Investigation of microstructure and wear properties of the coatings produced by HVOF in weldox steel surface

In this thesis study, it is aimed to improve the surface properties of Weldoks 700 steel. Three different coatings were coated on the Weldoks 700 steel surface using high speed oxyfuel (HVOF) spray method. The coating powder used was Diamalloy 2001, Sulzer Metco 5810 and Diamalloy 4454 commercial powders. The powders used contain NiCrBSi, WCCo and CoNiCrAlY, respectively. Constant parameters are used as overlay parameters. Microstructure, hardness and wear properties of the produced coatings have been examined in detail. Microstructure and phase composition of coatings were investigated by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffractogram (XRD), energy dispersive spectroscopy (EDS). Hardness measurements were made only on the upper surfaces of the coatings using a microhardness equipment. Wear tests of the substrate and coating layer were carried out under different loads by pin-on-disc method. During the wear tests the temperature change was determined by means of the thermal camera. NiCrBSi, WCCo and CoNiCrAlY based coatings have been successfully produced on the Weldoks 700 steel surface with HVOF. SEM and optical photographs show that coatings have a generally homogeneous structure. It is also seen that the manufactured coatings have a lamellar structure positioned parallel to each other. Microstructure was determined by XRD analysis of double and triple carbides and hard phases. The mean hardness values of the coatings varied from 285 HV0.5 to 740 HV0.5, respectively. There was a 2.8 times increase in hardness of the coatings to the lower layer (265 HV0.5). This increase in hardness is related to the hard-metallographic phases occurring in the coating layer. According to the wear tests, it was determined that the coated samples had better tribological performance than the lower layer. The lowest coefficient of friction was obtained in WCCo coatings with a loading of 0.315-0.414 (10N-15N-20N), depending on the applied load. The wear rate of this coating is in the range of ~ 2.05x10-3 mm3/N/m to ~ 3.22x10-3 mm3/N/m. Coefficient of friction and wear rates of coatings increased with increasing applied load. This has been associated with increased load, increased contact area between the wearing part and abrasive ball, and local low temperature increases detected with the thermal camera.