Grain Boundary Analysis of Crept Alloy 617
- PDF / 349,465 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 24 Downloads / 208 Views
Grain Boundary Analysis of Crept Alloy 617 Fan Zhang and David P. Field School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99163, U.S.A. ABSTRACT Alloy 617, a high-temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the next generation nuclear plant, which is highly influenced by thermal creep. The main objective of this study is to inspect the crept grain boundaries under its imitated working condition, and to determine which boundaries are susceptible to damage and which are more resistant, in order to help improve its creep resistance in future manufacturing. Electron backscatter diffraction was used to measure the proportions of each boundary by observing and analyzing these crept microstructures. The grain-boundary distribution can be expressed in terms of five parameters including three parameters of lattice misorientation and two parameters of the grain-boundary plane normal. Three conditions were analyzed: the original material, metal that was annealed without stress, and ones that were crept at 1000ºC at 19 MPa and 25 MPa for various times. Though observation, it is found that the voids seldom occur at low angle grain boundaries, and coherent twin boundaries are also resist to creep damage. INTRODUCTION INCONEL alloy 617, one of the austenitic nickel-chromium-based superalloy, is a solid-solution strengthened alloy with exceptional combination of metallurgical stability and oxidation resistance at high temperatures [1]. Recently it has been considered to be used as heat exchanger for next-generation nuclear power reactor on the next generation nuclear plant (NGNP) [2]. One of the major damage types of heat exchangers during their service life in NGNP is thermal creep, which is occurs over extended time under high stresses or high temperatures. There is considerable interest in creep phenomena for alloy 617, which includes creep microstructure of foil material [3], internal oxidation [4], carbide precipitation [5], and creep behavior and long-term creep life extrapolation [6]. Among all these topics, grain boundary structure appears to relate with crack generation in many conditions. Similar to alloy 617, alloy 600 and 718 have been investigated and it was found that grain boundary structure is related to grain damage (voids, cavitations, and cracking) that occurs on boundary misorientation [7-8]. It has been shown that misorientation distribution function (MDF) alone is not sufficient to characterize the boundary structure [10]. The stereological analysis provides a five-parameter grain boundary character distribution (GBCD) description, which includes three parameters of misorientation (which can be obtained from the MDF), and two of the orientation of the grain boundary plane normal (which consists of the boundary trace vector and the boundary inclination angle). Included in the definition are the coincident site lattice (CSL) and knowledge of where the boundary plane lies in the coordinate frame defined by the cryst
Data Loading...
