Investigation On Microstructure And Mechanical Properties Of Inconel 625 Fabricated By CMT Wire Arc Additive Manufacturing

Inconel 625 alloy has superior mechanical properties,high oxidation resistance and corrosion resistance,therefore it is considered as one of the key materials for manufacturing high temperature parts of aerospace engines.Cold Metal Transfer Wire Arc Additive Manufacturing,compared with other additive manufacturing technologies,has the advantages of low cost,high efficiency and large flexibility for depositing large parts,and is one of the most promising technologies for manufacturing Inconel 625 alloy with superior performance at low cost and high efficiency.In this paper,single layer welds and multi-layer thin-walls of Inconel 625 were produced by CMT-WAAM technology.The effects of processing parameters on single deposited layer formation were investigated.Furthermore,the typical characteristics of microstructure,texture and mechanical properties of multi-layer thin wall were characterized to reveal the effects of processing parameters on the microstructure and mechanical properties.The main research results are as follows:(1)The influence of process parameters on single-pass deposited layer formation of Inconel625 alloy during additive manufacturing was identified.First of all,the deposited layer width and height are linearly related to the Linear Energy Density(LED).With increasing LED,the deposited layer width obviously increases,while the deposited layer height slightly increases.When 175 < LED ≤ 382 J/mm,the deposited layer surface spreads evenly and smoothly.Secondly,with the increase of wire feeding speed or the decrease of traveling speed,the deposited layer width and height both gradually increase.(2)The microstructures of deposited layers in the multi-layer thin wall are mainly characterized by a varied microstructure from planar/cellular crystals to dendrites(planar/cellular crystals→cellular dendrites→dendrites)with increasing the distance from the interface between deposited layer.The temperature gradient G(G gradually decreases from the bottom to the top of the melt pool)and solidification speed R(R gradually increases from the bottom to the top of the melt pool)at various locations in the melt pool of each deposited layer were analyzed,and G and R were brought into the supercooling criterion and the columnar-toequiaxed transition model,which were used to rationalize the mechanisms responsible for the microstructural evolution from the bottom to top of the melt pool.(3)Inconel 625 multi-layer thin wall has a strong <001> texture along the Build Direction(BD).The growth axis of the grains coincides with the preferred growth direction <001> and the direction of the temperature gradient,and coarse columnar grains tend to traverse the layer boundary,mainly because the heat of deposition dissipates through the substrate along the opposite direction of BD,which provides favorable conditions for the growth of coarse columnar grains.In addition,the increase of wire feeding speed(decrease of traveling speed)leads to the increase of linear energy density,which in turn leads to the decrease of cooling speed of deposited layer,and thus the size of columnar crystals increases gradually.Moreover,in the deposition process,as the linear energy density increases,the region satisfying the recrystallization condition at the layer boundary becomes large,and the number of recrystallized small grains at the layer boundary increases,resulting in weakened texture intensity along the BD direction.(4)The microhardness of Inconel 625 multi-layers thin-walled shows a decreasing trend from bottom to top.Tensile tests along the Travel Direction(TD)indicates that the yield strength and ultimate tensile strength of the samples taken at the bottom are higher than those at the top,and the strengths of samples in BD direction are in between.Nevertheless,the uniform elongation of the sample tensiled in BD direction is significantly higher than that in TD direction.Furthermore,with increasing the wire feeding speed,the BD strength of the thin-walled sample is slightly increased,which is mainly due to the increase in the amounts of interlayer recrystallized small grains.In contrast,the strength along TD direction decreases slightly accompanied with a slow increase on the uniform elongation,which can be ascribed to the coarsened grains with increasing wire feeding speed.With the increase of the traveling speed,the strength along BD and TD directions samples increases slightly,and the uniform elongation does not change significantly.