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 cooling rate upon the microstructure and mechanical properties of in-situ TiC reinforced high entropy alloy CoCrFeNi

Three types of in-situ TiC(5 vol%,10 vol%and 15 vol%)reinforced high entropy alloy CoCrFeNi matrix composites were produced by vacuum induction smelting.The effect of two extreme cooling conditions(i.e.,slow cooling in fu rnace and rapid cooling in copper crucible)upon the microstructure and mechanical properties was examined.In the case of slow cooling in the furnace,TiC was found to form mostly along the grain boundaries for the 5 vol%samples.With the increase of TiC reinforcements,fibrous TiC appeared and extended into the matrix,leading to an increase in hardness.The ultimate tensile strength of the composites shows a marked variation with increasing TiC content;that is,425.6 MPa(matrix),372.8 MPa(5 vol%),550.4 MPa(10 vol%)and 334.3 MPa(15 vol%),while the elongation-to-failure(i.e.,ductility)decreases.The fracture pattern was found to transit from the ductile to cleavage fracture,as the TiC content increased.When the samples cooled rapidly in copper crucible,the TiC particles formed both along the grain boundaries and within the grains.With the increase of TiC volume fraction,both the hardness and ultimate tensile strength of the resulting composites improved steadily while the elongation-to-failure declined.Therefore,the fast cooling can be used to drastically improve the strength of in-situ TiC reinforced CoCrFeNi.For example,for the 15 vol%TiC/CoCrFeNi composite cooled in the copper crucible,the hardness and ultimate tensile strength can reach as high as 595 HV and 941.7 MPa,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.