X ray fractography on fatigue fractured surfaces of Ti 6Al 4V alloy
Choi Seong Dae; Misawa Hiroshi; Akita Koichi; Kodama Shotaro
Abstract:Fatigue tests were carried out with Ti 6Al 4V alloy CT specimens after three kinds of the heat treatments, namely, 1) solution at 1223 K, aging at 813 K(STA), 2) annealing at 1123 K(AN850) and 3) annealing at 1373 K( plus or minus b AN). X ray fractography, which is a technique to estimate applied stress conditions when a fracture occurs and to be used for analyzing a mechanism of fracture, was applied on the fatigue fractured surface. Distributions of residual stress and half value breadth were measured on the fractured surface along the crack propagation direction as a function of a stress intensity factor. It was found that the residual stress on the fatigue fractured surface had a peak value when maximum stress intensity factor was nearly equal to 25 MPa root m. The strain induced transformation was confirmed on the fatigue fractured surface from X ray diffraction profile pattern. Depth of monotonous plastic zone size was estimated from the distribution of the residual stress beneath fractured surface. Depth of monotonous plastic zone size omega sub y was expressed by following equation; omega sub y equals a (Kmax/ sigma sub y) super 2, where the values of a were 0.7 for STA and 0. for AN850. By using X ray fractography technique on fatigue fractured surfaces of Ti 6Al 4V alloy, a value of maximum stress intensity factor Kmax where the residual stress reach maximum value can be predicted. Key Words:Ti-6Al-4V alloy, heat treatment, fatigue fractured surface, X-ray Fractography technique, residual stress, half-value breadth, monotonous plastic zone size