SOLID SOLUTION STRENGTHENING AND WEAKENING OF BCC SOLID SOLUTIONS

Tension and compression tests were conducted on single crystal samples of tantalum and tantalum-base solid solutions as a function of temperature and strain rate. The activation parameters were investigated as a function of stress and strain. In considering the solid solution effects it is necessary to take into account the division that is made of the yield or flow stress into the two components. These two components are: a thermal component called the effective stress, and an athermal component. The thermal component may increase or decrease due to a solute addition, but the athermal component only increases due to a solute addition. The change in the thermal component of the yield stress due to niobium and tungsten addition to tantalum can readily be accounted for by a change in a Peierls' stress due to a change in the modulus of the alloy. However in the case of tantalum-rhenium the strengthening is much greater than that which can be accounted for by an increase in the Peierls' stress as a result of the increase in the modulus of the alloy. Of the possible mechanisms considered, the double kink mechanism can best account for the large increase in the thermal component if 'demixing' is assumed for the tantalum-rhenium alloy. © 1969.