Investigation and use of thermo physicochemical mechanism of surface deoxidation using silane-doped argon in low vacuum brazing processes

本课题的目的是研究和阐明真空钎焊过程中自然钝化钢表面的脱氧机理，从而了解和优化不锈钢的真空钎焊工艺。首先，将开发分析方法，允许在使用真空炉样工艺条件退火金属试样期间对金属表面进行表面敏感的原位分析。这些方法必须能够承受加热条件的变化，以及气体气氛的变化，包括其成分和高达1mbar的压力。特别是使用硅烷掺杂的氩气来实现规定的脱氧条件是研究计划的一个主要方面，因为在低真空过程中，这种气体混合物有望显著改善不锈钢的钎焊。现场调查将通过使用类似工艺条件的真空钎焊试验来证实。真空炉，配备了一个排气系统，允许规定的硅烷-氩气成分高达1mbar在炉内接收，用于回火和钎焊钢样品与适当的钎焊金属。通过对钎焊试样的分析，得出了钎焊在钢表面上的表面脱氧和润湿行为随工艺条件变化的相关性。此外，现场测量的实验数据将用于澄清脱氧机制和量化检测到的表面反应的动力学。这些数据是建立物理模型的基础，该模型描述了观察到的表面反应的热力学和动力学方面，并将允许预测真空钎焊的最佳工艺条件，特别是难以钎焊的不锈钢。这项跨学科研究将由汉诺威莱布尼茨大学材料科学研究所和克劳斯塔尔工业大学能源研究和物理技术研究所这两个专门研究钎焊技术和表面物理的研究所进行。此外，申请人是Clausthal材料工程中心（CZM）的创始成员，该中心是该跨学科项目的管理机构。

The objective of the proposed project is the investigation and clarification of deoxidation mechanism of natural passivated steel surfaces in vacuum brazing processes, in order to understand and then optimize vacuum brazing of stainless steels. Firstly, analytical methods will be developed, which allow a surface-sensitive in situ analysis of metal surfaces during annealing of metal specimens using vacuum-furnace-like process conditions. The methods must tolerate variations of the heating conditions as well as a variation of the gas atmosphere concerning its composition and its pressure up to 1 mbar. Particularly the use of silane-doped Argon for realizing defined deoxidizing conditions is a major aspect of the investigations planned, since significant improvements for the brazing of stainless steels are expected from this gas mixture in a low vacuum process. The in situ investigations will be confirmed by vacuum brazing tests using similar process conditions. A vacuum furnace, which is equipped with a gassing system that allows for defined silane-argon-compositions up to 1 mbar within the furnace recipient, is used for tempering and brazing steel specimens with appropriate braze metals. From an analysis of the brazed specimen a correlation between the in situ investigations of surface deoxidation and the wetting behavior of brazes on the steel surfaces as function of the performed process conditions will be worked out. Furthermore the experimental data from in situ-measurements will be used to clarify the deoxidation mechanism and quantify the kinetics of the detected surface reactions. These data are the base for a physical model to be developed, which describes the thermodynamic and kinetic aspects of the observed surface reactions and shall allow for a prediction of optimal process conditions for vacuum brazing of particular difficult-to-braze stainless steels. This interdisciplinary research will be conducted by two institutes with particular focus on brazing technology and surface physics, namely the Institute of Materials Science of the Leibniz University Hannover and the Institute of Energy Research and Physical Technologies of the Technical University Clausthal. In addition the applicants are founder members of the Clausthal Center of Materials Engineering (CZM), which serves as managing institution for this interdisciplinary project.