關鍵字：SP-700、應力誘發、冷加工 The study analyzes the characteristics of tensile deformation under the different microstructures for SP-700 titanium alloy undergoing solution treatment and water quenching, followed by applying different amount of coldworking and aging treatment through the analysis of microstructure and mechanical properties. The results show that the microstructure of SP-700 titanium alloy contains block primary α-phase (αp), residual β-phase (βr) and lamellar-martensite phase (α”) distributed in βr after solution treatment and water quenching. The application of coldworking for water quenching alloy does not show difference on primary α-phase (αp) and lamellar-martensite phase (α”) due to work and quenching alloy. However, residual β-phase (βr) will reduce the quantity due to changes in the stress induced for lamellar-martensite phase, which then turns into hardened and brittle lamellar-martensite phase (α”). Lamellar-martensite phase (α”) increases following the rise in the amount of coldworking to become more intense and delicate. The lamellar-martensite phase (α”) and residual β-phase (βr) will both undergo phase change into α+β equilibrium phase for water quenching alloy after receiving aging treatment, whereas the microstructure becomes the previously exiting primary α-phase (αp) while the lamellar-martensite phase (α”) transits into spherical α equilibrium phase distributed with tiny particles of β equilibrium phase and the residual β-phase (βr) transits into β equilibrium phase distributed with tiny particles of α equilibrium phase. After applying coldworking and aging treatment to the quenching alloy, the amount of α” lamellar-martensite phase increases following the rise in coldworking while becoming more delicate. After the aging treatment, the amount of α equilibrium phase becomes more and finer, while the cooling work causes the crystalline grains of residual β phase (βr) to increase and deform, forming more delicate β equilibrium phase after aging treatment. When the water quenching alloy undergoes tensile testing, the alloy will undergo phase change with “stress induced for lamellar-martensite” due to the soft-tenacity phase contained in βr, which causes alloy to present significant hardening and the quenching alloy to exhibit high ductility and strength. After undergoing coldworking, quenching alloy will have less significant secondary hardening phenomenon during tensile testing with increasing coldworking, due to the change of stress induced for lamellar-martensite already occurred during coldworking. Water quenching alloy will have substantial increase of yield strength after aging treatment since its microstructure increase in more hardened and brittle α equilibrium phase and without the phase change in “stress inducted for lamellar-martensite.”The ductility appears low due to the lack of significant secondary hardening phenomenon during the tensile process. The microstructure of water quench alloy undergone coldworking and aging treatment will have slightly highly yield strengthen than alloy without work while ductility remains low in the similar manner.
