Study On The Microstructure Of Nickel-based Superalloy And Titanium Alloy Surface Coating

Due to corrosion and wear, many components of aero-engine and other industry gas turbine engines were destroyed. Thus aluminizing and electrospark deposition coating have been applied to components surface to increase their resistance to surface corrosion or wear for industrial applications. Coating microstructure decides coating performance and is decided by protective coating techniques. With the research of coating microstructure and the protective coating techniques, we can optimize the technique parameters, guide the working process and acquire the anticipated surface performance.An aluminizing and Al-Si diffusing coating on a nickel-based superalloy K4104 by pack cementation and slurry, a TiC strengthening coating on a titanium alloy by In-situ electrospark deposition, a strengthening coating on a titanium alloy by electrospark deposition and a strengthening coating by electrospark deposition with ultrasonic vibration on a titanium alloy using WC electrode were studied in this paper. By the means of X-ray diffraction (XRD), scanning electron microscope (SEM) and etc., the phase, morphology and element distribution of the coatings were analyzed, and the formation mechanisms of coatings were also discussed. Main conclusions are as follows:1. An Al-Si coating was prepared on a nickel-based superalloy by slurry. During the reaction, Ni in the substrate diffused in the surface, Al in the surface diffused in the substrate and they had formed the phases of β and γ ' . Owing to the difference of solid solubility, Cr in substrate was enriched and separated so that the phases of Cr-rich disappeared. Si in the surface layer formed the phases of Cr_xSi_y with Cr. Compared with the aluminizing by pack cementation, there was a transition layer. Thus the Al-Si coating was thicker than solo aluminizing and the thickness of Al-Si coating was 70 μ m.2. The TiC strengthening coatings on BT20 and TC1 titanium alloys were deposited by In-situ electrospark process using the graphite electrode. The result showed that the coating divided into two layers, including TiC strengthening layer and substrate-melted layer and the thickness of TiC coating was 20-30μm. The strengthening coating is a reaction coating and the phases of coating consisted of Ti, TiC and graphite. Ti came from substrate and C came from electrode.3. The coatings on BT20 and TCI titanium alloys were deposited by electrospark process using YG8 electrode. The result showed that the surface coating was splash. The thickness of TiC coating is 20—30 u m and the coating divided into two layers, including strengthening layer and substrate-melted layer. But the substrate-melted layer on the TCI titanium substrate was not clear. The phases of TiC, W and W2C were formed during electrospark process and metallurgical joint between coating and matrix were realized by electrospark process.4. The coatings on TCI titanium alloy were deposited by electrospark with ultrasonic vibration using WC electrode. It was found that the quality of coating couldn't be enhanced with just changing parameter of electrospark deposition. However, the high quality coating was produced on the titanium substrate when the frequency of ultrasonic vibration applied reached to a certain value.