Rapid Preparation And Performance Of Large-area Thin-layer Of N-BiTeSe Thermoelectric Material Through 3D Printing

Thermoelectric materials have attracted much attention because of their potential to enable solid-state refrigeration and power generation.Especially in the Internet of things,5G light communication,micro thermoelectric devices have a promising application in precision solid-state refrigeration and power generation.The properties,fabrication efficiency,and good rates of thermoelectric legs are important for industrial production of thermoelectric devices.Bismuth telluride based thermoelectric materials are the most widely used room temperature thermoelectric materials commercially,which are generally prepared by zone melting method,and the bismuth telluride materials obtained by zone melting method are single crystals,and the grains have a strong preferential orientation and are very easy to cleave under the action of mechanical force,thus limiting the good quality of regional molten particles and the good quality of micro devices.Selected laser melting（SLM）,as an important way of 3D printing with fast moving Gaussian heat source,higher temperature gradient with extremely fast cooling rate,is widely used in materials synthesis,molding as well as cutting,and has shown great potential in thermoelectric materials.In this paper,Self-propagating combustion synthesis（SHS）is combined with Selected laser melting（SLM）technology to simplify the powder preparation process,reduce the overall process time,and prepare large-area n-Bi₂Te₃ thermoelectric materials by SLM technology to improve the preparation efficiency while enhancing the yield of thermoelectric particles.The contents and results of the study are as follows:（1）After sieving（400 mesh）by manual grinding,the average particle sizes of Bi,Te,and Se powders are 9μm、12μm and 7μm.And the slurry fluidity are better after mixing with alcohol,and the surface of the powder bed after spread by a duster had no obvious high difference,which can meet SLM printing.The SLM process（laser power P,scan rate v,composition of protective atmosphere）study find that the optimal SLM process for n-BiTeSe materials is as follows:6≤E_v≤24 J/mm³,protective atmosphere 85%Ar+15%H₂.（2）Neglecting the solid solution with a small amount of Se,the microzone composition as well as the structural analysis can reveal that the reaction process is that Bi first reacted with Te upon laser scanning to form the BiTecompound in the molten pool,and under continued laser scanning,Te reacted with the mesophase BiTeto form the Bi₂Te₃ phase.（3）As can be obtained by calculating the volatilization characteristics of elements in n-BiTeSe materials,the volatilization rates of non-metallic elements Te to Se are all much greater than that of metallic element Bi at the molten pool temperature（～1600 K）,and the excess Te to Se content in the raw materials can make up for the elemental volatilization in the SLM process,and their surface room temperature Seebeck coefficient average value is-174μV/K after annealing.（4）Samples of different sizes can be successfully prepared（Φ20 mm,Φ30 mm,30×60 mm²）.As visualized by homogeneity analysis,and for the powder bed,the absence of powder at the edge of the 30×60 mm² sized sample powder bed can be resolved by subsequent multiple dusting;For the electrical transport performance,by partitioning the 30×60 mm² sample and testing its surface room temperature Seebeck coefficient,the results show that the deviation of the Seebeck coefficient in the middle area of the sample is not large,and the Seebeck coefficient at the periphery and edges is lower than that in the middle area,the deviation is within 10%;In terms of anti-cutting performance,the particle integrity in the middle area of the sample after cutting is high,and the surrounding and edges are more damaged.On the whole,the 30×60 mm² size sample can cut 4000 effective particles,and the yield is80%.（5）The n-BiTeSe material prepared by SLM has strong（110）orientation and the orientation factor F is 0.89.By comparing the thermoelectric properties of the samples annealed with and without the substrate,it is found that the thermoelectric properties of the samples with the substrate annealed are better,and the ZT_max（//BD）=0.73 at 375 K.The compressive mechanical properties of the samples prepared in this way have obvious anisotropy,and the compressive strength in both directions is higher than that of the zone-melting material.The average compressive strength value parallel to the construction direction is 81 MPa,which is much higher than that of the zone-melting material（32 MPa）,the minimum complete particle size of n-BiTeSe prepared by SLM is 0.2×0.2 mm²,which is comparable to commercial hot extrusion materials in terms of cutting resistance.（6）Micro thermoelectric devices（4.7×4.9×0.88 mm³）were fabricated by SLM prepared n-BiTeSe material（n-type particles）and commercial hot extruded material（p-type particles）,with a maximum cooling temperature difference of 44℃ for solid-state cooling;For thermoelectric power generation,whenΔT is 40 K,the open-circuit voltage U_oc is 324 m V,the maximum output power P_max reaches 4.97m W,and the device power density P_d is 0.615 m W/mm².