摘要
利用有限元方法,对自反应喷射成形制备Ti(C,N)-TiB2复合陶瓷坯件过程中单个喷射复合粉在火焰场中反应熔融的温度场变化过程进行了数值模拟研究.结果表明:粒径50μm的喷射复合粉粒子沿轴线进入火焰场0.35ms后,粒子表面温度即达到体系的引燃温度,复合粉开始发生自蔓延高温合成(Self-propagation High-temperature Synthesis,简称SHS)反应,此期间复合粉粒子升温速率约为2.82×106℃.s-1.反应开始后,受火焰加热与反应放热双重作用,复合粉粒子的升温速率进一步加快,之后由于复合粉粒子温度升高,超过火焰温度,并由吸热变为向外散热而使升温速率大幅下降(约为1.20×106℃.s-1),复合粉粒子在0.88ms后完成反应并达到最高温度2 920℃.反应结束后粒子由外向内快速冷却,在0.34ms后粒子表面达到复合陶瓷产物的理论共晶熔点2 620℃,之后粒子在一定过冷度下开始凝固,很快完全凝固成为陶瓷颗粒.喷射粒子在反应前、中、后阶段的温度场数值模拟结果与粒径约为50μm的喷射粒子在相应阶段的水淬熄实验结果相符较好.数值模拟结果基本体现了复合粉粒子在喷射过程中历经受热、反应放热及冷却凝固的热过程及相应的温度变化规律.
By applying the finite element method, the temperature change process of the single sprayed composite powders during self-reactive spray formation is numerically simulated for preparing the Ti（C, N）-TiB2 ceramic preforms. Accordingly, it is found from the results that, after the sprayed composite powders with particle size of 50 μm enter the flame field within 0.35 ms, the Self-propagating High- temperature Synthesis, SHS） reaction occurs with relevant surface temperature towards the ignition temperature. In this period, the heating rate of composite powders is about 2.82 × 106℃·s^-1. In the start of reaction, the heating rate increases due to the flame heating and reactive heat release. When the temperature of the sprayed composite powders is higher than that of the flame, the heat exchange will be first turned into heat absorption from heat release, which leads to significant drop of heating rate （about 1.20 × 10^6℃·s^-1）. Then, the reaction of composite powders is completed within 0.88 ms with the highest temperature of 2 920 ℃ in the form of molten ceramic droplets. Upon completion of reaction, the molten droplets are quickly cooled down from the exterior to the interior, the surface temperature of which descends to the theoretic eutectic melting point of composite ceramics （2 620℃ ） after 0. 34 ms. Subsequently, the molten ceramic droplets are solidified as ceramic particles at a specific degree of overcooling. Consequently, the numerically-simulated results from pre-reaction, reaction and post-reaction are consistent with the experimental results from water quenching for sprayed composite powders with particle size of 50/~m. Therein, it is indicated from the numerical results that the heating process （i. e. heating, heat release, cooling and solidification） and corresponding temperature change of sprayed composite powders.
出处
《中国工程机械学报》
2011年第1期25-31,共7页
Chinese Journal of Construction Machinery
基金
国家自然科学基金资助项目(51001118
50672130)
关键词
自反应喷射成形
复合粉
温度场
数值模拟
self-reactive spray formatiom composite powder
temperature field
numerical simulation
