金相抛光，就像金相磨光一样，是金属样品制备过程的最后阶段。其目的是纠正先前工作步骤（取样和切割期间）引起的变形。
下面的介绍提供了样品准备过程中一些一般考虑事项以及提示。
金相抛光包括几个步骤，每个步骤均使用比前个步骤更细的磨料。通常，可区分为三个操作阶段：预抛光、中间抛光和最终抛光。
最终目标是产生一个无变形、无划痕和高度反射的样品表面。为了获得准确的结果，需要选择合适的耗材、抛光机和与各个仪器设置匹配（根据材料优化）的制样指南。
QATM是一家领先的高质量抛光耗材的制造商和供应商，以及一系列创新的金相抛光机，从手动到全自动的型号。QATM应用专家结合了几十年的经验和成千上万的处理样品，很乐意帮助您的制样应用。
QATM提供满足所有需求的金相磨抛机
The general aim of the first process step is to achieve the best possible material removal in the shortest amount of time. A good flatness of the surface after the grinding process can only be maintained by ensuring that the diamond is always in motion, always rolling, if possible. This rolling motion causes the necessary removal of of excess material.
Consumables used: Diamond 15 µm to 9 µm / Hard-woven or hard-pressed cloths
In the intermediate step, deformation and smear layers are removed. If the material is very hard, several intermediate steps may be necessary.
Consumables used: Diamond 9 µm to 3 µm / Hard-woven or lightly pile cloths
The last step is intended to remove deformations and especially smearing on the surface. This step is not easy but possible. However, a final-polished finish is not necessary for every task.
Consumables used: Diamond 3 µm to 0.5 µm / Oxide polishing 0.1 µm to 0.06 µm / Pile or flocked cloths, foamed for oxide suspensions
In metallographic final polishing, a distinction is made between purely mechanical removal by the diamond grits and chemical-mechanical removal, which is achieved by slightly alkaline suspensions. Which agent is is the most suitable must be determined for the individual application.
In metallographic polishing, diamond polishing agents are differentiated according to the diamond shape. There are poly- and monocrystalline diamonds.
Polishing agents containing polycrystalline diamonds have clear advantages over polishing agents containing monocrystalline diamonds. The polycrystalline diamond has a uniform grain shape and many sharp edges.
The removal rate of diamond polishing agents depends on the number and size of diamond cutting edges that are working simultaneously.
For the right choice of diamond polishing or grinding abrasive (i. e. whether mono- or polycrystalline), it is important to determine its requirements beforehand. Basically, a good result can also be achieved with the cheaper monocrystalline diamond, even though the way to get there requires more effort.
Diamond polishing agents also differ in the type of their carrier material. Which of the three common carrier materials is chosen depends on the circumstances.
Diamond paste: High concentration on the cloth, an additional lubricant is always necessary
Diamond suspension: Ensure well and uniform distribution on the cloth, pay attention to segregation in case of a longer stationary period
Diamond spray: Ensure well and uniform distribution on the cloth, an additional lubricant is always necessary, higher consumption due to dosage
In metallography, oxide agents are primarily used for the final process step.
A distinction is made between silicon dioxide and aluminium oxide suspensions. Both are available as "ready-to-use" aqueous or alcoholic suspension. The grain sizes are between 0.1 and 0.06 µm.
There are no absolute rules for the application of the suspensions. Alcohol-based suspensions should be used for specimen susceptible to corrosion.
Silicon dioxide: All austenitic steels, aluminium alloys, titanium alloys, precious metal alloys
Aluminium oxide: Brass, low to unalloyed steels, grey cast iron grades
With the use of oxide agents, a mechanical or chemo-mechanical removal can be achieved, which removes the smear and deformation layers that may still be present from previous metallographic polishing; the quality of this process ranges from good to very good.
The 'double' attack also results in short polishing times. Significantly lower material costs is another advantage over diamond agents
Cloths for metallographic polishing are available with different surface structures or materials (e. g. silk, artificial silk, wool fabrics, flocked and foamed plastics). Specially developed discs with integrated diamonds are also available.
Metallographic pre-polishing is usually carried out on less elastic (hard) cloths using lubricant (low impact elasticity is important to maintain edge sharpness). If edges are rounded off by cloths that are too soft, this has a negative effect on the evaluation of thin layers.
During final polishing, switch to more elastic, long-napped cloths and to lubricants with a higher viscosity.
The elasticity of the cloths for intermediate polishing lies between the two extremes just described.
With metallographic vibratory polishing, preparations that are nearly deformation- and scratch-free can be carried out on materials which are prone to deformation. This method is also particularly suitable for samples for EBSD analysis.
With metallographic vibratory polishing, the relative movement between a sample and polishing base necessary for removal is achieved by a vibrating work surface. The working surface is set into vertical vibrations which are superimposed by torsional vibrations. These combined vibrations cause the samples, which are weighted down with a weight, to run in a circle on the working wheel.
The metallographic vibratory polisher QPol Vibro automatically finds the best frequency for the sample movement on the cloth depending on the mass to be moved. Due to the very gentle material removal, the method is particularly suitable for very soft and ductile materials such as copper or copper alloys, aluminium and aluminium alloys, Ni-based materials, as well as soft steels. However, this gentle and therefore very low material removal results in long processing times that sometimes take considerably more than 30 minutes.
Grinding and polishing is a standard technique in metallography. Expert knowledge in processing is available for almost all materials. However, a number of potential sources of error must be taken into account when searching for the appropriate procedure. The procedure is very time-consuming due to the multi-stage workflows, especially in manual processing. On the other hand, larger investments must be expected if a higher degree of automation is desired.
The following risks must be evaluated in each individual case:
The market for grinding and polishing equipment is very diverse and offers suitable solutions for a large variety of applications. Depending on application and capacity, simple semi-manual to fully automated systems are available. The wide range of applications also speaks for itself. With carefully matched consumables and suitable preparation parameters, excellent results can be achieved for almost all materials. Mechanical grinding and polishing often is the only preparation technique suitable for ceramics, composite materials and filled/reinforced plastics.
To provide assistance to the user, a few tips and tricks are listed below.
The positioning of the sample holder in relation to the working wheel is a particularly important point in semi- and fully automatic preparation. The positioning of the holder, the speed of rotation, the direction of rotation and the contact pressure are important factors for the durability of the consumables and the resulting surface quality.
If the holder is positioned too close to the centre, most unfavourable grinding and polishing dynamics will be the result (sketch 1).
The positioning as shown in sketch 2 is ideal: The sample holder should extend slightly beyond the edge of the working wheel, approximately 5 to 10 mm. With this setup, the samples still move on the cloth!
In metallography, the so-called comet tails usually occur with non-metallic inclusions, pores and hard phases in a soft basic matrix, if the section is only held in one direction during manual preparation. This artefact is typical for large material samples. For optimum metallographic sample preparation, the specimen should be moved in a way that prevents creation of a preferred direction.
In metallographic polishing, the 'pencil effect' is a widespread artefact formed during manual or single pressure preparations. The surface tapers towards the center which is clearly visible in the pattern on the surface. This problem occurs when preparing specimen with single pressure.
The causes can be:
Abrasives and other polishing agents for metallography, such as silicon carbide particles from the grinding paper, diamonds from diamond polishing agents or oxides from the oxidic final polishing agents, can be pressed into the surface during preparation.
This may occur in the following situations:
The grinding direction may also influence the quality of the final result: In this manual preparation, the specimen on the left was held on the SiC paper in such a way that the grinding direction of the abrasive grain led from the steel specimen to the mounting material. The brittle nitrided layer was thus pressed into the smallest gaps of the mounting compound which resulted in breakouts.
The problem was solved by rotating the sample. It had to be ground from the mounting compound to the sample. The result (specimen on the right) has not been fully polished to make the problem and the solution clearly visible.
DIN 30902:2016-12 (Heat treatment of ferrous materials – Light microscopic determination of the thickness and porosity of the compound layer of nitrided and nitrocarburised workpieces) recommends to wrap the specimen with an aluminium or copper foil before mounting to protect the compound layer during preparation.
Here such a sample is shown in the first image on the left, on the right for comparison the unwrapped sample. Both were then mounted in a ground joint to ensure identical metallographic preparation (second image).
The results of the metallographic preparation show that the compound layer in the upper image is unevenly thick and shows strong chipping. On the other hand, the compound layer in the lower image is uniform and free of break-outs and can therefore be evaluated reliably. It is important to ensure that the thicker white layer above the actual bonding layer is not evaluated, this is the aluminium foil.
QATM提了各种创新的金相抛光设备，从手动抛光机到全自动系统。相应的QATM切割耗材经过深入测试和选择，以与我们的机器完美交互。敬请联系我们进行咨询，报价或与我们的专业应用专家交谈！
