ABSTRACT
Among all well-known structural and functional ceramics, alumina deserves special mention owing to its large-scale applications as wear-resistant inserts, biomedical implants, high strain rate impact-resistant plates, etc. Now the question is what is the major noticeable property of alumina that makes it suitable for such large-scale applications? What makes it different from other structural ceramics? The hardness of alumina is the single most important mechanical property that plays a major role in all contact-related applications of alumina. You may wonder why the focus is on hardness but not the other mechanical properties. Actually, materials science has been linked with all the mechanical properties of a material that ultimately describe the characteristics of that material, but hardness is important in materials science because it describes the intrinsic contact deformation resistance of the material. In particular, the hardness evaluated at the nanoscale of the microstructure assumes significant importance because it is at this scale that the mechanical integrity of a structural ceramic in-service gets determined. The defects that ultimately define the mechanical integrity of a structural ceramic originate at the ultralow length scale (nano-or microscale) of the microstructure during its service lifetime. Thus, evaluation of the nanohardness of alumina is a very important checkpoint in order to make it suitable for global applications.
The hardness of a dense (≈99.9%), coarse grain (≈10 μm) alumina possesses moderately high value (≈20 GPa), as we have already discussed in Chapter 16. In this chapter we shall try to understand the influence of loading rates
