The Effect of Laser Heating on the Ductile to Brittle Transition of Silicon Carbide

Semiconductors and ceramics, such as silicon carbide, share common characteristics of being nominally hard and brittle, which stems from their covalent chemical bonding and crystal structure. These materials are important in many engineering applications, and are particularly difficult to machine in traditional manufacturing processes due to their extreme hardness and brittleness [1]. Silicon carbide (SiC) has many desirable properties, such as excellent wear resistance, chemical stability, and high strength even at elevated temperatures. All of these properties make it an ideal candidate for tribological, semiconductor, MEMS and optoelectronic applications. In spite of all these characteristics, the difficulty during machining and material removal has been a major obstacle that limits the wider application of this material [1]. The plastic deformation of SiC materials at room temperature is much less than in metals, which means they are more susceptible to fracture during material removal processes. Surface cracks generated during machining are generally subsequently removed in lapping and polishing processes, which significantly increases the machining time and cost. Machining mirror-like surface finishes contribute significantly to the total cost of a part. In some cases, grinding alone can account for 60-90% of the final product cost [2]. In this context, developing a cost effective method to achieve a flawless surface in ultra fine surface machining of an optical lens or mirror has become a challenge. In many engineering applications, products require a high quality surface finish and close tolerances to function properly. This is often the case for products made from semiconductor or ceramic materials. The real challenge is to produce an ultra precision surface finish in these nominally brittle materials at low machining cost.