MODIFICATION OF GAS-THERMAL COATINGS THROUGH СО2 LASER IMPACT

Abstract

The research results on determining the dependence of gas-thermal coating porosity on the laser radiation parameters are presented. At the first stage of solving the problem, on the basis of the analytical relationships, laser impact on the surface layers of the gas-thermal coating is described. Here, its discontinuity caused by the occurrence of open and closed pores is recognized. It is shown that for reducing the coating porosity under the laser impact, the coating surface temperature is to be set in the range of “fusion point-boiling point”. A temperature rise above this range caused by the radiation intensity increase leads to evaporation of surface coating layers through its complete removal in the heat effected zone. At the second stage, field research is conducted: pre-sprayed gas-thermal coatings of two types are processed by laser. The coatings based on the metallic (PN-85-U-15) and non-metallic (Al₂O₃) components are studied. The porosity modification is evaluated quantitatively using the image processing program developed in Visual Studio 2008 by pixel comparison of microstructure of the area occupied by pores and the coating material. It is established that the laser impact leads to decreasing in the average porosity of the gas-thermal coatings. Porosity of the coating based on the PN-85-U-15 alloy decreases from 17 % at the initial state to 5–8 % after the laser treatment. The corresponding figures for the ceramic coating Al₂O₃ are 24.5 % and 15–18 %.