Elastic modulus of shape-memory NiTi from in situ neutron diffraction during macroscopic loading, instrumented indentation, and extensometry

The elastic modulus of B19’ shape-memory NiTi was determined using three techniques; from the response of lattice planes measured using in situ neutron diffraction during loading, instrumented indentation using a spherical indenter and macroscopic extensometry. The macroscopic measurements resulted in a modulus of 68 GPa, significantly less than the 101 GPa from indentation and the lattice plane average of 109 GPa from neutron diffraction. Evidence from the neutron measurements suggests that the disparity derives from the onset of small amounts of twinning at stresses less that 40 MPa, which might otherwise be considered elastic from a macroscopic view point.