Effects of the Prefabricated Cu-Ti Film on the Microstructure and Mechanical Properties of the Multiphase Coating by Thermo Plasma Nitriding on C17200 Cu Alloy

Abstract

To improve the surface wear resistance, plasma nitriding of the prefabricated Cu-Ti films on the C17200 Cu alloy is performed to investigate the effects of the composition of the Cu-Ti films on the microstructure and the mechanical properties of the modified surface. The results firstly showed that obvious microstructure evolution appeared during the thermo-plasma nitriding process, where both the surface morphology of the composed phases and the cross-sectional profiles of the multiphase coatings varied for the three types of films. Small amounts of Ti-N compounds, Be 3 Ti 2 Cu, and different types of Cu-Ti intermetallics formed in the multiphase coating after plasma nitriding, which is dependent on the composition of the prefabricated Cu-Ti film. Correspondingly, the surface hardness and the wear resistance of the C17200 Cu substrates were obviously improved, with the obtained adhesive strength of the substrate reaching a satisfactory range. Coatings 2019, 9, 694 2 of 15where the Cu-Ti intermetallics of varying Cu/Ti ratios and the Ti-N compounds of different Ti content were identified. The simulation results by the first-principle study also indicated the possibility for the formation of these phases and the possible contribution to the improvement of the surface mechanical properties [14,15]. However, the low efficiency of the surface modification process prompts us to propose the novel process by combination of the fabrication of a gradient Cu-Ti film and the plasma nitriding in our recent research, which shows great potentiality to produce the multiphase coating efficiently, with the obtained wear properties at the same level [16], which can also help to solve the problem of weak bonding strength between the single-layered Ti-N coating and the subsurface layer by the formation of Cu-Ti intermetallics between the Cu substrate and the Ti-N surface layer [8]. Actually, the Cu content in the prefabricated film should also contribute to the changing mechanical properties of the coating [17,18]. However, the previous investigations paid little attention to the influence of the initial Cu-Ti film composition on the obtained mechanical properties for the multiphase coating on C17200 Cu alloys.This paper discusses a further study on the effects of the prefabricated Cu-Ti film on the microstructure and mechanical properties of the multiphase coating by thermo plasma nitriding on C17200 Cu alloy. First, the microstructure and the surface characteristic of the prefabricated Cu-Ti film were studied. Then, the microstructure evolution during the plasma nitriding process was explored. Finally, the mechanical properties and the wear performance of the three types of coatings were evaluated. Materials and Methods Experimental Material and MethodThe chemical composition of the C17200 Cu alloy is listed in Table 1. The copper alloy bar was processed into a size of φ20 mm × 4.5 mm, by wire-cutting for the subsequent surface modification treatment, the structure analysis of the modified layer, and the mechanical performance tes...

Cross-Sectional Profile Evolution of Cu-Ti Gradient Films on C17200 Cu by Vacuum Thermal Diffusion

“…According to the previous diffusion experimental results of pure Ti film on C17200 Cu-Be and C61900 Cu-Al alloys [14,18,22], the coating is composed of the Ti-rich layer, the Cu-Ti intermetallic transition layer and the Cu-rich layer close to the matrix. The content of Ti drops with increasing depth.…”

“…The subsequent thermal diffusion of the obtained films was undertaken to generate a multi-phase coating in a vacuum resistance furnace at varying temperatures and time durations, where the samples were sealed into a vacuum tube before the thermal diffusion in a medium-temperature resistance furnace. Detailed information on the magnetron sputtering and thermal diffusion processes can be found in the previous studies [14,18]. The coated samples were then cut into two parts, and successive polishing of the crosssection by SiC abrasive papers was undertaken from 240# to 2000# to achieve a smooth morphology in the cross-section.…”

“…The reaction between Cu and Ti atoms results in different Cu-Ti intermetallics [6,16], including CuTi, Cu 4 Ti, CuTi 2 , and so on [17], which provides certain improvement in wear resistance. In addition, the adhesion of the coating plays a critical role in the wear resistance [18], and a gradient Cu-Ti film is applied to fabricate a hard surface coating during the plasma nitriding process, which provides an intermediate layer for better support than the Cu substrate [14,18]. Moreover, vacuum annealing has been proposed as a simple and viable method to tune the diffusion process and the microstructure of the multi-phases coating [19].…”

Microstructure Formation and Mechanical Properties of Multi-Phase Coating by Thermos Plasma Nitriding of Gradient Cu-Ti Films on C61900 Cu Alloy

“…The subsequent thermos plasma nitriding of the obtained films was undertaken to generate a multi-phase coating in a homemade pulsed plasma multicomponent infiltration furnace (LDMC-30 kW), with a nitrogen and hydrogen gas flow rate ratio of 0.3:0.1 L/min to generate a high nitrogen phase. Detailed information on the magnetron sputtering and plasma nitriding processes can be found in previous studies [31,32]. The phase structures of the gradient Cu-Ti films and the multi-phase coating were characterized by the D/max-rB rotary anode X-ray diffractometer, and the CuKα target was applied at a voltage of 40 kV and current of 30 mA, with a scanning range from 20 • -100 • and scanning speed of 5 • /min.…”

“…In addition, the pin-on-disk wear performance was measured against a WC ball of 5 mm in diameter. The test was carried out under dry friction conditions with a positive pressure of 4 N, a rotating speed of 200 r/min and a test time of 1800 s. A Wyko NT8000 white light interferometer was used to measure the cross-sectional profiles of the worn tracks, by which the volume wear rate was calculated [31].…”