“…The gaps had a tapered shape with about 200 μm maximum width and 1.2 mm depth. The cross-sections of the cut samples showed no damage in the base metal as observed in our previous work [17]. Two kinds of filler metals were used: the BNi-1a powder, and a mixed powder of 50 wt-% BNi-1a and 50 wt-% DF-4B.…”
Section: Methodssupporting
confidence: 71%
“…The gaps had a tapered shape with about 200 µm maximum width and 1.2 mm depth. The cross-sections of the cut samples showed no damage in the base metal as observed in our previous work [17]. Figure 1 Experiment procedure.…”
Slots with uneven width were cut by femtosecond laser in small plates of IN738LC superalloy to imitate service cracks. The 'cracks' were repaired by diffusion brazing using BNi-1a or a mixed filler alloy at 1100°C. The joint region was composed of isothermal solidification zone (ISZ), diffusion affected zone (DAZ) and precipitate zone (PZ). The compositions were different between the upper and lower ISZ due to the variation of gap width. The sample, repaired with two kinds of filler metals, had similar DAZ microstructure. PZ of mixed filler alloy bonded sample had a similar microstructure with that of BNi-1a, but less borides. The maximum gap sizes of complete isothermal solidification were almost the same for different filler alloys, followed a square root relationship with time. However, PZ of BNi-1a bonded was larger, resulting from a more base metal dissolution. The relationship between the PZ, ISZ and crack width is discussed.
“…The gaps had a tapered shape with about 200 μm maximum width and 1.2 mm depth. The cross-sections of the cut samples showed no damage in the base metal as observed in our previous work [17]. Two kinds of filler metals were used: the BNi-1a powder, and a mixed powder of 50 wt-% BNi-1a and 50 wt-% DF-4B.…”
Section: Methodssupporting
confidence: 71%
“…The gaps had a tapered shape with about 200 µm maximum width and 1.2 mm depth. The cross-sections of the cut samples showed no damage in the base metal as observed in our previous work [17]. Figure 1 Experiment procedure.…”
Slots with uneven width were cut by femtosecond laser in small plates of IN738LC superalloy to imitate service cracks. The 'cracks' were repaired by diffusion brazing using BNi-1a or a mixed filler alloy at 1100°C. The joint region was composed of isothermal solidification zone (ISZ), diffusion affected zone (DAZ) and precipitate zone (PZ). The compositions were different between the upper and lower ISZ due to the variation of gap width. The sample, repaired with two kinds of filler metals, had similar DAZ microstructure. PZ of mixed filler alloy bonded sample had a similar microstructure with that of BNi-1a, but less borides. The maximum gap sizes of complete isothermal solidification were almost the same for different filler alloys, followed a square root relationship with time. However, PZ of BNi-1a bonded was larger, resulting from a more base metal dissolution. The relationship between the PZ, ISZ and crack width is discussed.
“…The tapered kerfs, with approximately 200 μm opening width and 1.2 ∼ 1.3 mm depth, were fabricated by femtosecond laser. The previous work showed that the cutting had not brought about the damage of the base metal [30]. The DF-4B powders were made into pastes by mixing a liquid binder, which will evaporate after heating up.…”
In this study, tapered slots with an opening width about 200 μm were artificially fabricated in IN738LC superalloy to imitate service cracks. The 'cracks' were repaired by diffusion brazing with a Ni-Cr-Co-Al-Ta-B filler alloy at 1150°C and then heat treated at 1180°C (HT-A) and 1190°C (HT-B), respectively. A joint with uniform microstructure, chemical composition and hardness was obtained using HT-B. The mechanisms of the borides evolution during homogenisation were discussed. The tensile strength of the HT-B joint tested at 20, 600 and 800°C reached up to approximately 96, 90 and 87% of the base metal, respectively. The fracture modes of the joints tensile tested at various temperatures were discussed.
“…A shorter creep rupture time was found in He than in air at 900 and 950 • C, mostly due to the thicker protective oxide grown on the material in He [14]. Given its excellent corrosion resistance and strength at high temperatures, Inconel 738 has been extensively studied [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The dispersion of gamma prime γ' particles was characterized as a function of the solidification rate, where the morphology of the particles transformed from round to cluster-like with a decreasing cooling rate, displaying different behavior in the inter-dendritic areas [31].…”
Nickel-based alloys are considered promising materials for primary circuits of high-temperature gas reactors (HTGRs), specifically for gas turbines. The primary helium (He) coolant in the gas-turbine-based HTGRs is expected to reach temperatures of up to 900 °C; therefore, the selected materials should adequately perform over a long service life at such an environment. A promising manufacturing method in the production of reactor components is precision casting, where the content of revert (recyclate) material in the alloy differs and can influence the material behavior. In our study, Inconel alloy 738 was manufactured by casting 50% and 100% of revert material and tested in HTGR conditions to examine the influence of helium coolant on the material’s properties. Tensile specimens were exposed at 900 °C for 1000 h in helium containing a specified amount of gaseous impurities. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), in combination with X-ray diffraction (XRD) and nano-, microhardness methods, were used for material characterization after performing the tensile tests at room temperature. The presence of three types of layers was observed: a thin layer formed by aluminum and chromium oxides on the surface; non-uniform surface oxides Ti3O5 with inner (Al,Cr)2O3; and the inner fine-grained Inconel Cr-enriched phase (approx. 10–20 µm below the surface), which can act as a protective surface layer. Mechanical properties of both revert materials decreased after exposure to HTGR conditions but did not show a significant difference as a result of the content of the revert material. The increase of nano-hardness in line profiles throughout the specimen’s cross-section was observed locally at the surface oxides and in the precipitates and grain boundaries. After exposure, Rp0.2 values decreased by 20% and 17.7%, and Rm values by 12.3% and 20.8% in samples with 50 and 100% revert content, respectively. Furthermore, a decrease in microhardness values (HV0.1) was detected by 4.98% in longitude and 5.80% in cross-section for samples with 50% revert material and by 3.85% in longitude and 7.86% in cross-section for samples with 100% revert material. It can be concluded that both revert materials have similar corrosion resistance in HTGR conditions. The presented results complement the knowledge about the degradation of alloys in the coolant environment of advanced gas-cooled reactors.
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