超高重力场燃烧合成TiB2基细晶自增韧陶瓷刀具材料研究

By using combustion synthesis in a ultra-high gravity field (2800 g) to prepare fine-grained TiB2 matrix self-toughening composites for ceramic tools, microstructure modification and performance improvement of the materials are studied. In terms of interface design of ceramic matrix composites and material thermodynamic and chemical-reaction thermodynamic, composition systems of the materials and the database for combustion system are firstly built up. By investigating solidification behaviors of TiB2 matrix ceramics far away from the equilibrium state, near-full-density fine-grained TiB2 matrix ceramics are achieved through controlling faceted growth of TiB2 crystals and microstructure development of the materials. By investigating fracture behavior, high-temperature oxidation behavior, thermal-shock fatigue behavior and cutting abrasion characteristic of fined-grained TiB2 matrix ceramics, self-toughening mechanisms induced by the reinforcements of fine TiB2 platelets are set up through composition optimization and microstructure modification of the materials, so that low-cost high-performance TiB2 matrix composites as tool materials suitable for high-speed continuous cutting iron-based or non-iron-based alloy of the hardness larger than HRC52 are achieved.

本立项采用超高重力场燃烧合成改进工艺（离心加速度最高可达2800 g），开展细晶TiB2基自增韧陶瓷刀具材料制备与改性研究。基于陶瓷基复合材料界面设计理念，根据材料热力学与化学反应热力学，建立制备TiB2基陶瓷的材料成分体系与燃烧合成体系数据库。通过对TiB2基陶瓷在超重力场远离平衡态下的凝固行为研究，达到控制TiB2小平面生长与陶瓷细晶组织发育之目的，制备出高致密性TiB2基细晶陶瓷材料。通过陶瓷断裂行为、高温氧化行为、热震疲劳行为与切削磨损特性研究，并通过优化材料成分与工艺进行材料改性，达到材料补强增韧之目的，进而制备出适于对硬度大于HRC52的铁基与非铁基合金进行高速连续切削的低成本、高性能TiB2基陶瓷刀具材料。

TiB2是一种前景广阔的新型陶瓷刀具材料，但是常规制备技术难以实现其成形与致密化，这也限制了该材料在切削加工领域的实际应用。本项目率先采用超重力下燃烧合成技术，开展TiB2基陶瓷刀具材料的凝固成形、致密化与切削性能研究。基于复相材料的相容性原理和燃烧合成热力学基本原理，选择和构建出了TiB2基陶瓷的合成体系。重点研究了TiB2片晶基陶瓷的凝固行为、致密化和补强增韧机理，发现(Ti+B4C+C+Si)体系的燃烧合成中间产物为TiB2(S)+[Ti-Si-C-B](L)，在其凝固过程中，TiB2的固有结晶属性是TiB2发育成片晶的前提，[Ti-Si-C-B](L)液相环境是TiB2发育成片晶的关键，TiC和SiC依次析出能够对TiB2片晶基体有效补缩，促进陶瓷致密化。由于具有更高的致密性，TiB2-TiC-5%SiC具有最佳力学性能，另外，SiC的存在也显著改善了材料的高温氧化性能，因而能够胜任淬硬20CrMnTi钢和不锈钢1Cr18Ni9Ti的机械加工。本研究的成果将为新型TiB2基陶瓷刀具的开发奠定理论与实验基础。