Metallographic Machine

Pull-outs are one such commonly encountered type of artifact when working with brittle parts. If pull-outs are not cast in cutting or mounting, these are usually a result of aggressive grinding or polishing. It can be avoided by using synchronous rotation in all grinding and polishing steps, except for the final polishing step, and ensuring the polishing cloth in use is relatively soft. Pull-outs may be found in cast iron, components, coatings and composites, though these may be wrongly identified as cavities in the material.

Foreign inclusions can arise when the pressure is too high or during the preparation of very soft materials with a very hard abrasive such as diamond. This results in abrasive particles becoming embedded in the sample surface - a frequently encountered issue when working with composite materials which feature components of soft and hard phases, or when working with materials with varying hardness on one polishing cloth.

Reliefs tend to occur when materials with different phases are polished for an extended period. The harder phases will, therefore, be more prominent than the softer phases. This artifact is generally the result of over-polishing and can be minimized by keeping the sample as flat as possible by using grinding disks that feature a hard carrier. Preparation time should be kept to a minimum, especially in the final steps. It is also advisable to use a polishing cloth with low elasticity.

Comet tails are found where non-metallic inclusions, pores and hard phases in a soft, basic matrix are held in one grinding and polishing direction during manual preparation. Comet tails are an issue when working with large sample materials but can be avoided by moving samples in such a way that there is no preferred direction.

Discoloration or stains on the sample surface may be the result of drying marks of residual suspension, water or ethanol left over due to insufficient cleaning. This issue is not serious and can be easily addressed by correctly identifying the stains and applying additional cleaning steps.

Sample corrosion may occur when using a water-based preparation method for corrosion-prone samples, or when the sample is not dried fast enough. It is advisable to use an alcohol- or oil-based method to prepare extremely corrosion-prone samples.

Edge rounding is an issue when working with components featuring different degrees of hardness, for example, composites or a hard material embedded in a softer resin. This results in a soft material being removed faster than a hard material. Edge rounding effectively leads to two levels of sample, with a transition occurring at the interface where the material is rounded off. Investigation in these regions is very challenging.

Scratches may be found when a sample is not appropriately polished. Scratches occur in composites from one of the previous grinding steps, when one component is well polished but another shows scratches because of their varying hardness. Scratches may also occur when samples are not handled with proper care.

The initial preparation of a new material often involves a degree of trial and error. Operators will identify artifacts and determine their cause throughout the process. To streamline this process, it is important to check the sample by microscope after each individual preparation step. This allows the operator to identify which step caused the issue.