Interface Structure And Mechanical Properties Of Al Matrix Composites Reinforced With TiNi Fibre

With the increase in speed of aircraft, the stiffness of structural materials is required to not decrease at high temperature. In this paper, a kind of lightweight composite with constant elastic property in a certain temperature range was design. Three different Ti Ni fibers Ti Ni50、Ti Ni50.3 and Ti Ni50.6 were used as reinforment, while 1060 Al was used as matrix. The Ti Nif/Al composites were fabricated by pressure infiltration process. Tensile deformation behaviors of the composites were tested by an Instron 5569 testing machine. The dynamic mechanical properties and damping capacity of the composites were studied by dynamic mechanical thermal analyzer(DMA). Furthermore, SEM(Quanta 200FEG) and TEM(Tecnai G2 F30) were used to study the microstructure and fracture morphology of the composites. The effects of phase transformation behaviors of Ti Ni fibers on th e constant elastic property and damping capacity of the composites were also discussed.The serious interfacial reaction between Ti Ni fibers and Al matrix could be prevented by the oxide layer. After being oxidized at the temperature of 400℃、500℃ and 600℃,the main component of oxide layer was Ti O2. It was confirmed that the oxide layer could be used to prevent the serious interfacial reaction when the Ti Ni fibers were oxidized at 600℃ for 1 h in the air. Moreover, the tensile strength of Ti Ni50.3f/Al composite was 268 MPa which was very close to the theoretical value when the volume fraction of Ti Ni fiber was 20%.A multilayer interface was formed in the composites. Three layers have been found in the multilayer interface: Ti Ni-B2 layer and Ti-Ni compounds layer close to the Ti Ni fiber, Ti-Al compounds layer with Ti and granular Ti O2 close to the Al matrix. Ni5 Ti O7 phase was formed between Ti Al3 and Ni Ti2 phase. The lattice relationship between Ti Al3 phase and Ni5 Ti O7 phase was confirmed:(002)Ti Al3 //(114)Ni5Ti O7 and [100]Ti Al3 // [794]Ni5Ti O7. Moreover, the lattice relationship between Ni Ti2 phase and Ni5 Ti O7 phase was also confirmed:(240)Ni Ti2 //(112)Ni5Ti O7 and [210]Ni Ti2 // [423]Ni5Ti O7.The tensile deformation process of Ti Nif/Al demonstrated two ―yield plateaus‖ and two ―strengthening periods‖ at room temperature. Two different deformation mechanisms were found. The first yield plateaus of Ti Ni50f/Al and Ti Ni50.3f/Al composite was corresponding to the martensite reorientation induced by stress in the Ti Ni50 and Ti Ni50.3 fiber. While the first yield plateaus of Ti Ni50.6f/Al compositeattributed to the martensitic transformation induced by stress in the Ti Ni50.6 fiber. With the increase in the volume fraction of Ti Ni fiber, the tensile strength of the composite increased. But it decreased with the increase of temperature. At different temperature, the composite exhibited typical ductile fracture pattern.The results show that the phase behaviors of Ti Ni fiber go hand in hand with the constant elastic property of the composite. In the heating process, the relative value of storage modulus as a function of temperature follows the mixing rule when the temperature is lower than phase transition temperature. However, it depends on the relative content of martensite and austenite in the Ti Ni fiber when temperature is higher than phase transition temperature. When the volume fraction of Ti Ni fiber is 50%, the constant elastic property of Ti Ni50f/Al、Ti Ni50.3f/Al and Ti Ni50.6f/Al was obtained in 130℃~300℃、110℃~300℃ and 30℃~300℃, respectively.The effect of aging and deformation treatment on the phase behavious of Ti Ni fibers was studied. The results show that the reverse martensitic and R phase transformation temperature of Ti Ni50.6 increased, while the martensitic transformation temperature decreased with the precipitation of Ti3Ni4. When the aging time was short, inhomogeneous precipitation of Ti3Ni4 was observed in the internal and boundary of the grains. It resulted that a three-stage transformation was found in the heating and cooling process. Furthermore, after tensile deformation, the stability of martensite could be increased. It resulted in the change of the temperature of phase transformation. When the amount of tension deformation was higher than 4 %, part of martensite induced by stress in Ti Ni50.6 fiber was reorientation, two peaks of phase transition was observed in the heating process.The effect of strain and frequency of oscillation on the storage modulus and damping capacity of composites were discussed. When the strain of oscillation was high, the density of mobile dislocation increased with the increase in the strain, which could result in the rapid decrease of relative values of storage modulus and the increase in damping capacity of the composites. However, the effects of frequency of oscillation on the storage modulus and damping capacity of composites were attributed to the grain-boundary relaxation. After tension deformation, the relative value of storage modulus was not change with the increase in the amount of pre-strain treatment. Moreover, the increase in vaule of damping peak was attributed to the compressive stress in the composite which was induced by shape memory effect of Ti Ni fibers.