Nanoscopic study and application of tribo-plastic deformation mechanism

为了充分利用位错理论所代表的塑性变形的微观方面，需要一种金属成形技术，将表面粗糙度控制在分子膜厚度，并在刚性约束下使试样塑性变形。在本项目中，研究了纳米级的表面形成过程，避免了滑动过程中表面损伤和接触界面上存在过量润滑剂的问题。此外，还举例说明了特殊几何形状的纳米级金属成形工艺。从塑性流体动力润滑的理论研究出发，采用顶角为150°的楔块压痕滑动过程。由超细硬质合金制成的楔形工具被研磨至表面粗糙度为20nm Rx。用防水砂纸对12mm宽的无氧半硬铜矩形块试样进行抛光处理，表面粗糙度达到150nm Ra。将楔形工具低速压入试样，形成约1.4mm宽的山谷。然后，在恒定的正常载荷下，刀具沿着刀具脊方向滑动0.5 mm。结果表明，刀具到试样的几何传递有两种方式。(1)微观扁化过程中留下几微米宽的谷。根据润滑剂的不同，边界接触率从80%到95%不等。(2)在AFM下，在边界接触区域进行纳米级压扁，表面粗糙度为0.5 ~ 1nm Ra，在500nm × 500nm平方范围内，与刀具表面粗糙度基本一致。通过钝楔的压痕和滑动，可以实现纳米级表面粗糙度的精确传递。润滑油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.