Reactive Sintering of B6O/TiB2 Composites at High Temperature and High Pressure
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摘要: 以B和TiO2为初始原料，依据压力可抑制原子长程扩散的动力学效应，通过高温高压(4~5 GPa，1 200~1 500 ℃)一步反应烧结法制备B6O/TiB2复合材料。当B和TiO2物质的量之比为14.0:0.8时，在5 GPa、1 200 ℃、保温30 min条件下得到的烧结样品性能较好，非晶硼(纯度93%~94%)过量混合粉末样品的硬度最高约为29 GPa，高纯晶体硼(纯度99.99%)过量混合粉末样品的硬度最高约为32 GPa，相对密度可高达99%。实验结果表明：高压抑制晶粒过度长大，同时又有利于B6O的合成，使其合成温度比常压下有所降低；在高压反应烧结过程中，合成的第二相TiB2晶粒和样品中的非晶相有效地消耗了残余应力，起到了增韧作用。Abstract: B6O/TiB2 composites were produced from B-TiO2 mixtures using "one step reactive sintering method" at high pressures between 4 and 5 GPa.The highest Vicker's hardness is 29 GPa for samples consisting of amorphous B and TiO2 (molar ratio:14.0:0.8).For samples consisting of crystal B and TiO2 (molar ratio:14.0:0.8) sintered at the condition of 5 GPa and 1 200 ℃ for 30 min, the highest Vicker's hardness is 32 GPa, and the ratio of densification is up to 99%.High pressure restrains the formation of large crystalline grains and promotes the synthesis of B6O, and reduces the sintering temperature comparing to that at atmospheric pressure.On the other hand, generated additional TiB2 and superfluous boron can improve the fracture toughness of the sintered samples.
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Key words:
- superhard material /
- high pressure sintering /
- hardness /
- relative density /
- toughening mechanism
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图 1 高压高温反应烧结实验样品组装图
Figure 1. Sample assembly schematic of reactive sintering experiment for producing B6O/TiB2 materials at high pressure and high temperature
图 2 真空热处理和高温高压烧结30 min后, 非晶硼完全混合粉末样品的XRD图谱
Figure 2. Comparison of XRD patterns showing phase compositions of a reactive sintered mixture consisting of amorphous B and TiO2 (molar ratio:14:1) after 30 minutes' treatment of vacuum heating and high-pressure high-temperature sintering
图 3 过量晶体硼块体烧结(5 GPa，1 200 ℃，60 min)样品的SEM图(深灰色：TiB2晶粒，亮灰色：B6O晶粒)
Figure 3. SEM image showing distributed TiB2 grains (dark grey) and B6O grains (bright grey) of a reactive sintered mixture consisting of crystalline B and TiO2 (molar ratio: 14.0:0.8) by high-pressure high-temperature (5 GPa, 1 200 ℃, 60 min) sintering
图 5 过量晶体硼块体烧结(5 GPa，1 200 ℃，60 min)样品抛光面裂纹偏转和弯曲的SEM图
Figure 5. SEM micrographs of the polished surfaces with deflecting and curving crack around TiB2 grains of a reactive sintered mixture consisting of crystalline B and TiO2 (molar ratio:14.0:0.8) under high-pressure high-temperature condition (5 GPa, 1 200 ℃, 60 min)
表 1 B6O/TiB2样品在不同条件下测量的密度和相对密度
Table 1. Measured density and relative density of B6O/TiB2 samples at different experiment conditions
Initial reactive
materialsMolar
ratioSintering conditions ρactual/
(g/cm3)κ/
(%)Pressure/(GPa) Temperature/(℃) Dwelling time/(min) Ba+TiO2 14.0:1.0 4.0 1 200 30 2.62 90.2 Ba+TiO2 14.0:1.0 4.5 1 200 30 2.67 91.9 Ba+TiO2 14.0:1.0 5.0 1 200 30 2.76 95.0 Ba+TiO2 14.0:0.8 5.0 1 200 30 2.68 95.3 Bc+TiO2 14.0:0.8 5.0 1 200 30 2.80 99.4 Note:Superscript ‘a’ means amorphous while ‘c’ means crystalline. 
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