Effects of Different Solution Treatments on Microstructure and Phases of Ti50Ni24.9Cu25Y0.1 Alloy

Abstract:

The effects of different cooling methods on the microstructure and phases of the Ti50Ni24.9Cu25Y0.1 alloy (at%) after the solution treatment at 900 oC for 9 h were studied by Optics Microscope and X-ray diffraction. The regularity of element distribution of the alloy during the solidification process was analyzed by energy dispersive spectrometer (EDS). Results show that there is obvious microsegregation of the alloy during the solidification process. Ni element is rich inside the grains, and Cu element is rich at the grain boundaries. Pure titanium precipitates both inside the grains and at the grain boundaries, which are of faceted crystal growth. The solution treatment at 900 oC for 9 h can effectively reduce the microsegregation of the alloy. XRD analysis reveals that the microstructure of the alloy after the solution treatment at 900 oC for 9 h followed by watering quenching (WQ) is composed of monoclinic B19’ martensite and a few fcc Ti2(Ni,Cu), while only B19’ martensite appears for the solution treated alloy after air cooling or furnace cooling. High-temperature XRD shows that there is only one-step B19’-B2 martensitic transformation.