Precipitation behavior and mechanical properties of Ti-Ni-Nb-Co alloys

Bo Cui, Jian Yao, Ye Wu, Xin Zhang, Fuli Wang, Jiehe Sui, Wei Cai

Index: 10.1016/j.intermet.2018.01.014

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Abstract

The Ti44.5Ni46.5-xNb9Cox (x = 0.5, 1, 2, 4) alloys were designated to investigate the effect of Co content and annealing treatment on the precipitation behavior and mechanical properties. The formation of nanoscale precipitates was being reported here for the first time in the Ti-Ni-Nb alloys due to the Co addition. For the Ti44.5Ni45.5Nb9Co1 and Ti44.5Ni44.5Nb9Co2 alloys, homogeneous GP zones and precipitates were observed at the lower annealing temperature. Additionally, the yield strength was enhanced by the higher strain field produced by the nano coherent precipitates. The effect of precipitation strengthening was weakened because of coarsened and clustered precipitates as annealing temperature increased. As a result, the highest yield strength of 520 MPa and the highest recovery stress of 482 MPa could be realized in the Ti44.5Ni44.5Nb9Co2 alloy annealed at 550 °C.