摘 要

19世纪20年代以来，刚铁材料始终主导军工，汽车制造，航空航天等领域。随着全球气候的日益变暖以及面临的能源枯竭问题，在环境及能耗的重压下，世界各国将环境友好作为材料选择的重要因素,热电转换技术则拥有巨大的应用潜力。所谓的热电转换技术是指，利用材料的热电效应实现热能直接转化为电能的技术。与传统内燃机不同的是，热电转化技术的能量主要依赖于固体材料内部载流子（空穴或电子）的运动。

热电效应的载体是热电材料（又称温差材料），相比于传统热机来说，热电材料具有体积小，无噪音，无振动，质量小，无磨损，寿命长，安全可靠以及环境友好等特点，能够满足人类绿色环保可持续发展的理念，因此，在环境污染以及能源危机日益严重的今天，热电材料的研究与发展具有重大的现实意义。碲化铋（Bi₂Te₃）自从1954年开始被大量研究，已经发展成最为成熟的热电材料之一，目前被广泛应用于制冷器件及低温区发电（200~400 k）。近几年来，人们开始追求产品的轻量化以及小型化 ，在微型化的过程中传统的制备工艺必须切割样品，而切割则很大可能会导致材料结构的破坏以及形状的破坏，材料的可靠性和成品率将会大大降低，并且切割过程中也会造成大量原材料的浪费，使成本进一步提高，这一系列的问题为探寻新的工艺提供了机遇。激光选区熔化技术（Selective Laser Melting，SLM）是一种增材制造手段，依靠他独有的特点，为微型碲化铋热电材料器件的制备提供了一个可行的方案。Bi₂Te₃塞贝克系数大并且它的热导率比较低，因此它的热电优值比较高，所以碲化铋是目前为止公认的最好的热电材料，碲化铋也是本次实验的主要研究体系。

本次研究以自蔓延方法制备的p型碲化铋粉末为原料，探索激光选区熔化技术可行的制备工艺参数，探究激光工艺参数对材料线、面成形质量的影响，寻找合适的工艺参数范围，为微型热电材料器件的制备提供参考。

实验结果表明，激光工艺参数对样品的成形质量有着至关重要的影响。在本实验工作条件下，我们以过300 目筛的Bi_0.5Sb_1.5Te₃ 粉末为原料，功率在5-15 W，扫描速率在50~300mm/s、铺粉厚度约0.1mm时，单道具有连续光滑的表面，且截面呈拱桥状，成形质量较高。超过这个范围，单道的连续性较差、与基板粘合不紧(能量较小)，或者整体较扁平、气化严重(能量较大)。

对于面成形来说，实验中获得较好的成形工艺为激光功率 5-10W、扫描速率 200-400mm/s、扫描间距0.05mm。当能量不在这个范围时，成形质量较差，能量过小时，粉末无法完全熔化，表面不平整：能量过大时，粉末过熔，导致样品形形变或开裂。

在多层块体制备中，其微结构上有两种典型特征样貌，一种是在扫描中心线上形成的层状晶粒结构，一种是扫描线边缘区域形成的细小近球形晶粒，通过扫描电镜观察可发现，多层样品内部无较大尺寸的裂纹，但存在孔洞等缺陷，其形成原因可能是激光能量较高，导致材料内部气化严重而形成的孔洞。

关键词:p型碲化铋，激光选区熔化（SLM），工艺参数，成形质量，热电材料器件

Abstract

Since the 1820s, the steel material always leads defense, automotive, aerospace and other fields.With the warming of the global climate and energy problems facing depletion，under the pressure of environment and energy,coutries over the world consider environmentally friendly as a important factor of the materials,The thermoelectric conversion technology has great potential.The so-called thermoelectric conversion technology refers to the use of the thermoelectric materials to achieve the effect of heat directly into electrical energy technology.What diffiernent with the traditional internal combustion engine is the thermoelectric energy conversion technology mainly relies on an internal carriers (electrons or holes) moving solid material.

The carrier of thermoelectric effect is a pyroelectric material (also known as the thermoelectric material), compared to conventional heat engine, thermoelectric materials have small size, no noise, no vibration, low quality, no wear, long life, safe, reliable and environmentally friendly features,able to meet the concept of sustainable and enviormental development,therfore,with environmental pollution and the increasingly serious energy crisis today, thermoelectric materials research and development has great practical significance.Bismuth Telluride (Bi2Te3)，which has been studied since 1954, is one of the most mature thermoelectric materials, having been widely used in refrigeration and low temperature power generation(200~400 k) at present.In recent years, more and more people prefer the miniaturization of products, but traditional cutting may leads to deformation of materials, which may reduce the reliability and yield of the material, and the cutting process will lead to the deterioration of the mechanical properties of the material, it will also lead to vast waste, resulting the increase of the cost, those series of questions provide a opportunity for finding a new processes. Selective Laser Melting (SLM) is one of the Additive Manufacturing, which provides a feasible direction for the preparation of micro Bismuth Telluride thermoelectric materials with its unique advantages .Bi2Te3 has large seebeck coefficient and low thermal conductivity,so it has relatively high figure of merit,therefore, bismuth telluride is recognized as the best by far of the thermoelectric material, bismuth telluride is the main system in this experiment.

In this research, we use the Bismuth Telluride powder which prepared by self-propagating to explore the available laser parameters in the SLM process, and study the influence of parameters on the forming quality of the material to find an available laser parameter, so that we can use a new technology to prepare micro thermoelectric materials.

Experimental results show that the laser parameters have a very important influence on the forming quality of the sample. In our condition, we use Bi_0.5Sb_1.5Te₃ as raw material, Laser power 5-~15W, Scanning rate in the range of 50mm/s to 300mm/s, powder thickness about 0.1mm, the single cladding has a good forming quality. Over this range, the single cladding has a poor continuity、cannot adhesive tight with the substrates(energy shortage), or has a flat shape and too wide(energy excess).

For forming it, the experiment obtained better extrusion process 5-10 w laser power, scan rate 200-400mm/s, scan spacing 0.05mm. When energy is not in this range, forming quality is poor, the energy after hours, powder can not be completely melted surface is not flat: energy is too big, the powder melt, resulting in sample deformation or cracking.

In the preparation of multi-layer block system, the micro structure has two kinds of typical appearance characteristics, a kind of is layered grain structure formed in the center of scan line, a is the edge area of the scanning line formed fine near spherical grains, by scanning electron microscope (SEM) observation can be found, multilayer sample is relatively large size of the crack, but there are defects such as holes. The formation may be due to the high energy laser, cause material internal gasification serious and the formation of holes.

Keywords: Bismuth Telluride, Selective Laser Melting (SLM), Process parameters, Forming quality,Micro thermoelectric materi

摘要 Ⅰ

Abstract Ⅲ