Thermal expansion measurement of pure aluminum using a very low thermal expansion heating stage for x-ray diffraction experiments

Precise lattice parameter measurements for residual stress analysis requires good specimen alignment in the beam path. If these measurements are to be performed at elevated temperatures, then the effects of thermal expansion must be accounted for in the alignment and calibration procedure. During a recent study, residual strains in a metal matrix composite were measured in situ during dynamic temperature cycling. These experiments required a stage capable of rapid heating and cooling as well as a very low thermal expansion to minimize the specimen displacement during the cycling. A low expansion stage, heated with a programmable infrared heater, was developed in which the front (irradiated) surface is the reference plane. The thermal expansion of the stage was measured using a diffraction technique to determine false lattice parameter shifts due to specimen displacement and was found to be less than the measurement limit of the apparatus. With small specimens, the temperature control became difficult and fluctuations of ±1.5 °C were observed. The temperature dependence of the lattice parameter for pure Al was measured between 30 and 386 °C. Very good agreement was obtained with previously published data. Thus a new rapid technique which allows complete measurement of the lattice thermal expansion in less than 2 h has been demonstrated. This technique can also be applied to measurement of the temperature dependence of residual stresses in complex materials such as metallizations for microelectronics and for metal matrix composites.