A Study of Mechanical Alloying of Metal Powders
Abstract:
This investigation was undertaken primarily to obtain information concerning the chemical and structural homogeneity of mechanically alloyed powders and to determine under what conditions, if any, true solid solutions may be formed. Four different alloy systems were selected for study 1 50 wo Cr - 50 wo Mo, 2 Type 316 stainless steel, 3 20.8 wo Mn - 79.2 wo Bi, and 4 a Beta-Ti alloy Ti-11Cr-8Mn-5Mo-3Al. In both the Cr-Mo system and Type 316 stainless steel system, it was established by x-ray diffraction methods that the elemental components had become interdispersed on an atomic scale as a result of high-energy milling, but that a minimum threshold speed is necessary to obtain a significant degree of alloying. However, annealing studies on the milled powders provided strong indications that the solid solutions formed by mechanical alloying are very inhomogeneous from a chemical and structural point of view. Milling difficulties were encountered with the Beta-Ti and Bi-Mn powder systems which precluded any conclusions pertaining to structural or chemical homogeneity in these systems. In both the Bi-Mn and Beta-Ti systems, the tendency toward cold-welding andor diffusion bonding of the particles was so pronounced that it was not possible to achieve a proper balance of cold-welding and particle fracturing in order to mechanically alloy component metals.