13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 2. Testing materials and experimental setup The brazed joints used for the actual investigations consisted of the steel AISI CA 6-NM (X 3 CrNiMo 13-4) as substrate material and of the gold-nickel alloy Au-18wt.-% Ni as filler metal. The substrate material contains 0.05 wt.-% carbon, 13wt.-% chromium, 4 wt.-% nickel and small amounts of molybdenum. Brazing was performed using foils of the filler metal with a thickness of d = 100 μm. Besides its comparably low melting point of 955°C, the filler metal is characterized by good corrosion resistance and excellent wetting behavior. The brazing process was performed at T ≈ 1000°C in reducing atmosphere with H2 as a shielding gas. After brazing, a two-step heat treatment procedure was performed at T1 ≈ 700°C and T2 ≈ 650°C with N2 was as a shielding gas to optimize the mechanical properties of the brazed joints and to improve the materials resistance against stress corrosion cracking. The mechanical properties of the substrate material, filler metal and brazed joints taken from round specimens are shown in Table 1. The mechanical properties of the filler metal were measured in the scope of in situ SEM investigations [9]. Table 1: Mechanical properties of base material, filler metal and brazed joint E [GPa] σy [MPa] σUTS [MPa] A [%] HV0.05 AISI CA 6-NM 203 726 844 20.0 327 Au-18wt.-%Ni 110 555 940 6.5 271 Brazed, round 200 721 841 10.3 -- Further tensile tests were performed with T-joint specimens. Due to their specimen geometry, conventional strain measurements with an extensometer were not applicable. The experiments show that the σUTS of brazed T-joints without defects averages 835 MPa. Figure 1: Microstructure and hardness measurements of a brazed joint As shown in the BSE-micrograph in Figure 1, the joint consists of base material, filler metal and diffusion zone.
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