ROOM-TEMPERATURE DEFORMATION OF A LEAD-BASED SUPERALLOY

Several lead alloys containing Pb3Ca, with volume fractions of from 0 to 100%, were produced by casting. The microstructures, as determined by optical microscopy and by scanning electron microscopy, consisted of large Pb3Ca particles (5-40 mum) in a lead matrix. The room temperature mechanical properties of the alloys were determined at an initial strain rate of approximately 1 x 10(-4) s-1. Yielding was continuous and the yield stress, sigma(alloy)y, can be modelled as that of a composite of Pb and Pb3Ca, that is, sigma(alloy)y = sigma(Pb) + (sigma(Pb3Ca - sigma(Pb))f(Pb3Ca) = 13.9 + 58.9 f(Pb3Ca) (in MPa). For alloys with up to 50% Pb3Ca the dependence of the UTS on the volume fraction of Pb3Ca can also be described approximately by a linear relationship. Fracture occurred by transgranular cleavage for the 100% Pb3Ca whilst for the two-phase alloys, fracture occurs in a ductile, dimple-type rupture mode, with a Pb3Ca particle at the bottom of each dimple. The failure strain, epsilon(f), can roughly be described by a relationship of the form epsilon(f) alpha(f(Pb3Ca)-1/2 Excluding the data for pure lead and 100% Pb3Ca (for which the fracture mechanisms are different), the maximum failure strain rate is described by epsilon(f)max = 0.80 - 1.08 f(Pb3Ca).