脉冲电流对再制造毛坯裂纹尖端组织及性能的影响

以再制造为目标,利用高能脉冲电流冲击装置对含有单边裂纹的316奥氏体不锈钢进行脉冲电流处理。采用金相显微镜、X-射线衍射仪、电子背散射衍射(EBSD)、透射电子显微镜(TEM)等表征手段,研究高密度脉冲电流对裂纹尖端区域微观组织与结构的影响,分析裂纹尖端组织加热熔化及热处理时的组织演变过程。结果表明:脉冲电流处理后,裂纹尖端组织发生了明显细化并出现组织梯度,包括柱状晶区、再结晶区及基体区。脉冲电流的快速加热和快速冷却、高速电子风的产生、电致塑性等作用降低了再结晶或相变时的热力学屏障,提高了形核率,抑制了晶粒长大过程,获得了比原始晶粒尺寸小的再结晶晶粒,材料的力学性能得到提高。

Effects of Electropulsing on Crack Tip in Remanufacturing Blank

Crack can constantly expand and then cause invalidation, even cause catastrophic damage under the reciprocating loading. Based on remanufacturing, high energy pulse current impacting device was used to treat 316 austenitic stainless steel containing prefabricated unilateral fatigue crack. The influence of high density pulse electric current on the microstructure at crack tip was investigated by means of metallographic microscope, X-ray diffraction, electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). And the evolution of microstructure by melting treatment was analysized. Results show that the sturture at crack tip obviously became refinement after the pulse current processing, and the gradient structure including the columnar crystal area, recrystallization zone and matrix was observed. Due to the rapid heating and cooling, the generation of high-speed electronic wind, electrically induced plasticity effect, the thermodynamic barrier of recrystallization or phase change was reduced by pulsed current treatment. The rate of nucleation was increased, inhibiting the grain growth process. Therefore the grain size of recrystallization zone was smaller than that of the matix, and hence the mechanical properties of materials was improved.