Properties erosive wear mechanisms

Higuera, V., Belzunce, F. J. Ferna ndez Rico, E. (1997). Erosion Wear and Mechanical Properties of Plasma-Sprayed Nickel- and Iron-Based Coatings Subjected to Service Conditions in Boilers. Tribological International, VoL 30, No. 9, p>p. 641-649, ISSN 0301679X... 

The abrasion resistance of cobalt-base alloys generally depends on the hardness of the carbide phases and/or the metal matrix. For the complex mechanisms of soHd-particle and slurry erosion, however, generalizations cannot be made, although for the soHd-particle erosion, ductihty may be a factor. For hquid-droplet or cavitation erosion the performance of a material is largely dependent on abiUty to absorb the shock (stress) waves without microscopic fracture occurring. In cobalt-base wear alloys, it has been found that carbide volume fraction, hence, bulk hardness, has Httie effect on resistance to Hquid-droplet and cavitation erosion (32). Much more important are the properties of the matrix. 

A property not listed in Table 5.14, but which is of paramount importance to this application, is wear rate. Wear rate was described briefly in Section 8.2.2, and those concepts apply here as well. As it applies to tooth enamel, abrasive wear occurs by fracture or chipping of the enamel, chemical erosion, which may arise due to acidic medications or drinks, dietary oxalate, or high oral hydrogen ion concentrations as a result of disease, physical erosion, or abrasion, which arises due to idiopathic mechanisms, dentrifices, toothbrushes, or abrasive diets. For example, the wear rate of enamel has been measured at about 10 ttm/hour due to brushing with a toothbrush and toothpaste for 86,400 strokes [7],... 

There are a wide range of substrates and films which can be produced as biomaterials. Metals such as titanium alloys are often used where high strength or toughness is required, such as hip implants. Their mechanical properties can be somewhat similar to bone, which makes them ideal candidates as structural bioimplants. However, as outlined by Skinner and Kay (2011), metal erosion can be a potentially dangerous problem. Ceramic films such as Ti02, Si02 or hydroxyapatite Caio(P04)6(OH)2 are often added to the surface to reduce wear of the implant and improve biocompatibUity. 

Significant progress has been made in improving surface-sensitive mechanical, chemical, and physical properties, such as hardness and resistance to wear, abrasion, erosion or chemicals, by ion beam processing... 

Usually for the estimation of the mechanical properties of the refractories, specialists use cold crushing strength (CCS or compressive strength), (flexural) bending strength (modulus of rapture, MOR), and elastic modulus (or Young s modulus). In the specification of refractory materials that will be subjected to abrasion, erosion, and wear, usually the characteristics of wear resistance are included. In research practice, the hardness, fracture toughness, and some other characteristics may be taken into account. 

As mentioned earlier, one of the main purposes of reinforcing thin sol-gel silica films is to improve their wear and scratch resistance, and for this reason scratch tests are usually performed to measure the scratch resistance and the fi iction coefficient of the coating [33,35,40,41]. These tests are usually conducted by using nanoindentation equipment or pencil scratch tests, but traditional wear tests using a tribometer can also be found in the literature [5,42]. Impact and erosion resistance [43] are also mechanical properties of sol-gel coatings that can be improved by the addition of fillers. 

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