Carburization-induced surface modification of Ti-6Al-7Nb alloy and its characterization

Abstract

The Ti-6Al-7 Nb alloy and its carbide possess a wide range of engineering applications, therefore, it is utmost required to fabricate high-quality carburized layers on the alloy surface. In this study, the carburization of Ti-6Al-7 Nb alloy was conducted using molten salts (including Carbon Nano Tubes, LiCl, KCl, and KF) in a planetary ball mill, followed by placement in an alumina tube furnace under a nitrogen atmosphere at 1050 °C for various durations. Several characterization techniques were employed to analyze the results, including X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The XRD results reveal that as the carburization duration increased, the alloy achieved complete carburization, forming a 120 µm thick layer of TiC0.3N0.7. After 24 h of carburization, the crystallite size of TiC0.3N0.7 increased, and the micro-strain decreased, indicating improved structural quality. The morphology of the carburized layer at shorter durations exhibits micro-cracks and defects due to incomplete carburization, where carbon (C) and nitrogen (N) could not effectively occupy in the grain boundaries of alloy. After 24 h, an agglomerated, cauliflower-like layer of TiC0.3N0.7 formed, enhancing the alloy's engineering properties. XPS confirmed the presence of carbon and nitrogen in the carburized sample, which contributed to the formation of the TiC0.3N0.7 layer on the alloy surface. AFM analysis supported the SEM findings, revealing broad islands with microgrooves on the carburized layer. These features indicate a thick and well-formed carburized layer, confirming the successful carburization of Ti-6Al-7 Nb. Overall, the study demonstrates that a 24-h carburization process at 1050 °C in molten salts under a nitrogen atmosphere effectively produces a high-quality, thick, and adherent TiC0.3N0.7 layer on Ti-6Al-7 Nb alloy, significantly enhancing its engineering properties.