Excellent damping properties and their correlations with the microstructures in the NiTi alloys fabricated by laser-directed energy deposition

The NiTi alloys have superior damping properties, which mainly originate from the stress-induced martensite phase transformations. The stress-induced martensite phase transformation can be improved by the intrinsic Ni4Ti3 precipitation in the NiTi alloys fabricated by laser-directed energy deposition (L-DED), making L-DED a promising method for fabrication of NiTi alloys. Reported investigations on L-DED of NiTi alloys focus on their microstructural features and phase transformation properties. There are no investigations on the damping properties of the NiTi alloys fabricated by L-DED. For the first time, NiTi alloys with excellent damping properties are in-situ synthesized by L-DED, in this paper. The processing parameters are optimized to fabricate NiTi alloys with relatively uniform distributions of small-sized Ni4Ti3 precipitates, which will benefit the damping properties. Dynamic mechanical analysis (DMA) tests were utilized to quantify the damping properties of the NiTi alloys in in two oscillation modes (loading mode and creeping mode) according to the different load conditions in industrial applications. Experimental results show that the damping ratios are in a range of 0.02–0.2, which is comparable or larger than the values of the NiTi alloys fabricated with more complex structures or fabricated using more complex methods. It can be concluded that L-DED can be a promising method to fabricate NiTi alloys without the need for additional post-processing methods. Besides, the correlations between the superior damping properties with the microstructures are discussed.