Simultaneous-Hammer-Forging-Assisted Laser Direct Energy Deposition Of 316L Stainless Steel

Plastic-deformation-assisted method has positive effect on regulating microstructure and mechanical properties of additive manufacturing metal samples.However,when fabricating weakly rigid metal samples by laser directed energy deposition（LDED）,there are great limitations in the applicability and process flexibility of the commonly used rolling deformation auxiliary methods,which needs to be further improved.In order to realize the effective application of the plastic deformation control method in LDED metal sample additive manufacturing process,a synchronous hammer forging-assisted LDED additive manufacturing device suitable for weakly rigid samples was developed in this paper.Using 316L stainless steel metal powder as the material,the macroscopic morphology,microstructure and mechanical properties of metal thin-walled samples fabricated by LDED and synchronous-hammer-forging assisted LDED are compared,and the effect of the addition of synchronous-hammer-forging on the microstructure and mechanical properties of LDED samples are discussed.The hammer forging temperature and hammer forging force are important parameters in the synchronous-hammer-forging-assisted LDED process.By adjusting the hammer position to change the hammer forging temperature,interlayer cold deformation,synchronous warm deformation,synchronous thermal deformation and synchronous melting deformation are prepared to assist LDED 316L stainless steel metal samples.By adjusting the input voltage to change the hammer forging force,316L stainless steel metal samples are fabricated by synchronous melting deformation under different hammer forging forces.The effects of hammer forging temperature and hammer forging force on the microstructure and mechanical properties of fabricated metal samples are revealed.The main research contents and conclusions of this paper are as follows:（1）Self-built synchronous-hammer-forging-assisted LDED system,consisting of hammering unit,control unit and measurement unit.Measurement of synchronous-hammer-forging-assisted LDED parameters using hammer forging temperature and hammer forging force measurement units.As the hammering voltage（hammering force）increases,the length of the straight section at the top of the synchronous hammer forging-assisted LDED sample gradually increases,the height of the deposited layer keeps decreasing,the width keeps increasing,and the surface roughness is improved.The large plastic deformation of 21%of the single-layer deposition material can be achieved with a small hammering force of 55 N.（2）The macroscopic morphology,microstructure and mechanical properties of LDED and synchronous-hammer-forging-assisted LDED 316L samples are compared.The three phases present in the LDED and synchronous hammer forging-assisted LDED 316L metal samples are basal austenite,striated ferrite,and spherical silicon oxides due to oxidation.Under the action of plastic deformation and mechanical vibration,the isotropy and refinement of grains and anisotropy of synchronous hammer forging-assisted LDED 316L samples decreased.Due to the combined effect of grain refinement and dislocation enhancement,the yield strength,ultimate tensile strength and hardness of synchronous hammer forging-assisted LDED samples reached 494±19 MPa,677±7 MPa and 243±10 HV_0.2,respectively,which are 41%,10%and 22%higher than LDED samples.（3）Synchronous-hammer-forging-assisted LDED 316L stainless steel metal samples are prepared at different hammer forging temperatures and hammer forging forces.The different hammer forging process assisted LDED 316L samples can be formed stably and achieved grain refinement and anisotropy reduction.With the increase of hammer forging temperature and hammer forging force,the microhardness of samples tends to increase.The microhardness of the synchronous fusion deformation sample reached 262±4 HV_0.2,which is 32%higher than that of LDED 316L sample.The yield strength and ultimate tensile strength of the samples increased and then decreased with the increase of hammering temperature due to grain refinement and dislocation enhancement,and the tensile strength in the synchronous thermal deformation region reached the maximum.Under the same hammering temperature,the yield strength and ultimate tensile strength of the samples increased with the increase of hammering force.The elongation of the samples prepared under different processes is good up to the level of conventional castings and forgings.