Hardness scratch/wear resistance

Hardness is closely related to strength, stiffness, scratch resistance, wear resistance, and brittleness. The opposite characteristic, softness, is associated with ductility. There are different kinds of hardness that measure a number of different properties (Fig. 5-5). The usual hardness tests are listed in three categories (a) to measure the resistance of a material to indentation by an indentor some measure indentation with the load applied, some the residual indentation after it is removed, such as tests using Brinell hardness,... 

Scratch tests have been used for microhardness measurements of polymeric materials (Bierbaum Scratch Hardness Test (ASTM D 1526)). These tests are related to cuts and scratches, and, to some extent, to the wear resistance of materials. Scratch tests are not always related to the resistance to local deformation and they are now being replaced by the preferred indentation test. 

Hardness, scratch and abrasion resistance, and wear (friction) properties are characteristics which can be important for the selection of the most suitable material for a specific job. For the purpose of comparison, the designer must make sure that the data shown in the various charts have been produced using the same test methods. 

The Mohs hardness test (the word scratch is assumed) is almost a nondestructive test. The hardness of a gemstone is usually referred to as its Mohs hardness. Since this hardness value is determined by a scratch test, it is not actually a hardness. The scale has many drawbacks including the fact that it is not linear, it does not necessarily relate to wear resistance, and it damages the specimen so it is not ideal for polished stones. 

Despite brittle characteristics, ceramic components enjoy several outstanding tribological properties, including their hardness (Table 6.2), which contributes to wear resistance and scratch resistance. Ceramic surfaces are also more hydrophilic than the CoCr surfaces of a femoral head, as illustrated in Figure 6.7 by the water droplets. The improved wettability of ceramics contributes to lower friction than CoCr when articulated against UHMWPE under physiologic loading and lubrication conditions (Morlock et al. 2002). 

Hardness measurements can be very valuable, particularly for comparing similar materials. Hardness measurements are often indicative of scratch, wear, and abrasion resistance. They can also be used to determine relative degree of cure, and in this manner are sometimes used as quality control tools. 

The property of hardness is based on die material s ability to resist scratching, wear, penetration, machinability, or the ability to cut. There are over 30 mediods used for measuring hardness. A representative listing is as follows ... 

The highly aromatic polymer is inherently flame resistant. The high surface hardness results in excellent scratch and wear resistance. Coefficient of friction is very low and has high compressive strength. Mechanical performance is maintained across a wide range of temperatures. For example, mechanical properties are retained all the way down to liquid Helium temperatures (4°K). Other characteristics include broad chemical resistance. 

PVD processes are traditionally used for the deposition of various coatings on tools and components and other metallic or ceramic substrates, for example, to improve surface hardness, wear resistance, and corrosion resistance. However, more and more plastic products are used today in fields where metals were previously predominant. In these cases, the end product should meet functional requirements (durability, scratch, corrosion, and chemical resistance) and decorative appearance. Another important application includes metallized and transparent inorganic gas-diffusion barrier layers on packaging films. 

Abrasion resistance is another complex area. One of the reasons for confusion is that the various test methods do not agree well with each other. There is a perception that hard surfaces lead to the best abrasion resistance, however, that does not jibe with the facts. In actuality, it is elastomeric surfaces that have excellent abrasion resistance. Look, for example, at rubber car tires and PVC flooring, which is always coaled with a polyurethane elastomer layer to provide wear resistance. Elastomers deform and spring back undamaged, so scratch and wear resistance is good [17]. 

Prevention of abrasive wear is possible through proper material selection and the use of surface engineering treatments. A number of material families have demonstrated good resistance to abrasive wear. They are typically hard materials that resist scratching, and include ceramics, carbide materials, alloyed white cast irons containing hard chromium carbides (see Fig. 8), and hardened alloy steels. 

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. 

Abrasion Resistance. Porcelain enamel is the most scratch resistant and hardest of commercial coatings (see Hardness). This property is used to distinguish between porcelain enamel and organic enamel or painted coatings. The rate of abrasive wear in surface abrasion increases with time, and the subsurface abrasion which follows exhibits a higher, but constant rate of wear. Abrasion resistance can be evaluated by loss of gloss or weight (35). 

Fracture occurs at the weakest joint of an object, which connects this type of damage with the production process. The resistance to mechanical wear is a function of the surface hardness once scratches have occurred, they represent prominent points for further attack. 

Hardness is the property of a material that enables it to resist plastic deformation, penetration, indentation, and scratching. Therefore, hardness is important from an engineering standpoint because resistance to wear by either friction or erosion by steam, oil, and water generally increases with hardness. 

A material which is hard is able to resist wear, scratching, indentation and machining. Its hardness is also a measure of its ability to cut other materials. Hard materials are required for cutting tools and for parts where wear must be kept to a rtnnimurtL... 

Sapphire fibers are hard, strong and scratch resistant to most materials and provide excellent wear surfaces. They can withstand higher pressures than polycrystalline alumina since they lack the grain boundary interface breakdown of the latter. Sapphire fibers transmit ultraviolet, visible, infrared and microwaves and serve as excellent wave guides between 10.6 and 17 microns, and offer durable and reliable IR transmission. By virtue of their high thermal conductivity they can be rapidly heated and cooled. 

Worldwide consumption of TPE for the year 2000 is estimated to be about 2.5 billion pounds, primarily due to new polymer and processing technologies, with an annual average growth rate of about 6% between 1996 and 2000. About 40% of this total is consumed in North America. TPE grades are often characterized by their hardness, resistance to abrasion, cutting, scratching, local strain (deformation), and wear. A... 

---