纳米结构AISI316L不锈钢的摩擦磨损性能研究

IMR OpenIR

	纳米结构AISI316L不锈钢的摩擦磨损性能研究
	王博
学位类型	硕士
导师	卢柯 ; 韩忠
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	纳米结构材料动态塑性变形耐磨性再结晶磨痕亚表层结构 Nanostructured Material Dynamic Plastic Deformation Wear Resistance Static Recrystallization Worn Subsurface Structure
其他摘要	" 奥氏体不锈钢因其优异的耐腐蚀性能和良好的加工成型性得到了广泛的工程应用，但是由于相对较低的硬度和较差的耐磨性限制了其在摩擦磨损领域的应用。众所周知，晶粒细化是一种强化材料的有效方法，通过塑性变形方法制备纳米结构材料一直受到研究者广泛关注。其中动态塑性变形技术 (Dynamic Plastic Deformation，DPD) 利用高应变速率，结合低变形温度，可以在AISI 316L不锈钢样品中引入高密度缺陷，包括位错、孪晶界和晶界，获得块体纳米结构材料，使其具有高硬度和强度，同时一定退火条件下的样品具有良好的强塑性匹配。为探索更全面的工业应用，针对具有优异综合力学性能的AISI 316L不锈钢，深入研究其摩擦磨损性能，并且分析不同微观结构对其摩擦磨损行为的影响，具有十分重要的意义。本研究工作利用动态塑性变形技术 (DPD) 制备块体纳米结构AISI 316L不锈钢，并进行不同条件的退火处理，研究其变形态及退火态样品微观结构演化。由于材料摩擦磨损行为是所处摩擦学系统的特性，与工况条件和环境密切相关。因此，研究不同微观结构AISI 316L不锈钢在不同工况条件下（干摩擦/油润滑、不同配副）摩擦磨损性能以及磨痕亚表层微观结构，探索微观结构对纳米结构不锈钢摩擦磨损行为的影响，理解相关摩擦磨损机制。主要结果如下： 1. 室温下动态塑性变形处理AISI 316L不锈钢微观结构中，随着变形量的增加，变形孪晶层片状厚度及所占体积百分数有所改变。随着应变量增大到饱和变形量e=1.65，最终形成稳定的纳米孪晶镶嵌于纳米晶区域的混合纳米结构。对于饱和变形量DPD样品进行退火处理，通过优化退火参数，可以获得由微米级动态再结晶晶粒和纳米晶两部分组成的混合结构，其中经750℃退火20 min样品中，再结晶晶粒呈网状分布在纳米结构基体中，并且两种结构体积百分比相当。 2. 干摩擦滑动条件下，随着应变量的增大，DPD样品磨损量相比粗晶态随之增加，饱和变形量DPD样品磨损量增加45%。经过退火处理后，随着退火时间增加、退火温度升高，样品磨损量随之降低至几乎接近粗晶态。在干摩擦滑动条件下，不同微观结构AISI 316L不锈钢耐磨性随着硬度的提高呈逐渐下降的趋势，表现为反常Archard关系，这主要归因于AISI 316L干摩擦磨损过程中剧烈的粘着磨损，由于结构细化导致硬度提高，但塑性的丧失使得材料在此摩擦磨损条件下更容易在亚表层形成微裂纹而发生剥离，造成耐磨损性降低。 3. 油润滑滑动条件下，饱和变形量样品磨损量相比粗晶态略微减小，在10 N载荷下，磨损量下降25%。经过退火处理后，材料在低载荷10 N条件下，磨损量随硬度提高而单调减小，大体上符合Archard公式，这主要是由于DPD样品中纳米孪晶界和纳米晶界的强化作用；在高载荷30 N条件下，样品磨损体积随着硬度提高，呈现先减小后增大的趋势。其中750℃退火20 min样品对应着最佳耐磨性，磨损量相比粗晶态下降46%，主要归因于样品中纳米结构适中的硬度结合再结晶晶粒一定的塑性，获得了良好的强塑性匹配。同时，摩擦配副材料的改变并没有影响耐磨性随硬度变化的规律。 4. 油润滑滑动条件下，粗晶态样品磨痕亚表层发生严重塑性变形，晶粒显著细化，硬度随着距磨痕表面距离减小而逐渐增大；DPD样品晶粒长大，变形层较浅，硬度随着距磨痕表面距离减小而逐渐减小；退火态样品亚表层变形中包含再结晶晶粒细化和纳米晶长大两个过程，再结晶晶粒提供承担塑性变形的能力，纳米结构维持硬的基体。塑性的回复导致其变形层深度增加，最佳的强塑性匹配导致其具有优异耐磨性。磨痕表面微观结构均为亚微米晶/纳米晶结构，硬度值约为3.0 GPa。"; " Austenitic stainless steels have widespread engineering applications for their excellent resistance to corrosion and good formability, but their further usage in tribological application is limited due to their relatively low hardness and poor wear performance. As it is known to all, grain refinement is an effective strengthening technique. Nano-sized materials can be produced via several plastic deformation techniques. Among of these methods, dynamic plastic deformation (DPD) is a novel synthesis method to get bulk nanostructured metals due to its high strain rate. This bulk nanostructured metals possess high hardness and strength. Meanwhile, after subsequent thermal annealing of the as-DPD samples, the material exhibits an enhanced strength-ductility combination. With the excellent and comprehensive mechanical property for AISI 316L stainless steel, in order to enlarge industry applications, there is a crucial guidance to further investigate its relative tribological properties and discuss microstructure effect on tribological behaviors. In this work, nanostructured AISI 316L stainless steel has been successfully synthesized via DPD. The microstructure characterizations of both the as-DPD 316L SS samples and the as-annealed DPD samples were investigated. The tribological properties of materials closely depend on the testing parameters and environments due to its extrinsic influence. Therefore, friction and wear tests under different conditions (dry sliding test/oil-lubricated test, different counterface) were performed on different samples by using SRVⅢ oscillating tester. The worn subsurface microstructure characterization was studied as well to further discuss the relatively wear mechanisms. The main results of this work are listed as follows: 1. Microstructural evolution of AISI 316L stainless steel via DPD at room temperature involves the formation and evolution of deformation twins. The thickness of twin lamellar and the volume fraction of nano-scaled twins change with the increase of the strain. As the strain further increases to a saturated value of 1.65, bulk nanostructured AISI 316L SS with nano-scaled twins embedded in nano grains was formed. After thermal annealing treatment, through the optimization of annealing parameters, the as-annealed DPD sample shows a mixed structure with static recrystallized (SRX) grains in remained nanostructured matrix. The volume fraction of two different structure are quite similar when annealed at 750℃ for 20 min. 2. Under dry sliding condition, the wear volume of the as-DPD sample increases with the increase of the strain compared to the CG sample. The wear volume of the as-DPD sample with a saturated strain is 45% higher than that of the CG sample. After thermal annealing treatment, as the annealing time increases and temperature rises, the wear volume falls down and is nearly close to that of the CG sample. The wear resistance of AISI 316L SS with different microstructure linearly decreases as the hardness increases under dry sliding condition. It is contradicted to the Archard’s equation due to severe adhesive wear. Because of the increase of hardness induced by grain refinement, the loss of ductility could make material easier to peel from the matrix, and then decrease the wear resistance in this wear mechanism. 3. Under oil-lubricated condition, the wear volume of the as-DPD sample with saturated strain is a little lower than that of the CG sample. Especially under a load of 10 N, the decreasing extent is 25%. After thermal annealing treatment, the wear resistance of the samples roughly follows the Archard’s equation under a load of 10 N. The wear volume decreases with the increase of the hardness. This is attributed to the strengthening of nano-twins and nano-grains boundaries after grain refinement via DPD. For a relatively high applied load of 30 N, the wear resistance increases with an increase of hardness and decreases with the further increase. The highest wear resistance was found in the DPD sample annealed at 750 oC for 20 min, which is more than 46% higher than that of the CG sample. The highest wear resistance is originated from moderate plastic deformation in SRX grained regions and certain hard matrix. Meanwhile, the change of counterface has no obvious influence on the wear resistance-hardness relation of different microstructure. 4. Under oil-lubricated condition, obvious grain refinement happens in the worn subsurface of the CG sample, while grain growth appears in the worn subsurface of the as-DPD sample. The deformed layer in the as-DPD sample is relatively shallow. On the other hand, the worn subsurface of the as-annealed DPD sample combines two former evolutions. It is understandable that ductile SRX grains provide the plasticity to undergo moderate plastic deformation in the hard matrix, which consumes the frictional work and inhibits peeling of materials. Meanwhile, grain growth may occur in the original nanostructured regions like the situation in the as-DPD samples. Therefore, excellent strength-ductility combination is responsible for the highest wear resistance of the DPD sample annealed at 750oC for 20 min. The microstructure near the worn surface consists of ultrafined grains/nanograined, and the hardness of which is about 3.0 GPa."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64532
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	王博. 纳米结构AISI316L不锈钢的摩擦磨损性能研究[D]. 北京. 中国科学院金属研究所,2012.