At Gd concentrations of 1.49 wt-% and higher, the fL values never drop below 0.10 in the mushy zone. Also note that the fL values do not decrease as substantially with increasing distance for these higher Gd alloys. Each of these factors would help promote a more continuous liquid phase between the fully molten weld pool and the solid + liquid mushy zone, thus permitting the backfilling that was observed experimentally. The decrease in solidification temperature range that occurs due to a reduction in the liquidus temperature also contributes to the improved cracking susceptibility of the alloys with Gd concentration higher than 1.49 wt-%. Summary The ever-increasing demand to produce energy from a variety of ever-decreasing resources has created the need to develop new plants that use existing fuel sources more efficiently. This, in turn, places a heavy demand on developing new engineering alloys that can be utilized in aggressive conditions that cannot be tolerated by existing alloy systems. As the alloys become more complex, it is likely that they will also be subjected to more complicated changes in microstructure during the weld thermal cycle. In view of this, it is important for alloy producers, end users, and research organizations to collaborate so that welding technology can be developed in parallel with the discovery of new materials. This approach will permit strategic changes to new alloys during the design stage, thus avoiding the potential for limited use of newly developed alloys in applications where welding is required. It is important to note that many of the inferior properties of fusion welds are related to the steep gradients in chemical composition and microstructure that form across the heat-affected zone and fusion zone. Thus, emphasis in future research should be placed on understanding, controlling, and where required, minimizing these gradients through alloy and process control. Computational modeling can play a key role in this area by accelerating the understanding of microstructure and property changes that occur during welding. While significant progress is being made on the front of microstructural modeling, much work is still needed to predict mechanical properties of welds from knowledge of the microstructure. Similarly, techniques are needed to determine long-term creep properties from short-term tests. This area is particularly challenging because the longterm creep properties are invariably controlled by microstructural changes that occur at very long times, and these changes can be difficult to properly simulate with short-term tests. Lastly, training of graduate-level engineers is also vitally important to ensure safe and reliable operation of welded structures that will be used in energy applications. While physical metallurgy forms the basic discipline for understanding the complex phase transformations that occur during welding, the number of engineers with basic skills in physical metallurgy has declined over the years as this form of training gets replaced with other “modern” materials topics in areas such as nanotechnology, biotechnology, etc. While these fields are certainly important, it is equally important to ensure a sufficient level of graduate engineers are trained to meet the demands of industrial fabrication and maintenance required in energy and other areas that rely so heavily on manufacturing. Industry can play an important role in this area through support of graduate research programs in order to fill the gap from government funding that has declined over the years. A successful example of industry/university collaboration is currently represented by the National Science Foundation Center on Integrated Materials Joining Science for Energy Applications. This center is a joint effort through four universities (Ohio State, Lehigh, Colorado School of Mines, and University of Wisconsin-Madison) that is supported by both NSF and 31 member companies. Research at the center is focused on a wide range of issues related to joining for energy applications while simultaneously supporting ~ 30 graduate students who are often hired by member companies. This type of industry/university collaboration is essential for continuing to meet the future needs of welding and metallurgical engineers. Acknowledgments The author gratefully acknowledges financial support of this work through the NSF I/UCRC Center for Integrative Materials Joining Science for Energy Applications (CIMJSEA) under contract #IIP-1034703 and the U.S. Department of Energy, Assistant Secretary for Environmental Management, under DOE Idaho Operations Office Contract No. DEAC07 99ID13727. The author is also grateful to collaborators who made significant contributions to the research presented in this study, including Drs. Charles Robino and Ron Mizia and graduate students Michael Minicozzi, Andrew Stockdale, and Daniel Bechetti. References 1. Annual Energy Review. 2011. U.S. Energy Information Administration, DOE/EIAReport 0384. 2. International Energy Outlook. 2013. DOE.EIA Report 0484. 3. Pauling, L. 1938. The nature of the interatomic forces in metals. Physical Review 54: 899–904. 4. Jones, C. 1997. Power January/February, pp. 54–60. 5. Whitaker, R. 1982. EPRI Journal pp. 18–25. 6. Urich, J. 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