Nanoscopic study and application of tribo-plastic deformation mechanism

为了充分利用微观方面的塑性变形所代表的位错理论，金属成型技术，控制表面粗糙度的分子膜厚度和变形的标本塑性刚性约束下是必需的。在本项目中，在纳米级的表面形成过程中，避免滑动过程中的表面损伤和接触界面上存在的过量润滑剂的问题进行了研究。通过对塑性流体动力润滑理论的研究，采用了顶角为150°的楔形体的压入滑动成形工艺。将来自超细烧结碳化钨的楔形工具研磨至20 nm Rx的表面粗糙度。用防水砂纸对宽12mm的无氧铜半硬铜矩形块试样进行抛光，使其表面粗糙度达到150nm Ra。楔形工具以低速压入试样中以形成约1.4mm宽的谷。然后在恒定的法向载荷作用下，沿工具脊方向滑动沿着0.5 mm，发现从工具到试样的几何转换是通过两种方式实现的。(1)显微镜下的扁平化继续进行，留下几微米宽的谷。根据润滑剂的不同，边界接触率在80%到95%之间. (2)纳米级平坦化在边界接触区域上进行，而在AFM下没有显示出任何表面损伤，以在500nm × 500nm的正方形上形成0.5至1nm Ra的表面粗糙度，这几乎与工具表面相同。举例说明，纳米级的表面粗糙度的精确转移是可能的钝楔的压痕和滑动。润滑剂结构和滑动距离的影响有待进一步研究。

To fully utilize a microscopic aspect of plastic deformation as being represented by dislocation theory, a metalforming technique that controls surface roughness at a molecular film thickness and deforms the specimen plastically under a rigid constraint is required. In the present project a surface formation process in a nanometer order avoiding problems of surface damage during sliding and excess lubricant present over contact interface is studied. Furthermore, nanometer-scale metalforming process is to be exemplified for a special geometry.From a theoretical study of plasto-hydrodynamic lubrication, an indentation-and-sliding process of a wedge with 150°apex angle is adopted. A wedge tool from ultra-fine cemented tungsten carbide is lapped to a surface roughness of 20 nm Rx. A rectangular block specimen of oxygen-free half-hard copper with 12mm wide is finished by a waterproof abrasive paper to have the surface roughness of 150 nm Ra. The wedge tool is indented into a specimen at a low speed to form a valley of about 1.4mm wide. Then the tool is slid up to 0.5 mm along the tool ridge direction under a constant normal load.It was found that the geometrical transfer from tool to specimen is made in two ways. (1) Microscopic flattening proceeds leaving valleys of several micron wide. The ratio of boundary contact ranges from 80 % to 95% depending on the lubricants. (2) Nanoscopic flattening proceeds over a boundary contact region without showing any surface damage under AFM to form a surface roughness of 0.5 to 1nm Ra over 500nm x 500nm square, which is almost the same as the tool surface. It is exemplified that nanometer-scale precise transfer of surface roughness is possible by the indentation-and-sliding of a blunt wedge. A further study is required to clarify the effects of lubricant structure and the distance of sliding.