Effect Of Rolling Deformation On Microstructure And Properties Of CrMnFeCoNiAl_0.6 High-Entropy Alloy

In this dissertation,the effects of rolling and recrystallization on microstructure and mechanical properties of CrMnFeCoNiAl_0.6high-entropy alloy(HEA)were investigated by means of X-ray diffraction(XRD),scanning electron microscope(SEM),electron backscatter diffraction(EBSD).Tensile tests of the HEA were carried out at room temperature,and the tensile deformation mechanism was determined on the fracture surface and the profile of the fracture.The CrMnFeCoNiAl_0.6HEA are consisted of Face Centre Cubic(FCC)phase and Body Centre Cubic(BCC)phase.The rolling amount and annealing time have little change in lattice constants.The morphology of BCC phase riching in Al and Ni is plate and block.The total grain size and the grain size of FCC phase as well as BCC phase decrease with increasing rolling amount to 60%.When rolled to 80%,the content of twinning boundary increases and the HEA have been fully dynamically recrystallized with the grain sizes increasing.The grain size of FCC phase and BCC phase decreases after annealing for 10 min.With annealing time increasing,the content of recrystallized grain in FCC phase increases,and the grain size further decreases.While the grain size of BCC phase is basically unchanged,and the recrystallized process of BCC phase is completed preferentially,which is contributed to the mismatch of strength and plasticity during deformation.During the rolling process,the texture in the FCC phase is mainly?-fiber(<110>//RD),while?-fiber(<111>//ND)is weak.The contents of BR type texture and S type texture increase with rolling amount.The normal direction of grains in BCC is parallel to[001]direction,and the texture is dominated by ND-fiber and then transforms to ND-fiber and RD-fiber.When the annealing time increases to 2h,the normal direction of grains in the FCC phase is parallel to the direction of[111]and[101].The content of Goss texture decreases gradually and that of BR texture enhances.The textures of BCC phase are mainly ND-fiber and RD-fiber,which both contain the texture of{111}<110>.The normal direction of grains in the BCC phase is parallel to the direction of[001].With the increase of rolling amount,the tensile strength increases from 664.55MPa(rolling amount 0%)to 1082.97 MPa(rolling amount 60%),results from the decrease in grain size and the increase in dislocation density.The tensile strength is1151.88 MPa when the rolling amount is upto 80%,which is related to the increase in the content of the twin(20.3%).The strengthening of twin boundary is the main deformation mechanism.The elongation decreases from 12.8%(rolling amount 20%)to6.3%(rolling amount 80%).After annealing for 10 min,the strength of the HEA decreases to 978.41 MPa and the plasticity increases to 19.5%due to the elimination of work hardening.With increasing annealing time,the strength of the HEA increases because of the decrease in grain size.For the rolled samples,the phase boundary and interphase of the BCC phase are the initiation of cracks.The fractgraphy mainly consists of dimples and cleavage tear.After annealing,there are lots of slip lines on the side-surface of the samples.With increasing annealing time,the fracture surface of the alloy is characterized by cleavage steps and river patterns.