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Influence of strain amplitude on the development of dislocation structure during cyclic plastic deformation of 304 LN austenitic stainless steel

机译:应变幅度对304 LN奥氏体不锈钢循环塑性变形过程中位错组织发展的影响

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In the present study, electron backscatter diffraction (EBSD) and electron channelling contrast imaging (ECCI) were used to document the evolution of dislocations in a 304 LN austenitic stainless steel subjected to cyclic plastic deformation at room temperature using different strain amplitudes. In particular EBSD was used to quantify the development of geometrically necessary dislocation density (GND) with varying strain amplitudes. Solution annealed multiple specimens were cyclically deformed at varying strain amplitudes ranging from +/- 0.25 to +/- 1.2% under completely reversed straining conditions until complete failure. It is found that GND density, which is independent of the character of the dislocations, increases with the increase of strain amplitude. This is consistent with the cyclic hardening characteristic of the investigated steel. It is found that the evolution of GND structure during the course of deformation is heterogeneous in nature with small grains having higher GND density than the coarse grains. The clustering of GNDs is visible near grain boundaries leaving the grain interior free. EBSD can capture the variation in GND storage patterns with strain amplitudes. The heterogeneity of the cyclic deformation induced GND structure decreased with the increase of the strain amplitude. The evolution of GND structure is also found to be sensitive to the size and orientation of the austenite grains. It has been found that the GND density is maximum in {111} < 0-11 > grains, those with the highest Taylor factor. The fidelity of dislocation storage pattern with strain amplitudes is assessed using ECCI. This is consistent with the GND storage pattern shown by EBSD and explains the cyclic hardening behavior of the steel.
机译:在本研究中,电子背散射衍射(EBSD)和电子通道对比成像(ECCI)用于记录在304 LN奥氏体不锈钢中,在室温下使用不同的应变幅度进行循环塑性变形时,位错的演变。尤其是,EBSD用于量化随应变幅度变化的几何必要位错密度(GND)的发展。在完全相反的应变条件下,固溶退火的多个试样在+/- 0.25至+/- 1.2%的变化应变幅度下循环变形,直到完全破坏。发现与位错特性无关的GND密度随着应变幅度的增加而增加。这与所研究的钢的循环硬化特性一致。可以发现,在变形过程中,GND结构的演化本质上是异质的,小晶粒的GND密度高于粗晶粒。在晶粒边界附近可以看到GND的聚集,而晶粒内部没有空间。 EBSD可以捕获GND存储模式随应变幅度的变化。周期性变形引起的GND结构的异质性随应变幅度的增加而减小。还发现GND结构的演变对奥氏体晶粒的尺寸和方向很敏感。已经发现,{111} <0-11>晶粒中的GND密度最大,泰勒系数最高。使用ECCI评估具有应变幅度的位错存储模式的保真度。这与EBSD显示的GND存储模式一致,并说明了钢的循环硬化行为。

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