| High-entropy alloy is a new type of alloy which is different from the traditional alloy design concept based on the research of bulk amorphous alloy.It has some special and excellent properties.However,high-entropy alloys with single-phase FCC structure have good ductility but insufficient strength.On the other hand,high-entropy alloys with single-phase BCC structures may be very strong,but at the expense of plasticity.In recent years,with the continuous breakthrough in the research field of high-entropy alloys,researchers have extended the concept of high-entropy alloys to non-isoatomic ratios in search of alloys with better mechanical properties.In this paper,Fe100-x(Co Cr Ni Mn)x alloy is used as the basis,and Al with a relatively large atomic radius is used to replace the Mn and Ni elements in the alloy.A series of Fe100-x(Co Cr Ni Al)x(x = 19,33,40,50,60,70,80)alloy step bars(diameters: 8mm,6mm,5mm,4mm,3mm)and Fe60(Co Cr Mn)30Ni10-x Alx(x = 0,2.5,5,6,7.5,10),Fe81(Co Cr Mn)14.25Ni4.75-x Alx(x = 0,0.95,1.9,2.85,3.8,4.75)alloy rod(diameter 6mm)were prepared separately.XRD,OM,SEM,EDS,tensile property test,and hardness test were used to study the microstructure and properties of the alloy under as-cast conditions,different cooling rates,and heat treatments.A series of Fe100-x(Co Cr Ni Al)x alloy stepped rods prepared by completely replacing the Mn element with Al element have a single-phase BCC structure as a whole,and the diffraction peaks are shifted.Through calculation,the factors affecting phase stability are studied.Change law.The metallographic structure changed from equiaxed dendrite to columnar cell crystal to martensite structure.The elongation of the alloy increased,and the analysis of the tensile fracture morphology showed that the fracture transitioned from cleavage brittle fracture to a morphology containing dimples.In the course of research,it was found that Fe81(Co Cr Ni Al)19 alloy is affected by the size effect.As the size of the alloy increases,due to the combined effect of fine grain strengthening and dislocation strengthening,its mechanical properties show a trend of first decline and then increase.Then,a larger size Fe81(Co Cr Ni Al)19 alloy ingot was selected for annealing heat treatment.The research found that the annealing treatment can effectively improve the mechanical properties of Fe81(Co Cr Ni Al)19 alloy.After annealing at 900℃ for 12 hours,the alloy’s comprehensive mechanical properties are the best.When Ni was completely replaced by Al,it was found that the mechanical properties of the alloy were significantly reduced.Therefore,Fe60(Co Cr Ni Mn)40 alloy with single-phase FCC structure and Fe81(Co Cr Ni Mn)19 alloy with single-phase BCC structure were selected.Element gradually replaces Ni element.For the as-cast Fe60(Co Cr Mn)30Ni10-x Alx alloy,as the Al element gradually replaces the Ni element,the phase structure continuously changes from a single-phase FCC structure to a FCC+BCC dual-phase structure,and then to a single-phase BCC structure.Energy spectrum analysis shows that The addition of Al element in Ni10Al0 alloy changed the distribution of alloy components and made Ni more segregated on dendrites.According to the XRD pattern,it can be inferred that the Al-Ni type B2 phase was formed in the alloy.Due to the strengthening effect of the second phase,the tensile mechanical properties of the Ni5Al5 alloy increased.For the as-cast Fe81(Co Cr Mn)14.25Ni4.75-x Alx alloys,they all show a single-phase BCC structure.The mechanical properties of the alloy are strongly affected by the microalloying of Ni and Al elements.When Ni is replaced with a small amount of Al element The strength of the alloy increases,while the elongation of the alloy increases,and the hardness and strength of the alloy are approximately positively related. |
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