Effect Of Argon Arc Remelting On Microstructure And Properties Of Ni-based Plasma Sprayed Coating

Wear and contact fatigue is the most important surface failure form of rotating parts.While plasma spraying is a technology that can effectively repair and strengthen such parts.But there are more micro defects in the as-sprayed coating,and the bonding between the coating and the substrate is mechanical combination.This defects affect the wear and contact fatigue properties of the plasma sprayedcoatings,thus limiting the application of the plasma sprayed coating in the more harsh conditions.TIG remelting is a post treatment technology that can effectively improve the performance of plasma sprayed coatings.Therefore,in order to expand the application scope of plasma sprayed technology and prolong its service life,it is necessary to intensively study the influence of TIG remelting on the microstructure and properties of plasma sprayed coatings.In this paper,the effect of TIG remelting on the microstructure,mechanical properties,wear and rolling contact fatigue properties of Ni-based plasma sprayed coatings were mainly studied.Firstly,the microstructure,phase composition and microhardness of the coating before and after remelting were analyzed with scanning electron microscope(SEM),energy spectrum analyzer(EDS),X ray diffractometer(XRD),transmission electron microscope(TEM)and microhardness tester.Secondly,the friction wear,corrosion wear and high temperature wear properties of the two coatings before and after remelting were tested.Finally,under pure fatigue and slip conditions,the contact fatigue properties of two coatings before and after remelting and the substrate materials were tested by roller-slip contact fatigue tester.The results of the study show that:(1)Remelting treatment can effectively eliminate micro defects such as oxide inclusions,pores and microcracks in Ni based plasma sprayed coatings,greatly reduce the porosity of the coatings,and make the bonding between the coating and the substrate change from mechanical combination into metallurgical combination.After remelting,the microhardness of the coating decreased somewhat,but the modulus of elasticity and fracture toughness improved significantly.(2)No matter in thefrictionwear test,corrosion wear test andin high temperaturewear test,the wear resistance of the remelting coating are better than that of the sprayed coating.In the friction wear test,the failure mode of the sprayed coatings is lamellar cracking and oxidation wear,and the failure mode of remelting coating is micro-scale abrasive wear and oxidation wear.In corrosion wear test,the failure modes of the sprayed and remelted coating under acidic conditions are corrosive wear,while in neutral and alkaline conditions abrasive wear is dominant.In the high-temperature wear test at 500°C,the failure mode of the sprayed coating is oxidative exfoliation and adhesive wear,whilethe failure mode of the remelted coatingis adhesive wear.(3)The Ni-based sprayed coating has poor contact fatigue property and is not suitable as a reference material for studying the contact fatigue performance of the remelted coating.Under the same experimental conditions,the fatigue life of the remelted coating is better than that of the surface hardened 45# steel,and the life dispersion is also lower than that of the latter.The fatigue life of the two specimens at 5% slip is slightly higher than that under pure rolling conditions.