The Constrained Phase Transformation Behavior And Model Of TiTi Alloy Fibers Embedded In Aluminum Matrix

The concept of intelligent materials system was proposed in the late 80抯. The development of intelligent materials system immediately obtained considerable attention in various research fields and now has evolved into a multidisciplinary science. Shape memory alloys (SMAs) are considered the most important components both as sensor and actuator in intelligent materials system. As sensors, SMAs can sense the variation of stress, temperature, magnetic field etc. As actuators, SMAs can modify the shape, position, strain, stiffness, natural frequency and damping capacity of the intelligent materials system. SMAs can be easily fabricated into ribbons, particles or fibers, and easily embedded into other materials. The study of SMAs reinforced composites belongs to the basic research of the intelligentizationof materials system Polymer matrix SMAs composites are the main research topic during the past decades. The study of metal matrix SMAs composites showed sluggish progress because there exist several key problems remaining unsolved. I) The insulation film between the SMA fibers and the metal matrix. 2) The control of the interface between the SMA fibers and the metal matrix. 3) The constrained martensitic transformation behavior of SMA embedded in matrix. A TiNi fibers reinforced aluminum matrix composite was developed in this study. DSC, SEM, XRD, thermal expansion strain measurement and scratch test were used to study the constrained martensitic transformation behavior of TiNi fibers. The conclusions are summarized as follows. Effects of prestrain on the reverse martensitic transformation of TiNI fibers have been studied. Results show that the reverse martensitie transformation temperatures A~ and A1 increase, the algebraic difference of (ArAs) decrease until reaching a minimum value then remains unchanged, the transformation erithalpy increase until reaching a maximum value and then decrease with ncreasing prestra~n. The rCSLllts are thought to be closely related with the release of elastic strain energy stored in martensitic variants by predeformation. l7tiects of prestrain on the constrained reverse martensitic transformation of TiNi flbers eilil)edded in the aluminum natri x have been stud ed. Results show that the temperature of pre~traiit attect~ the ievcrsc traimtorttt;itiori ot ~I Ni dllu\ si~nificatitlv. If the coniposite ~ 慽i prestrained in martensite, only one endothermic peak appears on the DSC heating curve. The aera of the peak decreases, the reverse transformation temperatures increase with increasing prestrain. If the composite is prestrained in parent phase state, also only one endothermic peak appears on the DSC curves. The aera of the peak decreases with increasing prestrain but the reverse transformation temperatures remain unchanged. If the composite is prestrained in mix phase state, two endothermic peaks appear on the DSC curve. The lower peak does not change its position with prestrain, the higher peak shifts to high ter1lperature with increasing prestrain. The areas of the two peaks both decrease with increasing prestrain. Martensite straining process and the concept of martensitic deformation degree are proposed. Effects of thermal cycling on the reverse martensitic transformation of TiNi fiber in composite have been studied. Results show that the reverse transformation temperatures increase in the first thermal cycling, but decrease significantly in the se...