Papers by Author: Kevin Spencer

Abstract: Cold spray technology is used to produce metal coatings with a variety of functions, including surface corrosion protection, improvement of wear resistance, etc. Cold sprayed materials exhibit a wide range of behaviours resulting in large variation of spraying efficiency, coating properties, quality and performance in service. Residual stress, being a result and attribute of the deposition process, can be studied to test whether the coating is in tension/compression stress state and also to provide information about the thermo-mechanical history of the material during the deposition process. Residual stress distributions in a variety of coating materials have been studied by neutron diffraction. Through-thickness residual stress profiles show that the stress magnitude varies significantly and depends mainly on the mechanical properties of the coating material.

Abstract: Cold spray coatings are considered promising for surface protection of light metal substrates but the mechanisms of bonding and coating build-up are still poorly understood and are the subject of continuing debate. A variety of coating/substrate combinations have been characterised in detail using electron microscopy to examine the nature of the interparticle and particle/substrate interfaces. Through-thickness residual stress profiles obtained via neutron diffraction show that the internal stress varies significantly depending on the coating materials. The work will present a picture of the cold spray deposition process using different material examples.

Abstract: Cold spray coatings are considered promising for surface protection of Mg alloys from wear and corrosion since the process temperature is low enough to avoid oxidation of the Mg or any adverse affects on artificial ageing heat treatments. A special version of cold spray known as Kinetic Metallization has been used to produce pure Al and Al alloy metal matrix composite (MMC) coatings on AZ91 Mg alloy substrates in the present work. This surface treatment produces dense coatings with high adhesive and cohesive strength, which have substantially higher hardness and wear resistance than the AZ91 substrate material. The influence of coating composition and subsequent heat treatment on wear and corrosion performance have been investigated, using pin-on-disc wear tests, salt spray testing and electrochemical polarisation techniques. The heat treatment of the cold spray coatings is compatible with the solutionising and T6 ageing heat treatment of AZ91Mg. The results show that cold spray deposition of MMC coatings is a simple and effective technique for improving the surface properties of Mg alloys, both in the as-cast and in the heat treated condition

Abstract: Cold spray is an emerging coating technology that allows hardness, corrosion and wear resistance, as well as thermal and electrical properties of surfaces to be optimised. The advantages of cold spray over thermal spray are discussed, with emphasis on a new cold spray variant called Kinetic Metallization. The influence of gas dynamics on surface adhesion are examined. Examples from the literature and from the present work of corrosion and wear resistance, bond strength and cohesive strength of cold spray coatings are reviewed.