Probing the polytypic transition of Laves phase Cr2Nb in the dual-phase Cr–20Nb–40Ti alloy

• The metastable structures of C36, 5R, 6H and 7R were detected.
• The effect of solute Ti on the polytypic transition of Cr2Nb was discussed.
• The formation of stable C15 structure by the second phase β-Ti was probed.

By employing XRD, EDXS, TEM, HRTEM, and SADPs methods, the polytypic transition of Laves phase Cr2Nb alloyed with Ti has been investigated in the dual-phase Cr–20Nb–40Ti (in at.%) alloy. The solute Ti in Cr2Nb is shown to inhibit the polytypic transition of Cr2Nb by substituting onto the Cr sites. This leads to the occurrence of metastable structures of C36, 5R, 6H and 7R. On the contrary, the second phase β-Ti is suggested to prompt the polytypic transition of Cr2Nb based on the lattice mismatch calculation. The low lattice mismatch between the β-Ti and the C15 polytype is beneficial to the formation of single C15 polytype at the interface.