Research On Microstructure And Properties Of CoCrFeNiTi_x High Entropy Alloys By Spark Plasma Sintering

High entropy alloys are generally defined as having five or more metal elements,having simple solid solution in alloys at an equimolar or approximately equimolar ratio. Different types of elements improve the internal chaos of multi-component alloy, while increasing the mixing entropy of system, this is called high entropy effect. High entropic effects contribute to element mixed to form a solid solution with a simple lattice structure, accompanied with a small part of the compound phase.As the performance of alloy improved, there are the solid solution strengthening,second phase strengthening and fine-grained strengthening to improve the overall properties of alloy. So most of high entropy alloy have a high strength, high hardness,wear resistance, corrosion resistance, anti-oxidation properties, good thermal stability,high temperature oxidation, softening, corrosion, impact strength, good fatigue and creep properties and other fine features. The above performance makes high-entropy alloy to have a good potential development and broad prospects.In this work, CoCrFeNiTi high entropy alloys with designed ratio of selection of Co?Cr?Fe?Ni?Ti were synthesized by mechanical alloying and spark plasma sintering. Phase structures and microstructures of alloys were investigated by using OM, XRD, SEM and EDS. Meanwhile, the Vickers hardness, compressive strength and fracture morphology of the alloys were also tested.Studies showed that the particle size of the CoCrFeNiTi high entropy alloy powder obtained by mechanical alloying milling at 10 h kept uniform, and the particle diameter of this powder was about 20 ?m. And the microstructure of CoCrFeNiTi_x high entropy alloy prepared by SPS possessed reticular structures, and formed a simple FCC and BCC lattice structure, also accompanied by precipitation of intermetallic compounds. When Ti content was much higher, a small amount ofLaves phase was precipitated. The Vickers hardness of alloys firstly increased with content of Ti, and then showed a decreasing trend after the first increase. When the Ti content reached to 1.0, the Vickers hardness reached to the maximum value of 670 HV. The Vickers hardness of CoCrFeNi Ti high entropy alloys firstly increased with sintering temperature increasing, and then showed a decreasing trend after the first increase. The process of highest Vickers hardness values was at 10 h milling time and sintered at 1150 ?, the maximum was 745 HV. During compression experiments,milling for 15 h and sintering at 1150 ?, the maximum compressive strength of alloy was 676 MPa, belonging brittle fracture.