Molybdenum Alloy Research Articles

The effect of melt temperature on the mechanical properties of cast ASTM F75 CoCrMo alloy as explained by nitrogen and oxygen content

Investment cast ASTM F75 Cobalt Chromium Molybdenum (CoCrMo) alloy is commonly used for orthopaedic implants due to its biocompatibility and wear characteristics. Apart from the values listed in the standard, the relationship between individual processing parameters and the resulting physio-mechanical properties are not well documented. This study characterises the effect of melt temperature on the physical properties and chemical composition of investment cast CoCrMo alloy. Furnace loads of ∼23−34 kg of alloy were inductively melted using 125 kW of power and cast into tensile test bars and chemistry coupons. The bars were ground to create samples conforming to ASTM E8M and tested per ISO 6892-1. The oxygen and nitrogen content of the chemistry coupons were assessed using Inert Gas Fusion (IGF) per ASTM E1019. It was found that increasing the melt temperature had the effect of removing nitrogen from the melt and adding oxygen. It was also determined that there was a strong positive correlation between nitrogen content and strength values. If desired, there is scope to minimise both oxygen pickup and nitrogen loss, nitrogen is correlated to increased mechanical properties, of this alloy system by targeting lower melt temperatures. However, this would be at the expense of melt viscosity and mould filling.

Transition Core Analysis for HEU to LEU Fuel Conversion at the University of Missouri Research Reactor

A new type of low-enriched uranium (LEU) fuel based on an alloy of uranium and molybdenum is expected to allow the conversion of U.S. domestic high-performance research and test reactors requiring high density fuel from highly enriched uranium (HEU) to LEU. The University of Missouri Research Reactor (MURR®) has undergone design and performance calculations for conversion to this LEU fuel. Presented in this paper is the analysis of a crucial step in the conversion process: the sequence of MURR transition cores from all fresh to equilibrium burnup LEU operations. During the initial conversion from HEU to LEU fuel, MURR will operate atypically due to the lack of burned LEU elements. Given the constraints of MURR operation and experiments, a proposed transition scheme minimizes the time MURR operates atypically compared to the prototypic cycles currently run with HEU fuel and moves quickly to the same sort of equilibrium cycles for the LEU fuel.

Fabrication of Molybdenum Alloy with Distributed High-Entropy Alloy Via Pressureless Sintering

Fabrication of Molybdenum Alloy with Distributed High-Entropy Alloy Via Pressureless Sintering

Effect of Ti Content on Microstructure and Wear Performance of TZM Alloys Produced by Mechanical Alloying Method

In this study, changes in microstructure, hardness and wear performance of titanium–zirconium–molybdenum (TZM) alloys produced by mechanical alloying method with the addition of different amounts of titanium (Ti) were investigated. Mechanically alloyed powders were sintered at 1300 °C for 4 h under 10–6 mbar vacuum environment. The produced alloys were characterized by scanning electron microscope (SEM + EDS), X-ray diffraction, grain size distribution, hardness and density measurements. In the wear tests, three different loads and five different sliding distances were used. Results showed that the produced TZM alloys were porous, and the pores in the alloys containing 0.40% and 0.45% Ti were generally located on the grain boundaries. In alloys containing 0.50% Ti, inside the grain the pore sizes increase, while in the alloy containing 0.55% Ti, the pore sizes in grain boundary decrease. Grain size distribution results show that as the Ti content increased, the amount of grain size over 6 µm decreased and smaller than 6 µm increased. Hardness and density results show that while the hardness of TZM alloys produced increases depending on Ti content, their density decreases. The highest hardness was obtained in the TZM alloy containing 0.55% Ti, while the lowest density was obtained in the same alloy. Wear test results show that the lowest weight loss was obtained in TZM alloy containing the highest amount of Ti (0.55%) under all loads.

On the role of carbon in molybdenum manufactured by Laser Powder Bed Fusion

Carbon is known to improve the ductility and grain boundary strength of molybdenum. Scientific consensus to explain this phenomenon is that carbon either replaces oxygen impurities at grain boundaries or suppresses the diffusion of oxygen towards the grain boundaries. The aim of this study is to clarify the mechanism on how the carbides interact with the oxygen impurities and the molybdenum matrix, thus to provide a better understanding for designing molybdenum alloy compositions. Molybdenum alloyed with 4500 μg/g carbon was manufactured in the additive manufacturing process of Laser Powder Bed Fusion (LPBF). The cellular grain structure of molybdenum cells with surrounding molybdenum carbide caused by constitutional undercooling during the solidification process was investigated by Transmission Electron Microscopy (TEM) for morphology, composition and crystal structure. The carbide was identified to be orthorhombic ζ-Mo2C, which has a solubility for oxygen. ζ-Mo2C shows a semi-coherent interface with α-Mo. No cracks could be found at the α-Mo / α-Mo or the α-Mo / ζ-Mo2C interfaces. Oxygen could not be detected at grain boundaries, but only within ζ-Mo2C, which traps the oxygen, thus avoiding oxygen segregation to the grain boundaries and improving the grain boundary strength.

Magnetron Sputtered Silicon Coatings as Oxidation Protection for Mo‐Based Alloys

Mo‐based alloys with solidus temperatures around and above 2000 °C are attractive high‐temperature structural materials for future applications in the hot section of gas turbines. However, their oxidation behavior is poor due to pesting starting at 600 °C and nonprotective oxide growth at temperatures above 1000 °C. To ensure a sufficient oxidation resistance over a wide temperature range, protective coatings become inevitable. Herein, silicon coatings have been applied by magnetron sputtering on Mo‐9Si‐8B and on titan–zirconium–molybdenum alloy (TZM). The coating architecture is designed to minimize the intercolumnar gaps and porosity, thereby increasing the density. Specimens are tested at 800 and 1200 °C in air isothermally for up to 300 h. The focus is put on the chemical reactions at the coating–substrate interface, the phase formation, and the evolution of the thermally grown oxide. An initially globular SiO2 evolves into a uniform SiO2 layer providing excellent oxidation protection. The investigations reveal a rather slow interdiffusion between the coating and the alloys when tested in air. At the coating–substrate interface exclusively, the Mo3Si phase develops. Finally, the phase formation at the coating–substrate interface is studied in detail for various heat treatments in air and vacuum.

Optimization of Heat Treatment Parameters of 25Cr–8Ni–4Mo–N Cast 5A Duplex Stainless Steel Using Thermodynamic Modelling and Taguchi Methodology

Duplex stainless steel (DSS) is having an equal fraction of ferrite and austenite. Chromium, Nickel, Molybdenum, and few minor alloying elements constitute a DSS system, which makes metallurgy of the system complex. Proper heat treatment is need of the hour when it comes to expecting desired properties from the material, subjected to a specific working environment. DSS is one of the favourite choices for oil and gas industries. This study focuses on optimizing the heat treatment parameters and heat treating the as-cast 5A DSS and investigating microstructural evolution of the material subjected to various quenchants such as brine, water, and polyethylene glycol. Heat treatment temperatures, quenching media, and the quenching time have been selected in accordance with ASTM standards. Thermocalc TCFE8 database is being used for understanding the material response to various heat treating temperatures.

A review and perspective on molybdenum-based electrocatalysts for hydrogen evolution reaction

Water electrolysis has been considered as a sustainable way for producing renewable energy of hydrogen. However, this process requires a low-cost and high-efficient hydrogen evolution reaction (HER) catalyst to improve the overall reaction efficiency. Molybdenum (Mo)-based electrocatalysts are regarded as the promising candidates to replace the benchmark but expensive Pt-based HER catalysts, due to their high activity and stability in a wide pH range. In this review, we present a comprehensive and critical summary on the recent progress in the Mo-based electrodes for HER, including molybdenum alloys, molybdenum sulfides, molybdenum selenides, molybdenum carbides, molybdenum phosphides, molybdenum borides, molybdenum nitrides, and molybdenum oxides. Particular attention is mainly focused on the synthetic methods of Mo-based materials, the strategies for increasing the catalytic activity, and the relationship between structure/composition and electrocatalytic performance. Finally, the future development and perspectives of Mo-based electrocatalysts toward high HER performance are proposed.

Passivation Charge Density of CoCrMo Alloy in Different Aqueous Solutions

Cobalt–Chromium–Molybdenum (CoCrMo) alloys are passive materials widely used in many engineering systems operating in aqueous solutions such as power plants and orthopedic implants. In these situations, material degradation occurs by the combined action of wear and corrosion (tribocorrosion). The cyclic loading in such tribological contacts causes a mechanical removal of the protective passive film of the CoCrMo alloys, depassivation, leading to a severe increase of their corrosion. The amount of charge needed to rebuild the passive film after the mechanical depassivation, passivation charge density, has been used to describe the wear accelerated corrosion of passive alloys. Theoretical mechanistic tribocorrosion models for CoCrMo alloys have been previously developed and highlighted passivation charge as a crucial parameter in the material removal rate. The passivation charge density depends in principle on different parameters, including the material, the electrode potential or the chemistry of the electrolyte. In this paper, the passivation charge density of a CoCrMo alloy has been systematically quantified and studied by electrochemical techniques and ex-situ surface analysis through X-ray photoelectron spectroscopy in different electrolytes, H2SO4, NaCl and calf serum solutions. A linear correlation between the passivation charge density of the CoCrMo and the applied potential was obtained independently on the solution chemistry.

Experimental Investigation of the Secondary and Backscatter Electron Emission from Spacecraft Materials

The emission of secondary and backscattered electrons influences spacecraft surface potentials and the surrounding plasma. Modern spacecraft use new materials for which secondary emission properties have been unavailable. In this work, the total electron yield (i.e., the sum of secondary and backscattered electron yields) was measured for niobium-C103 alloy, molybdenum Titanium, Zirconium, Molybdenum (TZM) alloy, tantalum-tungsten alloy, Elgiloy®, graphite lubricant (DAG 213®), and titanium nitride. The surface properties of tungsten were also measured for comparison with past test data. The materials were readied as spacecraft flight materials and temperature-treated (“annealed”) to predicted peak flight temperatures. The yield properties for 10 eV–5 keV incident electron energies for all samples were measured. Both unannealed and annealed states were tested, except DAG 213, which was only tested annealed. Three-parameter and four-parameter models were used to fit the secondary and backscattered electron yield data, respectively. The emitted electron energy distributions are also obtained and fit with a Chung-Everhart model for secondary electrons and a Gaussian function for backscattered electrons. The secondary and backscattered electrons’ current densities were calculated for different ambient plasma conditions. For ready reference, the normalized primary electron, secondary electron, and backscattered electron current densities versus ambient electron temperature were computed and plotted from 1 eV to 8 keV.

Highly Molybdenum-Alloyed Materials Hastelloy BC-1 (2.4708) and B3 (2.4600): Diffusion Bonding Experiments and Evaluation of both Mechanical Behavior and Corrosion Resistance in Hot 70% Sulfuric Acid

Sulfuric acid is a widely used raw material in the chemical industry. Its corrosive effect on materials varies considerably, depending on impurities, temperature and water content. This is an issue for micro process apparatuses with thin walls. Such devices are often joint by diffusion bonding what may alter materials properties due to high temperatures and long dwell times. In this paper, two high molybdenum alloys, namely Hastelloy B3 and BC-1, were investigated. Diffusion bonding tests were performed at different temperatures. Tensile tests were carried out for different material conditions, to determine the change in mechanical strength and elongation at fracture values. The fracture behavior of both alloys was ductile and the fracture surfaces showed dimple structure. For diffusion bonded samples, weak spots or rather non-bonded areas were found. These obviously caused the onset of material failure and thus, degradation of mechanical properties. Tensile samples, aged in 70% sulfuric acid at 100 °C for 1000 h showed local corrosion attacks at the grain boundaries at the circumferential surfaces and joining planes—for Hastelloy B3 more pronounced than for Hastelloy BC-1. Accordingly, a further decrease of stress and elongation at fracture values was observed. However, 0.2% yield strength used for dimensioning components are found to be reasonable. As conclusion, at least Hastelloy BC-1 reveals both good mechanical properties and an excellent corrosion resistance, regardless of the heat treatment. This is a significant advance compared to the results obtained from a previously research project on four different alloys.

Features of electron beam welding of molybdenum alloy ZrMo2А

ABSTRACT The paper demonstrates the positive experience of fighting hot cracks in electron beam welding of molybdenum alloy СМ2А by double passage by an electron beam, which led to a decrease in the content of harmful impurities in the seam. The structure of the compounds obtained is shown, and their hardness and the content of harmful impurities are measured.

Fiber laser spot welding of molybdenum alloy in a hyperbaric environment.

The effect of the growth of ambient pressures on the penetration of laser welded molybdenum (Mo) alloy was explored. It was found that when ambient pressure rose from 0.1 MPa to 1.8 MPa, the penetration of base metal (BM) was significantly reduced, which was only 17% of that obtained under ambient pressure of 0.1 MPa. Moreover, the mechanism underlying the significant reduction of the penetration of BM was analyzed. At first, by using a high-resolution scanning electron microscope (SEM), the size and the number of nano-sized metallic particles generated during laser welding under different ambient pressures were surveyed. Furthermore, the scattering and absorption of the nano-sized metallic particles for laser energy under different ambient pressures were investigated; afterwards, by applying a high-speed camera and a spectrometer, the transient behaviors and spectral signals of plasmas during fiber laser spot welding under different ambient pressures were monitored. On this basis, the inverse bremsstrahlung absorption of plasmas for laser energy under different ambient pressures was explored; finally, fiber laser spot welding test was carried out on glass/metal composite samples under different ambient pressures to survey the influence of the change of ambient pressure on dynamic behaviors of the molten pool during the welding.

Five million wear simulation and particle analysis of carbon-based nano-multilayer coatings titanium alloy femoral head

Objective: To analyze the wear debris characteristics ofcarbon-based nano- multilayer coatings on Ti(6)Al(4)V alloys and compared with the cobalt chromium molybdenum alloy (CoCrMo) femoral head to evaluate the friction and wear performance of the new coated femoral head. Methods: Three groups were set up in the wear simulation experiment according to the type of femoral head. Group A: imported Cobalt-Chromium-Molybdenum alloy femoral head (CoCrMo); group B: Titanium alloy femoral head (Ti(6)Al(4)V) with carbon-based nano-multilayer coatings; group C: domestic Cobalt-Chromium-Molybdenum alloy femoral head (CoCrMo). All heads were jointed with an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. Serum samples were collected and stored in the hip joint simulator. After the sample has been digested and diluted, it was filtered through 5 μm, 1.2 μm and 0.4 μm filters, and the filter paper was collected for testing. Scanning electron microscope (SEM) was used to randomly select regions on the filter to obtain images of wear debris. Energy dispersive X-ray spectroscopy (EDS) was used to determine the elemental type of the particle and to eliminate possible contamination. The composition and structure of the abrasive chips were measured using Fourier transform infrared spectrometer (FTIR). The parameters related to the wear debris includingparticle size, shape, number and volume were calculated. The differences in correlation parameters between the groups were compared to evaluate the friction and wear properties of the new coated joints. Results: The main component of the wear debris produced was UHMWPE, and the particle size was mostly below 1 μm. The submicron particle ratio of group B was 49.4%, which was significantly lower than that of the group A and C (75% and 60%, respectively; χ(2)=66.032, 31.754, both P<0.017). The shape was mainly round, and there was no statistical difference between the groups (χ(2)=0.590, P=0.744). The number of particles in group B was significantly less than that of group C on all filters (t=9.960, 8.019, 5.790, all P<0.01), and less than group A on the 0.4 μm filter (t=7.810, P=0.000). Conclusion: The frictional wear performance of the new carbon-based nano-multilayer coatings femoral head is significantly better than that of the domestic femoral head, and even partially exceeds the imported femoral head level, which helps to reduce the production of particles and prevent osteolysis and aseptic loosening induced by UHMWPE particles.

Research Status and Progress of Welding Technologies for Molybdenum and Molybdenum Alloys

Owing to its potential application prospect in novel accident tolerant fuel, molybdenum alloys and their welding technologies have gained great importance in recent years. The challenges of welding molybdenum alloys come from two aspects: one is related to its powder metallurgy manufacturing process, and the other is its inherent characteristics of refractory metal. The welding of powder metallurgy materials has been associated with issues such as porosity, contamination, and inclusions, at levels which tend to degrade the service performances of a welded joint. Refractory metals usually present poor weldability due to embrittlement of the fusion zone as a result of impurities segregation and the grain coarsening in the heat-affected zone. A critical review of the current state of the art of welding Mo alloys components is presented. The advantages and disadvantages of the various methods, i.e., electron-beam welding (EBW), tungsten-arc inert gas (TIG) welding, laser welding (LW), electric resistance welding (ERW), and brazing and friction welding (FW) in joining Mo and Mo alloys, are discussed with a view to imagine future directions. This review suggests that more attention should be paid to high energy density laser welding and the mechanism and technology of welding Mo alloys under hyperbaric environment.

Oxide-fibre/molybdenum-alloy-matrix composites: A new way of making and some mechanical properties

Ultra-high temperature metal matrix composites are to be constructed using a sufficiently strong refractory matrix. Oxide fibres are primary candidates to reinforce molybdenum matrix by the internal crystallisation method. However, strong molybdenum alloys have not been used as the matrix until recently because the matrix preparation requires the alloys in form of foil and wire, which are not available. Hence, a way to strengthen pure molybdenum is now found through introducing reinforcing phases into it on the stage of matrix preparation prior to its reinforcement by oxide fibres. This communication presents the results of first experiments which show that such modification of the matrix yields composites of high strength at temperatures up to 1400 °C. The composites are characterized by sufficiently high fracture toughness at room temperature.

Контактные взаимодействия при обработке абразивным потоком средой высокой вязкости заготовок из сплавов порошкового молибдена

Контактные взаимодействия при обработке абразивным потоком средой высокой вязкости заготовок из сплавов порошкового молибдена

Microstructural features of biomedical cobalt–chromium–molybdenum (CoCrMo) alloy from powder bed fusion to aging heat treatment

The design freedom of powder bed fusion process selective laser melting (SLM) enables flexibility to manufacture customized, geometrically complex medical implants directly from the CAD models. Co-based alloys have adequate wear and corrosion resistance, fatigue strength, and biocompatibility, which enables the alloys to be widely used in medical devices. This work aims to investigate the evolution of microstructures and their influence on tribological property of CoCrMo alloy processed by SLM and aging heat treatment. The results showed that very weak <110> texture along the building direction and microsegregation along cellular boundaries were produced. The presence of high residual stress and fine cellular dendrite structure has a pronounced hardening effect on the as-SLM and aging-treated alloys at moderate temperatures. Furthermore, the hexagonal ε phase transformed from the γ matrix during SLM became significant after subsequent aging at moderate temperatures, which further increased the nanohardness and scratch resistance. High temperature (1150 °C) heating caused homogenized recrystallization microstructure free of residual stress and ε phase, which sharply decreased the hardness and scratch resistance. The material parallel to the building direction exhibited improved tribological property in both SLMed and aging-treated alloy than that of the material perpendicular to the building direction. The anisotropy in frictional performance may be considered when designing CoCrMo dental implants using laser additive manufacturing.

Molybdenum alloying in high-performance flat-rolled steel grades

Considerable progress in developing flat-rolled steel grades has been made by the Chinese steel industry over the recent two decades. The increasing demand for high-performance products to be used in infrastructural projects as well as in production of consumer and capital goods has been driving this development until today. The installation of state-of-the-art steel making and rolling facilities has provided the possibility of processing the most advanced steel grades. The production of high-performance steel grades relies on specific alloying elements of which molybdenum is one of the most powerful. China is nearly self-sufficient in molybdenum supplies. This paper highlights the potential and advantages of molybdenum alloying over the entire range of flat-rolled steel products. Specific aspects of steel property improvement with respect to particular applications are indicated.

Mechanical properties and strengthening mechanism of the hydrothermal synthesis of nano-sized α-Al2O3 ceramic particle reinforced molybdenum alloy

Nano-sized α-Al2O3 ceramic-particle-reinforced molybdenum alloy plates were fabricated by a series of processes including hydrothermal synthesis, powder metallurgy, and rolling. The quantitative effect of α-Al2O3 ceramic (particle size and volume fraction) on the microstructures and mechanical properties of molybdenum alloy plates was investigated. Nano-sized α-Al2O3 ceramic particles were obtained and uniformly dispersed in the molybdenum matrix. The α-Al2O3 ceramic refined the molybdenum grains and remarkably increased the microhardness, elastic modulus, and yield strength. The yield strength of the alloy reached a peak value when the α-Al2O3 ceramic content was 1.28 vol% and increased by 61.07%–90.2% compared with that of pure molybdenum after annealing at 1000 °C-1300 °C. A quantitative yield strength model correlating α-Al2O3 particle size, α-Al2O3 volume fraction, molybdenum grain size, and annealing temperature was built. This model attributes the strengthening of alloy to the synergy effects of grain refinement strengthening (σHP) and Orowan strengthening (σp). The addition of fine α-Al2O3 ceramic resulted in Orowan strengthening and fine molybdenum grains, thereby increasing yield strength of alloy.