The effect of beam shape in laser surface treatment of ceramics

Abstract

Laser surface treatment of ceramics with melting and re-solidification is generally associated with the development of thermally-induced cracks. These cracks result from the low thermal conductivity of ceramic materials, their brittleness and high melting temperatures, which lead to the built-up of large temperature gradients. Avoiding crack-formation is possible by controlling the cooling rate and thermal gradient. This can be achieved by applying pre- and post-heating methods or by scanning the laser beam at relatively slow speeds. The latter technique has been successfully applied for the development of crack-free surfaces in alumina-based refractory ceramics. However, the relatively slow speed limits the practicability of the technique. This paper investigates the effects of various beam shapes on cooling rate and, hence, interaction time and processing speed. A commercial finite element package program (ADINA) has been used to simulate beam geometries, including, rectangular, line, triangular and rhomboid. The cooling rates associated with these beam geometries have been assessed and compared with those for the circular beam shape. Experimental results have been used to assess the reliability of the model predictions.Laser surface treatment of ceramics with melting and re-solidification is generally associated with the development of thermally-induced cracks. These cracks result from the low thermal conductivity of ceramic materials, their brittleness and high melting temperatures, which lead to the built-up of large temperature gradients. Avoiding crack-formation is possible by controlling the cooling rate and thermal gradient. This can be achieved by applying pre- and post-heating methods or by scanning the laser beam at relatively slow speeds. The latter technique has been successfully applied for the development of crack-free surfaces in alumina-based refractory ceramics. However, the relatively slow speed limits the practicability of the technique. This paper investigates the effects of various beam shapes on cooling rate and, hence, interaction time and processing speed. A commercial finite element package program (ADINA) has been used to simulate beam geometries, including, rectangular, line, triangular and rho...