مقاله انگلیسی رایگان در مورد جوشکاری لیزری آلومینیوم حافظه ای Cu-Al-Be – الزویر 2018

Shape memory alloys have the ability to undergo a reversible thermoelastic phase transformation from the parent phase austenite to a product phase martensite. This particular behaviour is responsible for two main functional properties: the superelasticity and the shape memory effect [1]. In the former one, the martensitic transformation is induced by applied thermomechanical loading of the austenitic phase, leading to important inelastic strains which are recovered upon unloading due to the reverse phase transformation to austenite. Austenite can transform into martensite during mechanical loading, leading to an inelastic deformation that can be recovered spontaneously upon unloading [2]. For the shape memory effect, the material is deformed in the martensitic state, leading to permanent inelastic strains upon unloading. These can be removed by heating up the material to the austenitic phase again: the initial shape is restored triggering the shape memory effect [3]. Cu-based shape memory alloys are considered to be possible substitutes of NiTi, the most used shape memory alloy, owing to their lower production costs and recent improvements on their mechanical properties [4,5]. There are different Cu-based systems, with the most important ones being Cu-Al-Mn [6], Cu-Al-Ni [7] and Cu-Al-Be [8]. The latter one presents, aside from the superelastic and shape memory effects, other interesting properties: strong sound, vibration and mechanical damping capability; high mechanical strength; and resistance to corrosion [9]. These alloys exhibit also a particular technological interest for low and intermediate temperature applications [8]: as a result of the introduction of small amounts of Be, the transformation temperatures decrease drastically, allowing for the occurrence of superelasticity at very low temperatures. In fact, some empirical formulae have been proposed to determine the transformation temperatures in Cu-Al-Be alloys based on their composition [10]. Thus, these alloys can be used in a wide range of temperatures, at ambient temperature or above, but they can be considered also for cryogenic applications [9]. One of the potential applications of Cu-Al-Be alloys is in seismic devices [11] as they combine several properties: high fatigue resistance, coupled with a low sensitivity for changes in the mechanical behaviour for near-ambient temperatures; they are not very sensitive to frequency changes in the 0.1 to 5 Hz regime. Moreover their properties suffer slow degradation due to the surrounding environment [12].