Research On In-situ Particles Reinforced Fe_xCoNiCu High Entropy Alloy Matrix Composites

Fe_xCoNiCu high entropy alloys were prepared by vacuum induction melting.The effect of Fe content on the microstructures and mechanical properties of the alloys was studied.Then Fe_2.5CoNiCu alloy was used as the matrix to prepare in-situ Ti C and Si C particles reinforced high entropy alloy matrix composites.The reaction mechanism of prefabricated blocks was analyzed,and the microstructures and mechanical properties of the composites were studied.The research on Fe_xCoNiCu high entropy alloys shows that with the increase of Fe content,the crystal structure of Fe_xCoNiCu alloy gradually transformed from a single FCC structure to a mix of FCC and BCC structure,and there was obvious Cu segregation in the inter-dendrites,and fine Fe-rich precipitates appeared in the alloys.With the increase of Fe content,the microhardness of the alloys gradually increased from 187 HV to 379 HV.The precipitated Fe-rich phase can increase the strength of the alloy,and the ultimate tensile strength first increased and then decreased,and reached a maximum value of 639 MPa when x was 2.5.Cu segregation in the alloy has a certain effect on the improvement of plasticity.When x was 2,the fracture elongation can reach 20.5%.The research on the reaction process of prefabricated blocks shows that in Ni-Ti-C prefabricated block,almost only the Ti C synthesis reaction occured,and the apparent activation energy was 2455 k J/mol.In Ni-Si-C prefabricated block,almost only the Si C synthesis reaction occured,and the apparent activation energy of the Si C reaction was 1376 k J/mol.The research on the microstructures of the composites shows that Ti C particles can be formed well in Fe_2.5CoNiCu alloy,and the addition of V and Nb elements can refine Ti C particles,but agglomeration occured when the Nb element content was high.Adding Si and C elements to Fe_2.5CoNiCu alloy can generate Si C particles.Some Si and C elements were dissolved in the matrix.Si element can be more uniformly dissolved in the matrix,and it had a certain effect of refining grains.When the content of C element was high,carbides were formed.The research on the mechanical properties of the composites shows that in Ti C/Fe_2.5CoNiCu composites,as the volume fraction of the reinforcement increased,the hardness increased,and the Ti C particles can increase the strength of the materials,but reduce the plasticity.The effect of Nb element to enhance the strength of composites was more obvious,and the ultimate tensile strength can reach 892 MPa.The V element can slightly increase the plasticity while increasing the strength.In the Si C/Fe_2.5CoNiCu composites,addition of Si and C elements can cause both strength and plasticity to increase at the same time,and the hardness also increased.The 10 vol.%Si C/Fe_2.5CoNiCu composite had a fracture elongation of 39.1%while the ultimate tensile strength reached 787 MPa.It was found that Si element can increase the strength and reduce the plasticity of the matrix alloy.The significant improvement of the plasticity of the composites was mainly the result of the action of the C element.