Effect of zirconium on grain growth and mechanical properties of a ball-milled nanocrystalline FeNi alloy

Grain growth of ball-milled pure Fe, Fe92Ni8, and Fe91Ni8Zr1 alloys has been studied using X-ray diffractometry (XRD), focused ion beam (FIB) microscopy and transmission electron microscopy (TEM). Mechanical properties with respect to compositional changes and annealing temperatures have been investigated using microhardness and shear punch tests. We found the rate of grain growth of the Fe91Ni8Zr1 alloy to be much less than that of pure Fe and the Fe92Ni8 alloy at elevated temperatures. The microstructure of the ternary Fe91Ni8Zr1 alloy remains nanoscale up to 700 degrees C where only a few grains grow abnormally whereas annealing of pure iron and the Fe92Ni8 alloy leads to extensive grain growth. The grain growth of the ternary alloy at high annealing temperatures is coupled with precipitation of Fe2Zr. A fine dispersion of precipitated second phase is found to promote the microstructural stability at high annealing temperatures and to increase the hardness and ultimate shear strength of ternary Fe91Ni8Zr1 alloy drastically when the grain size is above nanoscale. (C) 2012 Elsevier B.V. All rights reserved.