ISSN:
1662-9779
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Physics
Notes:
Using the self-consistent field approximation, the static concentration waves approachand the Onsager-type kinetics equations, the descriptions of both the statistical thermodynamics andthe kinetics of an atomic ordering of D019 phase are developed and applied for h.c.p.-Ti–Al alloy.The model of order–disorder phase transformation describes the phase transformation of h.c.p. solidsolution into the D019 phase. Interatomic-interaction parameters are estimated for bothapproximations: one supposes temperature-independent interatomic-interaction parameters, whilethe other one includes the temperature dependence of interchange energies for Ti–Al alloy. Thepartial Ti–Al phase diagrams (equilibrium compositions of the coexistent ordered α2-phase anddisordered α-phase) are evaluated for both cases. The equation for the time dependence of D019-type long-range order (LRO) parameter is analyzed. The curves (showing the LRO parameterevolution) are obtained numerically for both temperature-independent interaction energies andtemperature-dependent ones. Temperature dependence of the interatomic-interaction energiesaccelerates the LRO relaxation and diminishes a spread of the values of instantaneous andequilibrium LRO parameters versus the temperature. Both statistical-thermodynamics and kineticsresults show that equilibrium LRO parameter for a non-stoichiometry (where an atomic fraction ofalloying component is more than 0.25) can be higher than for a stoichiometry at high temperatures.The experimental phase diagram confirms the predicted (ordered or disordered) states for h.c.p.-Ti–Al
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/24/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.138.283.pdf
