Papers by Keyword: Ti-Ni-Cu Alloy

Abstract: Microstructure and mechanical properties of Ti_51.5Ni₂₅Cu_23.5 ribbon fabricated by melt spinning were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile tests. Some B19 martensite crystalline with (011) compound twin was embedded in the mainly amorphous ribbon, while the ribbon annealed at 450°C for 1 h is at fully martensitic state. Annealing process alter the preferential orientation from (022)-B19 to (111)-B19. Tensile fracture stresses of as-spun ribbon and the annealed ribbon are 1257 MPa and 250 MPa, respectively. The tensile fracture morphology of as-spun ribbon shows typical vein fringe while that of the annealed ribbon reveals fine but depth-inhomogeneous dimples. After tensile deformation, the annealed ribbon exhibits typical martensitic detwinning behavior accompanying with the strain contrast.

Abstract: The shape memory alloy strips of Ti50Ni15Cu35 and Ti50Ni10Cu40 had been fabricated by arc melt overflow. Their microstructures and shape memory characteristics were investigated by means of X-ray diffraction, optical microscopy and differential scanning calorimetries. The microstructure of as-cast strips exhibited columnar grains normal to the strip surface. X-ray diffraction analysis showed that one-step martensitic transformation of B2-B19 occurred in the alloy strips. According to the DSC analysis, it was known that the martensitic transformation temperature (Ms) of B2→B19 was 71.2°C in Ti50Ni15Cu35 and 64.5°C in Ti50Ni10Cu40 alloy strip, respectively. During thermal cyclic deformation with the applied stress of 60 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be 4.9°C and 1.4% in Ti50Ni15Cu35 alloy strip. However, Ti50Ni10Cu40 alloy strip was so brittle that its mechanical properties could not be measured.

Abstract: Ti-51Ni(at%) and Ti-40Ni-10Cu(at%) alloy wires with diameters of 0.3mm, 0.5mm and 0.7mm were prepared by drawing the alloy ingots fabricated by vacuum induction melting. Heating rates of the wires were investigated by measuring changes in temperatures of them while applying currents in the range of 1 A and 6 A to them and cooling rates were investigated by measuring changes in temperatures of them after cutting currents. Heating rate increased with increasing the amount of current, while cooling rate was kept constant. Both heating rate and cooling rate increased with decreasing diameter of wire. This suggested that high amount of current and small wire diameter were required for high heating and cooling rate. Comparing Ti-50Ni alloy wires with Ti-40Ni-10Cu alloy wires, heating rates of the latter was faster than that of the former, although cooling rates were almost same. This suggested that Ti-40Ni-10Cu alloy wires is better than Ti-50Ni alloy wires for the applications requiring high actuating rates.

Abstract: Effects of hydrogen doping on the internal friction (IF) of ternary Ti50Ni50-xCux (x=15, 20, 25)
shape memory alloys, prepared by rolling and annealing laminating Ti and Ni-Cu alloy sheets, have been measured with a damping mechanical analyzer in a forced bending oscillation mode at temperatures from 173K to 423K at three frequencies, 0.1, 1 and 5Hz. The effects of hydrogen doping on IF are common to the three alloys: a hydrogen IF peak appears at around 260K; the IF peak value (tanφ) increases rapidly with increasing hydrogen concentration up to tanφ=0.03 at 0.5at% and then decreases; the peak temperature also increases rapidly and then gradually decreases. From the frequency dependence of the peak temperature, the activation energy E and the pre-exponential factor ω0 have been analyzed to be E=0.6-0.7eV and ω0=1013-14s-1. The origin of the hydrogen IF is interpreted to be the Snoek-Koester effect due to interaction of twin boundary dislocations and segregated hydrogen atoms. Effects of hydrogen on mechanical properties of the alloys have also been studied.