Oleg D. Sherby

CORRELATIONS OF RUPTURE DATA FOR METALS AT ELEVATED TEMPERATURES

Abstract : The general validity of the concepts leading to the equation f(sigma) = t sub r e-Delta H sub r/RT was tested by applying the equation to available high-temperature stress-rupture data for relatively pure metals and dilute alloys. The equation relates the time to rupture t sub r at high temperatures to the test temperature T (Kelvin) and applied stress sigma; R is the gas constant and Delta H sub r is the activation energy for rupture. The equation was successfully applied to data for Al, Be, Ti, Ni, Nb, and Mo. The formula was also applied successfully to rupture data for 24 complex high-strength commercial alloys. The activation energy Delta H sub r appeared to be constant for a given metal; for relatively pure metals it is believed to be equal to the activation energy for creep or self-diffusion.

Some observations on grain boundary shearing during creep

McLean’s technique was employed to determine the effect of temperature on the contribution of grain boundary shearing to the total creep strain in pure aluminum over the range of 610° to 747°K. The contribution of grain boundary shearing at the same stress was found to depend upon a temperature-compensated time, te−ΔH/RT, where the activation energy ΔH was practically identical with that for total high temperature creep.

Effect of Alloying Elements on the Elevated Temperature Plastic Properties of Alpha Solid Solutions of Aluminum

Solid solution alloying increases the plastic properties of aluminum at elevated temperatures by solid solution strengthening, by restraining recovery and recrystallization, and by a Cottrell effect. When binary aluminum alloys are strained and aged at 194° to 300°K they develop a yield point. This is attributed to a migration of dislocations to solute atoms during aging.