Table of Contents

Materials and Structure




When the Cu - 30 wt% Ni alloy solidifies it develops the microstructure shown in the photograph. The solid is not a single crystal, but is made of many crystals joining together at their boundaries. This polycrystalline material will have properties that depend upon both the grain size and composition of the alloy.

The lower diagram shows how the alloy composition alters mechanical properties such as the yield stress, tensile stress, and the ductility of the alloy. The vertical green line shows the Cu-30 wt % Ni composition. The diagram shows that the pure elements have the lowest yield and tensile stress and the highest ductility. As alloying elements are added their tensile and yield stress increase and their ductility decreases. The alloy with the approximate composition Cu-60 wt% Ni has the highest yield and tensile stress values and a ductility similar to that of pure copper.

Control of the crystal structure of the alloy can be achieved by controlling the cooling rate, or by heat treating the alloy after it has been solidified. This will permit further control of properties if the result is worth the extra production cost.

From: Newey and Weaver, "Materials Principles and Practice," Butterworths (1990)