Microstructural Development and Performance of Welds in Energy-Related Alloys

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The global demand for cheap energy pushes our industries to ever increase the efficiency and decrease the cost of natural resources exploitation. Energy exploitation equipment, such as drilling shafts, piping, and pressure vessels, are increasingly designed for higher temperature, higher pressure, and more severe chemical environments, which require the usage of higher-grade alloys, such as new chrome-moly steels and nickel-based superalloys. As an indispensible process for fabricating or repairing the equipment, welding generally induces unfavorable microstructure changes and thermal stresses in the joint, which often becomes the weakest link in a structure. The Short-term Objectives in this application are (1) to conduct a well-justified study of microstructural evolution for selecting welding and post-weld heat treatment conditions, and to correlate microstructure with room-temperature and high-temperature strength of chrome-moly steel welds, and (2) to develop an innovative laser cladding process for a nickel-based superalloy to produce minimal dilution and distortion to the directional drilling shafts, and to prove rapid heating cycles during laser cladding will promote finer microstrucure and suppress the formation of detrimental phases. The educational objective of this program is to train future highly qualified personnel in non-equilibrium phase transformations of steels and superalloys, advanced mechanical testing methods, and numerical modeling of heterogeneous material performance. Our Long-term Objective is to develop a new welding metallurgy for advanced alloys in order to manufacture high-performing structures and maintain Canada’s competitiveness in welding and metal fabrication for energy and natural resources. The techno-economic impact of the proposed program on Canadian industry is expected to be very large. Firstly, the research results will directly enhance the efficiency and safety of hundreds of Cr-Mo steel structural units in chemical, power generating, and natural resources industries. The direct savings in the material cost of alloy shafts are estimated to be millions of dollars in Alberta alone. Secondly, the technical findings will contribute to materials engineering and physical metallurgy by offering new knowledge on the microstructure-process-properties relationship for an important class of engineering alloys. There will be expected technical innovations in the testing methods for chrome-moly steels, and new inventions in laser welding of precision and expensive Alloy 718. Last but not least, this research program will help maintain the applicant’s track record in HQP training and serve as a unique platform for training high-quality graduate students in non-equilibrium physical metallurgy of critical alloys.