TiNi Particle-Reinforced Magnesium Matrix Composites: Production, Microstructure, Phase Transformations, and Mechanical Properties

Abstract

Magnesium matrix composites reinforced with 5–25 vol% Ti_49.2Ni_50.8 microparticles are produced by uniaxial hot pressing technique. Powder mixtures are hot pressed in cylindrical graphite dies under 50 MPa pressure for 1 h at 600 °C. Density measurements show that specimens reach almost full density and do not contain any pores. Microstructural analyses demonstrate that undesired secondary phases or compounds do not form at matrix/reinforcement interface. As a result of aging heat treatment performed simultaneously with the manufacturing process, martensite phase (B19′) and Ti₃Ni₄ precipitates are also observed in the microstructure of reinforcing materials in addition to the main austenite (B2) phase. The room-temperature yield strength and compressive strength of the composite materials range between 60 and 86 MPa and 232 and 296 MPa, respectively. Although the ductility values decrease with increasing reinforcement content, the decrease is less than those of ceramic and other metallic reinforced composites. The ductility is determined to be 17.6% for the composite with the highest reinforcement content. In contrast to the reference and conventional materials, the yield strengths of the composite samples produced increase significantly with the increasing temperature up to 100 °C. This unusual behavior is attributed to the stress-induced martensitic transformations observed in TiNi alloys.