| Pipe-connector made from Ti44Ni47Nb9 shape memory alloy has been considered to be good component to connect the titanium alloy tube with the stainless steel tube in nuclear powered naval vessels. Comparing to the conventional techniques, shape memory connectors have many advantages such as simpler and lighter structures, easy installation and minimal working space required, no production of injurant, etc. Due to its special application conditions, it is required that the pipe-connector must be preserved and installed at ambient temperature and it must have a large enough connecting strength which should not be weakened significantly when the device is exposed for a very long time to an environment with weak irradiations and at intermediate temperatures (less than 350癈) and to thermal cycles between this temperature to room temperature. According to these requirements, systematic studies have been contacted in the present thesis on the microstructures, martensitic phase transformation characters, mechanical properties, recovering process, stress relaxing and electron irradiations of Ti44Ni47Nb9 shape memory alloys.The microstructure of 850℃ annealed Ti44Ni47Nb9 shape memory alloyspecimen was investigated by means of XRD, Metallography Microscope, SEM and TEM. In addition to the often reported TiNi solid solution matrix, p-Nb phase and (Ti,Nb)2Ni phase, a new phase: Ti2Ni3 was observed. It has been found that the grains are rather small with equal axis and few dislocations. The p-Nb phase shows a spherical shape inside grains and an ellipsoid on grain boundaries. Ti2Ni3 appears as a spindle shape with its one end in contact with the spherical P-Nb phase.The phase transition behavior and the mechanical properties of the 850℃ annealed Ti44Ni47Nb9 shape memory alloy specimen were studied using DSC and MTS. Particular attention .is paid to find the effect of the pre-deformation on the reverse transformation temperature and the recovery process during the reverse transformation. The results show that the reverse transformation temperature was raised significantly after pre-deformation of 12~18% at -120℃ -40℃ . The higher the pre-deformation and the deformation temperature are, the higher the reverse transformation temperature is. In particularly, after pre-deformation of 16% at -60℃, the reverse transformation temperature has been increased to 63℃, much higher than room temperature, the hysteresis in temperature is about 150℃, the recoverable strain is 5.3%, the recovery rate is 43% and the maximal recovery stress is 436Mpa. If the pre-deformation is increased to 18%, the reverse temperature will be raised further to 87℃ with 3.5% recovery strain, 23% recovery rate and 385Mpa maximal recovery stress.Combine electric resistance measuring device with MTS, the stress-temperature and the electric resistance-temperature curves were measured simultaneously for -60℃ pre-deformed 850℃ annealed Ti44Ni47Nb9 shape memory alloy specimen under various constrains of the total strain in order to study the effect of the pre-deformation and the strain constrains on the recovery stress and the reverse phase transition process. The results indicated that the recovery stress increased with the temperature with a nearly constant slope until a maximal value. The temperature of the maximal recovery stress is clearly lower than the finish temperature of the reverse transition. The maximal recovery stress increases initially with the pre-deformation, reaches a maximum (623Mpa) near10% and decreases for larger pre-deformation. It has a value of 436Mpa for 16% pre-deformation and 385Mpa for 18% pre-deformation.Stress relaxation is studied on MTS for the 850℃ annealed Ti44Ni47Nb9 shape memory alloy specimen. It has been found that for an initial stress of 360Mpa, there is little stress relaxation at 350℃ but rather strong relaxation at 500℃. At 400癈, stress relaxation was not significant for initial stresses of 260MPa and 360MPa in contrast to larger initial stress of 460Mpa.When the speci...
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