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WELDING RESEARCH -S209WELDING JOURNAL Ti interface of aged brazed joints. Repre- sentative EMPA traces are provided in Fig. 1

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Content	WELDING RESEARCH -S209WELDING JOURNAL Ti interface of aged brazed joints. Repre- sentative EMPA traces are provided in Fig. 12 for the aging conditions of 150°C (302°F) for 100 days and 575°C (1067°F) for 300 days. Recall that the interface of the as-fabricated condition (Fig. 7B) was comprised of two sublayers, each approx- imately 2 to 3 µm (7.9 x 10–5in. to 1.2 x 10–4in.) thick and separated by a narrow band having a high concentration of iron. Aging at 150°C (302°F) for 100 days re- sulted in the following changes: There was a slight thickening of both sublayers to values of approximately 3 to 5 µm (1.2 to 2.0 x 10–4in.). The intensity of the iron peak separating the two sublayers grew slightly. The midpoint composition of sublayer No. 1 (located next to the base metal) was unchanged when compared to the as-fabricated condition ((Fe,Ni,Cu)3(Ti,Cr,Nb,Mo)2). The sub-layer No. 2 composition changed from (Fe,Ni,Cu)2(Ti,Cr,Nb,Mo) to (Fe,Ni,Cu)7(Ti,Cr,Nb,Mo)3after aging. The aged sublayer No. 2 also exhibited an increased level of titanium, as well as significant spatial fluctuations in the chromium, iron, and copper concentra- tions. In fact, for two of the five EMPA traces, the chromium and iron concentra- tions increased to an average of 14% and 22%, respectively, and the copper concen- tration dropped to approximately 3%, re- sulting in a composition of (Fe,Ni,Cu)3(Ti,Cr,Nb,Mo)2, which resembled that of sublayer No. 1. Aging the Inconel™ 718/Ag-Cu-Ti specimens at 575°C (1067°F) for 300 days (Fig. 12B) caused the interface reaction layer thickness to grow to 22 µm (8.7 x 10–4 in.). Two sublayer compositions were identified from the EMPA traces, both having compositions similar to those ob- served after aging for 100 days at 150°C (302°F): sublayer No. 1, (Fe,Ni,Cu)3(Ti,Cr,Nb,Mo)2and sub-layer No.2, (Fe,Ni,Cu)7(Ti,Cr,Nb,Mo)3. Sublayer No. 2 ex- hibited locally higher concentra- tions of chromium (8–9%) and iron (25%) that were compensated by proportional de- creases in the con- centrations of other elements; the cop- per content re- mained the same for all five traces. In summary, the effect of aging treat- ments on Thermo-Span™/Ag-Cu-Ti braze joints was a slight decrease in the interface reaction zone thickness; there were no sig- nificant changes to the sublayer composi- tions. In the case of the Inconel™ 718 /Ag- Cu-Ti specimens, aging treatments caused a noticeable increase in the thickness of the reaction layer. Aside from local chromium, iron, and copper fluctuations in the composition of the No. 2 sublayer, the sublayer compositions were similar to those recorded for the as-fabricated con- dition. Four-Point Bending Strength: Post-Aging Condition The four-point bend strength data from the aged Thermo-Span™/Ag-Cu-Ti and Inconel™ 718/Ag-Cu-Ti specimens appear in Fig. 13. The aging treatments did not appear to cause a significant change to the strength of the Thermo- Span™/Ag-Cu-Ti brazed joints — Fig. 13A. The possible exception was the sin- gle specimen aged at 350°C (662°F) for 100 days. The repeatability of this latter test was not confirmed. The fracture surfaces of samples aged at 350°C (662°F) for 100 days and 575°C (1067°F) for 200 days were examined. At low magnification, the fracture surfaces appeared similar to those of the as-fabri- cated case (Fig. 9A) in which the fracture path was located near the filler metal/base metal interface. Shown in Fig. 14 are higher magnification SEM images of the fracture surfaces. The specimen aged at Fig. 14 — SEM micrographs of the fracture surfaces of Thermo-Span™/Ag-Cu-Ti bend bars aged at different temperatures. A — 350°C (662°F) for 100 days; B — 575°C (1067°F) for 200 days. Fig. 15 — Optical micrograph of the fracture path in a Thermo-Span™/ Ag-Cu-Ti specimen that was aged at 575°C (1067°F) for 200 days prior to testing. AB
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