Solidification Microstructure And Properties Of Al_xCoCrFeNi_2.1 High-Entropy Alloy Manufactured By Laser Additive Manufacturing With Coaxial Powder-feeding

The AlCoCrFeNi_2.1 eutectic high-entropy alloy with lamellar microstructure is prepared using traditional casting technique.It is recently of great interest due to its high strength and high ductility.Laser additive manufacturing with coaxial powder feeding is an advanced manufacturing technology.Its unique heat and mass transfer mode in the molten pool will have an important impact on the evolution of the solidification microstructure.Therefore,combining this new material with a new process method,this thesis uses laser 3D printing technology to prepare Al_xCoCrFeNi_2.1 high-entropy alloy.The solidification microstructures and mechanical properties have been studied through the methods of changing aluminum content and laser processing parameters.When changing the aluminum content,it was found that solidification microstructure changed.The specific performance is that the ratio of the second phase precipitation increasing.Combined with X-ray diffraction pattern analysis,the phase structure of the alloy changes from fcc to fcc+bcc,and the hardness of the sample will be higher.When the aluminum content continues to increase,the sample crackes.The eutectic AlCoCrFeNi_2.1 high-entropy alloy with better microstructure and properties is studied.Using quasi-continuous laser,the microstructure of the eutectic high-entropy alloy has a fine dendrite microstructure.When the laser beam is large,the microstructure of the prepared alloy is coarse dendrite.When the laser beam is small,the sample using the low power and fast scanning speed is the coexistence of dendrite and cell microstructure.When the scanning speed is reduced,a typical lamellar eutectic mirostructure will appear.The study finds that the lamellar eutectic microstructure will appear at a slow cooling rate.Before the heat treatment,the specimen with the non-eutectic microstructure mainly composed of dendrites was tested in the tensile test.But the elongation is poor.On the premise that the tensile strength is kept at the same level,the specimen mainly composed of fine lamellar eutectic structure has a better elongation rate.After annealing treatment,the elements in interdendritic are fully diffused,so that the total elongation is significantly improved.Using laser additive manufacturing technique to prepare AlCoCrFeNi_2.1 eutectic high-entropy alloy with fine lamellar structure,the process parameter is adjusted to high power,slow sanning speed,small laser beam and continuous wave.Compared with traditional casting technique,which needs complex processing procedures such as cold rolling and annealing,the unique advantage makes laser additive manufacturing important in high-entropy alloys.