Failure dynamics of spherical and irregular shaped Ti splats deposited on sapphire by cold spray

Abstract

Single splats of commercially pure (CP) Ti are deposited onto sapphire by cold spray under two spray conditions to achieve different in-flight powder velocities. The powders used have two morphologies: spherical powder (SP), manufactured by plasma gas atomization and irregular powder (IP), manufactured by the Armstrong process, with a coral-like morphology. The adhesion strength of the single splats is measured by splat adhesion testing. By use of a specialized in situ scratch tester, interface failure during splat adhesion testing is observed through the sapphire substrate. Particle velocity does not significantly influence the adhesion strength and failure mechanism of SP splats. After deposition, the SP splat has an interface pore in its center which acts as an initiation site for crack propagation during splat adhesion testing. After failure, a well bonded portion of Ti remains on the substrate in the shape of a ring. IP splats deposited at low velocity show similar, well adhering, rings on the surface in localized locations scattered throughout the interface. An increase in velocity for IP splats led to an increase in adhesion strength and a nearly continuous well adhering interface. The behaviour of IP splats is understood by electron channelling contrast images of cross-sections where low velocities resulted in little change in microstructure while high velocities led to a highly deformed microstructure at the interface.

Factors Affecting Adhesion in Metal/Ceramic Interfaces Created by Cold Spray

“…A shear contact is required to promote jetting (Ref 39). Above the critical velocity, adhesion by jetting occurs at the periphery of the splat where an appropriate angle is encountered between the interfacing materials ( Ref 39,42,54). A gap in the center is often observed as the parallel contact prevents viscoplastic deformation (Ref 39,42).…”

New scaling procedure for quantitative determination of surface anisotropy–application to plastic deformation of AISI 316 L stainless steel

“…For example in the case of electrode materials the surface morphology determines the electrochemically active surface area [1][2][3], for optical materials the surface should be homogeneous, sufficiently smooth and transparent [4][5][6]. Additionally, for coating materials such physical properties like corrosion resistance, apparent Young's modulus and/or adhesion coefficient strongly depend on a given surface texture pattern [7][8][9][10][11]. In the case of tribological materials, some surface modifications, such as polishing, abrasion, and surface wear intensity are often tested [12,13].…”