Brazing Under Microgravity in a Resistance Heated Furnace
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BRAZING UNDER MICROGRAVITY IN A RESISTANCE HEATED FURNACE
FRIELER Key, STICKLER Roland, University of Vienna, 1090 Wien, Austria SIEGFRIED Eberhard, Bundesanstalt for Materialprfifung, Berlin, FRG
ABSTRACT Vacuum brazing under 1-g and microgravity (carried out on TEXUS II in preparation of an experiment for FSLP) conditions revealed the effect of various parameters (e.g. thermal history, hydrostatic pressure, buoyancy forces) on the microstructure of the joint and the gap filling phenomena. The following results will be presented: (a) Design of brazing specimens (b) Variations of microstructure depending on gap width, gravity, and thermal history (c) Flow patterns of molten braze as revealed by radioactive tracer experiments (d) Evaluation of Plateau-type simulation experiments INTRODUCTION Joining metals by means of vacuum brazing is still considered an art involving numerous empirical parameters. Basic studies on the physical metallurgy of brazing require a reduction in the number of these parameters in order to reduce the complexity of the brazing process. In the present experiment we used a well defined base-metal/filler-metal system to be brazed with various gap width-s under 1-g and p-g conditions, respectively, leaving unchanged within the limits of experimental reproducibility the geometry of the specimen and the thermal cycle. In order to obtain some preliminary experience with the problems of vacuum brazing in
a space craft
environment,
a precursor experiment with simplified spec.
geometry was carried out on the TEXUS II sounding rocket flight(l). The results of this experiment serve to prepare a brazing experiment for the FSLP flight (Exp. no. 304/305). DESIGN OF THE BRAZING EXPERIMENTS The following base-filler-metal system was used in all brazing experiments carried out in the course of this investigation: Base metal: Commercial grade pure Ni (99,6 wt. % Ni, chemical analysis: 0,029 C, 0,07 Mn, 0,003 P, 0,002 S, 0,01 Cr, 0,01 Mo, 0,07 Co, 0,01 Cu, 0,14 Fe, rem. Ni, in weight %) Filler metal: Near eutectic alloy of A4 and Cu with a small of addition of Li (71,7 Ag, 28 Cu, 0,3 Li, weight %) The filler metal melts at 1033 K. The small quantity of Li is known to promote spreading of the molten filler metal. In addition to its commercial availability and a considerable amount of basic knowledge this particular base-metal/fillermetal system was selected to facilitate a comparison with results from earlier NASA brazing experiments under p-g conditions (2-7). The geometry and dimensions of the TEXUS II and the proposed FSLP specimens are shown in Fig. 1 and 2, respectively. A simple experimental setup, Fig. 3, was used to study the microstructure of joints with gap-widths up to 2 mm. Under 1-g condition gaps of this dimension cannot be filled with braze to any significant length, when the specimens are oriented with the longitudinal axis of the gaps in the direction of the gravity force. In this case the capillary force is
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ALLDI•IN-S-SINMILLIMETERS
Fig.
1: TEXUS II
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