Fatigue Crack Initiation Behavior in Ultrafine-Grained Steel Observed by AFM and EBSP

Abstract

Ultrafine-grained specimens with the average grain size of less than 2 µm and mediumgrained specimens were prepared from steel plates produced by an advanced thermomechanical control process. The smooth specimens were fatigued under axial tension compression at room temperature in air. The fatigue crack initiation process was investigated by orientation imaging microscopy based on EBSP in combination with atomic force microscopy and scanning electron microscopy. The results show that fatigue cracks initiated in the simple slip lines in the medium-grained specimens. On the other hand, in the ultrafinegrained specimens, complex slip deformation was formed in the vicinity of the grain boundaries prior to the fatigue crack initiation. Fatigue cracks were nucleated at the boundary between the grains with the concentrated complex slip deformation. The crystallographic orientation analysis revealed that the complex slip deformation was formed by the cross slip of active slip systems with the largest Schmid factors. It was found that the relation between the fatigue limit and grain size of the ultrafine-grained specimens does not conform to the Hall-Petch relation of conventional ferritic-pearlitic steel due to the texture and cross slip.

<i>In-situ</i> Tensile Tester for Scanning Three-Dimensional X-ray Diffraction Microscopy

“…Yujiro HAYASHI, 1) Daigo SETOYAMA, 1) Hidehiko KIMURA, 1) * Yusuke YONEYAMA 2) and Keisuke TAKEUCHI 2) 1) Materials Analysis & Evaluation Research-Domain, Toyota Central R&D Labs., Inc., 41-1, Yokomichi, Nagakute, Aichi, 480-1192 Japan.…”

“…Today, orientation microscopy (OM) with electron backscatter diffraction (EBSD) is widely used to investigate the mechanical responses of engineering materials with a numerous number of grains with different orientation. 1,2) In EBSD-OM, three-dimensional (3D) orientation maps necessary for materials modeling can be produced with serial sectioning of samples. However, we cannot track changes in orientation due to the deformation or damage processes because the samples are destroyed and continuous measurement is not possible.…”

Fatigue Crack Initiation in Proton-Irradiated Austenitic Stainless Steel

“…[7][8][9][10] However, the effect of irradiation was not considered in those studies. The objective of this study is to investigate the effect of irradiation on slip band formation and growth and microcrack initiation behavior under low cycle fatigue in the austenitic stainless steel via accelerator-based proton irradiation.…”

Fatigue Crack Initiation in Proton-Irradiated Austenitic Stainless Steel

“…The analysis and prediction method of microcrack initiation under fatigue have been reported for austenitic stainless steel. [7][8][9][10] However, the effect of irradiation was not considered in those studies. The objective of this study is to investigate the effect of irradiation on slip band formation and growth and microcrack initiation behavior under low cycle fatigue in the austenitic stainless steel via accelerator-based proton irradiation.…”