【作者】 刘飞燕；

【导师】 樊新民；

【作者基本信息】 南京理工大学 ， 材料学， 2008， 硕士

【摘要】 利用强烈塑性变形诱发晶粒细化的机理,构建了高速旋转丝变形实验装置,分别对低碳钢、工业纯钛进行了表面处理,探讨实现表面纳米化的可行性。运用X射线衍射、扫描电子显微镜和透射电子显微镜等研究变形处理后样品的显微结构变化特征。运用显微硬度计对处理样品表面性能进行测试分析。结果表明:经过普通镀铜钢丝轮高速旋转塑性变形处理后,在低碳钢表面可以形成厚度为10～15μm左右的纳米晶层,最表面层的平均晶粒尺寸约为8nm,晶粒尺寸沿深度方向不断增大;表层显微硬度显著提高,与心部基体相比,提高了2倍以上,最高达到约491HV0.05。工业纯钛表面层晶粒细化至纳米量级,尺寸为15nm左右,沿深度方向,晶粒尺寸逐渐增大;表面层硬度高达489HV0.05,约为基体硬度的3倍,随着距表面深度的增加,显微硬度逐渐降低。研究了低碳钢和工业纯钛在高速旋转丝变形表面纳米化处理前后的离子渗氮行为。实验结果发现:在500℃以下渗氮时,经过表面纳米化预处理的低碳钢,其表层所形成的化合物层厚于原始渗氮样品,且表层硬度显著提高,是相同条件下原始渗氮样品的1.7倍;当温度高于600℃渗氮5h后,表面纳米化预处理的优势消失。工业纯钛经表面纳米化预处理后,在480℃下渗氮8h,就能够形成化合物,且在600℃以下渗氮,形成较原始样品更厚的化合物层,在相同条件下与原始渗氮样品表层硬度值(703HV0.05)相比,预处理渗氮表层硬度增高到909HV0.05。更多还原

【Abstract】 Based on the grain refinement mechanism induced by severe plastic deformation, a novel technique of high-speed rotation wire-brushing deformation (HRWD) was used to treat the surface of low carbon steel and commercially pure titanium(TA2) with the purpose of exploring the feasibilities of realizing surface nanocrystallization by HRWD. The experimental set-up was designed and rebuilt. The refined microstructure features were systematically characterized by means of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The microhardness variation along the depth of the treated sample was examined by microhardness tester. Experimental evidences showed that after the HRWD treatment with ordinary coppered steel wire, a nanostructured surface layer of about 10-15μm in thickness was formed on low carbon steel. The mean grain size in the top surface layer was approximately 8nm. It was found that a gradient microstructure with grain size from nanoscale to microscale was obtained along the depth of its surface layer. The microhardness of nanostructured surface layer was enhanced significantly after HRWD, compared with that of the original sample, and reached 491 HV0.05. The microstructure of the surface layer was refined into the nanoscale on TA2 by HRWD. Its mean grain size in the top surface layer was up to 15nm. In the top surface nanostructured layer, the microhardness reached 489HV0.05, which was about three times that of the coarse-grained matrix. And along the depth from the top surface, the microhardness in the surface layer gradually decreased to that of the matrix.Plasma-nitriding behavior of low carbon steel and commercially pure titanium after the HRWD treatment was investigated in comparison with that in the original materials. Experimental results showed that improved nitrogen transport could be obtained by plasma nitriding after the samples were subjected to HRWD. For low carbon steel nitrided below 500℃, the surface nanocrystallized samples could produce thicker compound layer than untreated samples. With the same nitriding treatment parameters, the surface microhardness of the samples treated by HRWD, increased significantly, which nearly doubled the value of plasma-nitrided coarse-grained ones. However, after 5 hours’ nitridation at 600℃, the surface nanostructured samples began to lose their good effects on the nitridation speed during the plasma nitriding. The compound layer came into existence on HRWD commercially pure titaniun nitrided at 480℃for 8 hours. Furthermore, nitrided below 600℃, the surface nanostructured TA2 could form thicker compound layer than untreated samples and raised the surface microhardness from 703HV0.05 (of nitrided coarse-grained TA2) to 909HV0.05.更多还原