Katsumi Nakajima

The effect of microstructure on fatigue crack propagation of α + β titanium alloys in-situ observation of short fatigue crack growth

Abstract Fatigue crack initiation and early stage of crack growth for Ti–6Al–4V and Ti–4.5Al–3V–2Fe–2Mo were investigated on notched specimens. In-situ observation on fatigue cracking processes was made on a fatigue testing machine mounted in a scanning electron microscope. It was found that Ti–4.5Al–3V–2Fe–2Mo alloy with very fine α grains of ≈2 μm exhibited a much higher fatigue strength at 107 cycles than that of Ti–6Al–4V alloy. However, an opposite trend in fatigue life was obtained in the short life regime for the materials tested in the present study. The observed fatigue behavior in both the long and short life regimes is discussed in terms of metallurgical factors responsible for the fatigue behavior of the present materials.

Phase-Field Simulation of Cooperative Growth of Pearlite

Cooperative growth of pearlite is simulated for eutectoid steel using the multi-phase field method. This allows to take into account diffusion of carbon not only in γ phase, but also in α phase. The lamellar spacing and growth velocity are estimated for different undercoolings and compared with experimental results from literature and theoretical results from analytical models. It is predicted, that diffusion in ferrite and growth of cementite from the ferrite increase the kinetics of pearlitic transformation by a factor of four as compared to growth from austenite only, which is assumed by the classical Zener-Hillert model. Further on the effect of stress due to inhomogeneous carbon distribution in austenite and due to transformation strain is discussed shortly.