Texture Evolution And Influence Mechanism Of The GH4145 Alloy Tubes

Superalloy precision tube is an important part of the aero-engine piping system,which is the blood vessel and trachea of the engine.To meet the requirements of high dimensional accuracy and stable microstructure properties,it is necessary to further study the texture evolution behavior of the tube.GH4145 alloy tube is used for the preparation of the engine casing ring,and its service condition is poor.Therefore,this paper studied the texture evolution of tubes and its influence mechanism on dimensional accuracy,roughness,and microstructure properties from several aspects,such as area reduction,Q value(the ratio of relative wall reduction to relative diameter reduction),and rolling pass.The main results are as follows:The effects of the area reductions on the crystal orientation,eccentricity,and mechanical properties of GH4145 alloy tubes were studied.A new full-size observation method was used to observe the microstructure of tubes with 0-72%area reductions,which found the crystal orientation rotated from random distribution towards the<101>//radial direction(RD),<111>//axial direction(AD),and<101>+<111>//tangential direction(TD).Brass,Copper,S,and {123}<111>textures formed and increased in strength with the area reduction increasing.As the degree of work hardening increased,the deformation mechanism changed,and the dislocations slipped in three directions and then transformed into slip bands and dislocation cells,whereas a few deformation twins formed as the reduction reached 64%,and then slipped in two directions.Roomtemperature tensile tests loaded along the AD and TD demonstrated yielding anisotropy of the tubes.When the reduction was 64%,the activated slip system transformed from{111}<110>to {110}<001>in most grains under applied AD loading,which was consistent with the loading in both directions at a reduction of 72%.As the grains in the preferential deformation zone near the inner and outer walls rotated to the<101>//RD orientation,the tubes plastically deformed,and the grains in the central layer then gradually begin to rotate.The ratio of radial length in the deformation hysteresis zone to wall thickness was used to represent the degree of non-uniformity of the deformation.A direct correlation was found between the eccentricity of the wall thickness and the non-uniformity of tube deformation as the area reduction increased from 13%to 50%.In addition,the radial delamination of the tubes disappeared,deformation became uniform,and the eccentricity decreased significantly as the area reduction increase up to 64%.The texture evolution of thin-and thick-walled tubes with different Q values was studied.For the thin-walled tubes,plastic deformation was evenly distributed along RD,and there was no orientation delamination,but the content of<101>//RD fiber textures affected the eccentricity of wall thickness.When Q=0.77,the dimensional accuracy of tubes was higher.For the thick-wall tubes,Q values affected the uniformity of plastic deformation.When Q=0.76,the plastic deformation was evenly distributed along the RD.The eccentricity and ovality of the tubes were lower than those of the tube blanks,and the dimensional accuracy was higher.When Q=0.76 or 2.28,the tube with low inner surface roughness can be obtained.The former was due to the appropriate Q value,which led to the uniform deformation and material flow.For the latter,the circumferential strain of the inner diameter was small,and the reduction of the wall thickness was sufficient.Through the study of tubes with different rolling passes,the best rolling process for GH4145 alloy tubes was identified:cold rolling through 3 passes,which resulted in an area reduction of approximately 24%per pass,followed by annealing at 920℃ for 30 min,via which the lowest ovality could be obtained.In terms of texture evolution,mainly S,Copper,Brass,and {123}<111>textures were distributed in all cold-rolled tubes,and Goss texture was only observed in 2-pass tubes.With increasing annealing temperature,the texture strength first decreased and then increased,and the type of recrystallization texture was the same as that of cold-rolling texture,which was dominated by oriented nucleation.The higher residual stress in the cold rolling process resulted in higher ovality of the tube due to the higher energy storage.The release of residual stress during heat treatment reduced the ovality,while the enhancement of recrystallization texture led to a slight increase in ovality.