ZrW₂O₈/ZrO₂Composites with Low/Near-Zero Coefficients of Thermal Expansion Fabricated at Ultralow Temperature: An Integration of Hydrothermal Assembly and a Cold Sintering Process

ZrW2O8/ZrO2 composites with tunable low/near-zero coefficients of thermal expansion (CTE) are promising candidates in several fields including aerospace, precision manufacturing and measurement, electronic circuit, etc., for counteracting the thermal expansion effect. However, bottleneck issues (such as the unstable decomposition of ZrW2O8 phase, manufacturing size limitation, etc.) caused by conventional high-temperature sintering impede the development and application of ZrW2O8/ZrO2. To solve these scientific issues, a methodology integrating hydrothermal assembly with a cold sintering process (CSP) is exploited. The ZrW2O8/ZrO2 composite powders with a mace-like structure, in which the spherical ZrO2 nanoparticles peripherally embed on the rod-like ZrW2O8 matrix particles, are hydrothermally assembled. Then, the relatively dense ZrW2O8/ZrO2 composites with excellent low or even near-zero CTE are successfully achieved by CSP (as low as 190 °C) with a postannealing treatment (550 °C). The evolution of sintering densification, phase composition, and microstructure followed by the fundamental mechanism regarding the hydrothermal assembly of the mace-like structure and densification of CSP are investigated in detail. This research not only effectively overcomes the bottleneck issues of ZrW2O8/ZrO2 via integrating the hydrothermal assembly with the sintering technology at ultralow temperature but also develops a promising prospect for the fabrication of a broader range of metastable functional materials.