Research On Microstructure And Mechanical Properties Of Fe-based Medium Entropy And Amorphous Alloys

The high-entropy alloys and amorphous alloys obtained by order/entropy control design subvert the traditional material design ideas and continuously make breakthroughs in performance.Among them,the non-equiatomic ratio-multiphase second-generation high-entropy alloy has greater design freedom and the cocktail effect in performance is more fully developed.At the same time,the developed mid-entropy alloy has fewer main elements and is easy to industrialize.This paper systematically studied the effect of Mn content change on the microstructure and mechanical properties of Fe-XMn-5Si-10Cr-0.9C(X=10?25,wt.%)medium-entropy alloy.The research results show that the structure of the alloy is fcc structure,and the dislocation density first increases and then decreases with the incr ease of Mn content.The dislocation density of the entropy alloy of Fe-15Mn-5Si-10Cr-0.9C is the highest,4.8×10¹⁵ m^-2,and its compressive plastic strain,fracture strength and work hardening index reach 16.8%,2381 MPa and 0.42,respectively.The fractur e shape there are a large number of small and uniform dimples and river-like patterns in the appearance.The addition of a proper amount of Mn can improve the mechanical properties of the alloy.On this basis,in this paper,the Fe-15Mn-5Si-10Cr-0.9C medium-entropy alloy is strengthened by cryogenic pre-deformation treatment.The research results show that the stacking fault energy of the alloy after cryogenic pre-deformation is significantly lower than that of room temperature.The dislocation type change s from edge dislocation to screw dislocation with the increase of the number of cryogenic cooling,and the dislocation density is higher at three times of cryogenic cooling.The room temperature is increased by an order of magnitude of 4×10¹⁶ m^-2,which makes the mechanical properties of the alloy significantly improved compared to room temperature.Its fracture strength,plastic strain and work hardening index are respectively 3002 MPa,24.6%and 0.57.The deformation mechanism of the alloy is the TWIP effect,TRIP effect and dislocation slip work together.After 3 times of cryogenic pre-deformation treatment,the cleavage steps in the fracture morphology of the alloy basically disappeared,and the number of dimples in the center and edge areas increased significantly compared with room temperature,and they were evenly and densely distributed,indicating that the cryogenic pre-deformation treatment can effectively improve the mechanical properties of alloy.Finally,this paper studies the influence of the c ontent of Cr element on the notch toughness of Fe-15Mn-5Si-XCr-0.2C(X=10?18,wt.%)alloy.The research results show that the alloy structure is composed of crystalline phase and amorphous phase,hcp phase appears after fracture,martensitic transformation is induced in the alloy system during deformation,and the matrix is toughened and plasticized by the TRIP effect.The atomic size difference(?)of the alloy system is greater than 9.9,the mixing enthalpy(?H_mix)is-14.34?-14.47 k J·mol^-1,and the mixing entropy(?S_mix)is8.73?10.06 k J·mol^-1·K^-1,which has a certain Amorphous formation ability and mixing entropy are in the range of medium entropy alloys.The fracture toughness and fracture energy of the Fe-15Mn-5Si-15Cr-0.2C specimens reached 108.466±5MPam^1/2 and 600.25 k Jm^-2,respectively,and the fracture surface showed a large number of equiaxed dimples and vein pattern areas.Appropriately increase Cr the element content is conducive to improving the tou ghness of the sample.