Experimental Study of the Process of Borazon Grinding of Thermal Barrier Coating of ZrO

Abstract

When grinding thermo-barrier sprayed coatings, there is always a potential danger of damage due to cutting forces. It is also necessary to take into account grinding contact temperatures, the thermal field of which can cause large residual stresses, cracks and peeling of the sprayed layer from the base metal. The studies of this work are aimed at establishing the values of these factors depending on the cutting conditions and grain size of the borazon wheel. Experimental studies have shown that the values of the component of the cutting force Py, depending on the processing conditions, can reach values of the order of 30N. The values of the cutting force component Pz, depending on the processing modes, can reach values of 15–17N. Cutting forces do not cause temporary stresses that could lead to cracks in the deposited ZrO₂ layer. Contact temperatures when grinding the sprayed ZrO₂ layer can reach values of the order of 700 to 900 ℃. The heat field during the passage through the thickness of the sprayed layer weakens sharply and at a depth of 2 mm from the surface (thickness of the deposited thermal barrier layer) reaches values close to room temperature, which eliminates the exfoliation of the thermal barrier layer during grinding. The residual stresses arising under the action of contact temperatures on the surface reach significant values of the order of 800 to 900 MPa, however these values are less than the thermal barrier layer strength and do not lead to cracks, naturally within the limits of the processing modes under study. Throughout the thickness of the thermal barrier layer, the residual stresses decrease and at the interface of the “sprayed layer - metal” reach values of the order of 10–15 MPa, which does not cause peeling of the sprayed layer. The amount of surface roughness when grinding a thermal barrier coating with borazon wheel LO 125/100 C10 100% LO 160/125 C10 100%, LO 250/160 C10 100%, then take Nz12, Nz16, Nz25, is within Rz 1.5–2.5 mcm.