Correlation between Mechanical Strength and Surface Conditions of Laser Assisted Machined Silicon Nitride

摘要

High power fiber-coupled diode lasers for Laser-Assisted Machining (LAM) of ceramics provides an efficient, cost effective solution for surface finishing of ceramic products. This paper presents experimental evidence of advantages of LAM over the traditional diamond wheel grinding, a standard technique currently utilized in the finishing of ceramic surfaces. LAM, utilizing fiber-coupled diode lasers, also provides advantages over other types of lasers such as CO_(2) and Nd:YAG lasers. The emphasis of this work is in the evaluation of LAM in the strength of finished products of two different sources of silicon nitride. An optical technique based on evanescent illumination was utilized to measure the Ra of the finished surfaces utilizing LAM, laser glazed, diamond ground, and as-received surface conditions. Four point bending test for specimens of each surface condition were utilized to measure the fracture strength. A correlation was found between the measured R_(a) and the predicted strengths resulting from Weibull analysis. The correlation shows a decrease of strength with the increase of R_(a). The fracture surfaces were observed both optically and with a SEM, and the flaw sizes were measured. The analysis of the fractographs indicated that the flaw sizes are consistent with Fracture Mechanics predictions. Explanations of the correlation between R_(a), strength, and flaw sizes require further testing.