Preparation And Damping Capacities Of Niti Based Syntactic Foams Reinforced By In-situ Formed Ti₃sn Phase

The influences of noise,vibration and impact are widespread in various fields,and they are extremely harmful to mechanical equipment and human beings.These problems can be effectively solved by using high damping materials.Commonly used lightweight and high damping materials,such as Al and Mg foams and their composites possess high damping capacities,but their strength and weatherability are relatively poor.It is difficult to meet the requirements of light weight,high strength and high damping for the Al and Mg foams in some special fields,such as new energy vehicles,high-speed rail,aerospace,national defense,etc.So,it is urgent to develop a novel metal matrix foam with low density,high strength and high damping capacity.In recent years,NiTi shape memory alloys and their foams have attracted much attention due to their excellent mechanical properties and damping capacities.However,the high temperature damping capacity of dense NiTi alloy and the compressive strength of NiTi foam are relatively low,which limits their further applications.Therefore,powder metallurgy and pressure infiltration processes were used to introduce Ti₃Sn phases and regular pores into NiTi alloy matrix to prepare lightweight TiNiSn foams and TiNiSn syntactic foams.The microstructures,phase compositions,phase transformation behaviors,compressive mechanical properties and damping capacities of these alloys were systematically studied,and the mechanisms of improving properties were explored.The following conclusions can be drawn:Firstly,TiNiSn alloy composites with different alloy compositions were prepared by arc melting.The results show that all TiNiSn alloys are mainly composed of proeutectic phase and lamellar Ti₃Sn/NiTi eutectic structure.The Ti₅₈Ni₃₄Sn₈ alloy can exhibit the best mechanical properties and damping capacities because it possesses more lamellar Ti₃Sn/NiTi eutectic structure.Its compressive strength and fracture strain are 1836MPa and 28%,and its intrinsic damping at martensite?M?and austenite?A?states can reach 0.042 and 0.014,respectively.Then,to reduce the density of the alloy and further improve the damping capacity,TiNiSn foams with low porosity?17%?and high porosity?60%?were fabricated by powder sintering with the Ti₅₈Ni₃₄Sn₈ alloy composition.When the alloy was sintered at 1050?,the alloy reaction is more sufficient,and the microstructures are mainly composed of NiTi phase and Ti₃Sn phase,the micron-bulk Ti₃Sn phase is uniformly distributed in the NiTi matrix without the lamellar Ti₃Sn/NiTi eutectic structure.The TiNiSn foam with low porosity sintered at 1050?exhibits better comprehensive properties,its compressive strength and fracture strain are994MPa and 11.2%,its intrinsic damping at M and A states reach 0.046 and 0.014.The compressive strength and fracture strain of the TiNiSn foam with high porosity decrease to77MPa and 3.2%,but the intrinsic damping at M and A states increase to 0.07 and 0.034.Because the sintered TiNiSn foams don't possess expected spherical pore structure and the lamellar Ti₃Sn/NiTi eutectic structure,finally,the TiNiSn syntactic foams were prepared by pressure infiltration process by infiltrating the alumina microspheres with Ti₅₈Ni₃₄Sn₈ alloy.Both the regular spherical pore structure and the fine lamellar eutectic structure were first introduced into the NiTi foams.The results show that the TiNiSn syntactic foam cooling at a faster rate possesses a higher ratio of lamellar Ti₃Sn/NiTi eutectic structure,and the thickness of lamellar spacing and Ti₂Ni interfacial layer formed between matrix and alumina microspheres are smaller,meanwhile,it presents better comprehensive property.The air-cooling TiNiSn syntactic foam can possess more than 80%lamellar Ti₃Sn/NiTi eutectic structure,the interlayer spacing of Ti₃Sn/NiTi is about 600⁹00nm,and the thickness of Ti₂Ni interfacial layer is about 10?m.The air-cooling TiNiSn syntactic foam exhibits extremely high compressive strength?402⁴16MPa?and good energy absorption capacity?119.8MJ/m³?at a wide temperature range?-50²5??,meanwhile,it presents excellent damping capacities?>0.066?at a wide temperature range?-150²00??.In addition,its comprehensive coefficient of specific strength and high temperature damping capacity reach as high as 4.98,which is the highest among all present lightweight and high damping metals.