There are only a few cost-effective solutions for coating applications in combined mechanical loading and corrosive environments. Stainless steel AISI 304 has the potential to fill this niche, showing excellent corrosion resistance while utilizing the deformation-induced phase transformation from γ-austenite to α’-martensite, which results in an increase in strength. However, it is not known whether this can occur in laser cladded material. Therefore, laser cladded AISI 304 coatings in as-cladded condition and after heat treatment at 1100 °C for 60 min were investigated before and after bending deformation, by means of light microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was shown that due to the dendritic microstructure accompanied by an inhomogeneous distribution of the main alloying elements (Cr and Ni), no deformation-induced phase transformation occurred in the as-cladded coating. The applied approach with subsequent solution heat treatment at 1100 °C for 60 min resulted in a homogeneous γ-austenite microstructure, so that a deformation-induced martensitic transformation (DIMT) could occur in the coatings. However, the volume fraction of martensite that had been formed locally at individual shear bands was rather low, which can be possibly attributed to the high Ni content of the feedstock, stabilizing the γ-austenite microstructure. This study shows the possibility of exploiting the DIMT mechanism in heat-treated laser-cladded AISI 304 coatings.

For lightweight constructions, joining dissimilar metals is often indispensable to achieve exceptional properties. A common challenge is the bonding of steel and aluminum parts. The use of cold-sprayed coatings as a bonding agent is an innovative approach for high pressure die casting (HPDC) aluminum-steel hybrid components in order to achieve a metallurgical bonding, although it comes with high requirements in terms of coating adhesive and cohesive strength. Therefore, the main aim of this study is the optimization of a post-processing treatment of cold-sprayed coatings in order to improve the cohesive strength to help the introduced coatings withstand the mechanical and thermal stresses during HPDC. The effect of the heat treatment on the mechanical properties of the cold-sprayed Al99.0 and AA7075 coatings was investigated. Freestanding coatings were heat-treated at a temperature of T = 400 °C for different dwell times in order to analyze the recrystallization kinetics through hardness measurements. Two different heat treatment states along with an as-sprayed condition were chosen to investigate the evolution of the mechanical properties of the coatings by means of 3-point bending tests. Besides the softening of the coatings during the heat treatment, sintering effects at splat boundaries and their impact on fracture mechanisms were investigated using electron microscopy.

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