Research On Processing And Corrosion Resistance Of Ta Modified Layers On Q235Steel Formed By Double Glow Plasma Surface Alloying

Q235steel has wide application prospect in petrochemical industry due to its good strength,goodductility and cheapness,but it also has a poor corrosion resistance performance.Tantalum has the bestcorrosion resistance in all rare metals,but tantalum is very expensive.To solve this problem, a Tamodified layer is explored for the surface modification of Q235steel using double glow plasmasurface alloying technique. This paper first studies the processing of plasma tantalizing on Q235steeland the microstructure, composition and phase structure of the surface modified layers areanalyzed.Subsequently, the hardness, critical load values and wear resistance of the modified layersare tested. And the research focuses on the corrosion resistance of the modified layers which is in thestrong reductive acid and sodium chloride solution.The results indicated that the process parameters are justified as follows: source voltage:900~950V, cathode voltage:300~450V, processing temperature:950℃, diffusing time:3h, workingpressure:30Pa, distance between source cathode and work-piece:15mm. The modification layer ishomogeneous, continuous, and dense, the effective thickness of modified layers is about33μm andthe elements distribute gradually from the surface to substrate. XRD shows that α-Ta is the majorphases of modified layer.Scratch testing shows that the modified layer is well adhered to thesubstrates. The modified layer enhanced the micro-hardness and wear resistance of the substrate. Theresults of polarization curves shows that the open circuit potential, the corrosion potential andpolarization resistance of Ta modified layer in3.5%sodium chloride and3.5%hydrochloric acidsolution were higher than the substrate.The electrochemical impedance spectroscopy shows that thecapacitance amplitude, IF phase angle peak phase angle and its frequency range are greater than thesubstrate.Ta modified layer exhibited the better corrosion resistance. The neutral salt spray tests showthat, after20days, compared with the modified layer, the substrate loss more weight. Indicating Tamodified layer well protected substrate in artificially accelerated conditions.Immersion tests show that,soak for30days, the substrate loss more weight and corrosion is more serious.Ta modified layer caneffectively protect the substrate and significantly improve the corrosion resistance of the matrix.