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Modeling of Process and Microstructure in DLD IN718 Deposits: Process

Modeling of Process and Microstructure in DLD IN718 Deposits: Process

\Users\Sub\Desktop\#1_Draft\Word Version\Figures and Tables for Welding Journal\Figure 6-2.tif                Ni superalloy is the metal most widely used for hot section component in the engine because it is very resistant to corrosion and maintains reasonably high strength at elevated temperature. In aircraft engine and gas turbine engine systems, single crystalline structures have been popularly used due to better creep resistance and fatigue behavior. However, the production cost of single crystal is not only significantly expensive due to complexity of process parameter control but also Ni superalloy itself is high in price. Thus, repair of the damaged parts instead of replacing have been strongly required from industry fields. In this research, laser additive manufacturing process is used to repair the damaged turbine blade. However, property degradation and micro-cracks are observed in the clad deposit. Therefore, a better understanding for the parameter-microstructure-property relationship of the clad deposit is required to solve the problems in this study. As seen before, micro-cracks and property degradation were found in the clad deposit. Therefore, developing new methodologies which ensure the desired high temperature properties is necessary. The research is separated into two areas: material modeling and process modeling. Ultimately, the two will be integrated into a unified model. The material modeling effort is being conducted by a collaborative group while process modeling is the focus of this project. The two models will be integrated for optimization of the turbine blade repair process. Detailed goals are discussed below.

▪ Goal 1 (material modeling): determine mechanism of cracking in laser cladding deposits

   - Task 1: characterize laser clad microstructure as a function of location in the deposit

   - Task 2: assess effect of small variations in the powder composition on deposit microstructure and cracking

▪ Goal 2 (process modeling): understand effects of cladding process parameters on defects

   - Task 1: determine the relationship of weld pool transport and solidification behavior to deposit microstructure and cracking

   - Task 2: find an effect of thermal cycle on the microstructure and cracking

▪ Integration of goal 1 and 2: develop new methodologies to control cracking tendency and achieve desired high-temperature properties

Sponsor:  Rolls Royce (through NSF I/UCRC)

Graduate Student: Yousub Lee (PhD)

Collaborator: Prof. Mike Mills

Publications

  1. Y.S. Lee, M. Nordin, S.S. Babu, D.F. Farson, 2013, “Influence of Fluid Convection on Weld Pool Formation in Laser Cladding”, submitted
  2. Y.S. Lee, M. Nordin, S.S. Babu, D.F. Farson, 2013, “Effect of Fluid Convection on Dendrite Arm Spacing in Laser Deposition”, submitted