Microstructure and tensile behavior of solution treated Fe-24Mn-6Si-9Cr-6Ni alloy
In order to reveal the evolution mechanism of microstructure and mechanical properties of Fe-24Mn-6Si-9Cr-6Ni iron-based shape memory alloy with solution temperature,the alloys were firstly solution treated at 950,1 050,and 1 100℃respectively.Subsequently,the microstructure was characterized by using metallurgical micro-scope,X-ray diffractometer,scanning electron microscope and transmission electron microscope.The mechanical properties were investigated using tensile tests at room temperature.The experimental results show a significant increase in austenite grain size with increasing solution temperature,along with an increase in lamella length of ther-mally induced ε martensite and twin size.The solution treated alloy is mainly composed of γ austenite and thermally induced ε martensite.When the solution temperature was increased to 1 100℃,α' martensite appeared in the alloy,which is a novel phenomenon.TEM analyses confirmed that α' martensite can form at the intersection of thermally induced ε martensite.Tensile tests showed that the alloys solution treated at 950℃had the highest yield and tensile strengths of 350 MPa and 805 MPa,respectively,with an elongation of about 50%.When the solution temperature was increased to 1 050℃,the strength decreased due to the increase in grain size,but the elongation can reach more than 70%.With a further increase in solution temperature,the strength and elongation of the alloy decreased,but the elongation was still higher than 60%.The work hardening rate of the alloy decreased significantly at the beginning of plastic deformation and gradually reached a stable value as the strain continued to increase.The work hardening rate decreased with increasing solution temperature at the same plastic strain.The Hollomon equation was used to fit the stress-strain relationship,and it was found that the work hardening exponent increased with the solution temperature when the plastic strain was higher than 0.1.
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