Electromigration-enhanced Kirkendall effect of Cu/Ti direct diffusion welding by sparking plasma sintering

Electromigration-enhanced Kirkendall effect is firstly observed in Cu/Ti diffusion welding by sparking plasma sintering. Microstructural evolution and mechanical properties of Cu/Ti joints were systematically investigated to clarify the electromigration-enhanced Kirkendall effect on the mechanism of diffusion joining. Four types of Cu-Ti intermetallic compounds were formed at the interface of bonded joint: CuTi2, CuTi, Cu3Ti2, and beta-Cu4Ti. At welding temperature less than 833 K, Cu atomic diffusion was enhanced by current, leading to large Kirkendall Voids along the Cu matrix near intermetallic, resulting in low joint strength. However, as the welding temper-ature increased to 833 K, a continuous CuTi2 Kirkendall plane was formed in the beta-Cu4Ti compound layer, and the growth of the brittle CuTi phase was impeded. A notable observation of this study is that the temperature range for manufacturing high-strength Cu/Ti joints diffusion welding by SPS was determined to be 813-863 K, which is much wider than that reported in the literature. The maximum average shear strength of the joints welded at 833 K was 103.1 MPa, which is twice as large as the value commonly reported. This difference is attributed to the suppression of the brittle CuTi phase by the electromigration-enhanced Kirkendall effect.