The microstructure and martensitic transformation of (Ti49.3Ni50.7)1−xGdx shape memory alloys

The microstructure and martensitic transformation of (Ti49.3Ni50.7)1−xGdx (x = 0, 1, 2, 10 at.%) shape memory alloys are investigated by optical microscopy, scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. The results show that the microstructure of the TiNi(Gd) alloy consists of Ti2Ni phase, a GdNi intermetallic compound, and the matrix. The GdNi phase is dispersed in the matrix with spherical or irregular shapes. With increasing Gd content, the GdNi phase becomes larger and interconnected, and the content of Gd in the GdNi phase also increases. The martensitic transformation type differs with different content of Gd in the TiNi(Gd) alloys. In the alloy containing 2 at.% Gd, a two-step martensitic transformation is observed, whereas a one-step martensitic transformation is observed in the alloy containing 10 at.% Gd. The martensitic transformation temperatures increase rapidly with increasing Gd content to 2 at.%, and then tend to be stable when the Gd content is further increased.