STRESS CONSTANTS OF CERAMICS FOR MEASURING RESIDUAL STRESS BY X-RAY DIFFRACTION

Abstract In x-ray stress measurement, it is important to determine the stress constant K experimentally in order to measure the stress accurately. Since the shift of the peak position of the diffraction line per unit strain increases proportionally to tanθ; and the relative error σ/K decreases inversely proportionally to tanτ, it is essential to choose a diffraction line having a diffraction angle 2θ as high as possible The stress constants of a silicon nitride Si3N4, silicon carbide SiC, alumina Al2O3, partially stabilized zirconia PSZ, and tungsten carbide WC in a WC-Co cemented carbide were determined by the Gaussian curve method by using an automated x-ray stress analyzer. The peak positions of the diffraction line from (323) and (2.0.15) planes of Si3N4., and Si3N4, respectively, were measured with copper Ka radiation. Also, those from (410), (044), and WC (121) planes of Al203, PSZ, and WC-Co, respectively, were measured with cobalt Ka radiation. The 95% confidence limits of the stress constant of these materials were -779±21, -971 ±48, -314±8, -224±4, and -578± 16 MPa/deg, respectively. The use of A1203 (410) and WC(121) planes with cobalt Ka radiation permits the most accurate stress determination because they have the highest diffraction angle of 168.5° and 165.0°, respectively.