Effect of Dy on microstructures and mechanical properties of Ni-44Ti-6Al alloy

The effects of Dy addition on the microstructure Ni-44Ti-6Al alloy were studied through electron scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements, and the mechanical properties of Ni-Ti-Al-Dy alloys were investigated by compressive tests at room temperature and elevated temperatures. The results showed that Dy existed as a solid solution element in NiTi phase in Ni-44Ti-6Al alloy with the small solubility of 0.03% (mass fraction), and, moreover, caused the refinement of crystal grains. The extra Dy tended to form Dy-O phase, distributing as small particles in gain boundaries. The yield stress and plasticity of Ni-44Ti-6Al alloy were improved by the addition of Dy. For Ni-44Ti-6Al alloy with Dy of 0.05%, the yield stress and plasticity reached the maximum values of 1570 MPa and 10.9%, respectively, but the corresponding values decreased with further increase of Dy content. The yield strength of Ni-44Ti-6Al alloy at 600~800 °C was remarkably increased by the addition of Dy and it exhibited the maximum value when Dy content was 0.05%. The improvement of mechanical properties was mainly attributed to the grain refinement and solid solution strengthening effects caused by Dy.