【作者】 史进；

【导师】 涂善东；

【作者基本信息】 南京工业大学 ， 化工过程机械， 2004， 硕士

【摘要】 高温钎焊技术具有很高的装配精度，焊件高温性能优异，出于诸多高科技产品制造的迫切要求，该技术在工业领域的应用日益广泛，如飞机的高温热交换器、喷气发动机涡轮叶片、微化工机械系统、高温回热器等。为了节约运行成本，提高生成效率，钎焊结构的使用温度不断提高。而在高温环境下，即使应力小于材料的屈服极限，材料办将发生蠕变，导致应力的再分布和损伤集中，使钎焊接头成为结构在高温下服役的薄弱环节。 目前钎焊接头长时高温强度数据的积累很少，无法保证基本的强度设计，同时也缺乏描述钎焊焊缝高温下的力学本构关系。钎焊接头的焊缝非常狭窄，一般为10-150μm，采用常规方法很难直接获取其蠕变数据。本文以与钎焊同工艺下浇铸得到的铸念钎料(As-cast filler)来模拟钎缝金属，通过实验测定各材料常数值，并建立合适的本构关系。 通过建立典型不锈钢钎焊接头的有限元模型，对其蠕变应力的再分布进行计算，讨论各因素的影响，分析应力再分布的规律，指出其高温强度设计的考虑因素，给出优化的接头形式。 论文的主要研究工作和取得的结论如下： (1)对铸态钎料的高温蠕变断裂性能进行测定，得到了用Kachanov-Rabotnov方程描述钎料高温蠕变损伤行为所需的材料常数。与同等条件下的0Cr18Ni9不锈钢相比，铸态钎料的蠕变变形小，这两种材料组成的钎缝是蠕变硬焊缝。 (2)建立典型不锈钢钎焊接头的有限元模型，对接头的应力及其分布随时间的变化进行计算，指出应力再分布的规律。 (3)以接头蠕变应力再分布为依掘，参数化分析了不锈钢钎焊接头的高温强度的影响因素，并给出了接头设计的优选形式。 (4)对补钎部位进行有限元模拟，发现补钎对母材局部应力集中有较大的改善作用，可以应用于钎焊结构延寿再设计。更多还原

【Abstract】 Brazing technology has aroused increasing concerns in response to the need of manufacture of high-tech products. For instance, heat exchangers inside the aero-plane, turbine blades of the jet engine, micro chemo-mechanical system, recuperators at high temperature, etc. In order to save operating cost and to increase the efficiency, the brazed structures must suffer higher service temperature. Although the stress is generally smaller than the yield limit of the material, creep takes place at high temperature, which leads to stress redistribution and damage occurrence. Therefore the brazed joint becomes the weak part of structures serviced at high temperature.The high temperature strength data of the brazing material are essential to evaluate high-temperature performance of brazed joint. However for its high cost and time consuming, the data are so absent that the basic strength design appears rather embarrassing. Due to the difficulty in sampling testing specimens from the narrow brazed zone(usually with a width of 10-150 祄), the as-cast Ni-based filler is adopted in the creep test in the present paper. The measured creep properties are compared with those of OCrl8Ni9 stainless steel. It is shown that the brazing material has lower creep ductility and lower creep strain rate which is more sensitive to stress change. The Kachanov-Rabotnov constitutive equation, with material constants obtained from creep experiments of as-cast filler, can be used to describe the creep behavior effectively. At the same time, the gauge length variation of stainless steel overlapped brazed joints is measured and compared with the results of FEM simulation.Typical finite element models of stainless steel brazed joint are established. Based on the Norton creep constitutive equation the stress redistribution of the joints is analyzed, and effects of different conditions are discussed. From the simulated results, the features of stress redistribution are obtained. Because the joint failure depends on the stress redistribution, the influence of various factors on the strength is indicated. Optimized joint types are recommended accordingly.The major research work and conclusions of this thesis are given as following: (1) Creep and fracture performances of as-cast filler at high temperature are observed and the material constants are obtained. A Kachanov-Rabotnov equation is determined to describe the creep behavior of the brazing material. By comparison ofspecimen testing with the simulation, it is seen that the K-R equation is capable of representing the mechanical behavior of braze metal at high temperature. Because the creep strain rate of the braze metal is much lower than that of the OCrl8Ni9 stainless steel at the same conditions, the brazed joint is referred to as a creep-hard joint.(2) Typical finite element models of stainless steel brazed joints are constructed. Stress distribution and its time-dependant features are calculated. The features of stress redistribution are obtained.(3) Based on the results of the stress redistribution, factors affecting the strength of stainless steel brazed joints at high temperature are discussed. Optimized joint types for design are recommended.(4) FEM is also utilized to investigate the effect of repaired brazing on the strength of the structures. It shows that after brazing repair the local stress of the parent metal is reduced, which is beneficial to the life extension of the brazing structures.更多还原