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

采用机械热处理的方法制备了超细晶材料，并用中子衍射仪和激光扫描电子显微镜对其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)严重拉拔的铁素体或珠光体钢丝，内应力，即相应力、块应力和片层应力是由塑性流动中的多尺度非均匀产生的。导致高加工硬化度。当珠光体钢承受1.6 Gp的应力时，嵌入铁素体基体的渗碳体片的应力约为5 Gpa。由亚微米级铁素体和渗碳体颗粒组成的铁素体钢具有高的强度，但加工硬化很小。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，发现拉深后的铁素体钢在塑性变形过程中表现出连续的再结晶，因此经退火后只观察到晶粒长大。这种纳米尺寸的试件的强度为1.4 Gpa。对于珠光体钢，渗碳体板材在拉拔过程中溶解，抗拉强度高达4 Gpa。拉伸加载过程中的原位中子衍射仪显示，在高应力区，材料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.