Preparation, microstructure and mechanical properties of MoAlB-0.15% Si ceramics with superior strength and toughness

Abstract

MoAlB has been regarded as a promising high-temperature structural ceramic, but the strength and toughness are still insufficient in the practical application. In this work, MoAlB ceramic bulk with superior hardness, strength and toughness has been fabricated by adding 0.15 mol. % Si. The MoAlB-0.15Si bulk is composed of Si-doped MoAlB, Mo(Al, Si)2 and ultrafine Al2O3. The Vickers hardness ranges from 14.2 to 12.5 GPa with the tested load increasing from 10 to 200 N. The Vickers indentation remains the intact tetragonum in spite of the appearance of corner cracks, indicating the excellent damage tolerance. The flexural strength, fracture toughness and compressive strength of MoAlB-0.15Si are 518.46 MPa, 7.01 MPa m1/2 and 2.62 GPa, respectively, obviously superior to the present MoAlB polycrystalline bulk. Si doping, grain refinement, strengthening effect of ultrafine Al2O3 and phase transformation from Al8Mo3 to Mo(Al, Si)2 jointly account for the improvement of comprehensive properties of MoAlB bulk.