Gan Guisheng, Yang Bin, Zhang Bo, Jiang Xin, Shi Yunlong, Wu Yiping
Chongqing Municipal Engineering Research Center of Institutions of Higher Education for Special Welding Materials and Technology, Chongqing University of Technology, Chongqing 400054, China.
College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
Materials (Basel). 2017 Feb 4;10(2):132. doi: 10.3390/ma10020132.
The nucleation undercooling of TiB₂/7075 Al matrix composites, the microstructure observed after solidification at different cooling rate, and the size and distribution of TiB₂ particles were investigated. The experimental results have shown that the grain sizes of TiB₂/7075 Al matrix composites firstly decreased, then increased, and finally decreased again with the increase of TiB₂ content. The nucleation undercooling of TiB₂/7075 Al matrix composites first increased, then decreased, and finally increased again with the increase of TiB₂ content when the cooling rates was 5 and 10 °C/min respectively, but kept decreasing with the increase of TiB₂ content at a cooling rate of 20 °C/min. The melting and solidification process showed no significant change with the decrease of cooling rate in 9.0% TiB₂/7075 Al matrix composites. Most small particles can act as heterogeneous nucleus, which induced grain growth and were captured into the grain by the solid/liquid interface. At the same time, most of the larger particles and a minority of the small TiB₂ particles are pushed into the grain boundary; locating in the grain boundary can hinder the Al atoms from diffusing during the solidification process and restrain α-Al phase growth. The influence of particles shifted from dominating by locating to dominating by nucleation as the quantity of TiB₂ particles increased.
研究了TiB₂/7075铝基复合材料的形核过冷度、不同冷却速率凝固后的微观组织以及TiB₂颗粒的尺寸和分布。实验结果表明，TiB₂/7075铝基复合材料的晶粒尺寸随TiB₂含量的增加先减小，后增大，最后又减小。当冷却速率分别为5和10℃/min时，TiB₂/7075铝基复合材料的形核过冷度随TiB₂含量的增加先增大，后减小，最后又增大；而当冷却速率为20℃/min时，形核过冷度随TiB₂含量的增加持续减小。在9.0%TiB₂/7075铝基复合材料中，随着冷却速率的降低，熔化和凝固过程无明显变化。大多数小颗粒可作为异质形核核心，促进晶粒生长并被固/液界面捕获到晶粒中。同时，大多数较大颗粒和少数小TiB₂颗粒被推至晶界；位于晶界处会阻碍凝固过程中Al原子的扩散，抑制α-Al相的生长。随着TiB₂颗粒数量的增加，颗粒的影响从以位置主导转变为以形核主导。
