Neutron diffraction and surface morhology observation of ultra-fine grained materials

采用热机械热处理方法制备了超细晶材料，并利用中子衍射和激光共形显微镜对材料的显微组织和拉伸行为进行了研究。所研究的材料包括（1）珠光体、（2）铁素体和（3）强拉铁素体或珠光体钢丝。塑性流动中的多尺度不均匀性会产生相应力、块体应力和层片应力。导致高加工硬化。当珠光体钢承受1.6GPa的外加应力时，嵌入铁素体基体中的铁素体板的应力约为5GPa。由亚微米级铁素体和铁素体颗粒组成的铁素体钢具有高强度，但加工硬化小。通过拉伸、压缩试验和表面观察，明确了拉伸变形早期的塑性失稳，发现大变形铁素体钢在塑性变形过程中出现连续再结晶，因此退火时只观察到晶粒长大。这种纳米晶粒尺寸的试样的强度为1.4GPa。在珍珠岩钢的情况下，在拉伸过程中，珍珠岩板溶解，并表现出高达4GPa的拉伸强度。在拉伸载荷下，通过原位中子衍射，揭示了在高应力区的弹性行为是非线性的。

Ultra-fine grained materials were prepared through themo-mechanical heat treatment and their microstructures and tensile behavior were examined by using neutron diffraction and laser conforcal microscopy. The materials studied include (1)pearlite, (2)ferrite and (3)severely drawn ferrite or pearlite steel wires.The internal stresses, i.e., phase stress, block stress and lamellar stress are generated by multi-scale inhomogeneity in plastic flow. Leading to high work-hardening. The stress in cementite plates embedded into the ferrite matrix was determined approximately 5GPa when a pearlite steel is subjected to the applied stress of 1.6GPa.A ferrite steel consisting of submicron meters ferrite and cementite particles exhibits a high strength but little work-hardening. Using tensile and compression tests and surface observations, the plastic instability in the early stage of tensile deformation was made clear.Heavily drawn ferrite steel was found to show continuous recrystalisation during plastic deformation and hence only grain growth was observed by annealing. The strength of such nano-grain sized specimen show 1.4GPa. In case of peralite steel, cementite plates dissolve during drawing and exhibited the tensile strength as high as 4GPa. The elastic behavior was revealed nonlinear at the higher stress regime by insitu neutron diffraction during tensile loading.