Mechanical properties of FeSi, FeSi2, and Mg2Si

As was described in previous publications, the main phases found in complex FeSiMg alloys (typical content: 45 % Si, 5 % Mg, a small amount of rare-earth elements, iron as balance) are FeSi, FeSi2 (high-temperature modification), Mg2Si, RE-Si and Mg2Si-Si eutectic. In order to understand the process of fines generation during disintegration of as-cast FeSiMg alloys it is further of interest to study the mechanical properties of selected pure phases. Thus, the scope of the present work is: i) to establish laboratory technique of pure FeSi, FeSi2 and Mg2Si production, ii) to apply a set of mechanical tests (compression test, fracture toughness test) in order to get a knowledge about modulus of elasticity and KIC of the phases, iii) to verify existing equations, which provide a relationship between mechanical properties of a brittle material (microhardness data, Young�s modulus, KIC). Based on the conducted experiments the following conclusions can be drawn: i) melting in an open induction furnace is can be used to produce the desired pure phases, ii) the hardness of the three investigated phases obtained by microhardness tests are 9.17 GPa (FeSi), 5.63 GPa (FeSi2) and 4.07 GPa (Mg2Si), iii) the cracks after microhardness indentations at 0.3, 0.5 and 1.0 kg in all three phases are of Palmqvist type, iv) the elastic moduli of the three phases are 142.5 MPa (FeSi), 107.6 MPa (FeSi2) and 76 MPa (Mg2Si), v) the fracture toughness of FeSi is 2.460.28 MPam1/2, vi) the equations by Niihara and Shetty give reasonable values for KIC for FeSi phase. By help of four equations for Palmqvist cracks the fracture toughness for FeSi2 and Mg2Si phases was calculated as well. Mg2Si appears as the most brittle phase from the three phases investigated.