Study On The Flowability Of Titanium Alloy Powder And The Selective Laser Melting

The laser material of the powder material is more and more widely used in the production process.The flowability of the powder material is very important to the quality of the molded parts.The fluidity of the powder material is evaluated synthetically and its influencing factors are of great significance for the selection of the powder for the laser selection.In addition,the laser selection and melting process in the process of more influence factors,in which the process parameters are extremely important factors.It is necessary to change the process parameters in the molding process and study its influence on the basic forming process of selective laser melting.In this paper,the flowability of TC4(Ti6Al4V)powders with different morphologies and grain sizes was tested.The effect of the powder samples on the fluidity was analyzed.The paper discusses the powder flow index which has great influence on the melting process of the laser selection,and provides the theoretical basis for selecting the appropriate powder material.The single-pass molding,monolithic molding,block forming and laser surface remelting were carried out using Renishaw commercial TC4 powder and AM 250 selective laser melting equipment combined with different molding parameters.The results show that the particle size and particle shape of the powder have a great influence on the flowability of the powder.The spherical powder with uniform particle size distribution has lower compressibility and flow energy,and the binding force inside the powder is smaller,it is easier to flow and the flow stability is better.This is of vital importance for the storage,transport,and flow of powder from the hopper for printing powder.The shear test better reflects the state of the powder material flowing out of the hopper,that is,under the action of gravity,the powder is subjected to a certain normal stress,and the powder undergoes shear behavior.The flow function can better characterize the yield stress of the powder and the binding strength of the powder itself.The greater the flow function value,the worse the powder particle bond,the better the fluidity of the powder.In the powder bed printing,the flowability of the powder used can be quantified by the flow function to complete the preliminary screening of the powder.In the selection of laser melting experiments,the choice of larger laser power and the appropriate point of exposure time can ensure that the fused molding is more uniform.The surface roughness Ra of the single-layer molded sample increases with the increase of the scanning distance,and the smaller the scanning distance can be obtained by selecting the smaller scanning pitch under the condition of good single-channel forming quality.The surface profile from the relative smooth into between the fused no overlap.In the premise of ensuring the quality of forming under the choice of 150?m scanning distance molding sample can improve the molding efficiency.When the energy density is too low,the density of the sample increases with the increase of the energy density when the energy density is low.When the energy density is too large,the density of the sample is reduced,and this phenomenon is increased in the multi-layer molding accumulation.The microstructures of the cross section and the longitudinal section of the specimen show that there are a large number of pre-?crystals in the sample,and the microstructures are martensite.Since the heating of the latter layer during the molding process has a cyclic heat treatment effect on the formed layer,a part of the ? + ? tissue is produced.Microhardness results show that the overall hardness of the sample is higher than that of the casting.Surface remelting treatment can significantly reduce the surface roughness of the sample,but with the increase in the number of remelting,can not eliminate the sample surface powder adhesion phenomenon.After the sandblasting treatment can remove the surface of the sample powder particles,improve the sample surface quality,but after blasting the sample surface roughness still did not reach a lower value.Surface remelting can reduce the unevenness of the surface of the specimen and the defects such as tiny holes.The surface roughness of the multilayer molded sample is worse than that of the single layer due to the different cooling rate and the forming effect.