Fabrication and Characterization of TiNi/AL Smart Composites
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FABRICATION AND CHARACTERIZATION OF TiNi/AL SMART COMPOSITES Gyu Chang Lee1, Jun Hee. Lee2, Young Chul Park3 1 2
Research Institute of Industrial Science and Technology (RIST), Pohang, Korea,
Department of Metallurgical Engineering, Dong-A University, Pusan, Korea, 3 Department of Mechanical Engineering, Dong-A University, Pusan, Korea
ABSTRACT An attempt was made to fabricate composite material of an Al alloy matrix reinforced by TiNi shape memory fiber using a hot-press method and to investigate its microstructures and mechanical properties. The analysis of SEM and EDS showed that the composite material had good interface bonding. The stress-strain behavior of the composite material was evaluated at room temperature and 363 K as a function of pre-strain, and it showed that the yield stress at 363 K is higher than that at room temperature. It is also found that the yield stress of the composite material increased with increasing the amount of pre-strain and depended on the volume fraction of the fiber and heat treatment. The smartness of the composite could be given due to the shape memory effect of the TiNi fiber, which generated compressive residual stress in the matrix material when heated after being pre-strained. Microstructural observation revealed that interfacial reactions occurred between the matrix and fiber, creating two intermetallic layers. INTRODUCTION Many studies have been performed on smart composite material reinforced by TiNi shape memory alloy (SMA) [1-3]. The design concept of this smart composite material is that as temperature increases, austenite transformation occurs from martensite phase in TiNi fiber and the fiber contracts up to the amount of tensile pre-strain applied at room temperature. This property is caused by the shape memory effect (SME) of TiNi fiber and compressive residual stress that occurs in the matrix due to this shape memory effect. As a result, this determines the strength of whole composite material [2,5,6]. Armstrong [4] reported the thermal behavior of Al6061 matrix composite reinforced by TiNi SMA fiber by using a one dimensional model. He compared the theoretical and experimental results; however, he did not focus on the fabrication process or strengthening mechanism. In addition, Hamada and co-workers [1] reported the optimal fabrication condition for TiNi/Al6061 composite material in vacuum using the hot-press method. They also reported the strengthening mechanism of composite material by comparison of theoretical and experimental methods. Due to the fabrication method, the volume fraction of fiber is limited so they restricted the volume fraction of fiber within 5.3% and the pre-strain within 2.9%. Thus, the relationship between volume fraction and pre-strain was not thoroughly examined. This was a fundamental study to develop a fabrication method of TiNi/6061 composite material into plates. In this study, an attempt was made to fabricate a composite material using hot-press method and to examine the strengthening mechanism. There have been many studie
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