Metastable phase formation in rapidly solidified Al–Mo alloys
Authors: Logan, E. A.; Pratt, J. N.; Loretto, M. H.
Source: Materials Science and Technology, Volume 5, Number 2, February 1989 , pp. 123-130(8)
Publisher: Maney Publishing
Abstract:In Al-Mo alloys, rapidly quenched from the melt at rates of approximately 106 KS−1, it has been demonstrated that single phase solid solution alloys can be obtained in materials with up to 1·3 at.-%Mo. Above this concentration, two new metastable phases are observed in the form of small precipitates within the matrix of aluminium-rich solid solution. These have been identified as a diamond cubic phase, space group Fd3m, a =1·4–1·5 nm and a hexagonal phase, space group P6/mmm or P6/mmc, a = 0·45 nm, c = 0·27 nm. The maximum supersaturation of the solid solution matrix, obtained in alloys containing such precipitates, was found to be 2·45 at.-%Mo. Upon annealing, both the solid solutions and the metastable intermediate phases decompose directly to the equilibrium structure of aluminium-rich solid solution and Al12Mo. The Al12Mo forms either as precipitates on the grain boundaries or as a layer around the metastable intermediate phases. From a good correlation between the maximum supersaturation obtained and that predicted by consideration of thermodynamic and kinetic factors it is suggested that a similar theoretical treatment may be used to provide an indication of the maximum supersaturation achievable in other systems.
Document Type: Research Article
Publication date: 1989-02-01
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