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Boronized alloys with high surface hardness has been revealed advance in enhancing the anti-wear performance of critical mechanic components. However, its application in industrial production is greatly limited due to the poor mechanical properties with crystallographic orientated brittle borides. In the present study, we demonstrated that high ductility and high strength were achieved for the boronized AlCoCrFeNi 2.1 eutectic high entropy alloy (EHEA) with the formation of nano-sized borides. The AlCoCrFeNi 2.1 EHEA was treated with electrochemical boronizing method, and its phase formation was studied by x-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and focused ion beam-transmission electron microscope (FIB-TEM). Results show that the nano-grained of FeB, NiB and Cr 3 B 4 with size of about 135.5 nm were formed on the boronized layer with non-preferred crystallographic orientation of the phase. The surface hardness of boronized AlCoCrFeNi2.1 EHEA reached to about 18 GPa, being about 4 times higher than that of the original alloy. Further investigation by tensile testing shows that the tensile strength of boronized samples is about 1.2 GPa with a respectable ductility of about 16.04% (± 0.49) tensile ductility to failure. Meanwhile, extension test and digital image correlation (XTDIC) test shows that the boronized layer failed when the tensile ductility is about 5.1%. The disordered nano-grained in the boronized layer benefit in preventing the formation and propagation of cracks, which improved the ductility of the boronized AlCoCrFeNi 2.1 EHEAs. [Display omitted] • The nano-sized borides of FeB, NiB and Cr 3 B 4 with grain size about 135.5 nm was generated on the AlCoCrFeNi 2.1 EHEA surface. • The elongation and strength of boronized EHEA reach 16.04% and 1197 MPa, and the surface hardness reaches 21 GPa. • The fracture of the brittle boronized layer occurred at the strain of 5.1%. • The crystallographic non-oriented nano-sized borides significantly inhibition crack generation and propagation. [ABSTRACT FROM AUTHOR]

The as-cast AlCoCrFeNi 2.1 eutectic high-entropy alloy (EHEA) has high fracture strength and ductility, which displays an excellent application prospect in key structural materials. However, its low surface hardness and poor wear resistance at room temperature limit the actual applications in tribology. Here we showed the enhancement of surface strengthening and self-lubrication properties of AlCoCrFeNi 2.1 EHEA by a powder-pack boronizing treatment. SEM and XRD analysis indicate that a double affected layer with a thickness of about 42 μm was formed on the surface at 900 °C for 4 h, which were mainly consisted of Ni 2 Si and FeB. The surface hardness of the alloy was significantly increased from 396 HV to 1108 HV after the treatment. Tribological results show a remarkable self-lubrication property of the boronized EHEA. The friction coefficient of boronized EHEA under the water condition was reduced by 21%, and the corresponding wear volume was decreased by 65%. EDS and XPS analysis demonstrate the formation of silicon/boron-containing tribofilm on the wear scar, which benefits in the achievement of self-lubrication properties with friction and wear reduction under the water condition. Our research provides a general strategy with the powder-pack boronizing method to strengthen AlCoCrFeNi 2.1 EHEA and enhance self-lubrication properties, which would certainly boost its industry application. • An impressive enhancement of surface hardness was achieved after boronizing. • The affected layer showed a double-layer structure, which was mainly Ni 2 Si and FeB. • Boronized EHEA showed the remarkable self-lubrication property in water. • The formed silicon/boron lubrication film benefited in self-lubrication property. [ABSTRACT FROM AUTHOR]

Laser cladding technology was utilized to construct protective coatings on the surfaces of service materials and to study the mechanical and fretting wear properties of the coatings. The coating mainly consists of diffuse Cr 2 AlC phase, interdendritic Cr 7 C 3 phase and dendritic Cr-based solid solution. The hardness of the coating was enhanced to 690 HV, which is 3.1 times higher than the hardness of the substrate. The change in H3/Er2 values of the coating and the substrate were calculated by nanoindentation to be 0.04 and 0.024, respectively, and the anti-fretting wear properties of the coating was excellent. The statistical distribution of the Schmidt factor of the coatings is between 0.41 and 0.5, which indicates that the coatings have a high probability of initiating slip and high plastic deformation capacity. For those grains with large Schmidt factors, dislocations can be easily activated in response to applied stresses. Strength is the first element of wear resistance, and with sufficiently high strength, the plasticity enhancement can be very effective in improving the fretting damage resistance. After the fretting wear test in liquid LBE, the Cr-Al-C composite coating has a huge increase in wear resistance compared to the substrate. The wear resistance of the coating was 33 times that of the 316 stainless steel substrate at a test temperature of 450 °C [ABSTRACT FROM AUTHOR]