The Effect of Heat Treatment on Tensile Yielding Response of the New Superalloy ABD-900AM for Additive Manufacturing
The heat treatment response of the new superalloy ABD-900AM, designed specifically for additive manufacturing (AM), is studied. The as-fabricated microstructure is characterised at multiple length-scales including by X-ray synchrotron diffractometry and t
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Abstract
Introduction
The heat treatment response of the new superalloy ABD-900AM, designed specifically for additive manufacturing (AM), is studied. The as-fabricated microstructure is characterised at multiple length-scales including by X-ray synchrotron diffractometry and transmission Kikuchi diffraction imaging. The very high cooling rates arising during the process suppress c′ precipitation; thus the details of heat treatment are shown to be important in establishing properties. The yield stress and tensile strength developed are marginally improved by supersolvus rather than sub-solvus heat treatment, but the ductility is then compromised. The tensile behaviour is superior to the heritage alloy IN939 which has a comparable fraction of c′; this is due to the larger refractory content of ABD-900AM and its finer scale precipitation. The internal strains developed during processing are sufficient to promote recrystallization during super-solvus heat treatment which breaks down microstructural anisotropy and promotes grain growth; however, this effect is absent for the sub-solvus case. Keywords
Additive manufacturing Ni-based superalloy HR-TKD/FSE Tensile yielding Recrystallization Synchrotron
Y. T. Tang (&) J. N. Ghoussoub C. Panwisawas D. Graham McCartney R. C. Reed Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK e-mail: [email protected] S. Amirkhanlou J. W. G. Clark A. A. N. Németh OxMet Technologies, Unit 15, Oxford Industrial Park OX5 1QU, UK D. M. Collins School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK
Additive manufacturing (AM) of superalloys presents a dilemma: an alloy must be processed without defects—more challenging as the degree of alloying increases—yet the strength level must be sufficient to justify its insertion into service. Thus for example, low-medium strength alloys such as IN625 have a wide processing window for AM [1], whereas high performance alloys such as CM247LC cannot be printed readily [2]. The broad consensus thus far is that it is the c′ content which governs processability [3]. But this broad rule-of-thumb is likely to be overly simplistic. The traditional trial and error iteration on composition and possessing design is usually experimental based, the power of complementary calculations and modelling is often underestimated. In recent years, computational modelling approaches being employed by different groups around the world are allowing new grades of alloy to be designed [4], specifically for processing by the AM method [5]. In this paper, the processing-microstructure-property relationship of a new superalloy ABD-900AM [6] is studied. The alloy is designed to operate up to 900 °C and has been engineered specifically with the objective of improving over heritage alloys which do not appear to be well matched to this new manufacturing technique. The alloy ABD-900AM contains about 33% c′ phase and studies indicate that it possesses excellent printability. The aim of this study i
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