Recrystallization and aging effects associated with the high temperature deformation of waspaloy and inconel 718
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INTRODUCTION Despite the many advantages offered by advanced techniques such as directional solidification, hot isostatic pressing and oxide dispersion strengthening, there remains a considerable demand for wrought superalloys produced by more conventional processes. When it comes to the behavior of superalloys under forging conditions, although the general relationships between microstructure and mechanical properties are understood at least generally, ~ the influence of the hot working conditions on the subsequent microstructure and properties is still incompletely known. This investigation was therefore aimed at a study of the hot working mechanisms involved in the deformation of the nickel-based superalloys. In particular, the softening processes that operate both during and after the deformation of Waspaloy and Inconel 718 were investigated. After its inception, the project was extended to obtain additional information concerning the appearance of the yield drops which occurred while testing both materials. EXPERIMENTAL MATERIALS AND PROCEDURE The materials investigated were: i) Waspaloy--a nickel-base superalloy supplied by TRW Inc., of Minerva, Ohio, and ii) Inconel 718--a nickel-iron base superalloy supplied by the Special Metals Corp., of New A. A. GUIMARAES is Manager, Metallurgical Services, Eletrometal Aqos Finos S.A., Campinas, S.P. Brazil. J. J. JONAS is Professor of Mechanical Metallurgy, McGill University, Dept. of Metallurgical Engineering, 3450 University Street, Montreal, Quebec, Canada H3A 2A7. Manuscript submitted November 28, 1980.
Hartford, New York. Both materials were received in the heat treated condition for optimum high temperature creep and stress rupture properties. The detailed chemical analyses of these alloys are given in Table I. The tests were carried out by hot compression under a high purity argon (~--10 ppm 02) atmosphere on cylindrical specimens of the form shown in Fig. 1. The specimens were machined from rods which were initially 12.7 mm in diameter. During each test, the crosshead speed was maintained proportional to the specimen height, so that constant true strain rates in the range 10-4 s-i to 1 s-l were applied. The grooves seen in Fig. 1 were designed to promote uniform flow, by retaining the glass lubricants used (Table II), and releasing them gradually in the course of the increase in the specimen/tooling interface area. To conduct an actual test, the temperature of the
Table I. Composition of the Materials Tested In Wt Pct Element
Waspaloy
Inconel 718
C Mn Si Cr Ni Co Mo Nb + Ta Ti A1 B S P Cu Fe Zr
0.062 0.02 0.10 19.35 Balance 13.34 4.19 -2.94 1.30 0.005 0.006 0.015 0.02 0.82 0.062
0.030 0.16 0.11 18.10 Balance 0.37 3.05 5.34 0.98 0.49 0.003 0.002 0.010 0.10 18.26 --
ISSN 0360-2133/81/0911-1655500.75/0 METALLURGICAL TRANSACTIONS A 9 1981 AMERICAN SOCIETY FOR METALS AND VOLUME 12A, SEPTEMBER 1981--1655 THE METALLURGICAL SOCIETY OF AIME
Table II. Lubricants Used for the Mechanical Tests
Glass
Type
Corning Corning Ferro Corning
Temperature Range
0010 7
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