Preparation and damping capacity of Mg/NiTi composites

The Mg/NiTi composites were prepared by pressureless infiltration of Mg powders to improve the strength and damping capacity of porous NiTi alloys. The microstructure of the Mg/NiTi composites were investiaged by OM, SEM, EDS and XRD, the compressive strength and energy absorption ability were analyzed by compressive test and the internal friction and storage modulus were tested by the thermal mechanical analyzer. The results show that the pores of the porous NiTi alloy are filled by Mg through the pressureless infiltration of Mg powders, and the porosity decreases from 50.38% to 5.6% for Mg/NiTi composites. Moreover, the interface bonding of Mg and NiTi alloy is good. The porous NiTi alloys are mainly composed of B2 austenite phase and B19' martensite phase with a few Ni₃Ti and NiTi₂ phases, while the Mg/NiTi composites are composed of infiltrated Mg phase and newly generated Mg₂Ni phase except the phases contained in the porous NiTi alloys. The transformation behavior of the porous NiTi alloys does not change but the transformation temperatures increase after the infiltration of Mg. The compressive strength of the Mg/NiTi composites is up to 554 MPa, 61% higher than that of the porous NiTi alloys. The compression fracture mode also changes from the pore wall collapsed fracture of the porous NiTi alloy to the shear fracture of the Mg/NiTi composites. The energy absorption ability of the Mg/NiTi is greatly improved compared to the porous NiTi alloys. At the same time, the internal friction value of Mg/NiTi composites has a little increase, while the storage modulus is significantly improved, presenting much better damping capacity.