Effect of Nd–YAG laser irradiation on surface microstructure of single crystal tungsten

Abstract

A number of interesting phenomena were observed in laser irradiated zones on single crystal tungsten surfaces during manufacture of ultrafine tungsten particles using a short pulse Nd–YAG laser in a low pressure inert gas atmosphere. Three patterns, square, rectangular, and triangular, were observed in the laser irradiated zone on three types of single crystal tungsten surface, namely (100), (110), and (111). These patterns were related to the cleavage plane of the tungsten. That is, under irradiation, cleavage fracture occurs in the crystal direction with weakest binding energy. At the same time, a coherent array of particles of about 500–800 nm diameter was observed around the laser irradiated zone on the single crystal tungsten surfaces. It is postulated that formation of the coherent arrays depends on the rapid solidification produced by laser irradiation, on crystal growth, and on crystal surface structure, rather than on the optical characteristics of the laser.