Molybdenum metal have high brittleness and ductile-to-brittle transition temperature (DBTT) due to the existence of interstitial oxygen impurities, so it is of great scientific significance to strictly control and accurately analyze the oxygen content. In this work, the effects of oxygen on microstructure and evolution mechanism of body-centred-cubic metallic molybdenum are studied. The X-Ray diffraction (XRD), oxygen nitrogen analyzer, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electron probe micro-analyzer (EPMA) are used to analyze the chemical composition, microstructure, oxygen existence and distribution form. The results demonstrate that Mo O specimens with up to 3300 ppm of oxygen content have single-phase body-centered cubic microstructure with no precipitates. When the oxygen content in molybdenum increases from 44 ppm to 2200– 3300 ppm, more oxygen exists in the pores between molybdenum grains, and the fracture mode changes from intergranular fracture to intergranular and transgranular mixed fracture. The microhardness increases with increase of oxygen content. These results provide new ideas for controlling the change trend of oxygen in molybdenum and regulating the properties of molybdenum.
Current machinery requires metallic materials to have better surface properties. Based on an orthogonal experimental design and analysis method, the CeO 2 -reinforced nickel nano-composite coatings were prepared by direct current electrodeposition in a nickel sulfate bath containing CeO 2 nanoparticles. Statistical results indicate that current density is the most significant variable in the electrodeposition processing, while temperature is the least important factor. The microstructure of Ni and Ni–CeO 2 nano-composite coatings was characterized by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The microhardness of the Ni coating is enhanced by the incorporation of CeO 2 nanoparticles. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to characterize the corrosion behavior of Ni and Ni–CeO 2 coatings. These studies show that Ni–CeO 2 coating has better corrosion resistance compared to Ni coating.
The eutectic FeNiCoCrTi0.6Nb0.4 high-entropy alloy coating (HEAC) is annealed in Argon at 450°C, 850°C and 1050°C to investigate the thermal stability. The results show that annealed coatings are all composed of BCC solid solution and Laves phase with no production of new phases. The fine eutectic cells can be maintained at a higher temperature in that continuous intracellular coarsening does not occur until annealing at 1050°C. With the increase of annealing temperature, the microhardness and wear resistance of FeNiCoCrTi0.6Nb0.4 coating increase first and then decrease slightly. Especially, the microhardness of FeNiCoCrTi0.6Nb0.4 annealed at 1050°C is only 6.03% lower than that of unannealed one, and the wear rate is only 10.70% higher than that of unannealed one, which strongly indicates that eutectic FeNiCoCrTi0.6Nb0.4 HEAC has excellent thermal stability and can be well applied in high-temperature environments.
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