Volume 49, Issue 7

Alloying with rare earth metals improves to the mechanical properties and corrosion resistance of aluminium base alloys at high temperatures. The rare earth metal erbium may be used for grain refinement. Within a project of computer-aided alloy development based on the CALPHAD ( CALculation of PHAse Diagrams ) method various alloys were melted on the Al-rich side of the ternary system Al-Cu-Er under argon atmosphere and their microstructures were characterized in the as-cast state or after long-term isothermal annealing (400°C/960 h) by means of different investigation techniques. As a result, the phases fcc(Al), τ 1 -Al 8 Cu 4 Er, θ-CuAl 2 , η-CuAl, and Al 3 Er were identified, their compositions and fractions were quantified, and their hardnesses were determined. The experimental obtained microstructures agree very well with the calculated solidification behaviors of the cast alloys. The knowledge gained from this work about the phase compositions and microstructures can also be utilized for the fine optimization of the phase diagram.

Preparation artifacts such as scratches, surface deformation and smearing are often difficult to remove by conventional grinding and polishing. Vibratory polishing is a mechanical process. It provides a very gentle polishing treatment. This final preparation step provides for a removal of ground specimen surfaces without causing deformations. The sample surface was examined on the basis of different mechanical and chemical/mechanical preparation steps with regard to its suitability for subsequent examinations using a scanning electron microscope (for example EBSD measurements).

Based on a mean-field approach a 3D grain growth model is presented which predicts the growth history of individual grains of a grain ensemble in terms of linear grain size and time. The analytical results are compared with the results of numerical simulations using the Monte-Carlo-Potts model. In addition, based on a stochastic model of grain growth, the diffusivity of the very discontinuous movements of individual quadruple and triple junctions is set in relation to the rate of growth. This allows the calculation of the average growth law of an ensemble of grains solely from the measurement of the stochastic growth kinetics of individual grains. The results from simulation and theory are compared with experimental results of in-situ scanning electron microscopy observations of grain growth in polycrystalline metals.