Microstructure and martensitic transformation of TiNiNbB shape memory alloys

• Microstructure of Ti44Ni47−xNb9Bx alloys depend on B content.
• With increasing B content, transformation temperature increase.
• The optimized mechanical properties can be obtained by the proper addition of B.

In present work, microstructure, martensitic transformation and mechanical properties of Ti44Ni47−xNb9Bx (x = 0, 0.5, 1, 5 at.%) alloys were investigated as a function of B content. The results show that the addition of B significantly influences the microstructure of the alloys. The microstructure of Ti44Ni47Nb9 alloy consists of B2 parent phase matrix and β-Nb phase. When the B content is 0.5 at.%, Nb3B2 phase presents. With further increasing B content to above 1 at.%, TiB and NbB phases present instead of Nb3B2 phase. With increasing B content, the transformation temperatures increase due to the reduced Ni/Ti ratio and Nb content in the matrix. The mechanical properties can be optimized by the addition of 1 at.% B.