Temperature field induced interfacial heterogeneous nucleation of nylon 66: ordered crystalline transition reliability modulation in PA66/TC4 composites

Regulating the polymer phase structure at the metal polymer boundary remains a bottleneck in lightweight polymer metal composites (PMCs). Here, we introduce a temperature-gradient-driven heterogeneous-nucleation strategy that in situ engineers the crystalline architecture of nylon 66 (PA66) directly on Ti-6Al-4 V (TC4) during hot pressing. By controlling hot pressed temperature field, we induce a progressive transition from γ- to α-crystal polymorphs of PA66 at the interface, creating an ordered crystalline phase transformation that functions as a mechanically graded transition zone. The resulting interfacial bonding strength reaches 14.56 MPa at 320°C, outperforming conventional bonding protocols by 78%. Failure mode reveals a micropore anchoring plastic pullout failure and plastic-pullout mechanism. XPS confirms the formation of Ti–O–C covalent bonds that chemically anchor the ordered crystalline phase transformation to the oxide-rich TC4 surface, rich in porous structures, provides it with heterogeneous nucleation sites. This thermally directed polymorphic templating approach offers a facile, scalable route toward ultra-reliable PMCs for next-generation lightweight structures.