Mo Alloy System Research Articles

Critical role of initial multi-phase microstructure on the phase transformations during hydrogenation in Fe–Mo alloy system

Given Fe is a low-cost earth-abundant element, there is a need to develop novel Fe-based metal hydrides. The conventional Fe-based hydrides consist of at least one metal with high hydrogen affinity. To synthesize novel low-affinity Fe-based hydrides, the high-pressure and high-temperature method is currently being used. The microstructure is known to influence the de-/hydrogenation processes in metal hydrides. However, in the context of low-affinity Fe-based hydrides, the role of the initial multi-phase microstructure is unknown, which is the objective of the current work. We investigate three as-cast Fe–Mo binary alloys: Fe0.33Mo0.67, Fe0.5Mo0.5, and Fe0.67Mo0.33. Firstly, we first explain in detail the formation mechanisms of the non-equilibrium initial as-cast microstructures caused by the sluggish diffusion of Mo. Subsequently, we present the phase transformations and microstructure evolution during the hydrogenation, depressurization, and aging of Fe–Mo alloys. We demonstrate that each phase in the initial microstructure act as an independent phase during hydrogenation.

Thermodynamic Characteristic and Phase Evolution in Immiscible Cr–Mo Binary Alloys

This paper systematically reports the thermodynamic characteristic and phase evolution of immiscible Cr–Mo binary alloy during mechanical alloying (MA) process. The Cr–35Mo (in at%) powder mixture was milled at 243 and 258 K, respectively, for different time. For comparative study, Cr–15Mo and Cr–62Mo powder mixtures were milled at 243 K for 18 h. Solid solution Cr(Mo) with body-centered cubic (bcc) crystal structure and amorphous Cr(Mo) alloy was obtained during MA process caused by high-energy ball milling. Based on the Miedema’s model, the free-energy change for forming either a solid solution or an amorphous in Cr–Mo alloy system is positive but small at a temperature range between 200 and 300 K. The thermodynamical barrier for forming alloy in Cr–Mo system can be overcome when MA occurs at 243 K, and the supersaturated solid solution crystal nuclei with bcc structure form continually, and three supersaturated solid solutions of Cr–62Mo, Cr–35Mo and Cr–15Mo formed. Milling the Cr–35Mo powder mixture at 258 K, the solid solution Cr(Mo) forms firstly, and then the solid solution Cr(Mo) transforms into the amorphous Cr(Mo) alloy with a few of nanocrystallines when milling is prolonged. At higher milling temperature, it is favorable for the formation of the amorphous phase, as indicated by the thermodynamical calculation for immiscible Cr–Mo alloy system.

MgB2 thin films grown on graphene/Ni–Mo alloy system

200nm Ni film is coated on 25μm thick Mo foil, and graphene is grown on the Ni–Mo system by CVD method. After the annealing process of CVD, the Ni/Mo bilayer transforms into Ni–Mo alloy, then we have successfully fabricated MgB2 films on graphene/Ni–Mo alloy system via the hybrid physical–chemical vapor deposition (HPCVD) technique. The transition temperature Tc onset is 38.25K with a corresponding transition width of 0.75K. The average thickness of MgB2 films is 200nm (25% concentration B2H6). The critical current density derives from the magnetization measurement at 5K is, jc (5K, 0T)=9.6×106A/cm2. We can easily deposite MgB2 on graphene/Ni–Mo alloy system with a lower B2H6 concentration and less gas flow, which lays a good foundation for depositing MgB2 thick films. The graphene in this system is multilayer and with defects, it may act like an intermediary film for the growth of MgB2, or a carbon-doping source.

Investigations on the microstructure and room temperature fracture toughness of directionally solidified NiAl–Cr(Mo) eutectic alloy

The microstructures and room temperature fracture toughness of directionally solidified NiAl-xCr-6Mo (x = 28, 32 and 36 at%) alloys were investigated. Fully eutectic microstructure could be obtained in the alloys over a wide composition range. High temperature gradient could increase the planar/cellular transition rate and expand the eutectic coupled growth zone. The volume fraction of Cr(Mo) strengthening phase increased with the increasing content of Cr, accordingly, the fracture toughness of NiAl–Cr(Mo) alloys also gradually increased. The fracture toughness of 26.15 MPa m1/2 was obtained in the NiAl-36Cr-6Mo hypereutectic alloy solidified at withdrawal rate of 10 μm/s and temperature gradient of 600 K/cm, which is the highest value in the NiAl–Cr–Mo alloy system until now. Well-aligned microstructure was beneficial to the enhancement of the fracture toughness, while the existence of primary phase seriously deteriorated the toughness. All the directionally solidified NiAl–Cr(Mo) alloy failed as brittle quasi-cleavage fracture. Some toughening mechanisms, such as crack bridging, crack nucleation, crack blunting, crack deflection, interface debonding and shear ligament toughening as well as linkage of microcracks were observed. In addition, mobile dislocation generated from the interface also had significant influence on the toughness.

Evolution of the ωo phase in a β-stabilized multi-phase TiAl alloy and its effect on hardness

The intermetallic β-stabilized Ti–43.5Al–4Nb–1Mo–0.1B alloy (in at.%), termed TNM alloy, is designed to be used at elevated temperatures, typically up to 750°C. To understand the evolution of the microstructures during heat treatments and subsequent creep tests, an understanding of the phase transformations and decomposition reactions that occur is necessary. The present study deals with the development and growth mechanism of the ωo phase, which forms in the βo phase during static annealing treatments and creep tests performed at 750, 780 and 800°C using an applied stress of 150MPa. In situ high-energy X-ray diffraction experiments were conducted to investigate the decomposition behaviour of the ωo phase during heating as well as to determine its dissolution temperature. High-resolution transmission electron microscopy was used to study the coarsening of ωo grains during creep. The chemical composition of βo and ωo was determined by means of energy dispersive X-ray microanalysis. In particular, the impact of the Mo content on the growth of the ωo grains within the βo matrix was investigated. Additionally, nanohardness measurements in γ, α2, βo and (βo+ωo) grains were performed by cube corner indentation. The results show that βo is the hardest phase in the TiAl–Nb–Mo alloy system when finely dispersed ωo precipitates are present.

Bioactivity of Ti - Nb - X (X = Zr, Mo) Alloy System with Low Elastic Modulus Modified by Anodic Oxidation and Precalcification Treatments

이 연구는 예술대학 중 연극영화과의 군사주의 현상을 조직문화이론과 제도주의 조직이론을 통해 접근한다. 특히 조직 내 개별 행위자들의 정체성 형성의 관점에서 군사주의 문화를 몇 가지 특징으로 분류하고, 이에 대한 조직 장 차원의 제도적 논리와 수사법을 정당성 획득의 차원에서 분석하였다. 그 결과 연극영화과의 군사주의 문화는 1. 의례와 의식, 2. 조직규범, 3. 성역할 등으로 구분될 수 있었으며, 개별 행위자들이 조직의 정체성 및 예술혼을 형성해가는 과정으로 군사주의 조직문화가 작용하고 있음을 확인하였다. 또 군사주의가 채택되고 유지되는 조직의 제도논리와 수사법의 측면에서 1. 준비된 예술가로서 현장진출을 위한 준비, 2. 일반 사회와의 구별을 위한 과시적이고 의례적인 행동, 3. 자기희생과 가난의 연습공간으로써의 공동창작조직이라는 요소들을 발견할 수 있었다. 이 연구는 예술대학에서 채택하고 운영하는 군사주의 및 조직문화의 기제와 그 의미를 발굴하고 분석함으로써 군대의 이데올로기와 행동양식을 왜 사적영역에서 채택했는지를 기초적으로 탐색했다는 점에서 그 의의가 있다.

Structural stability of Ni–Mo compounds from first-principles calculations

Abstract The Ni–Mo alloy system is studied. In contrast to the existing Ni–Mo binary phase diagram that shows three stable compounds, β-Ni 4 Mo, γ-Ni 3 Mo, and δ-NiMo, it is determined that δ-NiMo is meta-stable at very low temperatures. It is also discovered that two additional compounds, Ni 2 Mo and Ni 8 Mo are stable at 0 K.

Ordering and phase separation around Ti 50Al 25Mo 25 composition in ternary Ti–Al–Mo bcc alloys

The phase equilibria of bcc-based phases in the Ti–Al–Mo alloy system has been studied from first-principles using a combination of ab initio total energy and cluster variation method (CVM) calculations. A set of effective cluster interaction parameters has been derived from the total energies, already computed, of 18 binary and ternary bcc superstructures. These interaction parameters were the input for CVM computation of alloy thermodynamics properties. The CVM has been used to determine the bcc composition–temperature phase diagram in the Ti–Al–Mo system and site preference for bcc-based phases. The investigation focuses its attention on the discussion about the formation of a two-phase field A2+B2 around the Ti 50Al 25Mo 25 composition to suggest some potential directions for future research and development activities on high temperature bcc based superalloys.

A study of the Al-rich region of the Al–Ni–Mo alloy system

The Al–AlNi–Al 8Mo 3 compositional range was investigated at 800–1050°C. Two ternary phases reported earlier were confirmed in this range. The (Al,Ni) 3Mo phase of the Al 3Ti-type structure was observed between 1.6 and 6.0 at.% Ni, the other phase is formed at about Al 75Ni 14Mo 11 and not at about Al 77Ni 18Mo 5 as reported previously. It was found to have an orthorhombic structure with a=1.0054(4), b=1.5288(4) and c=0.8519(2) nm. Partial isothermal sections at 1050, 1000, 950 and 800°C are presented.

Microstructure and room temperature deformation of Nb ss/Nb 5Si 3 in situ composites alloyed with Mo

Room temperature deformation behavior of Nb 5Si 3 based intermetallics in the ternary Nb–Si–Mo alloy system is investigated by compression testing in relation to microstructure and compositional effect. The partial ternary phase diagram of the Nb-Si-Mo alloy system containing phase equilibrium information at 1973 K is determined by metallography, X-ray diffraction and scanning electron microscopy (SEM) equipped with wavelength-dispersive X-ray fluorescence spectroscopy (WDS). A pseudo-binary compound of Nb 5Si 3–Mo 5Si 3 is confirmed to form at Nb 5Si 3-rich compositions by Mo addition, without having a solubility range of Si. The phase transformation from α-Nb 5Si 3 to β-Nb 5Si 3 is found to occur at about 5 at.% of Mo content on the Nb 5Si 3–Mo 5Si 3 pseudo-binary line. The observed yield stresses are largely dependent on not only the volume fraction and morphology of constituent phases but also the strength of Nb 5Si 3 phase equilibrating with Nb solid solution. The in situ composites consisting of α-Nb 5Si 3 phase and bcc solid solution exhibit higher yield stress than those consisting of β-Nb 5Si 3 phase and bcc solid solution when yield stress is compared at the same volume fraction of bcc phase. It is suggested that room temperature deformability of β-Nb 5Si 3 is superior to that of α-Nb 5Si 3 phase. Room temperature deformation behavior of the present composites will be discussed in relation to microstructural evolution.

Correlation between crystal structure and electrochemical properties of C14 Laves-phase alloys

By examining the relationships between the structure and the thermodynamic and electrochemical properties for Zr 1− x Ti x (V 0.1Mn a Ni b E c ) α ( x=0.1–0.3, a=0.28–0.30, b=0.50–0.57, c=0.05–0.12, α=1.6–1.8, E=Co, Fe, Mo) alloy system with C14 type structure, the following results were obtained. The partial molar enthalpy for hydride formation decreases linearly with decreasing cell volume V C14 of the C14 phase. This means that the hydride becomes unstable with decreasing V C14, as is the case for the C15 type structure. Both −Δ H and V C14 decrease with decreasing average atomic radius of the alloy, and the correlation coefficient was sufficiently high for each value. The discharge capacity and dischargeability also depend on −Δ H and V C14.

A study of a cellular phase transformation in the ternary Ni- Ai- Mo alloy system

Orthorhombic Ni3Mo has been observed as a product of a cellular precipitation reaction occurring at grain boundaries in both Ni-12Al-15Mo and a ternary eutectic Ni-12.8Al-22.2Mo (compositions in at. pct) when heat treated at intermediate temperatures (600 to 850 °C). Convergent beam electron diffraction and energy dispersive X-ray spectroscopy techniques have been employed to characterize the structure and composition of this phase in these alloys. Since this phase is usually heavily faulted, the diffraction symmetries are reduced, causing ambiguities in analysis. Therefore, a binary (nominally) stoichiometric Ni3Mo alloy was produced and heat treated in a manner designed to minimize faulting. Convergent beam patterns obtained from this material exhibited symmetries that identify it as having the mmm point group; further analysis of the diffraction patterns led to the conclusion that the space group is Pmmn. These patterns were then used to aid in the interpretation of those taken from the ternary alloys. Orthorhombic Ni3Mo was also observed within the grains of the ternary eutectic alloy following prolonged aging treatments; the orientation relationship between the Ni3Mo and the fee matrix was determined to be identical with that in the cellularly transformed regions.

Microstructural Changes near the Coherent Spinodal Line in the Fe–Mo Alloy System

Microstructural changes near the coherent spinodal line during ageing in Fe–18.5 and 19.2 at%Mo alloys were investigated by means of transmission electron microscopy. A mixed microstructure of the 〈100〉 modulated structure and the plate-shaped Mo-rich zones was observed in the alloys aged at a temperature just above the coherent spinodal temperature, Ts. With further ageing this morphological distinction became obscure, and consequently the modulated structure appeared. When the alloy was aged at a higher temperature, the plate-shaped zones were only nucleated on the {100} matrix planes, while the ageing at a temperature just below Ts only produced a typical 〈100〉 modulated structure. A series of results implies that the microstructures produced near Ts become continuously inhomogeneous with increasing ageing temperature, which has been proposed by Binder.