原位TiB晶须加纳米硅化物颗粒混杂增强TMCs的制备及其强化机制研究

TiB crystal whiskers prepared with in-situ techniques, which present high strength and modulus, large aspect ratio and excellent interface bonding with matrix, make it an ideal reinforcement for Ti matrix composite (TMCs). However, orientation of TiB crystal whiskers prepared with this method distributes randomly in TMCs in most cases. This random distribution of in-situ TiB whiskers orientation results in a lower strengthening effect along a given loading direction for TiB whiskers. On the other hand, due to the in-situ TiB whiskers with a coarse network structure in TMCs, it provides plenty of space for nano particle to strengthen TMCs further. In this proposal, it is suggested to prepare hybrid reinforcement TMCs by introducing nano silicides into in-situ TiB whiskers network structure. Furthermore, thermal deformation process will be carried out to the hybrid reinforcement TMCs to increase the strengthening effect of TiB whiskers along the given loading direction. The increase in the TiB whiskers strengthening effect along this direction by thermal deformation process results from two mechanisms, i.e. the variation of TiB whisker orientation and the refinement of matrix of TMCs. These studies will be performed intensively in this proposal, including, the effects and models of in-situ TiB whiskers orientation and its strengthening effect along the given loading direction by thermal deformation, the variation of interface bonding strength between TiB whiskers with the matrix during thermal deformation process, main factors and mechanisms resulting in broke of TiB whiskers during thermal deformation process, strengthening effect and model of hybrid TMCs reinforced with in-situ TiB whiskers plus nano silicide particles. The method suggested in this proposal can be used for TMCs to optimize the part design in different loading conditions. These studies suggested in this proposal will provide very valuable theoretical guidance for the present TMCs research for adding component design and process techniques.

原位TiB晶须具有高强度、高模量、高长径比和良好的增强体/基体界面结合，是TMCs的理想增强体。但原位TiB晶须取向在TMCs中随机分布，该取向分布造成TiB晶须对既定受力方向的强化作用低。而且，原位TiB晶须在TMCs中为粗大的网络结构，为纳米颗粒强化提供了充足的空间。本项目拟在TiB增强TMCs中引入纳米硅化物，制备TiB晶须加纳米硅化物混杂强化TMCs，并通过热变形改变晶须取向，细化基体组织，增加TiB沿既定受力方向的强化效果。本项目重点研究变形对原位TiB晶须取向以及沿既定受力方向的强化效果的影响及作用模型；变形对TiB晶须/基体界面结合强度的影响规律；变形中TiB晶须断裂的主要影响因素和作用机制；晶须加颗粒混杂强化的强化效果和强化模型。本项目可在不同受力条件下对TMCs中TiB晶须位向和强化效果进行设计和优化，本项目对于优化目前TMCs的组分设计和加工工艺有重要理论指导作用。

本项目利用原位熔铸法制备了一些列TiB晶须加纳米硅化物混杂强化的钛基复合材料材料(TMCs)，研究了热变形对原位TiB晶须取向分布的作用效果及其作用模型，热变形对原位TiB晶须沿既定受力方向的强化作用的影响效果。研究了钛基复合材料中TiB晶须的不同强化机制及其强化作用的大小和定量化模型，研究了晶须加纳米颗粒混杂强化的复合强化效果和强化模型。研究了热变形中影响TiB晶须断裂的主要因素和作用机制。研究发现，铸态下 TiB 对TMCs 强化作用较低，载荷传递强化因子仅为 0.12，未能发挥 TiB晶须的载荷传递强化作用。项目建立了变形温度 850~1050 ℃和应变速率 0.02~2.5 s-1 条件下TMCs的变形的本构方程，基于其热变形行为，建立了TMCs 热加工图。通过热加工有效地改善了TMCs 微观组织和增强体 TiB 的取向，显著提高了 TMCs 的机械性能，该提升主要来自于：载荷传递强化、细晶强化和位错强化。项目重点研究了热加工中增强体 TiB 的取向变化，采用概率密度分布函数 p(θ)模型对TiB晶须强化因子 C0 的值进行了计算，分别得到铸态和热加工变形量 n=2.5 的 对应∆σ(TiB)的值为 23.56 MPa 和146.46 MPa。本项目的研究成果可用于在不同受力条件下对TMCs中对TiB晶须位向和强化效果的设计和优化提供理论参考和依据，项目成果对于优化目前TMCs的组分设计和加工工艺有重要的理论指导作用。