Silicon crack propagation

To increase the wear resistance of surfaces, silicon and metals are often coated with a hard nitride, carbide, boride, or oxide film. Nanoindentation and fracture simulations have been used extensively to elucidate failure mechanisms of these typically more brittle surfaces, which include crack propagation and film delamination. Considerable attention has also focused on nanocomposite materials, which possess nanocrystalline inclusions in an otherwise amorphous matrix. The nanocrystalline component is sufficiently small to preclude the formation of stable dislocations, and thus provide a higher hardness. 

Figure 14.9 Image of crack propagation through silicon at high loading, showing surface steps and dislocations (after [61]).

Recent advances further enhance their commercial potential in metal matrix composites such as aluminum, nickel, and copper ceramic matrix composites, such as alumina, zirconia and silicon nitride and glass ceramic matrix composites such as lithium aluminosilicate. Silicon carbide whiskers increase strength, reduce crack propagation, and add structural reliability in ceramic matrix composites. Structural applications include cutting tool inserts, wear parts, and heat engine parts. They increase strength and stiffness of a metal, and support the design of metal matrix composites with thinner cross sections than those of the metal parts they replace, but with equal properties in applications such as turbine blades, boilers and reactors. 

Microcapsules containing a small amount of additives that will be released by crack propagation or other triggering mechanisms have been incorporated into polymeric coatings [21]. Urea/formaldehyde capsules containing silicone oil are shown in Figure 21.6. 

Buehler Ml, van Duin ACT, Goddard WA (2006) Multiparadigm modeling of dynamical crack propagation in silicon using a reactive force field. Phys Rev Lett 96(9) 095505-(4)... 

Stress-relief additives additives Up to 25 Inhibit crack propagation Reduce crack initiation Reduce CTE Silicones, acrylonitrile-butadiene elastomers, poly(butyl acrylate)... 

---