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Oxides formed in the combustion process significantly affect the flame retardancy of titanium alloys, however, the evolution mechanism and formation mechanism of the combustion products of 600 ℃ high temperature titanium alloy remain uncertain. Frictional ignition method is employed in this paper to study the combustion behaviors of 600 ℃ high temperature titanium alloy, and the flame retardancy is evaluated according to the friction time, oxygen content and combustion state. In-situobservation of the burning phenomenon at the friction position and morphology after combustion is investigated, and the combustion states can be divided into oxidation stage, ignition stage and extended combustion stage. Further microstructure analysis is conducted subsequently by focus ion beam (FIB) and high resolution transmission electron microscope (HRTEM) to characterize the oxidation products with different valences in different zones of combustion microstructure. Al 2O 3, Ti 2O 3and TiO 2are observed as the main combustion products in the heat-affected zone, melting zone and combustion zone, respectively. Notably, TiO 2is found to be formed by Ti 2O 3under the combustion condition, which is different from the TiO 2transformed from the TiO mesophase under oxidation condition. This results in a lax structure composed of spherical Ti 2O 3particles and porous Ti matrix in the melting zone. Thermodynamic calculations including Gibbs free energy and decomposition pressure are discussed to explain the evolution mechanisms and formation mechanisms of different oxides. It is revealed that an Al content of 6% is insufficient to form a continuous protective Al 2O 3layer at the interface of the melting zone and heat affected zone. The difference in reaction path between TiO 2formed by TiO and by Ti 2O 3can be ascribed to the formation of gaseous TiO phase. The sharp increase of TiO vapor pressure at about 1800 K reduces the stability of titanium oxide, thus causing the as-formed TiO to evaporate rapidly and forcing titanium to transform into TiO 2via a more stable phase, Ti 2O 3. The formation of the porous structure composed of Ti 2O 3and Ti at the melting zone provides a path for the rapid internal diffusion of oxygen, which severely deteriorates the oxygen prevention capability of as-formed oxide layers. Besides, the TiO 2synthesized from Ti-O melt in the combustion zone can hardly protect the inner structure. Therefore, the flame retardancy of 600 ℃ high-temperature titanium alloy is far from satisfactory.
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Keywords:
- 600 ℃ high temperature titanium alloy/
- combustion microstructure/
- combustion mechanism/
- thermodynamic calculation
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摩擦时间t= 3 s 摩擦时间t= 4 s 摩擦时间t= 5 s 氧浓度/% 燃烧状态 氧浓度/% 燃烧状态 氧浓度/% 燃烧状态 37.3 充分燃烧 36.0 充分燃烧 35.5 充分燃烧 37.0 充分燃烧 35.7 充分燃烧 35.2 充分燃烧 36.8 临界燃烧 35.4 临界燃烧 34.9 临界燃烧 36.5 未燃烧 35.1 未燃烧 34.6 未燃烧 36.2 未燃烧 34.8 未燃烧 34.3 未燃烧 
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元素 区域1/% 区域2/% 区域3/% 区域4/% 区域5/% Ti 81.3 83.0 74.0 80.3 65.4 Al 11.1 11.1 10.9 10.8 10.1 Zr 1.9 1.9 1.7 1.7 1.5 Sn 1.5 1.6 1.3 1.6 1.2 O 4.2 2.4 12.1 5.6 21.8 DownLoad:
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元素 区域1/% 区域2/% 区域3/% 区域4/% Ti 32.7 62.7 41.2 67.2 Al 2.2 2.2 2.5 10.3 Zr 0.9 0.7 1.6 1.3 Sn 0.1 0.3 1.0 1.4 O 64.1 34.1 53.7 19.8 DownLoad:
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元素 区域1/% 区域2/% 区域3/% 区域4/% 区域5/% Ti 72.1 33 32.8 40.8 59.4 Al 14.5 5.3 5.1 3.3 5.2 Zr 1.3 0.8 0.5 1.1 0.9 Sn 1.0 0.2 0.4 0.7 0.6 O 11.1 60.7 61.2 54.1 33.9 DownLoad:
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间距/Å 区域 1 区域 2 区域 3 区域 4 区域 5 区域 6 区域 7 d 2.81 3.09 3.12 3.14 3.13 3.06 2.95 h 2.91 2.94 2.98 2.93 2.81 2.64 2.77 间距/Å 区域 8 区域 9 区域 10 区域 11 理想TiO 理想TiO2 理想β-Ti d 2.62 2.59 5.41 4.80 2.41 3.57 4.68 h 2.95 2.94 2.91 2.88 2.48 2.48 2.34 DownLoad:
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物理量 数值 熔体密度$ \rho $/(kg·m3) 4000 液相线温度TM/K 1873 摩尔质量M/(kg·mol) 0.04674 Ti原子半径rTi/(10–10m) 2.00 Al原子半径rAl/(10–10m) 1.18 DownLoad:
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T= 900 K O2(g) Ti(s) Ti(g) TiO(s) TiO(g) Ti2O3(s) Ti2O3(g) TiO2(s) TiO2(g) 自由能G –196.7 –38.3 302.4 –592.2 –169.3 –1638.9 –1100 –1009.1 –400 自由能变化${ {\Delta } }{G^\varTheta }(T)$ 0 0 +340.7 –455.5 –32.7 –1267.3 –728.4 –774.1 –165.0 平衡常数对数lgKp — — –19.8 26.4 1.9 73.6 42.3 44.9 9.6 T= 1900 K O2(g) Ti(s) Ti(g) TiO(s) TiO(g) Ti2O3(s) Ti2O3(g) TiO2(s) TiO2(g) 自由能G –451.5 –115.7 +88.2 –695.2 –457.7 –1921.6 –1600 –1171.0 –750 自由能变化${ {\Delta } }{G^\varTheta }(T)$ 0 0 +203.9 –367.6 –116.2 –1012.8 –691.4 –603.7 –182.8 平衡常数对数lgKp — — –5.61 10.1 3.19 27.9 19.0 16.6 5.0 T= 2200 K O2(g) Ti(l) Ti(g) TiO(s) TiO(g) Ti2O3(s) Ti2O3(g) TiO2(s) TiO2(g) 自由能G –532.4 –145.2 +21.2 –756.6 –548.8 –2028.9 –1710 –1229.4 –860 自由能变化${ {\Delta } }{G^\varTheta }(T)$ 0 0 +166.3 –345.2 –137.5 –939.9 –621.0 –551.8 –182.4 平衡常数对数 lgKp — — –3.9 8.2 3.2 22.3 14.7 13.1 4.3 DownLoad:
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16-20230396 补充材料.pdf
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