Post-spray heat treatment of cold-sprayed coatings: A review

Cold spray is a solid-state coating and repair technology that limits melting-related oxidation and grain coarsening; however, as-sprayed deposits can contain residual porosity, high residual stresses, and weak interparticle interfaces that restrict mechanical reliability. This review surveys post-spray heat treatment (PSHT) routes reported for cold-sprayed coatings, with primary emphasis on annealing/ageing and induction-based heating, while more limited HIP-related evidence is discussed where relevant. PSHT strengthens deposits primarily through diffusion-assisted consolidation, pore closure, and recovery/recrystallization that convert mechanically interlocked contacts into more continuous metallurgical bonds. Reported outcomes include higher interparticle/adhesive strength, improved tensile strength–ductility balance, tailored hardness (system-dependent), and enhanced fatigue and wear resistance; in some alloys, atmosphere control during PSHT plays an important role in governing interfacial stability and overall coating integrity. The evidence shows strong material dependence: precipitation-hardenable aluminum alloys benefit from moderate ageing schedules, whereas titanium alloys require higher-temperature treatments to maximize strength–ductility synergy but may soften due to loss of cold-work. Excessive temperatures or air exposure can trigger oxidation, intermetallic formation, and grain coarsening, underscoring the need for system-specific process windows. Key gaps include standardized reporting and long-term durability data under combined corrosion–thermal cycling–fatigue loading, and multivariate optimization linking spray conditions with PSHT.