Research On Evolution,Function And Wear Mechanism Of Artificial Tribo-layers For TC11 Alloy

The poor tribological properties of titanium alloys limit their applications involving in the working conditions of friction and wear.Controlling the formation of tribo-oxide layers is a new approach to improve the friction and wear properties of titanium alloys. However, the research on the evolution, function and wear mechanism of tribo-layers was not thorough. In this study, a double-layer antifriction and antiwear tribo-layer was artificially manufactured by adding different types of nanomaterials onto the sliding interfaces. The friction and wear behaviors of TC11 alloy were studied under different loads, addition amounts and sliding revolutions. The morphology, structure and composition of tribo-layers were characterized. The wear transition and mechanism as well as the formation and destruction mechanism of artificial tribo-layers and their relations were explored. The function mechanism and stability of artificial tribo-layers were investigated and their sustainability was verified by double sliding wear test. This research will provide essential data and scientific basis for the tribological design and performance improvement, engineering application and wear theory of titanium alloys,and possess significant theoretical and engineering values.The study found that the friction and wear behaviors were closely related to additive types as well as sliding and addition conditions.Irrespective of the load, addition amount and revolution, the friction and wear performances of TC11 alloy would be not improved with the additive of MLG. The wear resistance could be enhanced under low loads by adding Fe₂O₃ nanoparticles, but the antifriction performance did not achieve synchronous improvement. However, the mechanical mixture or composite additives of Fe₂O₃ and MLG leaded to the simultaneous improvement of wear resistance and antifriction performance for TC11 alloy. For pure MLG or Fe₂O₃ nano-additives, severe wear always occurred except for adding Fe₂O₃ under low loads. The main wear mechanism was adhesive and abrasive wear. The severe-mild wear transition was accelerated with the mechanical mixture and composite additives of Fe₂O₃ and MLG. The critical load and revolution were increased and the critical addition amount decreased. With an increase of MLG proportions in additives, TC11 alloy underwent severe-mild-severe wear double transition on the whole.MLG- and Fe₂O₃-contained single-layer artificial tribo-layers were formed via adsorption-compaction and tribo-sintering and possessed good lubrication and load-bearing capacity, respectively, owing to the low shear force of MLG and high hardness of Fe₂O₃. But the single-layer tribo-layers presented poor stability and sustainability because of a deficiency of respective load-carrying or lubricant capacity. For the mechanical mixture or composite additives, Fe₂O₃ and MLG successively experienced sintering and adsorption to form the double-layer artificial tribo-layers, and the former ones were obviously layered. The double-layer tribo-layers colligated the excellent properties of MLG and Fe₂O₃ and presented synergistic protection effect of lubrication and load-bearing, which resulted in a significant improvement of their stability and sustainability. The double-layer artificial tribo-layer formed by adding Fe₂O₃-rich composite possessed strong load-bearing capacity and stability, which was attributed to high content and dispersity of Fe₂O₃ in the tribo-layer. When MLG-rich mechanical mixture additives were applied, the double-layer tribo-layer contained high content MLG with more number of layers, presenting excellent lubricant performance and sustainability, which was verified by double sliding wear test.The formation and destruction mechanism of artificial tribo-layers were initially clarified, and their relations were established. Based on this,the evolution of tribo-layers experienced three stages of growth period,stabilization period and degeneration period. They corresponded to VF/VD>1, VF/VD?1 and VF/VD<1, respectively. A double-layer artificial tribo-layer was designed and prepared to synchronously improve the friction and wear performances of titanium alloy under normal conditions without consuming substrate materials, which possessed high stability and sustainability. Correspondingly, the optimal nano-additive types and proportions were MLG/Fe₂O₃ ?1:4? and MLG+Fe₂O₃ ?2:1?,respectively.