Development of aluminum-based coatings produced by Cold Gas Dynamic Spraying

Abstract

Cold Gas Dynamic Spraying (CGDS) has emerged as a promising coating technology able to produce coating layers for a wide variety of applications. In CGDS, fine particles are accelerated in a high velocity gas flow and undergo solid-state plastic deformation upon impact on the substrate. The distinctive feature of CGDS is that the process gas temperature is well below the melting point of the sprayed materials. The undesirable effects of high temperatures found in conventional thermal spray processes, such as oxidation, grain growth and thermal stresses, are therefore avoided. In response to the potential of CGDS, this study primarily explores and expands the range of applicability of CGDS and specifically addresses the development and characterization of aluminum-based coatings consolidated by the CGDS process. The first part of this thesis is dedicated to particle in-flight velocity measurements. Two different particle in-flight velocity measurement tools, a Cold Spray Meter (CSM) and a Particle Image Velocimetry (PIV) system, are compared based on their operating characteristics and limitations. In the second part of this work, Al-Co-Ce, Al-5083 and Al-12Si coatings are consolidated by the CGDS process. Blends of Al-12Si and silicon carbide and a composite powder consisting of Al-5083 alloyed with boron carbide are also sprayed to synthesize metal-matrix composite coatings. A microstructural characterization of these coatings is carried out to evaluate the porosity, thickness, defects and microhardness. The adhesion strength and the fatigue strength are respectively measured using the ASTM C 633-01 and the ASTM B 593-96 tests. The relationships between the particle velocities, the coating microstructures and their properties are explained. The nozzle exit-to-throat area ratio, the gas stagnation temperature and the powder feed rate are factors that influenced the particle velocities and their effects on the coating properties are described. The effects of other parameters, such as the substrate traverse speed, the substrate surface roughness and the stand-off distance are also investigated.