Mechanical and microstructural characterization of copper microsamples after cold drawing.

摘要

Copper is a robust elemental metal with favorable mechanical, material, electrical, thermal, and alloying properties. Copper have been exploited mechanically and constitutively for applications that range from munitions for firearms, building material found in roofing and plumbing, electrical wire/interconnects in electrification and integrated circuits, germicide protection, cookware, and many other widely varying products. In munitions, copper is widely used as a bullet jacketing material protecting the steel core and lead slug during rifling, flight to the target, and delivery at target.;In this study, an approach is developed to investigate and link the mechanical and microstructural evolution of the cold drawing of a copper jacket. Copper jackets are fabricated in a multi-step drawing process where an as-received copper plate is transformed into a 'cup', and then a pre-swaged jacket for the bullet. The drawing process causes deformation and rotation in the material, which develops anisotropy and texture that varies along the length of the copper jacket. Microsample test specimens have been extracted longitudinally from the copper jacket, with nominal dimensions of 3 mm x 1 mm and a gage cross-section of ∼150 microm square by electro-discharge machining. Metallographic analysis performed on the matching gage section area of each microsample revealed high levels of cold working as a result of the drawing process. Qualitative x-ray diffraction performed on the gripping ends showed strong texturing and evolution in texture for the copper microsamples longitudinally as a function of location on the jacket. Nanoindentation experiments mapped Young's Modulus and Hardness information on the gage section of the copper microsamples as a function of position. The microhardness showed no variability in the through-thickness of the microsample gage section and supported the Hardness trends of the nanoindentation results. Microsample tensile testing provided Young's Modulus, Yield Strength, and Ultimate Tensile Strength as a function of location on the copper jacket.