Microstructure and property alterations and toughening mechanism of cast TC4 alloy by solid state treatment with low-density DC electric field

Abstract

In this paper, the impact of low-density DC electric field treatment (LDCT) on the microstructure and mechanical properties of cast TC4 titanium alloy (CTC4) was investigated. The findings indicate that the driving force for the current provided by LDCT enhances the texture of CTC4. When the current density is sufficiently high, the induced recrystallization effect weakens the texture, leading to an isotropic state. The polygonization of grain boundaries in the LDCT state CTC4 has been identified, along with the emergence of a secondary α phase due to recrystallization. Additionally, this study highlights the phenomenon of preferential nucleation and growth occurring at the grain boundaries. LDCT induces a grain refinement effect in the CTC4 material, whereby the average grain size of the LDCT3 sample decreases from 31.05 μm in the untreated sample to 28.93 μm. The observed reduction in dislocation density in the LDCT states is believed to result from the diffusion of impurity atoms and vacancies. The observation of dislocation plugging at the inner grain boundary of the LDCT3 sample suggests that the electron wind promotes dislocation slip toward the grain boundary. Furthermore, the simultaneous enhancement of strength and toughness in the LDCT state of the CTC4 alloy has been achieved. The LDCT3 sample demonstrates superior performance, exhibiting noteworthy increases of 7.7%, 22.0%, and 10.9% in tensile strength, elongation, and fracture energy, respectively, compared to the untreated sample. The significant role of non-thermal effects in LDCT and the mechanism of atomic diffusion induced by this effect are discussed. The origins of dislocation motion and phase transition are elucidated from the perspective of atomic diffusion.