Tribological Properties Of Several Typical Plasma Spray Coatings In Water Environment

Many mechanical equipment running in water environment,such as pump shaft of water pump often failed before an expected life due to the abrasion,while surface treatment technology which prepare the wear-resistant coatings on the surface of wearable parts have been shown to increase its service life effectively.In this paper,Al₂O₃-TiO₂,NiCrBSi（Ni60AA）andWC/NiCrBSi（WC content is 30 wt.%,marked as 30WC）coatings were deposited successfully on the surface of 316 stainless steel substrate by means of plasma spraying,then NiCrBSi and WC/NiCrBSi coatings were heat-treated under 980℃ for 20 min in an tube furnace（respectively marked as Ni60 AAT and 30WCT）.The tribological properties of Al₂O₃-TiO₂,NiCrBSi,WC/NiCrBSi and the heat-treated coatings were studied in ambient air and distilled water under laboratory conditions,failure mechanisms were investigated combining with the coating microstructure,several conclusions were listed as follow:1.The Al₂O₃-x TiO₂（x = 0%,3%,0%,3%,40%）coatings prepared by plasma spraying combined well with the 316 L substrate,coating thickness was controlled between 100 to 200μm.With the increase of TiO₂ content,coating the main phase of the Al₂O₃-TiO₂ coatings transformed from γ-Al₂O₃ to Al₂TiO₅ phase;and the microhardness of the coatings gradually reduced from 1274.4 Hv_0.5 of the pure Al₂O₃ coating to 708.9 Hv_0.5 of AT40 coating;The coating porosity present a trend of decrease.2.In the atmosphere environment,the AT3 coating showed the best antifriction and wear resistance,friction factor is 0.55,the volume wear rate was 5.16 x 10^-6mm³·N^-1m^-1.Al₂O₃ and AT3 coatings occured stress fatigue wear;while AT13,AT20 and AT40 coatings occured strain fatigue wear.In water environment,the Al₂O₃ coating showed best antifriction property,friction factor is 0.34,while AT20 coating showed the best wear resistance whose wear rate was 3.53 x10^-6mm³·N^-1m^-1.The five composite ceramic coatings all occured stress fatigue wear.3.Ni60 AA coating is mainly composed of γ-Ni,CrB,Cr₇C₃ and Cr₂₃C₆ phase.Ni60 AA heat-treated coatings phase organization changed,and the hard phase precipitation was mainly composed of Cr₂₃C₆ phase,and the typical lamellar structure disappeared.Heat-treatment improved the plasma sprayed Ni-base coatings hardness,while the porosity is reduced.4.Heat-treatment improved the wear resistance of the corresponding coating accordingly.In ambient air and distilled water conditions,30 WCT coating showed the best wear resistance.During dry wear,when sliding against GCr15 ball,Ni60 AA and 30 WC coatings mainly occured fatigue wear,while Ni60 AAT and 30 WCT coatings were mainly occurred adhesive wear;when sliding against Si₃N₄ ball,all the four kinds coatings occured fatigue wear.In water environment,when sliding against GCr15 ball,Ni60 AA and 30 WC coatings occured fatigue wear,while Ni60 AAT and 30 WCT coatings mainly occured adhesive wear;when sliding against Si₃N₄ ball,Ni60 AA coating occur fatigue wear,and the main wear of 30 WC coating was the fatigue spalling of WC particle,while the The wear mechanism of 30 WCT and Ni60 AAT coatings was mainly dhesive wear.