Structural state and tribological properties of Co-P coatings

Abstract

The structural state and the tribological properties of electrochemical Co-P coatings with a con centration of phosphorus of 1.5-20 at % have been studied. It has been found that, in the Co-P coatings with phosphorus concentrations of less than 8 at %, a solid solution is formed of phosphorus in the matrix α Co phase. The Co 92 P 8 coating has an amorphous crystalline structure. At phosphorus concentrations of ≥10 at %, coatings with an amorphous structure are formed. The mechanism of the formation of the structure during the deposition of coatings with various concentrations of phosphorus has been discussed. It has been shown that the best tribological properties are characteristic of the crystalline Co-P coatings with a phosphorus con centration of 3 at % and of the amorphous coatings with a phosphorus concentration of 20 at %. The conclu sion has been drawn that the wear resistance of the amorphous Co-P coatings is determined by the deforma tion thermal stability of their amorphous structure.

Effects of heat treatment on the properties of Co–P–TiO2 nanocomposite coatings

“…However, we should note the wear behaviour depends on diverse factors in addition to coating microhardness. As the heating temperature increases to 400°C, the coating is transformed into the crystalline structure which has a significantly smaller specific atomic volume and possesses higher tensile stress [26]. This would help to generate more microcracks and holes during the wear tests, thereby causing the substantially decreased wear resistance of Co–P–TiO 2 coating heated at 400°C.…”

Effect of Waveform and Heat Treatment Processes on the Performance of Electrodeposited Co-P Coating

“…The wear rate of coatings was controlled not only by hardness, but also other factors such as microstructure (grain size, crystalline, P concentration [22]). Co-P coatings transformed from amorphous to a nanocrystalline state after heat treatment.…”

“…Co-P coatings transformed from amorphous to a nanocrystalline state after heat treatment. The crystallized zones of coatings, having a substantially smaller specific atomic volume than the amorphous matrix, underwent higher tensile stresses, leading to the accelerated nucleation and propagation of microcracks in the crystalline layer, eventually increasing the wear rate of coatings during friction [22]. The second possible reason is that the nanocrystalline structure and Co-P compounds made it easier for the coatings to form hard particles during the wear, rather than only plastic deformation.…”