扩散焊接头断裂预测热力学解析模型及韧化机制研究

面对高端制造业对高韧性扩散焊的迫切需求与现有接头“韧性过低且分散”共性不足间的突出矛盾，本项目提出：从金属断裂裂尖塑变的非线性非平衡热力学属性与自洽性本质出发，首先，基于“Onsager-Ziegler最大熵产生原理”及其推知的体系演变法则，克服传统材料学断裂模型或机制的准确性局限，以及传统力学断裂模型的完备性不足，构建正定（完备）性热动力学方程组，以及金属母材断裂热力学自洽解析模型；其次，系统分析扩散焊典型缺陷“界面微孔”所引发的应力应变集中，对裂尖塑变与裂纹扩展的影响，建立接头断裂解析模型，并通过塑变体积、耗散功以及微孔附近局域韧-脆断裂转变，建立裂尖塑变与直接扩散焊接头韧性的量化关系；最后，基于断裂模型揭示的静、动态裂尖体系形成与演变机制，分别针对两类裂尖的塑变耗散强化，研究“纳米孪晶强化”与“多层级架构+晶内第二相”韧化中间层制备，获得高韧扩散焊接头制造技术与设计原则。

The diffusion bonded joint with excellent toughness is highly demanded for high-tech manufacturing, but the joint produced by diffusion bonding usually presents the common shortcoming of “insufficiency and dispersion of toughness”. To deal with this apparent contradiction, this project proposes the following research program. Firstly, the Onsager-Ziegler maximum entropy production principle (OZ-MEPP) and its deduction of system evolution laws are used, the aim of which is to overcome the limited precision of the fracture model in the materials science field and the incompleteness of the fracture model in the mechanics field. Then a self-consistent and analytical thermodynamic model with positive definite (complete) property is constructed for characterizing the base metal fracture; secondly, the effect of the stress and strain concentration caused by the typical defect “interfacial micro voids” of diffusion bonding joints on the crack tip plastic deformation and crack propagation is systematically analyzed, so as to establish an analytical model of joint fracture. And through the plastic volume, dissipation work, and the local toughness-brittle fracture transition near the micro voids, the quantitative relationship between the crack tip plastic deformation and the toughness of the directly diffusion bonding joint is established; finally, according to the formation and development of static and dynamic crack tip systems based on the fracture model, the preparation of toughened interlayers of “nano-twin strengthing” and “multilayer structure + intracrystalline second phase” are studied for the plastic dissipation strengthening of two types of crack tips. Consequently, the design principles and manufacturing techniques are set up for the strengthening and toughening of the diffusion bonded joint.