Investigation Of Plasma Sprayed Mo Coating On Piston Skirt Surface

In this paper, Mo coatings were fabricated on cast iron substrate using a plasma spray technique. To get the optimized parameters of plasma sprayed Mo coatings through orthogonal experiment with the bonding strength, porosity and microhardness as comprehensive index. The microstructure and phase structure of Mo coatings which prepared with the optimized parameters were studied by means of SEM, EDS, XRD, etcetera, and the bonding strength, porosity microhardness and porosity of the coatings were determined; the thermal fatigue and frictional behaviour of the coatings were evaluated by thermal fatigue tests and wear tests; the feasibility of improving the comprehensive properties of Mo coating was studied through ultrasonic impact treatment. Within the processing parameters of this experiment, the results of the study revealed that:The effect of plasma spraying parameters on the comprehensive performance of coating is as follows: spray Power> primary gas flow > spray distance > powder feeding rate. Mo coatings were fabricated with the optimized parameters, bonding strength is obtained to be 67.161 MPa, porosity of 5.78%, micro-hardness of 310 HV.No oxidation behavior of plasma spraying process, the coating is dense and uniform, combined with good, by means of mechanical anchoring. The surface and cross-sectional micro-hardness of Mo coating has greatly dispersion, and the former is higher than the latter, they significantly conform to weibull distribution.Mo coating has good thermal fatigue life, which reaches higher number of macro-crack initiation and failure times. It transformed to Mo O and Mo O3 during the thermal cycling process. The hardness of coating increased after thermal shock, but there is still a large dispersion.Under the dry friction condition the wear resistance of cast iron substrate is better than that of coating. In the room temperature, the main wear mechanism of Mo coating is fatigue and oxidation wear; and the main wear mechanism of substrate are adhesive wear and abrasive wear, accompanied by oxidation wear.Under the lubrication condition the friction properties of the coatings has been significantly improved, the friction coefficient of coating increases with the increase of load, decreases with the increase of rotational speed. The Wear resistance of coating is better than that of the substrate under the same conditions. In the room temperature, the wear mechanism of substrate is the same as the dry friction condition, but the wear mechanism of coating has changed, which is adhesive wear accompanied by oxidation wear.Ultrasonic impact treatment technology can significantly improve the comprehensive performance of Mo coating. The surface roughness of coating decreases from 35.279 um to 2.845um;surface hardness increases about 35%; porosity of near surface layer decreased by 41.4%; thermal fatigue life of the coating is improved in a certain extent.