Effect of silicon addition on the microstructures, mechanical properties and helium irradiation resistance of NiCoCr-based medium-entropy alloys

• Published in: Journal of alloys and compounds 2020-12, Vol.844, p.156162, Article 156162
• Main Authors: Liu, Shaofei, Lin, Weitong, Zhao, Yilu, Chen, Da, Yeli, Guma, He, Feng, Zhao, Shijun, Kai, Ji-jung
• Format: Article
• Language: English
• Subjects: Deformation mechanism; Ductility; Grain boundaries; Hardening rate; Helium; Helium irradiation; Irradiation; Mechanical properties; Mechanical twinning; Medium entropy alloy; Medium entropy alloys; Phase decomposition; Shear modulus; Silicon; Silicon addition; Stacking fault energy; Strain hardening; Ultimate tensile strength
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.156162

A series of NiCoCrSix (x = 0, 0.1, 0.2, 0.3) medium-entropy alloys were synthesized to investigate the effect of Si addition on the microstructures, mechanical properties and helium irradiation resistance of the NiCoCr-based alloys. The microstructures and the phase evolution of these alloys were examined using electron microscopy as well as the existing models. The results show that the alloys exhibit a single face-centered-cubic structure when the Si content is in the range of 0–6.25 at.%, whereas phase decomposition occurs as the Si content further increases (∼9 at.%). Comparing with NiCoCr, NiCoCrSi0.2 exhibited improved strength without sacrificing the ductility. The yield strength and ultimate tensile strength increased from 438 to 599 MPa and 921 to 1032 MPa, respectively, whilst the ductility kept as high as ∼50%. Our analysis indicates that the increased strength is mainly ascribed to the grain boundary strengthening. The large ductility is primarily due to the low stacking fault energy and shear modulus of the NiCoCrSi0.2 alloy, which makes mechanical twinning in small grains accessible and provides a steady strain-hardening rate in a wide strain regime. Besides, the enhanced compositional complexity and local lattice distortion induced by the introduction of Si can improve the helium irradiation resistance of NiCoCr, resulting in reduced average bubble size. •Microstructure,mechanical properties and helium irradiation resistance of NiCoCrSix MEAs were investigated.•Enhanced strength was obtained in NiCoCrSi0.2 without the sacrifice of ductility.•Comparing with NiCoCr, NiCoCrSi0.2 exhibits improved helium irradiation resistance.