| High-entropy alloys, first published at 2004, cause great research attention about multi-principal-element alloys. High-entropy alloys refer to those contain at least five major elements (n≥5), and atomic percentage of each major element is set in the range of 5 to 35 %. High-entropy alloys break through the traditional alloy design frame work which was on the base of one major alloy element. And we can optimize the design of alloy composition to obtain an exceptional combination of high-strength, high hardness, high temperature creep resistance, high temperature oxidation resistance and corrosion resistance.In this paper, the phase formation law and the relationship between microstructure and mechanical properties, physical properties of multi-principal component alloy were studied. On the base of multi-principal component alloy phase formation law, this paper have successfully developed multi-principal-element intermetallic alloy and multi-principal-element alloy matrix composites by equal atomic ratio, multi-principal-element design concept.Up to now, the phase constitute of multi-principal-element alloys is not clear. Researchers simply calibrate the XRD result as the face-centered cubic or body-centered cubic solid solution. By the combination of X-ray diffraction, high-resolution spectroscopy microscopy and high-resolution transmission electron microscopy analysis, this paper accurately identified the phase composition of AlCrFeCoNiCu are NiAl intermetallic compound phase, (α-Fe, Cr) solid solution and Cu-rich phase. The results clearly show that the AlCrFeCoNiCu multi-principal-element alloy is not BCC solid solution alloy. By the criterion of Gibbs free energyΔG =ΔH ? TΔS, disordered solid solution of AlCrFeCoNiCu alloy is unstable at room temperature. The alloy system with intermetallic is more stable at room temperature. When the mixing enthalpy between the elements of multi-principal component alloy close to zero, the system is easy to form multi-principal solid solution structure. Experimental results show that the alloy composed of Cr,Fe,Co,Ni,Mn transition group elements can form solid solution structure. If the alloy system contain early transition group elements, late transition group elements and main group metal elements, the effect of mixing entropy is not sufficient to overcome the effect of enthalpy of formation of compounds to the decrease of Gibbs free energy.The compressive yield strength of CrFeCoNiCu is 331MPa. While the compressive yield strength of AlCrFeCoNiCu is 1303MPa. This is because of the nanoscale NiAl and (α-Fe, Cr) two-phase modulation structure, not just because of solution strength effect of Al atom like previous studies pointed. In addition, as-cast AlCrFeCoNiCu and CrFeCoNiCu have different magnetic properties: multi-principal component alloy CrFeCoNiCu is paramagnetic, while AlCrFeCoNiCu shows semi-ferromagnetic propertiy. The saturation magnetization of AlCrFeCoNiCu alloy is about 40 emu/g, and its coercivity is 28Oe.In this paper, the effect of Mn,Ti,V the on microstructure and mechanical properties to AlCrFeCoNiCu alloy were studied. The alloy is also dendrite morphology when adding V, and the yield strength, hardness and damping properties will enhance; When adding eutectic type Ti,the dendrite structure becomes a two-phase eutectic structure. The addition of Ti induced the rise of hardness and the decrease of plasticity; The results show that adding Mn will form long-strip Cr-rich phase, and the mechanical properties also decrease. Adding Mn, Ti, V integrately obtain the highest compressive strength and hardness. Further more, the damping properties of AlCrFeCoNiCuMnTiV alloy is yield 0.01 when the strain is 2×10-4. Thus AlCrFeCoNiCuMnTiV belongs to damping alloy. Inside the grain of AlCrFeCoNiCuMnTiV, nanoscale ordered phase and disordered phase were observed. Even 9 principal-element alloy, it can not form single phase solid solution alloy.Base on the study of AlCrFeCoNiCu alloy, dual phase intermetallics were developed by the design concept of multi- principal-element alloys. AlCrFeNi alloy is eutectic alloy of NiAl/(α-Fe, Cr). The room temperature compression yield strength, compression strength and compression rates are 1180MPa, 2162MPa and 40% respectively. The microstructure of AlCrFeCoNi alloy is nano-(α-Fe, Cr) phase distribute on the order NiAl matrix. The yield strength, compressive strength and compression rates are 1250 MPa, 2004 MPa and 33% respectively. Compared with AlCrFeCoNiCu alloy and NiAl alloy, the above two multi-principal-element alloys have excellent mechanical properties. To furtherly enhance the mechanical properties of multiple principal component alloys, in-situ TiC ceramic particle-reinforced multi-principal-element alloys matrix composites were first successfully prepared by "pre-self-propagating and casting" process. In the AlCrFeCoNiCu-10vol.%TiC composite, the spherical particles of TiC are distributed uniformly in matrix of multi-principal-element alloy, the size of TiC is about tens of microns. The hardness of composite is 552HV, which is 10% more than the matrix alloy. |
PDF Full Text Request