Methods for controlling the composition and morphology of electrodeposited Fe–Mo and Fe–Co–Mo coatings

The effect of the electrolyte composition and the stationary electrolysis parameters on the composition and morphology of Fe–Mo and Fe–Co–Mo coatings deposited from complex citrate electrolytes based on Fe(III) is studied. It is shown that, at a constant component ratio of с(Fe³⁺): с(Co²⁺): с(MoO^2? ₄): с(Cit^3–) = 2: 2: 1: 4, an increase in the electrolyte concentration leads to a decrease in the pH of the solution in a range of 4.85–4.30 and in the molybdenum content in the coating. An increase in the current density contributes to the molybdenum enrichment of the electrodeposited alloy in the entire range of electrolyte concentrations. The Fe–Mo alloy coatings have a rough microporous surface; an increase in the current density does not lead to significant changes in the surface topography. It is found that the formation of ternary coatings is characterized by the competitive reduction of iron and cobalt in the alloy; the molybdenum content depends on the current density. At a metal ratio of 3: 2: 1 and a molybdenum content of up to 17 at % in the Fe–Co–Mo alloy, the surface has a fine-grained needlelike structure typical of cobalt. With an increase in i _c, the atomic fraction of molybdenum increases, while the surface becomes microglobular. The Fe–Co–Mo electrodeposits with a metal ratio of 2.5: 1.5: 1.0 and a molybdenum content of 19–20 at % have a more developed surface with a high density of spheroids.     

Electronic structures and physical properties of pure Cr,Mo and W

1　INTRODUCTIONIntheframeworkofthemetallicmaterialssys tematicscience[1] ,therearethreescientifictheorysystems :puremetalsystematicscience ,alloysphysicsandchemistry ,andalloysstatisticalthermodynamics .Thecoreofthepuremetalsystema ticscienceistheoneatomtheory (OA ) [2 5] ,andthatofthealloysphysicsandchemistryandalloysstatisticalthermody namicsisthecharacteristiccrystaltheory(CC) .Inordertomakethematerialsdesignstepfromempiricaltoscientificundertheguidanceofthemetallicmateri alssystemati…     

Microstructure and properties of β-NiAl and its eutectic alloy with Cr and Mo additions

NiAl-0.3Ru and NiAl-30Cr-4Mo alloys were fabricated by arc melting method and then annealed at 1 423 K for 12 h. It has been revealed that NiAl-0.3Ru was in a single-phase with large grain size and NiAl-30Cr-4Mo consisted of multiple eutectic cells. Each cell consisted of alternating plates NiAl and Cr（Mo）. The compressive properties including the brittle-ductile transition temperature （BDTT） were tested. NiAl-0.3Ru and NiAl-30Cr-4Mo fractured with a little plastic deformation after yielding below the BDTT, and almost no fracture was found after large deformation up to 60% above the BDTT. Fractograph showed that at the room temperature, the fracture in NiAl-0.3Ru was intergranular and the NiAl-30Cr-4Mo in transgranular along the interface between fiNiAl and Cr （Mo）. The compressive properties of NiAl were obviously improved by eutectic alloying with Mo and Cr additions.     

Environmental Resistance of Mo–Si–B Alloys and Coatings

For high temperature application beyond the range of Ni-base superalloys, multiphase Mo–Si–B alloys with compositions, that yield the ternary intermetallic Mo₅SiB₂ (T₂) phase as a key microstructure constituent together with the Mo and Mo₃Si phases, offer an attractive balance of high melting temperature, oxidation resistance and mechanical properties. The investigation of reaction kinetics involving the T₂ phase enables the analysis of oxidation in terms of diffusion pathways and the design of effective coatings. From this basis kinetic biasing is used together with pack cementation to develop multilayered coatings and in situ diffusion barriers with self-healing characteristics for enhanced oxidation resistance. While a combustion environment contains water vapor that can accelerate attack of silica based coatings, the current pack cementation coatings provide oxidation resistance in water vapor up to at least 1500 °C. An exposure to hot ionized gas species generated in an arc jet confirms the robust coating performance in extreme environments.     

Surface structure and catalytic activity of electrodeposited Ni-Fe-Co-Mo alloy electrode by partially leaching Mo and Fe

1 Introduction The chlorine alkaline industry and the production of hydrogen by electrolyzing water have disadvantages of high cost and energy consumption, so it is especially important to study and develop a high catalytic activity and good stability el…     

热喷涂 Mo 及 Mo 基复合涂层研究进展

热喷涂Mo及Mo基复合涂层因熔点高、硬度高、耐磨损、耐腐蚀及高温性能稳定等诸多特点,而广泛应用于机械零件生产及表面修复。随着以资源有效利用和机械产品再制造为一体的可持续发展战略不断推进,此类涂层将拥有更为广阔的应用前景。首先介绍了国内外在热喷涂Mo及Mo基复合涂层方面的研究发展和应用现状;随后依据热喷涂技术的发展历程,分别总结论述了不同热喷涂技术,即火焰喷涂(普通火焰喷涂、高速火焰喷涂)、等离子喷涂(普通等离子喷涂、超音速等离子喷涂、微束等离子喷涂、低压等离子喷涂)及电热爆炸喷涂中,Mo及Mo基复合涂层的制备工艺、涂层性能特点及存在的问题;接着指出了热喷涂Mo及Mo基复合涂层在新概念武器、航空航天等高科技领域的应用前景。最后,就进一步拓展Mo及Mo基复合涂层在贫油减摩、高温高速耐磨、高温耐腐蚀及氧化等复杂环境下的应用范围,结合热喷涂技术的研究热点及发展方向,指出了未来热喷涂Mo及Mo基复合涂层在材料组分设计和工艺优化研究中应重点关注的方面。     

Synthesis and crystal structure and nonlinear optical properties of polymeric W （Mo）-Cu-S cluster

The polymeric chalcogenide [W2O2S6Cu4（NCMe）4]n （compound 1） was synthesized by the self-assembly reaction of （NHa）2（WOS3） with CuBr in MeCN in the presence of tricyclohexylphosphane （PCy3） under a purified nitrogen atmosphere using standard Schlenk techniques. It gives rise to a novel ID polymeric compound 1 with solvent MeCN coordinated to the copper atom. This situation is unprecedented in the W（Mo）/Cu/S system. The crystals were characterized by elemental analysis, IR and single-crystal X-ray crystallography. The configuration of the polymeric compound can be viewed as a helical chain which is propagated along the crystallographic c axis. The excited state absorption and refraction of compound 1 in CH3CN solution were studied by using the Z-scan technique with laser pulses of 40 ps pulse-width at a wavelength of 532 nm. The polymeric compound possesses an optical self-focusing performance. The positive nonlinear refraction is attributed to population transitions between singlet states. Compound 1 displays a strong excited-state absorption.     

Extrusion and selected engineering properties of Mo–Si–B intermetallics

In this study, an extrusion process has been developed to produce defect free, high-density rods of Mo–Si–B material. An initial powder composition (53.5 vol.%, 91 wt.%) of 66 vol.% Mo₅Si₃B_x (T1)–16 vol.% MoB–18 vol.% MoSi₂ was mixed with a paraffin-wax based binder (46.5 vol.%, 9 wt.%) and extruded using a twin-screw extruder. Following binder removal by a combination process of wicking and thermal degradation, the material was sintered at 1800°C. The bulk density of the sintered material was 90–92% of theoretical. Thorough binder removal was evidenced by low impurity levels: 258±6 ppm carbon and 772±10 ppm oxygen. The material demonstrated excellent high temperature oxidation resistance. The calculated parabolic rate constant is 1.1×10⁻² mg²/cm⁴/h at 1600°C. The extruded material was also successfully tested as a resistance heating element. These materials show promise for the development of heating elements with enhanced performance compared to current MoSi₂-based heating elements.     

Microstructure and phase transformation behavior of Mo–MoSi_2 gradient material

Mo-MoSi_2 gradient coating on Mo substrate was prepared by siliconizing process,using the polysilicon as silicon atoms.The gradient layer was analyzed by the experimental results,theoretical analysis,and thermodynamic calculation.The silicon,molybdenum content of gradient coating shows a gradual change regulation.The reaction between silicon and molybdenum is most likely to generate Mo_5Si_3,then MoSi_2,finally Mo_3Si,but when the silicon content is excessive,the Mo_5Si_3 and Mo_3Si will react with silicon and generate MoSi_2.The gradient layer is mainly constituted by Si and MoSi_2,only about 1/10 gradient layer is constituted by Mo_5Si_3 and Mo_3Si,and the stable existences of Mo_5Si_3 and Mo_3Si are mainly determined by the silicon content.Along the Mo substrate to the surface of the coating,the phase composition of gradient coating changes as follows:Mo → transition layer,Mo(main phase) + Mo_3Si + Mo_5Si_3 →intermediate layer,and MoSi_2(main phase) + Mo_5Si_3 +Si→surface layer MoSi_2(main phase) + Si,and the experimental temperature has no effect on phase composition of gradient coating.     

Fabrication of nano-crystalline W-Ni-Fe alloy with Mo and rare earth element additives

Three kinds of nano-crystalline high density alloys (86W-7Ni-3Fe-4Mo, 90W-4Ni-2Fe-4Mo and 90W4Ni-2Fe-3.8Mo-0.2RE) were fabricated by a technique combining lower temperature vacuum sintering with highenergy ball milling mechanical alloying. The crystalline size and microstructures of the specimens sintered at different sintering temperatures were examined by X-ray diffraction(XRD) and scanning electron microscope(SEM). The results show that the optimal sintering temperature of 86W-7Ni-3Fe-4Mo, 90W-4Ni-2Fe-4Mo and 90W-4Ni-2Fe-3.8Mo-0.2RE alloys are 1 300 - 1 350℃. When they are sintered at 1 300℃ for 75 min， the hardness of three kinds of specimens can reach above HRC30, the relative density can reach above 96%, and 90W-4Ni-2Fe-3.8Mo-0.2RE alloy possesses the best integrated properties, its hardness is HRC35 and its relative density is 98%.     

Interfacial reaction between Co–Cr–Mo alloy and liquid Al

The interfacial reaction between Co–Cr–Mo alloy and liquid Al was investigated using immersion tests. Microstructure characterization indicated that the Co–Cr–Mo alloy was corroded by liquid Al homogeneously, with the formation of a (Co,Cr,Mo)₂Al₉ layer close to alloy matrix and “(Cr,Mo)₇Al₄₅ + Al” layer close to Al. Kinetics analysis showed that the corrosion of the Co–Cr–Mo alloy followed a linear relationship with the immersion duration. Compared with pure Co–liquid Al reaction system, the alloying of Cr and Mo changed the solid–liquid interface structure, but the corrosion of the solid metal was still dominated by the dissolution of an intermetallic layer.     

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 and258 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.     

Influence of Nb and Mo contents on phase stability and elastic property of β-type Ti-X alloys

The energetic, electronic structure and elastic property offl-type Ti-Xx （X=Nb and Mo, x=0.041 7, 0.062 5, 0.125 0, 0.187 5, 0.250 0, 0.312 5 and 0.375） binary alloys were calculated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The elastic moduli of the polycrystals for these Ti1-xXx alloys were calculated from the elastic constants of the single crystal by the Voigt-Reuss-Hill averaging method. Based on the calculated results, the influence of X content on the phase stability and elastic property offl-type Ti1-xXx alloys was investigated. The results show that the phase stability, tetragonal shear constant C, bulk modulus, elastic modulus and shear modulus offl-type Ti1-xXx alloys increase with an increase of X content monotonously. When the valence electron number offl-type Ti1-xXx alloys is around 4.10, i.e. the content of Nb is 9.87% （molar fraction） in the Ti-Nb alloy and Mo is 4.77% （molar fraction） in Ti-Mo alloy, the tetragonal shear constant is nearly zero. The Ti1-xXx alloys achieve low phase stability and low elastic modulus when the tetragonal shear constant reaches nearly zero. In addition, the phase stability offl-type Ti1-xXx alloys was discussed together with the calculated electronic structure.     

Influence of Gd and B on solidification behaviour and weldability of Ni–Cr–Mo alloy

Abstract

The influence of Gd and B on the solidification behaviour and weldability of Ni–Cr–Mo alloy UNS N06455 has been investigated by Varestraint testing, differential thermal analysis and microstructural characterisation. These alloys are currently being developed as structural materials for nuclear criticality control in applications requiring transportation and disposition of spent nuclear fuel owned by the US Department of Energy. The Gd containing alloys were observed to solidify in a manner similar to a binary eutectic system. Solidification initiated with a primary L→y reaction and terminated at ~1258°C with a eutectic type L→y+Ni₅Gd reaction. The solidification cracking susceptibility of the Gd containing alloys reached a maximum at ~1 wt-%Gd and decreased with both higher and lower Gd additions. Low cracking susceptibility at Gd concentrations below ~1 wt-% was attributed to a relatively small amount of terminal liquid that existed over much of the crack susceptible solid+liquid zone. Low cracking susceptibility at Gd concentrations above ~1 wt-% was attributed to a reduced solidification temperature range and backfilling of solidification cracks. The addition of B above the 230 ppm level leads to the formation of an additional eutectic type reaction at ~1200°C and the secondary phase within the eutectic type constituent was tentatively identified as Mo₃B₂. The B containing alloys exhibited a three step solidification reaction sequence consisting of primary L→y solidification, followed by the eutectic type L→y+Ni₅Gd reaction, followed by the terminal eutectic type L→y+Mo₃B₂ reaction. Boron additions had a strong, deleterious influence on solidification cracking susceptibility. The high cracking susceptibility was attributed to extension of the crack susceptible solid+liquid zone induced by the additional eutectic type L→y+Mo₃B₂ reaction and extensive wetting of the grain boundaries by the solute rich liquid. Simple heat flow equations were combined with solidification theory to develop a relation between the fraction liquid f _L and distance x within the solid+liquid zone. Information on the phenomenology of crack formation in the Varestraint test were coupled with the calculated f _L–x curves and were shown to provide useful insight into composition–solidification–weldability relations.     

Microstructure and Tensile Properties of a Nb–Mo Microalloyed 6.5Mn Alloy Processed by Intercritical Annealing and Quenching and Partitioning

The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing(IA) and quenching and partitioning(Q P),respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity(TRIP) effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation(YPE) of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.     

Preparation of Mo/Cu composites by SLS method and its post-treatment techniques

A multi-component polymer-coated molybdenum powder was chosen for selective laser sintering（SLS）. The powder was prepared by coating polymer on Mo particles and frozen by grinding techniques. The laser sintering activities and sound densification response were obtained by optimizing the process parameters. The post-treatment process of SLS samples was developed, which was high temperature sintering Mo framework combined with Cu impregnation. Then, the Mo/Cu composites are gained. The microstructure evolution of post-treatment samples was investigated by scanning electron microscopy. Mo grains frequently string together. The microstructural characterization of Mo/Cu composites is homogeneous compound structure of adhesive phase Cu linked with Mo grains. There is little ellipsoidal Mo grains singly existing around Cu phase. Between Mo grains and Cu zone, there is a medium changing zone with width of 10-20 nm. Post-treatment mechanism is Mo framework sintering of solid phase and Cu impregnation of melting/solidification. The mechanical and thermal properties concluding tensile strength, elastic modulus, elongation and linear expansion of Mo/Cu composites were studied.     

Mo在W—Mo梯度复合材料中的行为特点

较详细地研究了Mo对W-Mo复合材料的强度、收缩比、密度等物理和机械性能,以及微观结构的影响。     

Phase stability and structural defects in high-temperature Mo–Si–B alloys

For high-temperature application beyond the range of Ni-base superalloys, Mo–Si–B alloys with composition that yield the ternary intermetallic, Mo₅SiB₂, T₂, phase as a key microstructure constituent, offer an attractive property balance of high-melting temperature, oxidation resistance, and useful high-temperature mechanical properties. With the T₂ ternary phase as the focal point of the microstructure designs, the fundamental basis of the alloying behavior in T₂ including the mutual solid solution with a wide range of transition metals has been established in terms of the governing geometric and electronic factors. For non-stoichiometric compositions, constitutional defects such as vacancies for Mo-rich compositions and anti-site defects for Mo-lean compositions control the homogeneity range. Moreover, the aggregation of constitutional vacancies has been discovered to play a key role in the development of dislocation and precipitation reactions in the T₂ phase that directly impact high-temperature structural performance. The characteristically sluggish diffusion rates within the T₂ phase have also been quantified and applied to the materials processing strategies. The materials design based on the phase stability, diffusion and defect structure analysis in the Mo–Si–B system can also be applied to the design of new multiphase high-temperature alloys with balanced environmental and mechanical properties.