p型碲化鉍基熱電材料的制備及力學(xué)性能研究
發(fā)布時間：2018-07-20 11:23
【摘要】：近年來,環(huán)境污染與能源短缺等問題日益突出,嚴(yán)重制約著人類生存及社會發(fā)展,因此發(fā)展清潔能源和新能源技術(shù)成為目前國際社會關(guān)注的重點。其中,熱電轉(zhuǎn)換技術(shù)作為一種環(huán)境友好型新能源技術(shù),能利用熱電材料的Seebeck效應(yīng)和Peltier效應(yīng)實現(xiàn)熱能和電能的直接相互轉(zhuǎn)換。Bi2Te3基化合物是目前發(fā)展最成熟、應(yīng)用最廣泛的一類熱電材料,在熱電制冷和低溫?zé)犭姲l(fā)電領(lǐng)域表現(xiàn)出極大的潛力。目前,商業(yè)上主要采用區(qū)熔法(ZM)批量制備n型和p型Bi2Te3基化合物,其最大熱電優(yōu)值ZT可達(dá)1.0左右,但區(qū)熔材料具有高度擇優(yōu)取向、力學(xué)性能差,導(dǎo)致其成品率低、加工缺陷多、使用過程中易破壞。此外,Bi2Te3體系應(yīng)用于熱電發(fā)電時會經(jīng)歷大量且長期的熱循環(huán)及振動應(yīng)力,因此改善區(qū)熔Bi2Te3基材料的力學(xué)性能和機械加工性對于提高器件的長期穩(wěn)定性和可靠性、拓展其應(yīng)用領(lǐng)域具有重要意義。本論文以p型Bi0.5Sb1.5Te3化合物為研究對象,針對其商業(yè)化區(qū)熔棒材的熱電性能較低和力學(xué)性能較差等問題,采用熔體旋甩結(jié)合等離子活化燒結(jié)(MS-PAS)技術(shù)同時優(yōu)化材料的熱電性能和力學(xué)性能。系統(tǒng)研究MS工藝參數(shù)(包括單次樣品制備量、腔體氣壓、銅輥轉(zhuǎn)速)對材料相組成、微結(jié)構(gòu)、熱電性能和力學(xué)性能的影響規(guī)律。與ZM材料對比,深入分析MS-PAS樣品的斷裂機理。通過疲勞實驗和熱穩(wěn)定性研究,模擬材料在實際服役條件下的狀態(tài),探索MS-PAS樣品中疲勞裂紋擴展及缺陷結(jié)構(gòu)演變規(guī)律。本論文的主要研究內(nèi)容和研究結(jié)果如下:以p型Bi0.5Sb1.5Te3區(qū)熔棒材為初始原料,系統(tǒng)研究了MS工藝參數(shù)對薄帶相組成、微結(jié)構(gòu)、產(chǎn)率及塊體材料熱電性能的影響規(guī)律。結(jié)果表明:改變MS工藝參數(shù)(單次樣品制備量、腔體氣壓、銅輥轉(zhuǎn)速)不影響薄帶的相組成,所有樣品均為Bi0.5Sb1.5Te3單相。薄帶的自由面和接觸面分別表現(xiàn)為典型的枝晶、納米晶結(jié)構(gòu),隨著銅輥轉(zhuǎn)速增加,接觸面上的納米晶逐漸細(xì)化;PAS燒結(jié)后的塊體材料沒有明顯取向,晶粒顯著細(xì)化,晶界處含有大量尺寸約為50 nm的富Sb第二相。其中,銅輥轉(zhuǎn)速為10 m/s的樣品因具有多尺度結(jié)構(gòu),能散射更寬頻段的聲子,導(dǎo)致樣品的晶格熱導(dǎo)率大幅降低,其最大ZT值在340 K達(dá)到1.22,相比ZM樣品提高近40%。系統(tǒng)研究了銅輥轉(zhuǎn)速對材料靜態(tài)力學(xué)性能的影響規(guī)律,結(jié)合FESEM微結(jié)構(gòu)表征,分析了MS-PAS樣品的斷裂機理和增韌機理。ZM樣品具有明顯擇優(yōu)取向,層間以較弱的范德瓦爾斯鍵結(jié)合,導(dǎo)致材料易發(fā)生解理,力學(xué)性能較差。采用MS-PAS技術(shù)能顯著改善ZM材料的力學(xué)性能和機械加工性,這主要是由于MS-PAS技術(shù)細(xì)化了材料晶粒,相比ZM樣品,其維氏硬度Hv和斷裂韌性KIC分別提高約50%和26-40%,彎曲強度和壓縮強度分別提高約6倍和8倍。靜態(tài)力學(xué)性能破壞機制研究表明,MS-PAS技術(shù)引入了多尺度結(jié)構(gòu)和納米結(jié)構(gòu),使材料在服役過程中出現(xiàn)裂紋偏轉(zhuǎn)、裂紋橋聯(lián)和晶粒拔出等效應(yīng),消耗了裂紋擴展能量,從而大幅提高了材料的力學(xué)性能,這對碲化鉍基材料的商業(yè)化應(yīng)用具有重要意義。以熱電性能和力學(xué)性能均表現(xiàn)優(yōu)異的樣品(即銅輥轉(zhuǎn)速為10 m/s樣品,MS10)為研究對象,系統(tǒng)研究了其壓縮疲勞實驗,確定其應(yīng)力-壽命曲線(S-N曲線),探索了材料的疲勞裂紋擴展及微結(jié)構(gòu)演變規(guī)律。結(jié)果表明:隨著應(yīng)力水平的提高,MS10樣品的疲勞壽命逐漸降低,其中60%應(yīng)力水平下材料的疲勞壽命可達(dá)9.0×105次。MS10樣品的疲勞斷口觀察到典型的疲勞條帶和疲勞裂紋,所有疲勞樣品中均觀察到大量位錯、晶格畸變等缺陷結(jié)構(gòu),其濃度隨應(yīng)力水平提高顯著增大,且在晶界及納米顆粒附近容易產(chǎn)生位錯塞積。闡明了ZM和MS-PAS材料的高溫力學(xué)性能及斷裂機理。隨著溫度升高,所有樣品的彎曲強度均先升高后降低,在373 K具有最大值。這主要是因為:一方面由于晶粒間的熱膨脹系數(shù)不匹配產(chǎn)生微裂紋,促使導(dǎo)致斷裂的主裂紋分岔,使其擴展路徑曲折,提高了材料的強度。另一方面高溫環(huán)境下晶界結(jié)合強度降低,導(dǎo)致裂紋易沿晶界擴展。473 K下ZM和MS-PAS樣品的彎曲強度和壓縮強度均出現(xiàn)顯著降低,其中MS10樣品在473 K的彎曲強度和壓縮強度相比室溫下分別降低約15%和25%。通過長時間退火系統(tǒng)研究了ZM和MS-PAS材料的熱電性能和力學(xué)性能的穩(wěn)定性,結(jié)果表明:473 K退火1周基本不改變材料的相組成和微結(jié)構(gòu),ZM和MS10樣品的熱電性能和力學(xué)性能均表現(xiàn)出優(yōu)異的穩(wěn)定性。然而MS10樣品在573 K退火1周后,室溫載流子濃度僅為7×1018 cm-3,相比未退火樣品降低約60%,導(dǎo)致退火樣品的室溫電導(dǎo)率大幅降低,Seebeck系數(shù)升高,室溫下約為300?VK-1,最終MS10樣品在573 K退火后的功率因子僅為2.2×10-3 Wm-1K-2,最大ZT值在室溫約為0.9。由此說明,MS-PAS樣品在473 K以下表現(xiàn)出非常優(yōu)異的熱穩(wěn)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.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TB34
本文編號：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.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TB34
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