Fiber phase transformation and matrix plastic flow in a room temperature tensile strained NiTi shape memory alloy fiber reinforced 6082 aluminium matrix composite

Macroscopic tensile and in-situ neutron diffraction measurements are reported from a 20.5 volume percent, 50.7 at% Ni-Ti fiber reinforced 6082-T6 aluminum matrix composite subjected to a room temperature, 4% tensile elongation. The austenite B2(110) diffraction intensity was essentially stable until approximately 0.9% strain, beyond which, the austenite B2(110) diffraction intensity strongly decreased with increasing tensile strain.

The martensite M(001) diffraction intensity strongly increased from a zero intensity intercept at approximately 2.3% strain to the conclusion of tensile straining. This report concludes that the initial decrease in austenite B2(110) diffraction intensity locates the initiation of stress induced transformations in the NiTi reinforcement, furthermore this feature corresponds with an elevated yield point region in the macroscopic tensile results.

Therefore, it appears that the elevated yield point region is caused by a temporary inhibition of fiber stress induced transformations.