Wear And Corrosion Resistance Of Double Glow Plasma Surface Alloyed Zirconium

Zirconium and its alloys have excellent nuclear properties and good corrosion resistance,but the strength and hardness of them are not high,and their mechanical properties and wear resistance need to be further improved.In addition,in order to take full advantage of their characteristics,zirconium and its alloys are mostly used in very harsh environments,such as high-energy particles,radiation,corrosive solutions,etc.,which destroy the zirconium materials and impose more stringent requirements on their properties.A large part of the failure of zirconium is initiated from the surface,and wear and corrosion on the surface are the most common form of damage to zirconium alloys.Therefore,it has become an important research topic to further improve the mechanical property and chemical stability of zirconium and its alloys by surface treatment.In this study,pure zirconium was copperized,carburized,Fe permeated and nitrided on the surface by double glow plasma surface alloying technique.The change of the wear resistance and corrosion resistance of the samples before and after alloying and the mechanism were discussed.It provided reference for surface alloying treatment of zirconium alloys.The influence of process parameters on the alloying layer was studied through the orthogonal experiments.The microstructure,composition and morphology of alloyed layer were analysed by means of X ray diffraction and scanning electron microscopy.The friction and wear behavior of the alloyed layers were analyzed by the measurement of the friction coefficient and wear profile,and the calculation of the specific wear rate.And the electrochemical corrosion behavior of the alloyed layers was analyzed by detecting the polarization curves of the alloyed layers in 3.5%NaCl,0.5 mol/L NaOH and 0.5 mol/L H₂SO₄ solutions.The result shows that,with Cu,C,Fe and N as alloying elements,the alloyed layers were formed on the surface of pure zirconium by double glow plasma surface alloying technique.The layers were generally homogeneous,dense,with no obvious crack or other defects,and robustly adhered with the matrix.Taking the thickness of copperized layer as the evaluation index,the L₉?3⁴?orthogonal experiment was designed for the four main experimental factors which affect the alloyed layer.It was obtained that the degree of influence of various factors on the thickness of alloyed layer from large to small order:electrodes spacing>time>temperature>pressure.X ray diffraction analysis showed that the alloyed layers were mainly composed of intermetallic compound of alloying elements and zirconium,which improve the surface hardness of the alloyed layer.The friction and wear behavior test showed that surface alloying is beneficial to improve the wear resistance of zirconium matrix,and the wear volume and specific wear rate of the alloyed samples are lower than those of pure zirconium.The wear volume and specific wear rate of copperized layer decreased to 45%⁷1%of pure zirconium;the wear volumes and specific wear rate of Fe permeated,carburized and nitrided layers decreased by an order of magnitude more than that of pure zirconium.The wear mechanisms of pure zirconium and copperized,carburized and Fe permeated layers are mainly adhesive wear and abrasive wear,while the wear of nitrided layer is characterized by fatigue wear and abrasive wear.The friction coefficient of all the alloyed layers were lower than that of pure zirconium,and it increased with the increase of load.Polarization curves showed that the corrosion resistance of zirconium in 3.5%NaCl and 0.5mol/L NaOH solutions can be improved by surface alloying treatment.In NaCl solution,the corrosion potential of the copperized,carburized and nitrided layers had a positive shift of 10 mV,50 mV and 186 mV compared with that of pure zirconium,respectively,and the corrosion current density decreased to 76.6%,38.3%and 88.5%of pure zirconium,respectively.Although the corrosion potential of the Fe permeated layer had a little negative shift?12 mV?compared with that of pure zirconium,the corrosion current density of the Fe permeated layer decreased to 55.5%of pure zirconium.In NaOH solution,the corrosion potential of the copperized,carburized,Fe permeated and nitrided layers had a positive shift of 111 mV,419 mV,220 mV and 226 mV,respectively,and the corrosion current density were reduced to 13.8%,96.6%,60.5%and 17.6%of pure zirconium,respectively.