Influence of B and Zr on microstructure and mechanical properties of alloy 718

The basic intent of this paper is to examine the role of the minor elements B and Zr within typical specification limits for alloy 718 with respect to (i) microstructure evolution; (ii) strengthening effects and (iii) thermal stability. For this purpose, thermodynamic calculations using the software THERMOCALC were performed, varying the content of B and Zr. In addition, alloys with precisely controlled chemical composition (with content variations of 20 to 100ppm B and/or of 50 to 200ppm Zr) were prepared by drop casting in a vacuum arc furnace and hot forged, so that it was possible to compare the theoretical predictions with experimental results. The microstructure evolution was studied in detail by means of scanning electron microscopy (SEM) and x-ray diffraction. Furthermore, mechanical properties including tensile and creep behaviour were examined. Based on these results, dependencies between chemical composition, microstructure and mechanical properties will be elucidated. (AU) © 2010 by The Materials, Metals, & Materials Society. All rights reserved.