Fabrication of Compositionally Graded NiTi Shape Memory Alloy Laminated Composites Through Hot Roll Bonding and its Characterization

The present study reports for the first time, development of a novel technique to fabricate compositionally graded monolithic NiTi shape memory alloy (SMA) laminated hybrid composites by joining two compositionally different equi‐atomic Ni 50 Ti 50 and Ni‐rich Ni 51 Ti 49 SMAs. A two‐step fabrication methodology involving a combination of spark plasma sintering (SPS)/diffusion bonding at 1050 °C followed by hot roll bonding (HRB) at 900 °C is adopted to produce three‐layer SMA laminated composites in four different architectures, which can be utilized for manufacturing passive damping devices. Microstructural characterization clearly shows that HRB is capable of producing a joining interface free from any oxides/voids having excellent metallurgical bonding. The measurement of martensitic transformation characterized through differential scanning calorimetry of these NiTi SMA composites reveals that in spite of forming a monolithic SMA composite material after HRB, the individual NiTi SMA layers still preserve their individual transformation characteristics. Tensile tests carried out on HRB NiTi SMA composites at ambient temperature demonstrate that laminated NiTi SMA hybrid composite comprising top and bottom layers of Ni 51 Ti 49 SMA and middle layer of Ni 50 Ti 50 SMA (in equal thickness proportion) exhibits the best pseudoelastic strain recovery, which can be further improved by aging treatment at 425 °C for 15 min.