Poza P, Llorca J
Departamento de Ciencia de Materiales, Universidad Politecnica de Madrid. E. T. S. de Ingenieros de Caminos, 28040 Madrid, Spain.
J Microsc. 1999 Nov;196(# (Pt 2)):113-23. doi: 10.1046/j.1365-2818.1999.00624.x.
The effect of SiC reinforcement on the microstructure of a naturally aged 8090 Al alloy as well as on the deformation and fracture micromechanisms was investigated. To this end, the microstructural characteristics (grain and reinforcement morphology, precipitate structure) were determined in the unreinforced alloy and in the composite reinforced with 15 vol.% SiC particles. The materials were tested under monotonic tension and fully reversed cyclic deformation and then carefully analysed through scanning and transmission electron microscopy to find the dominant deformation and failure processes for each material and loading condition. It was found that the dispersion of the SiC particles restrained the formation of elongated grains during extrusion and inhibited the precipitation of Al3Li. As a result, the plastic deformation in the composite was homogeneous, while strain localization in slip bands was observed in the unreinforced alloy specimens tested in tension and in fatigue. The unreinforced alloy failed by transgranular shear along the slip bands during monotonic deformation, whereas fracture was initiated by grain boundary delamination, promoted by the stress concentrations induced by the slip bands, during cyclic deformation. The fracture of the composite was precipitated by the progressive fracture of the SiC reinforcements during monotonic and cyclic deformation.
研究了碳化硅增强体对自然时效8090铝合金微观结构以及变形和断裂微观机制的影响。为此，测定了未增强合金和含有15体积%碳化硅颗粒的复合材料的微观结构特征（晶粒和增强体形态、析出相结构）。对材料进行单调拉伸和完全反向循环变形测试，然后通过扫描电子显微镜和透射电子显微镜仔细分析，以找出每种材料和加载条件下的主要变形和失效过程。结果发现，碳化硅颗粒的弥散抑制了挤压过程中拉长晶粒的形成，并抑制了Al3Li的析出。因此，复合材料中的塑性变形是均匀的，而在拉伸和疲劳测试的未增强合金试样中观察到滑移带中的应变局部化。在单调变形过程中，未增强合金沿滑移带发生穿晶剪切而失效，而在循环变形过程中，断裂由晶界分层引发，滑移带引起的应力集中促进了这种分层。在单调和循环变形过程中，复合材料的断裂是由碳化硅增强体的逐渐断裂引起的。
