Microstructure And Mechanical Properties Of Oxide Dispersion Strengthened Nickel-based Superalloys By Laser Additive Manufacturing

Nickel-based powder superalloys are extensively utilized in hot-end components,such as aviation engines,owing to their exceptional performance at high temperatures.The stability of precipitated phases（γ?）determines both the service life and the service temperature.However,the service temperature ofγ?phase-strengthened Ni-based superalloys can only be maintained at approximately 1000°C.Simultaneously,the presence of large-sized and complex nickel-based superalloy components introduces new challenges to the traditional powder superalloy forming processes:hot isostatic pressing,hot extrusion,and isothermal forging.By incorporating the advantages of laser additive manufacturing,the introduction of a nano-scale oxide dispersion-strengthened（ODS）phase,which exhibits high stability above 1000°C,is expected to enhance the service temperature of nickel-based superalloy components with large and complex structures.The main research content of this article is summarized as follows:（1）This study aims to solve the problem of selective laser melting（SLM）ODS nickel-based superalloy.On the one hand,the optimization effects of different experimental design methods on the mechanical properties of SLM ODS nickel-based superalloy were studied.The laser power,scanning speed,and hatch spacing process parameters for optimizing tensile strength were obtained using the Taguchi method and response surface methodology.Experimental results were verified using a prediction model.It was found that the optimal parameter combination of the Taguchi and response surface methods can achieve better tensile strength.On the other hand,the effect of yttrium on the microstructure and high temperature tensile properties of SLM ODS nickel-based superalloy was studied.Comparing the tensile stress-strain curves,microstructure characteristics,and fracture morphology of samples with and without yttrium at different temperatures,it was found that adding yttrium can form a flatted melt pool and columnar dendritic structure oriented along the<001>direction.There are high density dislocations and Y₂O₃ oxides,resulting in better high temperature tensile properties of SLM samples with yttrium addition.Analyzing the microstructure and fracture morphology after high temperature tensile,it was found that the interaction between oxides and dislocations at grain boundaries can maintain dislocations and increase their annihilation temperature.These results indicate that the excellent performance of SLM samples with yttrium addition mainly stems from the tenacity nest and serpentine sliding generated by oxides and dislocations,as well as their impede on the expansion of microvoids.（2）For laser metal deposited（LMD）ODS nickel-based superalloy,on the one hand,the impact of single/multi-track on the microstructure and performance optimization is studied.The Taguchi method,principal component analysis,grayscale correlation analysis,and response surface methodology were used to optimize power,scanning speed,and powder feed rate to improve the dilution rate,wetting angle,powder efficiency,and hardness of a single-track.A predictive model was established to verify the experimental results.In the single-track deposition,thermocapillary convection drives the movement of bubbles,leading to the aggregation of surface pores along the edge of the track.By comparing multi-track with different overlapping ratios,it was found that multi-track with a 60%overlapping ratio can significantly reduce cracks.On the other hand,the influence of precipitation on the microstructure and high temperature mechanical properties of LMD ODS nickel-based superalloy was also studied.Research has found that the microstructure includes columnar grain to equiaxed grain and Cr-rich shell/Y-Al-O core oxides.When comparing LMD alloy without oxide,and hot extruded ODS alloy after hot compressed deformation,it was found that the LMD ODS nickel-based superalloy has excellent high temperature mechanical properties due to the strong<001>oriented grains and high density oxides.（3）For laser additive manufacturingγ?and dispersoid cooperative strengthening（γ?+ODS）nickel-based superalloy,on the one hand,the issue is focused on the preparation of mechanically alloyed powders suitable for laser additive manufacturing,and the experimental design optimizes the preparation process with multiple objectives.Design a small package powder hot compaction method,combined with machine learning to optimize process parameters with the goals of flowability of ball milling powder,porosity,and hardness of the hot compacting alloy,establish a prediction model and verify experimental results,and use SLM to prepareγ?+ODS nickel-based superalloy.On the other hand,a multioutput classification method is used to classify the defects that appear in SLM samples,search for suitable processing windows from a wide range of SLM process parameter space,and establish multidimensional process maps to prepare low defect samples.In addition,analyze the microstructure and mechanical properties of SLMγ?+ODS nickel-based superalloys.The results indicate bimodalγ?and Y-Al-O nanoparticles in the microstructure.These precipitates can effectively weaken texture and inhibit cracks as well as recrystallization.The main strength of the alloy is due to weak anisotropic grains and the interaction between high density dislocations and precipitates.