Cold spray additively manufactured pure iron for magnetic applications

• Increasing the process gas temperature from 900 to 1000°C improved the relative density of cold spray additively manufactured pure iron from 97.3% to 98.0% and increased the ultimate tensile strength from 196 to 252 MPa. • Residual porosity and weaker inter-particle bonding limited elongation (< 0.3%) and reduced the fracture toughness. • Fatigue crack growth mechanism changed from trans-particle cracking in the near-threshold range to inter-particle decohesion at higher stress intensity factors. • The magnetic response was lower than that of a cold-drawn low-carbon steel with higher coercivity and hysteresis loss. • Electrical resistivity was higher than that of high-purity wrought iron. Pure iron powder combines excellent plastic deformability under a high-velocity impact with high magnetizability and permeability, making it an economical candidate for cold spray additive manufacturing (CSAM) and repairs in magnetic applications. This work explores the fracture mechanics and electromagnetic (EM) properties of CSAM pure iron deposited using cheaper nitrogen as the process gas at temperatures of 900°C and 1000°C, achieving relative densities of 97.3% and 98.0%, respectively. The deposits exhibited an ultimate tensile strength greater than 250 MPa and elongation to fracture of less than 0.3%, a behavior consistent with the characteristic results of as-sprayed CSAM deposits. The fatigue crack growth rate analyses showed the propagation being faster than in wrought iron through different mechanisms: trans-particle crack propagation near the threshold stress intensity factor, and inter-particle decohesion at higher loads. The EM testing indicated that CSAM pure iron saturated at a lower induction and had lower permeability than wrought low-carbon steel, while its coercivity and hysteresis losses were higher, and electrical resistivity was similar. Despite the lower mechanical and magnetic performance, CSAM pure iron or similarly deformable ferritic alloys can meet the requirements for low-field, low-frequency, or direct-current applications, and provide a route for direct near-net-shape additive manufacturing or in-situ repair of magnetic components without scraping existing parts.