Interface Reaction And Wetting Of The Sm-Co Alloys/glass Coatings Interface

Sm-Co alloys have received considerable attention due to its high Curie temperature,excellent magnetic properties,excellent thermal stability and superior corrosion resistance,which make them suitable for wide applications in many fields such as national defense,military industry,aerospace,high precision instrument,highend motors and so on.However,irreversible deterioration of magnetic properties occurs due to the decomposition of their magnetic phases lead by oxidation during long term service at high temperature in air.To resolve this problem,oxidation mechanism has been focused on since the end of the twentieth century,and protective coatings and alloying were proposed to improve the oxidation resistance of Sm-Co alloys.In this thesis,we review research progress of oxidation mechanism for Sm-Co alloys,and then summarize types and effects of oxidation protective coatings,at last propose a novel glass protective coating technique.However,the mechanism of interface reaction between glass coating and Sm-Co alloy is not clear,so in order to realize the surface protection technology of glass coating for Sm-Co alloys,it is urgent to carry out relevant basic research We explore interfacial reaction and wetting mechanisms under argon and air atmosphere to provide theory fundamentals for designing glass coating which has excellent physical and chemical compatibility with Sm-Co alloys.(1)Under argon atmosphere,oxygen is provided only by the glass coating,and the oxygen partial pressure is low,so Sm-Co alloys were internal oxidized without external oxidation.A CoFe solid solution layer formed between Sm-Co alloys and glass coatings.This layer could resist the erosion of molten glass.(2)Under air atmosphere,the oxygen partial pressure is high enough,thus external and internal oxidation occurred simultaneously in the Sm-Co alloys.With temperature the external scale broke down and was separated from the Sm-Co alloy.Then a crevice formed between the external scale and the Sm-Co alloy,resulting in crevice corrosion.Just few particles remained at the interface because the oxygen in air strengthened the electrochemical corrosion.High stable samarium zirconate layer hindered the corrosion of molten glass.(3)Sm-Co alloys exhibit typical internal oxidation morphology in both argon atmosphere and air atmosphere,while the particle size and orientation of internal oxides are obviously different.According to the theory of internal oxidation of alloy,the reason of the difference is explained by the different diffusion rate of samarium and oxygen.(4)In the temperature range of 675℃-725℃,increasing surface roughness can promote the wetting of molten glass on the surface of the Sm-Co alloy.When the temperature exceeds 725℃,increasing surface roughness could hinder the wetting of molten glass on the surface of the Sm-Co alloy due to the interfacial reaction.The wetting stated transfer from the Cassie state to the Wenzel state through the sagging mechanism.