【作者】 张东明；

【导师】 傅正义；

【作者基本信息】 武汉理工大学 ， 材料学， 2002， 博士

【摘要】 脉冲大电流快速烧结技术是材料制备新技术之一，具有很大的发展潜力，但烧结机理一直存在争议。本文对脉冲电流的烧结机理进行了系统研究。 重点研究了脉冲电流烧结非导电材料的机理，认为模具腔体中同时存在脉冲电磁场及二次电磁波的作用，而这些都与脉冲电流在压头前端发生的偏转有关。 烧结Al₂O₃块体不同深度的XRD分析表明：样品上表面的烧结温度高于下表面，且上表面有被高能粒子轰击的痕迹；进一步的XPS表面分析表明：SPS上表面、下表面及热压样品表面的Cls峰位与标准值的偏差依次增大，显示出C脱离表面束缚所需的能量依次增高，由此证明存在脉冲电场的作用，且上表面电场强度高于下表面。脉冲电场诱发场电子发射及C粒子对表面的轰击。烧结Al₂O₃-ZrO₂-Ni样品中的磁性粒子成分偏聚证明存在脉冲磁场的作用；BN包敷Cu的烧结结果表明导电性金属材料能有效吸收脉冲磁场能而被加热。对反应烧结ZnO-AL₂O₃块体中的裂纹分析发现：样品中存在规律性局部高温，并且高温区之间的距离与模具尺寸有关。分析了二次电磁波的产生及谐振腔振荡频率与腔体尺寸的关系，证明存在二次电磁波的作用。 脉冲电流烧结导电性TiB₂的研究发现：同时存在颗粒间放电效应与脉冲电流的趋肤效应。升温速率小时表现为趋肤效应；升温速率大时表现为放电效应。放电效应使颗粒表面活化。导电材料的烧结晶粒既受控于烧结时间，也受控于晶粒生长激活能，存在最佳升温速率。 利用球磨和酸洗方法制备出粒径均匀的TiB₂纳米粉，对纳米化机理的研究发现：其与Ti的吸氢性和TiB₂的层状结构有关。由于纳米粉的吸附性使其成为纳米复合粒子。这种复合粒子具有半导性，周围材料的电阻远小于复合粒子的电阻时表现为非导电材料烧结的性质；周围材料的电阻远大于复合粒子的电阻时表现为导电材料烧结的性质。即半导性材料的烧结与周围环境有关。更多还原

【Abstract】 Pulse electric current sintering is an advanced technology for materials synthesis and processing with potential application. But the sintering mechanism is in dispute. In order to get best sintering effects,the mechanism of pulse electric current sintering was investigated in present dissertation.Main efforts were put on mechanism of sintering of non-conductive materials. The effects of magnetic and electric fields as well as high frequency wave were believed to exist in sintering of non-conductive materials,which have relationship with the current turning direction at the surface of punch.XRD analysis at different depth of A12O3 sintered body indicates that the temperature at top surface is much higher than that at bottom surface,and it has trace to be bombarded by high-energy particles at top surface. Further XPS analysis shows that:the difference of Cls peak site between practical and standard for SPS top surface and bottom surface as well as HP surface increase gradually which indicate that the escaping energy of C particles from body bonding increase gradually. These results are the evidence for the existence of pulse electric field. As the electrons and C particles sprayed by electric field are more at top surface than at bottom,the top surface get more bombardment and make the temperature higher. The result of magnetic particles migrating in sintering of Al2O3-ZrO2-Ni sample is the evidence for the existence of pulse magnetic field. Cu body bathed in BN is heated in edge side indicates that conductive metal material absorbs magnetic energy easy. The results of crack analysis for reaction sintering of ZnO-Al2O3 indicate that periodic high temperature region exists in sintering body. And the periodicity has relationship with die diameter. As the graphite die has all of the conditions to induce high frequency electric-magnetic wave,and the frequency of resonance body also has relationship with diameter,which is the evidence for existence of high frequency electric-magnetic wave.The results of sintering conductive TiB2 indicate that the spark effect between powders and tending-to-skin of pulse current exist at the same time. It behaves the tending-to-skin effect with lower heating rate,and it behaves spark effect with higher heating rate. Powder surfaces are activated by spark. The grain sizes are controlled not only by sintering time but also by activation energy,so optimum heating rate exists in order to get smallest grain size.TiB2 nano-powders were prepared by ball milling and acid treatment. The investigation of nano mechanism indicates that it has relationship with absorbing H+ of Ti and layered structure of TiB2. The composite powders exhibit semi-conductive property because of the absorption of nano-powders. It exhibits non-conductive property when its resistance is much higher than circle materials;while it exhibits conductive property when its resistance is much lower than circle materials.更多还原