Establishment of The Inspection Technique for Strength of Ti-Ni Shape Memory Alloys And Its Clarifying The Fracture Mechanisms

Establishment of the结构控制方法for the most suitable functional properties and thematerial inspection technique of ni shape memory alloys are the main object of thisproject.transformation temperatures,observation of microstructures and mechanical properties of variously heat-treated Ti-Ni-Co andTi-Ni-Cu alloys were Mechanical properties of the alloys，which were at T < A - D2f - D2 （martensite phase）T = A - D2f d - 2 (austenite + martensite phase) and T > A - D2f d - 2 （austenite phase）test temperature, A - 2f - D2：reverse transformation finish temperature)were investigated by using a serva -hydraulic type material testing machine with an environmentalchamber. Then fracture surfaces observed by a high resolution scanning electron microscopy andx - ray diffractometer,和microstructure of near fracture region was observed by a transmission electron microscopytensile deformation behaviors and fatigue properties are strongly affected by deformation speed. Allthe values of inflection stresses on the stress - strain curves increased with increasing tensileThe fatigue life obtained at 20hz was about 2 times longer than that at 0.5 Hzreferring to the maximum stress versus the number of cycles to failure curve. Striation patterns areclearly observed on the fatigue fracture surface, and the crack growth rates, dl/dN方法来自these striation patterns. The deformation process model of Ti-Ni shape memoryalloys was proposed on the basis of the above experimental results

Establishment of the structural control method for the most suitable functional properties and the material inspection technique of Ti-Ni shape memory alloys are the main object of this project.Transformation temperatures, observation of microstructures and mechanical properties of variously heat-treated Ti-Ni-Co and Ti-Ni-Cu alloys were estimated. Mechanical properties of the alloys, which were at T < AィイD2fィエD2 (martensite phase), T = AィイD2fィエD2 (austenite + martensite phase) and T > AィイD2fィエD2 (austenite phase) ( T : test temperature, AィイD2fィエD2 : reverse transformation finish temperature ), were investigated by using a servo-hydraulic type material testing machine with an environmental chamber. Then fracture surfaces were observed by a high resolution scanning electron microscopy and X-ray diffractometer, and microstructure of near fracture region was observed by a transmission electron microscopy. The tensile deformation behaviors and fatigue properties are strongly affected by deformation speed. All the values of inflection stresses on the stress - strain curves increased with increasing tensile speed. The fatigue life obtained at 20 Hz was about 2 times longer than that at 0.5 Hz, referring to the maximum stress versus the number of cycles to failure curve. Striation patterns are clearly observed on the fatigue fracture surface, and the crack growth rates, dl/dN, were measured from these striation patterns. The deformation process model of Ti-Ni shape memory alloys was proposed on the basis of the above experimental results.