Ultrahigh-strength NiTi-based in-situ composite prepared by directional solidification

NiTi metal matrix in-situ composite was prepared by directional solidification in-situ method, adding a small amount of Al, Nb, Hf. The directionally solidified bars were homogenized at 950 ℃ for 12 h, 50 h and 100 h, respectively, and the tensile strength was tested at room temperature. The results indicate that a vimineous, acicular cellular structure that grow along the [001] orientation is achieved after the directional solidification. The β-Nb and Ti₂Ni reinforcement particles distribute along the [001] orientation in the intercellular regions. The cellular structure becomes coarser with the increase of the homogenizing time, and the two reinforcement particles are more dispersed and distributed more homogeneously. After heat treatment, the highest tensile strength reaches to 1972 MPa, exceeding that of the 4130 and 8640 ultrahigh-strength steel, being almost equal to 4140 and 4340 ultrahigh-strength steel, and reaching or surpassing many kinds of ultrahigh-strength titanium alloy.