The influence of grain size on the indentation hardness of high-purity copper and aluminium
The influence of grain size on the indentation hardness of high-purity copper and aluminium
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DOI：
10.1080/01418610208235717
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发表时间：
2002-07
期刊：
影响因子：
--
通讯作者：
Y. Y. Lim-Y.;M. M. Chaudhri-M.
中科院分区：
文献类型：
--
作者：
Y. Y. Lim-Y.;M. M. Chaudhri-M.
用维氏金刚石和半径为200μm的碳化钨钴球在室温下对高纯多晶和铜铝单晶样品进行了准静态显微压痕硬度研究。铜多晶样品经大变形后在不同温度和不同时间进行不同温度和不同时间的热处理，得到的铜多晶样品的晶粒度在15-520μm之间。铝的多晶样品的晶粒度为330±40μm。不同晶粒度的铜样品具有不同的位错密度，晶粒度越小，位错密度越高。对于给定的压痕载荷，维氏硬度由压痕的投影接触面积确定，发现随着颗粒尺寸的减小而增加。同样，Meyer硬度也随着晶粒度的减小而增加。我们认为，随着晶粒度的减小，多晶硬度的增加是由于晶内初始位错密度的增加，而不是由于晶界，因为晶界上没有杂质，所以在这些高纯面心立方金属中不起位错势垒的作用。此外，由于不同取向的铜单晶的压痕硬度值非常相似，相邻颗粒取向的任何差异都不会影响多晶的硬度值。因此，对于大尺寸(10 mm×10 mm×10 mm)的铜单晶，其位错密度与晶粒度为15±7μm的铜多晶试件的位错密度相同，其压痕硬度值非常接近。用维氏压痕和球头压痕对多晶铝和较大的单晶进行的压痕硬度测试结果表明，晶粒度对压痕硬度的影响不大。
Abstract Quasistatic microindentation hardness studies of specimens of high-purity polycrystals and single crystals of copper and aluminium have been made at room temperature using a Vickers diamond and a tungsten carbide-cobalt sphere of radius 200 μm. The polycrystalline specimens of copper were prepared by heavy deformation of as-received specimens followed by thermal annealing at different temperatures and for different times; the grain sizes produced were in the range 15-520 μm. The polycrystalline samples of the as-received aluminium had a grain size of 330 ± 40 μm. As-formed specimens of copper of different grain sizes were found to have different dislocation densities; the smaller the grain size, the higher was the dislocation density. The Vickers hardness for a given indenter load, determined using the projected contact areas of indentations, was found to increase with decreasing grain size. Similarly, the Meyer hardness increased with decreasing grain size. It is argued that the observed increase in hardness of the polycrystals with decreasing grain size is due to the initial dislocation densities in the grains and not due to the grain boundaries which, because of the lack of impurities at them, do not appear to act as dislocation barriers in these high-purity fcc metals. Moreover, as the indentation hardness values of single crystals of copper of different orientations are very similar, any differences in the orientations of contiguous grains will not affect the hardness values of polycrystals. Thus for large single crystals of copper (10 mm × 10 mm × 10 mm), having the same dislocation density as that of the polycrystalline specimens of copper of grain size 15 ± 7 μm, the indentation hardness values were quite similar. Experimental results from the indentation hardness tests, made using both Vickers and spherical indenters, on polycrystalline aluminium specimens and relatively large single crystals showed that there was insignificant influence of the grain size.