Comparison of nanocrystalline material produced using mechanical milling and a RF-plasma heating source

Abstract

This paper reports on nanocrystals which are polycrystalline materials with a grain size on the order of one to ten nanometers and appear to be a new class of materials with interesting properties and characteristics. Since the grain size of these materials is so small, a large percentage of their atoms are located in the interfaces; thus, the material can be thought of as a composite consisting of a crystalline component and a boundary component. The properties of these materials are, therefore, expected to be dependent upon the relative amounts of these two components. A study has been initiated to produce nanocrystalline Cr{sub 3}Si and Ti{sub 5}Si{sub 3} material. It has been shown that by reducing the grain size to the nanometer scale, the ductility of brittle compounds increases, due presumably to the increase in the percentage of the boundary component. Thus, these materials were examined as models of how hard, brittle, high temperature intermetallic compounds may behave in the nanocrystalline state. The silicide compounds also are being studied since they have excellent properties such as low densities, high melting temperatures, good corrosion resistance at low temperatures and fairly good oxidation resistance at high temperatures. It is hoped that withmore » this combination of characteristics, plus increased ductility due to the small grain size, these materials will find practical industrial applications. The nanocrystalline material studied was produced using mechanical milling techniques and an inductively coupled plasma (ICP) system. Mechanical milling was chosen since it has been demonstrated to be a convenient way to produce large quantities of nanocrystalline material. However, ball milling may produce a significant amount of contamination from the containment vessel and milling medium, the actual amount being dependent upon the specific method, length of milling time, container and medium used.« less