过渡族金属元素和内生陶瓷颗粒对TiAl压缩性能的影响规律及机制
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摘要
TiAl合金由于具有低密度、高熔点、高的比强度和比模量、低的蠕变速率和出众的抗高温氧化能力，其比强度、抗蠕变性和抗氧化性优于Ti_合金和Ni_基高温合金，使TiAl合金具有替代镍基高温合金成为高温轻质合金的潜力。然而，TiAl合金较差的室温塑性和高温强度限制了其广泛应用。因此，关于提高TiAl合金强度和塑性的研究对其取代镍基高温合金成为重要的航空、航天材料具有重要的理论和应用价值。当前，关于改善TiAl合金强度和塑性的研究仍是当前国际上急需解决的世界难题，关于金属元素种类、含量及内生陶瓷颗粒种类、尺寸、形状、数量、分布对TiAl合金强度和塑性的影响机制尚不明确，限制了TiAl材料在实际中的广泛应用，因此不同金属元素及内生陶瓷颗粒对TiAl合金强度和塑性的影响机制需要进一步的探索与揭示。
因此，本论文以采用燃烧合成后施加压力的方法制备出的合金化TiAl合金和内生陶瓷颗粒增强TiAl基复合材料作为研究对象，将第一原理计算与实验相结合，探索不同种类、含量的过渡族金属元素(Zr/Hf/V/Nb/Ta/Cr/Mo/W/Mn/Fe/Co/Ni_/Cu/Zn)及不同种类、尺寸、形状、数量、分布的原位内生陶瓷颗粒(Ti_2AlC/TiB_2/Ti_5Si_3/TiB_2–Ti_2AlC)对TiAl合金压缩性能的影响规律，建立组织和性能之间的关系，提出改善TiAl合金强度和塑性的机制。
本文主要研究结果如下：
1)首次采用燃烧合成后施加压力的方法成功地制备出原位内生陶瓷颗粒(Ti_2AlC、TiB_2、Ti_5Si_3、TiB_2–Ti_2AlC)增强TiAl基复合材料。发现原位内生陶瓷颗粒的尺寸达到亚微米和纳米级尺寸，Ti_2AlC、Ti_5Si_3和TiB_2的尺寸分别为：~700nm、60–80nm和30–50nm。
2)发现金属元素(Fe、Co)、内生陶瓷颗粒(Ti_2AlC、TiB_2、Ti_5Si_3、TiB_2–Ti_2AlC)及金属元素+内生陶瓷颗粒(Mn+Ti_2AlC、Mn/Fe/Co+TiB_2)都可以细化TiAl合金的晶粒尺寸。ⅰ)添加3at.%的金属元素Fe和Co使TiAl合金的晶粒尺寸从~66μm分别细化到~15μm和25μm。ⅱ)6vol.%的内生陶瓷颗粒Ti_2AlC、TiB_2、Ti_5Si_3和TiB_2–Ti_2AlC使TiAl合金的晶粒尺寸分别细化到~30μm、~15μm、~22μm和~10μm。ⅲ)2at.%Mn+4vol.%Ti_2AlC和2at.%Mn/Fe/Co+4vol.%TiB_2使TiAl合金的晶粒尺寸分别细化到~26μm和~10μm。
3)揭示出4vol.%Ti_2AlC/TiAl–2Mn复合材料具有最好的压缩性能，其屈服强度(637MPa)、最大压缩强度(1694MPa)和断裂应变(22.2%)分别比TiAl合金的屈服强度、最大压缩强度和断裂应变提高了172MPa、279MPa和4.9%；4vol.%TiB_2/TiAl–2Co复合材料具有最高的压缩强度，其屈服强度(820MPa)和最大压缩强度(1906MPa)分别比TiAl合金的屈服强度和最大压缩强度提高了355MPa和491MPa，断裂应变与TiAl合金相当。
4)提出了金属元素(Mn、Fe、Co)、内生陶瓷颗粒(Ti_2AlC、TiB_2、Ti_5Si_3、TiB_2–Ti_2AlC)和金属元素+内生陶瓷颗粒(Mn+Ti_2AlC、Mn/Fe/Co+TiB_2)分别对TiAl合金强塑性的影响机制。
ⅰ)提高强度机制:a)金属元素：固溶强化和细晶强化。b)内生陶瓷颗粒：第二相强化和细晶强化。c)金属元素+内生陶瓷颗粒：固溶强化、第二相强化和细晶强化。
ⅱ)改善塑性的机制：a)金属元素：晶体结构、电子结构和弹性性质的改善及晶粒细化。b)内生陶瓷颗粒：晶粒细化和细小内生陶瓷颗粒的均匀分布。c)金属元素+内生陶瓷颗粒：晶体结构、电子结构和弹性性质的改善、晶粒细化和纳米内生陶瓷颗粒的均匀分布。
总之，本文将第一原理计算与实验相结合，探索了不同种类、含量的过渡族金属元素及不同种类、尺寸、形状、数量、分布的原位内生陶瓷颗粒对TiAl合金压缩性能的影响规律，提出了过渡族金属元素和原位内生陶瓷颗粒改善TiAl合金强度和塑性的机制。为发展高强度和高塑性的原位内生陶瓷颗粒增强TiAl基复合材料及其制备新技术奠定必需的理论基础。
The TiAl alloy possesses the potentiality for substituting Ni–base superalloy to becomehigh temperature light weight alloy, due to its low density, high melting point, high specificstrength and specific modulus, low creep rate and excellent high temperature oxidationresistance. Moreover, the specific strength, creep resistance and oxidation resistance of TiAlalloy are better than those of the Ti alloys and the Ni–base superalloy. However, the lowroom temperature ductility and high temperature strength limit its extensive application.Thus, the investigation for improving the strength and ductility of TiAl alloy has importanttheory and application value for TiAl to substitute Ni–base superalloy and become importantaerospace material. At present, the investigation about improving the strength and ductilityof TiAl alloy is still a problem to be solved quickly in the world. The influence mechanismsof the kind and content of metal elements and the kind, size, shape, quantity and distributionof in situ ceramic particles on the strength and ductility of the TiAl alloy are still unclear,which limits the extensive application of TiAl in practice. Thus, the influence mechanisms ofdifferent metal elements and in situ ceramic particles on the strength and ductility of TiAlalloy need to be further explored and revealed.
Therefore, in this thesis, the alloying TiAl alloys and the in situ ceramic particlesreinforced TiAl matrix composites fabricated by the method of combustion synthesis and hotpress consolidation were studied. The influence law of different kinds and contents oftransition metal elements (Zr/Hf/V/Nb/Ta/Cr/Mo/W/Mn/Fe/Co/Ni/Cu/Zn) and differentkinds, sizes, shapes, quantities and distribution of in situ ceramic particles(Ti_2AlC/TiB_2/Ti_5Si_3/TiB_2–Ti_2AlC) on the compression properties of TiAl alloy wereexplored by the combination methods of first principle calculation and experiments. Therelationship between microstructures and properties was built and the mechanisms forimproving the strength and ductility of the TiAl alloy were discussed.
The main results are as follows:
1) The in situ ceramic particles (Ti_2AlC/TiB_2/Ti_5Si_3/TiB_2–Ti_2AlC) reinforced TiAl matrix composites were successfully fabricated by the method of combustion synthesis and hotpress consolidation for the first time. It is found that the in situ ceramic particles are allin submicron–size and nano–size. The sizes of Ti_2AlC, Ti_5Si_3and TiB_2are~700nm,60–80nm and30–50nm, respectively.
2) It is found that the metal elements (Fe, Co), in situ ceramic particles (Ti_2AlC, TiB_2,Ti_5Si_3, TiB_2–Ti_2AlC) and metal elements+in situ ceramic particles (Mn+Ti_2AlC,Mn/Fe/Co+TiB_2) all could refine the grain size of TiAl alloy.ⅰ) With the addition of3at.%Fe and Co, the grain size of TiAl alloy decreases from~66μm to~15μm and25μm, respectively.ⅱ) With the generation of6vol.%Ti_2AlC, TiB_2, Ti_5Si_3and TiB_2–Ti_2AlC, the grain sizeof TiAl alloy decreases to~30μm,~15μm,~22μm and~10μm, respectively.ⅲ) The2at.%Mn+4vol.%Ti_2AlC and the2at.%Mn/Fe/Co+4vol.%TiB_2decreasethe grain size of the TiAl alloy to~26μm and~10μm, respectively.
3) It is revealed that the4vol.%Ti_2AlC/TiAl–2Mn composite possesses the bestcompression properties, of which the yield strength (637MPa), ultimate compressionstrength (1694MPa) and fracuture strain (22.2%) are172MPa,279MPa and4.9%higher than those of the TiAl alloy; The4vol.%TiB_2/TiAl–2Co composite possessesthe highest compression strength, of which the yield strength (820MPa), ultimatecompression strength (1906MPa) are355MPa and491MPa higher than those of theTiAl alloy, the fracture strain is similar with that of TiAl alloy.
4) The influence mechanisms of metal elements (Mn, Fe, Co), in situ ceramic particles(Ti_2AlC, TiB_2, Ti_5Si_3, TiB_2–Ti_2AlC) and metal elements+in situ ceramic particles(Mn+Ti_2AlC, Mn/Fe/Co+TiB_2) on the strength and ductility of TiAl alloy were putforward.
ⅰ) Mechanisms for improving strength:a) Metal elements: the solid solution strengthening and the grain refinementstrengthening.b) In situ ceramic particles: the second phase strengthening and the grainrefinement strengthening.c) Metal elements+in situ ceramic particles: the solid solution strengthening, thesecond phase strengthening and the grain refinement strengthening.
ⅱ) Mechanisms for improving ductility:a) Metal elements: the grain refinement and the improvement of crystal structures,electronic structures and elastic properties.b) In situ ceramic particles: the grain refinement and the uniform distribution of fine in situ ceramic particles.c) Metal elements+in situ ceramic particles: the improvement of crystalstructures, electronic structures and elastic properties, the grain refinement andthe uniform distribution of nano–size in situ ceramic particles.
In summary, the influence law of different kinds and contents of transition metalelements and different kinds, sizes, shapes, quantities and distribution of in situ ceramicparticles on the compression properties of TiAl alloy were explored by the combinationmethods of first principle calculation and experiments; the mechanisms of transition metalelements and in situ ceramic particles for improving the strength and ductility of TiAl alloywere put forward, which laid the necessary theoretical basis for the development of the insitu ceramic particles reinforced TiAl matrix composites with high strength and ductility andits new fabrication technology.
因此，本论文以采用燃烧合成后施加压力的方法制备出的合金化TiAl合金和内生陶瓷颗粒增强TiAl基复合材料作为研究对象，将第一原理计算与实验相结合，探索不同种类、含量的过渡族金属元素(Zr/Hf/V/Nb/Ta/Cr/Mo/W/Mn/Fe/Co/Ni_/Cu/Zn)及不同种类、尺寸、形状、数量、分布的原位内生陶瓷颗粒(Ti_2AlC/TiB_2/Ti_5Si_3/TiB_2–Ti_2AlC)对TiAl合金压缩性能的影响规律，建立组织和性能之间的关系，提出改善TiAl合金强度和塑性的机制。
本文主要研究结果如下：
1)首次采用燃烧合成后施加压力的方法成功地制备出原位内生陶瓷颗粒(Ti_2AlC、TiB_2、Ti_5Si_3、TiB_2–Ti_2AlC)增强TiAl基复合材料。发现原位内生陶瓷颗粒的尺寸达到亚微米和纳米级尺寸，Ti_2AlC、Ti_5Si_3和TiB_2的尺寸分别为：~700nm、60–80nm和30–50nm。
2)发现金属元素(Fe、Co)、内生陶瓷颗粒(Ti_2AlC、TiB_2、Ti_5Si_3、TiB_2–Ti_2AlC)及金属元素+内生陶瓷颗粒(Mn+Ti_2AlC、Mn/Fe/Co+TiB_2)都可以细化TiAl合金的晶粒尺寸。ⅰ)添加3at.%的金属元素Fe和Co使TiAl合金的晶粒尺寸从~66μm分别细化到~15μm和25μm。ⅱ)6vol.%的内生陶瓷颗粒Ti_2AlC、TiB_2、Ti_5Si_3和TiB_2–Ti_2AlC使TiAl合金的晶粒尺寸分别细化到~30μm、~15μm、~22μm和~10μm。ⅲ)2at.%Mn+4vol.%Ti_2AlC和2at.%Mn/Fe/Co+4vol.%TiB_2使TiAl合金的晶粒尺寸分别细化到~26μm和~10μm。
3)揭示出4vol.%Ti_2AlC/TiAl–2Mn复合材料具有最好的压缩性能，其屈服强度(637MPa)、最大压缩强度(1694MPa)和断裂应变(22.2%)分别比TiAl合金的屈服强度、最大压缩强度和断裂应变提高了172MPa、279MPa和4.9%；4vol.%TiB_2/TiAl–2Co复合材料具有最高的压缩强度，其屈服强度(820MPa)和最大压缩强度(1906MPa)分别比TiAl合金的屈服强度和最大压缩强度提高了355MPa和491MPa，断裂应变与TiAl合金相当。
4)提出了金属元素(Mn、Fe、Co)、内生陶瓷颗粒(Ti_2AlC、TiB_2、Ti_5Si_3、TiB_2–Ti_2AlC)和金属元素+内生陶瓷颗粒(Mn+Ti_2AlC、Mn/Fe/Co+TiB_2)分别对TiAl合金强塑性的影响机制。
ⅰ)提高强度机制:a)金属元素：固溶强化和细晶强化。b)内生陶瓷颗粒：第二相强化和细晶强化。c)金属元素+内生陶瓷颗粒：固溶强化、第二相强化和细晶强化。
ⅱ)改善塑性的机制：a)金属元素：晶体结构、电子结构和弹性性质的改善及晶粒细化。b)内生陶瓷颗粒：晶粒细化和细小内生陶瓷颗粒的均匀分布。c)金属元素+内生陶瓷颗粒：晶体结构、电子结构和弹性性质的改善、晶粒细化和纳米内生陶瓷颗粒的均匀分布。
总之，本文将第一原理计算与实验相结合，探索了不同种类、含量的过渡族金属元素及不同种类、尺寸、形状、数量、分布的原位内生陶瓷颗粒对TiAl合金压缩性能的影响规律，提出了过渡族金属元素和原位内生陶瓷颗粒改善TiAl合金强度和塑性的机制。为发展高强度和高塑性的原位内生陶瓷颗粒增强TiAl基复合材料及其制备新技术奠定必需的理论基础。
The TiAl alloy possesses the potentiality for substituting Ni–base superalloy to becomehigh temperature light weight alloy, due to its low density, high melting point, high specificstrength and specific modulus, low creep rate and excellent high temperature oxidationresistance. Moreover, the specific strength, creep resistance and oxidation resistance of TiAlalloy are better than those of the Ti alloys and the Ni–base superalloy. However, the lowroom temperature ductility and high temperature strength limit its extensive application.Thus, the investigation for improving the strength and ductility of TiAl alloy has importanttheory and application value for TiAl to substitute Ni–base superalloy and become importantaerospace material. At present, the investigation about improving the strength and ductilityof TiAl alloy is still a problem to be solved quickly in the world. The influence mechanismsof the kind and content of metal elements and the kind, size, shape, quantity and distributionof in situ ceramic particles on the strength and ductility of the TiAl alloy are still unclear,which limits the extensive application of TiAl in practice. Thus, the influence mechanisms ofdifferent metal elements and in situ ceramic particles on the strength and ductility of TiAlalloy need to be further explored and revealed.
Therefore, in this thesis, the alloying TiAl alloys and the in situ ceramic particlesreinforced TiAl matrix composites fabricated by the method of combustion synthesis and hotpress consolidation were studied. The influence law of different kinds and contents oftransition metal elements (Zr/Hf/V/Nb/Ta/Cr/Mo/W/Mn/Fe/Co/Ni/Cu/Zn) and differentkinds, sizes, shapes, quantities and distribution of in situ ceramic particles(Ti_2AlC/TiB_2/Ti_5Si_3/TiB_2–Ti_2AlC) on the compression properties of TiAl alloy wereexplored by the combination methods of first principle calculation and experiments. Therelationship between microstructures and properties was built and the mechanisms forimproving the strength and ductility of the TiAl alloy were discussed.
The main results are as follows:
1) The in situ ceramic particles (Ti_2AlC/TiB_2/Ti_5Si_3/TiB_2–Ti_2AlC) reinforced TiAl matrix composites were successfully fabricated by the method of combustion synthesis and hotpress consolidation for the first time. It is found that the in situ ceramic particles are allin submicron–size and nano–size. The sizes of Ti_2AlC, Ti_5Si_3and TiB_2are~700nm,60–80nm and30–50nm, respectively.
2) It is found that the metal elements (Fe, Co), in situ ceramic particles (Ti_2AlC, TiB_2,Ti_5Si_3, TiB_2–Ti_2AlC) and metal elements+in situ ceramic particles (Mn+Ti_2AlC,Mn/Fe/Co+TiB_2) all could refine the grain size of TiAl alloy.ⅰ) With the addition of3at.%Fe and Co, the grain size of TiAl alloy decreases from~66μm to~15μm and25μm, respectively.ⅱ) With the generation of6vol.%Ti_2AlC, TiB_2, Ti_5Si_3and TiB_2–Ti_2AlC, the grain sizeof TiAl alloy decreases to~30μm,~15μm,~22μm and~10μm, respectively.ⅲ) The2at.%Mn+4vol.%Ti_2AlC and the2at.%Mn/Fe/Co+4vol.%TiB_2decreasethe grain size of the TiAl alloy to~26μm and~10μm, respectively.
3) It is revealed that the4vol.%Ti_2AlC/TiAl–2Mn composite possesses the bestcompression properties, of which the yield strength (637MPa), ultimate compressionstrength (1694MPa) and fracuture strain (22.2%) are172MPa,279MPa and4.9%higher than those of the TiAl alloy; The4vol.%TiB_2/TiAl–2Co composite possessesthe highest compression strength, of which the yield strength (820MPa), ultimatecompression strength (1906MPa) are355MPa and491MPa higher than those of theTiAl alloy, the fracture strain is similar with that of TiAl alloy.
4) The influence mechanisms of metal elements (Mn, Fe, Co), in situ ceramic particles(Ti_2AlC, TiB_2, Ti_5Si_3, TiB_2–Ti_2AlC) and metal elements+in situ ceramic particles(Mn+Ti_2AlC, Mn/Fe/Co+TiB_2) on the strength and ductility of TiAl alloy were putforward.
ⅰ) Mechanisms for improving strength:a) Metal elements: the solid solution strengthening and the grain refinementstrengthening.b) In situ ceramic particles: the second phase strengthening and the grainrefinement strengthening.c) Metal elements+in situ ceramic particles: the solid solution strengthening, thesecond phase strengthening and the grain refinement strengthening.
ⅱ) Mechanisms for improving ductility:a) Metal elements: the grain refinement and the improvement of crystal structures,electronic structures and elastic properties.b) In situ ceramic particles: the grain refinement and the uniform distribution of fine in situ ceramic particles.c) Metal elements+in situ ceramic particles: the improvement of crystalstructures, electronic structures and elastic properties, the grain refinement andthe uniform distribution of nano–size in situ ceramic particles.
In summary, the influence law of different kinds and contents of transition metalelements and different kinds, sizes, shapes, quantities and distribution of in situ ceramicparticles on the compression properties of TiAl alloy were explored by the combinationmethods of first principle calculation and experiments; the mechanisms of transition metalelements and in situ ceramic particles for improving the strength and ductility of TiAl alloywere put forward, which laid the necessary theoretical basis for the development of the insitu ceramic particles reinforced TiAl matrix composites with high strength and ductility andits new fabrication technology.
引文
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