Effect of Morphological and Microstructural Variations on the Properties of Electroless Nickel Boron Coatings

The effect of TiO2concentration on morphology, wear and corrosion properties of NiB-TiO2composite coatings by ultrasonic-assisted pulse electrodeposition

“…When figures 2(a) and (b) are examined, it is understood that NiB alloy coatings have a cauliflower structure. As it is known, the cauliflower structure contributes to the increase of tribological properties by reducing both lubrication and real contact area [13,14]. Figures 2(a) and (b) show the surface view of the cauliflower structure of the NiB alloy coating at different magnifications, while figures 2(c) and (d) are the crosssectional images of the NiB alloy coating and show a columnar structure.…”

“…In the composite coatings containing the highest concentrations of 15 g l −1 (figure 8(d)) and 20 g l −1 (figure 8(e)) TiO 2 , wear occurred on the contact surfaces of the cauliflower structure due to the decrease in the actual contact area. It is understood that both the actual contact area and the metal-to-metal contact area decrease as a result of wear on the tops of the cauliflower structure [13,37,45]. It is seen that a very smooth surface and microcrack-free wear surface appearance is obtained in the composite coating containing 20 g l −1 TiO 2 , where the lowest friction coefficient and wear rate are obtained due to the decrease in metal-to-metal contact with increasing particle content.…”

“…The friction coefficient decreased from approximately 0.38 μ to 0.25 μ, 0.23 μ, 0.19 μ and 0.18 μ, respectively. As the reasons for this decrease in the friction coefficient; It can be stated that the cauliflower structure and the ceramic particles embedded in the coating layer reduce the actual contact area/ metal-to-metal contact area and increase hardness values [13,[39][40][41]. It is also known that the cauliflower structure provides lubrication and thus contributes to the reduction of the friction coefficient [42][43][44].…”

“…Compared with the NiB alloy coating, the corrosion potential (Ecorr) of the composite coating produced with 20 g l −1 TiO 2 concentration changed positively by about 100 mV and the corrosion rate (mpy) decreased by about 3 times. The lower corrosion current density and more positive corrosion potential values demonstrate increased corrosion resistance [13,49]. The presence of secondary phase TiO 2 particles, which act as a barrier against the corrosion environment, can be said to be the reason for the increase in corrosion resistance in composite coatings [47,50,51].…”

“…In addition, heat treatment of this type of alloy also improves its properties. Hardness and strength are increased by forming intermetallic compounds with heat treatment [13,14]. Thus, both corrosion and tribological properties can be improved.…”