Ti-6Al-4V合金の疲労破面におけるX線フラクトグラフィ

抄録

Fatigue tests were carried out with Ti-6Al-4V alloy CT specimens after three kinds of the heat treatments, namely, 1) solution at 1223K, aging at 813K(STA), 2) annealing at 1123K(AN850) and 3) annealing at 1373K(±β-AN). X-ray fractography, which is a technique to estimate applied stress conditions when a fracture occurs and to be used for analysing 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 25MPa√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 ω_y was expressed by following equation; ω_y=α(K_max/σ_y)², where the values of α were 0.17 for STA and 0.13 for AN850. By using X-ray fractography technique on fatigue fractured surfaces of Ti-6Al-4V alloy, a value of maximum stress intensity factor K_max where the residual stress reach maximum value can be predicted.