TS-144
Erosion Characteristics of Alumina Coatings
Shigeyasu Amada* and Masayoshi Amanuma**
ABSTRACT
Surface topography and mechanical characteristics of ceramic coatings are very important to apply to heat, wear, erosion and corrosion resistant where the coatings contact with a hot flowing gas containing small particles. In particular, they are heavily eroded and eventually lead to failure when they are attacked by particle impingement. Since ceramic coatings by thermal spraying has a lamella structure which is different from the sintered ceramics, their erosion characteristics is expected to be different from the sintered ones. The Alumina coatings are deposited by plasma spraying with varying spray distance and their erosion property is investigated by grit blasting technique. The wear volume is measured with respect to blasting time and the eroded surfaces are evaluated by average surface roughness and fractal dimension. It was concluded that the wear volume rate decreases with increase of spray distance, that is, the bonding strength between lamella decreases with the spray distance.
Key Words ; Erosion, Ceramic coating, Thermal spraying, Blasting, Wear volume
1. Introduction
Ceramic material has superior characteristics, for example, heat, wear, erosion and corrosion resistant. As compared with the sintered ceramics, the ceramic coatings by plasma spraying have lower and weak adhesion to the substrates due to its lamella microstructure. The lamella structure leads to a weak bonding between lamellae. Therefore, it is predicted that an erosion performance becomes lower than the sintered ceramics.
It has been well established that the erosive wear due to impacting of particles is caused by formation and quasi-static growth of lateral cracks which eventually causes removing material. For the sintered ceramics, Wiederhorn [1], Evans [2], Wada [3] and Akimune[4] studied the problem using single particle collision. Particular attention was paid to the kinetic energy of the collision particles, physical properties of the material, influence of the material properties of the target samples on wear, and elucidation of the wear mechanism. Amada and Ichimura studied about the surface topography of the eroded surfaces for several ceramics [5].
However, the wear behavior of the ceramic coatings with a lamella structure may be different from the sintered materials. The erosion wear of the ceramic coatings under a high temperature environment has been studied by Nicoll [6] and the erosion of the inside surface for a boiler tube was investigated [7]. The Al203 and ZrO2 were eroded by blasting with varying abrasive weight and attacking angles [8].
This paper presents the erosion evaluation of Alumina coatings by grit blasting. The specimens are provided by plasma spraying with changing spray distance and their wear volume are measured with blasting time. The measured weight loss is compared with the sintered ceramics one and discussed with the Evans' theory. The average surface roughness and fractal dimension developed by Mandelbrot are evaluated for the surface topography of the eroded roughened specimens. It is finally related to the wear volume.
* Gunma University
1-5-1, Tenjin, Kiryu, Gunma 376-8515, JAPAN
FAX: +81-0277-30-1553,
E-mail: amada@me.gunma-u.ac.jp
* Ogura Clutch Co. Ltd
