chapter6材料的变形.ppt

* * * * * * * * * * * * * * * * * * * * * * * 70 Cu - 30 Zn合金（黄铜）中晶粒大小与屈服强度的关系 Brass 晶粒尺寸 屈服强度 σ0为一个单晶平均屈服强度；ky是反映晶界提升屈服强度有效性的系数；d为晶粒直径。 这个公式表明屈服强度和晶粒大小有线性关系。 晶粒愈细小，晶界总长度愈长，对位错滑移的阻碍愈大，材料的屈服强度愈高。 Hall-Petch公式 * 金属的晶粒越细，其塑性和韧性也越高。 ? 通过细化晶粒来同时提高金属的强度、硬度、塑性和韧性的方法称细晶强化。是金属的重要强化手段之一 因为晶粒越细，单位体积内晶粒数目越多，参与变形的晶粒数目也越多，变形越均匀，使在断裂前发生较大的塑性变形。强度和塑性同时增加,金属在断裂前消耗的功也越大，因而其韧性也比较好。 Then Hall-Petch strengthening (or Grain-boundary strengthening) is a method of strengthening materials by changing their average grain size. In the early 1950s two groundbreaking series of papers were written independently on the relationship between grain boundaries and strength. In 1951, while at the University of Sheffield,UK, E.O. Hall wrote three papers which appeared in volume 64 of the Proceedings of the Physical Society. In his third paper, Hall showed that the length of slip bands or crack lengths correspond to grain sizes and thus a relationship could be established between the two. Hall concentrated on the yielding properties of mild steels. In 1953, N.J. Petch of the University of Leeds, England published a paper independent from Halls based on his experimental work carried out in 1946-1949. Petchs paper concentrated more on brittle fracture. By measuring the variation in cleavage strength with respect to ferritic grain size at very low temperatures, Petch found a relationship exact to that of Halls. Thus this important relationship is named after both Hall and Petch. 多晶体的应力-应变曲线 抛物线—线性硬化—抛物线 ● 第一阶段，变形有少数晶粒逐渐扩展到全部晶粒 ● 第二阶段与第三阶段与单晶体类似 6.4 合金的塑性变形（Plastic deformation of alloys） 1) 合金塑性变形的基本过程仍然是滑移和孪生 2) 合金的组织结构的复杂性决定了其塑性变形 的特点 (1) 合金为单相合金时， 固溶体，Cu-Ni (2) 合金为复相合金时 ● 聚合型合金： 第二相的尺寸与基体相相近， Pb-Sn 1 基本特点 ● 分散分布型 (dispersion distribution)： 第二相非常细小且分散分布， Fe-Fe3C、Sn-Ag3Sn 2 固溶体的塑性变形 (plastic deformation of solid solution) 1) 固溶强化(solid-solution strengthening)： 溶质原子的加入引起点阵畸变，增加了位错运动的阻力， 增大了晶体滑移阻力 2) 宏观表