Enhanced mechanical properties of spark plasma sintered NiTi composites reinforced with carbon nanotubes

To enhance the mechanical strength of NiTi, 0.5 vol% CNT/NiTi composite was fabricated by high-energy ball milling followed by spark plasma sintering. NiTi and 1 vol% TiC/NiTi composites were also fabricated using the same process for comparison. Unreacted CNTs were observed in the CNT/NiTi composites, although some CNTs had reacted with Ti to form a TiC phase. Thermal hysteresis increased with the addition of CNTs due to increased frictional resistance to interfacial motion between CNT and NiTi matrix, and relaxation of the elastic strain energy in the NiTi matrix. The addition of CNTs, however, had little influence on the shape memory effect of NiTi. The elastic modulus, yield strength and ultimate tensile strength of the 0.5 vol% CNT/NiTi composite were greater than that of the NiTi. This improvement was attributed to the effective load transfer to the unreacted CNTs.