Texture and Thermal Expansion Anomalies of B19'-Martensite in Tensile Deformed TiNi Shape Memory Alloy

Abstract

The dilatometric studies of Ti-50.5 at.% Ni alloy have shown that the thermal expansion coefficient (TEC) of B19'-martensite varies considerably for the solution-treated and tensile-strained samples. In the undeformed state the TEC has the positive value α=9.7.10^-6 K^-1. After tensile straining the TEC decreases sharply and takes on a negative value (down to – 10.8.10^-6 K^-1). The reasons for the variation of the TEC of the B19'-phase of the solution-treated and deformed samples are discussed. The tensile straining was found to create in the samples an extremely sharp texture of the phase transformation, with the texture axis parallel to the strain direction. The TEC of monoclinic B1939;-lattice is different in various crystallographic directions and assumes a negative value in the [0 01]_B19' direction.