Phase transformations in thermally cycled Cu/ZrW₂O₈ composites investigated by synchrotron x-ray diffraction

A Cu/ZrW₂O₈ metal matrix composite was thermally cycled between 298 and 591 K while being subjected to x-ray diffraction in transmission using high-intensity synchrotron radiation. The reversible allotropic phase transformations of ZrW₂O₈ between its two low-pressure phases and its high-pressure phase were observed within the composite bulk as a function of temperature. This observation gives experimental proof of the existence of the reversible pressure-induced phase transformation, which had been inferred indirectly from dilatometry in a previous investigation and assigned to the large thermal mismatch stresses in the composite. The volume fraction of each ZrW₂O₈ compound was determined from the measured diffracted intensity, and the thermal expansion behaviour of the composite was then calculated. Good agreement was found with the experimental dilatometric curve reported in a recent investigation.