| 摘要: |
| 回顾了20世纪70年代表面形变的研究成果，并和21世纪表面形变纳米化作比较。结构方面，上世纪所提的位错胞可以在电镜下直接观察到，而且由动态回复试验得到旁证。21世纪表面纳米化的晶粒碎化，小角晶界变成大角晶界则未见直接的实验结果，也无充分理论依据。此外，20世纪注重定量分析的结构参数是位错胞间错角，21世纪表面纳米化则强调细化的尺度，用谢乐公式计算出晶粒大小及其分布。但位错胞不是晶粒，不能简单套用谢乐公式，文中详述了其理论依据。性能方面，形变强化以牺牲塑性为代价。20世纪将磨损和切削形成的纳米尺度白亮层视作损伤，21世纪的表面纳米化不是用性能优化作导向，而是以纳米化为目标，也即趋向白亮层的损伤程度，显然有悖材料学常理。工程应用方面，20世纪喷丸参数选择已有定量的规范和标准。21世纪为达到纳米化，喷丸必须超高强度，导致塑性大幅下降，粗糙度急剧提高，旋转弯曲疲劳试验表明，过喷使疲劳强度明显下降。即使对抗磨而言，强变形也只是在有限条件下起作用。至于形变后易于氮化的说法，上世纪初就发现在含氮环境中的磨损件易生成氮化物。实践表明，并非一个利于扩散的因素就可以认定工艺全过程具有可行性。强喷丸缺陷易于在氮化中扩大而萌生裂纹，应用效果存疑。 |
| 关键词: 表面摩擦 位错胞 动态回复 谢乐公式 |
| DOI：10.3969/j.issn.1007-9289.2014.05.001 |
| 分类号: |
| 基金项目: |
|
| Comments on Nanotreatment of Surface Attrition via Historical Review |
|
HE Jiawen
|
|
State Key Laboratory of Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049
|
| Abstract: |
| The research results of surface attrition in the seventies of 20th century are reviewed and compared with that of 21st century. In terms of microstructure, the dislocation cells can be directly observed in TEM and approved by dynamic recovery test in the last century, however, no direct experimental results for grain fragmentation as well as grain boundaries turning smallangle into large angle suggested in this century, and no appreciable theory to support these hypotheses. In addition, in the 20th century, the quantitative analysis of disorientation angles among dislocation cells was emphasized, and the study of this century was focusing on the size of refinement structure, of which the grain size and distribution were calculated by Scherrer equation. Dislocation cells are not grains, the Scherrer equation cannot be simply applied. The argument is discussed in detail in the paper. Regarding the performance of the surface attrition layer, the increase of strength is at the expense of plasticity. In the 20th century, the white layer characterized in nanoscale structure formed on the worn surface or cutting edge was regarded as material damage. The nanotreatment by surface attrition in the 21st century is not oriented in the performance optimization, but aimed at nanosize, which approaches to the damage level of the white layer. It is apparently against the common sense of material science. For engineering applications, the parameters and standards of shot peening have been well established in the 20th century. To achieve the nano structure suggested in this century, the shot peening intensity must be higher than normal, thus the plasticity substantially decreased and the roughness sharply increased. Rotating bending fatigue tests show the fatigue strength decreases significantly by abusive peening. Even for wear, sever attrition layer is only appreciable in limited cases. As for the saying that surface attrition is good for nitriding, in fact, in the beginning of last century it was already found that the wear parts in the nitrogen environment were easy to generate nitrides. Practical experience indicates that one factor being favorable is not enough to approve the feasibility of the entire process. The defects induced in severe peening would be easy to expand during nitriding and initiate cracks, thus its applicable is doubtful. |
| Key words: surface attrition dislocation cell dynamic recovery Scherrer equation |
