High-temperature creep behavior and microstructure analysis of binary Ti-6Al alloys with trace amounts of Ni

High-temperature creep behavior of two binary, equiaxed Ti-6Al alloys with varying trace amounts of Ni (<3 ppm and 3 ppm) was studied. Uniaxial compression tests were performed over a temperature range of 510-593 degrees C at applied stress ranging from 150 to 300 MPa. Stress and temperature jump tests were per-formed to obtain the stress exponents and the creep activation energy, respectively. Results show that increased amounts of Ni increased the minimum creep rates at all stress levels. Detailed transmission electron microscopy (TEM) analysis of the deformation structure was performed on samples crept monotonically at 200 MPa and 538 degrees C. From the TEM analysis of the dislocation structures, a modified jogged-screw model has been developed that provides quantitative predictions of the observed creep rates. The effect of Ni on the creep rates are explained with reference to the recently reported trends associated with lattice self-diffusion in alpha-titanium in the presence of fast diffusing impurities. (C) 2008 Elsevier B.V. All rights reserved