| Recently, the Fe-Mn alloys which undergo the y(fcc)??(hcp) martensitic transformation have attracted wide attention due to their pronounced damping capacity at the great strain amplitude. Therefore, these alloys can be widely used in automotive industry and a range of structural applications for vibration and noise control. The as-cast Fe-Mn alloys possess very high damping capacity, but the mechanical poperties are low, especially the yield strength is poor. The mechanical properties of Fe-Mn alloys will be increased after deformation, but the damping capacity will be decreased. Particularly, an Fe-17%Mn alloy possesses the highest damping capacity in the Fe-Mn binary system, but the corrosion resistance of the Fe-Mn binary alloy is poor and the yield strength is lower, which limits its application in industrial manufacture. In this paper, the addition of Cr was intended for corrosion resistance improvement; Multi-directional forging (MDF) was adopted to refine the microstructures of the Fe-17Mn-XCr alloy to improve mechanical properties and annealing treatment was used to improve damping capacity of the as-forged samples. The main contents are as follows:(1) The effect of Cr on microstructure, damping, mechanical and corrosive properties of Fe-17Mn alloy is investigated. The results show that Cr increases the stacking fault energy of Fe-Mn alloy, the volume of ?-martensite slightly decreases with the addition of Cr. The ultimate tensile strength (UTS) increases gradually with increases the Cr content, the yeild tensile strength (YTS) slightly decreases and then increases but there is no obviously changes. The corrosion resistance of Fe-17Mn-XCr alloy is better than that of C45E4 steel, and the higher content of Cr there is, the better the corrosion resistance of the alloy have. And there is no obviously changes of the damping capacity with different addition of Cr.(2) The deformation behavior of Fe-17Mn-8Cr alloy and its microstructure and mechanical properties at different MDF process is investigated. The results show that the dynamic recrystallization of Fe-17Mn-8Cr alloy initiated at more than 1100?, and the lower the strain is, the easier the dynamic recrystallization happens. The ?-martensite and y-austenite plates of Fe-17Mn-8Cr alloy are greatly refined after MDF process, and the mechanical properties are remarkably enhanced. The UTS slightly increases with increasing the times of the MDF process. The mechanical properties further enhanced with increasing the reduction of the MDF process, theYTS and elongation (El) after MDF 20% are 786MPa?537MPa and 41.7%, respectively.(3) The microstructural evolution, mechanical property and damping capacity of Fe-17Mn-8Cr alloy during MDF 20% process are investigated. The results show that after MDF process the ?-martensite and y-austenite plates are greatly refined and more uniformly distributed and?meanwhile, a high density of dislocations is introduced. MDF process can remarkably enhance the YTS of the Fe-17Mn-8Cr alloy, the YTS of the Unidirectional Forging (UDF) alloy and the MDF alloy are 416MPa and 537MPa respectively, which is 160 MPa and 281 MPa higher than that of the as-homogenized alloy. The Q-1 is gradually reduced during the MDF process, but there is still a great damping capacity. The main damping mechanism of this alloy is believed as the serious crossing of e-martensite plates and the high density of dislocations hindering the operation of the damping sources such as the interface and the stacking faults.(4) The effect of annealing treatment on the microstructure?mechanical properties and damping capacity of the MDF Fe-17Mn-6Cr alloy is investigated. The results show that the MDF process can remarkably enhance the mechanical properties of the as-homogenized Fe-17Mn-6Cr alloy; but decreased the damping capacity, the Q-1 of the as-forged alloy at the strain of 6×10-4 is only 0.021. With the increasing annealing temperature, the ?-martensite and the y-austenite plates become larger in size, and the dislocation density becomes lower due to dynamic recovery; the UTS and YTS decrease gradually due to the remarkable growth of the ?-martensite and the ?-austenite plates; the Q-1 at 6×10"4 increases gradually and reaches the maximum of 0.041 after annealing at 900?, the interaction between the crystal defects, such as vacancies-. solute atoms and dislocation, and the stacking faults plays the main role in the damping capacity of the deformation Fe-Mn alloys. The optimal balance of strength and damping capacity can be achieved after annealing at 800 ? for 1h.The UTS, YTS and El of this alloy are 746MPa,382MPa and 45.2%respectively and its Q-1 value at the strain amplitude of 6×10-4 is up to 0.037. |
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