Rapid Consolidation of Hf Doped NiTi for High Transformation Temperatures

The objective of this study is to develop high transformation temperature shape memory alloys (SMAs) for actuation applications at elevated temperatures. We developed a process to consolidate NiTi micron powders doped with Hf using Material Modification Inc.’s (MMI) proprietary Plasma Pressure Compaction process (P2C). NiTi and NiTiHf samples were characterized to identify the material’s microstructure and composition using Scanning Electron Microscopy (SEM) and Energy Dissipative Spectroscopy (EDS) for both as consolidated and heat treated materials. Chemical and porosity analyses were also conducted to track impurities and microstructure (grain size and porosity). Extensive thermo-mechanical testing of the NiTi and NiTiHf samples were conducted to determine phase transformation temperatures and mechanical properties (Young’s Modulus). An acoustic elastometer was used to obtain the phase transformation temperatures for both NiTi and NiTiHf samples. By doping the SMA powder with 10% Hf (atomic percent), we were able to realize an increase in the austenite finish temperature to over 160 C.