Ta And W-Ta-V-Cr Surface Alloying On Pure Tungsten

Tungsten and tungsten alloy materials are widely applied in weapon equipment,nuclear fusion development,aerospace and electronic information and other advanced technology fields due to its high melting point,high hardness,high thermal conductivity,excellent high temperature strength and strong neutron irradiation resistance.However,with the development of science and technology and the expansion of the application field of tungsten materials,their performance need to be further improved.A large part of the failure of tungsten is initiated from the surface,and wear and corrosion are the main surface degradation or failure modes of the tungsten materials during operation.It is an effective way to combat surface damage and then obtain an increased service lifetime of tungsten and its alloys by surface modification technology.In this study,Ta alloyed layers and W-Ta-V-Cr alloyed layers were prepared by double glow plasma surface alloying technology on pure tungsten.The microstructure,composition and morphology of alloyed layers were studied by means of SEM,EDS and XRD.The change of the mechanical properties,wear resistance and corrosion resistance of the samples before and after alloying and the mechanism were discussed.The main research results are as follows:(1)The Ta alloyed layers and W-Ta-V-Cr alloyed layers were successfully fabricated on pure tungsten using double glow plasma alloying technique.The alloyed layers indicated a dense and homogeneous microstructure with no obvious defects such as pores and cracks.Ta alloyed layers were mainly composed of pure Ta phase and its thickness increases with the increase of temperature.Only BCC structure solid solution phase was formed on the surface of W-Ta-V-Cr alloyed layers,and the maximum thickness of the alloyed layer was 8.57?m.(2)The results of mechanical properties showed that:The surface microhardness of Ta alloyed layers and W-Ta-V-Cr alloyed layers was significantly higher than that of the substrate,and the fracture toughness was lower.Further,the W-Ta-V-Cr alloyed layers have a higher surface hardness and a smaller reduction in fracture toughness,showing relatively good comprehensive mechanical properties.(3)The friction and wear results showed that:1)The Ta alloyed layers prepared at different temperature did not improve the wear resistance of the substrate,this is because the surface brittleness of the tantalum layers increased,and the alloyed layers broke locally under the effect of friction pair,which aggravated the wear.2)The wear resistance of W-Ta-V-Cr alloyed layers was superior to that of pure tungsten.The specific wear rate of samples at1200?+1000?was 5.60×10^-6 mm³/(N·m),which was one order of magnitude smaller than that of the substrate(4.66×10^-5 mm³/(N·m).3)The wear scar morphology analysis results showed that the wear mechanism of tantalum alloyed layers was contact fatigue,abrasive wear and oxidation wear.The wear mechanism of W-Ta-V-Cr alloyed layers was oxidation wear and abrasive wear.(4)Electrochemical test results showed that both Ta alloyed layers and W-Ta-V-Cr alloyed layers can improve the corrosion resistance of pure tungsten in 3.5 wt%Na Cl solution.The W-Ta-V-Cr alloyed layers prepared formed at1200?+1000?exhibited the best corrosion resistance,its self-corrosion potential had a positive shift of 146.34 m V,the corrosion current density was one order of magnitude less than that of the substrate.It meant that the alloyed layers had more difficult electrochemical reaction and lower corrosion rate in the3.5 wt%Na Cl solution.