Kinetics of martensitic transformation induced by a tensile stress pulse |
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| Affiliation: | 1. Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai 400085, India;2. Materials Processing & Corrosion Engineering Division, Bhabha Atomic Research Centre, Mumbai 400085, India;1. INEGI – Institute of Science and Innovation in Mechanical and Industrial Engineering, Rua Dr. Roberto Frias, 400, 4200-465 Porto, Portugal;2. Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal;1. Osmaniye Korkut Ata University, Science and Letters Faculty, Chemistry Department, 80000 Osmaniye, Turkey;2. Osmaniye Korkut Ata University Engineering Faculty Energy Systems Engineering Department, 80000 Osmaniye, Turkey;3. Çukurova University, Science and Letters Faculty, Chemistry Department, 01330 Adana, Turkey;1. City University of Hong Kong Shenzhen Research Institute, Shenzhen, Guangdong 518057, China;2. Center for Advanced Structural Materials (CASM) and Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong Special Administrative Region;3. Department of Chemical and Materials Engineering, University of Alberta, Edmonton T6G 1H9, Canada;4. Department of Engineering Mechanics, SVL, Xi’an Jiaotong University, Xi’an 710049, China;1. Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen, 361005, China;2. Institute of Pattern Recognition and Intelligent System, Department of Automation, Xiamen University, Xiamen, 361005, China;1. Bialystok University of Technology, Faculty of Mechanical Engineering, ul. Wiejska 45C, 15-351 Bialystok, Poland;2. Air Force Institute of Technology, Division of Aircraft Engines, ul. Ks. Bolesława 6, 01-494 Warsaw, Poland;3. Bialystok University of Technology, Faculty of Electrical Engineering, ul. Wiejska 45D, 15-351 Bialystok, Poland |
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| Abstract: | The kinetics of martensitic transformation induced by a tensile stress pulse (generated by the reflection of a compressive shock wave at a free surface) in time durations in the microsecond range, were studied in an Fe-32wt%Ni-0.035wt%C alloy. The tensile hydrostatic component of stress interacts with the dilatational strain (~0.04) of the martensitic transformation and increases the Ms temperature. Shock waves were produced by normal impact of a projectile on a target in a one-stage gas gun. Impact experiments were conducted by varying either the temperature (−10 to −50°C), or pulse duration (0.22−1.76 μs) at a constant pressure. The martensitic transformation, normally considered to be athermal in Fe-Ni-C alloys, exhibits an isothermal nature in the microsecond regime. The fraction transformed increases with decrease in temperature at a constant pulse duration, and increase in pulse duration at a constant temperature. The mean volume of the lenticular martensite was found to be constant throughout the progress of the transformation, consistent with the autocatalytic spreading of clusters. The activation energies for γ→α' transformation in the Fe-32wt%Ni-0.035wt%C alloy, calculated with a modified version of Pati and Cohen's kinetic equation Acta metall. 17, 189 (1969)], range from 38,000 J/mol at −10°C to 25,000 J/mol at −60°C. The activation energies are linearly related to the total driving force (chemical free energy change + mechanical work due to the transformation). The activation volume for the transformation was calculated and found to be equal to approximately 60 atoms (0.7nm3). This indicates that the martensitic nucleation in this alloy, and under the imposed stress conditions, is interface-mobility controlled. |
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