ENVIRONMENTAL EFFECTS ON FRETTING WEAR

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In this work, we examined the fretting wear properties of Zr-alloy under dry in air, in distilled water and in Na_2SO_4solution. Zr-alloy is used as fuel rods in the reactor of nuclear power plan. Furthermore, we examined the corrosive wear mechanism to understand the mechanism of fretting wear in corrosive environment. The critical slip amplitude of the fretting was 100 μm in air and in distilled water for the apparatus of Kyungpook University. As load increased, wear increased. But wear decreased with increasing load in distilled water, which was caused by the change in slip regime from gross slip to partial slip.In corrosive wear, which was examined using the reciprocating sliding wear apparatus, the parameters were solution concentration from lO^<-1> mol/l to 10^<-5> mo1/1, potential, load and anode area / cathode area ratio. As corrosive wear consisted of mechanical wear and electrochemical wear, mechanical wear was obtained in pure water. In the corrosive wear in Na_2SO_4 solution, the effect of concentration on wear volume appeared above 10^<-3> mol/l, and it increases with potential. The effects of load and area ration on wear and free potential drop were examined. The increase in load results in the increases in wear and potential drop. This is caused by the increase in fresh surface exposed. The contribution of electrochemical factor was obtained from the difference between total wear volume and wear volume in pure water. It was about 15 % in this case. The increase in potential meant that the electrochemical effect on wear (dissolution of metal) was reduced because of the decrease in anodic current density. Wear decrease with increasing the area ratio due to the increase in the potential drop.As the fretting wear has small wear scar, and the very low area ratio, the electrochemical contribution would increase.More investigation is needed for getting the data at high temperature and high ambient pressure like nuclear power reactor.