Preparation Of High Entropy Alloys And Their Microstructure And Propertieses

In the middle of 2004, the notion of high entropy alloy is formally proposed. Based on the high entropy alloy theory and traditional smelting technology, we father study the property of high entropy alloy.High entropy alloy is composed by varies elements with nearly the same molar ratio in order to form the single solid solution.The theory of high entropy come from Boltzmann's hypothesis on the relationship between entropy and system complexity, the configurational entropy change per mole,ΔSconf, during the formation of a solid solution from n elements with equimolar fractions may be calculated from the following equation:ΔSconf=-klnw=-R(1/nln1/n+1/nln1/n+…1/nln1/n)=-Rln1/n =Rlnnwhere k is Boltzmann's constant, w is the number of ways of mixing, and R is the gas constant: 8.314 J/Kmole. For example, when n is 5, theΔSconf is 1.618R, larger than that of metal fusion.We study the property of the alloys of series of AlTiNiMnBx, AlxCoNiCrFe, CuNiCrFe, TiNiMn, AlNiCuCr.In the study, we find that the crystal lattice parameters, hardness and densities increase when the content fraction of B element increases from 0.1 to 0.5 and they all can be formed into single BCC structure . Taking the sample AlTiNiMnB0.5 as an example, we find that the hardness of the sample reaches to 779HV. This series alloys have excellent thermodynamic stabilization. However, they have large brittleness. In the case of AlxCoNiCrFe series alloys, they also can be formed into single BCC solid solution structrue. The crystal lattice parameters, hardness and densities increase when the content fraction of Al element increases. Their hardness holds 300-400HV. The compress strength of AlCoNiCrFe alloy is 1454MPa.After studying the series alloys of CuNiCrFe, TiNiMn, AlNiCuCr, we find that Cu contributes to FCC, while Al and Mn contributes to BCC. Si and Zr is not in favor of forming single solid solution structure, while they are propitious to obtain complex compounds.The alloys with FCC structure have low hardness, while those with BCC structure have high hardness. Especially when mainly BCC with intermetallic compound, the alloy gain highest hardness.When the composition and element of alloys increase, the binding energies and the lattice deformations increase, and the solid solutions are enhanced. Especially the hardness achieves 820HV in the six-element alloy.