An explanation of phase deformation tension–compression asymmetry of TiNi by means of microstructural modeling

Phase deformation of mono- and polycrystalline TiNi specimens due to the direct martensitic transformation is simulated by means of a microstructural model. These simulations show that the deformation of a polycrystalline specimen loaded by a constant stress and cooled down across the temperature interval of the direct martensitic transformation depends on the mode of the stress being much less in the case of compression than in the case of tension. For most orientations of a single crystal modeling predicts a positive tension–compression asymmetry: the phase deformation in tension dominates over that in compression. Only for few orientations a small negative asymmetry is observed. A hypothesis is suggested that the positive tension–compression asymmetry of the phase deformation is inherent to TiNi because of the specific value of the third invariant of the Bain's deformation tensor. This hypothesis explaining the experimentally observed tension–compression asymmetry of untextured TiNi polycrystals is supported by microstructural modeling. Modeling also shows how the texture when it exists affects the phase deformation. By varying only the third invariant of the Bain's deformation tensor one can construct a model material either having no tension–compression asymmetry or having a negative asymmetry when the strain in tension is less than that in compression.

► Mode angle of Bain's deformation determines tension/compression asymmetry of SMA.
► For a given SMA the texture is the main reason for tension/compression asymmetry.
► Microstructural model considering Bain's variants can describe the effect of texture.