NITI-BASE INTERMETALLIC ALLOYS STRENGTHENED BY AL SUBSTITUTION

A series of NiTi-base alloys with Al additions substituting the Ti wer e designed and evaluated in terms of the microstructure and mechanical properties. It was found that the compression strength is improved dr astically by the Al additions, especially when the Al amount is high e nough to precipitate Ni2TiAl (Heuslar compound) phase which is coheren t to the NiTi(B2) phase matrix; an alloy with 8.4 mol.% Al showed comp ressive yield strengths as high as 2300 and 200 MPa at room and high ( 1000 degrees C) temperatures, respectively. When the Al content exceed s 11 mol.%, however, Ni2TiAl phase started to deposit in a dendritic m anner to reduce the strength. Although compressive ductility declined with the increase in Al content, 5.2% deformation was achieved with th e 8.4 mol.% Al-containing alloy at room temperature. (C) 1997 Elsevier Science S.A.