Two-body abrasion

In 1999, Luo and Domfeld [110] proposed that there are two typical contact modes in the CMP process, i.e., the hydro-dynamical contact mode and the solid-solid contact mode [110]. When the down pressure applied on the wafer surface is small and the relative velocity of the wafer is large, a thin fluid film with micro-scale thickness will be formed between the wafer and pad surface. The size of the abrasive particles is much smaller than the thickness of the slurry film, and therefore a lot of abrasive particles are inactive. Almost all material removals are due to three-body abrasion. When the down pressure applied on the wafer surface is large and the relative velocity of the wafer is small, the wafer and pad asperity contact each other and both two-body and three-body abrasion occurs, as is described as solid-solid contact mode in Fig. 44 [110]. In the two-body abrasion, the abrasive particles embedded in the pad asperities move to remove materials. Almost all effective material removals happen due to these abrasions. However, the abrasives not embedded in the pad are either inactive or act in three-body abrasion. Compared with the two-body abrasion happening in the wafer-pad contact area, the material removed by three-body abrasion is negligible. 

Abrasion occurs when one material is in contact with a harder material. Surface asperities of the harder material cut, plough, or indent characteristic scratches or grooves into the softer material (two-body abrasion). Abrasion can also be caused by hard particles that are trapped in between two surfaces (three-body abrasion). Irregular patterns of small indentations are formed. Contamination in the lubricants can significantly contribute to this type of abrasion. 

Attrition is the mechanical removal of hard tissue by direct contacts between teeth (either natural or restored) with no foreign substance intervening [5]. This mechanism causes wear by tooth-tooth contacts as well as by tooth-restoration, and indeed restoration-restoration contacts. The action of mastication and bruxism are known causes of attrition. In the field of tribology, the term abrasion refers to the loss of material from a surface by sliding, rubbing or scratching. Two-body abrasion refers to abrasion caused by two contacting surfaces in relative motion, i.e. the mechanism in dentistry that is described as attrition. Three-body abrasion refers to abrasion caused by surfaces in... 

In abrasive wear by hard particles we often find either two-body abrasive wear or three-body abrasive wear, as shown in Figure 5.3. Two-body wear is caused by hard protuberances on the counterface, while in three-body wear hard particles are free to roll and slide between two sliding surfaces. Wear rates due to three-body abrasion are generally lower than those due to two-body abrasion. Various mechanisms of material removal in these two cases differ only in relative importance. Slurry erosion belongs to the abrasive wear category. Erosion is caused by hard particles sticking to the surface entrained in a flowing liquid. 

Figure 5.3 Abrasive wear by hard particles often means either two-body abrasive wear or three-body abrasive wear (a) three body and (b) two body.

In abrasion or erosion, particles with lower hardness cause less wear than harder particles. When particles are much harder than a surface, the exact value of their hardness matters much less. The relative wear rates by two-body abrasion are associated with a wide range of metals and ceramics, abraded by various types of grit particle. The wear rate becomes much more sensitive to the ratio of abrasive hardness //., to the surface hardness Hs when H.J1 Is is less than 1. Table 5.2 lists the bulk material hardness values for common abrasive particles.12... 

Abrasion is a form of cohesive wear that can occur in two modes, viz. two-body and three-body abrasive wear. Two-body abrasion refers to a hard rough surface, of which the asperities plough through the relatively stiffer counterface. The surface penetrations cause localised plastic displacement and indentations. Three-body abrasion refers to hard particles between two sliding surfaces, ploughing through at least one of the surfaces. The two are not mutually exclusive, as two-body abrasion can often lead to three-body when hard wear particles are detached from a surface. Abrasive wear is dependent on the bulk properties of the materials and the geometry of... 

The governing principle of pad conditioning is to introduce friction between the polishing pad and the diamond disc, which characterizes a two-body abrasive wear mechanism. As illustrated in Figure 13.3, the diamond abrasives embedded on the disc create microscopic cuts or furrows on the pad surface to continually regenerate new pad surface and asperities. At the same time, they remove the glazed or accumulated particles on the polishing pad surface. 

As conditioning is primarily considered as a mechanical process characterized by a two-body abrasive wear mechanism [8], the classical Preston equation [62], originally used to model polishing of glass, has been widely used to describe material removal (polishing) rate in [61]. Considering the similarity between wafer—pad interaction and pad—conditioner interaction, the Preston s equation has been adopted by many to model pad wear caused by conditioning. The Preston equation states that MRR is proportional to the applied pressure P and the relative velocity V between the wafer and the pad and Kp is a constant, called Preston s coefficient. 

Table 11.10 Two-body abrasion of restorative dental materials ...

Anti-body cleavage A hard anti-body or an anti-body from soft base material with hard inclusions wears out the base body (two-body abrasion). 

Abrasive wear is defined as the material loss when a hard particle is made to slide against a soft material. Abrasive wear is classified as two-body abrasion or three-body abrasion. In two-body abrasion, abrasive particles move freely over a material face as in sand sliding down a chute. In three-body abrasion, abrasive particles act as interfacial elements between the solid body and the counter body. It can be classified as high stress abrasion or low stress abrasion depending on the applied stresses. 

The work of Soemantri et al. [76] is presented in Fig. 6.15. Figure 6.15a shows the results of the two-body abrasion test, whereas Fig. 6.15b pertains to three-body abrasion. This work was carried out with commercially pure Al and Cu. As can be seen from Fig. 6.15, the wear rate of Cu is independent of temperature for two-body abrasion. Similarly, the two-body abrasive wear rate of Al is also nearly constant even though an increase in wear rate is noted at 323 K. In contrast, the wear rate of Cu increases with increase of temperature during three-body abrasion. However, for Al, the three-body... 

Effect of test temperature on abrasive wear rate (a) two-body abrasion (b) three-body abrasion [76]. 

Results of two-body abrasion testing on experimental and commercial composites and resins are shown in Table 1 (1,3). These data indicate the effect of silanation, amount of filler, type of filler, and characteristics of the resin on the rate of abrasion. Wear characteristics of various experimental dimethacrylate resins have been studied also as shown in Table 2 (4). Two-body abrasion is a useful method for comparison of differences in formulation of composites. 

---