A novel method for fabricating NiAl alloy sheet components using laminated Ni/Al foils

A novel technology combining forming and reaction synthesis has been developed to manufacture NiAl alloy sheet components which are difficult to form using conventional fabrication approaches. A semi-circular shaped NiAl sheet component was successfully fabricated using forming-reaction synthesis integrated process (FRSIP) with laminated Ni/Al foils. Through microstructure characterization, the mechanism of the reaction synthesis of laminated Ni/Al foils was studied for manufacturing homogenous components. The process was performed at 650 °C under the pressure of 15 MPa for 4 h to consume Al layers and produce the multilayered composite of Ni/Ni₂Al₃/Ni, and further annealed at 1200 °C under the pressure of 25 MPa for 1 h to produce fully dense and homogeneous NiAl alloy. Based on electron back-scatter diffraction (EBSD) analysis, the NiAl sheet contains inter-laminated coarse-grain layers (CGLs) and fine-grain layers (FGLs), which formed at original Al foil layers and original Ni foil layers, respectively. The grain sizes of the CGLs can be adjusted by controlling the thickness of the original Ni foils. The mechanical properties of NiAl sheet were studied by means of nano-indentation tests and tensile tests, which showed that the weak grain boundary weakened the Hall-Patch (H-P) phenomenon. The bimodal grain structure was a main factor influencing the performance of plastic deformation at high temperature.