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Copper-zirconium tungstate composites exhibiting low and negative thermal expansion influenced by reinforcement phase transformations
Authors:Dorian K Balch  David C Dunand
Affiliation:(1) the Engineered Materials Department, Sandia National Laboratories, 94551 Livermore, CA;(2) the Department of Materials Science and Engineering, Northwestern University, 60208 Evanston, IL
Abstract:A fully-dense Cu-75 vol pct ZrW2O8 metal matrix composite was fabricated by hot isostatic pressing of Cu-coated ZrW2O8 particles. A small amount of the high-pressure γ-ZrW2O8 phase was created during the cooldown and depressurization following densification; near complete transformation to γ-ZrW2O8 was achieved by subsequent cold isostatic pressing. The thermal expansion behavior of the composite between 25°C and 325°C was altered by the cold isostatic pressing treatment, and also depended on the length of time that had passed between thermal cycles. The measured thermal expansion coefficients within specific temperature ranges varied from −6·10−6 K−1 to far above the thermal expansion coefficient of the copper matrix. The complex temperature-dependent expansion/contraction behavior could be justified by considering the evolution of phase transformations taking place in the ZrW2O8 phase, which were observed by in-situ synchrotron X-ray diffraction measurements.
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