Solid Solution Strengthening of Titanium by Aluminium at Low Temperatures

Abstract

Solid solution strengthening of polycrystalline Ti by Al in the temperature range of 4.2-650K was investigated regarding the increase in yield stress, strain hardening and grain size hardening by concurrent measurements of the flow stress and the dislocation density. It was found that the flow stress σ increases linearly with the square root of the dislocation density ρ relatively independent of strain and grain size yielding σ = σf(T, Ci,Cs) + αEb[p(e, d,Ci,Cs)]1/2 where E is Youngs modulus, b the Burgers vector and α a constant whose value is approximately 0.7 independent of temperature. Ci and Cs are the interstitial and substitutional solute contents, respectively. The experimental results indicated that the solid solution strengthening of Ti by Al consisted of two components: (a) that due to the increase in dislocation density for a given strain resulting from the Al atom additions and (b) that due to the interaction of mobile dislocations with the Al atoms. The strengthening due to the former is explained in terms of a long-range interaction between mobile dislocations and the dislocation structure; the latter was found to be in some accord with Friedel's model for solid solution strengthening.