Preparation and properties of negative thermal expansion Zr2P2WO12 powders and Zr2P2WO12/TiNi composites

Zirconium tungsten phosphate (Zr2P2WO12, denoted as ZWP) powders were synthesized via hydrothermal method for the first time. Nickel titanium (TiNi), as a shape memory alloy, is a very important industry material with large positive coefficient of thermal expansion (CTE), while ZWP is a kind of negative thermal expansion materials. TiNi alloys with and without addition of ZWP powders were compacted by hot-pressing sintering method at 1100 ̊C for 3 h. The obtained ZWP ceramics showed a CTE of about −2.012 × 10−6/K. The ZWP/TiNi composites with reduced CTEs were successfully synthesized without decomposition of ZWP or reactions between ZWP and TiNi alloy. From the results of X-ray powder diffraction, no phase transitions occurred during sintering. SEM images show that the ZWP powders consist of relatively homogeneous particles with sizes around 360 nm. With increasing the ZWP content in the composites, the relative density of the obtained ZWP/TiNi composite materials reduced and the hardness increased.