Abstract

It is well known that cold spraying ceramic materials can be difficult because cold spraying requires plastic deformation of the feedstock particles for adhesion to the substrate. The challenge lies in the difficulty of plastically deforming hard and brittle ceramic materials, such as TiO2. Previous studies have reported the possibility of cold spraying thick pure TiO2 but the bonding mechanism of cold sprayed TiO2 is not fully understood. The factor like substrate condition as oxide film thickness and mechanical properties may also affect cold spray deposition but not fully understood in cold spraying ceramic. The aim of the present research is to investigate the correlation between the oxide thickness and substrate deformation with the adhesion strength of cold-sprayed TiO2 coatings toward the bonding mechanism involved. Relevant experiments were executed using Al 1050, subjected to various annealing temperatures and cold-sprayed with TiO2 powder. The results indicate a decreasing trend of coating adhesion strength with increasing annealed substrate temperature from room temperature to 400°C annealed. Metallurgical bonding is pronounced as bonding mechanism involved between TiO2 particle and annealed 1050 substrate.

Highlights

  • Cold spraying, referred to as kinetic spraying, represents a relatively novel technique for material deposition that has been in development for over twenty years

  • At temperatures exceeding 900°C, which is above the melting point of TiO2 (1908°C), the anatase stage irreversibly changes into the rutile stage

  • This suggests that the TiO2 coating adhered well to the annealed Al 1050 substrate from room temperature to 400°C annealing

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Summary

Introduction

Referred to as kinetic spraying, represents a relatively novel technique for material deposition that has been in development for over twenty years. The process involves the high-velocity acceleration of powder particles, typically in the 300–1200 m/s range, in a jet flow of supersonic velocity with the projection directed onto a substrate or a coating that has been pre-deposited at an absolutely solid state. Due to the impact at high velocity, intensive deformation of plastic manifests in the cold-sprayed particles or substrate, allowing the formation of a low oxidized cold-sprayed coating [1]. The crystalline framework of TiO2 has a major impact upon its photocatalytic performance where TiO2 in anatase stage supplies greater photocatalytic activity than in its rutile stage. At temperatures exceeding 900°C, which is above the melting point of TiO2 (1908°C), the anatase stage irreversibly changes into the rutile stage. Cold spraying is the best solution because it sprays below the material melting temperature

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