摘 要

选择性激光熔融(SLM)作为增材制造技术的一种，具有成型速度快，自动化程度高，节省原料等优点。可用于制备复杂结构的模型件或者原件，在制备微型原器件方面具有独特的优势。热电材料作为一种能源转换材料，可以实现热能发电和电能制冷。研究发展热电材料及器件，可以缓解日趋紧张的能源压力，同时也可以替代传统的制冷方式保护我们的环境。探所使用SLM技术制备热电材料及其器件不仅拓宽了SLM技术研究范围，也为热电材料及器件的高效快速，微型化制备带来了契机。

近年来，SnTe热电材料因其特殊的电子能带结构和晶体结构而备受关注，被视为是一种很有潜力的热电材料。常温常压下，SnTe具有NaCl型面心立方结构，这为制备近球形粉体提供了可能。SnTe的相图比较简单，不存在第二相，在SLM成型过程中，有利于得到单相化合物。

本论文系统地探索了采用SLM技术制备SnTe热电材料的阶段性工作。我们首先研究SnTe粉体的制备。通过研究卧式球磨机的不同工艺参数对粉体的粒径分布和形貌的影响，优化了制粉的工艺参数。研究发现当球磨转速n =400 r/min，球磨时间t =1 h，球磨的球料比 =10时，所得粉达到了SLM技术对粉体的要求。探索了激光的功率和扫描速度对单道成型质量的影响，分析得到了单道成型的工艺窗口。在铺粉厚度d =40 m时，发现激光功率P =15-50 W和扫描速度v =60-120 mm·s^-1的窗口上，单道成型质量普遍较高。

在单道成型的基础上，研究了在不同扫描间距下成型面的质量。发现了最优扫描间距与单道成型的线宽有关，要求扫描间距h应该小于线宽度s；同时不能过分减小扫描间距，否则会致使成型面成型失败。大量试验表明，扫描间距h =0.04 mm时有一个良好成型面。当扫描间距h =0.04 mm，铺粉厚度d =40 m时，通过实验得到了良好成型面的工艺窗口，区域为P =9-10 W，v=200-300 mm·s^-1。

铺粉厚度d=40 m的面成型工艺窗口范围比较狭窄，根据熔池动力学可知，减小熔池的体积有利于提高成型的稳定性。由于设备的激光半径不能够改变，故我们决定降低铺粉厚度寄希望增大良好成型面的工艺窗口面积。调节铺粉厚度d =25 m，扫描间依旧取h =0.04 mm时，发现良好面的成型窗口面积明显增大，其范围为P =5-10 W，v=100-600 mm·s^-1，有利于提高SLM制备SnTe热电材料的稳定性。对成型面的相和成份分析发现，尽管可以得到良好的成型面，但是过大的激光扫描能量密度会导致杂相的生成，降低了表面Seebeck系数，不利于优良热电材料的制备。

接下来我们初步研究了退火对单层面的的影响，发现退火之后，扫描面上的微裂纹增加，表面成份和性能变现变差，这有待进一步研究。

关键词：SLM，热电材料，工艺窗口，单道成型，单层面成型

Abstract

Selective laser melting (SLM) as a sort of additive manufacturing technology is characterized with high speed of forming, high degree of automation, saving materials and so on. It can be used for the manufacturing of mould and work with complex structure. Also, it has a unique advantage in terms of the micro-device fabrication. Thermoelectric materials as an energy conversion material, can achieve thermal power generation and electric refrigeration. Development of thermoelectric materials and devices not only can ease the increasingly demand for energy, but also can replace the traditional cooling methods to protect our environment. Exploring the use of SLM technology to fabricate thermoelectric materials and devices not only broadens the scope of the SLM technology, but also bring an opportunity for preparation of thermoelectric materials and micro-device with fast and efficient methods.

In recent years, SnTe thermoelectric materials, due to its special electronic band structure and crystal structure, have attracted much attention. Under normal temperature and pressure, SnTe having NaCl type face-centered cubic structure, which provides the possibility for the preparation of nearly spherical powders. It is favourable to fabricate single phase compound on account that SnTe phase diagram is relatively simple without second phase.

In this paper, we have systematically explored the stage work of SnTe thermoelectric materials prepared by SLM technology. First of all, we study the preparation of SnTe Powder. By studying the regular pattern between different horizontal ball mill process parameters and particle size distribution and apparent morphology of the powder to optimize the process parameters of ball milling. Study found that when the ball milling speed n = 400 r/min, ball milling time t = 1 h, the ratio of ball mass to powder mass = 10, the obtained powder reaches the SLM technology requirements. Explore the effects of laser power and scanning speed on the quality of single-line forming. We have acquired the process domain of single-line forming process. When thickness of powder layer d =40 m, laser power P = 15-50 W and the scanning velocity v =60-120 mms^-1, the single-line forming quality is generally high.

On the basis of single-line forming, we studied the the quality of surface forming at different scanning interval. Finding the relationship between optimal scanning interval and single-line forming width. Research shows the scanning interval scanner h should be less than the single-line forming width s. A large number of experiments show that there is a good forming surface at scanning interval h =0.04 mm. When scanning interval h =0.04 mm, thickness of powder layer d = 40 m, the experiment has been a good forming surface bound for P = 9-10 W, v = 200-300 mm·s^-1.

The process domain of surface forming at thickness of powder layer d =40 m is relatively narrow. According to the melting pool of dynamics, reducing the volume of the melting pool will help improve the stability of the forming process. Since the radius of the light spot can not be changed, so we decided to reduce the thickness of powder layer hoping to increase the process domain of surface forming. By adjusting thickness of powder layer d =25 m, the scanning interval still take h =0.04 mm, and found the process domain of surface forming significantly increased finally at the range of P = 5-10 W, v = 100-600 mm·s^-1. It’s good for improving the stability to fabract SnTe thermoelectric material by means of SLM. In spite of the good forming surface parameters, the large energy density of laser scanning can lead to the formation of the hybrid phase, which reduces the surface Seebeck coefficient and is not conducive to the preparation of excellent thermoelectric materials.

Finally, we have studied the effect of annealing on the single-layer and found that the micro cracks on the scanning surface increase, the surface composition and performance of the surface becomes complex and worse, which needs further research.

Keywords：SLM, thermoelectric materials, process domain, single-line forming, single-layer forming

目 录

第1章 绪论 1