Preparation And Tribological Properties Of Electroless Ni-B Coating On 45# Steel Substrates

The electroless plating technique, proposed by Brenner and Riddle in 1946, have been widely used in the industry. Electroless Ni-B alloy coatings have been used to improve the corrosion-resistance and tribological properties of stainless steel, aluminum and magnesium alloys. However, there is few reports about the structure and performance of the Ni-B coatings on 45# steel. Moreover, pevious research mostly focus on the tribological properties of the Ni-B cating under the dry sliding condition. With regard to good corrosion resistance of Ni-B coating, it is necessary to investigate the tribological properties of the Ni-B coating under the condition of corrosion by water, especially by salt water.In this thesis, electroless plating technique is used to construct Ni-B coating on 45# steel. The surface morphology, crystalline performance and corrosion resistance of Ni-B coating are systematically studies, with focusing on its tribological behavior under the corrosion by salt water. The Ni-B coating is also surface modified by using dip-coating mechod, chemical etching and self-assembly techniques. The Ni-B/PTFE composite coating and high hydrophobic stearic acid films on Ni-B coatings can be obtained and their tribological properties are also studied. The main results are showed as the follows:(1) The crystal structrue and surface morphology of electroless Ni-B coating on 45# steel may be correlated with its deposition rate. When the deposition rate is low, the Ni-B coating on 45# steel shows a cauliflower-like morphology with amorphous structure. This coating layer is a good cathodic protection to 45# steel. Meanwhile, it has excellent properties of antifriction and wear-resistance under the dry sliding condition and the corrosion by water and by 3.5% NaCl solution. The wear mechanism is mainly adhesive wear.(2) Heat treatment can significantly affect the crystal structure and tribological properties of Ni-B coating. The surface hardness and wear resistance of Ni-B coating have been greatly improved by annealing at 400℃ because of the formation of Ni2 B and Ni3 B phase, but friction coefficient of coating increase by approximately 75%. Once the heat treatment temperature is up to 550℃, the coating is severely damaged and its wear resistance will also drop sharply, although Ni2 B and Ni3 B phase was still remained and Ni4B3 phase was also detected in the Ni-B coating.(3) The PTFE solid lubrication coating, deposited on surface of Ni-B coating via dip-coating method, can greatly improve the wettability and tribological properties of Ni-B coating. The Ni-B/PTFE composite coating, prepared by using 60% PTFE emulsion, has a good corrosion resistance and its static contact angle is 129°. The Ni-B/PTFE composite coating shows friction coefficient of around 0.08 under the dry sliding condition, but around 0.04 under the 3.5% NaCl water condition.(4) With using the molecular self-assembly technology, the stearic acid monolayer is deposited on the surface of Ni-B coating. It is found that the static contact angle is 147° and its rolling angle is 18° after Ni-B coating etched by HCl and deposed by stearic acid layer. The high hydrophobic film also shows good wear-resistanc and anti-friction performance.