Stephen Yue’s research while affiliated with McGill University and other places

Numerical studies directly quantifying particle-substrate adhesion under different spray process parameters during impact remain scarce, primarily due to the lack of consideration for adhesion models. This study addresses this gap by investigating bonding behavior under varying spray conditions using a single-particle model with the PD numerical method, incorporating adhesion forces.

As cold spray transitions from a coating technology to an additive manufacturing process, the variety of part shapes and sizes is significantly increasing while the drive to optimize the mechanical properties of cold-sprayed deposits has emerged. This study investigates the effect of substrate characteristics, a variable typically neglected, on copper cold-sprayed deposit hardness and tensile properties before and after deposit heat treatment. Substrate material, shape and size were varied, resulting in a range of substrate process temperatures as evaluated using IR camera measurements. Deposits sprayed on the smallest parts, i.e., those displaying the highest temperatures, exhibited lower hardness due to spontaneous in situ annealing caused by the thermal energy rise intrinsic to the cold spray process. Smallest parts also presented the best ductility from a combination of spontaneous in situ annealing and improved interparticle cohesion. The as-sprayed deposit strength was rather optimized at an intermediate substrate size and temperature where partial spontaneous in situ annealing was combined with improved interparticle cohesion. After deposit heat treatment, differences among tested substrate sizes vanish. Deposit heat treatment at 350 °C causes softening, a decrease in strength and an increase in ductility due to the annealing effect. The sintering effect becomes predominant for deposit heat treatment at 600 °C, leading to an increase in ultimate tensile strength and further improvement in deposit ductility. This work has important implications for cold spray process scale-up, as one cannot assume the properties achieved after process optimization on small laboratory-size coupons will be maintained on larger parts.

The quality of cold-sprayed copper coatings in the as-sprayed condition heavily relies on the characteristics of the feedstock powder. While previous studies have delved into the influence of particle velocity, size and surface oxides on the quality of as-sprayed coatings, little attention has been paid to investigating the heat treatment responses of coatings with distinct initial characteristics. In previous work, the effects of particle velocity, size and surface oxides on as-sprayed coating properties (i.e., microstructural characteristics, mechanical properties and electrical conductivity) were investigated. Coatings with different as-sprayed quality were produced, ranked from “best” to “worst.” The differences in properties were attributed to variations in the amounts of defects at the particle–particle interfaces (PPIs), caused by different process parameters (i.e., gas pressure) and powder characteristics (i.e., particle size) for each coating. The present study focuses on the subsequent heat treatment of these coatings under identical conditions (1 h at 350 °C, under ambient atmosphere), to monitor the evolution of their microstructural characteristics, mechanical and electrical properties. The results show that in all cases, the ductility and electrical conductivity of the coatings generally improved with heat treatment, compared to the as-sprayed condition. This is primarily attributed to the redistribution of interparticle oxides at the PPIs that improved the bonding between the particles. However, it is also indicated that the general belief that coatings that have superior properties in the as-sprayed condition will remain superior post-heat treatment is not necessarily true. It is shown that it is possible that coatings that originally had superior as-sprayed features may be surpassed by inferior ones, after heat treatment.

This study examines the microstructure, mechanical properties, and precipitation behavior of 1000 MPa grade GEN3 steel when subjected to various quenching processes, with a focus on the quench and partition (Q&P) technique. The Q&P-treated samples achieved 1300 MPa tensile strength and demonstrated superior yield strength, attributed to their refined substructure and their large amounts of precipitates. The quenched samples exhibited the thinnest martensite laths due to the highest martensite volume. Despite the as-annealed samples having the smallest grain size, the Q&P treatment resulted in optimal microstructural refinement results and a high dislocation density, reaching 1.15 × 10¹⁵ m⁻². Analysis of the precipitates revealed the presence of V8C7, M7C3, M2C, and Ti(C, N) across various heat treatments. The application of the McCall–Boyd method and the Ashby–Orowan correction model indicated that quench and tempered (Q&T) samples contained the largest volume of fine precipitates, contributing to their high yield strengths. These findings offer valuable insights for optimizing heat treatment processes to develop advanced high-strength steels for industrial applications.

Cold spray is a solid-state powder deposition technique and has evolved into an additive manufacturing process. Unlike conventional additive manufacturing technologies that rely on melting and solidification, cold spray additive manufacturing (CSAM) forms components at low temperatures at a relatively high build rate. This article introduces the technical principles, process parameters and typical microstructure of cold spray, as well as its applications in the fabrication of 3D components and damaged component repair. Current issues faced in cold spray research and future development directions in CSAM are also discussed.