Low temperature deformation of MoSi$_2$ and the effect of Ta, Nb and Al as alloying elements

TL;DR

This study investigates how alloying elements like Al, Nb, and Ta influence the low-temperature deformation mechanisms of MoSi$_2$, revealing activation of new slip systems and reduced hardness, which could improve ductility for structural applications.

Contribution

It demonstrates that alloying MoSi$_2$ with Al, Nb, or Ta activates additional slip systems and decreases hardness, offering insights into enhancing ductility at lower temperatures.

Findings

Alloying decreases hardness of MoSi$_2$

Activation of {110}<111> slip system in microalloyed MoSi$_2$

Critical resolved shear stresses measured for different slip systems

Abstract

Molybdenum disilicide (MoSi$_2$) is a very promising material for high temperature structural applications due to its high melting point (2030 {\deg}C), low density, high thermal conductivity and good oxidation resistance. However, MoSi$_2$ has limited ductility below 900 {\deg}C due to its anisotropic plastic deformation behaviour and high critical resolved shear stresses on particular slip systems. Nanoindentation of MoSi$_2$ microalloyed with aluminium, niobium or tantalum showed that all alloying elements cause a decrease in hardness. Analysis of surface slip lines indicated the activation of the additional {1 1 0}<1 1 1> slip system in microalloyed MoSi$_2$, which is not active below 300 {\deg}C in pure MoSi$_2$. This was confirmed by TEM dislocation analysis of the indentation plastic zone. Further micropillar compression experiments comparing pure MoSi$_2$ and the Ta-alloyed sample enabled the determination of the critical resolved shear stresses of individual slip systems even in the most brittle [0 0 1] crystal direction.