Comparative Study of Structures and Properties of Detonation Coatings with α-Al2O3 and γ-Al2O3 Main Phases

Bauyrzhan Rakhadilov,Daryn Baizhan,Sapargali Pazylbek,Dauir Kakimzhanov,Gulnar Muslimanova,Laila Zhurerova

doi:10.3390/coatings11121566

Abstract

This study is aimed at obtaining a coating of aluminum oxide containing α-Al2O3 as the main phase by detonation spraying, as well as a comparative study of the structural, tribological and mechanical properties of coatings with the main phases of α-Al2O3 and γ-Al2O3. It was experimentally revealed for the first time that the use of propane as a combustible gas and the optimization of the technological regime of detonation spraying leads to the formation of an aluminum oxide coating containing α-Al2O3 as the main phase. Tribological tests have shown that the coating with the main phase of α-Al2O3 has a low value of wear volume and coefficient of friction in comparison with the coating with the main phase of γ-Al2O3. It was also determined that the microhardness of the coating with the main phase of α-Al2O3 is 25% higher than that of the coatings with the main phase of γ-Al2O3. Erosion resistance tests have shown (evaluated by weight loss) that the coating with α-Al2O3 phase is erosion-resistant compared to the coating with γ-Al2O3 (seen by erosion craters). However, the coating with the main phase of γ-Al2O3 has a high value of adhesion strength, which is 2 times higher than that of the coating with the main phase of α-Al2O3. As the destruction of coatings by the primary phase, α-Al2O3 began at low loads than the coating with the main phase γ-Al2O3. The results obtained provide the prerequisites for the creation of wear-resistant, hard and durable layered coatings, in which the lower layer has the main phase of γ-Al2O3, and the upper layer has the main phase of α-Al2O3.

Highlights

Alumina coatings have been widely applied in aviation, aerospace, energy, transportation, national defense and other industries for their remarkable characteristics, such as high hardness, heat insulation, anti-wear, thermostability, anti-oxidation and corrosion resistance [1,2,3]
In order to obtain coatings having the main phase of α-Al2 O3, we carried out a series of experiments in various modes of detonation spraying
The results showed that despite the fact that the initial powder was from α-Al2 O3, γ-Al2 O3 phases were formed after spraying using an acetylene-oxygen mixture

Summary

Introduction

Alumina coatings have been widely applied in aviation, aerospace, energy, transportation, national defense and other industries for their remarkable characteristics, such as high hardness, heat insulation, anti-wear, thermostability, anti-oxidation and corrosion resistance [1,2,3]. The phase composition of an alumina coating depends on the application method, process parameters, substrate temperature, spray particle size and a number of other factors These coatings are obtained by microarc oxidation [4,5], anodic oxidation [6,7], sol–gel [8,9], plasma [10,11], flame [2,12,13] and detonation spraying [14,15]. Our earlier studies [22,23,24] showed that when changing the technological modes (firing frequency, barrel filling volume) of detonation spraying, the ratio of the α-Al2 O3 and γ-Al2 O3 phases changes In these studies [22,23,24], α-Al2 O3 was used as the initial powder, and the maximum possible parameters (frequency of firing and barrel filling) of the CCDS-2000 detonation unit were studied using an acetylene–oxygen mixture. We are trying to obtain a ceramic coating containing α-Al2 O3 as the main phase by detonation spraying, changing the composition of the combustible mixture and comparing the structure and properties of two coatings having the main phases of α-Al2 O3 and γ-Al2 O3

Objectives

Methods

Results

Conclusion