第六章淬火与时效(2).ppt

第六章无多型性转变合金的
淬火与时效(2)
时效前后合金性能的变化
影响时效过程及材料性能的因素
淬火(固溶处理)与时效规程
时效前后合金性能的变化
力学性能
时效时间
硬度
合金成分、时效温度、力学性能的变化关系
I
II
Generally, a peak corresponds to a kind of precipitate.
For Al-Cu alloys, there can be more than 4 peaks resulted from the formation of GP, ’’, ’ and ’.
However, there is also the case where different peaks can not be discriminated, or one peak corresponds to several kinds of precipitates.
时效强化机制解析:位错与脱溶质点间的相互作用
Orowan机制:位错绕过机制
切割机制:短程作用(界面,反相畴)、长程作用
Interpretation: Microstructure contains a number of heterogeneities, which can contribute both to localization of plastic flow, and to initiation and propagation of crack. In order of decreasing size, the heterogeneities include intermetallic particles, quench induced intergranular and intragranular precipitates, and precipitate-free zones situated at the grain boundaries.
Failure Modes: intermetallic decohesion, intergranular fracture and intragranular fracture.
Orowan机制:位错绕过机制
位错环绕机制(Orowan机制)强化理论
Dislocation theory:
K=1 for screw, K=1- for knife,  is poisson coefficient, G is shear module, b burgers vector, r0 radius of dislocation, R half of the distance between particles, f volume fraction, r radius of particle.
切割机制强化作用
(以10b为界限,小于10b为短程作用; 大于10b为长程作用)
-----短程作用--------
(1) 界面能增加导致的额外切应力计算:
新增面积:
新增能量:
for a single particle
If the fact that dislocation will be incurvated in front of precipitate is
taken into account, the above equation es to
for all particles in a unit area.
(2) 反相畴界能增加导致的附加切应力机算:ordered particles
可见短程作用中,增加的切应力具有以下形式
Parabolic-type
-----长程作用-----
(3) 长程作用计算:两应变场的相互作用
where E is Young’s module, , a function of the mismatch  of lattices of
the 2 phase. The other parameters have the conventional meanings.
If the increase of the stress needed to incise the particles excesses that
introduced by the long-range effect, then the long-range effect is to be
neglected.
两种机制的相互作用---强化与沉淀粒子尺寸的关系
质点半径
强化增量
开始阶段:
粒子小、共格,易被切割