Thermal mismatch strain induced disorder of YMoO and its effect on thermal expansion of YMoO/Al composites.

Fully dense YMoO/Al composites were prepared by squeeze-casting. Relatively mild conditions of 750 °C/20 min/50 MPa were used in order to avoid reaction of the components. SEM, Raman spectroscopy, XRD and dilatometry were used to characterize the microstructures and morphologies of the composites. Zero thermal expansion was achieved in the temperature range where the thermal mismatch strain was zero. We show that the CTE mismatch of Al and YMoO results in compressive and tensile strains that distort the YMoO lattice. We establish a novel method to measure the negative thermal expansion (NTE) materials' CTE under strain by measuring the composites' CTE and calculating the thermal mismatch strain between the NTE ceramic and the metal matrix. The relationship between thermal strain and Raman shift is established and measured and the simulated results are in good agreement. We also find YMoO to have a positive CTE when the surface strain is ≥0.80 × 10%.