NiTi-base intermetallic alloys strengthened by Al substitution

A series of NiTi-base alloys with Al additions substituting the Ti were designed and evaluated in terms of the microstructure and mechanical properties. It was found that the compression strength is improved drastically by the Al additions, especially when the Al amount is high enough to precipitate Ni2TiAl (Heuslar compound) phase which is coherent to the NiTi(B2) phase matrix; an alloy with 8.4 mol.% Al showed compressive yield strengths as high as 2300 and 200 MPa at room and high (1000°C) temperatures, respectively. When the Al content exceeds 11 mol.%, however, Ni2TiAl phase started to deposit in a dendritic manner to reduce the strength. Although compressive ductility declined with the increase in Al content, 5.2% deformation was achieved with the 8.4 mol.% Al-containing alloy at room temperature.