Structural designation and mechanical properties of TiNi/Ti₂Ni laminated composites

TiNi/Ti2Ni laminated composites were fabricated using hot isostatic pressing (HIP) furnace together with structural designation by the control of Ti and Ni foil thicknesses. During HIP processing, Ti reacts with Ni, leading to the formation of softer TiNi and harder Ti2Ni. Through adjusting the thickness ratio of Ti and Ni foils, the ratio of TiNi and Ti2Ni fraction can be controlled. Hard-soft-hard, soft-hard-soft and hard-intermediate-soft laminated composites were designed, where hard layer was made by 50 μm Ti and 20 μm Ni, soft layer was made by 40 μm Ti and 20 μm Ni, and the intermediate structure between hard and soft ones was made by 45 μm Ti and 20 μm Ni. The mechanical properties were characterized using uniaxial tension, uniaxial compression, single edge-notched beam and split-Hopkinson pressure bar. The results show that all three laminated composites have compression strength of 1690 ∼ 1853 MPa and fracture toughness of 27.2 ∼ 37.9 MPa• m1/2 due to the same constituents of TiNi and Ti2Ni. However, the soft-hard-soft structure shows the best response under high strain rate because it was fractured into larger pieces while the other two structures were fractured into smaller pieces together with smaller fracture strain.