Scratch resistance test technique

The scratch tests are very similar to the nanoindentation tests and can be considered side by side. In both teclmiques, a prime tip is used for the adhesion measurements by dragging across the measuring surface under an increasing load, which results in an indentation. Scratch and indentation tests are suitable for the analyses of the coatings and thin films [100]. Sharp diamond indenters are usually used for the adhesion and scratch resistance determination between the substrate and coating. These techniques can fail for the analyses of hard coatings on soft substrates due to no detectable failures as a result of small critical loads. Therefore,... 

Hardness is a measurement of material resistance to plastic deformation in most cases. It is a simple nondestructive technique to test material indentation resistance, scratch resistance, wear resistance, or machinability. Hardness testing can be conducted by various methods, and it has long been used in analyzing part mechanical properties. In reverse engineering, this test is also widely used to check the material heat treatment condition and strength, particularly for a noncritical part, to save costs. The hardness of a material is usually quantitatively represented by a hardness number in various scales. The most utilized scales are Brinell, Rockwell, and Vickers for bulk hardness measurements. Knoop, Vickers microhardness, and other microhardness scales are used for very small area hardness measurements. Rockwell superficial and Shore scleroscope tests are used for surface hardness measurements. Surface hardness can also be measured on a nanoscale today. 

Hardness of a material may be determined in several ways (1) resistance to indentation, (2) rebound efficiency, and (3) resistance to scratching. The first method is the most commonly used technique for plastics. Numerous test methods are available for measuring the resistance of a material to indentation, but they differ only in detail. Basically they all use the size of an indent produced by a hardened steel or diamond indentor in the material as an indication of its hardness—the smaller the indent produced, the harder the material, and so the greater the hardness number. Hardness tests are simple, quick, and nondestructive, which account for their wide use for quality control purposes. 

Basically, scratch hardness is a measure of the resistance the test sample has to being scratched by other materials. The most common way of qualifying this property is by means of the Mohs scale. On this scale various materials are classified from 1 to 10. The materials used, as shown in Figure 3.46, range from talc (1) to diamond (10). Each material on the scale can scratch the materials that have a lower Mohs number however, the Mohs scale is not of much value for classifying plastic materials, because most common plastics fall in the 2-3 Mohs range. However, the basic technique of scratch hardness may be used to establish the relative merits of different plastic materials fi om their ability to scratch one another. 

H—Hardness. There are different types of hardness. Why Because the value of a material s hardness depends on how it is tested. The hardness of a material is its resistance to the formation of a permanent surface impression by an indenter. You will also see it defined as resistance of a material to deformation, scratching, and erosion. So the geometry of the indenter tip and the crystal orientation (and therefore the microstructure) will affect the hardness. In ceramics, there tends to be wide variations in hardness because it involves plastic deformation and cracking. Table 16.4 lists hardness values on the Mohs hardness scale, a scratch test that can be used to compare hardness of different minerals. For example, quartz has a Mohs hardness of 7, which made flint (a cryptocrystalline quartz) particularly useful in prehistoric times for shaping bone (the mineral component is apatite with hardness 5) and shell (the mineral component is calcite with hardness 3). Mohs hardness scale was not the first scratch hardness technique. As long ago as 1690, Christian Huygens, the famous astronomer, had noticed anisotropy in scratch hardness. 

Chandrasekhar et al. [934] used several independent methods to monitor corrosion, including Tafel Scan, Cyclic Polarization and Polarization Resistance among electrochemical methods Immersion methods Salt Spray Fog techniques vide ASTM B-117-94 and MIL-C-5541E scratch tests and adhesion tests. They found that their coatings had excellent adhesion, passing the ASTM tests mentioned above, and excellent durability in salty atmospheres, as evidenced by the samples differing very little in appearance before and after the Salt Spray Fog tests. 

Another mechanical property that may be important to consider is hardness, which is a measure of a material s resistance to localized plastic deformation (e.g., a small dent or a scratch). Early hardness tests were based on natmal minerals with a scale constructed solely on the ability of one material to scratch another that was softer. A qualitative and somewhat arbitrary hardness indexing scheme was devised, termed the Mohs scale, which ranged from 1 on the soft end for talc to 10 for diamond. Quantitative hardness techniques have been developed over the years in which a small indenter is forced into the surface of a material to be tested under controlled conditions of load and rate of application. The depth or size of the resulting indentation is measured and related to a hardness number the softer the material, the larger and deeper the indentation, and the lower the hardness index number. Measured hardnesses are only relative (rather than absolute), and care should be exercised when comparing values determined by different techniques. 

Physical and chemical tests quantify technical performance (scratch/mar, ultraviolet (UV) resistance, oil resistance, color shift, etc.). Despite the economic importance of surface treatment selection, techniques for the quantification of sensorial attributes of the interior surface to measure their importance to the consumer have not been developed. Renault and other OEMs (3,4) have employed techniques derived from methods used in the agro-business sector to... 

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