Laser Alloying as an Effective Way to Fabricate NiTiPt Shape Memory Alloys

The formation of NiTiPt high-temperature shape memory alloy was examined using laser alloying of NiTi and PtIr alloys. In this regard, four different peak powers were implemented to study their effects on NiTiPt laser-fabricated materials. The lowest (1.0 kW) and highest (2.5 kW) peak powers were disregarded due to the lack of bonding and significant crack formation in the sample, respectively. The NiTiPt phase was successfully formed using the intermediary peak powers due to laser alloying. At a lower peak laser power (1.5 kW), the ternary NiTiPt alloy had a chemical composition that varied from less than 5at. pct to than 30at. pct Pt. At a higher peak power (2.0 kW), a more homogenous material was achieved with slightly higher than 30at. pct Pt. B2 and B19 phases of NiTiPt and various other binary phases were characterized inside the mixed zone (MZ), which were highly dependent on the Pt content of the fabricated NiTiPt. The variation of the chemical composition and formation of different phases resulted in the inhomogeneity of microhardness values in the low-power sample, whereas the high-power sample showed homogenous microhardness values within the mixed zone. The formation of the NiTiPt alloy was inferred from the presence of nanoscale p-phase precipitates which is the main characteristic of NiTiPt alloys, as characterized by Transmission Electron Microscopy (TEM) and Selected Area Diffraction (SAD) patterns. Finally, it was observed that the phase formed inside the mixed zone shifted the critical transformation temperature more than 200°C which also indicates that a high-temperature shape memory alloy was successfully fabricated. This study may open the door for fabricating high-temperature shape memory alloys using laser alloying.