Anisotropy study of the microstructure and properties of AlCoCrFeNi2.1 eutectic high entropy alloy additively manufactured by selective laser melting

The AlCoCrFeNi2.1 eutectic high-entropy alloy(EHEA) was prepared by selective laser melting(SLM), focusing on the anisotropy of microstructure and mechanical performance. The AlCoCrFeNi2.1 EHEA printed by SLM has face-centered cubic(FCC) and body-centered cubic(BCC)/B2 phases, and the FCC phase accumulates at the boundary of the molten pool. With the increase in volumetric energy density(VED), the content of the FCC phase parallel to the surface in the direction of the building increases from 30.9% to 41%. The X–Z plane mainly produces columnar crystals along the temperature gradient, while a large number of equiaxed crystals are produced in the X–Y direction. When the volume energy density is 157 k J/mol(VED 157), the average grain size is 1.33 μm for BCC and 1.14 μm for FCC, which is significantly smaller than other preparation methods. Due to defect distribution and size, the microhardness of the X–Y plane is generally higher than that of the X–Z plane, with maximum hardnesses of 660 HV and 655 HV, respectively, which is much higher than those of traditionally manufactured counterparts.The compression performance of SLM process AlCoCrFeNi2.1 EHEAs shows maximum yield strength of 1567 MPa, and the ultimate compressive strength can reach 3276 MPa.

Surface modification of plasma nitriding on AlxCoCrFeNi high-entropy alloys

Plasma nitriding is successfully employed in treating AlxCoCrFeNi high-entropy alloys(HEAs)with finelydivided Al content(i.e.,x values in molar ratio,x=0.1-0.8)to develop wear-resistant structural materials.Nitridation greatly removes the Al from the matrix that completely deplete the Ni-Al enriched phase,forming nanoscaled nitrides(AIN and CrN)precipitations near the surface.Nitriding promotes the hardness of present alloys with values widely ranging from 276 HV to 722 HV.Interestingly,the higher content the Al,the smaller thickness the nitrides layer,but the higher hardness due to the increased amount of hard nitrides phases and volume fraction of BCC phase.Significantly,plasma nitriding considerably improves the wear re sistance of AlxCoCrFeNi HEAs by 4-18 times.

Unique Duplex Microstructure and Porosity Effect on Mechanical Properties of AlCoCrFeNi_(2.1) Eutectic High-Entropy Alloys Processed by Selective Laser Melting

Selective laser melting(SLM)was performed on AlCoCrFeNi_(2.1) eutectic high-entropy alloys(EHEAs),and the unique duplex microstructure and porosity were investigated as well as the negative effect on mechanical properties.SLM printed AlCoCrFeNi_(2.1) EHEAs is composed of face-centered cubic and BCC/B2 phases,and the surface texture of samples perpendicular to and parallel to the building direction is different.From the bottom of the molten pool to the inside,the structure changes from dendrites to columnar crystals and then to cellular crystals,the distribution of elements in and around the molten pool is uniform,and there is no element segregation.The surface hardness of as-printed AlCoCrFeNi_(2.1) EHEAs is higher than that of as-cast ones due to the grain refinement strengthening,and there is anisotropy in different surface hardness,the highest hardness is 580 HV(X–Y plane)and 560 HV(X–Z plane).The reduction of bearing area and tip stress concentration caused by pores have adverse effects on the tensile strength and elongation of the alloy,the ultimate tensile strength increased from 1060 to 1289 MPa.