p型碲化铋基热电材料的制备及力学性能研究
发布时间：2018-07-20 11:23
【摘要】：近年来,环境污染与能源短缺等问题日益突出,严重制约着人类生存及社会发展,因此发展清洁能源和新能源技术成为目前国际社会关注的重点。其中,热电转换技术作为一种环境友好型新能源技术,能利用热电材料的Seebeck效应和Peltier效应实现热能和电能的直接相互转换。Bi2Te3基化合物是目前发展最成熟、应用最广泛的一类热电材料,在热电制冷和低温热电发电领域表现出极大的潜力。目前,商业上主要采用区熔法(ZM)批量制备n型和p型Bi2Te3基化合物,其最大热电优值ZT可达1.0左右,但区熔材料具有高度择优取向、力学性能差,导致其成品率低、加工缺陷多、使用过程中易破坏。此外,Bi2Te3体系应用于热电发电时会经历大量且长期的热循环及振动应力,因此改善区熔Bi2Te3基材料的力学性能和机械加工性对于提高器件的长期稳定性和可靠性、拓展其应用领域具有重要意义。本论文以p型Bi0.5Sb1.5Te3化合物为研究对象,针对其商业化区熔棒材的热电性能较低和力学性能较差等问题,采用熔体旋甩结合等离子活化烧结(MS-PAS)技术同时优化材料的热电性能和力学性能。系统研究MS工艺参数(包括单次样品制备量、腔体气压、铜辊转速)对材料相组成、微结构、热电性能和力学性能的影响规律。与ZM材料对比,深入分析MS-PAS样品的断裂机理。通过疲劳实验和热稳定性研究,模拟材料在实际服役条件下的状态,探索MS-PAS样品中疲劳裂纹扩展及缺陷结构演变规律。本论文的主要研究内容和研究结果如下:以p型Bi0.5Sb1.5Te3区熔棒材为初始原料,系统研究了MS工艺参数对薄带相组成、微结构、产率及块体材料热电性能的影响规律。结果表明:改变MS工艺参数(单次样品制备量、腔体气压、铜辊转速)不影响薄带的相组成,所有样品均为Bi0.5Sb1.5Te3单相。薄带的自由面和接触面分别表现为典型的枝晶、纳米晶结构,随着铜辊转速增加,接触面上的纳米晶逐渐细化;PAS烧结后的块体材料没有明显取向,晶粒显著细化,晶界处含有大量尺寸约为50 nm的富Sb第二相。其中,铜辊转速为10 m/s的样品因具有多尺度结构,能散射更宽频段的声子,导致样品的晶格热导率大幅降低,其最大ZT值在340 K达到1.22,相比ZM样品提高近40%。系统研究了铜辊转速对材料静态力学性能的影响规律,结合FESEM微结构表征,分析了MS-PAS样品的断裂机理和增韧机理。ZM样品具有明显择优取向,层间以较弱的范德瓦尔斯键结合,导致材料易发生解理,力学性能较差。采用MS-PAS技术能显著改善ZM材料的力学性能和机械加工性,这主要是由于MS-PAS技术细化了材料晶粒,相比ZM样品,其维氏硬度Hv和断裂韧性KIC分别提高约50%和26-40%,弯曲强度和压缩强度分别提高约6倍和8倍。静态力学性能破坏机制研究表明,MS-PAS技术引入了多尺度结构和纳米结构,使材料在服役过程中出现裂纹偏转、裂纹桥联和晶粒拔出等效应,消耗了裂纹扩展能量,从而大幅提高了材料的力学性能,这对碲化铋基材料的商业化应用具有重要意义。以热电性能和力学性能均表现优异的样品(即铜辊转速为10 m/s样品,MS10)为研究对象,系统研究了其压缩疲劳实验,确定其应力-寿命曲线(S-N曲线),探索了材料的疲劳裂纹扩展及微结构演变规律。结果表明:随着应力水平的提高,MS10样品的疲劳寿命逐渐降低,其中60%应力水平下材料的疲劳寿命可达9.0×105次。MS10样品的疲劳断口观察到典型的疲劳条带和疲劳裂纹,所有疲劳样品中均观察到大量位错、晶格畸变等缺陷结构,其浓度随应力水平提高显著增大,且在晶界及纳米颗粒附近容易产生位错塞积。阐明了ZM和MS-PAS材料的高温力学性能及断裂机理。随着温度升高,所有样品的弯曲强度均先升高后降低,在373 K具有最大值。这主要是因为:一方面由于晶粒间的热膨胀系数不匹配产生微裂纹,促使导致断裂的主裂纹分岔,使其扩展路径曲折,提高了材料的强度。另一方面高温环境下晶界结合强度降低,导致裂纹易沿晶界扩展。473 K下ZM和MS-PAS样品的弯曲强度和压缩强度均出现显著降低,其中MS10样品在473 K的弯曲强度和压缩强度相比室温下分别降低约15%和25%。通过长时间退火系统研究了ZM和MS-PAS材料的热电性能和力学性能的稳定性,结果表明:473 K退火1周基本不改变材料的相组成和微结构,ZM和MS10样品的热电性能和力学性能均表现出优异的稳定性。然而MS10样品在573 K退火1周后,室温载流子浓度仅为7×1018 cm-3,相比未退火样品降低约60%,导致退火样品的室温电导率大幅降低,Seebeck系数升高,室温下约为300?VK-1,最终MS10样品在573 K退火后的功率因子仅为2.2×10-3 Wm-1K-2,最大ZT值在室温约为0.9。由此说明,MS-PAS样品在473 K以下表现出非常优异的热稳定性。
[Abstract]:In recent years, the problems of environmental pollution and energy shortage have become increasingly prominent, which seriously restrict the survival and social development of human beings. Therefore, the development of clean energy and new energy technology has become the focus of the international community. As a new environment friendly new energy technology, the thermoelectric conversion technology can make use of the Seebeck effect and Peltier of thermoelectric materials. The direct mutual conversion of.Bi2Te3 based compounds with the effect of thermal energy and energy is the most mature and widely used kind of thermoelectric materials, showing great potential in the field of thermoelectric refrigeration and low temperature thermoelectric power generation. At present, the commercial use of zone melting (ZM) is used to batch production of N and P type Bi2Te3 based compounds, and their maximum thermoelectric properties The value of ZT can reach about 1, but the zone melting material has high preferred orientation and poor mechanical properties, which leads to low yield, many machining defects and easy destruction in the process of use. In addition, the application of Bi2Te3 system to thermoelectric power will experience a lot of heat cycle and vibration stress for a long time. Therefore, the mechanical properties and mechanical processing of the Bi2Te3 base material are improved. It is of great significance to improve the long-term stability and reliability of the device and expand its application field. In this paper, the P Bi0.5Sb1.5Te3 compound is used as the research object. In view of the low thermoelectric performance and poor mechanical properties of the commercial zone melting bar, the melt spinning and closing plasma activated sintering (MS-PAS) technology is used simultaneously. The thermoelectric properties and mechanical properties of the material. A systematic study of the influence of MS process parameters (including single sample preparation, cavity pressure, copper roll speed) on the phase composition, microstructure, thermoelectric properties and mechanical properties of the material. Compared with the ZM material, the fracture mechanism of MS-PAS samples was deeply analyzed. In the condition of actual service conditions, the fatigue crack propagation and defect structure evolution law in MS-PAS samples are explored. The main contents and results of this paper are as follows: P type Bi0.5Sb1.5Te3 zone melt rod is used as the initial raw material to systematically study the formation, microstructure, yield and thermoelectric properties of MS process parameters for thin band phase. The results show that the change of MS process parameters (single sample preparation, cavity pressure, copper roll speed) does not affect the phase composition of the thin strip, and all samples are Bi0.5Sb1.5Te3 single-phase. The free surface and contact surface of the thin strip are typical dendrites and nanocrystalline structure, with the increase of the speed of the copper roll, the nanocrystals on the contact surface are gradually refined. The bulk material after PAS sintering has no obvious orientation and grain refinement, and the grain boundary contains a large number of rich Sb secondary phases with a large size of about 50 nm. Among them, the sample of 10 m/s of the rotational speed of copper roll can scatter the phonon of the wider band, resulting in a large reduction in the thermal conductivity of the lattice, and the maximum ZT value of 340 K to 1.22, compared to ZM. The influence of copper roll speed on the static mechanical properties of the material was studied by the near 40%. system. The fracture mechanism and toughening mechanism of MS-PAS samples were analyzed with the FESEM microstructural characterization. The.ZM samples had obvious preferred orientation. The weak Van Der Waals bond was used in the interlayer, and the lead material was easily cleavage and the mechanical properties were poor. MS -PAS technology can significantly improve the mechanical properties and machinability of ZM materials. This is mainly due to the refinement of the grain size of the material by MS-PAS technology. Compared with the ZM sample, the hardness of Vivtorinox and the fracture toughness KIC are increased by about 50% and 26-40% respectively, and the bending strength and compressive strength are increased by about 6 times and 8 times respectively. The static mechanical properties failure mechanism studies show MS-PA S technology introduces the multi-scale structure and nanostructure, which makes the crack deflection, crack bridging and grain pulling out in the service process, which consumes the crack propagation energy, thus greatly improves the mechanical properties of the material, which is of great significance to the commercial application of bismuth telluride material. The present excellent samples (that is, copper roll speed 10 m/s sample, MS10) as the research object, the compression fatigue experiment was studied systematically, and its stress life curve (S-N curve) was determined. The fatigue crack propagation and microstructure evolution of the material were explored. The results showed that the fatigue life of MS10 samples decreased gradually with the increase of stress level, of which 60% The fatigue life of the material at the stress level can reach the fatigue fracture of 9 x 105.MS10 samples. The typical fatigue strip and fatigue crack are observed. In all the fatigue samples, a large number of dislocation, lattice distortion and other defect structures are observed. The concentration increases significantly with the stress level, and the dislocation plug is easily produced near the grain boundary and nanoparticles. The high temperature mechanical properties and fracture mechanism of ZM and MS-PAS materials were clarified. With the increase of temperature, the bending strength of all the samples increased first and then decreased, and the maximum value at 373 K. This was mainly due to the fact that the thermal expansion coefficient between the grains was mismatched to produce the micro cracks, which could lead to the breakout of the main crack and the path of expansion. On the other hand, the strength of the material is improved. On the other hand, the bonding strength of grain boundary is reduced in high temperature environment. The bending strength and compressive strength of ZM and MS-PAS samples are significantly reduced under the grain boundary expansion.473 K. The bending strength and compressive strength of MS10 samples at 473 K are reduced by about 15% at room temperature and by 25%.. The thermal and mechanical properties of ZM and MS-PAS materials are studied by the annealing system. The results show that the phase composition and microstructure of the materials are basically unchanged at 473 K annealing for 1 weeks. The thermoelectric properties and mechanical properties of the samples of ZM and MS10 show excellent stability. However, the room temperature carrier concentration is only at room temperature after 1 weeks of annealing at 573 K. 7 x 1018 cm-3, compared with unannealed samples by about 60%, resulting in a significant reduction in the room temperature conductivity of the annealed samples, the increase of Seebeck coefficient and about 300? VK-1 at room temperature. The power factor of the final MS10 sample after 573 K annealing is only 2.2 x 10-3 Wm-1K-2, the maximum ZT value is 0.9. in chamber temperature, and the MS-PAS sample is very good below 473 K. Different thermal stability.
【学位授予单位】：武汉理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB34
本文编号：2133357
[Abstract]:In recent years, the problems of environmental pollution and energy shortage have become increasingly prominent, which seriously restrict the survival and social development of human beings. Therefore, the development of clean energy and new energy technology has become the focus of the international community. As a new environment friendly new energy technology, the thermoelectric conversion technology can make use of the Seebeck effect and Peltier of thermoelectric materials. The direct mutual conversion of.Bi2Te3 based compounds with the effect of thermal energy and energy is the most mature and widely used kind of thermoelectric materials, showing great potential in the field of thermoelectric refrigeration and low temperature thermoelectric power generation. At present, the commercial use of zone melting (ZM) is used to batch production of N and P type Bi2Te3 based compounds, and their maximum thermoelectric properties The value of ZT can reach about 1, but the zone melting material has high preferred orientation and poor mechanical properties, which leads to low yield, many machining defects and easy destruction in the process of use. In addition, the application of Bi2Te3 system to thermoelectric power will experience a lot of heat cycle and vibration stress for a long time. Therefore, the mechanical properties and mechanical processing of the Bi2Te3 base material are improved. It is of great significance to improve the long-term stability and reliability of the device and expand its application field. In this paper, the P Bi0.5Sb1.5Te3 compound is used as the research object. In view of the low thermoelectric performance and poor mechanical properties of the commercial zone melting bar, the melt spinning and closing plasma activated sintering (MS-PAS) technology is used simultaneously. The thermoelectric properties and mechanical properties of the material. A systematic study of the influence of MS process parameters (including single sample preparation, cavity pressure, copper roll speed) on the phase composition, microstructure, thermoelectric properties and mechanical properties of the material. Compared with the ZM material, the fracture mechanism of MS-PAS samples was deeply analyzed. In the condition of actual service conditions, the fatigue crack propagation and defect structure evolution law in MS-PAS samples are explored. The main contents and results of this paper are as follows: P type Bi0.5Sb1.5Te3 zone melt rod is used as the initial raw material to systematically study the formation, microstructure, yield and thermoelectric properties of MS process parameters for thin band phase. The results show that the change of MS process parameters (single sample preparation, cavity pressure, copper roll speed) does not affect the phase composition of the thin strip, and all samples are Bi0.5Sb1.5Te3 single-phase. The free surface and contact surface of the thin strip are typical dendrites and nanocrystalline structure, with the increase of the speed of the copper roll, the nanocrystals on the contact surface are gradually refined. The bulk material after PAS sintering has no obvious orientation and grain refinement, and the grain boundary contains a large number of rich Sb secondary phases with a large size of about 50 nm. Among them, the sample of 10 m/s of the rotational speed of copper roll can scatter the phonon of the wider band, resulting in a large reduction in the thermal conductivity of the lattice, and the maximum ZT value of 340 K to 1.22, compared to ZM. The influence of copper roll speed on the static mechanical properties of the material was studied by the near 40%. system. The fracture mechanism and toughening mechanism of MS-PAS samples were analyzed with the FESEM microstructural characterization. The.ZM samples had obvious preferred orientation. The weak Van Der Waals bond was used in the interlayer, and the lead material was easily cleavage and the mechanical properties were poor. MS -PAS technology can significantly improve the mechanical properties and machinability of ZM materials. This is mainly due to the refinement of the grain size of the material by MS-PAS technology. Compared with the ZM sample, the hardness of Vivtorinox and the fracture toughness KIC are increased by about 50% and 26-40% respectively, and the bending strength and compressive strength are increased by about 6 times and 8 times respectively. The static mechanical properties failure mechanism studies show MS-PA S technology introduces the multi-scale structure and nanostructure, which makes the crack deflection, crack bridging and grain pulling out in the service process, which consumes the crack propagation energy, thus greatly improves the mechanical properties of the material, which is of great significance to the commercial application of bismuth telluride material. The present excellent samples (that is, copper roll speed 10 m/s sample, MS10) as the research object, the compression fatigue experiment was studied systematically, and its stress life curve (S-N curve) was determined. The fatigue crack propagation and microstructure evolution of the material were explored. The results showed that the fatigue life of MS10 samples decreased gradually with the increase of stress level, of which 60% The fatigue life of the material at the stress level can reach the fatigue fracture of 9 x 105.MS10 samples. The typical fatigue strip and fatigue crack are observed. In all the fatigue samples, a large number of dislocation, lattice distortion and other defect structures are observed. The concentration increases significantly with the stress level, and the dislocation plug is easily produced near the grain boundary and nanoparticles. The high temperature mechanical properties and fracture mechanism of ZM and MS-PAS materials were clarified. With the increase of temperature, the bending strength of all the samples increased first and then decreased, and the maximum value at 373 K. This was mainly due to the fact that the thermal expansion coefficient between the grains was mismatched to produce the micro cracks, which could lead to the breakout of the main crack and the path of expansion. On the other hand, the strength of the material is improved. On the other hand, the bonding strength of grain boundary is reduced in high temperature environment. The bending strength and compressive strength of ZM and MS-PAS samples are significantly reduced under the grain boundary expansion.473 K. The bending strength and compressive strength of MS10 samples at 473 K are reduced by about 15% at room temperature and by 25%.. The thermal and mechanical properties of ZM and MS-PAS materials are studied by the annealing system. The results show that the phase composition and microstructure of the materials are basically unchanged at 473 K annealing for 1 weeks. The thermoelectric properties and mechanical properties of the samples of ZM and MS10 show excellent stability. However, the room temperature carrier concentration is only at room temperature after 1 weeks of annealing at 573 K. 7 x 1018 cm-3, compared with unannealed samples by about 60%, resulting in a significant reduction in the room temperature conductivity of the annealed samples, the increase of Seebeck coefficient and about 300? VK-1 at room temperature. The power factor of the final MS10 sample after 573 K annealing is only 2.2 x 10-3 Wm-1K-2, the maximum ZT value is 0.9. in chamber temperature, and the MS-PAS sample is very good below 473 K. Different thermal stability.
【学位授予单位】：武汉理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB34
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