Investigation On The Phase Transitions And Mechanical Properties Of Titanium And Titanium-aluminum Compound Based Alloys With The Valence Electron Theory

Great progress are obtained on theoretical and experimental studies and developments in titanium and Ti_Al- and TiAl-base alloys by means of alloying, process technology and heat treatment during recent years, which need profound research on the relationships between basic theories of phase transitions, valence electron structure (VES) of phases and phase-interfaces, microstructures and corresponding mechanical properties for further study. In this paper, Yu's empirical electron theory of solids and molccules (EET) and Cheng's improved Thmoas-Fermi-Dirac (TFD) theory and the valence electron theory of composition design of alloy are applied to calculate the VES and study the relationships between parameters of VES, phase transitions process and mechanical properties and analyze alloying behaviors of alloying elements, attempting to interpret the microscopic principle of strength and ductility of alloy from electron structure level and calculate volume fractions of phases and β transus in titanium alloys and quantitatively calculate mechanical properties of alloy based on alloy composition and structure. The investigation results are listed as following:1. The parameters of VES related to phase transitions and mechanical properties, i.e., phase structure factors (PSF) and interface conjunction factors (ICF) are interpreted. The calculation model and method of VES of titanium alloys are presented, so the parameters of VES are calculated.2. The VES of α phase and β phase and α/β interface are analyzed and the relationships between the parameters of VES and mechanical properties are discussed. When PSF n_A^β-Ti-M > n_A^β-Ti the β stabilizer M is benefit to the extend of β phase and stabilizes β phase anddecrease β transus. All β stabilizers can increase PSF σ_N of β solid solutions and can make the stability stronger. The PSFs F of β phase with Al, Sn are less than F of β-Ti, F of β phase with Cr is little more than F of β-Ti, so alloying elements Al, Sn and Cr are not benefit to the stability of β phase. The adding of alloying elements decrease lattice electron density ρ_V^L of...