In-situ synthesis of MAB phases by spark plasma sintering and chemical exfoliation to 2D MBenes

This thesis reports synthesis of MAB phases by SPS and obtaining two-dimensional MBenes by chemical etching of layered MAB phases. Firstly, MoAlB and Cr2AlB2 were synthesized as precursor phases for 2D MoB and CrB, respectively. MoAlB was exfoliated with NaOH at various concentrations or LiF+HCl solution. Cr2AlB2 was delaminated with HCl at various molarities and NaOH. XRD, SEM, and EDS analyzed composition and microstructures of 2D MBene phases. The production parameters of pure and high-density MoAlB (1300℃, 30 MPa, 10 min) were determined. Moreover, the hardness, fracture toughness, and oxidation resistance of MoAlB were improved by Si-doped MoAlB solid solution and SiC-reinforced MoAlB composite. The highest hardness and fracture toughness were obtained in MoAlB-SiC composite with 12.39 GPa and 7.38 MPa.m1/2, respectively. Grain growth in MoAlB was inhibited by SiC reinforcement. Moreover, SiC particles quench crack energy during crack propagation through crack deflection mechanism. Their electrical and thermal conductivities were also investigated for the first time in the literature. The hardness, fracture toughness, and oxidation resistance of MoAlB were also increased with MoWAlB, MoCrAlB, and MoWCrAlB solid solutions. Inhibition of grain growth by solid solution improved the mechanical properties. These behaviors are explained in detail by establishing structure-property relationships. Cr2AlB2 and Cr3AlB4 phases were synthesized by SPS for the first time in the literature. Starting powders, excess Al, temperature, pressure, and dwell time were optimized to determine the optimum parameters for forming Cr2AlB2. For Cr3AlB4, suitable temperature ranges were determined by synthesizing at different temperatures.