Kinetic Study of the Solid-State Transformation of Vacuum-Plasma-Sprayed Ti-6Al-4V Alloy
- PDF / 1,306,948 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 46 Downloads / 177 Views
H. R. Salimijazi, Z. A. Mousavi, M. A. Golozar, J. Mostaghimi, and T. Coyle (Submitted May 15, 2013; in revised form August 12, 2013)
Because of the nature of the plasma spraying process, the physical and mechanical properties of vacuumplasma-sprayed structures of Ti-6Al-4V alloy are completely different from those of conventionally manufactured alloys such as bulk materials from casting and forging. To obtain desired mechanical and physical properties, vacancy and internal defects must be reduced, splat boundaries must be eliminated, and optimal phase compositions should be obtained through postdeposition heat treatments. To determine appropriate heat treatment processes, one needs to study the kinetic behavior of the as-sprayed microstructure at elevated temperatures. In the current study, the kinetics of the solid transformations found in Ti-6Al-4V alloys produced during the vacuum plasma spraying process was studied based on the JohnsonMehl-Avrami theory. For the kinetic behavior of this alloy, the nonconstant temperature dependence of the transformation rate constant exhibits an irregularity at 900 °C, marking a change in the transformation mechanism. For the lower-temperature (900 °C), a gradient change indicates a change in the transformation mechanism. The first mechanism was the formation of a-phase grain boundary, and the second mechanism was a-plate nucleation and growth from grain boundaries. The value of the transformation rate constant in the kinetics study of as-sprayed Ti-6Al-4V alloy was much higher than for material produced by the casting method. Using the results obtained from the kinetics of the b ! a þ b phase transformation at different constant temperatures, a time–temperature–transformation (TTT) diagram for as-sprayed Ti-6Al-4V alloy was developed.
Keywords
heat treatment, net-shape forming, Ti-6Al-4V, vacuum plasma spray, characterization, TTT diagram
1. Introduction Titanium and titanium alloys have found widespread applications in the aerospace industry for more than three decades due to their desirable combination of properties such as high specific strength, good corrosion resistance in many environments, and high fatigue strength (Ref 1-3). Titanium is an allotropic element. At room temperature, titanium has a hexagonal close-packed (hcp) crystal structure, which is referred to as the ‘‘alpha’’ phase. This structure transforms to a body-centered cubic (bcc) crystal This article is an invited paper selected from presentations at the 2013 International Thermal Spray Conference, held May 13–15, 2013, in Busan, South Korea, and has been expanded from the original presentation. H.R. Salimijazi, Z.A. Mousavi, and M.A. Golozar, Materials Engineering Department, Isfahan University of Technology, 84156-83111 Isfahan, Iran; and J. Mostaghimi and T. Coyle, Centre for Advanced Coating Technologies, University of Toronto, Toronto, ON Canada. Contact e-mail: jazi@mie. utoronto.ca.
Journal of Thermal Spray Technology
structure, the so-called beta phase, at 883 C. Titanium alloys are classified
Data Loading...
