Solidification behavior of Inconel 713LC gas turbine blades

Significance 

Inconel is a superalloy of nickel that is comprised of chromium and iron, and portrays excellent resistance to corrosion at high temperatures. Inconel-713LC is a low carbon nickel-based superalloy, generally produced by investment casting, which is widely used in hot section components of gas turbines engines. The efficiency and reliability of a gas turbine heavily depends on the material from which it is crafted from. To this end, Inconel-713 low carbon alloy is the most suitable material for the fabrication of turbine blades that are subject to tensile loading at high temperature. Research has shown that the excellent strength of this alloy is mainly provided by the γ’ coherent precipitates (an intermetallic Ni3(Al, Ti) compound) within the γ matrix. Unfortunately, despite much having been done on this, there is no single report on a comprehensive analysis of the solidification behavior of Inconel-713LC gas turbine blades under a variety of cooling conditions during electron beam welding.

Dr. Mohsen K. Keshavarz in collaboration with Professor Sylvain Turenne at École Polytechnique Montréal and Dr. Ali Bonakdar at Siemens Canada developed a physical model that could be used to predict the evolution of the microstructure of the Inconel-713 low carbon alloy in the fusion zone. They also aimed at establishing the empirical correlation between the secondary dendrite arm spacing in the fusion zone and cooling rate. Their work is currently published in Journal of Manufacturing Processes.

The outcome of this research can be employed to determine the hot crack index which assists in evaluating the risk of crack formation during cooling and also in locating the spots where the phenomenon is likely to occur. The team utilized the results of a numerical model for the electron beam welding process to compute the cooling rates during solidification of the weld. Eventually, the solidification behavior of the Inconel-713LC under a variety of cooling conditions during electron beam welding was investigated.

The authors observed that the rapid solidification of fusion zone led to very fine dendritic microstructure of the weld. Additionally, by incorporating the calculated cooling rates with the microstructural observations, they introduced an empirical relation between cooling rate and secondary dendrite arm spacing. To be more precise, the calculated cooling rates during solidification of electron beam welding of Inconel-713LC showed some high magnitudes ranging from 700 K/s to more than 5600 K/s at different points in the fusion zone.

The study has successfully presented a model that accurately predicts the evolution of the microstructure of the Inconel-713 low carbon alloy in the fusion zone. From the analysis undertaken, it has been revealed that the segregation of elements related to the formation of NbC occurs in the interdendritic regions in the fusion zones and at the grain boundaries in heat affected zone and parent material. To this end, the results and observations of this work can be used to understand hot cracking causes in the electron beam welding of Inconel-713LC and reduce its occurrence.

Solidification behavior of Inconel 713LC gas turbine blades during electron beam welding

  1. Shroud, weld line, and position of studied zones in this work.
  2. Calculated solidification cooling rates during cosmetic pass (the 2nd pass) of EBW of Inconel 713LC blades.

About the author

Mohsen K. Keshavarz, Ph.D.
Department of Mining & Materials Engineering- McGill University

Dr. Mohsen K. Keshavarz is a Postdoctoral Research Fellow at the Department of Mining and Materials Engineering in McGill University. He earned his Ph.D. in Materials Engineering (Metallurgy) in 2014 at Polytechnique Montreal (University of Montreal).  He has also received his BSc (IAUN, 2005) and MSc (Shiraz University, 2009) degrees in Materials Engineering. Dr. Keshavarz gained valuable experience working on several research projects where he synthesized, developed, manufactured, and characterized metals, ceramics, semiconductors, and composite materials.

His expertise and most recent research activities are in engineering the micro- and nano-structure of advanced and functional materials, synthesis and characterization of materials for energy applications, and manufacturing of materials with high biocompatibility, and enhanced antibacterial and corrosion behaviors.

About the author

Sylvain Turenne, ing., Ph.D.
Department of Mechanical Engineering
École Polytechnique Montréal

Sylvain Turenne is a Professor of Mechanical Engineering at École Polytechnique of Montréal, Québec, Canada. He has obtained his engineering degree (B. Eng., 1984) in engineering physics and his master’s degree (M. A. Sc., 1986) in metallurgical engineering, both from École Polytechnique. He has obtained his Ph. D. (1992) in metallurgical engineering from Laval University (Québec, Canada). During nearly ten years from 1986 to 1995, he worked as a researcher and group leader for the Processes Development Section at the Industrial Materials Institute, a division of the National Research Council of Canada.

His main fields of expertise were related to powder metallurgy, foundry processes and metal matrix composite processing. In 1995, he was hired at École Polytechnique as professor involved in research fields related to shaping processes applied to metals and composites, particularly in powder metallurgy and semi-solid processing. From 2010 to 2016, he was the Chairman of the Department of Mechanical Engineering.

About the author

Ali Bonakdar, Ph.D.
Power and Gas Division
Siemens Canada

Dr. Ali Bonakdar is working at Siemens Canada, Power and Gas division, as Advanced Manufacturing Technology Lead responsible for strategic development of different advanced manufacturing processes including additive manufacturing. In addition to his industrial role, he is an Affiliated Professor at the University of Waterloo, Concordia University and École de technologie supérieure (ÉTS) all based in Canada.

Reference

Mohsen K. Keshavarz, Sylvain Turenne, Ali Bonakdar. Solidification behavior of inconel 713LC gas turbine blades during electron beam welding. Journal of Manufacturing Processes 31 (2018) 232–239

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