Influence of the Reprocessing by Plasma Melting and Injection Molding on the Thermomechanical Properties of a Ni-Ti SMA
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Influence of the Reprocessing by Plasma Melting and Injection Molding on the Thermomechanical Properties of a Ni-Ti SMA Manufactured by VIM Jackson de Brito Simões1-2, Francisco Fernando Roberto Pereira1-2, Jorge Otubo3, Carlos José de Araújo1-2. 1
Universidade Federal de Campina Grande (UFCG), Campina Grande - PB, Brazil. Laboratório Multidisciplinar de Materiais e Estruturas Ativas (LaMMEA), Mechanical Engineering Depart. 3 Instituto Tecnológico de Aeronáutica (ITA), São José dos Campos – SP, Brazil. 2
ABSTRACT Shape Memory Alloys (SMA) metallic materials that change their mechanical and physical properties with temperature variation and mechanical loading, surprising engineers and researchers. In this way, one can develop thermomechanical actuators capable, for example, of generating force by blocking the shape recovery or change the natural frequency of a mechanical system by blocking resonance. The processing of these SMA are countless, each one with its specific limitation and particularity. This study aims to evaluate the influence of rapid solidification of a Ni-Ti SMA that is originally manufactured by Vacuum Induction Melting (VIM) and reprocessed by Plasma Melting (PM) followed by injection molding into different metal molds (steel, brass, aluminum and copper). The influence of such a processing is analyzed through Differential Scanning Calorimetry (DSC) and Electrical Resistance as a function of Temperature (ERT) to determine the effects on transformation temperatures. The results demonstrate that by using the copper mold one can provide greater uniformity of the material properties. Thus, there is the possibility of obtaining different kinds of SMA mini-actuators by PM injection in a copper mold and that includes different shapes and sizes that can be studied further. INTRODUCTION Shape Memory Alloys (SMA) are functional materials which can recover from being deformed when heated. These materials are challenging because they can work either as sensors and actuators at the same time [1]. NiTi-based SMA have attracted much interest for its potential use as a functional material in many engineering applications such as an active, adaptive or smart structure as well as certain biomedical application. Applications of SMAs are related to several areas as aerospace, automotive, telecommunications, health, among others [1, 2] Due to their unique properties such as corrosion resistance and excellent biocompatibility there are many attempts to develop new applications. However, the complicated manufacturing and processing of these alloys place obstacles to applications [3, 4]. The main inconvenient of NiTi alloys, besides the chemical composition control, is their extreme reactivity at melting temperatures. In order to avoid atmospheric contamination and to ensure high ingot purity, the melting process of NiTi alloys is carried out in vacuum or inert atmosphere [5]. There are different melting processing alternatives for these alloys such as Air Induction Melting (AIM), Vacuum Induction Melting (VIM), Vacuum co
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