Study On Microstructure And Properties Of GH3039 Nickel-based Superalloy Block Cladding Layer With Laser Metal Wire Deposition

Additive Manufacturing(AM)is a technique for manufacturing solid parts by gradually adding materials.It can produce parts with complex shapes,which can be quickly and freely formed,and it can also complete complex parts that cannot be completed by conventional manufacturing methods.AM can be used to simplify processing,increase production efficiency,and shorten production cycle.But fabricating of large parts in manufacturing technology in China,there is a big gap.Laser metal deposition to make preparation of metal parts and micro structure evolution mechanism research is still in its infancy,so research on the basis of laser fuse to add material manufacture in large aerospace engineering,ocean engineering in our country and other key parts and components manufacturing is of great significance.In this paper,the laser metal wire deposition was conducted to prepare the as-deposited nickel-based superalloy GH3039 block.Optical microscopy(OM)and scanning electron microscopy(SEM)was used to investigate the macromorphologies and microstructure of three different orientations(cross section,side section and horizontal section)GH3039 alloy prepared by additive manufacturing,the investigation also included dimensions,macro defects grain morphology,grain distribution and size.The defect types and distribution in different regions were also studied.The types and distribution of microscopic defects in different areas were explored.Finally,hardness test was conducted with nano indentation instrument for the overall cross section of the sedimentary layer and the micro structure of typical areas.The results show that two kinds of macroscopic defects were existed in the bulk as-deposited cladding layer:"collapse" and "sticky silk".The "collapse" of the bulk as-deposited cladding layer occurs at the edge of the sedimentary layer,while the"sticky silk" is distributed irregularly.The "collapse" of the as-deposited cladding layer is due to the unstable formation of the molten pool at the edge of the as-deposited cladding layer,which is easy to be affected by airflow and vibration and flow.The flow of the liquid molting pool eventually leads to the "collapse" of the sedimentary layer.In addition,as the lap rate between the weld pool and the melting pool is not ideal during the forming process,the lap rate changes in the subsequent forming process make the laser focus deviate from the position of the outlet end of the wire material,which is also the reason for the occurrence of "collapse" and"sticking" of the as-deposited cladding layer.There are mainly two types of grains,columnar dendrites and equiaxed grains in the cladding layer.Columnar dendrites are mainly distributed at the bottom of the cladding layers,the central part is a mixture of columnar dendrites and equiaxial grains,and the top is mainly distributed with equiaxed grains.The same pattern appears in a single molting pool in the bottom,middle and top different regions of the sediment.By counting the grain size of different regions,it was found that the average width of the columnar dendrites is 18.6 ?m at the bottom region and 9.6 ?m at the top region.The average grain size of the equiaxial crystals is the smallest at the bottom region and the largest at the top region,with 14.5 ?m and 17.2 ?m,respectively.This result is mainly related to heat dissipation conditions and temperature gradients in different regions.In addition,the defect types mainly include interbedded interlaminar gaps,microscopic cracks and pores.Overlap between as-deposited cladding layers of gap width in the middle of the bottom sediments,with the top three areas,at the bottom of the lap joint gap width,the largest of 176 ?m,and the middle and top is relatively small,60 and 76 ?m,respectively,the main is metallurgical combination between as-deposited cladding layers is insufficient,cooling speed too fast in the process of forming and deposition in the process of rapid cooling process of thermal stress and residual tensile stress within the larger cause.The hardness value of the top of the sedimentary layer is relatively high,while the hardness value of grains of different shapes in different regions of the middle and bottom of the sedimentary layer is not significantly different.It can be attributed to insufficient metallurgical bonding between the sedimentary layers,and also thermal stress generated by the rapid cooling process during the deposition process and large internal residual stress.In this paper,the microstructure,defects and properties of the bulk as-deposited cladding layer are studied on macroscopic and microscopic scales,which lays a foundation for the additive manufacturing of laser fuse and is of great guiding significance for the later process design and optimization.It has important guiding significance for the later process design and optimization,and also provides a certain basic research theory for the preparation of high-performance large metal parts by additive manufacturing in China.