Mechanical properties of Mo5SiB2 single crystals

Mo5SiB2 is a new refractory metal silicide with great potential for ultra-high temperature structural applications. We succeeded to grow high purity single crystals of Mo5SiB2 using an optical floating zone method. Single-crystal elastic constants at room temperature (RT) of the silicide were measured. Mo5SiB2 has less anisotropic single crystal elastic moduli and a lower shear modulus and a lower Debye temperature than MoSi2. Mo5SiB2 has a slightly higher bulk, shear, Youngʹs moduli and Debye temperature than Mo5Si3. Mo5SiB2 has a RT Vickers hardness of around 18 GPa, which is much larger than those of Mo5Si3 and MoSi2. Fracture toughness around 2 Mpa√m is comparable to those of Mo5Si3 and MoSi2. Compression tests were performed at 1500 °C. Slip was observed on [001](010) for [021] orientation. However, slip on 〈100〉(001), which has been reported to be activated, was not observed. Mechanical properties of Mo5SiB2 single crystals are discussed in relation to the complex crystal structure of Mo5SiB2.