Industries developing cold spray aim at dense and resistant coatings for component repair. However, as-sprayed 316L coatings display non-equilibrium microstructure and brittle fracture behavior. Improving their mechanical properties requires controlling their microstructure; post-spraying heat treatment is a promising approach. The recovery and recrystallization of coatings were little studied, and heat treatments reported in literature mostly used holding for long time in furnaces, not adapted to on-site repairs. This study aimed at gaining insights into recovery and recrystallization mechanisms of 316L coatings, for a broader range of heat treatment kinetics. A study of powders and as-sprayed coatings was conducted to characterize the initial state. In situ XRD measurements provided input for heat treatment definition. Microscopy, room temperature XRD and hardness measurements allowed to better understand the microstructural evolutions and to select treatments leading to original microstructures. In this work, a variety of microstructures were produced by adapting heat treatment conditions for a given set of spraying parameters. The recrystallization path of the heterogeneous skin-core microstructure of deposited particles, as well as the interaction between grain growth and precipitation was revealed. A novel, optimized fast heat treatment led to a fully recrystallized, fine-grained coating and significantly reduced hardness.

We develop a machine-learning image segmentation pipeline that detects ductile (as opposed to brittle) fracture in fractography images. To demonstrate the validity of our approach, use is made of a set of fractography images representing fracture surfaces from cold-spray deposits. The coatings have been subjected to varying heat treatments in an effort

Industries developing cold-spray processes aim at producing dense and resistant coatings. Controlling microstructure and inter-particular fracture characteristics of sprayed coatings is essential to improve their properties. To do so; post-spraying heat treatment is a promising approach. This work addresses the development of such heat treatments and focuses on the analysis of recovery and recrystallization. Different heat treatment parameters were explored; namely; holding temperature and time; heating rate; and heating method. This approach revealed a competition between recrystallization and other microstructural evolution mechanisms; such as precipitation and porosity coalescence. An optimized heat treatment; allowing microstructural softening and adequate mechanical properties; was sought after. First; differential scanning calorimetry measurements applied to as-sprayed coatings enabled to identify recovery and recrystallization temperature ranges. Then; a variety of heat treatments was applied; involving long-time isothermal holdings as well as shorter cycles. Microstructure analysis and hardness measurements allowed making a first selection of treatment conditions.