Enhancing joint strength in direct-injection-molded PPS-Ti composite through plasma electrolytic oxidation coated interfaces

Abstract

This study investigates the enhancement of bonding strength between titanium alloy (Ti-6Al-4V) and polyphenylene sulfide (PPS) in injection molded direct joining (IMDJ) composite structures through a combined sand blasting and plasma electrolytic oxidation (PEO) method. The primary objective is to explore how surface modification, particularly the introduction of chemical functional groups, influences joint strength. A porous surface structure with both macro- and micro-scale features was created on the titanium alloy surface using the sand blasting and PEO process. Urea (CO(NH₂)₂) was added to the electrolyte to successfully introduce amino (-NH₂) and hydroxyl (-OH) groups onto the metal surface, which promote hydrogen bonding and σ-hole interactions with the PPS. The results showed that increasing the urea concentration led to a corresponding increase in -NH₂ and -OH group density on the metal surface. The maximum bonding strength was observed at a urea concentration of 6 g/L, where the bonding strength was 17 times higher than that of the sand blasting group and 2.4 times stronger than the group without urea addition. This enhancement is attributed to both mechanical interlocking and the formation of chemical bonds between the titanium alloy and PPS. The findings suggest that the combined sand blasting and PEO treatment is a highly effective and simple method to achieve high-strength, durable connections in metal-polymer composite structures, with significant implications for advanced manufacturing and materials design.