MICROSTRUCTURE AND THERMAL-STABILITY OF AL-CR-X (X=NI, MO, SI) POWDERS OBTAINED BY CENTRIFUGAL ATOMIZATION

The microstructure and the thermal stability of rapid solidified centr ifugally atomised Al-3Cr-X (X=1Ni, 3Ni, 0 . 3Mo, 1Si, or 3Si, at.-%) p owders were studied. Three main types of microstructure were observed int he powders: cellular, globular, and rosettelike. some powders exhi bited a mixture of these. In the atomised state the alloys usually had two phases, intermetallic Al13Cr2 and alpha-Al solid solution. Therma l stability was studied for a range of temperatures from 20 to 500 deg rees C. The phase Al3Ni appeared in the nickel containing alloys and g rew upon heat treatment. The molybdenum containing alloy did not show any noticeable change upon heat treatment. With respect to the silicon containing alloys, the intermetallic Al13Cr2 transformed into Al13Cr4 Si4 at high temperatures. On the basis of bibliographic information a nucleation map was calculated relating the prevalence of the intermeta llic Al13Cr2 phase and the alpha-Al phase to the particle diameter and the chromium concentration of powder obtained by centrifugal atomisat ion. (C) 1996 The Institute of Materials.