双峰晶粒尺寸分布的室温塑性研究课件.pptVIP

下一步实验计划 1. 制备nc,?m以及两个双层 NiFe 合金四个试样，双层的即在nc上面镀制近一个微米的微米层。 2.对其中一个双层结构进行180℃退火3h，并通过透射电镜观察两个双峰晶粒结构，大小晶粒晶界附近结构及形貌。 3.纳米压入,测定硬度与微米晶和纳米晶比较，以及三种试样压痕形貌的比较。 * * * Wang和Ma等人总结了目前在保持纳米材料高强度情况下提高其塑性的方法。通过改进制备方法获得高质量的纳米试样和在低温下变形，都能一定程度的提高纳米材料的塑性和强度。但室温下获得具有高强度高塑性纳米材料的手段主要概括两个方面：提高应变硬化和应变速率硬化。 不均匀结构使材料在变形过程中拥有不同的应变梯度和方式，而这种大的应变梯度便于存储稳定塑性变形所必须的 几何位错来调节变形，这就提供了额外的加工硬化 with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine ( 300 nm) grains. Our processing starts by rolling the Cu at liquid nitrogen temperature to a high value of percentage cold work (CW; see Methods). The resulting material has a typical heavily deformed microstructure with high densities of dislocations in nanoscale networks he use of the low temperature suppresses dynamic recovery,allowing the density of the accumulated dislocations to reach a higher steady-state level than that achievable at room temperature. recovery annealing and recrystallization ,The recrystallized grains have well-defined, high-angle boundaries 1~3微米 此后，研究发现具有这样双峰晶粒尺寸分布的纳米结构Fe、Al和Al-Mg合金也表现出较好的力学性能 粗晶镍的室温m值为 0.001-0.004而实验中得到的纳米镍的m值提高到了 0.01-0.03，并且V也只有十几b3 The high near-uniform elongation at low strain rate can be explained by its corresponding high m value. The inset selected area diffraction pattern in Fig. 1(a) shows some large diffraction spots enchased in the diffraction rings, which is in agreement with the observed broad grain size distribution of the nc Ni.(20~160) high strength of about 1200 MPa and enhanced ductility of 7.5–8.3%（5~80nm) 文章认为主要原因是S的偏析，事实上根据下面的文章， It is well known that in the as-prepared state sulphur is present in both the grain interior and the grain boundaries. 可能退火引起S的偏析。 几十和几百nm, 磁控溅射可以控制晶粒尺寸吗？ Vc ～ 50% there is a significant difference in the hardness in the fine-grained nanocrystalline region and the coarse-grained region;these results suggest that in a sample with bimodal grain-size distributions, it is possible for the fine and coarse grains to deform at different str