Study On Plastic Formability And Weldability Of NiCuCrMoTiAlNb Nickel-based Alloy

Nickel-based alloy is widely used because of their excellent properties such as high strength,good thermal properties,low thermal conductivity,corrosion resistance and good structural stability.With the rapid development of petrochemical,energy,marine,aerospace and other fields,the performance requirements of nickel-based alloy are also getting stricter.China has made considerable progress and development in the nickel-based superalloy filed,but there are still some gaps compared with developed countries.From the design and preparation of materials to the processing of materials,a great deal of practical exploration is needed.In order to adapt to the increasingly complex application environment,the alloy with single component can not meet the actual requirements.The design for composition of materials can effectively improve the performance by adding alloying elements.Material processing is the most critical approach to industrial applications,so the study of plastic forming properties and weldability has important theoretical and practical significance.In this paper,we choose NiCuCrMoTiAlNb alloy as the research object,to study the high temperature plastic deformation behavior of the material and the welding performance by a variety of experimental methods.The specific research work and results are as follows.The microstructure,chemical composition and mechanical properties of NiCuCrMoTiAlNb alloy were analyzed by means of metallographic microscope,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,energy dispersive spectrometer（EDS）and compression experiments.The results show that the organization of original as-cast alloy is typical dendritic structure,the heat-treated material reduces the dendrite structure by homogenization annealing,resulting in partial equiaxed crystal.The matrixes of as-cast and heat-treated materials were bothγ-Ni solid solution and the precipitated phase was Ni₃（AlTi）.Elements in grain distribute uniformly,and grain boundaries segregate seriously.The mechanical properties of different heat treatment process materials were analyzed,and it was found that 1100℃×3h homogenization annealing and 950℃×2h solution treatment result in good mechanical properties of alloy at room temperature and high temperature.Heat-treated materials are compressed at various temperatures and strain rates.According to the change law of true stress-strain curves,it is found that with the increase of temperature,the flow stress of the material decreases,and with the increase of deformation rate,the flow stress of the material increases.The effects of compressive deformation,deformation temperature and strain rate on the microstructure of the material and the evolution of the structure were analyzed by the metallographic picture of the compressed sample.Based on the experimental data of true stress-strain of NiCuCrMoTiAlNb Ni-based alloy under different temperatures and different compressive rates,a high-temperature constitutive equation of Ni-based alloy was established based on Arrhenius model and linear fitting method.According to the stress of different strains in the process of compression,the hot processing map was established on the basis of the dynamic material model.From the hot processing map,it can be seen that when the strain is constant,the dissipation rate decreases with the increase of strain rate,and is more prone to instability under high strain rate.As the temperature increases,the instability area decreases.By analyzing the hot processing map and taking into consideration the microstructure of the material under different deformation conditions,the optimal hot processing temperature of the nickel-based alloy is about 950℃¹000℃and the strain rate is controlled at a relatively low level.TIG（Tungsten Inert Gas Welding）was used to investigate weldability of NiCuCrMoTiAlNb nickel-based alloy,including the same metal welding and dissimilar metal welding.The influence of different welding current on microstructure and microhardness of welded joint was studied.The results show that the microstructure and hardness distribution of the same metal welded joints is relatively uniform.Nickel-titanium alloy welded joints appear a fusion zone where Cr-rich precipitates appear in a certain width when dissimilar alloys are welded,and the hardness is quite different from nickel-titanium alloy base material.When the welding current is 80A,the welded joints have finer grains,more uniform hardness distribution and better performance.