NiTiNb Alloy Tube Expanding Deformation And Its Impact On Memory Performance

NiTiNb alloy is a wide hysteresis shape memory alloy which was successfully developed in1986by the United States. Martensitic reverse transformation temperature of the alloy is above room temperature after it was deformed. Pipe joint and fastening ring made of this alloy are widely used in the aerospace and marine hydraulic piping gas pipeline connection.Current research on shape memory alloys NiTiNb mainly include impact of components, deformation and deformation temperature on memory performance of the alloy. Literature about the size design of the pipe fittings and the impact of size on the performance of memory performance is less. This paper studies the effects of heat treatment on NiTiNb alloys, the strain distribution in the process of expanding was analyzed with elastic-plastic mechanics and finding that three important parameters diameter ratio R/r, expanding deformation s and integral average strain ε have an important influence on the strain distribution. Besides thick-walled tube is divided into different thin-walled tube, and the memory performance of each pipe fittings was studied.The hardness of the alloy gradually decreases and the phase transition temperature rises with increasing annealing temperature when NiTiNb alloy was annealed at less than850℃. Annealing at850℃for1h, the phase transition temperature is stabilized, substantially no change in the hardness of the alloy microstructure, the alloy sufficiently complete recrystallization, with grain size of about11μm. Annealing at900℃for1h grain size grow to20μm.The radial strain, circumferential strain and axial strain are calculated based on elastic-plastic mechanical in the deformation process, getting the deformation ratio η of radial direction and circumferential direction. The measurement value and theoretical values are consistent through experimental verification. The three important parameters R/r, ε and ε have an important influence on the strain distribution which are the same important in memory performance.Research on heat recovery properties after deformation of NiTiNb alloy pipe fittings showed that reducing R/r, increasing ε or increasing the can improve reverse martensitic transformation temperature of the tube member. Increasing R/r, reducing s or reducing ε can improve the response rate of the pipe fittings. While increasing R/r, reducing ε or reducing ε can also increase the fastening stress at the same time.Split tube studies show that Each tube The reverse phase transition temperature of all tubes were positively correlated relationship with ε. Response rates of inner tube and the outer tube of are negatively correlated with ε and the ε of outer tube is significantly less than inner tube. Correspondingly the response rate of the outer tube is also significantly higher than the response rate of the inner tube. The pull-off force of unit wall thickness tube increase with ε decreases and it is greater in outer tube than that in inner tube.