TOUGHENING OF BRITTLE MATERIALS BY GRAIN BOUNDARY DESIGN AND CONTROL

研究了难熔金属钼、定向凝固Ni_3Al和快速凝固Fe-50%Co合金带状三种不同加工方法制备的脆性多晶材料的晶界特征分布（GBCD）。发现了加工和后续热处理的晶界特征分布条件。研究表明，可以通过提高抗晶间断裂的低能边界的频率来控制晶间脆性，反之，通过降低易发生晶间断裂的高能随机边界的频率来控制晶间脆性。研究了与晶间脆性相关的其他微观结构因素：提出了实际多晶材料的晶界相关数和晶界三重结特性，并进行了实验研究。对多晶断裂过程和断裂特征的模拟表明，断裂韧性和脆性-韧性转变强烈依赖于晶界特征分布（GBCD）和晶界的几何排列。这一发现为本研究中实现的晶界设计和控制对脆性材料增韧的基本概念提供了有力的支持。所得结果可应用于陶瓷领域。

The grain boundary character distribution (GBCD) was investigated on three different types of brittle polycrystalline materials produced by different processing methods: refractory metal molybdenum, directionally solidified Ni_3Al and rapidly solidified Fe-50%Co alloy ribbon.It has been found that the grain boundary character distribution (GBCD) condition of processing and subsequent heat treatments. It has been reveal ed that intergranular brittleness can be controlled by enhancement of the frequency of low-energy boundaries which are resistant to intergranular fracture, or conversely by reduction of the frequency of high-energy random boundaries which are prone to intergranular fracture.Other microstructural factors associated intergranular brittleness have been investigated: The grain boundary correlation number and the grain boundary triple junction character have been proposed and experimentally studied for real polycrystalline materials.The modelling of fracture processes and characteristics in polycrystals has made clear that the fracture toughness and brittle-ductile transition strongly depend on the grain boundary character distribution (GBCD) and geometrical arrangements of grain boundaries. This finding has provided a strong support to the basic concept of toughening of brittle materials by grain boundary design and control achieved in this investigation. The result obtained from this work may be applied to ceramics.