Fabrication of metal matrix composites with negative thermal expansion zinc pyrophosphate filler

Abstract

We fabricated Cu matrix composites with low thermal expansion and high thermal conductivity using Zn2P2O7-based negative thermal expansion (NTE) filler. Magnesium and aluminum co-doped Zn2−x−yMgxAlyP2O7 exhibits large NTE over a wide temperature range including room temperature. While achieving high density of the phosphate filler using spark plasma sintering and its uniform dispersion by an ultrasonic process, we reduced thermal expansion of the Cu matrix composites and retained their high thermal conductivity. Particularly, the 30 vol. %-Zn1.70Mg0.25Al0.05P2O7/Cu composite had a linear expansion coefficient as low as 5.1 ppm/K at temperatures of 300–400 K. The results reported herein demonstrate that Zn pyrophosphates, which are superior in terms of environmental impact and cost, are effective for controlling the thermal expansion of metals and are expected to support widely diverse engineering applications in the future.