选区激光熔化技术制备n型Bi_(2)Te_(2.7)Se_(0.3)热电材料工艺、取向性及性能的研究

Study on Process, Orientation and Properties of n-Type Bi_(2)Te_(2.7)Se_(0.3) Thermoelectric Materials Prepared by Selective Laser Melting Technology

采用选区激光熔化技术制备了n型Bi2Te2.7Se0.3块体样品,并探索了激光工艺参数对材料成形质量、化学组成、微结构、取向性以及热电性能的影响,最终打印出性能与区熔制备材料接近的高致密样品。结果表明,在基板上最开始的若干单层成形过程中,激光体能量密度Ev=33.3~46.67 J/mm3时,样品成形质量较好。当打印厚度超过约0.1 mm时,成形质量出现劣化,可能的原因是打印样品具有较强的取向性,导致其热导率的各向异性以及与基板具有较大的差异,因而影响了成形粉体的熔化和凝固过程。后续打印过程中采用重熔的方法,消除了因热导率变化带来的成形劣化。当打印厚度超过约1 mm时,样品成形质量再次劣化,这是由于样品的厚度已经足够大,基板对成形过程中熔池附近的温度场影响逐渐减小,而主要受打印样品的影响。考虑到打印样品热导的关系,于是进一步改善工艺,提高了激光的体能量密度,最终得到了半径为20 mm、厚度为15 mm的样品。研究了激光成形过程中元素挥发对最终样品化学组成的影响规律,通过调节粉体的初始配比最终得到了组分稳定、性能接近区熔工艺制备的块体材料。

n-type Bi2Te2.7Se0.3 bulk samples were prepared by selective laser melting technology, and the influences of laser process parameters on the material forming quality, chemical composition, microstructure, orientation and thermoelectric properties were investigated. A highly dense sample with properties closing to the zone melting material was prepared. The results show that the sample forming quality is best when the energy density of the laser volume energy density Ev=33.3-46.67 J/mm3 in the first single layer forming process on the substrate. When the printing thickness exceeds about 0.1 mm, the forming quality deteriorates. The possible reason is that the printed sample has a strong orientation, resulting in anisotropy of thermal conductivity and a large difference from the substrate, thereby, affecting the melting and the solidification process of the powder. Therefore, in the subsequent printing process, the remelting method was adopted to eliminate the formation deterioration caused by the change of the thermal conductivity. When the printing thickness exceeds about 1 mm, the sample’s forming quality deteriorates again.Because the thickness of the sample is already large enough, and the influence of the substrate on the temperature field near the molten pool during the forming process gradually reduces, and it is mainly affected by the printed sample. Taking into account the thermal conductivity of the printed sample, the process improves and the bulk energy density of the laser increases, resulting in a sample with a radius of 20 mm and a thickness of approximately 15 mm. The effects of element volatilization on the chemical composition of the final sample during laser forming were studied. By adjusting the initial ratio of the powder, the bulk material with stable composition was obtained and the performance is closed to that of the zone melting ingots.