Solid-solution strengthening in Ni-C alloys

“Pure” nickel and Ni-C solid-solution alloys of various grain sizes (ASTM no. 2 to 10), with eight different carbon concentrations in the range 0.008 to 0.304 wt pct, were strained in tension between 4° and 474°K at a strain rate of 8.3 × 10⁻⁵per sec. The critical resolved shear stress (CRSS) was independent of temperature in the range 200° to 474° K (athermal region). Below 200°K, the CRSS increased sharply with decreasing temperature, the increase being larger for alloys of high carbon concentration. Both the temperature-dependent and the athermal alloy hardening were found to be linear functions of carbon concentration. The strain-rate sensitivities of flow stress of alloys did not change with strain and were larger for alloys of higher carbon concentrations. The Hall-Petch relation was used to calculate the CRSS of Ni-C single crystals, Τ₀ ^f, so that the data can be compared with existing alloy hardening theories. The data are compatible with the solid-solution theory of Friedel in which the hardening is attributed to both elastic and electrical interactions between dislocation cores and solute atoms. Formerly with the Edgar C. Bain Laboratory for Fundamental Research, U.S. Steel Corp., Research Center, Monroeville, Pa. Formerly with the Edgar C. Bain Laboratory for Fundamental Research.