Polymer matrix composites (PMCs) have emerged as critical materials in lightweight engineering applications due to their excellent mechanical properties and design versatility. However, their inherent limitations in electrical and thermal conductivity necessitate metallization, particularly for applications such as lightning strike protection (LSP) and electromagnetic interference (EMI) shielding. Cold spraying, a low-temperature metallization technique, addresses the shortcomings of conventional methods by enabling the deposition of dense, oxide-free, and highly conductive coatings with minimal damage to the composite substrate. This review provides a comprehensive overview of advancements in metallization techniques, with a focus on cold spraying, to enhance the electrical and thermal performance of PMCs for LSP and EMI shielding. The combination of PMCs with conductive materials presents an innovative approach to achieving lightweight, corrosion-resistant, and efficient LSP and EMI shielding solutions, offering significant advancements in surface functionalization. Future research directions include the exploration of hybrid metallization strategies and the integration of cold spraying with additive manufacturing, highlighting their potential to create multifunctional and high-performance PMC-based systems. Additionally, emerging trends such as novel or smart materials, optimization of cold spray processes through advanced modeling, and the translation of these innovations into industrial applications are discussed.

Stainless-steel feedstocks achieve increasing importance as sustainable and cost-efficient alternative regarding thermal spraying. However, the wear resistance is often insufficient for demanding applications. Therefore, an additional surface hardening step by thermochemical processes, in particular by gas nitriding, is promising for enhancing surface functionality. The characteristic porosity of thermally sprayed coatings facilitates deep nitrogen diffusion increasing hardness and wear resistance, due to the formation of precipitates. Because nitrides are thermally stable, applications at elevated temperatures are enabled. The process combination was examined for the ferritic stainless-steel AISI 431 applied on mild steel by high-velocity oxygen fuel spraying (HVOF), followed by subsequent gas nitriding. The influence of the thermochemical treatment with respect to a variation in the nitriding potential has been determined in terms of microstructure, phase formation, hardness distribution as well as reciprocating wear resistance at room and elevated temperature. The increase in hardness over 900 HV0.01 and wear resistance with wear rates consistently lower than 1.3 × 10^-4 mm³ Nm⁻¹ can be attributed to the successful enrichment of nitrogen and the formation of mainly Fe₄N precipitates at the coating’s surface. Even at 350 °C, the nitride surface layer provides better wear protection compared to the as-sprayed condition. Graphical Abstract

The development of multi‐principal‐element alloys (MPEAs) with unique characteristics such as high work hardening capacity similar to well‐known alloy systems like Hadfield steel X120Mn12 (ASTM A128) is a promising approach. Hence, by exploiting the core effects of MPEAs, the application range of conventional alloy systems can be extended. In the present study, work‐hardening MPEAs based on the equimolar composition CoFeNi are developed. Mn and C are alloyed in the same ratio as for X120Mn12. The production route consists of cast manufacturing by an electric arc furnace and surface functionalization via mechanical finishing using ultrasonic‐assisted milling (USAM) to initiate work hardening. The microstructure evolution, the hardness as well as the resulting oscillating wear resistance are detected. A pronounced lattice strain and grain refinement due to the plastic deformation during the USAM is recorded for the MPEA CoFeNi‐Mn12C1.2. Consequently, hardness increases by ≈380 HV0.025 in combination with a higher oscillating wear resistance compared to the X120Mn12. This shows the promising approach for developing work‐hardening alloys based on novel alloy concepts such as MPEAs.