The TC21 alloy (Ti-6Al-3Mo-1.9Nb-2.2Sn-2.2Zr-1.5Cr) is considered a new titanium alloy that replaced the commercial Ti-6Al-4V alloy in aerospace applications due to its higher operating temperatures. Recently, direct energy deposition was usually applied to enhance the hardness, tribological properties, and corrosion resistance for many alloys. Consequently, this study was performed by utilizing direct energy deposition (DED) on TC21 (α/β) titanium alloy to improve their mechanical properties by depositing a mixture powder of stellite-6 (Co-based alloy) and tungsten carbides particles (WC). Different WC percentages were applied to the surfaces of TC21 using a 4 kW continuous-wave fiber-coupled diode laser at a constant powder feeding rate. This study aimed to obtain a uniform distribution of hard surfaces containing undissolved WC particles that were dispersed in a Co-based alloy matrix to enhance the wear resistance of such alloys. Scanning electron microscopy, energy dispersive X-ray analysis (EDAX), and X-ray diffractometry (XRD) were used to characterize the deposited layers. New constituents and intermetallic compounds were found in the deposited layers. The microhardness was measured for all deposited layers and wear resistance was evaluated at room temperature using a dry sliding ball during a disk abrasion test. The results showed that the microstructure of the deposited layer consisted of a hypereutectic structure and undissolved tungsten carbide dispersed in the matrix of the Co-based alloy that depended on the WC weight fraction. The microhardness values increased with increasing WC weight fraction in the deposited powder by more than threefold as compared with the as-cast samples. A notable enhancement of wear resistance of the deposited layers was thus achieved.
The effect of heat treatment on microstructure and tensile properties as well as wear behavior on TC21 (Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-Si, wt.%) Ti-alloy was investigated. The samples were solution treated at 900˚C for 15 min followed by furnace cooling to 800˚C with a cooling rate 1˚C/min and holding for 20 min, then the samples cooled down to room temperature either using water quenching (WQ) or air cooling (AC). Consequently, aging treatment was applied at 575˚C for 4 hr. The microstructure feature showed a secondary α phase (α s ) precipitated in residual β phase due to the step cooling from 900˚C to 800˚C inside furnace as well as the aging treatment. The highest wear rate was obtained for WQ samples due to increasing in volume fraction of α p (58%). However, the lowest wear rate was reported for WQ + Aging samples due to the high hardness. Optimum mechanical properties of the studied TC21 Ti-alloy were obtained for AC + Aging condition. A better combination of hardness, tensile properties, and wear resistance was achieved for AC + Aging samples, although their wear resistance was found to be slightly lower than that of WQ + Aging samples.
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