Microstructure And Properties Of Novel Ni-base Superalloy Containing Co Made By Additive Manufacturing

It's vital to develop the complex structure and high temperature bearing capacity of casing for improving the overall performance of aeroengine and gas turbine.It is difficult to prepare the casing with traditional technology as the casing structure becomes more complex and refined.Additive manufacturing,as a promising new technology for casing fabrication,can make complex structure lightweight.For now,the materials of casing have low temperature bearing capacity,therefore,in this research,a new type of Ni-based superalloy has been studied,and the influence of Co on the microstructure and properties has been investigated.The main conclusions are as follows.(1)Scanning path and process parameters are very important for the forming quality of samples.Controlling the energy input by adjusting the laser power and scanning speed can efficiently inhibit the generation of cracks in the samples.(2)The results show that columnar crystalline structure with directional solidification characteristics can be attained during the additive manufacturing.The loss of elements during additive manufacturing will lead high Ti/Al ratio.Additionally,Ti is more preferentially segregated to the interdendritic region making the content of Ti in the interdendritic region rather high,leading ?' phase transforming to ? phase which is more stable at high temperatures.It can also be observed that 5 Co alloy has much more ? precipitates than 23 Co alloy,illustrating that Co can inhibit the precipitation of ? phase.Additionally,the morphologies of the?' precipitate are different attributed to the different ?' compositions and the differences in lattice mismatch between ?' and ? in the two alloys,the coarsened ?'precipitates in 5Co alloy are almost spherical,while the coarsened ?' precipitates are nearly cuboidal in 23Co alloy.(3)In the temperature regime from room temperature to 800?,tensile tests of additive manufacturing 5 Co and 23 Co alloys were carried out,what's more,and the strength of the cast&wrought alloys was also exhibited for comparison.The test results revealed that,in the tested temperature regime,the yield strength of alloys made by two different manufacturing are similar.Additive manufacturing alloys have lower ultimate strength as well as elongation when tested from room temperature to 500?.It shows the characteristic of the cleavage-like feature on the fracture surfaces of the samples.While,when tested at 750? and 800?,alloys made by additive manufacturing have higher ultimate strength and elongation.And the fracture surfaces with apparent dimples indicate ductile deformation occurred.In order to reveal the failure mechanism of the alloys,observations of the deformed alloys reveal that stacking fault and deformation microtwins are more likely to occur in 23 Co alloy,which has a higher ultimate strength and ductility.(4)There are slight serrations on the true stress and true strain curve of additive manufacturing 5Co and 23Co alloys,illustrating that PLC phenomenon happened during the process of tensile deformation.The decreasing of stacking fault energy caused by the increasing of Co content will lead the temperature range of PLC occurrence move higher.With the increasing temperature or decreasing of strain rate,the serrations change from type A to B to C.The additive manufacturing 5Co and 23 Co alloys exhibit normal PLC effect when tested at high temperature or low strain rate and inverse DSA effects when tested at low temperature or high strain rate.However,compared with cast&wrought alloys,the PLC phenomenon of additive manufacturing 5 Co and 23Co alloys are not as obvious as cast&wrought alloys by comparison,and the values of average stress decrement of cast&wrought alloys are almost ten times of alloys made by additive manufacturing.