Study On Microstructure And Properties Of Eutectic High-Entropy Alloys By Spark Plasma Sintering

The discovery of high-entropy alloys（HEA）in 2004 open up a new field of metal materials,and has became a hot spot because of their unique composition and excellent properties.The newly developed eutectic high-entropy alloys（EHEAs）combine the excellent casting performance of eutectic alloys with the high strength and ductility of high-entropy alloys and has received wide attention.In this dissertation,the eutectic high-entropy bulk alloys were prepared with gas-atomized AlCoCrFeNi_2.1eutectic high entropy alloy（EHEA）powders by spark plasma sintering（SPS）,and the relationship among sintering process,microstructure,and properties were investigated.On the basis of this,C and Al elements were added to study the effects of these two elements on the microstructure,mechanical properties,high-temperature oxidation properties,corrosion resistance and wear resistance of AlCoCrFeNi_2.1EHEA.The main results are as follows:The higher sintering temperature and longer holding time,the higher relative density of the bulk AlCoCrFeNi_2.1EHEA.The increase of the sintering temperature causes the hardness,yield strength and compression ductility to increase first and then decrease.The alloy sintered at1000℃shows best comprehensive compression performance.Therefore,the optimized sintering temperature and holding time are determined to be 1000℃and 15 min,respectively.The phase composition of the obtained bulk AlCoCrFeNi_2.1EHEA were FCC phase and BCC phase.The as-prepared(AlCoCrFeNi_2.1)C_xalloys consist of FCC phase,BCC phase and carbide.The abundance of carbide increases with the increase of C content.The addition of C increases the hardness and yield strength of the alloys,but decreases the compressive ductility.The hardness of the alloys is highest with addition of 0.5 at.%C,and the alloy containing 0.3 at.%C has the best comprehensive compression properties at room temperature.In terms of the oxidation-resistance property,alloy containing 0.3 at.%C has the best high-temperature oxidation resistance at 900°C,and the alloy containing 0.1 at.%C has the best resistance to oxidation at 1000°C.They are fully antioxidant and antioxidant grades,respectively.In Na Cl and H₂SO₄solutions,the alloys containing 0.7 at.%C and 0.5 at.%C are the best corrosion resistance,respectively.While the addition of element C reduces the corrosion resistance of the alloy in Na OH solutions.the alloy containing 0.1 at.%C has the best wear resistance,with adhesive wear as the main wear mechanism.The phase composition of as-prepared(AlCoCrFeNi_2.1)Al_xalloy is FCC+BCC phase/BCC phase.The more Al content,the more BCC phase.When the Al content is 10 wt.%,a single stable BCC phase is formed.The hardness and yield strength of the alloy increase due to the addition of Al elements,while its compressive plasticity decreases.The alloy containing 6 wt.%Al has the best comprehensive compression properties.It has the best oxidation resistance at900°C and 1000°C,with both oxidation resistance levels.The alloy containing 4 wt.%Al in Na Cl solution,10 wt.%Al alloy in Na OH and H₂SO₄solutions have the best corrosion resistance,respectively.The alloy containing 6 wt.%Al has the best wear resistance,with the wear mechanism being adhesive wear.