Variation of Mechanical Properties According to Deposition Process

Coatings are predominantly produced by physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes, which are being continuously developed and improved, with their indication depending on the end product [29-31]. The surface properties are strongly dependent on the bonding nature of the film structure and the substrate [32]. Coatings with an intense covalent bond nature have a tendency to present the highest hardness values, while metals are the lowest, and ionic coatings have intermediate values. Typical applications of coatings are scheduled below simultaneously with their basic composition [33-34]:

• magnetic and electronic films (Nd-Fe-B; Sm-Fe-N; Al-Co; Fe-Co; Cu; Au)

• decorative, hard, and wear-resistant films (Ti-Al-N; Ti-O-N; B-Ti-Nb-N; DLC; Ti-Al-O-N; h-BN; c-BN; Zr-Cu-N; SiC; VC; VN; TiC; WC; AlN; CrAlY)

• corrosion barriers (Nb-Cr; Fe-Cr alloys; Ti-Al-Cr-N-C)

Figure 7 shows the range of hardness and elastic modulus values that can be obtained by using the nanoindentation technique for different material compositions and at different deposition processes as found in the literature. The values present a great dispersion associated not only with the different tailoring processes, but also with different methodologies to obtain the mechanical properties.

Despite the substrate influence on the hardness or film modulus values, typical load/unloading curves can be used to obtain global information about the film-tailoring process. In a comparative study of different coatings, it was recommended to extract these values at a depth on the order of 10% of the coating thickness or, as in some situations, obtain

Figure 7. Hardness and elastic modulus of coatings for different deposition processes.

the ones at depths that were reached at the same applied load [25, 28, 36].

Detailed studies of hardness, elastic modulus, and elastic recovery for metal nanocomposite coatings were performed by Musil et al. [36] and Kourtoukova et al. [37]. They showed the relation between hardness to elastic modulus (E/H), hardness to elastic recovery (E2/H3), and elastic modulus to elastic recovery (E/We and H/We) that can be used to tailor the best ensemble of mechanical properties, depending on the end application of the coating.

Literature data are very extensive on the subject of mechanical and tribological properties of coatings using the nanoindentation technique. These properties, referred to before, are strongly dependent on the deposition process used, and the following references are indicated to the reader to be consulted:

• carbides and nitride-based coatings [38-53]

• polymeric coatings [93-95]

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