Si和C的添加对Fe_(2.5)CoNiCu高熵合金显微组织和力学性能的影响

为了评估非金属元素(Si和C)对Fe_(2.5)CoNiCu高熵合金显微组织演变和力学性能的影响,采用真空感应熔炼法制备Fe_(2.5)CoNiCuSix(x=0.1~0.3,摩尔分数)和Fe_(2.5)CoNiCuCx(x=0.15~0.4,摩尔分数)两种系列高熵合金。结果表明,C和Si的加入显著促进BCC/FCC双相向单一FCC结构的转变,且添加C对BCC/FCC组织演变的影响更明显。Fe_(2.5)CoNiCuSi0.2高熵合金具有较高的硬度(HV439.5)和抗拉强度(868MPa),这与固溶强化和晶粒细化作用有关。随着C含量的增加,Fe_(2.5)CoNiCuCx高熵合金的硬度和强度均增加,这是碳化物的形成和固溶强化所致。这表明在高熵合金中添加非金属元素(C或Si)是提高合金强度和硬度的可行途径。

Mechanical properties and fracture mechanism of as-cast MnFeCoCuNix high-entropy alloys

MnFeCoCuNix high-entropy alloys(HEAs)with different Ni contents were fabricated by vacuum induction melting.XRD and SEM−EDS were used to analyze the phase constitution and structure,and the tensile properties of the samples were determined using a universal tensile tester.The results show that the HEAs consist of a dual-phase structure,in which FCC1 phase is rich in Fe and Co,while the FCC2 phase has high contents of Cu and Mn.As Ni content increases,the segregation of Cu decreases,accompanied by the decrease of FCC2 phase.Moreover,the tensile strength of the HEAs increases first and then decreases,and the elongation increases slightly.This is attributed to the combined effect of interface strengthening and solid solution strengthening.The in-situ stretched MnFeCoCuNi0.5 alloy shows obvious neck shrinkage during the tensile fracture process.In the initial deformation stage,the slip lines show different morphologies in the dual-phase structure.However,in the later stage,the surface slip lines become longer and denser due to the redistribution of atoms and the re-separation of the dissolved phase.

In Situ TiC/FeCrNiCu High-Entropy Alloy Matrix Composites:Reaction Mechanism,Microstructure and Mechanical Properties

In situ TiC particles-reinforced FeCrNiCu high-entropy alloy matrix composites were prepared by vacuum induction melting method.The reaction mechanisms of the mixed powder(Ti,Cu and C)were analyzed,and the mechanical properties of resultant composites were determined.Cu4Tiwere formed in the reaction of Cu and Ti when the temperature rose to 1160 K.With the temperature further increased to 1182 K,newly formed Cu4Tireacted with C to give rise to TiC particles as reinforcement agents.The apparent activation energy for these two reactions was calculated to be 578.7 kJ/mol and 1443.2 kJ/mol,respectively.The hardness,tensile yield strength and ultimate tensile strength of the 15 vol%TiC/FeCrNiCu composite are 797.3 HV,605.1 MPa and 769.2 MPa,respectively,representing an increase by 126.9%,65.9%and 36.0%as compared to the FeCrNiCu high-entropy base alloy at room temperature.However,the elongation-to-failure is reduced from 21.5 to 6.1%with the formation of TiC particles.It was revealed that Orowan mechanism,dislocation strengthening and load-bearing effect are key factors responsible for a marked increase in the hardness and strength of the high-entropy alloy matrix composites.

Microstructure and mechanical properties of in situ(TiC+SiC)/FeCrCoNi high entropy alloy matrix composites

In situ(TiC+SiC)particles(5 vol.%and 10 vol.%,respectively)-reinforced FeCrCoNi high entropy alloy matrix composites were fabricated via vacuum inductive melting method,with equal volume fractions of TiC and SiC particles.X-ray diffraction,scanning electron microscope and energy diffraction spectrum were employed to analyze the microstructure and composi-tion of the samples.The results manifested that the FeCrCoNi matrix is composed of FCC phase,and the in situ particles are homogeneously scattered in the matrix.The presence of reinforcements augmented the ultimate tensile strength from 452 to 783 MPa,and raised the yield strength from 162 to 466 MPa at room temperature,whereas the elongation to fracture was reduced from 70.6%to 28.6%.All the tensile fracture surfaces consisted of numerous tiny dimples,indicating that the composites exhibited ductile fracture.Furthermore,the enhancement of strength ascribes to a combination of thermal mis-match strengthening,load-bearing effect,grain refinement,Orowan strengthening and solid solution strengthening effect,which contribute about 58.0%,2.4%,12.3%,11.1%and 16.2%to the improvement of yield tensile strength,respectively.

Effect of vanadium content on microstructure and properties of in situ TiC reinforced V_(x)FeCoNiCu multi-principal-element alloy matrix composites

V_(x)FeCoNiCu high entropy alloy matrix composites reinforced by in situ TiC particles(10 vol.%),i.e.,V_(x)FeCoNiCu/TiC composites,were fabricated from V–Fe–Co–Ni–Cu–Ti–C system using vacuum inductive melting method.With the content of vanadium increasing,the size of TiC particles decreased gradually.Meanwhile,vanadium agglomeration occurred slightly.The reaction mechanism of the mixed powder(Fe,V,Ti and C)and the mechanical properties of obtaining V_(x)FeCoNiCu/TiC composites were studied.It was found that three reactions occurred(Fe-Ti-FeTi-Fe_(2)Ti,FeTi-Fe_(2)Ti-Fe-Ti and Ti-C-TiC)in the heating process.The apparent activation energy for these three reactions was calculated and found to be 26.4,698.3 and 1879.0 kJ/mol,respectively.At room temperature,tensile strength and elongation increased first and then decreased with the increase in vanadium content and the microhardness increased gradually.The maximum tensile strength of the composites was determined to be 666 MPa,representing a 17.7%increase over that of FeCoNiCu/TiC high entropy alloy composites.