| In this thesis,the effects of Mn content and pre-deformation on the microstructure and properties of Fe-Mn damping alloy were studied by means of Formastor-FII automatic phase transformation analyzer,electron backscatter diffraction,transmission electron microscopy,X-ray diffractometer and dynamic thermome-chanical analyzer.The research on Fe-17Mn,Fe-18Mn and Fe-19Mn alloys showed that the M_s(the martensite start temperature),A_s(the austenite start temperatue)and A_f(the austenite finish temperature)of Fe-Mn damping alloy decreased with the increase of Mn content.The M_s of Fe-17Mn was 157?,and it decreased to 143?when the Mn content increased to 19%.Besides,the stacking fault energy increased with the increase of Mn content in Fe-Mn alloy.And the prior austenite grain size decreased,the?-martensitic content increased,and the lath size of?-martensite decreased.The change of microstructure resulted in great increase of the damping source in the Fe-Mn alloy,so the damping property of Fe-Mn alloy increaseed with Mn content increasing.In addition,the mechanical properties test results showed that the yield strength and tensile strength increased with the increase of Mn content,while the toughness and plasticity decreased.The tensile strength of Fe-19Mn alloy was the highest,reaching 755 MPa.The effect of 5%,10%and 15%pre-deformation on Fe-19Mn alloy was studied.A TRIP effect occured during the pre-deformation due to the low stacking fault energy of this alloy.The content of?-martensite in the Fe-19Mn alloy first increased then decreased with increasing the deformation amount,while the content of?'-martensite gradually increased.When the deformation was small,?-austenite to?-martensite transformation was dominative,accompany with a partial of?-martensite to?'-martensite;when the deformation exceeded 5%,?-martensite to?'-martensite transformation became dominative,and a partial of?-austenite to?-martensite.Meanwhile,as the pre-deformation increased,the size of?-martensite in the alloy increased.Besides,due to the nucleation of?'-martensite mainly at the?-martensitic boundaries,the?/?phase interface and the small-angle grain boundary of single?-martensitic,the size of?'-martensite also increased.As a consequence,the damping property of the alloy was improved with increasing the pre-deformation amount for small amplitude-tests(<25?m);while for large amplitude-tests(>25?m)the damping performance reduced with pre-deformation increasing.The best damping performance was obtained after 5%pre-deformation.The tan?could reach a maximum value of0.046,which was about 20%higher than that of the non-pre-deformed alloy. |
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