Abstract
In this study, pre-alloyed Ti-48Al-2Cr-2Nb (TiAl-based) powder was consolidated using automated spark plasma sintering (SPS) machine (model HHPD-25, FCT GmbH Germany) into 20 mm and 40 mm samples. The drive to tailor the microstructure of the TiAl-based alloy motivated the choice of utilizing SPS technique due to the numerous benefits it offers such as the capability to restrict grain growth and achieve homogenized microstructure through control of process conditions. Attainment of the tailored microstructure of TiAl-based alloy presents opportunities for broadening their applications, especially to components requiring some wear resistance in the service conditions. Characterization of spark plasma sintered (SPSed) TiAl-based alloy was performed using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDS), and SEM images were processed for quantitative analysis using Python software. The mechanical properties and tribological properties of the SPSed TiAl-based alloy were evaluated using a nanoindentation system and tribometer, respectively. Results show that both the microstructure of the SPSed TiAl-based alloy and test conditions play a significant role in the performance of the alloy. The nearly lamellar consisting of coarse lamellar colonies and fine equiaxed γ-grains (in the case of 20 mm samples) presented better wear resistance at room temperature, while the duplex microstructure (of the 40 mm samples) consisting of equiaxed γ-grains and lamellar colonies demonstrated favourable anti-wear properties at high temperatures of 600°C. High temperature conditions encouraged the rapid formation of a robust oxide layer capable of withstanding low-medium loads (1-5 N). At a higher load of 10 N, wear protection was provided by the formation of a compacted surface through rapid dual actions of oxidation and smearing of debris thus, restricting further surface damage. The wear mechanisms transited from dominantly abrasive at room temperature to dominantly oxidative and adhesive at high temperatures. Both the nearly lamellar and duplex microstructure showed satisfactory mechanical properties at the nano and micro scale. The improvement in the wear and mechanical properties of the TiAl-based alloy is attributed to the excellent densification of the alloy and the tailored microstructural features such as the nearly lamellar (for the 20 mm sample) and duplex (for the 40 mm sample) microstructures obtained through optimized SPS process parameters, 1200°C-50MPa-7.5min-50°C/min and 1250°C-50MPa-7.5min-100°C/min, respectively.