Vacuum Furnace Brazing Research Articles

Effect of Vacuum Brazing Conditions of Inconel 718 Superalloy Sheets on Microstructure and Mechanical Properties of Joints

Vacuum furnace brazing is one of the most commonly used joining processes in the aerospace industry, utilized in the manufacturing of the complex components of turbine jet engines, working in both their cold and hot sections. The modern aerospace industry demands continuous improvement of production processes to enhance the engine performance, while ensuring its reliability. Therefore, a better understanding of the processes that shape the properties of engine assemblies joints is crucial. This paper presents an analysis of the influence of key brazing process parameters – brazing time and gap width – on the microstructure and mechanical properties of Inconel 718 superalloy joints obtained with the Palnicro 36M filler alloy. The analysis was conducted basing on results from SEM/EDS analysis and peel, shear and spreadability tests.

Study on element diffusion behaviour of vacuum-furnace brazing 316 L/BNi-2 joints based on Boltzmann-Matano model

Study on element diffusion behaviour of vacuum-furnace brazing 316 L/BNi-2 joints based on Boltzmann-Matano model

Effect of process conditions on the evolution of microstructure and mechanical properties of AA3003 vacuum furnace brazing joints

In this study, vacuum furnace brazing was used for joining AA3003 alloy with different thicknesses of 0.6 and 3 mm using BALSI-4 filler metal. Firstly, the samples were degreased using water and soap and then cleaned with acetone. The set-up was assembled and pre-heated for two-steps at 235 and 339 °C and subsequently, moved to furnace. Vacuum brazing was conducted at temperature range of 590 to 630 °C for different holding times of 5 and 10 min followed by furnace cooling. After primary visual checking, three samples for each thickness were selected for evaluation of microstructure and mechanical properties. Results indicated that furnace temperature and holding time significantly influenced microstructural evolution and mechanical properties. This effect was attributed to the distribution of Si and its relevant eutectic and pro-eutectic phases. It was deduced that the amount and distribution of such phases together with joint assembling design controlled the mechanical and fracture behavior. Furthermore, it was found that the quantitative amounts of pro-eutectic Si and Al–Si eutectic phases significantly increased the hardness of the joint. Therefore, the joint brazed at 610 °C and dwelling time of 10 min was identified to offer the optimal mechanical properties.

Optimization of Process Parameters for the Manufacturing of High Temperature Vacuum Brazed WC-NiCrBSi Coatings

Process parameters play a crucial role in the final characteristics and properties of every product. The current work focuses mainly on improving the vacuum furnace brazing process for tungsten carbide reinforced Ni-based alloy (NiCrBSi) metallic composite coatings, by establishing the best set of parameters adapted to this specific chemical composition. In order to determine the optimum parameters, a fine adjustment of a typical vacuum brazing process was performed. The melting interval of the filler metal was identified by means of Differential Thermal Analysis. Morphology, microstructure and metallurgical bond of the cladding to the substrate material were investigated by Scanning Electron Microscopy and Light Microscopy combined with a Porosity Analysis Software. The process optimization resolved the initial problem of fractures and crack initiation, making possible to achieve high quality hardfacing coatings with a low degree of porosity (approximately 1 %).

High heat flux performance of brazed tungsten macro-brush test mock-up for divertors

Plasma facing components (PFCs) of divertor will be exposed to steady state and transient heat loads up to 20MW/m2, during operation of ITER-like plasma fusion device. The critical task in fusion research is to design, fabricate and test of PFCs. To withstand high heat loads, PFCs are designed and fabricated in flat tile, mono-block type geometries using tungsten as plasma facing material and CuCrZr alloy is used as a heat sink. These fabricated mock-ups are tested under thermal cyclic heat loads using intense electron beam in pulsed mode. Tungsten macro-brush type of mock-up has been developed by vacuum furnace brazing route. Mock-up was tested to the absorbed heat flux in the range of 0.5–9MW/m2. Simulation of high heat flux (HHF) test under steady state and cyclic heat loads has been done using ANSYS12 finite element analysis (FEA) software. HHF tests have been successfully performed on the tungsten mock-up.

Effect of mechanical milling on Ni–TiH 2 powder alloy filler metal for brazing TiAl intermetallic alloy: The microstructure and joint's properties

A TiH 2–50 wt.% Ni powder alloy was mechanically milled in an argon gas atmosphere using milling times up to 480 min. A TiAl intermetallic alloy was joined by vacuum furnace brazing using the TiH 2–50 wt.% Ni powder alloy as the filler metal. The effect of mechanical milling on the microstructure and shear strength of the brazed joints was investigated. The results showed that the grains of TiH 2–50 wt.% Ni powder alloy were refined and the fusion temperature decreased after milling. A sound brazing seam was obtained when the sample was brazed at 1140 °C for 15 min using filler metal powder milled for 120 min. The interfacial zones of the specimens brazed with the milled filler powder were thinner and the shear strength of the joint was increased compared to specimens brazed with non-milled filler powder. A sample brazed at 1180 °C for 15 min using TiH 2–50 wt.% Ni powder alloy milled for 120 min exhibited the highest shear strength at both room and elevated temperatures.

The study of vacuum-furnace brazing of C103 and Ti–6Al–4V using Ti–15Cu–15Ni foil

C103 and Ti–6Al–4V alloys jointed with Ti–15Cu–15Ni (wt.%) commercial brazing foil by vacuum-furnace brazing were investigated. Our previous study [I.-T. Hong, C.-H. Koo, Mater. Sci. Eng. A 398 (2005) 113] demonstrated that Ti–15Cu–15Ni (wt.%) filler-metal can successfully braze C103 and Ti–6Al–4V alloys, and identified all phases in the joint interface. The relationship between the microstructure and the joint performance, and the solidification process of the liquid filler-metal in the joint interface were also studied in detail. Therefore, the current study mainly focuses on how to further improve the microstructure and mechanical properties of the C103/TiCuNi/Ti–6Al–4V joint via post-brazing treatments or using various joint designs, such as overlap-length of joints, surface roughness of the parent-metals and joint clearance. Moreover, the high temperature shear strength of the C103/TiCuNi/Ti–6Al–4V joint was investigated to evaluate its limit service temperature. The experimental results reveal that the fracture load of joint reaches a maximum of 31,076N, and the joint fractures in C103 parent-metal when the overlap-length of the joint increases to 3.5 times the thickness of the parent-metal (3.5T, 7mm). However, the joint shear strength decreases with the overlap-length of the joint because of the non-uniform stress distribution in the lap joint during shear test. Post-brazing treatment at 880°C for 4h increases the shear strength of the joint brazed at 960°C for 15min by 16%, from 352 to 411MPa. However, prolonging the post-brazing time to 6h reduces the shear strength of the joint to 299MPa. A comparison with the coarse Widmanstätten structure reveals that the presence of some fine Widmanstätten structure that forms in the joint interface during post-brazing treatment does not seem to deteriorate the joint shear strength. Moreover, the shear strength of joints decreases as the surface roughness of parent-metals decreases or the joint clearance increases. The results of the high temperature shear test reveal that the shear strength of the C103/TiCuNi/Ti–6Al–4V joint maintains at around 300MPa at the test temperature below 600°C. However, as the test temperature exceeds 600°C, the shear strength of C103/TiCuNi/Ti–6Al–4V joint declines greatly.

Vacuum-furnace brazing of C103 and Ti–6Al–4V with Ti–15Cu–15Ni filler-metal

C103 and Ti–6Al–4V alloys joined by vacuum-furnace brazing using Ti–15Cu–15Ni (wt.%) commercial filler-metal was investigated. This study examines how brazing conditions affect the microstructural evolution and shear strength of the C103/TiCuNi/Ti–6Al–4V joint. According to the microstructural observations, all the characteristic structures of the joint interface can be classified into seven categories, based on their morphology and chemical composition. The microstructural morphology of each characteristic zone depends on the brazing time and the brazing temperature. Excessive increasing the brazing time and the brazing temperature form the coarse acicular Widmanstätten structure in front of Ti–6Al–4V parent-metal and cause grain growth of Ti–6Al–4V alloy. However, if the brazing time is too short or the brazing temperature is too low, the continuous intermetallic-layer consisting of intermetallic compounds, such as Ti2(Cu, Ni) and Ti2(Ni, Cu), will remain in the brazed joints after brazing. Additionally, during brazing, the diffusion of molten liquid filler-metal and the dilution of parent-metals cause the composition of the filler-metal to deviate from the Ti–Cu–Ni eutectic into the hypoeutectic or hypereutectoid. Therefore, the joint interface is anticipated to be comprised mostly of eutectic and/or eutectoid structures. The fine hypoeutectic and hypereutectoid structures consisting of α-Ti, Ti2(Ni, Cu) and Ti2(Cu, Ni) are observed in the joint interface brazed at 960°C for 15min. The maximum shear strength reaches 354MPa under this brazing condition. Further increasing the brazing time and/or raising the brazing temperature cause excessive growth of the Widmanstätten structure and the grain of Ti–6Al–4V alloy, which significantly deteriorate the shear strength of joint. The high temperature shear strength of the C103/TiCuNi/Ti–6Al–4V joint was investigated to evaluate its limit service temperature. Moreover, the overlap-length and the joint clearance investigations are also conducted to realize the relations between different brazing conditions and the joint performance.

Brazing of Mo and Nb using two active braze alloys

The brazing of molybdenum and niobium using two active braze alloys, 63Ag–35.25Cu–1.75Ti and 68.8Ag–26.7Cu–4.5Ti, has been extensively evaluated. Both infrared and traditional vacuum furnace brazing are included in the experiment. Two active braze alloys demonstrate excellent wettability on Mo and Nb substrates, especially upon increasing the test temperature from 900 to 950 °C. For 63Ag–35.25Cu–1.75Ti braze alloy, the brazed joint primarily consists of Ag-rich and Cu-rich phases. Because the Ti is completely miscible with Mo and Nb, there is no reaction product at the interface among the braze alloy and two substrates. Accordingly, dimple-dominated fracture is extensively observed in the brazed joint. The brazed Mo/68.8Ag–26.7Cu–4.5Ti/Nb joint primarily consists of Ag-rich, Cu-rich and Nb-rich phases. A few Cu–Ti intermetallics are found in the brazed joint due to higher Ti content in the braze alloy. However, the presence of Cu–Ti intermetallic phases demonstrates little effect on the shear strength of the brazed joint. Dimple-dominated fracture is observed for the 900 °C brazed joint. The Nb-rich phase is found in both brazed joints, and its amount is increased with increasing brazing temperature and/or time. Accordingly, the growth of the Nb-rich phase is greatly inhibited during rapid infrared brazing. The coarsening of the Nb-rich phase significantly deteriorates the shear strength of the brazed Mo/68.8Ag–26.7Cu–4.5Ti/Nb joint, and finally results in cleavage fracture of the brazed joint.

Heat-Resistant, Electrically Conducting Joint Between Ceramic end Plates and Metallic Conductors in Solid Oxide Fuel Cell

ABSTRACTCeramic parts made of doped lanthanum chromite are used as interconnects and end plates in stacks for several solid oxide fuel cell (SOFC) designs. Metallic conductors have to be attached to enable a low-resistance connection between individual stacks in each SOFC unit and to permit power to be drawn from the SOFC. The resistances of the metal-ceramic bond and the metallic conductors have to be stable under operating conditions, i.e., 1000°C in air. Consequently, heat-resistant materials have to be used. A two-step process has been developed to connect commercially available, Ni- or Febased metallic conductors to ceramic SOFC end plates by vacuum furnace brazing. In the first step, a metallic sheet, which acts as the current collector, is brazed onto the ceramic end plate. Thereby, the much lower electrical conductivity of the ceramic part is compensated by that of the metal. The chromium alloy CrFe5Y2O31 is suitable because it is heat-resistant, and its thermal expansion coefficient is close to that of lanthanum chromite. In the second step, metallic wires or strips are brazed on the current collector. Since this joint area is significantly smaller than that of the first joint, materials with a different thermal expansion coefficient can be used, such as conventional heat-resistant nickel alloys (Inconel 617) and ferritic stainless steels (FeCrAl 25 5). Filler alloys for both brazing steps with matching melting points have been found. Hence, both brazing steps can be performed cost-effectively in one heating step. Suitable parameters for vacuum furnace brazing of both joints are presented, and the composition of the filler alloys is given. Data concerning the long-term behavior of the joint resistances in air at 1000'C are discussed.

Brazing of the Tore Supra actively-cooled Phase III limiter

The head of the water-cooled Tore Supra Phase III Limiter is a bank of 14 round OFHC copper tubes, curved to fit the plasma radius, onto which several hundred pyrolytic graphite (PG) tiles and a lesser number of carbon fiber composite tiles are brazed. The small allowable tolerances for fitting the tiles to the tubes and mating of compound curvatures made the brazing and fabrication extremely challenging. The paper describes the fabrication process with emphasis on the procedure for brazing. In the fixturing for vacuum furnace brazing, the tiles were each independently clamped to the tube with an elaborate set of “window frame” clamps. Braze quality was evaluated with transient heating tests. Some rebrazing was necessary.

Application of vacuum processes in engineering including electron beam welding, vacuum furnaces and metallizing

This paper is a brief review of some of the main ways in which industry is using some vacuum processes which are, by this time, well established. Nonetheless, they are still far from reaching their potential and as application development problems are solved or new industries become aware of the opportunities so their use is widening steadily, perhaps at 20% compound per annum. The processes being discussed are vacuum furnace brazing and heat treatment, vacuum metallizing and electron beam welding. Other vacuum processes are in use in engineering or are coming into use and these include: sintering, sputter coating, induction melting, electron beam melting and ion plating. For the purpose of this paper electronics is excluded, but, as is well known, the electronics industry is very advanced in its application of vacuum processes such as sputtering, evaporation and ion implantation.

Vacuum heat treatment and brazing of metallic materials

Vacuum heat treatment is applicable to most common metals. Vacuum heat treating processes show a distinct advantage over conventional processes in that vacuum heat treatment obtains a bright surface free of defects such as decarburization and intergranular oxidation. Distortion of the parts normally occuring during conventional processing is minimized in vacuum. Parts may therefore be processed in the fully machined condition. Vacuum furnace brazing renders the use of flux unnecessary; it allows the use of a wide variety of brazing filler metals; improves the physical properties of the joint by eliminating such defects as porosity and oxide inclusions; it enables the successful brazing of the nickel and cobalt base superalloys, a difficult task to achieve by conventional means. A cost comparison between vacuum and conventional heat treating processes indicates that vacuum is the most economical method of processing. The paper intends to relate the above to actual processes and to indicate where considerable savings in labour and time may be obtained by the application of vacuum processing.