BNi-2 Filler Metal Research Articles

Transient liquid phase bonding of Hastelloy X to Ni3Al intermetallic compound: Microstructure and phase transformation study

The microstructure of dissimilar transient-liquid-phase (TLP) bonding of Hastelloy X nickel base super alloy to Ni3Al intermetallic by AWS BNi2 filler metal at different temperatures (1000–1150 °C) and time ranges (60–180 min) was investigated. A novel study was done to correlate the phase transformation during bonding with microstructure and phase transformation using field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HR-TEM), and high temperature X-ray diffraction (HTXRD). Efforts were performed to correlate the phase transformation stages during isothermal solidification (IS), formation of Cr-Mo precipitates in diffusion affected zone (DAZ) and dissolution of nickel silicides (eutectic morphology) in athermal solidification zone (ASZ) with their respective reaction temperatures. The high tendency of Hastelloy X to react intensely with filler metal generated Mo-Cr rich phase in DAZ. The ISZ was developed across the joint area after holding at 1100 °C for 180 min. High temperature XRD results on half joint of HX revealed new phases generated at above 1050 °C including BNi2,BNi3, and Ni2Si (Ni-Si eutectic phase) confirmed by FESEM. On the other half joint (Ni3Al), no BNi phases were generated nor nickel silicides by increasing temperature as high as 1150 °C.

Investigating the microstructure and mechanical properties in furnace brazing Ti–6Al–4V to 17-4 PH stainless steel dissimilar joint with BNi-2 filler metal

Due to the distinct physical and metallurgical characteristics of titanium and steel, the welding of these two materials poses challenges and holds significant importance. This study investigates the impact of brazing time and temperature on the microstructure and mechanical properties of dissimilar brazing between 17-4 PH stainless steel and Ti–6Al–4V using BNi-2 as a filler metal, focusing on the formation of brittle compounds like FeTi and Fe2Ti during the brazing process. The joint between these materials is commonly utilized in various industrial applications. The assessment involved the use of optical microscope, scanning electron microscope, shear – tensile test, microhardness test, and wettability measurement. Brazing of the base metals was conducted at temperatures of 1050/1100 °C for durations of 15 and 30 min to determine the optimal temperature and time combination. The results indicated that the best joint properties were achieved at 110 °C for 15 min, with an average shear strength of 38.46 MPa. Contact angle measurements revealed that BNi-2 exhibited superior wettability on 17-4 PH compared to Ti–6Al–4V. Furthermore, increasing the temperature from 1050 to 1100 °C led to a reduction in contact angle from 9.98 to 8.83° for 17-4 PH, and from 16.51 to 10.12° for Ti–6Al–4V indicating an improvement in wettability.

The effect of vacuum brazing time on the microstructure and mechanical properties of Ti-6Al-4 V to 316 L dissimilar joint using BNi-2 filler metal

Due to the distinct differences in physical and metallurgical properties, it is hard to join titanium alloys to stainless steels directly via conventional welding processes. In this research, the grade 5 titanium alloy was subjected to brazing with austenitic stainless steel through the vacuum furnace, and the process was conducted above the β transition temperature (BTT). In order to reduce brittle intermetallic formation, a nickel base filler metal (Ni-6.6Cr-4.5Si-3B) was employed under a vacuum condition, and the effect of time on the microstructure and mechanical properties of the joints was investigated. The brazing temperature led to the thickening of the interface to 400 µm, toward the titanium alloy, and the FeTi formed adjacent to the diffusion affected zone (DAZ). Moreover, the isothermal solidified zone (ISZ) widened during the whole process, which, led to higher dissolution of the titanium base metal in the ISZ. Because of the widening of the interfaces, there were no Ni-rich compounds or residual filler metal in this region. SEM result showed that TiB strengthening borides, which were distributed after 45 min, and this evolution caused an increase in the shear strength of the joint up to 67 MPa. Fractography analyses and XRD results of the fractured surfaces revealed that the Ti2Ni phase, which formed in the athermaly solidified zone (ASZ) during a two-step solidification reaction, caused the brittle fracture in all joints.

Microstructural and mechanical investigation of brazing 304L Stainless Steel with corner joint using a Ni-based shim and wire

This study investigated a suitable filler metal, diffusion depth of the elements of this filler metal in the base metal, and its effect on the mechanical properties of brazing bonding of sheets with different thicknesses of 304L stainless steel. For this purpose, brazing was performed with thermal induction under a vacuum of 10−5 mbar and filler metal BNi-2 at the corner structures. First, the microstructure of different joint regions including base metals, Ni affected areas, and interfaces were examined by scanning electron microscopy and then the relationships between microstructure and microhardness were compared. In sheets with different thicknesses, the differences in diffusion depth were observed. Moreover, the microhardness of different areas of the braze was revealed to be completely affected by the diffusion of nickel. Finally, it was found that, for the bonding between 304L sheets with different thicknesses, BNi-2 filler metal had reasonable strength, diffusion, and filling for vacuum applications.

Microstructure and mechanical properties of the brazed region in the AlCoCrFeNi high-entropy alloy and FGH98 superalloy joint

In this study, brazing of Al0.3CoCrFeNi high-entropy alloy to FGH98 superalloy was achieved using a BNi-2 filler metal. The microstructure of the Al0.3CoCrFeNi/FGH98 joint was examined, and mechanical properties of the joints brazed at different brazing temperatures were evaluated. During the brazing process, boron diffused from the filler alloy into the Al0.3CoCrFeNi substrate, and mainly reacted with Cr to form the Cr-rich boride exhibiting Cr5B3 structure. Eventually, the reaction zone was composed of a Cr-rich boride and Ni-rich HEA matrix with a coherent relationship of [0 1 1]Ni-rich HEA//[2 4 0]Cr-rich boride and (2 0 0)Ni-rich HEA//(0 0 2)Cr-rich boride. The dissolution of the FGH98 substrate induced the island-like (γ + γʹ) phase in the brazing seam. With the brazing temperature increasing, the voids and borides disappeared, and finally the brazing seam transformed into homogeneous Ni(s.s). Moreover, when the brazing temperature reached 1090 and 1110 °C, the volume of intergranular Cr-rich borides increased significantly, and the precipitation of carbides (or borides) in the FGH98 substrate adjacent to the brazing seam was dispersive. The optimum shear strength of 454 MPa was obtained when the brazing was carried out at 1070 °C for 10 min, and ductile fractures occurred in the joint during the shear test.

Effect of transient liquid phase bonding followed by homogenization on the microstructure and hot tensile behavior of Inconel 738 superalloy

Inconel 738LC (IN-738LC), a nickel-based superalloy, was joined by the transient liquid phase (TLP) bonding method using a BNi-2 filler metal. The bonding process was carried out at 1120 °C under vacuum for 45 and 120 min and was followed by the standard heat treatment (SHT) to homogenize the joints. The microstructures of the specimens were studied by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM). Following the microstructural investigation, the microhardness tests on the homogeneous specimen showed a uniform distribution in the bond region. Next, the base metal (BM) and the homogeneous TLP joint were subjected to hot tensile testing at 650, 750, and 850 °C under similar conditions. A comparison of the hot tensile test results revealed two significant facts about the effects of TLP bonding followed by homogenization on the tensile properties, namely, the lack of any increase in the hot tensile behavior over the studied temperature range and the degradation of mechanical properties. The yield strength and the elongation of the homogenized TLP joint were found to be, respectively, 96% and 61% of those of the BM at 850 °C.

Bonding temperature effects on the wide gap transient liquid phase bonding of Inconel 718 using BNi-2 paste filler metal

Transient liquid phase (TLP) bonding of Inconel 718 with BNi-2 filler metal has traditionally been carried out using thin filler metal (narrow gap) to achieve complete eutectic-free isothermal solidification layer joints. However, for the aerospace components with relatively large cracks or worn areas where a large amount of filler metal is needed, narrow gap TLP bonding is insatiable to meet the bonding requirements. In this paper, wide gap TLP bonding of Inconel 718 with the BNi-2 paste filler metal was carried out in a vacuum furnace. The bonding temperature effects on the interfacial microstructure, phase evolution and the mechanical properties of the bonded joints were investigated. It was found that the ultimate tensile bonding strength increased by 98% as the bonding temperature increased from 1015 °C to 1150 °C and the joint with the maximum tensile strength of 482 MPa was achieved after bonding at 1150 °C for 15 mins. However, more adverse heating was induced on the base metal of the joint under a higher bonding temperature. In addition, increasing bonding temperature from 1015 °C to 1150 °C improved the local plasticity of the bonded joints owing to the reduction of the homogeneously distributed Ni3B type borides to a more heterogeneous distribution of borides.

Transient liquid phase bonding of Inconel 617 superalloy: effect of filler metal type and bonding time

Transient liquid phase (TLP) bonding has enormous potential to repair cracks in the gas turbine hot section parts that are made of Ni-based alloys. The experiments were carried out by BNi-1 and BNi-2 filler metals in a vacuum furnace at the bonding times of 45 and 300 min. The shear strength, microhardness, microstructure, and homogeneity of chemical composition during TLP bonding of Inconel 617 superalloy, which is the base metal, were evaluated. The shear strength of about 620 MPa was obtained using the BNi-1 filler metal. Hence, the BNi-1 filler metal and the bonding time of 300 min are recommended for repair of hot section components of a gas turbine. The gap size is an important parameter on the diffusion especially at the lower bonding times but the preliminary difference in the chemical composition may play an important role at the longer bonding times. The results show that the type of filler metal is an important parameter in this process.

Ultrasonic guided wave inspection of Inconel 625 brazed lap joints: Simulation and experimentation

The aerospace industry has been investigating the use of structural brazed joints. As a result of this effort, there is now a need for a rapid, robust, and cost-effective non-destructive testing method to evaluate the structural integrity of the joints. The mechanical strength of brazed joints is known to depend on the microstructural quantity of brittle phases. Ultrasonic guided waves offer the possibility of detecting brittle phases in joints using spatio-temporal measurements. This study focused on the development of a technique based on ultrasonic guided waves for the inspection of Inconel 625 lap joints brazed with BNi-2 filler metal. A finite element model of a lap joint was used to optimize the inspection parameters and assess the feasibility of detecting the quantity of brittle phases in the joint. A finite element parametric study simulating the input signal shape, the center frequency, and the excitation direction was performed. The simulations showed that the ultrasonic guided wave energy transmitted through, and reflected from, the joints was proportional to the amount of brittle phases in the joint. Experimental validations were then performed on three distinctive samples with variable amount of brittle phases in the joint. The samples had three different brazing times (1, 60 and 180 min). Finally, experimental results were in accordance with simulations and demonstrate the potential of the inspection method to estimate the quantity of brittle phases in a lap joint.

The Microstructural Evolution of Vacuum Brazed 1Cr18Ni9Ti Using Various Filler Metals.

The microstructures and weldability of a brazed joint of 1Cr18Ni9Ti austenitic stainless steel with BNi-2, BNi82CrSiBFe and BMn50NiCuCrCo filler metals in vacuum were investigated. It can be observed that an interdiffusion region existed between the filler metal and the base metal for the brazed joint of Ni-based filler metals. The width of the interdiffusion region was about 10 μm, and the microstructure of the brazed joint of BNi-2 filler metal was dense and free of obvious defects. In the case of the brazed joint of BMn50NiCuCrCo filler metal, there were pits, pores and crack defects in the brazing joint due to insufficient wettability of the filler metal. Crack defects can also be observed in the brazed joint of BNi82CrSiBFe filler metal. Compared with BMn50NiCuCrCo and BNi82CrSiBFe filler metals, BNi-2 filler metal is the best material for 1Cr18Ni9Ti austenitic stainless steel vacuum brazing because of its distinct weldability.

Metallurgical characterisations of CMSX-4 vacuum-brazed with BNi-2 and BNi-9

High temperature brazing of nickel-based superalloys often produces joints containing hard, brittle micro-constituents that can be detrimental to mechanical properties and challenging to characterise consistently. In this study, techniques including low angle micro-sectioning, image analysis with ImageJ and electron probe micro-analysis were used to determine the composition, hardness and dispersion parameters of phases in single crystal superalloy CMSX-4, vacuum furnace brazed with BNi-2 and BNi-9 filler metals (FMs). Both FMs produced similar joints with hard centreline eutectic phases, a soft isothermally solidified zone and boron diffusion-affected zone in the CMSX-4. The volume fraction, particle size distribution and inter-particle spacing data generated will provide a framework for future metallurgical characterisations and assist in the development of microstructure–mechanical property relationships.

Effect of processing parameters on the microstructure and mechanical properties of wide-gap braze repairs on nickel-superalloy René 108

Gas turbine components experience large temperature gradients due to thermal cycling that often result in cracking. When brazing wide gaps greater than 500 μm in width, capillary action is inadequate to fill the joint and activated diffusion healing (ADH) is applied for repairs. ADH utilizes a mixture of a low melting temperature filler metal and an additive powder with a composition similar to that of the base metal. This research studies the effect of processing parameters on the microstructure and mechanical properties of repaired joints on DS Rene 108 superalloy. AWS BNi-2 and BNi-5 grade filler metals were mixed with MAR-M 247 alloy powder at weight percent ratios of 40:60, 50:50, and 60:40. For BNi-2 containing brazes, the mechanical properties improved with increasing additive powder. In contrast, the BNi-5 containing brazes showed an opposite trend. Brazing temperatures were held at 1200°C and 1232°C. The mechanical properties for both braze alloys improved at the higher brazing temperature. Diffusion hold temperatures were held at 1100°C and 1121°C for 2 h and 4 h. For the BNi-2 alloys, the higher temperature and longer brazing time improved mechanical properties. For the BNi-5 alloys, the lower brazing temperature and shorter brazing time improved mechanical properties.

The Study Of The Impact Of Surface Preparation Methods Of Inconel 625 And 718 Nickel-Base Alloys On Wettability By BNi-2 And BNi-3 Brazing Filler Metals

Abstract The article discusses the impact of surface preparation method of Inconel 625 and 718 nickel-base alloys in the form of sheets on wettability of the surface. The results of the investigations of surface preparation method (such as nicro-blasting, nickel plating, etching, degreasing, abrasive blasting with grit 120 and 220 and manually grinding with grit 120 and 240) on spreading of BNi-2 and BNi-3 brazing filler metals, widely used in the aerospace industry in high temperature vacuum brazing processes, are presented. Technological parameters of vacuum brazing process are shown. The macro- and microscopic analysis have shown that nicro-blasting does not bring any benefits of wettability of the alloys investigated.

The Study of the Impact of Surface Preparation Methods of Inconel 625 and 718 Nickel-Base Alloys on Wettability by BNi-2 and BNi-3 Brazing Filler Metals

Abstract The article discusses the impact of surface preparation method of Inconel 625 and 718 nickel-base alloys in the form of sheets on wettability of the surface. The results of the investigations of surface preparation method (such as nicro-blasting, nickel plating, etching, degreasing, abrasive blasting with grit 120 and 220 and manually grinding with grit 120 and 240) on spreading of BNi-2 and BNi-3 brazing filler metals, widely used in the aerospace industry in high temperature vacuum brazing processes, are presented. Technological parameters of vacuum brazing process are shown. The macro- and microscopic analysis have shown that nicro-blasting does not bring any benefits of wettability of the alloys investigated.

Nanoindentation Experimental Study on Mechanical Properties of As-cast BNi-2 Solder Alloy

Nanoindentation testing has been used to study mechanical properties of as-cast BNi-2 solder alloy. Hardness and modulus were measured by the nanoindentation experiments. It is confirmed that it is loading rates insensitive to as-cast BNi-2 filler metal from the elasto-plastic nanoindentation responses. In this study, indentation size effect has been discussed. It is found that as-cast BNi-2 is independent of the indentation size effect. Using the model proposed by Dao et al., the yield strength and work hardening exponent were regressed from the loading–unloading behavior during indentation. The purpose of the present work is to obtain a comprehensive elastic–plastic properties understanding of as-cast BNi-2 filler metal which can be better application for engineering.

Creep analysis of solid oxide fuel cell with bonded compliant seal design

Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located.

Three-dimensional simulation to study the influence of foil thickness on residual stress in the bonded compliant seal design of planar solid oxide fuel cell

Bonded compliant seal (BCS) design, which uses a thin S-shaped foil to connect the cell and frame by brazing, is a new sealing method for planar solid oxide fuel cell (SOFC). This paper studies the brazed residual stress in BCS design of a planar SOFC by three-dimensional finite element method. The effect of foil thickness on residual stress has been investigated. The results show that the peak residual stresses are located in S-shaped foil and BNi2 filler metal and have exceeded the yield strength. Therefore S-shaped foil and BNi2 filler metal are the most dangerous zone. The foil thickness has a great effect on residual stress. The peak residual stresses in foil and BNi2 are increased with the foil thickness increase. With the foil thickness increase, the residual stresses in window frame are increased, while residual stresses in Ag–CuO filler metal are decreased.

Effect of Brazing Clearance on Microstructure and Strength of Welded Joint of 316L Stainless Steel

To study the effect of brazing clearance and temperature on strength and microstructure, vacuum brazing of 316L stainless steel was carried out with BNi-2 nickel-based solder. Choose the different brazing clearance to be processed at 1070°C, analyzed the welding tissue by SEM and XRD, and found that hardness has been greatly improved to 664HV. The results showed that when the 316L stainless steel was brazed with BNi-2 filler metal at 1070°C, the structures of the welded joint were composed of FeNi3, Fe5C2, Cr5FeB3 metallic compounds and solid solutions. The microhardness of the welded joint by the center to both sides had a W-type distribution. When the width of the welded joint was 40μm, the microharedness of the center welded joint was lower than others, and shear strength of this clearance was the highest, about 300MPa.

Effect of brazing temperature on tensile strength and microstructure for a stainless steel plate-fin structure

This paper presented a vacuum brazing technology for 304 stainless steel plate-fin structures with BNi2 filler metal. The effect of brazing temperature on tensile strength and microstructure has been investigated. The tensile strength is increased along with the increasing of brazing temperature. The microstructure is very complex and some Boride compounds are generated in the brazed joint. Full solid solution can be generated in the middle zone of joint when the brazing temperature is increased to 1100 °C. The brittle phases always exist in the fillet no matter how the brazing temperature changes, but the microstructure in fillet becomes more uniform and the tensile strength is increased with the brazing temperature increasing. In total, the brittle Boride compounds are decreased with the brazing temperature increase. Brazing with a filler metal thickness 105 μm and 25 min holding time, 1100 °C is the best suitable brazing temperature and a tensile strength of 82.1 MPa has been achieved for 304 stainless steel plate-fin structure.

Effect of holding time on vacuum brazing for a stainless steel plate–fin structure

This paper presents a vacuum brazing of 304 stainless steel plate–fin structures with nickel-based BNi-2 filler metal. The effect of brazing holding time on tensile strength and microstructure has been investigated, aiming to obtain the optimal brazing holding time. The microstructure in brazing joint consists of diffusion-affected zone (DAZ), interface reaction zone (IRZ), isothermally solidified zone (ISZ) and athermally solidified zone (ASZ). The structure in the fillet is composed of solid solution, nickel silicon, nickel boron compound and a mixture with nickel silicon and nickel boron. The tensile strength increases along with the increase of holding time, but decreases when the holding time is over 25 min. A maximum tensile strength of 65.1 MPa is obtained with 25 min holding time. Too short holding time will make boron diffuse insufficiently and generate a great deal of brittle boride components, and too long holding time will make the base metal dissolve into the filler metal excessively and creates more corrosion voids.