Study On SPS Sintered Nickel Base Superalloy And High Temperature Oxidation

Nickel-based superalloys are widely used in the aerospace field,and their actual service conditions are extremely harsh,it is not only required to have excellent high temperature mechanical properties,but also to have good oxidation resistance.Generally,increasing the Cr and Al content makes the nickel-based alloy form a complete Cr2O3 or Al2O3 film in the service environment to achieve high temperature corrosion resistance,but this will affect the creep properties and high temperature strength of the material.Therefore,this article will improve the oxidation resistance of nickel-based superalloys by controlling the structure of nickel-based superalloys,rationally designing the Al content,and doping nano CeO2,so as to provide support for the development of nickel-based superalloys with excellent high temperature oxidation resistance.In this paper,Ni20Cr alloy is consolidated by controlling the sintering temperature and holding time,and the optimal sintering process of powdered nickel-based superalloys is determined to be 1200?,holding for 15 minutes,and the pressure is 40 MPa.The high temperature oxidation performance of Ni20Cr alloy sintered by SPS was studied and compared with as-cast Ni20Cr alloy.The results show that in the constant temperature oxidation experiments at 800?,850?,and 900?,the oxidation kinetics of Ni20Cr alloy prepared by both methods is parabolic,but the Ni20Cr alloy sintered by SPS has a lower oxidation rate.SPS sintered Ni20Cr alloy formed a dense single Cr2O3 film with an oxidation activation energy of 232.06 kJ,while as-cast Ni20Cr alloy formed Cr2O3,NiO,NiCr2O4 with an oxidation activation energy of 128.59 kJ.The results show that SPS sintered Ni20Cr alloy has a higher grain boundary density,which increases the effective diffusion coefficient of Cr in the alloy,promotes the formation of Cr2O3,and improves the high temperature oxidation resistance of the alloy.Adding sub-micron Al(2.5wt.%)and nano-CeO2(0.5wt.%)to Ni20Cr alloy by mechanical alloying,and comparing with Ni20Cr alloy and Ni20Cr2.5Al alloy.The results show that the addition of Al and nano-CeO2 has a significant effect on the grain refinement of Ni20Cr alloy.The average grain size is reduced from 1.98 ?m to 0.54 ?m,the grain size was refined by 72.73%.In constant temperature oxidation(950?,1000?)and cyclic oxidation(1000?)experiments,the oxidation products of Ni20Cr alloys were found to be Cr2O3 and NiCr2O4.The oxidation products of Ni20Cr2.5Al alloy are Al2O3 and NiCr2O4.In the Ni20Cr2.5Al alloy containing 0.5wt%CeO2,the oxides are single Al2O3 during the above oxidation process,the oxide film is thinner(<1 ?m)and combines well with the alloy.Through research,it was found that the fine-grained structure can promote the selective oxidation of Al,and the nano-CeO2 promoted the formation of nail-like structures under the Al2O3 film,which played a pinning role on the oxide film and improved the anti-stripping performance of the oxide film.At 1000?,Ce4+can diffuse outward along Al2O3 grain boundaries,and dynamic scgregation occurs at the columnar grain boundaries of Al2O3.On the one hand,it blocks Al3+from diffusing outward to reduce the oxidation rate;on the other hand,it can improve the creep resistance of Al2O3 films,significantly improve the oxidation resistance of the alloy.