Study On Microstructure And Crystallization Characteristics Of Arc - Based Amorphous / Nanocrystalline Composite Coatings

This paper focused on the excellent properties of amorphous alloy and surfacing welding methods, based on the requirement of wear resistance and corrosion resistance, a kind of Fe-based amorphous/nanocrystalline composite coating with excellent properties was expected to be obtained by surfacing welding. In this study, Fe-based amorphous surfacing electrode was prepared, and then manual arc welding method was adopted to prepare amorphous/nanocrystalline composite coating on Q235steel, with thickness of5mm. OM, XRD, SEM, TEM, DSC were used to analyze the microstructure, thermal stability and crystallization characteristic. Hardness test, wear test and electrochemical experiment were used to study the wear resistance and corrosion resistance of the surfacing layer; In addition, the effect of different heat treatment on the microstructure and properties of the Fe-based amorphous/nanocrystalline composite coating was also researched. The main conclusions were shown as follows:A kind of amorphous surfacing electrode was prepared successfully, the electrode core of Fe41Co7Cri5Mo14C15B6Y2(atom percent,%) with diameter of5mm and low hydrogen coating with coating weight coefficient of0.6. Fe-based amorphous/nanocrystalline composite coating by manual arc welding method, the coating had a good metallurgical bonding with Q235base metal and no defects such as porosity, cracks were found. The surfacing layer with150A welding current had good thermal stability with crystallization energy of107kJ/mol and crystallization temperature of619℃under10K/min heating rate, amorphous phase was47.44%, Fe3B, Cr23C6, Y4C5nanocrystallized and the size of nanocrystals was15-40nm; when the welding current increased to160A, the grain size of nanocrystals increased, the content of amorphous phase decreased to41.16%, with decreasing crystallization energy of58kJ/mol and crystallization temperature of549℃.After heat treatment, the microstructure of amorphous/nanocrystalline coating changed, the main crystallization phases were Fe3B, Cr23C6, FeCrMo and Fe23(C, B)6. Surfacing layer with150A welding current were annealed under550℃、600℃、650℃、700℃, the content of amorphous phases were separately60.61%、73.30、84.53%、91.0%; meanwhile, surfacing layer with160A welding current were annealed under560℃、580℃、600℃、620℃, corresponding to amorphous phase of63.94%、75.85%、85.48%、100%. It could be concluded that crystallization and grain size of nanocrystals increased with the increasing of heat treatment temperature.Surfacing layer with150A welding current had quite high hardness of1226HV1and decreased to806HV1when welding current was160A. The experiment results showed that wear resistance of surfacing layer with150A welding current was better than that of160A surfacing layer, which is far better than that of Q235base metal. In3.5%corrosion media, the two surfacing layer exhibited excellent corrosion resistance because of high corrosion potential in the polarization curve. After heat treatment, there was little increase in hardness of150A surfacing layer and quite obvious increase in150A surfacing layer, however, there is not a simple linear relationship between the properties change of surfacing layer and the proportion of amorphous and nanocrystallines.