Mo Solid Solution Research Articles

Effect of synergistic microalloying on the microstructural optimization of Mo/NiAl alloy with excellent mechanical properties under rapid non-equilibrium solidification

Low room-temperature plasticity and poor high-temperature strength extremely restrain the extensive application of NiAl composites. Herein, our work synergistically optimized the NiAl microstructure via alloying of Mo to relieve imbalance of strength and ductility under rapid non-equilibrium solidification supplemented with the first principle calculation. Remarkably, the addition of Mo significantly refined the microstructure of NiAl–15Mo. Moreover, enhanced by the uniform precipitation Mo phase, the coordinately deformed Mo phase at the grain boundary and the partial Mo solid solution occupied Ni sites, the NiAl–15Mo showed superior strength-ductility. The mechanical properties (σ0.2, σUCS, UT) of NiAl–15Mo composites at room temperature were 944 MPa, 1841 MPa, and 27,068 MPa·%, which were increased by ∼55.3 %, ∼48.7 % and ∼41.0 % compared with the conventional NiAl composites, respectively. In particular, owing to solid-solution Mo atoms restrict the climb of dislocations and the stronger covalent bond orbital hybridization between Ni-3d and Mo-4d, the mechanical properties (σ0.2, σUCS, UT) of NiAl–15Mo at 1000 °C are 212 MPa, 265 MPa and 7922 MPa·%, which has an increase of ∼175.3 %, ∼120.8 % and ∼228.0 %, respectively. This work provides a new perspective to manipulate and coordinate Mo multiple reinforcing ways and achieve the high strength and plasticity of NiAl composites.

Effect of Oxygen in Mo-TM (TM = Ti, Zr, Hf) Solid Solutions as Studied with Density Functional Theory Calculations

Mo-Ti-Si, Mo-Zr-B, and Mo-Hf-B are promising alloy systems for high-temperature applications as they show higher toughness and higher creep resistance than other Mo-based alloys. Regarding ductility and toughness, the chemical composition of the Mo solid-solution phase is the main parameter with which to tweak these properties of multiphase Mo-based alloys. Besides the common solid-solution hardening, one goal is to minimize embrittlement by decreasing the detrimental effects of interstitials like oxygen atoms in Mo alloys, which might be present in the bulk material due to trapping. For a better understanding of the trapping mechanisms and behavior of Mo solid solutions, the bonding situation and interaction of Mo atoms with the atoms of the alloying partners, as well as oxygen atoms, is worthwhile to investigate. For this, an in-depth analysis of the chemical bonding situation with calculations based on density functional theory in selected Mo-TM(-O) (TM = Ti, Zr, Hf) solid solutions is conducted in this work. It is shown that Ti atoms in a Mo solid solution are strong traps for oxygen atoms, while Hf and, even more clearly, Zr atoms are not. It is pointed out that the ionic and covalent interactions are the primary influence on the trapping behavior, as the change in ionic and covalent interactions between trapping and nontrapping models follows the trend Mo-1Ti > Mo-1Hf > Mo-1Zr, which resembles the trend of the trapping energy.

Structure, antibacterial property and cytocompatibility of sputter deposited MoO–Ag films

MoO–Ag films with silver content up to 18.6 at.% along with MoO films were prepared by magnetron sputtering. The film color reveals oxidation of Mo element in both groups of films. XRD analysis shows bcc Mo phase, fcc Mo(O) solid solution and fcc silver phase (only for MoO–Ag films), and XPS analysis reveals oxidation of Mo element. SEM displays the increased density of silver nanoparticles at film surface with silver content of the MoO–Ag films. With the addition of oxygen the conductivity of MoO films is decreased to above 2 kΩ. Both groups of samples are hydrophilic, with the contact angles of 51.2–83.9°. The electrochemical test suggests microgalvanic coupling in the composite MoO–Ag film (11.8 at% Ag). The composite film sample also has the higher Mo ion releasing rate in water. Both groups of films exhibit good antibacterial activity against E. coli (antibacterial ratio up to 100%) contributed by the released Mo and Ag ions. The extracts of MoO–Ag films with silver content up to 11.8 at% are well compatible with MC3T3-E1 cells. With the biologically advantageous Mo element and acceptable released Ag ion concentration, the sputter deposited MoO–Ag films would have high potential in biomedical applications.

Effect of Mo Oxides on the Phase Composition and Characteristics of Mo-10Re Pre-Alloyed Powders Co-Reduced with NH4ReO4.

Mo-Re pre-alloyed powders are crucial raw materials in fabricating Mo-Re alloys, and their properties can significantly impact the properties of the resulting alloys. The powders are usually produced by the co-reduction of a mixture of Mo and Re oxides. However, it remains unclear if the overall characteristics of the produced Mo-Re powders rely on the different combinations of the Mo and Re oxide precursors. Therefore, in this work, a comparative study is conducted on the co-reduction processes of different Mo oxides together with NH4ReO4, along with its influence on the size distribution and phase composition of the resulting Mo-10Re pre-alloyed powders. The results show that MoO3 is more promising than MoO2 as a precursor material. The powders fabricated using MoO3, when compared to MoO2, have a much more uniform size distribution, with a primary particle size ranging from 0.5-4 μm. In addition, it is also beneficial to achieve atomic-scale homogeneous mixing with Mo and Re elements and the formation of a solely Mo(Re) solid solution if MoO3 is used as a precursor oxide. In contrast, such desirable features were not identified when using the MoO2 route. The reason for this discrepancy may relate to whether Mo-O-Re metallurgical bonding has formed during the co-reduction process.

Off-stoichiometry and molybdenum substitution effects on elastic moduli of B1-type titanium carbide

B1-type MX ceramics are composed of transition metals (M) and C, N, and/or O (X) occupying the M and X sites, respectively, and having M–X nearest neighbor (NN) bonds and M–M and X–X next nearest neighbor (NNN) bonds. Substitution of the elements and the formation of structural vacancies in B1-type ceramics change the numbers and strengths of the bonds, leading to novel properties. The change in elastic modulus of off-stoichiometric TiC in equilibrium with a Ti–Mo solid solution phase was experimentally investigated based on the rule of mixtures from the Voigt model. The experimentally obtained values agreed well with the results of density functional theory calculations. The bulk modulus (K) of TiC increased from 205.6 to 239.2 GPa as the fraction of Ti sites occupied by Mo increased from 0.11 to 0.33, whereas the Young’s modulus (E) and the shear modulus (G) remained nearly constant. On the other hand, all three elastic moduli decreased with increasing vacancy fraction at the C sites. These results suggest that the M–X bond strength should be the dominant factor in these moduli and the effect of M–M bond on K is greater than that of G and E.

Co-deposition of nanocrystalline Co–Mo catalysts with a new fluffy microstructure for hydrogen evolution reaction based on N, N-dimethylformamide and ethylene glycol system

The co-deposition behavior of Co(II) and Mo(VI) in N,N-dimethylformamide and ethylene glycol system is observed. The result implies that Co–Mo co-deposition is typical induced deposition, while containing ordinary deposition process. Mo(VI) species in the system can suppress the reduction of Co(II) and its effect can be improved as the increase of Mo(VI) concentration, however, Co(II) species can promote the reduction of Mo(VI) and the effect can also be improved as the increase of Co(II) concentration. SEM micrographs indicate that all these films exhibit a fibrous surface morphology with a new fluffy microstructure. XRD pattern reveals that the Co–Mo film is a Mo solid solution in Co and its average size of crystalline grain is 9.5 nm. In addition, the electrocatalytic activity for hydrogen evolution reaction (HER) on these Co–Mo films is investigated. These results indicate that its electrocatalytic activity can be improved as Mo content increases from 1.02 to 2.84 wt% and the prepared Co–Mo film with 2.84 wt% Mo presents a high electrocatalytic activity and stability for HER with an overpotential of 81 mV at 10 mA cm−2.

Alloy designs for high temperature Mo-base systems

For high temperature applications Mo base alloy requirements include both superior structural performance and environmental resistance. To address these requirements alloys in the Mo-Si-B system and refractory multi-principal element alloys (RMPEA) are being developed that exhibit a promising potential, but also have some remaining challenges to improve ductility, lower density and enhance environmental resistance. In the Mo-Si-B system microstructures with a Mo solid solution (Moss) Mo3Si and Mo5SiB2 (T2) phases have been the focus of attention. However, the Si solubility in the Moss phase diminishes the ductility and toughness. In order to address this issue a new design based upon Moss, Mo2B and T2 phases lowers the Si solubility in the Moss to improve ductility while the T2 phase maintains the oxidation performance. Selected additions of Al and Ti enable a density reduction to below 8 g/cm3. The RMPEA designs for Mo-rich alloys provide for excellent structural performance, but the complex oxidation products provide no protection. In this case a new coating design has been introduced that provides the required environmental resistance.

Preparation and properties of multiphase solid-solution strengthened high-performance W–Cu alloys through alloying with Mo, Fe and Ni

In this study, high performance W–Mo–Cu–Ni–Fe alloy samples with additions of Mo (0–6 wt%), Ni and Fe (total content: 2.5 wt% and 5 wt%) were obtained through liquid-phase sintering at lower temperature, with the raw material of ultrafine W–Mo–Cu–Ni–Fe composite powder. Ultrafine W–Mo–Cu–Ni–Fe alloy powder with strong sintering activity and uniform composition was obtained by two-stage reduction means composed of carbothermic pre-reduction and hydrogen deep deoxidation steps. Significantly, the bonding ability of W/Cu phase interface and the wettability of two phases are greatly improved due to the presences of Ni and Fe. Moreover, the addition of appropriate Mo content was advantageous to the formation of W–Mo solid solution. All alloy samples achieved higher densification degrees to guarantee that the sintered blocks possess outstanding overall performances. Especially, by adjusting Ni/Fe ratio, the highest tension strength and elongation of were achieved by W-2wt.%Mo-1.75 wt%Ni-0.75 wt%Fe-27.5 wt%Cu sintered block, which were 567 MPa and 10.37%, respectively. Moreover, owing to the presences of W–Mo and Cu–Ni–Fe solid solutions, this alloy also had the highest microhardness and bending strength of 446 HV and 1473 MPa, respectively. As increasing Mo content from 0 wt% to 6 wt%, the compression strength of sintered blocks was improved, and failure strains of all the sintered blocks are close to 100%, respectively. However, even though the Cu matrix network structure is more evenly distributed as a result of the existences of added Ni and Fe, the electronic movement ability of the sintered blocks was reduced, leading to a significant decrease in conductivity.

Powder Fabrication and Laser Powder Bed Fusion of a MoSiBTiC-La2O3 Alloy

In the present work, an approach of freeze-dry pulsated orifice ejection method (FD-POEM) was utilized to fabricate monodispersed MoSiBTiC-La2O3 composite powders for laser powder bed fusion (L-PBF). The FD-POEM powders were spherically shaped, possessing a narrow size range and uniform element distribution. As revealed by the single-track and single-layer experiments, the porous FD-POEM particles were sufficiently fused under laser irradiation, leading to the generation of continuous laser tracks and low surface roughness layers, which proved a feasible L-PBF processability of MoSiBTiC-La2O3 powders. Careful microstructural observations confirmed that the microstructure of the molten pools was primarily composed of Mo solid solution dendrites reinforced with La2O3 nanoparticles. Consequently, the single MoSiBTiC-La2O3 track had a high Martens hardness of 3955 HM. The result of this work reveals that the combination of FD-POEM and L-PBF has a great potential of developing advanced heat-resistant Mo-based alloys with tailored structures for ultrahigh-temperature applications.

Preparation and properties of W-Mo-Cu composite using solution combustion synthesized W[sbnd]Mo solid solution nanopowder

Due to the high melting points of W and Mo, WMo solid solution powder needs to be prepared at extremely high temperatures using W and Mo elemental powder. Herein, the nano-sized WMo solid solution powders with different Mo content were successfully fabricated by solution combustion synthesis. And then the WMo nanopowders were used to prepare W-Mo-Cu composites by liquid phase sintering. The results revealed that the addition of Mo can promote the densification of the W/Cu composite powders and improve the microhardness of the WCu composites, while the conductivity will inevitably be reduced. When the amount of Mo addition is <10 wt%, the Mo element is uniformly distributed in the W particles in the W-Mo-Cu composites, while the segregation of Mo was observed when Mo addition >10 wt% due to inhomogeneous Mo distribution in the starting powder. Meanwhile, the Mo segregation region may be responsible for the formation of Mo2C phase in (W20Cu)-30Cu, due to the susceptibility of Mo to react with carbon. During the arc ablation process, the Mo in the W particles dissolves into the liquid-phase Cu, increasing the viscosity and reducing the splashing of the Cu.

Gas-Phase Synthesis of PtMo Alloy Electrocatalysts with Enhanced Activity and Durability for Oxygen Reduction Reaction

The proton-exchange membrane fuel cell is a promising technology to effectively utilize hydrogen energy, which is the ideal alternative to fossil fuels. However, the high dependency on scarce Pt as an oxygen reduction reaction (ORR) electrocatalyst is still a severe barrier that hinders widespread commercialization. Herein, we propose a facile synthetic strategy facilitating mass production of Pt–Mo solid-solution alloy nanoparticles on a carbon support (PtMo/C) as a highly active ORR electrocatalyst. Without using organic surfactants or reducing agents, our synthesis process based on the gas-phase method in an inert atmosphere is cost-effective and does not require any post-treatment, unlike most reported solution-based reduction processes. Both molybdenum metal and carbon monoxide decomposed from molybdenum hexacarbonyl contribute to the reduction of the PtMo alloy during the annealing process. By elucidating the growth and synthesis mechanisms, we optimized the particle size of PtMo/C to approximately 3.1 nm, annealed at 800 °C (PtMo/C-800). Consequently, PtMo/C-800 shows high mass activity (146 mA mgPt–1), which is superior to that of commercial Pt/C, and excellent durability after accelerated degradation tests.

Phase Continuity, Brittle to Ductile Transition Temperature, and Creep Behavior of a Eutectic Mo–20Si–52.8Ti Alloy

Mo–Si–Ti alloys, like eutectic Mo–20Si–52.8Ti (at%), have previously been intensely investigated, owing to their excellent oxidation and creep resistance. To better understand high‐temperature mechanical behavior, a holistic assessment of microstructural features is necessary. Correspondingly, 3D‐focused ion beam tomography is carried out in Mo–20Si–52.8Ti. The results indicate a severely interconnected network of Mo solid solution (MoSS) and intermetallic (Ti,Mo)5Si3. Both phases retain similar network connectivity, lamellar sizes, etc. The brittle to ductile transition temperature (BDTT) is then determined through a series of bending tests and interpreted using the microstructural information. The BDTT is found to be ≈1100–1150 °C, different from Mo–9Si–8B with a continuous MoSS network. The BDTT is an immediate consequence of the continuous network of both MoSS and (Ti,Mo)5Si3. The MoSS network is instrumental in crack trapping and bridging, indicating that the present phase distribution maximized the mechanical performance over (Ti,Mo)5Si3. Having determined the network microstructure and BDTT, tensile creep behavior is evaluated and compared to previously published compressive creep results. The results show consistency in terms of strain rate, stress exponent, and microstructural features indicating a reliably good creep resistance for the network microstructure of Mo–20Si–52.8Ti regardless of loading direction.

Synthesis of a novel MoSS+Mo5SiB2+Mo5Si3 based Mo–Si–B alloy and its enhanced fracture toughness

Mo–Si–B based alloys are promising ultrahigh-temperature structural materials for turbine blades. Different from traditional MoSS (Mo solid solution)+Mo5SiB2+Mo3Si based alloy, present paper focuses on a novel non-equilibrium MoSS + Mo5SiB2+Mo5Si3 based alloy, which shows more potential for excellent comprehensive performance. This alloy was synthesized by SPS (spark plasma sintering) technique using pure Mo and Mo5SiB2+Mo5Si3 powders as raw materials. SEM, EDS, XRD, EPMA, single-edge notched bending and nano-identation tests were used to reveal the formation mechanism of this alloy and evaluate its fracture toughness. The results showed that this MoSS + Mo5SiB2+Mo5Si3 based alloy was composed of MoSS, Mo5SiB2, Mo5Si3 and a little Mo3Si. Mo5SiB2+Mo3Si halos were found around the original Mo5SiB2+Mo5Si3 particles as a result of inter-diffusion between Mo and Mo5SiB2+Mo5Si3 during sintering processes. Compared with traditional cast or reaction sintered MoSS + Mo5SiB2+Mo3Si based alloy with the same composition, this MoSS + Mo5SiB2+Mo5Si3 based alloy showed superior fracture toughness benefiting from its higher MoSS content, larger coarseness of MoSS and lower Si concentration in MoSS.

Influence of B contents on the microstructure, fracture toughness and oxidation resistance of Mo-Si-B alloys

The Mo-10Si-(0, 5, 10, 15)B (at.%) alloys located in Moss (Mo solid solution) +Mo3Si +T2 (Mo5SiB2) region were prepared by arc melting. The effect of B content on the microstructure, microhardness, fracture toughness and oxidation resistance of the alloys was studied. In the Mo-10Si alloy, there are primary Moss and peritectic Mo3Si phases. With the addition of B, (Moss + T2) binary and (Moss + T2 + Mo3Si) ternary eutectics emerge in Mo-10Si-(5, 10)B alloys. For Mo-10Si-15B alloy, primary Moss disappears and the microstructure is only composed of binary and ternary eutectics. With the increase of B content, the proportion and grain size of Moss decrease. The microhardness of alloys increases with the increase of B content due to the increasing intermetallics. The fracture toughness of alloys decreases obviously in single-edge notched three-point bending testing (SENB) and the fracture mode transforms from transgranular fracture to intergranular fracture because of the refinement of Moss. In the high-temperature oxidation test at 1250 °C, the oxidation weight loss of the alloys decreases with the addition of B due to the densification of the borosilicate layer.

Effect of microstructural evolution on mechanical and electrical properties of Ag–Mo thin films

ABSTRACT Herein, Ag–Mo films were deposited on Si(100) substrates by magnetron co-sputtering. The phase evolution and microstructural investigation revealed that the pure Ag phase and no Ag(Mo) solid solution were formed in the Ag-rich films even though the Mo content reached 53 at.%. However, the metastable Mo(Ag) solid solution was formed on the Mo-rich side. The Young’s modulus, hardness, resistivity and the relationship between these properties and the microstructural evolution of Ag–Mo films were studied. Precisely, when the Mo content was controlled at 86 at.%, the hardness reached the maximum value of 14.64 GPa, and exceeded that of the pure Mo film. Meanwhile, the resistivity appeared to be a minimum value because the film had the maximum solid solubility and better crystallinity. The study on the microstructural, mechanical and electrical properties of Ag–Mo films provided a basis for the application of the film in electrical contact coatings.

Selective laser melting of MoSiBTiC alloy with plasma-spheroidized powder: Microstructure and mechanical property

Spherical MoSiBTiC alloy powder with little internal gas pores and cracks was successfully fabricated using plasma-spheroidization method. This powder fabrication process significantly decreased the oxygen content of the raw crushed powder. Then, MoSiBTiC alloy samples were fabricated via selective laser melting (SLM) with the plasma-spheroidized powder, and the microstructural characteristics and mechanical property were investigated. The as-built MoSiBTiC alloy exhibited a bimodal microstructure; the microstructure inside the melt pool (MP) was different from that at a melt pool boundary (MPB). The microstructure inside the MP consisted of primary Mo solid solution (Moss) dendrites, and other constituent phases, such as Mo5SiB2 (T2) phase, were formed at the inter-dendritic regions. On the other hand, (Ti,Mo)C precipitates around the Moss dendrites were preferentially coarsened at the MPB, forming a heat affected zone (HAZ) at the underside within the MPB. At the upside within the MPB, the microstructure of the previous layer was partially remelted, and ternary eutectic lamellar structure (Moss/T2/(Mo,Ti)2C) was newly formed. The as-built samples were subsequently subjected to heat treatment at different temperatures of 1600, 1700, and 1800 °C for 4 h. With increasing in the heat-treatment temperature, the Moss dendritic microstructure decomposed, and other constituent phases were coarsened at the inter-dendritic regions. Through a detail microstructural characterization of both the as-built and heat-treated samples, it was confirmed that any large oxide was not formed in this study. Rapid solidification via SLM resulted in the refinement of microstructure and the formation of a supersaturated Moss phase, which hardened the as-built sample but simultaneously decreased the crack resistance of the Moss phase.

Continuous 3D-nanopatterned Ni–Mo solid solution as a free-standing electrocatalyst for the hydrogen evolution reaction in alkaline medium

A free standing 3D-nanopatterned solid solution of Ni–Mo has been fabricated for excellent hydrogen evolution reaction (HER) activity.

Construction of magnetron sputtering non-equilibrium Miedema's model for application in Ag-Mo thin films

The Miedema's model is a phenomenology for studying the thermodynamics of transition binary metals. In this paper, the magnetron sputtering non-equilibrium Miedema's model was constructed by using the single atomic collision theory. The Gibbs free energy diagrams of the crystalline and amorphous phase of the Ag-Mo system were calculated by using this model, the curves were convex and were greater than zero. Combined with the valence rule in the Hume-Rothery's rules, it was found that Ag atoms had a tendency to dissolve into Mo lattice under the non-equilibrium magnetron sputtering condition. The experimental results showed that metastable Mo(Ag) solid solution was formed in the Mo-rich region, which corresponds to the calculated Gibbs free energy curves under the constraints of the Hume-Rothery's rule.

First Principles Density Functional Theory Prediction of the Crystal Structure and the Elastic Properties of Mo2ZrB2 and Mo2HfB2

The Molybdenum rich ternary alloys Mo-M-B (M = Zr, Hf) contain, next to the Mo solid solution (bcc Mo with small amounts of Zr or Hf as substitutional atoms), the binary borides Mo2B, MB and MB2. Recently, it was found that there is also ternary Mo2MB2, but the crystal structure and further properties are currently unknown. Density functional theory (DFT) calculations were used not only to predict the crystal structure of the Mo2MB2 phases, but also to estimate the isotropic and anisotropic elastic properties like bulk, shear and Young’s modulus, as well as the Vickers hardness of these new borides. Several known crystal structures that fulfill the criterion of the chemical composition were investigated, and the AlMn2B2 type structure seems to be the most stable crystal structure for Mo2HfB2 and Mo2ZrB2 as there are no signs of electronic or dynamic instability. Regarding the elastic properties, it was found that Mo2HfB2 shows higher elastic moduli and is less elastically anisotropic than Mo2ZrB2.

Effect of hot isostatic pressing on the microstructure and fracture toughness of laser additive-manufactured MoSiBTiC multiphase alloy

MoSiB-based alloys are extremely promising ultrahigh–temperature materials, owing to their high melting points, good thermal stability, and excellent elevated-temperature mechanical properties. However, their fabrication is limited to conventional manufacturing techniques. In this work, a MoSiBTiC multiphase alloy, mainly consisting of Mo solid solution (Moss), Mo5SiB2 (T2), and TiC phases, was fabricated by laser powder bed fusion (L-PBF) using ball-milled alloy powders; subsequently, the effect of hot isostatic pressing (HIP) on its microstructure and fracture toughness was investigated. Due to the non-equilibrium metallurgical characteristics of L-PBF, the as-built alloy included uniform and fine-grained structures, as well as internal microcracks. The length of microcracks was effectively reduced with the assistance of the TiC bridging effect during HIP. As revealed by a high-resolution transmission electron microscope, the TiC was uniformly dispersed and was in close contact with the Moss or T2 phase. Consequently, the MoSiBTiC multiphase alloy exhibited a high fracture toughness of 9.0 MPa(m)1/2 after HIP at 1973 K. This work could be an important step towards the fabrication of high-performance refractory components with advanced properties in ultrahigh–temperature use.