Microstructures, Martensitic Transformation and Mechanical Properties of TiNi-Based Amorphous-Crystalline Composites

Abstract

By successively introducing minor Al and Sn into the (Ti46.5Ni46.5Hf2Si5)98Nb2 alloy, the amorphous-crystalline composites were fabricated by rapid solidification. The main microstructures were identified as B2 TiNi dendrites together with a few TiNi martensitic crystals. The intercrystalline regions were composed of amorphous phase, B2 TiNi phase, and Ni3.02Ti2Si0.98 intermetallic compounds, whose morphology gradually transformed into striped microstructures. The segregation of Si within intercrystalline regions leads to the formation of the amorphous phase. During deformation, the amorphous-crystalline composites exhibit a double yielding behavior. The yield strength and fracture strength increase to 1114 ± 10 MPa and 2470 ± 15 MPa, respectively, resulting from the reduction of grain size, the existence of the amorphous phase, Ni3.02Ti2Si0.98 intermetallic compounds, and martensitic transformation. All the samples exhibited plastic strains larger than 10% due to the interaction between martensitic transformation and the shear banding process.