Optimizing the Diffusion Welding Process for Alloy 800H: Thermodynamic, Diffusion Modeling, and Experimental Work
- PDF / 560,719 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 91 Downloads / 198 Views
UCTION
DIFFUSION welding of superalloys, including Alloy 800H, is a critical operation in the manufacture of components for the aerospace and nuclear industries.[1–3] It involves practically all of the phenomena studied by physical and mechanical metallurgy: control of grain growth and crystallographic texture across the weld interface, diffusion processes, and phase transformations resulting in concentration profiles of different components and precipitates, and the prevention of high-temperature oxidation of different components (especially chromium). It is also necessary to optimize the welding temperature and the duration of exposure, applied compressive stress, heat-up schedule, and post-welding heat treatment.[1] Given a significant number of parameters involved, the whole process development can require hundreds of expensive experiments, their mathematical planning, and the application of multiple linear regressions or artificial neural networks.[4] RONALD E. MIZIA, Directorate Fellow, DENIS E. CLARK, Staff Research Engineer, TEDD E. LISTER, Senior Staff Research Engineer, and TAMMY L. TROWBRIDGE, Microscopy Staff Engineer, are with Materials Science Division, Idaho National Laboratory, Idaho Falls, ID. MICHAEL V. GLAZOFF, Senior Staff Research Engineer, is with the Advanced Process and Decision Systems Division, Idaho National Laboratory. Contact e-mail: Michael.Glazoff@inl.gov Manuscript submitted June 1, 2011. Article published online November 30, 2011 S154—VOLUME 44A, JANUARY 2013
However, during the last 10 to 15 years, powerful thermodynamic, diffusion, and finite element simulations (coupled to a state-of-the-art plasticity model) have come of age.[5–10] Several researchers convincingly demonstrated that their application could provide valuable guidance for the process as a whole, as well as for its individual stages.[1,6–9] For this article, an effort was made to apply the computational tools Thermo-Calc and Dictra (Thermo_Calc Software, Inc., McMurray, PA) to reduce dramatically the number of experiments required for obtaining diffusion welded parts with excellent mechanical properties and weld quality on a consistent, repeatable basis. Several of modern experimental techniques have helped to achieve that goal for Alloy 800H, which will be used in a compact, micro-channel, diffusion-welded, intermediate heat exchanger (IHX) for a proposed very high temperature reactor (VHTR). The VHTR will be a graphite–moderated, helium– cooled, prismatic or pebble bed, thermal neutron spectrum reactor. The IHX will transfer heat from the primary (reactor side) heat transport system (PHTS) to the secondary heat transport system (SHTS). The IHX will transfer this heat to downstream applications such as hydrogen production, process heat, and electricity generation through a steam generator. The micro-channel plates that make up the heat transfer surfaces of the IHX will have to be assembled into an array; a strong candidate joining process for this assembly is diffusion welding. To achieve the formulated goals, several experimental a
Data Loading...
