Reaction Of Plasma Spraying Aluminum And Titanium Dioxide In Situ Composite Coating

Plasma-sprayed Al₂O₃ coating exhibit high hardness,wear resistance,and chemical stability,but it toughness and thermal shock resistance is poor.The ingredient TiO₂ will obviously enhance the adhesion strength and density of Al₂O₃ coating as well as significantly improving its toughness,wear resistance corrosion resistance and thermal shock resistance.With the rapid development of Nano-Science,nano-materials have been successfully applied to the plasma-sprayed industry.The nanostructured coatings by Plasma sprayed has more excellent performances compare with the traditional microstructure coatings.However,with nanostructured feedstock for plasma spray for preparation of nano Al₂O₃-TiO₂ coating process is hard to realize because the preparation of nanostructured feedstock is complicated,meanwhile nanometer grain easy to grow up.Therefore,nano Al₂O₃-TiO₂ coating prepared by in-situ reactive plasma spraying with Al-TiO₂ system composite powders will be discussed in this paper.This paper begins with a review of the spray power,additives（ZrO₂,CeO₂）,and its possible influence on the microstructure and properties of the nano Al2O3-TiO2 coating.Study on in-situ reaction thermodynamics and dynamics of the Al-TiO₂ system,the reaction mechanism of Al-TiO₂system in the process of plasma spraying,the relationship between properties（toughness,hardness,wear resistance,high temperature corrosion resistance and thermal shock resistance）and structure.Plasma sprayed Al-TiO₂ coating contain main phase of TiO,Al₂O₃,in addition there are a small amount of Ti₃O₅ and TiO₂.Composite coatings with various phases of fluvial forms structure,inside the fluvial forms structure distributed spherical particles.The phase of Al-TiO₂ system coating does not change with different spray power.The structure is uniform and the hardness is supreme under 32kW.The new phase Al-Ti intermetallic compound comes out after adding ZrO2 and CeO2,this phase is the deep gray part of the fluvial forms structure,which is different with the original fluvial forms structure because it doesn’t have the distributed spherical particles.The coating becomes uniform and fine after adding additives.Compared with the Al-TiO₂ system coatings by plasma spraying,after adding additives ZrO2 and CeO2 can increase the hardness of the coating.Al-TiO2+5wt%ZrO2and Al-TiO₂+6wt%CeO₂ coating have the maximum hardness.The toughness of coating has been increased.Bonding strength between Al-TiO₂ system coating and substrate is higher than 25MPa,which is in a high level.Al-TiO₂+ZrO₂ coating’s friction coefficient increases along with ZrO₂ content,and larger than the original Al-TiO₂ system coating（0.69）.The wear rate of Al-TiO₂+ZrO₂coating less than Al-TiO₂ coating,and the Al-TiO₂+5wt%ZrO₂ coating has the least wear rate and the best performance on wear resistance,it wear mechanism is adhesive wear and fatigue wear.The coating friction coefficient is smaller than the original system coating if the CeO₂content is under 8wt%,and it decreases along with the increases of CeO₂ content.When the CeO₂ content is 8wt%,it friction coefficient（0.82）is larger than the original one.Al-TiO2+4wt%CeO2 coating’s wear rate is the lowest,it wear mechanism is adhesive wear and fatigue wear.In the process of high-temperature corrosion under different temperature（500、700℃、850℃、900℃、1100℃）.In the Al-TiO₂ coating,TiO will be oxide firstly,and then Ti₃O₅.Passivation oxidation and phase change oxidation occurred with high-temperature corrosion of the coating,it is passivation oxidation when the temperature is under 900℃,and phase change oxidation when the temperature is upon 900℃.The Al-TiO₂ system coating has the excellent thermal shock resistant ability.Under the thermal shock 500℃,700℃and 850℃,Al-TiO₂ coating Thermal shock circle number are 370（without any damage）,28 and 14 times,respectively.