B4C/钛合金粒径微纳错配-原位自生复合增材制造冶金组织调控及其机理研究

增材制造是航空航天等领域新兴的重要加工手段，但成型后粗大柱状晶和组织不均匀等冶金问题，已成为推动其深入应用的瓶颈。项目提出利用B4C与钛合金粒径差异及表面纳米修饰对增材制造冶金组织调控的新思路，建立错配度Ф（D钛/DB4C），利用原位自生增加非自发形核密度，提高形核动力，实现柱状晶向等轴晶转变(CET)。系统研究错配度作用下沉积组织演变规律，揭示其对原位自生、非自发形核量、晶粒择优生长的热-动力学作用，获得CET转变临界错配度(Ф微临界和Ф纳临界)；研究循环沉积过程层间原位自生及增强相重熔再生对形核质点的促进作用，揭示非平衡凝固过程临界错配度对细晶化调控机制;采用微/纳双临界Ф协同沉积，明晰等轴晶形成机理，揭示非自发形核主导机制，优化工艺；借助外场，提供组织均匀性、降低缺陷，建立错配度-添加比例-工艺参数-晶粒尺寸-缺陷-力学性能相关性，成果可为增材制造冶金组织精准控制提供理论和实验依据，

Additive manufacturing is a new and important processing method in aerospace and other fields, but metallurgical problems such as coarse columnar crystal and uneven structure after forming have become the bottleneck to promote its in-depth application. The project proposes a new idea of using the difference of particle size between B4C and titanium alloy and in-situ autogenous control of metallurgical structure in additive manufacturing. The degree of mismatch Ф (D-Ti / DB4C) was established, the density of non spontaneous nucleation was increased by in-situ autogenesis, the nucleation power was increased, and the transformation from columnar crystal to equiaxed crystal (CET) was realized. The evolution rule of deposition structure under the effect of mismatch degree was studied systematically, and its thermokinetic effect on in-situ, non spontaneous nucleation and preferred grain growth was revealed. The critical mismatch degree of CET transition (Ф micro critical and Ф nano critical) was obtained. The promotion of nucleation and nucleation by in-situ intergranular growth and enhanced phase remelting during cyclic deposition was studied; Study promoting effect of in-situ autogenous and enhanced phase remelting on nucleation and particle formation between interlayer of cyclic deposition process. Reveal the mechanism of critical mismatch on fine crystallization in non-equilibrium solidification process. Co deposition of micro / nano double critical Ф, clarify the formation mechanism of equiaxed crystal, reveal the dominant mechanism of non spontaneous nucleation and optimize the process. With the help of outfield, it can provide tissue uniformity and reduce defects.Finally determining the correlation between mismatch degree, addition ratio, process parameters, grain size, defect and mechanical properties. The research results can provide theoretical basis and experimental basis for precise control of grain size and metallurgical microstructure in Additive Manufacturing, and promote development of metallurgical theory of incremental manufacturing.