Effect of VC precipitation on microstructure and properties of Fe-Ni-Co invar alloy
Adding alloying elements to enhance the mechanical properties of invar alloy usually results in a substantial increase in the expansion coefficient of it.Based on the precipitation strengthening mechanism of VC and the theory of Co element inhibition of thermal expansion of invar alloy,this study explored the effects of different C,V addi-tions on the microstructure,physical properties and thermal expansion of Fe-Ni-Co invar alloy.OM,EBSD,TEM were used to characterize and test the microstructure of alloy,using tensile electronic universal tensile testing ma-chine to test the mechanical properties of the alloy,thermal expansion tester was used to test the thermal expansion properties of the alloy.The results show that the grain size of the alloy gradually decreases,and the hardness of the microstructure increases with the increase of C and V addition,the yield strength and tensile strength reached 295Mpa and 588Mpa respectively in a medium temperature environment of 200 ℃,which is significantly improved compared with the original Invar alloy.The coefficient of thermal expansion α20-220 ℃=3.3686 × 10-6/℃ remained at a low level,which was mainly attributed to the addition of appropriate Co elements.Solution strengthening,fine grain strengthening and second phase precipitation strengthening are the main reasons for the improvement of me-chanical properties of the invar alloy,which has certain reference significance for the optimization of alloy composi-tion and improvement of comprehensive properties of new invar alloy.
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