Microstructure and thermal stability of Al–Cr–X (X=Ni,Mo,Si) powders obtained by centrifugal atomisation

Abstract

The microstructure and the thermal stability of rapid solidified centrifugally atomised AI–3Cr–X (X=1Ni, 3Ni, 0·3Mo, 1Si, or 3Si, at.-%) powders were studied. Three main types of microstructure were observed in the powders: cellular, globular, and rosettelike. Some powders exhibited a mixture of these. In the atomised state the alloys usually had two phases, intermetallic Al₁₃Cr₂ and α-Al solid solution. Thermal stability was studied for a range of temperatures from 20 to 500°C. The phase Al₃Ni appeared in the nickel containing alloys and grew 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 Al₁₃Cr₄Si₄ at high temperatures. On the basis of bibliographic information a nucleation map was calculated relating the prevalence of the intermetallic Al₁₃Cr₂ phase and the α-Al phase to the particle diameter and the chromium concentration of powder obtained by centrifugal atomisation.

MST/3273