Effect of a Disperse Phase on the Ductile Brittle Transition of Body Centered Cubic Metals

Abstract:
The tensile properties of electron-beam melted columbium and a series of columbium-nitrogen alloys containing up to 0.036w/o nitrogen have been examined at room temperature over a range of grain sizes.  The variation of lower yield stress σ_LY with grain-size d has been used to determine the values of σ₀ + kd-1/2. Whereas k was not influenced by nitrogen content and was, with one exception, immeasurably small, σ₀ was particularly sensitive to nitrogen content. Some dispersion-hardened structures (Cb₂N as dispersed phase) were studied and, employing the Petch equation, a quantitative measure of the contribution of the dispersion to yield strength was made. A measure of the Peierls-Nabarro force for the columbium lattice at room temperature was obtained.