• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.803-808
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• 2002

A computer-aided alloy-designing technique to develop the insert metal for transient liquid phase (TLP) bonding was applied to high aluminum Ni-base superalloys. The main procedure of a mathematical programming method was to obtain the optimal chemical composition through rationally compromising the plural objective performances of insert metal by a grid-search which involved data estimation from the limited experimental data using interpolation method. The objective function Z which was introduced as an index of bonding performance of insert metal involved the melting point, hardness (strength), formability of brittle phases and void ratio (bonding defects) in bond layer as the evaluating factors. The contour maps of objective function Z were also obtained applying the interpolation method. The compositions of Ni-3.0%Cr-4.0%B-0.5%Ce (for ${\gamma}$/${\gamma}$/${\beta}$ type alloy) and Ni3.5%Cr-3.5%B-3%Ti (for ${\gamma}$/${\gamma}$ type alloy) which optimized the objective function were determined as insert metal. SEM observations revealed that the microstructure in bond layers using the newly developed insert metals indicated quite sound morphologies without forming microconstituents and voids. The creep rupture properties of both joints were much improved compared to a commercial insert metal of MBF-80 (Ni-15.5%Cr-3.7%B), and were fairly comparable to those of base metals.

• Journal of Welding and Joining
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• 제21권3호
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• pp.78-84
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• 2003

The changes of microstructure and hardness of TLP bonds of directionally solidified Ni base superalloy, GTD-111, with variation of homogenizing and aging treatment were investigated. The specimens were bonded at 1403K for 7.2ks using different insert metals such as MBF-50, MBF-80 and MBF-90 and they were homogenized at 1393K with various holding time. At center of bonded interlayer homogenized for hold time 30h, the contents of aluminum and titanium were approximately 90% and 95% of base metal, respectively. In this study, aging was performed at three different kinds : one step aging ; 1113K $\times$ 16h, two step aging ; 1113K $\times$ 10h ⇒ 1103K $\times$ 10h, three step aging ; 1113K $\times$ 10h ⇒ 1103K $\times$ 8h ⇒ 922K $\times$ 24h. ${\gamma}$' volume fraction and hardness of joints were high in the sequence of one step, two step and three step aging, whereas ${\gamma}$' volume fraction and hardness of joints obtained by three step aging treatment were higher than those of raw material. Tensile properties of joints bonded with MBF-80 and MBF-90, homogenized at 1393K for 30h and then three step aged became excellent than those of raw material, however, joint bonded with MBF-50 was poor.

• Corrosion Science and Technology
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• 제13권5호
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• pp.178-185
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• 2014

Alloy 617 is considered as a candidate Ni-based superalloy for the intermediate heat exchanger (IHX) of a very high-temperature gas reactor (VHTR) because of its good creep strength and corrosion resistance at high temperatures. Helium is used as a coolant in a VHTR owing to its high thermal conductivity, inertness, and low neutron absorption. However, helium inevitably includes impurities that create an imbalance in the surface reactivity at the interface of the coolant and the exposed materials. As the Alloy 617 has been exposed to high temperatures at $950^{\circ}C$ in the impure helium environment of a VHTR, the degradation of material is accelerated and mechanical properties decreased. The high-temperature strength, creep, and corrosion properties of the structural material for an IHX are highly important to maintain the integrity in a harsh environment for a 60 year period. Therefore, an alloy superior to alloy 617 should be developed. In this study, the mechanical and high-temperature corrosion properties for Ni-Cr alloys fabricated in the laboratory were evaluated as a function of the grain boundary strengthening and alloying elements. The ductility increased and decreased by increasing the amount of Mo and Cr, respectively. Surface oxide was detached during the corrosion test, when Al was not added to alloy. However the alloy with Al showed improved oxide adhesive property without significant degradation and mechanical property. Aluminum seems to act as an anti-corrosive role in the Ni-based alloy.