Towards Ultra-Dense Functionally Graded Conductive Coatings via Micro-Forging Assisted Cold Spray

As a solid-state additive manufacturing technology, cold spray enables high-conductivity deposition of oxidation-sensitive metals such as copper without thermal degradation, positioning it as a key enabler for electrified mobility, power electronics, aerospace electrification, and repair of high-value components. Although direct deposition of Cu onto Al using high-pressure cold spray can produce well adhered conductive coatings, single material deposits do not always provide the optimum through thickness property distribution, thermal cycling resistance, or multifunctional performance required in demanding service environments. Functionally graded coating architectures offer a route to tailor the transition from substrate compatible layers to highly conductive top layers, thereby improving interface robustness and extending application flexibility.

However, conventional copper coatings produced using medium-pressure cold spray systems with nitrogen at relatively lower processing parameters often retain residual porosity in the range of 0.5–2%, limiting achievable electrical conductivity (typically 60–80% IACS) and multifunctional loading. In-situ shot peening or micro-forging (MF) assisted cold spray has recently emerged as a promising strategy to overcome these limitations by introducing high kinetic energy secondary particles that locally enhance plastic strain, promote oxide disruption, and improve metallurgical contact during impact without relying on expensive helium gas or extreme processing conditions.

In this study, the MF concept is extended to the development of ultra-dense functionally graded conductive coatings. The influence of MF particle fraction and graded layer design on particle velocity distribution, deposition efficiency, coating porosity, and electrical performance was systematically investigated. MF assisted deposits exhibited enhanced particle flattening, reduced residual porosity, and improved interfacial integrity compared with conventional coatings. The proposed approach provides a scalable pathway for manufacturing dense conductive coatings under industrially relevant conditions and offers new insights into deformation-driven densification mechanisms for multifunctional conductive coating applications in advanced electrified systems.