Effect of Mg and Al alloying on the valence electron structure and properties of MoSi2-based alloys

The valence electron structure (VES) of MoSi2-based solid solution alloys was studied herein by the bond length difference (BLD) method based on the empirical electron theory (EET) of solids and molecules and the average atomic model. Compared to those for a MoSi2 alloyed with Al or Mg separately, alloying with Mg + Al together significantly decreased the bond energy of the main bond branch and the ratio of the number of covalent valence electrons to the total number of valence electrons in the Mo(Si0.92AlxMg0.08-x)2 solid solutions and increased the lattice electrons. Thus, alloying MoSi2 with Mg + Al together reduced the hardness and strength of MoSi2 and increased its fracture toughness above what occurred when Mg or Al were added separately. The combined impact of the impurities was especially noticeable when MoSi2 was alloyed with 4 at% Mg+4 at% Al. Based on those results, Mo(Si0.92AlxMg0.08-x)2 solid solution alloys were made, their mechanical properties were tested, and the experimental results were consistent with those of the theory.