Mechanical properties and oxidation behavior of (Mo,W)AlB, (Mo,Cr)AlB, and (Mo,W,Cr)AlB MAB solid solutions synthesized with spark plasma sintering

This study reports the effects of solid solution on the mechanical and oxidation behavior of MoAlB ceramics. (Mo, W)AlB, (Mo,Cr)AlB, and (Mo,W,C)rAlB were synthesized under 30 MPa at 1200 degrees C by Spark Plasma Sintering (SPS). Composition and microstructure were characterized by X-ray diffraction (XRD), scanning electron mi-croscope (SEM), and energy-dispersive X-ray spectroscopy (EDS). Although it was determined that the main phase was MoAlB solid solution, it was observed that binary borides such as WB were also present in the (Mo,W) AlB and (Mo,W,Cr,)AlB. Hardness was measured by the Vickers indentation test. The hardnesses of MoAlB solid solutions improved considerably compared to pure MoAlB and were obtained as 13.65, 12.72, and 13.37 GPa, respectively, for (Mo,W)AlB, (Mo,Cr)AlB, and (Mo,W,Cr)AlB. The reasons for the improvement in hardness are estimated to be grain refinement and solid solution hardening mechanism. Fracture toughnesses calculated from radial cracks formed during Vickers indentation are 6.52, 5.88, and 6.40 MPam1/2, respectively. Although crack bridging and deflection mechanisms work with solid solutions, as in pure MoAlB, the brittle binary borides in the structure did not improve fracture toughness. The oxidation test was carried out at 1200 degrees C for 12 h. A dense and continuous protective oxide layer was formed in all samples. The scale thicknesses of (Mo,W)AlB, (Mo,Cr)AlB, and (Mo,W,Cr)AlB are 3.2, 2.1, and 2.6 mu m, respectively.