The brittle-to-ductile transition in cold rolled tungsten plates: Impact of crystallographic texture, grain size and dislocation density on the transition temperature
The brittle-to-ductile transition in cold rolled tungsten plates: Impact of crystallographic texture, grain size and dislocation density on the transition temperature
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DOI：
10.1016/j.ijrmhm.2018.09.010
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发表时间：
2019-01-01
影响因子：
3.6
通讯作者：
Reiser, Jens
中科院分区：
文献类型：
--
作者：
Bonnekoh, Carsten;Jaentsch, Ute;Reiser, Jens
本文以冷轧钨为例，从同一块烧结钨锭中轧制出不同变形程度的五块板材，分别代表1.8，2.5，3.0，3.4，和4.1（这是指技术符号中的83.5%、91.8%、95.0%、96.7%和98.3%）。韧性测试表明，BDT温度随着变形程度的增加而从115 ℃ +/-15 ℃（388 K +/-15 K）下降到-65 ℃ +/-15 ℃（208 K +/-15 K）。与烧结锭相比，温度提高了600 K以上。本文对上述五种板材的显微组织进行了深入的分析。该分析包括评估（i）晶体织构、（ii）晶粒尺寸和（iii）位错密度。显微结构特征和实验数据之间的比较证实了我们的工作假设，即BDT是由螺旋位错的滑移控制的，并且转变温度随着位错源沿着裂纹前缘的间距λ的减小而降低。位错源可以是晶界与裂纹前缘的交点（BDT-温度-晶粒尺寸-关系）或位错增殖过程，例如，开环和闭环的扩展（位错密度的影响）。
The aim of this paper is to elucidate the mechanisms controlling the brittle-to-ductile transition (BDT) in pre deformed, textured, polycrystalline body-centred cubic (bcc) metals by the example of cold rolled tungsten (W).For this purpose, five sheets were rolled out from one and the same sintered ingot, by various levels, representing degrees of deformation of 1.8, 2.5, 3.0, 3.4, and 4.1 (this refers to 83.5%, 91.8%, 95.0%, 96.7%, and 98.3% in the technical notation). Toughness tests show that the BDT temperature decreases with increasing degree of deformation from 115 degrees C +/- 15 degrees C (388 K +/- 15 K) down to -65 degrees C +/- 15 degrees C (208 K +/- 15 K). This is an improvement of > 600 K compared with a sintered ingot.In this paper we perform an in-depth analysis of the microstructure of the five sheets mentioned above. This analysis includes the assessment of (i) crystallographic texture, (ii) grain size and (iii) dislocation density. A comparison between microstructural features and experimental data confirms our working hypothesis which states that the BDT is controlled by the glide of screw dislocations and that the transition temperature decreases with decreasing spacing, lambda, of dislocation sources along the crack front. Sources for dislocations may be the intersection points of grain boundaries with the crack front (BDT-temperature-grain-size-relation) or dislocation multiplication processes such as e.g., the expansion of open and closed loops (impact of dislocation density).