Huang Haiyou

ANISOTROPIC DEFORMATION BEHAVIOR OF CONTINUOUS COLUMNAR-GRAINED CuNi10Fe1Mn ALLOY

In continuous unidirectional solidification process, an unidirectional heat transfer condition can be established to control grain growth direction along the solidification direction(SD). By this method, continuous columnar- grained(CCG) polycrystalline alloys without transverse grain boundary can be obtained, which possess high orientated texture and straight grain boundary morphology. High orientated texture can significantly improve the consistency among the grains, and the straight grain boundaries reduce the number of coordinated strain compo-nents, resulting in high plasticity and excellent extension behavior along the SD in the CCG alloys. For example,the CCG polycrystalline Cu Ni10Fe1 Mn alloy has a high tensile elongation(40%). However, as described above,the CCG polycrystalline alloy has an extremely anisotropic microstructure. In order to improve its performance, select the appropriate processing methods, and establish a reasonable process, its mechanical properties and deformation behavior were investigated with tensile direction along the SD or perpendicular to the solidification direction(PD) in this work. The electron back- scatter diffraction(EBSD) and digital image correlation(DIC) techniques were introduced to study the effects of microstructure anisotropy on the mechanical properties and deformation behavior. The results indicate that both SD and PD samples have [100] preferred orientation. All grains in SD samples(Taylor factor m=2.17) are nearby [100], while some grains in PD samples(Taylor factor m=2.93) scatter among [001]- [011]. Microstructure characteristics of low orientation dispersion and no horizontal grain boundary in SD samples contribute to the uniform stress distribution and consistent deformation behavior in each grain along the tensile direction. The yield strength, tensile strength and elongation are 85 MPa, 215 MPa and 42%, respectively. Compared to SD samples, PD samples appear to grain boundary stress concentration and zigzag surface morphologies due to the orientation dispersion and horizontal grain boundaries. As a result, the yield strength markedly increases to 115 MPa, and the elongation decreases to 36%. The SD and PD samples occur ductile and mixed fracture, respectively. The anisotropic deformation behavior of CCG polycrystalline Cu Ni10Fe1 Mn alloy is attributed to the anisotropic grain orientation and the grain boundary distribution.