预测钛合金超塑成形－扩散连接(SPF/DB)界面层的断裂韧度

提出根据超塑成形－扩散连接(SPF/DB)的工艺技术参数预测扩散连接界面层断裂韧度的计算方法，并对TC4/TA2连接件，开发了相应的界面层断裂韧度的分析和预测软件系统。该计算方法首先在理论分析和试验的基础上，建立扩散连接界面层成长模型，获得扩散连接件界面层厚度的计算公式，确定材料过渡参数m的计算方法；其次对已有的混合型外载的界面断裂准则进行修正，使其适用于扩散连接件界面层断裂时能量释放率曲线的函数模型。计算结果与试验结果吻合良好。分析结果表明：在允许工艺参数范围内，扩散连接件界面断裂韧度随成形温度、成形压力和保压时间的提高而提高。其中，成形压力影响最大，然后依次为保压时间和成形温度。为了提高扩散连接界面层的断裂韧度，必须通过界面层设计来提高其界面裂尖断裂混合度，而上述各工艺技术参数，正与其裂尖断裂混合度的大小密切相关。

PREDICTION OF FRACTURE TOUGHNESS OF SUPERPLASTIC FORMED / DIFFUSION BONDED INTERFACES FOR TITANIUM ALLOYS

A calculating method is put forward for predicting the fracture toughness of SPF/DB interfaces according to the process parameters, and further, a corresponding interfacial fracture toughness analysis and prediction software system for TC4/TA2 are developed. For the calculating method, first, based on the theoretical analyses and experimental results, the growing model of the diffusion bonded interfaces is established, then the formula for calculating the thickness of interface layer is obtained and the calculation for material transition parameter m is established. Secondly, the modified general criterion for fracture toughness under mixed-mode loading is proposed for fitting the functional model of the fracture toughness curves of the interfaces in the diffusion bonded component. The results that are computed agree very well with experimental data. The analytical results show that within the limits permitted of process parameters, the fracture toughness increases with increase in forming temperature, forming pressure and in time applied pressure. Among them, the influence of forming pressure is maximum, the influence of time and temperature are in proper order. In order to increasing the interfacial fracture toughness of the components diffusion-bonded, the fracture mode mixture of the fracture tip in the interfaces must be increased with the interfacial layer design. The process parameters above mentioned are just concerned with the fracture mode mixture of the fracture tip closely.