Composite Fretting Wear Performance Of HVOF Sprayed WC-CoCr Coatings

Tangential, radial, rotational, and torsional fretting are four basic types of frettingrunning modes. Presently, the absolute majority of researches have been focused ontangential fretting, and the research concerning composite fretting compounded oftwo basic modes has not been reported so far. In this dissertation, the rotationalfretting tests of the substrate(45#steel) and HVOF sprayed WC-CoCr coating havebeen carried out in the high-precision fretting wear test machine under differentamplitudes of40μm,80μm,120μm by using the ball-on-flat contact configuration.Fretting wear dynamic analyses in combination with the microscopic examinationssettled by micro-hardmeter, optical microscopy(OM), scanning electronmicroscopy(SEM), energy dispersive spectroscopy(EDX), X-ray diffractometer(XRD)and profilometer have been systematically utilized to study the fretting runningbehaviors and damage mechanisms of coatings. The main conclusions are as follows:(1) Here were three basic types of load-displacement(F-D)curves includingqusi-trapeziform cycle, elliptic cycle and linear cycle. and some other types of curveunder special conditions, including quasi-triangle cycle, quasi-tetragonal cycle andnot-closed oval cycle. According to the three types of F-D curve, the kinetic processof composite fretting might be outlined as three stages.(2) The variations of the load-displacement curves as function of number ofcycles were strongly depended upon the displacement amplitudes, surface roughnessand the characteristics of materials.(3) Compared the dynamic behaviors of45#steel with WC-CoCr coating, whenthe amplitude was40μm, the fretting of45#steel ran in partial slip region, while theWC-CoCr coating ran in mix region. When the amplitude was80μm, the appearanceof stage I and II was deferred with the increase of amplitude, although the amplitudewas80μm, the fretting of WC-CoCr coating always ran in elastic-plastic behavior anddemonstrated stable wear because that the high hardness of WC-CoCr coating couldplay a good protection effect.(4) Three kinds of F-D curve corresponding to different damage stages wasanalyzed in detail, which revealed that the main feature of wear in stage I weremicro-cutting and sticking, and the main mechanism was particles detachment bydelamination in stage II and III, while the degree of damage of45#steel was moreserious than WC-CoCr coating. (5) The main damage mechanism of45#steel was abrasive wear, adhesive wearand oxidation wear, material loss mainly due to micro-cutting, plastic deformation andlayers peeling. Whereas WC-CoCr coating had excellent resistance to compositefretting wear, and the wear mechanism was fatigue wear, layer stripping methodsleads to debris peeling as lamellar.