Deformation mechanisms of polycrystalline MoSi 2 alloyed with 1 at.% Nb

Abstract

Molybdenum disilicide (MoSi 2) is a high Peierls stress material with a strong temperature dependence of the yield stress at low homologous temperatures. We have investigated the effects of alloying with 1 at.% Nb on the mechanisms of deformation of polycrystalline MoSi 2 by compression testing from room temperature to 1600 °C. While polycrystalline unalloyed MoSi 2 fractured before plastic yield at temperatures ≤900 °C, the Nb-alloyed MoSi 2 could be deformed in compression even at room temperature. Transmission electron microscopy (TEM) investigations indicated that the presence of 1 at.% Nb increased the stacking fault width of 1/2〈111〉 dislocations and promoted 1/2〈111〉 slip at low temperatures. The solution softening is interpreted in terms of easier kink nucleation on partial dislocations (especially in the vicinity of solute atoms) with increasing partial spacing. With increasing deformation temperature, thermal activation makes kink nucleation easy, and presumably, kink migration is hindered by the solute atoms leading to the expected solid solution hardening at elevated temperatures. At very high temperatures (∼1600 °C), the yield strengths of Nb-containing alloys may be up to an order of magnitude higher than pure MoSi 2; the related hardening mechanisms are discussed.