A materials engineer records the following qualitative stress–strain behavior for two…
CHEMISTRY · Multi-part · GCSE · Chemistry · Bonding, Structure and the Properties of Matter · Bonding, Structure and the Properties of Matter
Problem
A materials engineer records the following qualitative stress–strain behavior for two samples tested at 298 K.
Verbal/Contextual Representation
• Sample I: pure copper—low yield strength, large region of uniform plastic deformation before fracture.
• Sample II: copper containing 5 mass % tin (a substitutional alloy)—higher yield strength, noticeably smaller plastic region before fracture.
The engineer also measures the electrical resistivity of Sample II and finds it higher than that of pure copper.
(a) Summarize the key mechanical differences between Sample I and Sample II as indicated by the stress–strain descriptions.
(b) Explain, at the particulate level, why introducing 5 % tin into copper increases the yield strength but decreases the ductility of the metal. Your answer should refer to metallic bonding, lattice imperfections, and atomic size mismatch.
(c) Predict how the electrical conductivity of Sample II compares with that of pure copper and justify your prediction using principles of metallic bonding and electron scattering.