Abstract
Abstract The origin of mechanical strengthening due to the early stage spinodal decomposition process in a Cu-9 wt.% Ni-6 wt.% Sn alloy has been investigated. The wavelength (λ) and relative amplitude ( A ) of the composition fluctuation were determined from the position and integrated intensity of X-ray sidebands for samples aged for varying times at 300°, 350° and 400°C. The incremental yield stress, Δσ (stress measured in tension at 0.01 per cent strain in excess of that measured for the undecomposed alloy) was found to increase substantially during aging (~ 80,000 psi at 400°C). As predicted by Cahn ( Acta Met. 11 , 1275 (1963)) Δσ was proportional to A 2 λ : no other proposed hardening mechanism showed any correlation with the experimental data. It is further shown that the Cahn theory can equally well account for the early stage decomposition process in other, previously studied spinodal alloys. Measurements of resistivity change on isothermal aging at the three temperatures investigated were interpreted using the theory of Kolomets and Smirnov ( Fiz. Met. Metalloved. 14 , 3 (1962)). The percentage decrease in resistivity was found to be proportional to A 2 , as predicted. Accordingly, the product ¦ Δ gr ρ0 ¦ λ may also be used to show confirmation to Cahn's theory.
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