Microcrack Formation And Stress Distribution Of Aluminized Layer Of Nickel-base Alloy Under During Torsion

Nickel base aluminized alloys can significantly improve its high temperature oxidation resistance.Aluminized nickel base alloys will be stressed during service,result in microcracks in the coating.In this paper,the aluminized layer was prepared on the surface of K403 alloy by thermal diffusion method.The formation and propagation of microcracks in the aluminized layer of K403 alloy under the effect of torsional stress were studied.In this paper,the relationship between the stress and strain rate(0.001-1000s^-1)of K403 alloy substrate,the relationship between stress and strain rate(0.001-1000s^-1)of the aluminum content of aluminized layer of K403 alloy are 20wt.%,25wt.%and30wt.%and the low temperature physical properties,such as young’s modulus,poisson’s ratio,density and hardness,were simulated by the JMatPro at 25℃.The parameters obtained by JMatPro and the three dimensional entities with the aluminized layer thickness of 20μm,25μm and 30μm were drawn by Auto-CAD and respectively imported into DEFORM finite element software for torsion simulation.The results of finite element simulation analysis show that:In the process of simulation of torsion,with the increase of the torsional angle,the equivalent stress on the surface of the specimen is increased,the maximum value of the equivalent stress appears first in the middle area of the spceimen surface,the microcrack is easily formed in the middle area.In the same torsion angle,the range of the equivalent stress distribution cloud and the equivalent stress of the middle zone of the sample with an aluminum content of 25wt.%and a thickness of 30μm are the minimum.The minimum possibility of formation of microcracks.The aluminized layer was prepared on the K403 alloy by heat diffusion aluminizing process.The effects of different aluminized temperature（800℃）,holding time（1⁴h）on the surface morphology,microstructure,phase structure and thickness of aluminized layer were investigated.The diffusion annealed of the specimen after aluminized,annealed temperature 980℃,holding time（1³h）.The annealed specimen were subjected to torsion tests（twist angles:1°,3°,5°,7°,9°,11°）,The microcracks on the twisted specimen were detected by coloring method.The microstructures of the aluminized specimen were characterized and the microcracks were investigated by metallographicmicroscope,X-raydiffractionandscanningelectron microscope/energy dispersive spectroscope,the relationship between the aluminum content,thickness and twist angle of different aluminized layer and the surface microcrack of specimen was discussed.The experimental results of torsion of aluminized K403 alloy show that:The torsion angle is 1°,aluminized layer no microcracks growth.The torsion angle is 3°,and some nickel-base alloy aluminized layers have microcrack propagation.When the twist angle is greater than 3°,microcrack propagation occurs in the aluminized layer.As the twist angle increases,the degree of microcrack increases.The content of aluminum in the aluminized layer increased from 20wt.%to 30wt.%.In the same torsion angle,aluminized layer of aluminum content of 25wt.%,the thickness of30μm is not easy to produce microcracks.The specimen with 25wt.%Al content and30μm thickness had the smallest number of microcracks and the shortest microcracks.