The fatigue crack growth behavior of electron-beam welded a286 superalloy
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I.
INTRODUCTION
JOINING of high strength materials by welding is used extensively in the airplane-, rocket-, and motor-vehicle construction industries, as it allows favorable combinations of high stiffness, low weight, and low volume in structures thus produced. To take advantage of this, a series of special welding processes have been developed. For complicated parts as well as for materials which can be welded only with difficulty, electron beam welding has been proven to be a useful method 1,2 Like other welding techniques, the problem arises that the material behavior is changed by the welding process within the weld bead and heat-affected zone. In most cases, the strength is reduced in these regions. Therefore, tests have been performed for quantitative characterization of static and dynamic properties of the welded material. In the literature, many tensile tests, 3-8 bending tests, 4'8 Charpy impact tests, 8 and fatigue tests 6'7 are reported. Few fracture mechanics studies have, however, been performed on electron beam welded material to the authors' knowledge. It is of great importance to understand the fatigue crack behavior of electron beam welded materials, as the structural integrity and service life of structures made of these materials depend on how fast small defects like porosity and microcracks within the weld and heat affected zone grow. In high temperature materials with a complex distribution of phases such defects are formed by nonoptimal welding conditions. 9 In this work we do not consider crack initiation at pores or the growth of small cracks from pores in the absence of their interactive effects; these topics will be the subject in a forthcoming work. The main topic of this study is the CaELMAR K. TSCHEGG is with Institut for Angewandte Physik, Technische Universit~t Wien, Karlsplatz 13, A-1040 Vienna, Austria. CHRISTIAN TAUSCHITZ is with Institut ffir Allgemeine Elektrotechnik und Elektronik, Technische Universit~it Wien, Gusshausstrasse 27-29, A-1040 Vienna, Austria. STEFANIE E STANZL is with Institut fiir Festkorperphysik, Universit~t Wien, Boltzmanngasse 5, A-1090 Vienna, Austria. Manuscript submitted February 23, 1981. METALLURGICAL TRANSACTIONS A
tigue crack growth behavior of iron base superalloy sheets which were electron beam welded under two different weld conditions. The two weld conditions were chosen such that one resulted in a nearly perfect weldment and the second in a weldment with microcracks.
II.
MATERIAL, WELDING PROCESSES, AND EXPERIMENTAL PROCEDURES
For the electron beam welding tests the alloy A 286 (X5 NiCrTi 26 15, W.-Nr. 1.4980), which is one of the most technologically important iron base superalloys, was used. The chemical analysis, the recommended heat treatment, and the mechanical properties at 20 ~ of this material are summarized in Table I. This alloy precipitates Cr-, Mo-, V-, Ti-, and B-carbides and the intermetallic 77 (= Ni3Ti) and y ' (= Ni3(Ti,Al)) phases during the recommended heat-treatment. The result is good mechanical properties up to 700 ~ w
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