Accession Number : AD0664823

Title :   SUPERPLASTICITY IN LEAD-TIN ALLOYS (THE FRACTURE OF DUCTILE METALS).

Descriptive Note : Technical rept.,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE

Personal Author(s) : Backofen,Walter A. ; Zehr,Stanley W.

Report Date : DEC 1967

Pagination or Media Count : 49

Abstract : Four alloys from the Pb-Sn system, including the eutectic, were tested in tension over a range of strain rates (approximately 0.00001 to 0.01/sec) from room temperature to 170C, and with large variations in grain size. In general, strain-rate hardening was characterized by a 3-stage pattern of rising and falling strain-rate sensitivity with increasing strain rate. A mechanism is suggested which incorporates non-Newtonian grain-boundary sliding and diffusional (Newtonian) creep acting first in parallel and then in series with non-Newtonian slip creep. It finds support in both mechanical and metallographic measurements. Observed stress:strain-rate relationships can be accounted for, at least approximately, and there is evidence from replica electron microscopy of boundary sliding together with diffusional creep, the latter being reflected in the formation of striated bands primarily along the transverse or tensile-loaded grain boundaries. (Author)

Descriptors :   (*LEAD ALLOYS, PLASTIC PROPERTIES), (*TIN ALLOYS, PLASTIC PROPERTIES), EUTECTICS, STRAIN(MECHANICS), HARDENING, METALLOGRAPHY, STRESSES, GRAIN BOUNDARIES, DIFFUSION, CREEP, FRACTURE(MECHANICS), DUCTILITY

Subject Categories : Metallurgy and Metallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE