Fabrication Of The Low Oxygen Partial Pressure Fusing Coatings Formed On Ti-6Al-4V Alloy And The Performances Analysis

Low oxygen partial pressure fusing (LOPPF) technology is the further development on the basis of the vacuum melting guitar technique and surface metallurgy process on the high-temperature metal surface. Put the self-fusion metal or alloy powders on the surface of the metal in advance, and then under the protection of the inert gas, the rapid heating, melting and infiltration solid substrate surface, and at the interface with the substrate to form a composition containing the two immiscible zone, condensation crystallization, coating and at last achieve the metallurgical bonding between the substrate and the coating by soluble diffusion and interfacial reaction. Therefore, preparation of the method is simple and does not require expensive equipment, the relatively low cost of the characteristics is a great potentials surface metallurgy technology. Up to now, But it is not too many researches about the Al-Si coating and the Ti₃SiC₂ particulate reinforced metal matrix composite coating formed on the Ti-6Al-4V alloy by LOPPF technology. Therefore, it needs to study the effect of fusing parameters on the microstructure and properties of the coating by LOPPF technology during the fusing process. Then study on the fusing mechanism and initial elements content of powders is useful for optimizing project design and data analysis and reducing melting blindness in the initial design process, obtaining the good organization and improving the performance of high temperature protective coating.Based on the above existing problems, the degree thesis research is the main purpose of using the LOPPF technology on the Ti-6Al-4V alloy surface to fabricate Al-Si coating and Ti₃SiC₂ particulate reinforced metal matrix composite coating. The aim of the present paper is to test LOPPF surface metallurgy technology to prepare the feasibility of high-quality coatings.This paper systematically studies the preparation methods, fusing mechanism, organizational structural and related performance characteristics, and the effect of fusing parameters and initial elements content of powders on the microstructure and properties of two coating. In order to obtain the optimum parameters of the fusing mechanism laid the foundation. Through the analysis of the fusing mechanisms of the two coatings, a clear statement of the sintering process of LOPPF fusion coatings is obtained. That provide reference for further optimizing performance. In this paper, the work content and results are as follows:1. Fabrication of the low oxygen partial pressure fusing coatings formed on Ti-6Al-4V alloyThe low oxygen partial pressure fusing coatings formed on Ti-6Al-4V alloy by LOPPF technique was fabricated successfully in this work. The binding between alloy layer and matrix is excellent, which is metallurgical binding. Thus the feasibility of the preparation of high-quality alloy surface with heat and abrasion-resistant coating by low oxygen partial pressure fusing technology is verified.2. Effect of the fusing parameters on the microstructures of the LOPPF coating(1) Effect of the fusing parameters on the microstructures of Al-Si coating(a) Microstructure of the LOPPF Al-Si coating in different fusing time (30min, 60min and 100min) fabricated from aluminum and silica mixed powder is extremely similar. However, SEM and XRD measurement indicate that the content of Ti5Si3 and silicon rich layer in the coating increases with the fusing time increasing.(b) Microstructure of the LOPPF Al-Si coating in different fusing time (10min, 60min, 120min) fabricated from Al-Si alloy is very similar. With the fusing time increasing, the content of Ti5Si3 and silicon rich layer in the coating increases.(c) Microstructure of the LOPPF Al-Si coating in different fusing temperature (700℃, 800℃and 1000℃) fabricated from Al-Si alloy is extremely similar is extremely similar. The content of Ti5Si3 and the thickness of silicon rich layer in the coating can be improved by the fusing temperature increases.(d) Microstructure of the LOPPF Al-Si coating in different content of Si powder (8%℃, 13% and 20%) fabricated from Al-Si alloy is extremely similar is very similar. The content of Ti5Si3 and the thickness of silicon rich layer in the coating can be improved by the content of Si increases.(2) Effect of the content of Si on the microstructures of Ti₃SiC₂ particulate reinforced metal matrix composite coatingDifferent content of Al of low oxygen pressure melting guitar Ti₃SiC₂ particle reinforced metal matrix composite coatings were compared and with the content of Al in the initial powder increasing the content of Ti₃SiC₂ and the thickness of the silicon rich layer in the coating decreases. However,under that condition, the interface composition gradients of of among layers are debased, thermal expansion coefficient between reinforced outer layer and substrate are decreased, the physical compatibility is inproved. Therefore increase the bond strength of coatings.3. Study on the microstructure of LOPPF coatingThe Al-Si coating consists of two layers, the outer layer contains Ti5Si3, Al, Si and TiAl3 and the inner is Si-rich layer. The Ti₃SiC₂ particle reinforced metal matrix composite coatings consists of three layers. The outer layer is characterized as high volume fraction (about 85%) of irregular polygonal particles disperse uniformly and a few of Al2O3 and Al. The middle layer is TiAl3 layer and an inner Si-rich layer formed at the interface between coating and substrate.4. Study on the fusing mechanisms of LOPPF coating(1) The fusing mechanisms of LOPPF Al-Si coatingIn the course of coating fusing, besides there are Ti-Si and Ti-Al duality phase, Ti-Al-Si ternary phase as reaction products exist in the coating layer. Study on the fusing mechanism and the thermodynamics of the coating can proved that the Ti-Al-Si ternary phase acted as a transient intermediate phase when the Ti-Si phase was forming and translated into Ti-Si phase after fusing. (2) The fusing mechanisms of LOPPF Ti₃SiC₂ particle reinforced metal matrix composite coatingsIn the course of coating fusing, amount of Ti of the matrix diffused outwards to the films reacted with the Al of the initial powder when the temperature increases. the With the temperature increases further, the producing Ti₃SiC₂ grains by reaction between Ti-Si phase and TiC. From the study on the fusing mechanism of the coating, the reaction with existence of Ti on the formation of Ti-Si phase can be absolutely controlled by Ti come from the matrix outwards.5. The performance analysis of LOPPF coatings(1) The performance analysis of LOPPF Al-Si coatingsThe oxidation resistance of LOPPF Al-Si coatings in cyclic oxidizing test was investigasted. The present results indicate that the coating consists of the continuous Al2O3 layer and it can improve effectively the anti-oxidation properties. Then the existence of Si-rich layer hinders the diffusion of anti-oxidation elements into the coating matrix and the degradation velocity could be controlled. And then extend the life. But the content of Ti5Si3 increase with increase of fusing time, fusing temperature and the content of Si in the initial powder. The amount of non-protective TiO2 in the coating increases correspondingly and the shortage to the improvement of the anti-oxidation is displayed. However, increasing these parameters is benefit to increase the thickness of Si-rich layer and then the anti-oxidation life time of Ti-6Al-4V alloys are improved.(2) The performance analysis of LOPPF Ti₃SiC₂ particulate reinforced metal matrix composite coatingWear resistance of the coating in dry sliding was emphatically researched under studying the anti-oxidation. Tested by experiments, there are wear-resistant phase Ti₃SiC₂ of high volume fraction (about 85%) distribute along the surface uniform, then it greatly improve the endurance of wear. Meanwhile, this article was focused on discussion of the effect of Al on the wear protective property of the coating.