Effect of cold rolling degree on texture evolution, eccentricity, and yielding anisotropy of GH4145 alloy tubes

The effects of the area reductions on the crystal orientation, eccentricity, and mechanical properties of GH4145 alloy tubes prepared by three-roller cold rolling were studied. Electron backscattered diffraction analysis showed that the equiaxed grains of the annealed tube blank gradually changed into elongated crystals along the axial direction (AD) with increased deformation. In addition, the grain orientations rotated from random distribution towards the <101>//radial direction (RD), <111>//AD, and <101> + <111>//tangential direction (TD). Brass, copper, S, and {123}< 111‾ > textures formed and increased in strength with increasing strain. Room-temperature tensile tests loaded along the AD and TD demonstrated yielding anisotropy of the tubes. With increasing strain, the work hardening increased continuously, 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. 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%. Therefore, the dimensional accuracy and uniformity of the tubes can be further improved by controlling the strain of the tube.