Influence of Heat Treatments on a NiTi Shape Memory Alloy Obtained Using Vacuum Induction Melting and Reprocessed by Pla
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Influence of Heat Treatments on a NiTi Shape Memory Alloy Obtained Using Vacuum Induction Melting and Reprocessed by Plasma Skull Push-Pull Jackson de Brito Simões1,2, Francisco Fernando Roberto Pereira1,3, Jorge Otubo4, Carlos José de Araújo1. 1 Universidade Federal de Campina Grande (UFCG), Campina Grande - PB, Brazil. 2 Universidade Federal Rural do Semi-Arido (UFERSA), Caraúbas – RN, Brazil. 3 University of Cambridge, Cambridge, United Kingdom. 4 Instituto Tecnológico de Aeronáutica (ITA), São José dos Campos – SP, Brazil. ABSTRACT Shape memory alloys (SMA) are metallic attractive engineering materials due to their capacity to store pre-defined shapes through a thermally induced phase transition from a solid state. This paper aims to evaluate the influence of solubilization thermal treatments on a NiTi shape memory alloy originally fabricated by vacuum induction melting and then reprocessed by plasma melting followed by injection molding (Plasma Skull Push Pull process) into different metal molds (steel, aluminum, brass and copper) in order to compare the thermal properties regarding to its raw state. The thermal treatments of solubilization were carried out at 850°C in different times (2n function, n = 0, 1, 2 and 3, in hours). The influence of solubilizing treatments in the NiTi shape memory alloy was analyzed using the following characterization techniques: Differential Scanning Calorimetry (DSC) and Electrical Resistance as a function of Temperature (ERT). The results demonstrate that the solubilization heat treatments applied on the reprocessed NiTi shape memory alloy through the plasma skull push pull process, provides important changes in the phase transformation of the material. Therefore, it was demonstrated that it is necessary to solubilize the material after melting or remelting the NiTi shape memory alloy via this process to obtain mini-actuators products with homogeneous properties. INTRODUCTION Since their discovery in 1960, NiTi shape memory alloys become the subject of numerous studies due to its response reaction when subjected to external stimuli (temperature, stress or magnetic field), providing the ability to perform mechanical work. Among all shape memory alloys, the binary NiTi systems provide the majority of commercially relevant products because they can work either as sensors and actuators at the same time [1]. Applications of shape memory alloys are related to several areas as aerospace, automotive, telecommunications, health, among others [1, 2]. Due to their unique functional properties associated with good corrosion resistance and excellent biocompatibility, there are many attempts to develop new applications. However, the complicated manufacturing and processing of these NiTi shape memory alloys place obstacles to applications [2, 3]. In recent years, ingot metallurgy processing of NiTi shape memory alloys has been discussed in great details [4]. Very different melting processes for these alloys such as Air Induction Melting (AIM), Vacuum Induction Melting (VIM), Vacuum consumable
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