Effect Of Laser Power On The Structure And Mechanical Properties Of Additively Manufactured GH3039 Alloy

Additive manufacturing technology is one of the most important developments in manufacturing in this century,used to make parts with uniquely complex geometries and superior functionality that are virtually impossible to achieve using traditional manufacturing techniques.Although the underlying technology has been in development for decades,it is only in the last decade that the technology has matured to a level where functional parts can be manufactured efficiently.Additive manufacturing not only means that complex geometries can be achieved without additional cost,but also geometries for which no viable manufacturing technology previously existed.However,the development of additive manufacturing technology is largely constrained by the inappropriate selection of process parameters that cause deformation and other defects in the prepared parts,leading to a shortened component life and greatly affecting the mechanical properties of the parts.Therefore,the investigation of the forming mechanism and influence law of additive manufacturing technology can help the promotion of this technology.Laser power,as one of the important process parameters of additive manufacturing technology,has an extremely important relationship to the quality of the product.In this paper,the single-layer and multi-layer deposited layers of GH3039 high-temperature alloy were prepared by adjusting the laser power,and the deposited layers were characterized by optical microscope,scanning electron microscope,energy spectrometer,universal testing machine and other test equipment,and the microstructure and mechanical properties of the deposited layers were compared,and the influence of laser power on the structure and mechanical properties of GH3039 alloy for additive manufacturing was comprehensively analyzed.The mechanism of laser power on the defects of the deposited layer is revealed,and the mechanism of laser power on the microstructure of the deposited layer and the mechanism of microstructure on the mechanical properties is also revealed.Some of the obtained research results can provide theoretical basis for additive manufacturing technology.The details of the research are as follows.(1)The bottom of the single-pass multilayer deposited layer is mainly distributed with columnar crystals,the middle is a mixture of columnar and equiaxed crystals,and the top is distributed with a large number of equiaxed crystals.There are obvious interfaces between single-pass multi-layers and layers,and the defect type mainly distributed at the interface is crack,and the cracks are mainly distributed at the top and bottom of the interface where the grain morphology is different;when the grain morphology at the top and bottom of the interface is the same,the possibility of cracks is small.When the laser energy input is not appropriate,the top layer of the deposited layer has two problems: inadequate melting of the filament or collapse of the melt pool,respectively.(2)Six major defect types,namely,inclusions,rough surfaces,large-angle grain boundary cracks,porosity,thermal cracks,and interlayer cracks,were observed in the multi-layer deposited layers,all of which were related to improper energy input.Improper laser energy input will lead to uneven temperature distribution,and when the temperature distribution in different areas is not uniform,the solidification rate is not consistent,which will lead to different forms of microstructure,and under the action of thermal stress,defects will be generated.The deposited layer formed by laser power reduction has a large reduction of defects at the top,middle and bottom,and the defect morphology also changes dramatically,from flat and long cracks to short and round holes.However,the surface of the samples prepared by laser power reduction was much rougher.(3)There is a certain regularity in the grain distribution of the multilayer deposited layers: the top of the melt pool is dominated by equiaxed crystals,the bottom of the melt pool is dominated by columnar crystals,and the middle region of the melt pool mostly exists in the form of columnar crystals toward equiaxed crystals.The effect of grain refinement can be achieved by using laser power reduction.As a result,the columnar crystals in different areas are converted to equiaxial crystals,the proportion of columnar crystals will decrease and the proportion of equiaxial crystals will increase overall.After the laser power reduction,the defects in the deposited layer are reduced as a whole;secondly,the heat input is controlled to reduce the temperature gradient and increase the solidification speed,which makes the grain refinement.The interfacial bonding strength,deposited layer microhardness and yield strength in different directions of the deposited layer are all improved to different degrees by laser power reduction.This paper shows that adjusting the laser power can reduce defects to some extent,promote grain refinement,improve the interfacial bonding strength and increase the strength of the deposited layer,and provide a new idea to solve the problems of thermal accumulation effect,remelting and collapse in additive manufacturing,which has positive significance for producing high performance GH3039 alloy additive manufacturing parts.