Powder plasma arc additive manufacturing of (AlTi)2x(CoCrNi)100-2x medium-entropy alloys: Microstructure evolution and mechanical properties

In this work the effects of Al and Ti element addition on the microstructure and mechanical properties of CoCrNi medium-entropy alloys (MEAs) has been investigated. A novel (AlTi)2x(CoCrNi)100-2x MEAs was fabricated by using powder plasma arc additive manufacturing technique. The influences of Al and Ti elements on the microstructure, mechanical properties and strengthening mechanisms were analyzed by XRD, EBSD and TEM. The (AlTi)2x(CoCrNi)100-2x MEAs exhibited columnar crystal structure, but the average grain size and texture decreased continuously with increasing values of x. Moreover, tensile test results showed that (CoCrNi)90Al5Ti5 alloy possessed strength-ductility balance (yield strength, ultimate tensile strength and elongation to failure of 664 MPa, 897 MPa and 19.3%, respectively). The analysis on the strengthening mechanism showed that the solid solution strengthening effect was more dominant with increasing of the x in all alloys. (CoCrNi)94Al3Ti3 and (CoCrNi)90Al5Ti5 have similar average grain sizes, wherein the difference in mechanical properties between both the alloys can be mainly attributed to the formation of fine grain sizes. (CoCrNi)90Al5Ti5 has a small amount of dislocations, solid solution strengthening and grain boundary strengthening are the main sources of the excellent properties.