Crack-free densification of ceramics by laser surface treatment

Laser surface melting and re-solidification has been applied to eliminate pores and create homogeneous surfaces in refractory ceramics, improving the high-temperature degradation resistance of such materials. The major problem in laser surface treatment of ceramics is the formation of cracks during cooling. Efforts have been made to eliminate this problem by applying pre- and post-heating techniques, as well as dual laser beam systems. Even though such efforts have been partially successful, they lack practicability. This paper reports on the formation of fully densified and crack-free surfaces of refractory ceramics by melting and re-solidification using a single laser beam in a one-step process, without applying any pre- and post-heating techniques. Formation of cracks was avoided due to modification in the heat transfer conditions on the material surface, resulting in slower surface cooling rates. The reduction in heat transfer rates led to change in the thermal shock conditions to which the material surface was subjected, since a constant cooling rate was established during the transition from plastic to elastic behaviour of the treated surface. (c) 2006 Elsevier B.V. All rights reserved.