In situ differential thermal analysis device for evaluating high-speed phase transitions
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Thixoforming involves heating different types of alloys to the semisolid state at high heating rates and forming in die-casting machines or conventional presses. At temperatures higher than the solidus and lower than the liquidus, the mush metal behaves like a high-viscosity thixotropic material. Therefore, determining the thermodynamic behavior of the solid-to-liquid transition is paramount to control thixoforming processes. This article describes a simple, novel experimental setup based on differential thermal analysis (DTA) for analyzing the phase transitions in an alloy heated using high heating rates typical of industrial applications. A365 alloy was chosen to demonstrate the effectiveness of the method as the phase transformations for this alloy in semisolid materials (SSM) processing are well understood. Samples were heated to 750 °C using constant linear heating rates of 5, 10, 15, 20, 25, 50, 75, 100 and 125 °C min in a Norax 25 kW 8 kHz induction furnace with an Omron E5CK temperature controller. AISI 316 austenitic stainless steel was used as the inert reference. Comparison of the results of DTA using the proposed method and the results of simulation with Thermo-Calc® indicates that the proposed in situ DTA device and its method is suitable for analyzing phase transitions when high heating rates are used.
KeywordsDTA Phase diagrams A356 alloy Thermal characterization High heating rates Instrumentation
The authors would like to thank CAPES (Federal Agency for the Support and Evaluation of Postgraduate Education, Brazil) (CAPES/MES-Cuba Program, Project No. 095/2010), CNPq (National Council for Scientific and Technological Development, Brazil) (CNPq PQ Grant No. 306896-2013-3) and FAPESP (São Paulo Research Foundation) (Project No. 2015/22143-3) for providing technical and financial support. The authors are also indebted to the Faculty of Mechanical Engineering at the State University of Campinas for the practical support very kindly provided.
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