Preparation And Properties Of Ti₃AlC₂ Particle Reinforced ZA27 Matrix Composites

High-performance Zinc-Aluminum alloy?ZA?-based composites have been prepared by adding layered ternary M_n+iAX_n phase ceramics as reinforcements,and the preparation technology,mechanical properties and friction-wear characteristics of the composites were investigated in this work.This dissertation is composed of six chapters:introduction of ZA-based composites,the reaction mechanism between layered ternary Ti₃AlC₂ ceramic and Zinc-Aluminum alloy ZA27,preparation and characterization of Ti₃AlC₂/ZA27 composites,the measurement and analysis of friction-wear characteristics of Ti₃AlC₂/ZA27 composites,and the effect of different kind of M_n+iAX_n phases?Ti₃AlC₂,Ti₃SiC₂ and Ti₂SnC?on structure and mechanical properties of M_n+iAX_n/ZA27 composites.The results showed that:?1?Pressureless sintering,hot pressing and a combination of pressureless sintering and hot pressing?two-step sintering?technology have been used to prepare Ti₃AlC₂/ZA27 composites.The result of XRD showed that,under the action of liquid ZA27 alloy,a weak reaction happened at the interface of Ti₃AlC₂ and ZA27 matrix at the temperature of 870?.And some new phases,such as TiC and Al0.64Tio.36 wereformed.The reaction equation was:???.However,the reaction will not happen when the sintering temperature is below 800?.?2?The size of the raw powders can be greatly decreased by mechanical alloying.And the effect of dispersion strengthening was enhanced significantly.Microscopic analysis found that Ti₃AlC₂ particles with the size of 30?50nm distributed in Ti₃AlC₂/ZA27 composites.This is an important factor for the high mechanical strength.?3?Different sintering processes may lead to different mechanical properties of Ti₃AlC₂/ZA27 composites.In our work,the appropriate pressureless sintering process was of sintering temperature at 870? with the holding time of 2.5h.For two-step sintering technology,the optimal sintering parameters was of sintering at 870? for 1h,and then hot-pressing with 30MPa at 500? for 1.5h.The improved performance of Ti₃AlC₂/ZA27 composites prepared by two-step sintering technology was achieved.?4?The content of Ti₃AIC₂ has an influence on the mechanical properties of Ti₃AlC₂/ZA27 composites.The strength of Ti₃AlC₂/ZA27 composites prepared by two-step sintering technology was first increased and then decreased with increasing Ti₃AlC₂ content.The suitable content of Ti₃AIC₂ as a reinforcement in the Ti₃AlC₂/ZA27 composites was 30vol.%.The 30vol.%Ti₃AlC₂/ZA27 composite possesses the enhanced mechanical properties with tensile strength,bending strength and Vickers hardness of 335MPa,570MPa,and 1204MPa,respectively.?5?The wear performance of Ti₃AIC₂/ZA27 composites was effectively improved by the addition of Ti₃ AIC₂ particles.In addition,the rise of temperature in composites caused by friction is smaller than that in ZA27 matrix.As the volume fraction of Ti₃AlC₂ increased,the friction coefficient of Ti₃AlC₂/ZA27 composites decreased firstly and then increased.The 30vol.%Ti₃AlC₂/ZA27 composite exhibits the best wear resistance.At a lubricated sliding wear test against 45#steel with speed of 3m/s and a normal pressure of 0.5MPa,comparing with the ZA27 matrix,the friction coefficient of 30vol.%Ti₃AlC₂/ZA27 composites decreased by 43%and the wear rate decreased by 33%.Besides,with increasing the applied load,the friction coefficient of Ti₃AlC₂/ZA27 composites was decreased,but the wear rate increased.As compared with the ZA27 matrix,the applied load has little effect on the friction coefficient of the Ti₃AlC₂/ZA27 composites.?6?Three kinds of Mn+1AXn phases including Ti₃AlC₂,Ti₃SiC₂ and Ti₂SnC have the similar effect on mechanical properties of M_n+1AX_n/ZA27 composites.However,the difference of structural stability affects the interfacial reaction,and the mechanical properties.The results of XRD analysis of the M_n+iAX_n/ZA27 composites fabricated by the "two-step" sintering technology at 870? showed that:Ti2SnC decomposed completely in Ti₂SnC/ZA27 composite,and a part of Ti₃AlC₂ decomposed in the Ti₃AlC₂/ZA27 composite.However,no reaction happened between Ti₃SiC₂ and ZA27 matrix.Compared the mechanical properties of composites and ZA27 matrix,a great improvement in strength and wear resistance was achieved as M_n+1AX_n ceramics added in ZA27 matrix.The 30vol.%Ti₃AlC₂/ZA27 composite has the best mechanical and wear resistance properties.While Ti₂SnC/ZA27 and Ti₃SiC₂/ZA27 composite exhibit unenhanced mechanical properties and wear resistance,respectively.The innovations of this work can are listed as following:?1?Ti₃AlC₂/ZA27 composites with excellent mechanical properties and wear resistance were obtained by using a better matching Ti₃AlC₂ as reinforcement.And the composition,preparation process and technological parameters of the composites were optimized unprecedentedly.?2?The interfacial reaction layer with 1-2nm thick was observed between Ti₃AlC₂ particle and ZA27 matrix.As a consequence,the Ti₃AlC₂/ZA27 composite possess the enhanced mechanical properties.?3?The differences in microstructure and mechanical properties of Ti₃AlC₂,Ti₃SiC₂ and Ti₂SnC reinforced ZA-based composites was revealed.And the results indicate that Ti₃AlC₂/ZA27 composite has the best mechanical and wear resistance properties.