Deformation mechanism and tribological behavior of hydrogen-free carburized layer on Ti-6Al-4V alloy

Purpose - The purpose of this paper is to expound the relationship among microstructure, mechanical property, tribological behavior and deformation mechanism of carburized layer deposited on Ti-6Al-4V alloy by double-glow plasma hydrogen-free carburizing surface technology. Design/methodology/approach - Morphologies and phase compositions of the carburized layer were observed by scanning electron microscope and X-ray diffraction. The micro-hardness tests were used to evaluate the surface and cross-sectional hardness of carburized layer. The reciprocating friction and wear experiments under various load conditions were implemented to investigate the tribological behavior of carburized layer. Moreover, scratch test with ramped loading pattern was carried out to illuminate the deformation mechanism of carburized layer. Findings - Compared to substrate, the hardness of surface improved to similar to 1,100 HV0.1, while the hardness profile of carburized layer presented gradual decrease from similar to 1,100 to similar to 300 HV(0.1)within the distance of the total carburizing-affected region about 30 mu m. The coefficient of friction, wear rate and wear morphology of carburized layer were analyzed. Scratch test indicated that the deformation process of carburized layer could be classified into three mechanisms (elastic, changing elastic-plastic and stable elastic-plastic mechanisms), and the deformation transition of the carburizing-affected region was from changing elastic-plastic to elastic mechanisms. Both the elastic and changing elastic-plastic mechanisms are conducive to the wearing course. Originality/value - Using this technology, hydrogen embrittlement was avoided and wear resistance property of titanium alloy was greatly improved. Simultaneously, the constitutive relation during the whole loading process was deduced in terms of scratch approach, and the deformation mechanism of carburized layer was discussed from a novel viewpoint. Peer review - The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2019-0489/