Microstructure and wear properties of WC particle reinforced composite coating on Ti6Al4V alloy produced by the plasma transferred arc method
Introduction
Titanium and its alloys are widely used in the aerospace, automotive, chemical, petrochemical, biomedical, and sports industries due to their high specific strength and superior corrosion resistance. However, their relatively poor tribological properties, such as high friction coefficient and low hardness, are barriers to their use in applications that require high surface hardness and wear resistance [1], [2], [3], [4], [5], [6]. Surface modification techniques, including chemical vapor deposition (CVD) [7], [8], [9], [10], [11], physical vapor deposition (PVD) [12], [13], [14], [15], [16], laser and plasma surface treatment [17], [18], [19], [20], thermal oxidation [21], [22], [23], [24], [25], [26], sol-gel processing [27], [28] and nitriding [29], [30], [31], [32], have been applied to improve the tribological and wear properties of Ti alloys.
Among the different surface treatments used to produce wear-resistant metal matrix composites, the plasma transferred arc (PTA) method has been widely used to improve the wear resistance of metallic materials. This process is based on the formation of a plasma arc between a tungsten electrode and a substrate. The main advantages of the PTA method are low operational cost, flexibility, high deposition rate, high heat input, high efficiency and wide applicability [33], [34], [35], [36], [37], [38], [39].
Most studies on the wear behavior of PTA-coated surfaces have focused on steel or cast iron substrates, and no information is available regarding the processing of Ti6Al4V alloys. Moreover, Fe–Ni–Co has been used in standard PTA applications as a powder material. In the present study, the surface of a Ti6Al4V alloy substrate was coated with WC powder as a wear resistance material to prevent the dissolution of particles during the process and obtain a composite structure using the PTA method. The microstructure and chemical composition of the composite layer was characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis. The wear resistance of the composite layers was investigated by ball-on-disc tests. The microhardnesses of the layers were measured using a Vickers indenter. The effects of the different arc current values (70 A, 80 A and 90 A) used in PTA processing on the microstructural and wear properties of the composite layers were also investigated.
Section snippets
Experimental procedures
Ti6Al4V alloy was used as the substrate material in this study, and the dimensions of the samples were 10 mm × 10 mm × 65 mm. A schematic drawing of the samples is presented in Fig. 1. WC powder (280 mesh, Alfa Aesar) was used as the coating material. An opened channel on the surface of the samples was covered with a paste prepared by mixing the WC powder with alcohol.
PTA processes were applied at current values of 70, 80 and 90 A. The diameter of the electrode used in the PTA process was 4.7 mm, and
Microstructure
Fig. 3 shows the XRD patterns of the composite coatings produced by PTA processing at 70 A, 80 A and 90 A. The figure clearly shows that the current values of the PTA process caused significant changes in the microstructure of the coatings. After PTA welding at an arc current of 70 A, a composite coating microstructure composed of the α- and β-phase of Ti and W, WC, TiC and W2C phases was formed. This result is similar to that previously reported by Pang et al. [40], in which a composite coating
Conclusion
In the present study, WC reinforced composite coatings were successively produced on Ti6Al4V alloys by the PTA process. The effects of the different arc current values used in the PTA process on the microstructural properties of the coatings were investigated. The hardness and wear behavior of the substrate and the coated alloys were determined, and the following conclusions were drawn.
- 1.
The PTA method is very suitable for producing wear-resistant composite coatings on Ti6Al4V alloy.
- 2.
The PTA arc
Acknowledgement
This work was partly supported by the Scientific Research Projects Committee of Eskisehir Osmangazi University (Project no: 200815040).
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