Papers by Keyword: TLP Bonding

Abstract: AISI304 stainless steel was bonded by a nickel base interlayer, using a TLP bonding method at 1150 °C with different holding times. The microstructure of the joint region was studied by optical and scanning electron microscopes. The results showed that 20 minutes holding time is sufficient for complete isothermal solidification. At the bonding times of 4, 10, 15 minutes, a eutectic structure was formed at the joint region. The distribution of alloying elements within the joint region and diffusion affected zone were detected using EDS. The results showed that the eutectic microstructure consists of Fe and Cr borides and the isothermal solidified zone consists of solid solution of Fe and Ni at the bonding temperature. Samples with complete isothermal solidified joint were homogenized at 950°C for different times from 30 to 360 minutes to study the distribution of alloying elements between joint region and parent alloy. The results showed more uniform distribution of alloying elements with increasing the homogenization time due to the diffusion of alloying elements between the joint region and the parent alloys. Microhardness and shear strength of joined samples were measured and compared to that of the parent alloy at the same heat treatment condition. The joint shear strength of TLP bonded samples was about 82% that of the parent alloy at the homogenization time of 180 minutes.

Abstract: Transient liquid phase (TLP) bonding of Ti₂AlNb, used for vacuum brazing furnace, was carried out using Ti-Cu-Zr based foil as filler alloy at 950, 1000 and 1050°C. The effect of bonding temperature on joint interface, phase constitutions and their distributions were investigated by taking advantages of OM, SEM, EDS and XRD analyses. The result revealed that the TLP joint consisted of isothermally solidified zone and diffusion affected zone. A non-isothermally solidified zone existed only when the bonding temperature was not high enough. The interface morphologies of the joints were found to be very sensitive to the bonding temperature. With the bonding temperature increased from 950°C to 1000°C, the width of non-isothermally solidified zone decreased from 69 μm to 23 μm. When the bonding temperature was 1050°C, the non-isothermally solidified zone disappeared. Meanwhile, more alloying elements of Cu and Zr diffused most adequately into the base material. Phase analysis showed that along with the increasing of bonding temperature, the secondary phase constitution of joint changed from Ti (Cu,Al)₂ + AlNb₂ + Ti solid solution to Ti solid solution + Nb (CuAl) + Al₄Cu₉ + Al₂Zr₃, and the proportion of secondary phase was 35.7%, 20.2%, 6.7%, respectively. The morphology of base metal changed because of the relatively high bonding temperature was higher than 980°C, the α→β transition temperature.

Abstract: A novel two-step heating process, consisting of a short-time high temperature heating followed by isothermal solidification at a lower temperature, was used to transient liquid phase (TLP) bond T91 steel. The interface morphology of the joint was investigated and compared with that of conventional TLP bond made at a constant bonding temperature. The results show that the two-step heating process produces a non-planar interface at the initial stage, which is different from the planar interfaces associated with conventional heating process. No interface can be found in the final joint by two-step heating process, however, a planar interface still exists in the final conventional TLP bond. Therefore, the bending ductility of the joint is dramatically improves by the two-step heating process, and the joint properties are similar to that of base metal.

Abstract: Finite element numerical dynamic simulation of the TLP bonding process of 20 steel tubes was conducted using ANSYS, finite element analysis software. The results show that there is a sharp decline in the performance of the joint and the neighboring parent material during the initial cooling stage in the transitional phase diffusion bonding process. When the isothermal solidification temperature is increased, the welding deformation becomes more apparent, and the residual stress on both sides of the joint is reduced. Thus, the weak area of TLP bonding can be found near the middle. A reasonable choice of interlayers can relieve stress concentration and increase the TLP bonding joint performance.

Abstract: Joining of different nickel-base superalloys could simplify the manufacturing of turbine blades. The used technique of choice is transient liquid phase bonding, which is an established repair technology for high temperature components. Two nickel-base superalloys with distinct composition and grain structure are bonded and the joints are analysed regarding the microstructure. To quantify the mechanical properties of these joints, tensile and short term creep rupture tests were performed at room and elevated temperatures.

Abstract: The as-cast FSX-414 Co-based superalloy samples were solution treated at 1150oC for 4h and then aged at 980oC for 4h. Specimens for joining were cut from the as-cast ingot and TLP bonding carried out at the same conditions as for the solution and solution+aging treatment, using MBF-30 interlayer. Microstructures were studied for as-cast, heat treated and TLP bonded specimens. These studies showed that the ununiform distributed carbides of MC type in the as-cast specimens replaced by M23C6 type carbides with uniform distribution in the heat treated microstructure. Due to complete isothermal solidification, no eutectic structure in the bond region were wasobserved, but some intermetallics in the diffusion affected zone (DAZ) were observed. Microhardness tests were used to compare the hardness of age hardened specimens with bonded specimens at the same heat treatment condition. Hardness profile also showed a peak in DAZ region in spite of complete isothermal solidification.

Abstract: a kind of as-cast nickel-base single crystal superalloy was TLP bonded using Ni-Cr-B amorphous foil at different temperatures. Special attention is paid to the formation of boride in diffusion zone of TLP joints at different conditions. The chemical composition and microstructure of borides were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At different bonding temperature, M3B2 precipitates appear distinct morphologies. At 1200°C, both blocky and plate-like borides formed owing to the diffusion of boron atoms into base metal and precipitation during the cooling process. At 1230°C or above, due to the diffusion of boron atoms the constitutional liquation of original γ/γ′ eutectics in the base metal occurs and borides formed when the system was cooled to room temperature. The analysis of TEM results reveals that M3B2 has a tetragonal structure and is rich in Mo, W, and Cr elements.

Abstract: In the case of transient liquid phase diffusion bonding with Ni base superalloy GTD-111, the bonding temperature was sustained at 1403K ~ 1453K. Thus, the microstructure of specimens heated at 1403K ~ 1453K was examined. In the raw material, γ-γ' eutectic phases, platelet η phases, MC carbide and PFZ were clearly observed in interdendritic regions or near the grain boundary and the size of primary γ' precipitates near the interdendritic regions were larger than the core. The primary γ' precipitated in the dendrite core dissolved early in the bonding process. γ' precipitated near the interdendritic regions were partially solubilized and their shape was changed. The dissolution rate increased with increasing temperature. Phases in the interdendritic regions or near the grain boundary changed continuously with time at the bonding temperature. At a bonding temperature of 1403K, the eutectic phases remained, but η phases were transformed from a platelet shape to a needle morphology and the PFZ region widened with time. The interdendritic region and near the grain boundary became partially liquid at 1423K and fully at 1453K by the reaction of η phases and PFZ. The interdendritic region and near grain the boundary became liquid and new phases which were mixed with η phases, PFZ and MC carbide crystallized during cooling at 1453K. Crystalline η phases were transformed from a rod shape to a platelet shape with increasing holding time.

Abstract: This study was carried out to investigate the effect of heating rate on the phase transition between additive base metal powder and liquid insert metal during transient liquid phase (TLP) diffusion bonding of Ni-based superalloy GTD-111. Heating rates studied were 10, 1, 0.5 and 0.1°Cs-1 in high vacuum conditions (3×10-5 torr) by means of a high frequency induction furnace. When heated at lower than 0.5°Cs-1, the transition of dissolution to solidification occurred during heating. In the case of very slow heating, the dissolution quickly finished at a lower temperature, and solidification soon started. The separated grains of additive base metal powders supplied the lager interface area for the diffusion of boron. Solidification transition temperatures of liquid phase were affected by the increase of diffusion interface and of duration time during slow heating. A minimum heating rate required to heat insert materials to a normal TLP isothermal bonding temperature of GTD-111 (≈1150°C) without a dissolution-solidification transition during heating should be higher than 1°Cs-1.