Electrodeposited Co-B alloy coatings were formed using dimethylamine borane (DMAB) as the boron source. The results showed that the concentration of boron in the coatings increased with increasing concentration of DMAB in the electrolytic bath. Additionally, Co-B bond formation and the presence of DMAB in the coatings were proposed on the basis of the results obtained by glow discharge spectrometry and X-ray photoelectron spectroscopy. The influence of boron concentration in the coating on the tribological characteristics of hardness, friction coefficient and wear volume are discussed. Co-B coatings without microfissures on their surface were obtained when the concentration of boron in the coating was between 2.9 and 3.0 wt.%. Co-B coatings with these boron concentrations exhibited a hardness value of 818 HV, which is higher than Ni-B coatings but lower than hard chromium coatings (867 HV). The volume of wear and friction coefficients of the Co-B coatings with 2.9 and 3.0 wt.% were also lower than those reported for Ni-B coatings.

This chapter describes the effect of SiC particle concentrations on the metallic continuous phase of the coating and the effect of heat treatment on the crystalline structure, hardness, and wear resistance of electrodeposited Ni-P-SiC coatings. The deposits were obtained via electrodeposition onto an AISI 1018 steel electrode and then heat treated at various temperatures ranging from 300 °C to 600 °C for 60 min in air. The tribological characteristics studied included hardness, friction coefficient, and wear resistance. The results indicated that the dispersion of SiC particles in the metallic matrix improves coating tribological properties such as hardness and wear resistance while diminishing the friction coefficient. The Ni-P-SiC alloy was originally amorphous and was transformed into a mixture of amorphous and crystalline phases when was thermally treated in the range from 400 °C to 500 °C. This phase transformation was associated with the precipitation of a mixture of Ni 3 P intermetallic compound and pure Ni crystals. In addition, the results showed that the wear resistance of the Ni-P-SiC coating increased with hardness. The maximum hardness (1453.4 HV) was obtained when the Ni-P-SiC coatings were thermally treated at 500 °C.

The Inconel 718 alloy is a nickel-based superalloy used to a large extent in the manufacture of critical parts for aircraft turbine engines due to its high mechanical properties, as well as good corrosion resistance. The main hardening phase in this alloy is the metastable γ"-Ni 3 Nb phase with tetragonal body centered arrangement (DO 22 ). After treatment at temperatures equal to or higher than 750°C, the particle size of the γ" phase increases rapidly, then the precipitates begin to dissolve in a stable orthorhombic phase (DOa) δ-Ni 3 Nb.In this work, the main interest has been the study of precipitates resulting from several isothermal aging performed after the homogenization, as well as the identification of the phases responsible for the different hardening stages γ'', γ' and δ. The analysis was made by SEM, dilatometry and Vickers hardness tests. The samples were brought to a homogenization annealing heat treatment at a temperature of 1060°C; then they were thermally aged at temperatures of 500, 600, 648, 700, 800, and 900°C.It was found that all samples contain the same amount of carbides and nitrides with a size no greater than 15 μm, which means that these are stable at the temperatures of aging. These findings are in agreement with the results of Zhang [1]. It is concluded that these precipitates were formed during the manufacturing process. It is worth mentioning that under the SEM these primary carbides are spherical and light colored, while the nitrides are polygonal and dark colored [2] (Figure 1).A relationship between the hardness (Table 1) and the precipitation of secondary carbides M 23 C 6 and M 6 C in the temperature range of 520 to 640°C was found. Figure 2a reveals that there are not carbides in the grain boundaries, while Figure 2b shows the presence of precipitates, which is in agreement with the results of the derivative in the dilatometric curve (Figure 3). This small material expansion is due to the phase precipitation, which coincides with the work of Zheng [3], who found that the formation of carbides M 23 C 6 and M 6 C occured at temperatures of 600 to 670°C. This means that samples aged at 600 and 648°C are mainly strengthened by these carbides. At 800°C there is a rapid growth of γ", which can be verified by the hardness results, since γ" is the main strengthener of the Inconel 718 alloy, and therefore the maximum hardening of the alloy is reached (360 HV). This fact is also suggested by the dilatometric curve, where it is observed a material expansion in the range from 760 to 820°C, indicating a phase change. At 900°C it is observe that the hardness decreases to 230 HV, due to the solubilization temperature of the γ' and γ" phase between 900 and 920°C, according to Chamanfara [4]. The precipitation velocity of the δ phase is higher (Figure 1), which is related to the material shrinkage in the dilatometric curve at the temperature range of 820 to 950°C.

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