Brazing Operations Research Articles

Optimization of Heat Treatment Cycles in Sub-atmospheric LiF-NaF-KF Based Fluoride Ion Cleaning for Removing Oxide Layers in Cracks of IN738-LC

An improved Fluoride Ion Cleaning (FIC) process required for removing all oxide layers by a molten mixture of alkaline fluoride salts under sub-atmospheric pressure was developed and applied to oxide layers on the cracks formed on the surface of Inconel 738-LC samples. This method is directly characterized by filling up the cracks with a molten mixture of alkaline fluoride salts (LiF-NaF-KF) overheated under sub-atmospheric pressure and subsequently, by injecting hot hydrogen gas into the process chamber. The effect of cleaning time on the microstructure of the finished surface was studied in time durations up to 120 min in intervals of 30 min using cross-sectional micrographs and elemental distribution maps. In accordance with the amount of mass loss and microstructural studies during the cleaning process, the optimum cleaning time was suggested to be 90-120 min. Perquisite microstructural outcome shows that in the suggested cleaning condition, all oxide scales in the cracks would be removed without any extra damage to the gamma prime depleted layer, which is a necessary layer for preventing sample oxidation before repair. In this regard, subsequent brazing operations need an oxide-free surface.

Study on Orange Peel Phenomena in Cu-Cr-Zr-Ti Alloy Thrust Chamber

Cu-Cr-Zr-Ti alloys are widely used for fabrication of thrust chamber in liquid rocket engines, because of their high thermal conductivity and adequate strength. The alloy should be used in peak aged condition to achieve the best combination of strength and conductivity. However, realization of final component involves different stages of forming, intermediate heat treatment and brazing operations, which limit the usage of the alloy in peak aged condition. The formability of material depends on grain size to a large extent. Larger grained metals have better formability, but the roughened surface that results from stretching metal with coarse grain structure results in surface defects like orange peel. Copper alloys on cold working sometimes exhibit a surface pebbling effect termed as ‘orange peel’ or alligator skin’.The plates of this copper alloy, finish hot rolled at 925 to 975°C and annealed at 980±10°C for 10 ±2 min followed by air cooling are subjected to different stages of forming to get the final profile of thrust chamber. During the course of forming of plate for divergent thrust chamber, orange peel defect is observed in areas of higher deformation. Detailed characterization of these formed shells in terms of microstructure, grain size and mechanical property has been carried out to find out the exact cause of this defect. Study revealed that the plate has coarse grain structure, which has resulted in orange peel defect during forming. To overcome this effect, the plates were realized with modifications in finish hot rolling and annealing temperatures, which has shown improvement in grain refinement and mechanical properties. It has suppressed the orange peel defect during forming.

Porous thick-film silver metallisation for thermally mismatched brazing operations in tokamak magnetic sensor

A novel sensor based on thick-film + LTCC (low-temperature cofired ceramic) technology has been recently developed for sensing high-frequency 3D magnetic fields in tokamak fusion devices. For integration within the walls of the tokamak, the sensor has to be connected to the mineral-insulated cabling, which is carried out by brazing to ensure sufficient thermal stability. However, thermal mismatch stresses between the braze and the cable vs. the alumina substrate may cause local cracking of the latter during cooling, as the basic dense silver metallisation of the alumina does not provide a sufficient degree of stress decoupling. To address this issue, a series of porous metallisations have been formulated by incorporation of a mix of silver and fugitive graphite powder into a thick-film paste. To allow co-firing of thick, multi-layered prints. Such porous metallisations have allowed successful brazing operations, without cracking of the alumina substrate. Metallisations were assessed by measuring their electrical resistivity and shear stress have been realised as preliminary results to measure the influence of the porosity on the maximal stress before cracking.

Investigation of Mechanical Properties of MIG Brazed DP 600 Steel Joints Using Different Working Angles*

Abstract In this study, dual phase (DP 600) steel plates with a thickness of 1 mm were joined by copper-based (CuAl8) wire using gas metal arc brazing technique. Specimens were prepared in butt joint form. Brazing operations were done at four different working angles: 50°, 60°, 70°, 80° and 90°, respectively. CuAl8 wire consisted largely of copper served as the filler metal. After completing the brazing operations, the tensile properties as well as the micro- and macro-structures of the joints were analyzed in order to investigate the joinability of DP 600 steel using gas metal arc brazing technique.

Investigation of Mechanical Properties of Metal Inert Gas-Brazed TRIP800 Steel Joints Using Different Shielding Gas Flow Rate

In this study, TRIP 800 (transformation induced plasticity) steel plates having 1.5 mm thickness were joined by copper-based (CuAl8) wire in gas metal arc brazing technique. Specimens were prepared in joining forms as butt joint. Brazing operations were done with ve di erent shielding gas ow rates of 8, 10, 12, 14, and 16 L/min. CuAl8 wire composed mostly of copper serves as the ller metal. Having accomplished the brazing operations, tensile properties of joints were detected, and microand macrostructures of joints were investigated in order to see the joinability of TRIP 800 steel by gas metal arc brazing technique.

Influence of current intensity and heat input in Metal Inert Gas-brazed joints of TRIP 800 thin zinc coated steel plates

In this study, TRIP 800 (transformation induced plasticity) steel plates having 1.5mm thickness were joined by copper-based (CuAl8) wire in gas metal arc brazing technique. Specimens were prepared in two different joining forms as butt joint and overlap joint. Both types of brazing operations were done with eight different arc voltages and weld currents as 45, 50, 55, 60, 65, 70, 75 and 80A. S Cu 6100(CuAl8) wire composed largely of copper serves as the filler metal were used. Having accomplished the brazing operations; tensile properties of joints were detected, and micro and macro-structures of joints were investigated in order to see the joinability of TRIP 800 steel by gas metal arc brazing technique.

Design and development of collector for C-band 250 kW CW Klystron

The paper presents the design and development of collector for C-band 250 kW high power klystron. The design criteria for the collector assembly is selection of material, vacuum and high temperature compatibility, proper electron beam dispersion, minimum back scattering of electrons and thermal design for proper cooling at high power dissipation. All these aspects have been discussed for collector development in details. The collector has been designed in TRAK and then beam propagation has been analyzed in MAGIC 2D software. The thermal simulation has been done using ANSYS 11.0 (multi-physics). The outer surface of the collector has been grooved to facilitate its proper cooling. Design results are presented for water cooling with different flow rates and channel dimensions. OFHC copper material is chosen for collector which is suitable for vacuum and hydrogen brazing operations and good thermal properties for efficient cooling.

An investigation of the failure of low pressure steam turbine blades

An analysis of the failure of LP turbine blades of a 210 MW thermal power plant has been presented in this paper. The blade material is of 12% Cr steel with tempered martensitic microstructure. Microstructural analysis as well as hardness and tensile tests did not indicate any degradation in terms of microstructure and mechanical properties. Physical discontinuities were observed in the braze joint which might have been formed due to improper brazing operation. Failure of the brazed joints between the blade and lacing rod was found to be due to improper brazing operations and corrosion effects during service. Fractographic evidence showed that the cracks were initiated from various points on the blade surface, which were at the interface with the lacing rod. Striations and beach marks were also observed which indicated the occurrence of high cyclic loading on the blades. Frequency data obtained from plant indicated the possibility of excessive vibration generated due to fluctuation in grid frequency during operation. Thus, the situation was aggravated due to a resonant condition of vibration, facilitating the propagation of cracks which were initiated earlier.

A case of service failure: turbine cone: Welding in the World 1990 28, (1–2), 2–5 (in English and French)

An analysis of the failure of LP turbine blades of a 210 MW thermal power plant has been presented in this paper. The blade material is of 12% Cr steel with tempered martensitic microstructure. Microstructural analysis as well as hardness and tensile tests did not indicate any degradation in terms of microstructure and mechanical properties. Physical discontinuities were observed in the braze joint which might have been formed due to improper brazing operation. Failure of the brazed joints between the blade and lacing rod was found to be due to improper brazing operations and corrosion effects during service. Fractographic evidence showed that the cracks were initiated from various points on the blade surface, which were at the interface with the lacing rod. Striations and beach marks were also observed which indicated the occurrence of high cyclic loading on the blades. Frequency data obtained from plant indicated the possibility of excessive vibration generated due to fluctuation in grid frequency during operation. Thus, the situation was aggravated due to a resonant condition of vibration, facilitating the propagation of cracks which were initiated earlier.

Examination of the Reaction Kinetics at Solder/Metal Interfaces via High Temperature X-Ray Diffraction

There is a great deal of interest by the electronics Industry in understanding the reactions occurring at the interface between a solid metal and a liquid solder or braze. This is due to the complex nature of current microelectronics Packaging, where soldering or brazing operations often involve complex metallurgies and tightly controlled furnace profiles. However, to date only a few studies have been carried out on the reaction kinetics at a liquid metal-solid metal interface. This is due in part to the difficulty in carrying out such , experiments. In the past, two main techniques have been used to obtain solid-state kinetic data. The first, quantitative metallography, is slow and tedious to perform, and generally of limited accuracy. The second technique involves measuring the change of some property, such as electrical resistivity, that is a function of the concentration of one of the phases. The main disadvantages of these techniques are that absolute values of concentration are not obtained, and that the relationships between a property and constitution are rarely available. In addition, most physical properties are sensitive to factors other than constitution, and interference from these factors can often result in erroneous data.

X-Ray Fluorescence Analysis of Welding Fume Particles

The technique of x-ray fluorescence is ideal for the analysis of metal fumes such as are produced in various welding and brazing operations. Although the constitution of welding and brazing fumes is dependent on the nature of the base metal, flux, and welding material used, they typically contain the oxides of iron, nickel, chromium, and manganese (stainless steel welding). The fumes are in the form of very small particles, usually 1.0 um, and are often agglomerated into long chains. Filter samples of these fumes, as are used in industrial hygiene monitoring, may contain 30-300 ug/filter of particles on one surface of a low-mass, 37-mm membrane filter.