Research On Surface-self Adaptive Tribological Properties Of A-sites Solid Solutions Of Titanium Aluminum Carbide

Ternary nanolayered MAX phases exhibit excellent properties,such as excellent capability in oxidation resistance,high demage tolerance,thermal shock resistance,and ductile-to-brittle transition,which are closely relevant to tribological performance.MAX phases hence are considered as promising candidates for tribological applications.Typical MAX phases of Ti₃Si C₂ and Ti₃AlC₂ are confirmed having good tribological behaviors during dry sliding against low-carbon steel.It is exactly the tribo-oxide film with self-lubricating effect plays an important role in sliding process.This self-generated tribo-film was composed mainly by various tribo-oxidation products contained disengagement A-site elements and Ti element,it is primarily attributed to the coexisting multiple interlayer bonding force that the M-A bonds are weaker than the M-X bonds.The present work tried to develop a series of tribological surface-self-adaptable A-sites solid solutions of titanium aluminum carbide based on the special nanolayered structures of MAX phases and the adjustability of the mixed A-oxide in property and morphology.The study results showed that:(1)A-site solid solutions of titanium aluminum carbide of Ti₂Al_(1-x)Sn_xC(1?x?0),Ti₃Al_0.8Sn_0.2C₂,Ti₃Al_0.8Si_0.2C₂,Ti₃Al_0.5Si_0.4Sn_0.1C₂ and Ti₃Al_0.6Si_0.2Sn_0.2C₂ were synthesized from Ti,Al,Si,Sn and TiC powders by pressureless sintering and hot-pressed sintering methods.Ti₃Al_0.5Si_0.4Sn_0.1C₂ and Ti₃Al_0.6Si_0.2Sn_0.2C₂ are the first successful synthetic contains three solid solutions elements of MAX phases.(2)Vickers hardness and flexural strength of the high-purity and dense A-site solid solutions of titanium aluminum carbide were tested.The addition of solid solution elements has obvious strengthening effect in Ti₃AlC₂,Ti₃Al_0.8Sn_0.2C₂,Ti₃Al_0.8Si_0.2C₂ and Ti₃Al_0.6Si_0.2Sn_0.2C₂.However,in Ti₂Al C and Ti₂Al_0.8Sn_0.2C,solid solutions hardening and strengthening are not effective in this system.The mechanism of strengthening or softening of the MAX phase is still unclear.(3)Dry sliding friction and wear behaviors of A-site solid solutions were evaluated using a homemade block-on-disk type high-speed tester.The results showed that Ti₂Al_0.8Sn_0.2C,Ti₃Al_0.8Sn_0.2C₂,Ti₃Al_0.8Si_0.2C₂exhibited excellent tribological behaviors.The self-generated tribo-oxide film are responsible for the observed tribological behaviors.Compared with Ti₂Al C,Ti₂Al_0.8Sn_0.2C has a lower friction coefficient and a higher wear rate.The friction coefficients of Ti₃AlC₂,Ti₃Al_0.8Sn_0.2C₂ and Ti₃Al_0.8Si_0.2C₂are arranged in the order of Ti₃Al_0.8Si_0.2C₂>Ti₃AlC₂>Ti₃Al_0.8Sn_0.2C₂,the wear rates are almost arranged in opposite.The type and content of A-site solid solution elements are the intrinsic factors affecting the tribological properties of titanium aluminum carbide.In comparison,the tribological behaviors of Ti₃AlC₂ and its A-site solid solutions are better than that of Ti₂AlC and Ti₂Al_0.8Sn_0.2C due to the large proportion of A element in stoichiometry.(4)The oxidation performance of Ti₃Al_0.6Si_0.2Sn_0.2C₂ was tested at 800-1200 ^oC in air.The results showed that the doping of the solid solution elements of Sn and Si had a negative effect on the oxidation resistance.The oxidation scale is multilayered,in which the outmost layer is basically a TiO₂ and Al₂O₃ mixed layer,then follows the layer of uncontinuous SnO₂,the third layer is mixture of TiO₂,Al₂O₃ and SiO₂and the inner layer is a mixed layer of TiO₂,Al₂O₃,SiO₂ and SnO₂,among the layers there are obvious micro-cracks and holes.(5)Ti₃Al_0.6Si_0.2Sn_0.2C₂ also showed good tribological behaviors in the same dry sliding conditions.The doping of solid solution element at A-site promotes the formation of oxide layer,leading to the accelerated oxidation rate of Ti₃Al_0.6Si_0.2Sn_0.2C₂.Nevertheless,it can play a positive role as frictional self-lubricating film in the dry sliding process.(6)Both the friction coefficient and wear rate are strongly dependent on sliding speed and normal load for all the A-site solid solution phases.The tribological film distributes sporadically in case of lower sliding speeds and normal load and the wear mechanisms are combination of abrasion wear caused by debris particles and adhesive wear,while it changes to the two-body abrasion wear and oxidation wear as sliding speed and normal load increase because of the continuous and smother tribological film.(7)By introducing different kind and content of A-site solid solution elemetns consciously to adjust the phase composition and chemical state of the tribo-oxidation induced films generated by mixed oxides of Ti,Fe,and variety of A-site elements,and then to adjust the tribological properties of titanium aluminum carbide is feasible.Making this kind of material can be applied to different friction conditions in order to enlarge its application scope.