【作者】 李闯；

【导师】 沈以赴； 顾冬冬；

【作者基本信息】 南京航空航天大学 ， 材料学， 2011， 硕士

【摘要】 金属基纳米复合材料根据增强相的加入方式可分为外加颗粒增强以及原位自生增强两种。实现纳米增强相均匀分布及防止纳米结构粗化是制备性能优异的金属基纳米复合材料的关键。本文利用行星式高能球磨机设备,高能球磨微米级TiC/Ti和SiC/Ti粉末体系,制备了纳米TiC增强非晶Ti基复合粉末及纳米TiC原位增强Ti₅Si₃基复合粉末,并利用选区激光熔化工艺成功制备了TiC/Ti和TiC/Ti₅Si₃纳米复合材料试件。TiC/Ti混合粉末随着球磨时间增加至15 h,由于高能球磨诱发Ti发生严重塑性变形,产生大量晶格缺陷,致使Ti发生非晶转变。复合粉末颗粒在球磨至10 h与20 h处经历了两次严重细化阶段。最终得到纳米颗粒TiC增强非晶Ti基复合粉末,纳米级TiC在Ti基体中分布均匀。在原位制备TiC/Ti₅Si₃纳米复合粉末过程中,SiC在25 h高能球磨中逐渐分解,而Ti在相对较短时间内（10 h）完全参加反应。TiC/Ti₅Si₃纳米复合粉末结构依次经历了初级细化-粗化-二次细化的过程。复合粉末颗粒的细化过程以分层碎化为主要机制。高能球磨25h后,纳米颗粒TiC在Ti5Si3基体中分散均匀。对TiC/Ti纳米复合粉末进行选区激光熔化实验,成功制备了TiCx增强Ti基纳米复合材料试件。激光线能量密度η为1100 J/m时,成形试件致密达95.6%。增强体TiCx为层片状纳米结构,平均厚度为54 nm,且在Ti基体中分布均匀。TiCx层片状纳米结构是由于自TiC核心开始形成之时,其生长就受到了激光熔池中特有的“微观有效应力”抑制,使其难以长大,加之TiCx特有的晶体结构,TiCx以层片状纳米结构生长。选区激光熔化SiC/Ti复合粉末,原位制备了TiC/Ti₅Si₃复合材料试件。当激光线能量密度η为800 J/m时,SLM试件保持了良好的凝固组织连续性和均匀性,致密度达94.6%。因激光能量密度呈Gauss分布,激光作用的熔池中心及边缘将形成明显的温度梯度与化学浓度梯度,进而产生熔池表面张力梯度,故易出现成分过冷,导致原位生成的TiC呈现枝晶状形貌。讨论了激光快速熔凝过程中TiC/Ti₅Si₃复合材料的形成机理。更多还原

【Abstract】 Normally, ceramic particulates reinforced metal matrix nanocomposites could either be added to the composite system exteriorly or be formed through an in-situ reaction manner. It was a rather significant task to homogeneously incorporate nanoparticles into a matrix and avoid nanostructure coarsening. In present work, nanocrystalline/amorphous Ti matrix reinforced with the TiC nanoparticles and in-situ synthesis of TiC/Ti₅Si₃ nanocomposites powders were obtained via high energy ball milling, using the micrometric TiC/Ti and SiC/Ti powders as the raw materials.Meanwhile, the TiC/Ti and TiC/Ti₅Si₃ nanocomposite parts were performed by selective laser melting. With increasing the applied milling time to 15h, the structures of the Ti constituent experienced a change of amorphization due to the large defect concentration induced by severe plastic deformation during milling. The milled powder particles underwent two stages of significant refinement at 10 h and 20 h during high energy ball milling. Finally, ball milled products were typically nanocomposite powder featured by the nanocrystalline/amorphous Ti matrix reinforced with the TiC nanoparticles, it was observed that the nanometer-sized TiC particulates were dispersed uniformly throughout the Ti matrix. The SiC constituent decomposed gradually within 25 h of milling, while the Ti constituent reacted speedily after a relatively short time of 10 h. The structures of the milled TiC/Ti₅Si₃ nanocomposites powders experienced a successive change: pre-refining–coarsening–re-refining on increasing the applied milling time. The refinement of the milled powder particles was based on a layered fracturing mechanism. After milled 25 h, the in situ nanometer-sized TiC particulates were dispersed uniformly within Ti matrix.The TiCx reinforced Ti matrix nanocomposites parts were prepared by selective laser melting. It showed that a high densification level of 95.6% was obtained for SLM-processed parts at a laser linear energy densityηof 1100 J/m. The TiCx reinforcing phase was dispersed uniformly in the Ti matrix, having an ultrafine lamellar nanostructure with an average thickness of 54 nm. The non-equilibrium microscopic pressure tended to prevent TiCx crystals growing up, additionally TiC crystal structure, TiCx reinforcing phase developed with a lamellar nanostructure during laser-induced rapid melting/solidification process. SiC/Ti composite powders after high energy ball milling were undergone selective laser melting, in-situ synthesizing TiC/Ti₅Si₃ composite structure. It showed that a high densification level of 94.6% was obtained for SLM-processed parts at a laser linear energy densityηof 800 J/m. Owing to the Gauss distribution of laser energy density, the local temperature gradient and chemical concentration gradient in the molten pool gave rise to surface tension gradient, producing a significant constitutional supercooling, the in-situ TiC tended to experience a dendrite growth. The formation mechanism of TiC in-situ reinforced Ti₅Si₃ during laser-induced rapid melting/solidification process was discussed.更多还原