Al-Mo Alloys Research Articles

Phase constituents of Al-rich U–Mo–Al alloys examined by transmission electron microscopy

To supplement the understanding of diffusional interactions involving Al-rich region of the U–Mo–Al system, alloys with composition 85.7Al–11.44U–2.86Mo and 87.5Al–10U–2.5Mo in at.%, were examined to determine the equilibrium phase constituents at 500 °C. These alloys were triple arc-melted, homogenized at 500 °C for 200 h, and water-quenched to preserve the high temperature microstructure. X-ray diffraction, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (XEDS), and transmission electron microscopy (TEM) with high angle annular dark field (HAADF) imaging via scanning transmission electron microscopy (STEM) were employed for the characterization. Alloy specimens for TEM/STEM were prepared using site-specific focused ion beam (FIB) in situ lift-out (INLO) technique. Despite the homogenization time and temperature, five different phases, namely fcc-Al solid solution, cubic-UAl 3, orthorhombic-UAl 4, hexagonal-U 6Mo 4Al 43 and diamond cubic-UMo 2Al 20, were observed. Based on U–Al, U–Mo and Al–Mo binary phase diagrams, previously proposed U–Mo–Al isotherms, and the solidification microstructure of these alloys, the Al-rich region of the equilibrium ternary isotherm at 500 °C was constructed. The fcc-Al solid solution, orthorhombic-UAl 4, and diamond cubic-UMo 2Al 20 which were determined to be the equilibrium phases in 85.7Al–11.44U–2.86Mo and 87.5Al–10U–2.5Mo alloys.

Nanocrystalline–amorphous transitions in Al–Mo thin films: Bulk and surface evolution

We investigate the bulk and surface features of the crystalline–amorphous transitions in binary Al–Mo alloy thin films as a function of Mo composition using transmission electron microscopy, X-ray diffraction and atomic force microscopy analysis, as well as thermodynamic modeling. Of the alloys tested, the minimum in the root mean square (rms) surface roughness and correlation length occurs at the Al–32 at.% Mo composition, which corresponds to the maximum volume fraction of the amorphous phase and the minimum volume fraction of the body centered cubic nanocrystallites. The rms surface roughness of the 32 at.% Mo films is on the order of a single nanometer, compared with nearly 80 nm for the 50 at.% Mo film. A structure–zone map is constructed to relate the surface morphology of the films to their bulk microstructure. A thermodynamic model developed by Miedema and coworkers was used to predict the general trends observed in the microstructural evolution as a function of film composition.

Dislocation Structure and Fracture Characteristics of Spray Deposited Ni3Al-Mo Intermetallic Compound Alloy (IC6)

Abstract A Ni 3 Al-Mo intermetallic compound alloy (IC6) was prepared by the multifunctional spray atomization and deposition plant. Tensile properties tests indicate that the spray deposited Ni 3 Al-Mo alloy possesses “ R ” characteristics in the yield strength, that is, the yield strength of the spray deposited IC6 increases with increasing of temperature and it reaches maximum at 760 °C. After that, it decreases with increasing of temperature. Analyses of dislocation structure by TEM reveal the relationship between the microstructure and yield strength. The results show that the change of the yield strength of the alloy with temperature is associated with the condition of dislocation winding, the pattern and quantity of the dislocation pairs and starting degree of the hexahedron slip system inside γ′ and γ phases. The TEM analysis of cracking by stereographic projection shows that with the increase of deformation stress the cracks form at grain boundaries and then quickly propagate, and some different slip bands exist in little planar zones; no matter at room temperature, middle temperature or high temperature, cracks craze along (111) plane octahedron slip.

On the structure of the B2 phase in Ti–Al–Mo alloys

The structure of the B2 phase has been investigated in Ti-26Al-20Mo and Ti-37.5Al-12.5Mo alloys using Rietveld refinement of x-ray diffraction data in homogenized conditions. Different initial structure models have been used for the refinement. The site occupancy of the B2 phase has been calculated and compared to those of earlier experimental and theoretical investigations.

Electrodeposition of Al–Mo–Ti Ternary Alloys in the Lewis Acidic Aluminum Chloride–1-Ethyl-3-methylimidazolium Chloride Room-Temperature Ionic Liquid

The electrodeposition of Al–Mo–Ti ternary alloys was examined in the Lewis acidic 66.7–33.3% mole fraction aluminum chloride–1-ethyl-3-methylimidazolium chloride room-temperature ionic liquid containing and . The Mo content in the alloys varied with the applied current density and the concentration ratio. The Ti content was small and constant at atomic fraction (a/o) and was independent of the deposition conditions. All the electrodeposited Al–Mo–Ti alloys were dense and compact and adhered well to the copper substrate. The deposit surface morphology depended on the applied current density and the Mo content of the alloys, as reported previously for the amorphous binary Al–Mo alloys. However, no amorphous glass phase could be detected in the Al–Mo–Ti ternary alloy samples; this behavior may be related to the presence of Ti. In summary, the addition of a small amount of Ti to the binary Al–Mo alloys resulted in a ternary alloy with a substantially improved chloride-induced pitting corrosion resistance compared to the related Al–Mo alloy.

Characterization and tribological behavior of cast In-Situ Al (Mg,Mo)-Al2O3 (MoO3) composite

Aluminum alloy—based cast in-situ composite has been synthesized by dispersion of externally added molybdenum trioxide particles (MoO3) in molten aluminum at the processing temperature of 850 °C. During processing, the displacement reaction between molten aluminum and MoO3 particles results in formation of alumina particles in situ and also releases molybdenum into molten aluminum. A part of this molybdenum forms solid solution with aluminum and the remaining part reacts with aluminum to form intermetallic phase Mo(Al1−xFex)12 of different morphologies. Magnesium (Mg) is added to the melt in order to help wetting of alumina particles generated in situ, by oxidation of molten aluminum by molybdenum trioxide, and helps to retain these particles inside the melt. The mechanical properties of the cast in-situ composite, as indicated by ultimate tensile stress, yield stress, percentage elongation, and hardness, are relatively higher than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The wear and friction of the resulting cast in-situ Al(Mg,Mo)-Al2O3(MoO3) composites have been investigated using a pin-on-disc wear testing machine under dry sliding conditions at different normal loads of 9.8N, 14.7N, 19.6N, 24.5N, 29.4N, 34.3N, and 39.2 N and a constant sliding speed of 1.05 m/s. The results of the current investigation indicate that the cumulative volume loss and wear rate of cast in-situ composites are significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy, under similar load and sliding conditions. Beyond about 30 to 35 N loads, there appears to be a higher rate of increase in the wear rate in the cast in-situ composite as well as in cast commercial aluminum and cast Al-Mo alloy. For a given normal load, the coefficient of friction of cast in-situ composite is significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The coefficient of friction of cast in-situ composite increases gradually with increasing normal load while those observed in cast commercial aluminum or in cast Al-Mo alloy remain more or less the same. Beyond a critical normal load of about 30 to 35 N, the coefficient of friction decreases with increasing normal load in all the three materials.

First-principles calculations and phenomenological modeling of lattice misfit in Ni-base superalloys

An integrated computational approach is proposed for evaluating the lattice misfit between γ and γ′ in Ni-base superalloys by combining first-principles calculations, existing experimental data and phenomenological modeling. In particular, the lattice misfits in Ni–Al and Ni–Al–Mo alloys were studied. This approach is validated by comparing the calculated lattice misfit with available experimental measurements as well as by comparing the predicted γ′ precipitate morphologies from phase-field simulations with experimental observations.

Magnetic behavior of Fe sites in Fe–Mo–Al alloys: The role of the first neighborhood

We analyse the influence of the nearest neighborhood on the magnetic behaviour at Fe sites in bcc-based Fe–Al, Fe–Mo and Fe–Al–Mo alloys. Theoretical ab initio calculations were performed in the framework of the Density Functional Theory using the Full Potential—Linear Augmented Plane Wave method as embodied in the WIEN97 code. The analysis is made through local magnetic moments considering the distribution of the first coordination shell of the Fe atoms. We find that the magnetic moment is nearly independent of the composition in the Fe–Mo binary. Although the magnetic behaviour of Fe–Al alloys is a very complex and controversial subject, our results clearly show that an increase in the number of Al nearest neighbours leads to a decrease or even to the suppression of the local moment at Fe sites. On the other hand, the ternary bcc-based Fe–Mo–Al alloys present no correlation between magnetism and the composition of the nearest neighbor shell. The results are discussed in connection with their implications for the thermodynamic modelling of magnetism in the CALPHAD approach.

Electrodeposition of Al-Mo-Mn Ternary Alloys from the Lewis Acidic AlCl3 - EtMeImCl Molten Salt

The electrodeposition of Al-Mo-Mn ternary alloys was examined in the Lewis acidic fraction (mol %) aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt containing Mo(II) and Mn(II). By adjusting the concentration ratio in the plating solution and employing different current densities, it was possible to prepare alloys with widely varying compositions and surface morphologies. All Al-Mo-Mn alloys were dense, compact, and adhered well to the copper substrate surface. The addition of small amounts of Mn to the Al-Mo alloy resulted in an improvement in the chloride pitting corrosion resistance and metallic brightness. For example, and displayed pitting potentials that were 725 and more positive than that for Al, respectively. Al-Mo-Mn alloys that contained more than about 10 atom % exhibited a metallic glass structure.

Laser developed Al–Mo surface alloys: Microstructure, mechanical and wear behaviour

Molybdenum forms a significant proportion of hard intermetallic compounds with Al, which greatly increase the strength of the material. Hence, Al–Mo alloys are potential candidates for coating materials to improve the surface hardness and wear resistance of Al-based light alloys. Surface alloys with composition ranging from 14.8 to 19.1 wt.% Mo were produced by laser surface alloying, injecting Mo powders into the melt pool created in Al substrates using a CO 2 laser. Their microstructure consists of intermetallic compound particles dispersed in a matrix of α-Al solid solution. The intermetallic particles present acicular morphology at low scanning speeds and an equiaxial, flower-like shape at high scanning speeds. TEM characterisation shows that both types of particles correspond to the rhombohedral intermetallic compound Al 5Mo(r), suggesting that the different morphologies result from changes in the local solidification conditions. The hardness of the Al–Mo alloys varies in the range 85–160 HV, while their Young's modulus, assessed by ultramicroindentation tests, varies from 84 to 92 GPa. Wear resistance was measured in dry sliding conditions against a hardened steel counterbody. The wear coefficient decreases with increasing load due to the protective effect of stable mechanically mixed layers that form on the surfaces of the samples and the counterbody during sliding. The wear mechanism in Al–Mo alloys is predominantly adhesion and material transfer and oxidation, with a minor contribution of abrasion.

Structure and thermal stability of Mo/Al multilayers for soft x-ray mirrors

The structure and thermal stability of Mo/Al multilayers prepared by a four facing target sputtering system have been studied. Cross-sectional high-transmission electron microscopy reveals that Mo and Al layers are polycrystalline and that the thickness of the mixed layers at Mo-on-Al interfaces is larger than that at the Al-on-Mo interfaces. Annealing treatment up to 450°C leads to the gradual period expansion and appearance of the 5th and 6th order Bragg peak, which can be attributed to grain growth and sharpness of the interfaces and/or improvement of the correlations of the roughness at different interfaces through annealing, respectively. Thermally induced interdiffusion or reaction at grain boundaries with high density restricts the further period expansion in spite of the increasing temperature. At 550°C, the modulation structure is still well maintained though the amorphous Al–Mo alloy layer replaces the Al layer. On the base of effective heat of formation, Mo3Al8 is suggested to be the first phase formed at the interfaces. Further annealing to 600°C would partly destroy the layered modulation structure.

P-166: Microstructural Characterization of the Interface between IZO and Mo/Al/Mo Metal Line Used in TFT-LCDs

Mo layer is used as a protective layer of Al metal line causing problems such as hillock and oxidation in TFT-LCDs. When the insulating SiNx and passivation layer is etched to form a contact hole in Mo/Al/Mo trilayered metal line, the upper Mo layer is also removed due to the lack of selectivity of the dry etching process. As a result, IZO layer appear to contact to Al directly, possibly resulting in the formation of Al2O3 increasing the contact resistivity. However, detailed investigation by TEM revealed that there are two amorphous layers, inner and outer layers, preventing the direct contact of IZO to Al layer. The inner layer was enriched with Mo, while the outer layer was enriched with Al and oxygen. Oxygen concentration was considerably reduced in front of the inner layer, indicating the Mo-rich inner layer as a barrier layer against oxygen diffusion. On the other hand, Al concentration was still higher and decreasing continuously across the inner layer, exhibiting fast Al diffusion through the inner layer. It was shown that Al-Mo alloy is able to form an amorphous phase at the interface during deposition because of large difference in melting point between Al and Mo. Based on the observed details, the interfacial amorphous layers are considered to produce thermodynamically stable phase, oxide and intermetallic compound, upon further annealing.

Phase development in Al-rich U–Mo–Al alloys

Abstract Al-rich U–Mo–Al alloys have been cast and heat-treated to study the development of Al-rich phases in the U–Mo–Al system. An Al-rich phase developed that is not expected based on the binary U–Al phase diagram. This phase is identical to one that reportedly develops in U–Mo alloy versus Al diffusion couples.

Alloys based on Fe 3Al or FeAl with strengthening Mo 3Al precipitates

Single-phase and two-phase ternary Fe–Al–Mo alloys with Al contents of about 30 or 40 at.% and Mo contents up to 23 at% have been studied with respect to hardness at room temperature, yield stress and fracture strain at room temperature and higher temperatures up to 1000 °C and oxidation at temperatures of 400–1000 °C. The alloys with atomic D0 3 or B2 order are strengthened by precipitation of the metastable τ 2 phase and/or the stable Mo 3Al phase, both hard and brittle intermetallic phases, depending on composition and heat treatment. The yield stress as well as the brittle-to-ductile transition temperature increases with increasing Mo content to reach yield stresses up to 1600 MPa with, however, fracture strains below 1% at low temperatures. The observed short-term oxidation is similar to that of other binary and ternary Fe–Al alloys.

Electrodeposition of Al-Mo Alloys from the Lewis Acidic Aluminum Chloride-1-ethyl-3-methylimidazolium Chloride Molten Salt

The electrodeposition of aluminum-molybdenum alloys was examined at copper rotating disk and wire substrates in the Lewis acidic 66.7-33.3 mol % aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt containing Mo(II) in the form of dissolved The molybdenum content of the electrodeposits depended on the electrode rotation rate, Mo(II) concentration, and bath temperature. It was possible to produce nonequilibrium alloys containing up to 11 atom % Mo. These alloy deposits were compact and chloride-free. Al-Mo alloys containing more than 8 atom % Mo exhibited a chloride corrosion pitting potential of approximately +800 mV against pure aluminum. The corrosion resistance of this alloy is superior to that of all the aluminum-transition metal alloys that have been electrodeposited to date from chloroaluminate molten salts. © 2004 The Electrochemical Society. All rights reserved.

Electrodeposition of Al-Mo-X (X: Mn or Ni) Ternary Alloys from Lewis Acidic AlCl3-EtMeImCl Molten Salts

The electrodeposition of Al-Mo-X (X: Mn or Ni) ternary alloys was examined in the Lewis acidic 66.7-33.3 percent mole fraction aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl3-EtMeImCl) molten salt. The electrodeposition of Al-Mo-Mn was investigated in solutions containing Mo(II) and Mn(II). By adjusting CMn(II)/CMo(II) in the plating solution and employing different current densities, it was possible to prepare alloys with very different compositions and surface morphologies. All Al-Mo-Mn alloys were dense, compact, and adhered well to the substrate surface. The addition of small amounts of Mn to the Al-Mo alloy resulted in an improvement in its chloride pitting corrosion resistance and metallic brightness. For example, Al90.1Mo9.9 displayed a pitting potential of +725 mV versus Al, whereas Al88.8Mo10.0Mn1.2 exhibited a pitting potential of +868 mV versus Al. Al-Mo-Mn alloys that contained more than about 10 a/o Mo+Mn exhibited a metallic glass structure. Al-Mo-Ni alloys that were electrodeposited from solutions of Ni(II) and Mo(II) in the AlCl3-EtMeImCl molten salt were fragile and powdery.

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.

Microstructure and mechanical properties of Ru–Al–Mo alloys

Alloys in the Ru–Al–Mo system were investigated and the microstructure and phase compositions of alloys produced by arc-melting and by a cold crucible Czochralski technique were examined. Two sets of alloys were examined. One consisted of eutectic microstructures between RuAl and a bcc (Mo, Ru) solid solution. The RuAl–(Mo, Ru) eutectic was found to have a room temperature yield stress of 1500 MPa. The microstructures from the other set of alloys consisted of RuAl and a hcp(Ru, Mo) solid solution. For these alloys, a change from eutectic to peritectic solidification occurs as the Mo concentration increases. The RuAl–hcp(Ru, Mo) eutectic microstructure was found to consist of RuAl fibers embedded in a (Ru, Mo) matrix. A near eutectic RuAl–(Ru, Mo) alloy was found to have a room temperature fracture toughness above 35 MPa√m.

Phase equilibria and microstructure evolution of Al–Mo–Ti ternary alloys

Phase equilibria in Ti-lean part of the Al–Mo–Ti ternary system is investigated to understand the microstructure evolution of near-equi-atomic MoAl alloys containing Ti up to 17 at.%. A partial reaction scheme is proposed based on experimental study. A high temperature ternary A2(bcc)-β phase with Ti concentrations ranging from 13 to 17 at.% decomposes into A15 Mo 3Al–D0 22 Al 3Ti two-phase lamellar structure in a manner similar with a eutectoid reaction through a continuous cooling. The decomposition kinetics of the high temperature A2 phase is suppressed by adding Ti. Fine equi-axed two-phase structure is also obtained by an isothermal aging of a retained high temperature A2 phase.

Fatigue behavior of a 4140 steel coated with a NiMoAl deposit applied by HVOF thermal spray

The fatigue behavior of a quenched and tempered AISI 4140 steel has been investigated in three different conditions: as-polished, as-grit blasted with Al 2O 3 particles and as-coated, after grit blasting, with a deposit of Ni–Al–Mo alloy (Metco 447) of approximately 300 μm in thickness, applied by HVOF thermal spraying. It has been determined that after grit blasting with particles of 20 mesh (83 μm) at a pressure of 345 kPa, a significant decrease in the fatigue properties of the material takes place. It has also been observed that such particles, are retained at the substrate surface during blasting and become stress concentrators that enhance the nucleation of fatigue cracks. The latter give rise to a decrease in the fatigue strength of the blasted material. Further coating of the grit blasted specimens with a deposit of Metco 447 of approximately 300 μm thick, applied by HVOF thermal spraying, leads to a further reduction in the fatigue strength of the material. Under these conditions, the fatigue cracks are also nucleated at the alumina particles retained after blasting. It is believed that such a further decrease is mainly associated with two different causes. Firstly, the extensive fracture and delamination of the coating from the substrate which has been observed from the microscopic analysis. Secondly, the possible existence of tensile residual stresses in the substrate, in the vicinity of the substrate–deposit interface, which would assist in the propagation of the fatigue cracks nucleated at the alumina particles. The fatigue properties of the steel substrate in the three different conditions investigated, has been described in terms of the simple parametric relationship earlier proposed by Basquin.