Mo Alloy Powder Research Articles

Effects of Al2O3 and Cr2O3 on the microstructure and properties of Mo alloys prepared via vacuum sintering

The dilemma of strength and ductility of Mo alloy at ultra-high temperature (above 1300 °C) limits its application in space reactors and other high-temperature environments. Single oxide enhancement has been unable to meet these use requirements. In this research, a strategy of synergistic reinforcement of Mo alloys with nanosized Al2O3 and Cr2O3 ceramic particles was proposed. A 300−400 nm Mo alloy powder was prepared by liquid‒solid doping, and in situ self-generated nanosized oxides were obtained. The grain size of vacuum sintered Mo alloy was very fine, at only 5.3 μm, which was one tenth of the particle size of commercial Mo alloy. Al2O3 and Cr2O3 particles were distributed in the grains of the Mo matrix, which effectively prevented the growth of Mo grains during vacuum sintering and reinforced the Mo alloy. The maximum flow stress of the Mo–Al2O3–Cr2O3 alloy reached 367 MPa at 1000 °C/1 s−1, which was better than that of the single-oxide reinforcement. The ultimate tensile strength (UTS) of the Mo–Al2O3–Cr2O3 alloy was 862 MPa, which was twice that of pure Mo. The preparation process is simple and available for industrial production. Synergistic strengthening of multiple oxides will be the best strategy for strengthening refractory alloys in the future.

Effects of various rare earth oxides on morphology and size of oxide dispersion strengthening (ODS)-W and ODS-Mo alloy powders

Ultrafine oxide dispersion strengthening (ODS)-Mo and ODS-W alloy powders containing different types of oxide nanoparticles were successfully synthesized by spraying method (solid−liquid mixing method) combined with the reductions with carbon black and hydrogen in sequence. It is concluded that the solution concentration and type of rare earth oxide have no effect on the grain size of ODS-Mo alloy powder, but have obvious effect on that of ODS-W alloy powder. The higher the concentration of rare earth solution is, the smaller the average grain size of ODS-W alloy powder is. Furthermore, compared with doping with CeO2, the grain sizes of reduction products of La2O3 and Y2O3 doped WO3 are relatively larger. Compared with the undoped case, there is almost no change for grain size of ODS-Mo alloy powder, while the grain size of ODS-W alloy powder becomes much larger. This is probably due to the appearance of the composite oxide (such as La2WO6) formed by the reaction between tungsten oxide and rare earth oxides, which promotes the heterogeneous nucleation and growth of tungsten grains during the reduction process of ODS-W, while there is no complex oxide composed of molybdenum and rare earth oxides in the reduction process of ODS-Mo.

Влияние энергомеханической обработки на структурно-механические свойства Co – Cr – Mo сплавов, полученных методом искрового плазменного спекания

We studied the effect of energy mechanical pre-treatment (EMT) of the initial (Co – Cr – Mo) alloy powders in a vortex layer of ferromagnetic bodies on the structural-mechanical properties of products obtained by spark plasma sintering (SPS). To study the properties of powder and compact samples, the methods of scanning electron microscopy (SEM), optical microscopy, determining the bending strength and microhardness on the Vickers scale were used. It was shown that the EMT of powders for a short time (1 – 3 min) leads to intense plastic deformation of a large part of the initial rounded particles, forming irregular- and plate-shaped particles with high surface roughness. As a result, EMT has a positive effect on spark plasma sintering process of powder, makes it possible to obtain a densely sintered material with a low-porous structure. It was found that the sample pre-treated under EMT for 3 min is compacted during sintering process to a high level (relative density reached 98.3 %) and its mechanical properties has greatly improved (microhardness and bending strength are 16 % and 14 % respectively higher than the sample without pre-treatment). The improvement of structural and mechanical properties of sintered specimens pre-treated under EMT is a result of intensification of diffusion mass transfer processes during sintering due to the plastic deformation of material, change in the shape, surface state of the powder particles and an increase in the total contact area between them. High surface roughness and deviation of particles from the round form lead to a decrease in the radii of curvature of their contact surfaces and, consequently, to an increase in the Laplace forces value, which play a dominant role in the diffusion mass transfer processes during sintering.

In situ synthesis of spherical W[sbnd]Mo alloy powder for additive manufacturing by spray granulation combined with thermal plasma spheroidization

In the present research, spherical WMo alloy powder for additive manufacturing was successfully synthesized by spray granulation (SG) in combination with thermal plasma spheroidization (TPS). Firstly, W and Mo particles (1–3 μm) were banded together through SG and formed porous agglomerated powder with desired particle size distribution and flowability. The porous agglomerated WMo powder was subsequently melted through thermal plasma, W and Mo dissolved together and formed solid solution accompanied with powder densification during TPS. Through optimization of the process conditions, the spheroidized WMo alloy powder exhibits homogeneous element distribution, low oxygen content (~0.08%), and good flowability (10 s/50 g), which meet the demand for laser powder bed fusion (LPBF). Remarkably, nearly full dense WMo alloy with few pores could be fabricated by LPBF based on the spheroidized WMo alloy powder.

Mechanistic understanding, gamma phase formation and morphological behaviour of the Reduction−Diffusion processed U-Mo alloy

Reduction−Diffusion (R-D) process has been attempted to synthesize U-Mo alloy powder for the first time, and the mechanism of alloy formation has been investigated. Calciothermic reduction of uranium dioxide in the presence of the alloying element Mo, followed by high temperature soaking; subsequent leaching to remove the calcia slag yields U-Mo alloy in powder form. Experiments were carried out to synthesize U-10 wt%Mo alloy powder. The alloy powder products were characterized by Scanning Electron Microscopy and X-ray Diffraction. Complete stabilization of the metastable isotropic gamma phase has been achieved in U-10 wt%Mo powder synthesized by R-D process, where the final soaking was carried out at 1300 °C and 4 h. Attempts were made to understand the mechanism of formation of U-Mo alloy by R-D process on two fronts, i.e. alloying within a single particle, and particle-to-particle homogenization. The intended application of the alloy powders is in high uranium density dispersion fuels for high flux nuclear research and test reactors.

Tailoring the Mechanical Properties of Laser Cladding-Deposited Ferrous Alloys with a Mixture of 410L Alloy and Fe⁻Cr⁻B⁻Si⁻Mo Alloy Powders.

The effects of different ratios of 410L alloy and Fe–Cr–B–Si–Mo alloy powders on the microstructure and mechanical properties of laser cladding-deposited ferrous alloys were investigated. The experimental results revealed that the 410L alloy had good strength and excellent ductility due to its microstructure consisting of large elongated ferrite dendrites surrounded by a small number of martensite grains, while the Fe–Cr–B–Si–Mo alloy had high strength and poor ductility because of its eutectic microstructure composed of ferrite and Fe2B/Cr2B. As the concentration of Fe–Cr–B–Si–Mo alloy powder added to the 410L alloy powder increased, the ferrite grains became finer and the volume fraction of the eutectic increased, which eventually improved the strength and reduced the plasticity. Then, 410L + 12.5% Fe–Cr–B–Si–Mo alloy powder was successfully deposited onto AISI 1060 steel substrate via laser cladding deposition, and the mechanical properties met those of the substrate, which verified that tailoring the mechanical properties of the laser cladding-deposited alloys with a mixture of 410L and Fe–Cr–B–Si–Mo alloy powders for steel repairing applications is a feasible solution.

Effect of metastable Cr(Mo)s/Cr(Mo)a powders on mechanical alloying the immiscible Cu–Mo–Cr system

Metastable-state alloy powders are usually synthesised by milling and occur as products of mechanical alloying (MA), but they are rarely used as starting materials for other MA processes. In this work, metastable-state alloy powders, including supersaturated solid-solution Cr(Mo)s and amorphous Cr(Mo)a were prepared in advance. Then, the Cr(Mo)s/Cr(Mo)a powder mixture was mechanically alloyed with elemental Cu to form Cu–Mo–Cr alloy. The effects of the metastable-state powder Cr(Mo)s/Cr(Mo)a on MA of the immiscible Cu–Mo–Cr system were evaluated. Phases and microstructures of the milled powders were analysed by XRD and TEM, respectively. The results show that amorphous Cu-60wt.%Cr(Mo) and supersaturated solid-solution Cu-20wt.%Cr(Mo) alloy powders can be synthesised by MA. It is concluded that MA of the Cu–Mo–Cr ternary alloy system is significantly promoted when elemental Cu powder is milled with metastable-state alloy powder Cr(Mo)s/Cr(Mo)a. Furthermore, the promoting effect of amorphous Cr(Mo)a on MA the Cu–Mo–Cr alloy system is much greater than that of supersaturated solid-solution Cr(Mo)s, during the milling process.

Deposition of Nanocomposite Coatings Employing a Hybrid APS + SPPS Technique

A novel approach hybridizing the conventional atmospheric plasma spraying and the solution precursor plasma spraying techniques has been explored to develop nanocomposite coatings. The above hybrid processing route involves simultaneous feeding of an appropriate solution precursor and commercially available spray-grade powder feedstock to realize microstructures comprising nanostructured and micron-sized features, which are unique in thermal spraying. The attractive prospects offered by this hybrid technique for deposition of nanocomposite coatings are specifically highlighted in this paper through a case study. Plasma sprayed Mo-alloy coatings are known for their good tribological characteristics and widely used in many applications. Further augmentation in performance of these coatings is expected through incorporation of distributed nanostructured oxide phases in the microstructure. Successful development of such coatings using a spray-grade Mo-alloy powder and a suitable oxide-forming solution precursor has been demonstrated. Splat formation under varied processing conditions has been comprehensively investigated and related to microstructure and tribological behavior of the coatings to assess the efficacy of the above nanocomposite coatings for wear resistant applications.

Microstructure and tensile properties of Mo alloy synthetically strengthened by nano-Y2O3 and nano-CeO2

Nano-Y2O3 and nano-CeO2 of different weight ratio mixed with deionizing water were doped into MoO2 powder by liquid–solid doping method. The diameter 1.80 and 0.18 mm alloy wires of Mo–0.3Y, Mo–0.3Ce, and Mo–0.15Y–0.15Ce were prepared through reduction, isostatic pressing, sintering, and drawing. Tensile properties, second phase microstructure and fracture surface appearance of wires were analyzed. The better refining effect for Mo alloy powder can be gotten after two kinds of nanoparticle oxide doped into MoO2 than only one doped. Nano-Y2O3 and nano-CeO2 have different influences on sintering process. For nano-CeO2, the constraining effect of grain growth focuses on the initial sintering stage, nano-Y2O3 plays refining grains roles in the later densification stage. Nano-Y2O3 is undistorted and keeps intact in the process of drawing; and nano-CeO2 is elongated and broken into parts in the drawing direction. The strengthening effect of nano-Y2O3 and nano-CeO2 keeps the finer grains and superior tensile properties for Mo–0.15Y–0.15Ce wire.

Martensitic transformation behaviors of rapidly solidified Ti–Ni–Mo powders

For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, consolidation of Ti–Ni–Mo alloy powders is more useful than that of elemental powders of Ti, Ni and Mo. Ti50Ni49.9Mo0.1 shape memory alloy powders were prepared by gas atomization, and transformation temperatures and microstructures of those powders were investigated as a function of powder size. XRD analysis showed that the B2–R–B19 martensitic transformation occurred in powders smaller than 150μm. According to DSC analysis of the as-atomized powders, the B2–R transformation temperature (TR) of the 25–50μm powders was 18.4°C. The TR decreased with increasing powder size, however, the difference in TR between 25–50μm powders and 100–150μm powders is only 1°C. Evaluation of powder microstructures was based on SEM examination of the surface and the polished and etched powder cross sections and the typical images of the rapidly solidified powders showed cellular morphology. Porous cylindrical foams of 10mm diameter and 1.5mm length were fabricated by spark plasma sintering (SPS) at 800°C and 5MPa. Finally these porous TiNi alloy samples are heat-treated for 1h at 850°C, and then quenched in ice water. The bulk samples have 23% porosity and 4.6g/cm3 density and their TR is 17.8°C.

Manufacturing of U–10 wt% Mo powder by hydride–dehydride processing

U–10 wt% Mo alloy powder production is prepared by hydride–dehydride processing. As a result of work it is shown that this method is suitable for preparation of U–10 wt% Mo alloy powder. It provides the production of fuel powder of needed size, structure and phase composition with high efficiency, and the size of U–10 wt% Mo powder is diminished with the degree of activation. At the same time, it is very important to pretreat the U–10 wt% Mo alloy samples. If only the suitable pretreatment technology is adopted, the samples can absorb hydrogen directly and need not through the phase transformation process.

Characterization of γ-U–10 wt.%Mo alloy powders obtained by hydride-milling-dehydride process

Uranium–molybdenum alloy powders are raw material of uranium alloy fuels prepared by powder metallurgic process in nuclear reactor. U–10 wt.%Mo alloy powders were prepared directly by hydride-milling-dehydride process without γ phase to α phase transformation under long time heat treatment, the powders were studied by XRD and SEM. During absorb–desorb hydrogen cycle, the absorbed hydrogen quantity of U–10 wt.%Mo alloy increased with the cycle number increasing, after eight cycles, the absorbed hydrogen quantity reached a stable value, and absorbed hydrogen was saturated in alloy. U–10 wt.%Mo alloy hydride was milled in argon atmosphere, then, alloy hydride were heated to desorb the absorbed hydrogen at 600 °C, after these processes, U–10 wt.%Mo alloy powders were obtained. XRD results show that U–10 wt.%Mo alloy powders was still γ phase, its indicated that during preparation, the alloy was always body centered cubic structure, phase transformation process did not exist. SEM observation showed that the particle shape of U–10 wt.%Mo alloy powders was nonuniform, but particle size was less than 50 μm, some were below 10 μm.

Neutron diffraction analyses of U–(6–10 wt.%)Mo alloy powders fabricated by centrifugal atomization

Lattice parameters of U–(6–10 wt.%)Mo alloy powders fabricated by a centrifugal atomization technique were measured by neutron diffraction analyses. A micro-segregation of Mo at cell boundaries was observed in the centrifugally atomized U–Mo alloy powders with varying Mo content. Lattice parameters of gamma phases decrease linearly with the increasing Mo content. By separating the overlapped diffraction peaks from cell boundaries and cell interior, lattice parameters and Mo contents of each region were calculated. The Mo content at cell boundaries is about 2–5 at.% lower than that in the cell interior and the lattice parameters for the cell boundaries are higher than those for the cell interior of the atomized U–Mo powder.

Electrocatalytic properties of mechanically alloyed Co-20wt%Ni-10wt%Mo and Co-70wt%Ni-10wt%Mo alloy powders

Mechanically alloyed Co-20wt%Ni-10wt%Mo and Co-70wt%Ni-10wt%Mo (nominal compositions) alloy powders were produced by milling of pure elemental powders. Mechanically alloyed powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. MA powder specimens were tested electrollitically in a 30% KOH aqueous solution at 298 K. X-ray diffraction analysis and transmission electron microscopy of milled powders showed the presence of two phases, an fcc solid solution and intermetallic compounds of Ni or Co with Mo. These phases showed a nanometric size. The linear sweep voltammograms confirmed also the presence of two phases in both mechanically alloyed alloy powders. The Co-20wt%Ni-10wt%Mo alloy powders showed the best electrocatalytic activity for hydrogen evolution reaction.

Rotary cold re-pressing and heat treatment of sintered materials from Co–Cr–Mo alloy powder

This paper presents the analysis of research results concerning the application of PM technology to produce porous implantation material from Co-Cr-Mo alloy. Rotary cold re-pressing and heat treatment has been used to increase the density and mechanical properties of sintered samples. The microstructure, hardness and compressive properties, and ultrasonic data of the obtained materials were investigated. The material had about 10% of porosity and has higher mechanical properties, i.e. UCS and plastic strain, compared with cast cobalt alloy, and had 25% lower values of Young's modulus and shear modulus.

Development of a Technology for the Production of Tubes from Ni ― Mo Alloy Powder

Technology for the production of tubes from mixtures of nickel and molybdenum powders by hot pressing and cold rolling was developed. The operational parameters for hot pressing were determined and the engineering and mechanical properties of the tubes studied. The effect of annealing temperature on the mechanical properties of the hot-pressed metal was investigated. Regimes for cold rolling the hot-pressed tubes in rolling mills were determined. The rolled tubes were tested in accordance with the accepted specifications for alloy EP982. All tubes passed the engineering tests; the mechanical properties of the tube metal are superior to those of alloy EP982. The proposed technology is quite economical, the yield of satisfactory product is 80-85%.

Titanium-Doped Molybdenum Disulfide Nanostructures

Ti-doped MoS2 nanotubes are produced by pyrolyzing a H2S/N2 mixture over an oxidized Ti–Mo alloy powder at elevated temperatures. Partial substitution of Mo by Ti does not significantly alter the 2H–MoS2 lattice.

Characterization of U-2 wt% Mo and U-10 wt% Mo alloy powders prepared by centrifugal atomization

The characteristics of high density UMo alloy powder solidified rapidly by the centrifugal atomization process have been examined. The results indicate that most of the atomized UMo alloy particles have a smooth surface and near-perfect spherical shape. The atomized powder, irrespective of particle size, is found to be single phase γ-U alloy with isotropic structure and non-dendritic grain. The continuous cooling DSC trace of U-2 wt% Mo alloy shows a small, broad endothermic peak originated from the formation of α-U phase and U 2Mo phase, whereas that of U-10 wt% Mo alloy shows no peak over all temperature ranges associated with the decomposition of γ-U phase. The γ-U phase of U-2 wt% Mo powder is decomposed as the α-U phase and the U 2Mo phase after an annealing treatment at 400°C for 100 h. But the γ-U phase of atomized U-10 wt% Mo powder remains as it was.

Preparation of Amorphous Ni-50 at.% Mo Alloy Powder by Mechanical Alloying

Preparation of Amorphous Ni-50 at.% Mo Alloy Powder by Mechanical Alloying

Kinetics of the martensitic f.c.c.→ h.c.p. transformation in CoCrMo alloy powders

The kinetics of isothermal martensìtìc nucleation in CoCrMo alloy powders is monitored. It is shown that a linear relation exists between the activation energy for martensite formation and the chemical free energy for the f.c.c. → h.c.p. transition. The nucleation kinetics is governed by the thermally activated motion of partial dislocations and the interaction between the Shockley partials and short range obstacles (stacking faults intersections and solute clusters).