Fangfang Wang

Microstructure and mechanical properties of NiTi-Al based alloys with addition of Fe

Abstract The influences of Fe on the microstructure and mechanical properties of Ni–43Ti–4Al–2Nb–2Hf–xFe (x = 0, 1, 3, 5 at-%) alloys were investigated, prepared by vacuum non-consumable arc-melting method. The results show that the microstructure of the alloys is refined gradually with increasing Fe content. The appropriate addition of Fe produces an improvement of the tensile strength and ductility of the alloy. The highest tensile strength and elongation of the study’s alloys was seen with the 3 at-%Fe addition, resulting in strength and elongation of up to 1308 MPa and 4·15%. The fracture characterisation changes from a quasi-cleavage fracture to a mixed fracture of quasi-cleavage and dimple. Further increasing the Fe content to 5 at-%, the mechanical properties deteriorated.

Precipitation behaviour of oxide in directionally solidified aerospace bearing steel

The directional solidification enables independently control of the holding temperature and withdrawal rate over a given range. This technology was used to investigate the precipitation behaviour of oxide in aerospace bearing steel M50NiL. Most of the oxides are Si–Al–Mn–Ti–O complex inclusions with spherical shape. With the increase of withdrawal rate, the size and volume fraction of oxides decrease. In contrast, the diameter and volume fraction increase remarkably with the increase of holding temperature. The composition of oxides with different sizes varies with holding temperature. The holding temperature of 1550°C accompanied with a cooling rate over 95.7°C min−1 is deemed as the optimal solidification parameters for M50NiL steel, which can significantly reduce the size and volume fraction of oxides.