. The pre-alloyed powder of Mg-Y-Nd-Zr was processed using powder metallurgy (PM) method, followed by further heat treatment at 250 °C for 12 h. The microstructural features of as-sintered and heat treated Mg-Y-Nd-Zr alloy showed secondary phases like Mg24Y5 and Mg41Nd5 in α-Mg matrix. In heat treated samples, the alloy showed improved compressive strength and hardness. The hardness and compressive strength was better for the heat treated Mg-Y-Nd-Zr alloy samples (54 ± 2 HV and 243 ± 30 MPa) compared to heat treated pure Mg samples (44 ± 5 HV and 129 ± 11 MPa). This is because of rearrangement of the secondary phases in the matrix. The corrosion current density of Mg-Y-Nd-Zr alloy samples reduced by 45% (82.2 μA/cm2 for heat treated and 149.3 μA/cm2 for as-sintered) after heat treatment indicating its better corrosion resistance than as-sintered samples. Both heat treated and as-sintered alloy exhibited good biocompatibility and therefore the Mg-Y-Nd-Zr alloy is a potential candidate for biodegradable implants.

A phase field methodology for simulating the microstructure evolution during laser powder bed fusion in-situ alloying process

A recently-developed [1] multi-component phase field model has been utilized to investigate microstructure evolution during in-situ alloying of a blended elemental Ti-1Al-8V-5Fe alloy powder via the Laser Powder Bed Fusion process. The process of in-situ alloying, where elemental powder is used instead of pre-alloyed powder, was studied by performing two simulations having: (1) a uniform initial composition, and (2) a spatially varying initial composition to represent different powder particles. Specifically, the grain morphology, solute distribution, competitive growth and nucleation under the two different scenarios were simulated and compared. To assist the microstructure simulations, a macro-scale finite element model was developed to simulate the heat transfer during LPBF process. The thermal history data calculated by the finite element model was provided to the phase field model in order to simulate transient dendritic growth behaviour. The results show that a set of evenly-spaced columnar dendrites form in the uniform initial composition case, whereas when the initial composition is spatially varying, non-uniform dendrites having elongated shape can develop. It is also shown that competitive growth between dendrites is influenced by nucleation. For the spatially varying initial composition case, the results indicate that full alloying is difficult to achieve during the LPBF printing process; this incomplete alloying greatly influences the dendrite morphology and solute distribution.

Fabrication and mechanical properties of Ti2AlN/TiAl composite with continuous network structure

Nitrogen was introduced into TiAl pre-alloyed powder using high-temperature gas nitriding, and Ti2AlN/TiAl composites with a continuous network structure of the reinforced phase were prepared via spark plasma sintering. The results show that the hardness of the composite is significantly higher than that of TiAl alloy, and increases with the increase of nitriding time. The strengthening effect is originated from the synergistic effect of the solid-solution strengthening caused by the nitriding of the powder, the continuous network of the Ti2AlN phase with high hardness and elastic modulus, and the increase of dislocation density. Additionally, the compressive strength of the Ti2AlN/TiAl composites is lower than that of the TiAl alloy, which is related to a part of Ti2AlN particles that are directly formed after nitriding and excessive reinforcement content.

Environment-friendly antifouling coating of Cu-bearing stainless steel prepared by pre-alloyed powder

Marine biofouling has become an urgent problem in the field of marine engineering equipment worldwide. In this study, an environment-friendly antifouling coating using pre-alloyed Cu bearing stainless steel powder as raw material was developed by cold spraying. The experimental results showed that pre-alloyed powder coating effectively inhibits the adhesion of marine fouling organism Pseudomonas aeruginosa. Due to the even distribution of Cu, it had better corrosion resistance and lower release rate of Cu ions compared with mixed powder coating, which made it appear protective of the marine environment. In addition, the coating has better wear resistance than commercial self-polishing copolymer coatings, which has the potential to become a new long-life marine antifouling coating.

Improvement in the PBF-LB/M processing of the Al-Si-Cu-Mg composition through the use of pre-alloyed powder

Among the many additive manufacturing technologies for metals, Powder Bed Fusion-Laser Beam (PBF-LB\\M) stands out for its capacity to produce complex-shaped functional parts. However, the PBF-LB\\M materials portfolio is still limited and the research into new high-performance Al-based alloys is ongoing. The improved properties with the addition of 4 wt% Cu to the AlSi10Mg alloy have been previously investigated in the literature through the in situ alloying approach in which the starting powders of Cu and AlSi10Mg are mechanically mixed and directly processed. However, inhomogeneities of alloying elements were found in samples produced with mixed AlSi10Mg+4Cu powders. To overcome this detrimental problem, the use of pre-alloyed AlSI10Cu4Mg powder obtained via gas atomisation process could be a powerful solution. With the aim of demonstrating the beneficial effects of pre-alloyed AlSi10Cu4Mg powders in laser-powder interaction, preliminary SEM investigations were conducted on cross-sectioned SSTs and bulk samples after optimising the process parameters. The deeper microstructural investigations conducted on pre-alloyed AlSi10Cu4Mg samples revealed a higher homogeneity of alloying elements, a smaller cell size of the Al-Si-Cu network (0.5 versus 0.8 μm) and a slightly smaller mean diameter of equiaxial grains compared to the mixed AlSi10Mg+4Cu ones (6.01 versus 7.34 μm). In addition, looking closer at the supersaturation level and the precipitation behaviour in pre-alloyed AlSi10Cu4Mg composition, a high solid solution level, a massive presence of Al2Cu in the cell network and only a few finely dispersed Al2Cu precipitates within the cells were found. Exploring the benefits of these microstructural features on mechanical properties, an increase in performance of about 18% in micro-hardness tests and more than 10% in tensile and compressive tests were found in the AlSi10Cu4Mg system with respect to the mixed AlSi10Mg+4Cu system. All the thorough investigations proved how using pre-alloyed powders is an important advantage in the PBF-LB/M production of complex Al-based systems.

Effect of heat treatment on mechanical and corrosion properties of an Al0.8CrFe2Ni2 alloy processed by laser powder bed fusion

This study presents an Al0.8CrFe2Ni2 high entropy alloy processed by laser powder bed fusion using prealloyed powder. Heat treatment of the near-single-phase face-centered-cubic microstructure, found in the as-built material, led to a fine dual-phase microstructure consisting of face-centered-cubic grains and Al-, Ni-rich body-centered-cubic B2 precipitates. Microstructure characterization, mechanical and corrosion testing revealed the effect of heat treatment on the properties of the novel alloy. The results suggested that tailoring the mechanical properties is possible with heat treatment, by controlling the precipitate size. Refinement of the precipitates led to enhanced strength without significant ductility loss. Corrosion tests in 3.5 % NaCl solution showed that the as-built samples provided an overall better corrosion resistance when compared to heat-treated samples. The presence of the precipitates enhanced the formation of micro-galvanic cells and influenced the corrosion behavior of the alloy in the heat-treated condition.

Computational Efficient Modeling of Supersolidus Liquid Phase Sintering in Multi-component Alloys for ICME Applications

One of the challenges in computational design of pre-alloyed powders for sintering is the absence of predictive, efficient, and fast acting models that enable the design space of alloys to be tractable. This study presents an efficient and predictive model to simulate the densification as well as shape distortion of pre-alloyed powder compacts during supersolidus liquid phase sintering (SLPS). The model combines the generalized viscous theory of sintering with microstructural models for diffusional creep accommodated by viscous grain boundary sliding. Critical model parameters are obtained from thermodynamic modeling based on the calculation of phase diagrams (CalPhaD) and simulations of diffusional transformations in metals. The model is validated by comparing simulation results with experimental data from the literature for various types of engineering alloys. In addition, a processing window for defect free sintering of samples is presented by defining a microstructural softening parameter for a sintering body. The model can be used in the design of pre-alloyed powders for SLPS within the context of an integrated computational materials engineering (ICME) frameworks.

Microstructural Characteristics of Ti‐Based Composites with Various Ceramic Reinforcements Manufactured via Hydrogen‐Assisted Blended Elemental Powder Metallurgy

Highly dense in situ reinforced titanium matrix composites are fabricated with hydrogen assisted two-stage press-and-sintering method as described in the article, number 2101689 by Yuchao Song, Tuo Cheng, Orest Ivasishin and co-workers. Type and size of starting ceramic additives have substantial impact on the microstructure formation, residual porosity, and hardness of the pre-sintered composites. Sintering of hydrogenated pre-alloyed powders at second processing stage ensures desirable microstructure, improved density and uniformity of composites.

About the relationship of the processing conditions, mechanical properties, and microstructure of a co-precipitated Fe/Cu prealloyed powder

The sinterability of a commercial Fe–Cu pre-alloyed powder, designed to be used as a metallic bond in diamond impregnated tools, has been greatly analyzed by combining dilatometry, computational thermodynamic calculations, and microstructural analysis. The effect of sintering temperature and alloying elements such as graphite and iron phosphide have been taken into consideration in order to demonstrate the capability of tailoring final properties through different strategies, and dilatometry and microstructural analysis have been used to understand the densification process of the alloys. Solid phase sintering was the mechanism taking place during thermal cycle. In fact, a liquid phase appears but because of the high densification level at that time mechanisms associated with LPS do not contribute to densification. Discussion about mechanical properties has been related to key microstructural phenomena, i.e., grain growth, phase transformation, precipitation, and solid solution. Obtained hardness ranged from 83 HRB to 106 HRB with yield stresses between 450 MPa and 700 MPa and elongations above 3%, while final tensile properties similar to those obtained by cobalt-based powders processed by hot pressing were also obtained.