Research On The Selective Laser Melting Preparation Mechanism And Properties Of Magnetostrictive Fe-Ga Alloys

Fe-Ga alloys show great application potential in the field of magnetically driven implants because of its ability to produce reciprocating strain under the action of magnetic field,good mechanical properties and cytocompatibility.However,single crystal Fe-Ga alloys have simple structure and limited size,while polycrystalline Fe-Ga alloys are affected by grain orientation,phase structure and other factors,and the magnetostrictive properties are difficult to meet the application requirements.In this paper,Fe₈₁Ga₁₉ polycrystalline alloys with good magnetostrictive properties were prepared by using the characteristics of high temperature gradient and nonequilibrium structure formation of selective laser melting（SLM）.The degradation performance and cytocompatibility of bulk Fe₈₁Ga₁₉ polycrystalline alloys prepared by SLM were also evaluated.The main research contents and innovations of this paper were as follows:1.The effect of SLM process parameters on the formability of Fe₈₁Ga₁₉ alloy was studied.The Fe₈₁Ga₁₉ pre-alloyed powders with good sphericity were prepared by high-pressure gas atomization method.The particle sizes of the powders were normally distributed between 10 m and70 m.Then,the Fe₈₁Ga₁₉ alloy was prepared by SLM.It was found that the molten pool gaps were mutually filled due to the opposite flow directions of molten pool between adjacent laser trajectories in zigzag scanning,thus the alloy had better surface flatness and mechanical properties.Moreover,it was found that when the laser power was too low,the powder could not be completely melted,and when the laser power was too high,alloys were prone to thermal stress concentration,which would reduce the formability of sample.Finally,the optimized SLM process parameters were obtained as follows:the laser scanning path was zigzag,the laser power was 115 W,the scanning speed was 50 mm/s,the scanning spacing was 0.05 mm and the powder spreading thickness was100μm.2.The effect of SLM process on microstructure and grain orientation of Fe₈₁Ga₁₉ alloy was studied.It was found that due to the layer-by-layer stacking forming method and the characteristics of high temperature gradient of SLM,elongated columnar grains were formed in the deposition direction by epitaxial growth.At the same time,the rapid solidification characteristics of SLM process improved the solid solubility of elements,so that Ga element was uniformly dissolved in Fe matrix,and no precipitated phase generated.In addition,the local heat transfer in SLM process promoted the grain growth toward the molten pool direction.Especially,the columnar grain of Fe₈₁Ga₁₉alloy prepared by zigzag laser scanning path was parallel to the deposition direction,with a better<100>preferred orientation.3.The effect of SLM process and element doping on the magnetostrictive properties of Fe₈₁Ga₁₉ alloy was investigated.It was found that due to the better preferred grain orientation in the 100 direction,the saturated magnetostriction of Fe₈₁Ga₁₉ polycrystalline alloy reached77.0±8.8 ppm,which was 23.9%and 25.1%higher than that of unidirectional and annular scanning,respectively.In the meantime,it was found that a small amount of Tb doping can increase the lattice constant of Fe₈₁Ga₁₉ alloy and further enhance the<100>preferred orientation of grain.The saturated magnetostriction of 0.3 at.%Tb doped alloy was increased by 46.1%to 112.5±15.2 ppm.However,excessive Tb doping would promote the formation of Tb-rich precipitated phase,resulting in the deterioration of the magnetostrictive properties of Fe₈₁Ga₁₉ alloy.4.The cytocompatibility and degradation performance of SLMed magnetostrictive Fe₈₁Ga₁₉ alloy were studied.Cell adhesion and CCK-8experiments showed that MG-63 cells adhered and extended on Fe₈₁Ga₁₉alloy,exhibiting the growth of filament-like pseudopods.Meanwhile,the cell viability of MG-63 cells increased with the extension of time,showing good cytocompatibility.The degradation rate of Fe₈₁Ga₁₉ alloy was determined to be 0.09 mm/y by immersion experiment,and the concentration of Fe ion and Ga ion in the extract was 1.96 mg/L and 0.05mg/L,respectively.It was far lower than the safe concentration of Fe（50mg/L）and Ga（14 mg/L）in human body.