Structure and stability of the precipitates in melt spun ternary Al-transition-metal alloys

The decomposition of supersaturated solid solution of ternary, melt spun Al-transition-metal alloys has been examined using analytical transmission electron microscopy. It has been found that the presence of small amounts of iron in AlV, AlMo and AlCr alloys can give rise to a fine dispersion of P-phase precipitate in the grain centres. It has been shown that the P-phase is quasicrystalline phase and has an orientation relationship with Al matrix as: i2|〈001〉_Al, 〈τ²τ1〉_Al, i3|〈111〉_Al, 〈τ²10〉_Al; i5|〈τ10〉_Al, τ = (1 + √5)/2. The stability of quasicrystals is significantly improved by the presence of iron in A1-transition-metal alloys. The effect of iron on stabilising the quasicrystal precipitates is believed to be due to the fact that iron replaces the oversized transition metal (TM) atoms V, Cr and Mo in the smaller TM sites, resulting in a reduction of structural stress of quasicrystalline phase. The significance of these observations on the structure and stability of quasicrystal precipitates is discussed in terms of the development of high temperature dispersion strengthening Al-based alloys with transition metals.     

Phase stability investigations of the palladium-cadmium system: part ii. structural studies

The crystal structure and the precise lattice parameters of palladium-cadmium alloys containing 33 to 60 at. pct Cd were determined by X-ray diffraction at 294 K, using samples quenched from 1073 K. The results indicate that at 1073 K the β₁(Ll₀) phase extends from 33 to 55 at. pct Cd while the β′(B2) phase is stable from 56 to 60 at. pct Cd. No evidence for the existence of a separate high-temperature phase between the β, and β′ phase fields was found. A modification of the currently accepted Pd-Cd phase diagram near the equiatomic composition is proposed. The lattice parameters of the fct β₁ - phase have the following values at the stoichiometric composition:a = 0.4 2817 nm,c = 0.3 6310 nm. The molar volume of the β₁-phase is a linear function of composition from 33 to 50 at. pct Cd. The partial molar volumes of Pd and Cd have the following values in this range: V_Pd = 8.87 cm³/g-atom, V_Cd = 11.18 cm³/g-atom. An analysis of Pd-and Pt-based Ll₀ phases indicates that the c/a ratio of these phases is related to their enthalpy of formation. Phases with a small enthalpy of formation have a high c/a ratio while phases with a large enthalpy of formation exhibit a small c/a ratio. Y. A. CHANG, formerly Professor of Materials Engineering and Associate Dean for Research, Graduate School, University of Wisconsin-Milwaukee     

Modeling of structural and compositional homogenization of plutonium-1 weight percent gallium alloys

The microstructure of as-cast Pu-1 wt pct Ga alloys is characterized by extensive Ga microsegregation often referred to as “coring”. This process results in grains that consist of Ga-rich cores (∼1.6 wt pct) with Ga-poor (∼0.1 wt pct) edges. Cored grains can be homogenized at moderately high (i.e., >400 °C) temperatures, though the time required to achieve chemical homogeneity is not well constrained. In this article, we apply several analytical diffusion modeling techniques to characterize the kinetics of alloy homogenization as a function of time and temperature. We also review the experimental investigations that have used analytical tools such as X-ray diffraction, density, dilatometry, and electron microprobe analysis to characterize Pu-Ga alloy homogenization. Data from these studies are used as a basis of comparison with modeling results. In particular, Ga coring-profile modeling appears to be a powerful tool for predicting alloy homogenization. FRANK E. GIBBS, formerly Technical Staff Member with the Nuclear Materials Technology Division, Los Alamos Laboratory     

Modeling of structural and compositional homogenization of plutonium-1 weight percent gallium alloys

The microstructure of as-cast Pu-1 wt pct Ga alloys is characterized by extensive Ga microsegregation often referred to as “coring.” This process results in grains that consist of Ga-rich cores (∼1.6 wt pct) with Ga-poor (∼0.1 wt pct) edges. Cored grains can be homogenized at moderately high (i.e., >400 °C) temperatures, though the time required to achieve chemical homogeneity is not well constrained. In this article, we apply several analytical diffusion modeling techniques to characterize the kinetics of alloy homogenization as a function of time and temperature. We also review the experimental investigations that have used analytical tools such as X-ray diffraction, density, dilatometry, and electron microprobe analysis to characterize Pu-Ga alloy homogenization. Data from these studies are used as a basis of comparison with modeling results. In particular, Ga coring-profile modeling appears to be a powerful tool for predicting alloy homogenization.