Effect of WC Addition on the Hardness of Ti-Zr Alloy

Ti-Zr alloys have displayed commendable mechanical and corrosion resistance attributes, largely due to the zirconium content. The remarkable biocompatibility and corrosion resistance of titanium alloys are attributed to the formation of a stable, dense oxide layer, predominantly TiO2 [1]. Introducing additional elements to the Ti-Zr base can modify its properties. Specifically, appropriate zirconium quantities enhance super elasticity recovery and bolster the emergence of shape memory traits. Ti-Zr alloys have demonstrated good mechanical strength and corrosion resistance due to the presence of Zr. However, to achieve the necessary hardness in Ti-Zr alloys, it is essential to subject them to heat treatment. Therefore, the use of WC is a viable option to enhance hardness without the application of heat treatments. The addition of WC to a Ti-Zr alloy offers multiple advantages. Firstly, WC increases the hardness and wear resistance of the alloy. Since WC has very high hardness, adding particles enhances the overall hardness of the Ti-Zr alloy, making it more resistant to wear. This study aims to assess the microstructure and mechanical attributes of Ti-Zr alloys with varied WC percentages (5, 10, and 15%). These alloys, synthesized via electric arc melting, were examined using optical microscopy, microhardness tests, and XRD; to observe the enhanced in mechanical properties and microstructure. In this study, four alloy compositions (each weighing 10 g) with varying tungsten carbide content were prepared: Ti0.475-Zr0.475-WC0.05, Ti0.45-Zr0.45-WC0.1, and Ti0.425-Zr0.425-WC0.15. The titanium and zirconium were sourced from rods boasting a purity of 99%, while the tungsten carbide was introduced as a powder, featuring a particle size around 45μm and purity exceeding 99%. Melting of the samples was performed in an Arc Melt Furnace-Tri Arc MODEL TA-200 electric arc furnace. This furnace utilized a non-consumable 2% W-Th electrode and a water-cooled copper crucible, all under a high-purity argon atmosphere. XRD patterns confirms the TiZr phase and the Prescence of W2C phase in the alloy with 15% WC. Figure 1 shows the microstructure of the four different alloys. In figure 1(a) is possible to observe the heterogeneity in the grain structure in the alloy without doping, the grain size is larger than that in samples doped with WC. In figure 1(b) (Ti0.475-Zr0.475-WC0.05 alloy), a discernible decrease in grain size is evident. Figures 1(c) and 1(d) confirm that the increase in WC content corresponds to a decrease in grain size. Therefore, with a low WC addition the Ti-Zr grain size decreases until the 15 %wt where the grains size slightly increases. Mechanical properties of materials often correlate closely with their microstructural characteristics. One such property influenced by microstructure is microhardness. This study investigates how the incorporation of WC affects the hardening of the material. Table 1 shows the values of Vickers hardness found for the four compositions, an increment in the hardness is observed as WC content increases. This improvement can be attributed to the inclusion of WC into the TiZr. Particularly, the Ti0.45-Zr0.45-WC0.1 alloy exhibited the highest hardness value, registering at 886 HV. Conversely, the Ti0.425-Zr0.425-WC0.15 alloy, although displaying some variability, showed a hardness lower than 886HV. As it was observed by optical microscopy and XRD when 15% WC is added to TiZr alloy there is a modification in the base alloy in addition to the formation of a W2C secondary phase, which could cause the variability of the hardness values in this alloy. As WC content was added to Ti-Zr Alloy changes in the structural and microstructural properties were observed. In all dopped conditions the grains presented lower size than in the alloy without WC. This is a typical microstructure found in ceramics with WC incorporation [2,3]. The pick shift observed in the XRD spectra could be a consequence of the W incorporation into the Ti-Zr lattice, as the W is incorporated into the lattice shift is observed towards larger angles, which indicates a decrease in the lattice parameter, what is expected if the W replaces the Zr as have been reported [4,5]. The WC additions even increased almost two times the hardness value for the alloy. Future research directions may also be highlighted in the direction of friction, wear resistance and biocompatibility to complete the investigations about this alloy. Microstructure of the sintered samples a) TiZr, b) TiZr-5WC, c) TiZr 10-WC and c) TiZr-15WC. Hardness values for all the compositions. Hardness values for all the compositions.