Nano-structural evolution of Ti(O, N, C) precipitates in V–4Cr–4Ti alloys studied by 3-dimensional atom probe

To investigate the effect of atmospheric impurities on the behavior of Ti(O, N, C) precipitates in V–4Cr–4Ti alloy at elevated temperatures, chemical and structural analysis were carried out using the laser-assisted 3-dimensional atom probe. After aging at 973 K for 40 h Ti(O, N, C) precipitates were observed around the depth of 1 μm from the specimen surface. The coarse precipitates with a diameter of about 50 nm consisted of mostly Ti, Cr, O and N. The O/N ratio of 142 was much larger than the value of 2 obtained from chemical composition of NIFS-HEAT1 alloy. The fine precipitates, which shows high O/N ratio of 4 seemed to be formed at the initial stage of aging. Thus, it is thought that the ingressed O affects the chemical composition and precipitation behavior of Ti(O, N, C) precipitates within the surface region.