Working Paper Article Version 1 This version is not peer-reviewed

Porosity Characterization and Its Effect on Thermal Properties of APS Sprayed Alumina Coatings

Version 1 : Received: 2 July 2019 / Approved: 3 July 2019 / Online: 3 July 2019 (14:49:12 CEST)

A peer-reviewed article of this Preprint also exists.

Tillmann, W.; Khalil, O.; Abdulgader, M. Porosity Characterization and Its Effect on Thermal Properties of APS-Sprayed Alumina Coatings. Coatings 2019, 9, 601. Tillmann, W.; Khalil, O.; Abdulgader, M. Porosity Characterization and Its Effect on Thermal Properties of APS-Sprayed Alumina Coatings. Coatings 2019, 9, 601.

Journal reference: Coatings 2019, 9, 601
DOI: 10.3390/coatings9100601

Abstract

In the present work, three different atmospheric plasma sprayed (APS) alumina coatings were fabricated using three fused and crushed alumina powders of different particle size fine, medium and coarse. The influence of the particle size on thermal properties and micro-structural features of the produced coating were investigated by thermal insulation test and detailed image analysis technique, respectively. The analyzed micro-structural features include the total porosity, pore size (fine, medium, and large) and cracks. All types of cracks were considered in calculations as voids and were evaluated according to their sizes as pores. All spray parameters except the particle size were fixed throughout the spraying process. The results revealed that the fine starting powder has produced the densest coating with the lowest total porosity and that the total porosity increases with an increasing particle size. This was expected as powders of smaller particle size will reach a higher in-flight temperature and velocity than powders of bigger particle sizes as long as the same spray parameters are applied. However, a detailed image analysis investigation on the three produced coatings showed that the fraction of fine pores and cracks versus the total porosity is substantially higher in coatings produced by using fine starting powders than those produced using medium and coarse powders. In this work, a connection between the thermal insulation and the porosity fraction, which includes fine pores and cracks, was revealed.

Subject Areas

atmospheric plasma spray (APS) process; particle size; thermal insulation; thermal barrier coating (TBC); thermal diffusivity; coating microstructure; coating porosity

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