Prediction of the microstructure evolution and hot cracking index in electron beam welding of Inconel 713LC gas turbine blades

点击翻译按钮获取中文摘要

Siemens Canada, one of the largest companies in the world in the field of electrical engineering, energy and transportation is specialised in gas turbine engines used for power generation. In such applications at high temperature, the selection of materials is critical in order to obtain high efficiency and reliability. For such applications, nickel-based superalloys are used due to their good creep resistance, tensile strength and oxidation resistance. Siemens selected specifically the Inconel 713LC alloy for the fabrication of turbine blades that are subjected to tensile loading at high temperature. The industrial problem to be solved appears during the joining of turbine blades in the shrouds location by electron beam welding (EBW). The lower heat input associated with this welding process leads to smaller fusion zone (FZ) and heat-affected zone (HAZ) and high cooling rates. As a consequence of fast solidification of the FZ, the microstructure becomes finer than that of the parent material resulting in localised reduced creep resistance. In addition to that, the high tensile stresses generated during cooling increase the risk of hot cracking in the FZ and HAZ. Depending on the welding operational conditions, the high level of rejected parts becomes an important issue for the company. During the last years, the engineers of Siemens Canada have deployed a major effort in the thermomechanical modeling of the EBW process. They could simulate the heat flow in the materials around the weld in order to obtain a map of temperature distribution and residual stresses that are known to increase the risk of hot cracking. The aim of the proposed research project is to evaluate the feasibility to predict the evolution of the microstructure of the Inconel 713LC alloy in the FZ and in the HAZ in order to determine a hot cracking index that could be used to evaluate the risk of crack formation during cooling and the locations where this phenomenon is more prone to occur. The originality of the project is related to this process-microstructure-properties relationship that is not normally present in commercial finite element software tools for welding processes.