材料期刊网

系统总结了面心立方(fcc)金属材料在等通道转角挤压(ECAP)变形后的晶粒细化、微观结构演化规律和力学性能. 根据ECAP变形的特点, 利用具有特殊取向的Al单晶体和Cu双晶体, 经过一道次ECAP挤压发现: 材料在ECAP模具对角面附近发生严重塑性变形; 除了沿模具对角面切应力的作用外, 沿垂直于模具对角面的切应力也起重要作用. 此外, 通过设计特殊取向的Cu单晶体、Al单晶体和粗晶Cu-3%Si合金经过一道次ECAP挤压, 系统研究了层错能、晶粒尺寸和晶体学取向对fcc金属形变孪生所需的孪生应力的影响. 对具有不同层错能的Cu-Al合金进行多道次ECAP挤压表明, 随着层错能降低, Cu-Al合金的晶粒细化机制逐步从位错分割机制转变为孪生碎化机制, 最小晶粒尺寸逐步减小, 具有较高或较低层错能材料比中等层错能材料更容易获得均匀的微观组织; Cu-Al合金的拉伸强度和均匀延伸率随着层错能的降低同步提高, 即随着层错能的降低, Cu-Al合金的强度--塑性匹配性提高.

Microstructure evolution, grain refinement mechanism and mechanical properties of face-centered cubic (fcc) metallic materials, subjected to equal channel angular pressing (ECAP), were systematically investigated. According to the special shear deformation mode of ECAP, Al single crystals with different orientations and Cu bicrystals with different initial grain boundary directions were subjected to ECAP for one pass, and it is found that shear deformations both parallel and perpendicular to intersection plane play important roles in the ECAP process. Moreover, Al single crystals, Cu single crystals and polycrystalline Cu-3%Si (mass fraction) alloy with different stacking fault energies (SFEs) and special crystallographic orientations, subjected to ECAP for one pass, were selected to experimentally and analytically explore the combined effects of crystallographic orientation, SFE and grain size on deformation twinning behaviors in several fcc crystals. Furthermore, ultrafine grained (UFG) or nanocrystalline (NC) Cu-Al alloys with different Al contents were prepared using multiple-passes ECAP. The results show that the grain refinement mechanism is gradually transformed from dislocation subdivision to twin fragmentation, and the equilibrium grain size decreases with lowering the SFE of Cu-Al alloys. Meanwhile, the homogeneous microstructures of materials with high or low SFE are much more readily gained than those of medium-SFE metals. More significantly, the strength and uniform elongation can be simultaneously improved with lowering the SFE, i.e., the better strength-ductility combination is achieved in the Cu-Al alloy with lower SFE.