*3.2.4 Effect of substrate temperature*

The growth of film during the deposition in sputtering system is dependent on the mobility of ions to the substrate. The substrate temperature can play a key role toward ion mobility and diffusion between deposited ions that affect the microstructure, composition, and properties of the coatings. Liang et al. investigated the effect of substrate temperature on the deposition of (TiVCrZrHf)N HEN coating using RF magnetron sputtering from room temperature (RT; 25°C) to 450°C with a fixed 4% RN and −100 V substrate bias [49]. The XRD analysis showed formation of FCC solid solution without any significant phase separation at all substrate temperatures. However, grain size decreased from 10.7 nm at RT to 8 nm at 250°C and then increased to 9.7 nm at 450°C. The surface morphology of (TiVCrZrHf)N HEN coating became more smooth and dense with increasing substrate temperature. The cross-section morphology changed from an amorphous phase at coatingsubstrate interface to FCC phase toward coating surface. This phenomenon was reported to be due to higher stresses generated in the initial coating deposition and the greater lattice mismatch of 19% between the HEN coating and silicon substrate. The hardness of the coating increased from 30 to 48 GPa with increasing substrate

**167**

*3.3.2 Effect of substrate temperature*

*High-Entropy Ceramics*

coating.

*DOI: http://dx.doi.org/10.5772/intechopen.89527*

**3.3 High-entropy carbide coatings**

*3.3.1 Effect of CH4 flow rate ratio*

temperature from RT to 450°C. The high hardness with increasing substrate

temperature was attributed to the higher mobility of deposited atoms and reduction of growth void leading to denser coatings. Similar studies on the effect of substrate temperature on structure and enhancement of mechanical properties were studied on the deposition of (AlCrNbSiTiV)N [50–52] and (TiVCrAlZr)N [53] HEN

Similar to high-entropy nitride coatings, high-entropy carbide coatings have been developed to obtain coatings for tribological and biomedical applications.

Braic et al. performed the initial studies on development of high-entropy carbide coatings for tribological and biomedical applications. Their research group deposited (TiAlCrNbY)C high-entropy carbide coatings from co-sputtering of elemental targets using DC-magnetron sputtering with different CH4 flow ratios (RC), and at constant substrate temperature and substrate bias of 400°C and −100 V, respectively [54], where CH4 flow ratio is given by: RC = CH4/(CH4 + Ar). The XRD data showed a change of structure from nanostructured broad FCC phase (0% RC) to a single FCC carbide phase (10 and 17% RC) and then to amorphous phase at higher carbon concentration (26 and 33% RC). The coating morphology changed from slightly higher surface roughness of 7 nm (0% RC) to fine grained surface roughness of 2 nm (33% RC) with increasing CH4 flow ratio. The hardness values increased from 8.2 GPa (0% RC) to 22.6 GPa (26% RC). Similarly, Braic et al. studied the effect of CH4 flow ratio on (TiZrNbHfTa)C high-entropy carbide coating with elemental target co-sputtering using DC-magnetron sputtering on Ti6Al4V alloy substrate [55]. However, in this work, formation of only FCC solid solution was observed at RC of 13 and 35% with hardness values of 22.4 and 32.1 GPa, respectively. Similar to earlier work, the surface roughness and crystallite size decreased, while the hardness increased with increasing CH4 flow ratio. In another work, Braic et al. deposited (CuSiTiYZr)C high-entropy carbide coating using elements with large atomic radii differences and reported the effect of different CH4 flow ratios on the structural and mechanical properties. In all the deposited high-entropy carbide coatings, the XRD showed the formation of amorphous phase irrespective of the amount of carbon. The higher lattice distortion in the high-entropy carbide coatings resulted in hardness values of 20.7 GPa (25% RC), 27.2 GPa (35% RC), and 29.5 GPa (50% RC). Thus, proving the work of Zhang et al. [56] and Guo et al. [57] in the case of high-entropy alloys, a solid solution is formed when the constituent elements have a close atomic radius. Similarly, Jhong et al. developed (CrNbSiTiZr)C highentropy carbide coatings and studied the effect of increasing CH4 flow ratio on the structural evolution and mechanical properties [58]. In this system, the structure of high-entropy carbide coating changed from FCC solid solution phase at lower RC of 3–10% to amorphous phase at higher RC of 15–20%. Such structural change from FCC to amorphous phase resulted in reducing the hardness from 32.8 to 22.3 GPa.

Braic et al. studied the effect of substrate temperature on the deposition of (CrCuNbTiY)C high-entropy carbide coating with DC co-sputtering of elemental targets with a constant substrate bias and two different CH4 flow ratios. The substrate temperature was increased from 80 to 650°C, and its effect on the structural

#### *High-Entropy Ceramics DOI: http://dx.doi.org/10.5772/intechopen.89527*

*Engineering Steels and High Entropy-Alloys*

showed FCC solid solution with a similar increasing and decreasing trends of lattice parameters and grain size, respectively. However, in this work, the hardness increased from 22 GPa with no bias to the highest hardness of 42 GPa achieved at −100 V bias. The (AlCrNbSiTiV)N HEN coating showed excellent thermal stability even after annealing at 800°C (5 h) and maintained a hardness of 40 GPa. Such increasing trend in hardness was attributed to changing grain size and residual stress with increasing substrate bias. Similar effect of substrate bias on the coating structure and properties were observed in (TiVCrZrHf)N [45], (AlCrTaTiZr)N

*(b) RN = 20%, (c) RN = 30%, (d) RN = 40%, and (e) RN = 50% [41].*

*Surface and cross-section SEM micrographs of (NbTiAlSiZr)N HEN coatings at various RN: (a) RN = 10%,* 

[46], (TiHfZrVNb)N [47], and (TiZrHfNbTaY)N [48] HEN coatings.

The growth of film during the deposition in sputtering system is dependent on the mobility of ions to the substrate. The substrate temperature can play a key role toward ion mobility and diffusion between deposited ions that affect the microstructure, composition, and properties of the coatings. Liang et al. investigated the effect of substrate temperature on the deposition of (TiVCrZrHf)N HEN coating using RF magnetron sputtering from room temperature (RT; 25°C) to 450°C with a fixed 4% RN and −100 V substrate bias [49]. The XRD analysis showed formation of FCC solid solution without any significant phase separation at all substrate temperatures. However, grain size decreased from 10.7 nm at RT to 8 nm at 250°C and then increased to 9.7 nm at 450°C. The surface morphology of (TiVCrZrHf)N HEN coating became more smooth and dense with increasing substrate temperature. The cross-section morphology changed from an amorphous phase at coatingsubstrate interface to FCC phase toward coating surface. This phenomenon was reported to be due to higher stresses generated in the initial coating deposition and the greater lattice mismatch of 19% between the HEN coating and silicon substrate. The hardness of the coating increased from 30 to 48 GPa with increasing substrate

*3.2.4 Effect of substrate temperature*

**166**

**Figure 5.**

temperature from RT to 450°C. The high hardness with increasing substrate temperature was attributed to the higher mobility of deposited atoms and reduction of growth void leading to denser coatings. Similar studies on the effect of substrate temperature on structure and enhancement of mechanical properties were studied on the deposition of (AlCrNbSiTiV)N [50–52] and (TiVCrAlZr)N [53] HEN coating.
