制备一种含Sc和一种含Cr、Mn、Ti、Zr的Al-Zn-Mg-Cu合金,采用透射电镜研究合金中第二相粒子周围的无析出微区和晶界上的无沉淀析出带及其相互的作用过程,给出单个第二相粒子对晶界作用力的方程.当驱使晶界迁移的动力大于粒子及其周围的无析出微区对晶界的阻碍作用时,晶界被粒子穿透而形成孔洞.在晶界扫过粒子的过程中,经历了先加速后减速两个阶段.晶界位于粒子直径区位置时所受的阻力最小、运动速度最大.当晶界能与相界能增量之和等于晶界运动的驱动力时,晶界被粒子钉扎而停止运动.在晶界迁移的过程中,溶质原子倾向于由高浓度区域向低浓度区域扩散,晶界和粒子周围的无析出区对晶界的迁移过程有明显的影响.
Two kinds of Al-Zn-Mg-Cu alloys containing Sc and Cr, Mn, Ti as well as Zr were prepared. The precipitation free zone (PFZ) around the second phase particle and the precipitation free band at grain boundary as well as the interaction between them were studied by transmitting electron microscopy (TEM). The equation for pinning force of single second phase particle to grain boundary was presented. Results show that when driving force for grain boundary migration exceeds the encumbrance force of particles and their circumference PFZs against the boundaries, grain boundaries are penetrated by particles to form holes. During grain boundaries sweep particles, their movement, e.g. acceleration stage and deceleration stage, undergoes two different stages. When the hole diameter is equal to the particle size, the encumbrance force is the least and the velocity of boundary migration is the highest. When the sum of grain boundary energy and surface phase boundary energy is equal to driving force, grain boundary is pinned by the particle and stops moving. Solute atoms diffusion takes on the trend from high-concentration zone to low-concentration zone; PFZ around grain boundaries and particles have great effect on migration of grain boundary.
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