金相样品制备的缺陷：圆角

------STRUERS，推介的知识；倒角、圆角，一个必须，一个避免

 

 

 

 

 

 

 

 

金相技能大赛的技术评价细节中，需要将样品起出倒角，这是因为不需要观察“边缘组织”，而为了不损伤抛光绒布，必须起出倒角。为什么需要倒角，技术原因的话你可以检索到：

 

如果试样的棱角对测试结果无影响的话，尽量倒角、倒边，以防止在细磨及抛光时将砂纸或抛光布料撕裂，甚至在抛光过程中使试样飞出，伤手指等；……

粗磨后，凡不做表面金相的，棱边需倒角。……

 

也有不允许的说法：

 

测定表层组织深度试样，其磨面需垂直。……

胶木粉不透明，有各种颜色，比较硬，试样不易倒角。……

 

       倒角，还是不倒角，是个问题。

 

理论上说，倒角并不一定需要，甚至，有的时候，不允许进行倒角，比如，表面热处理的工件样品。而要想练出一手绝活儿，不镶嵌保护还可以不出现倒角（准确说，是圆角edge rounding。），就不是幸运可以保障的。

有人说：

If sample edges are to be examined, mounting may be required along with other measures to be described in this chapter.

不过，我见识过企业金相实验室的老师傅的一手绝活儿，叹为观止！当然，我并不羡慕，因为，如果是我，会采用技术手段来得到同样的效果。

 

不过，严格区分的话，需要的倒角和不允许的倒角，不应当同一个中文词汇。主动起出来的斜面，可以称之为“倒角”，由于技术能力所限而产生的“边缘组织与心部组织”无法同时聚焦清楚的现象，是由于“圆角”的形成。表面热处理的样品，既不允许有意识地倒角，也不允许出现无意识的圆角缺陷。对应缺陷“圆角”就是，边角、边缘保留（edge retention），简化为“保角、保边”，不知道如何？

 

George Frediric Vander Voort，在《Metallography - Principles and Practice》中提及：

 

Figure 2-5a Example of excellent edge retention achievable with mechanical clamps. No spacers between sheet metal samples.

Figure 2-5A Example of excellent edge retention achievable with mechanical clamps. Plastic spacers between sheet metal samples.

 

Bakelite is the most commonly used compression molding material because of the simplicity of its use, the good results obtained with it, and its low cost. Edge retention with Bakelite is poorer than with many other resins but can be improved if the resin is cooled under pressure and if automatic polishing is employed （see Fig. 2-8）. Shrinkage is lower with diallyl phthalate than with Bakelite （0.003 to 0.005 in/in versus 0.004 to 0.008 in/in） [11]. Diallyl phthalate exhibits better resistance to strong acids or heated etchants than Bakelite. Diallyl phthalate or compression mounting epoxy are more resistant to heated etchants, such as boiling alkaline sodium picrate, than Bakelite, which deteriorates substantially.

 

Figure 2-8 Example of limited edge retention of Bakelite mounts. Left, automatic polishing; right, hand polishing（320×, 2% nital etchant, low-carbon steel）. poor edge retention.

 

 

       edge rounding，不是“倒角”，是“圆角”；倒角，不是磨、抛出现的缺陷，是操作者有意为之。

 

对于我们常见的术语“起倒角”，国内的表述过于随意了。

 

 

 

 

 

参考资料：

[1]  http://www.struers.com/zh-CN/Knowledge/Grinding-and-polishing 

故障排除--倒角

使用高弹性的抛光表面可从样品表面和侧面去除材料。这样可引起倒角，可在树脂磨损速率大于样品材料时见于镶嵌试样中。查看“研磨和抛光简介”一节中的抛光动态特性，以了解详细信息。 请在每个步骤之后查看您的样品，以确定故障出现的时间，以便您确定需要在制备中做出哪些变更。

查看以下示例和专家系统：

1. 由于树脂与样品之间的间隙，边缘将出现倒角。不锈钢。放大：500×，蚀刻剂：Beraha I

 

      2. 良好的边缘保护，不锈钢。放大：500×，蚀刻剂：Beraha I

 

    问题

不接受边缘保护。与图 1+2 进行比较

 

[2]  http://www.struers.com/en/Knowledge/Grinding-and-polishing  

Troubleshooting - edge rounding

Using a polishing surface with high resilience will result in material removal from both the sample surface and the sides. The effect of this is edge rounding and can be seen with mounted specimens if the resin wears at a higher rate than the sample material. Look in polishing dynamics in the "About Grinding & Polishing" section for more information. Please check your samples after each step to see when the fault occurs so you can determine what changes you will need to make in the preparation.

Look at the examples and expert system as follows:

1.  Due to a gap between the resin and the sample, the edge is rounded. Stainless steel Mag: 500×, Etchant: Beraha I

2.  Good edge retention, stainless steel. Mag: 500×, Etchant: Beraha I

Problem

The edge retention is not acceptable. Compare with figs. 1+2.

 

[3]  http://www.metallography.com/etching/examples.htm  Several Applications Of Tint Etching

Tint etching is particularly well suited for copper and copper alloys. Klemm's I reagent works very well with most of these compositions. Beraha's lead sulfide tint etch is also useful. All of the copper samples to be shown were attack polished using 1% aqueous ferric nitrate added to colloidal silica. Coloration is generally somewhat different, and sometimes less sharp, when other polishing abrasives are used.

Composition of Beraha's tint etchant: 100mL HCL, 50 mL H2O,1 g potassium metabisulfite, and 1 g ferric chloride.

 

References:

Color Metallography, by E. Beraha and B. Shpigler: American Society for Metals, Metals Park, Ohio, 1977.

"Metallographic Reagents Based on Sulfide Films," by E. Beraha: Praktische Metallographie, Vol 7, 1970, p 242-248.

"Metallographic Reagents Based on Molybdate Solutions," by E. Beraha: Praktische Metallographie, Vol 11, 1974, p 271-275.

 

[4]  http://book.kongfz.com/11886/389242129/  《彩色金相》美.比腊哈（E.Beraha，1926-1976）美.希皮格尔（B.Shpigler，1932-，joint author）著  出版社：冶金工业出版社 出版时间：1984 - 01 印刷时间：1984-01-01 印数：5200千册 装订：硬精装

 

[5]  http://allaboutmetallurgy.com/wp/wp-content/uploads/metallography.pdf  Metallography Principles and Procedures   LECO Corporation（简短的英语资料）