Brazing Alloy Research Articles

Plasma etching as a surface engineering technique for SiC/SiC composites to improve joint strength

Silicon carbide fiber reinforced silicon carbide (SiC/SiC) composites have unique properties that make them suitable for demanding applications. These materials have to be joined with other materials or with the same type of material to produce the final component. This work investigates the effectiveness of a fluorine-based plasma process on SiC/SiC composites as a surface engineering technique to manufacture a brush-like texturized surface. The studied pre-treatment induced an interlocking effect at the composite/joining material interface, thus improving the joint strength of the joined components.Several plasma conditions were considered and the most promising one (CF4, 20 sscm, 200 W, 30 min) was selected to assess the effect on the mechanical performance of SiC/SiC brazed with a commercial brazing alloy (Cusil-ABA®). The selected plasma pre-treatment led to a 55% increase in the apparent shear strength of the joined SiC/SiC composites.

Development of the interfacial microstructure between aluminum nitride and Cu–P–Sn–Ni brazing alloy for different initial titanium layer thicknesses

Development of the interfacial microstructure between aluminum nitride and Cu–P–Sn–Ni brazing alloy for different initial titanium layer thicknesses

Interfacial Microstructure and Mechanical Properties of Pressureless Sintered SiC Ceramic and Stainless Steel Joints Brazed by AgCu/AgCuTi Alloy

A high-quality joint of pressureless sintered SiC ceramic (PS-SiC) and stainless steel brazed by AgCu/AgCuTi brazing alloy was realized. The effects of brazing temperature and holding time on the interfacial microstructure and mechanical properties of PS-SiC-stainless steel were analyzed. During brazing, Fe and Cr diffused into a brazing seam, and the typical interfacial microstructure of joints brazed at 890 °C for 15 min was stainless steel/Cr5Si3 + FeSi2 + Ag(s,s)/Cr5Si3 + FeSi2 + Ag(s,s) + Cu(s,s) + TiSi2 + TiC/FeSi2 + Ag(s,s) + Cu(s,s) + TiSi2/Ag(s,s) + Cu(s,s) + SiC/PS-SiC ceramic. Cu-Fe system improved the toughness of the joint, and the shear strength of the joint increased to ~67 MPa. With increasing brazing temperature and holding time, the element Fe continued diffusing into the brazing seam, and the uniformity of Cu-Fe system became worse. Then Cu(s,s) infiltrated into the surface layer of PS-SiC ceramic and FeSi2 brittle phase gathered in the brazing seam. Then, the brittleness of the joint increased and the shear strength of the joint decreased.

Effects of gravity on the capillary flow of a molten metal

Repair and construction in space by means of brazing requires understanding of the effect of gravity on the capillary flow of a molten metal. We perform two sets of experiments: (1) spreading of a sessile drop of liquid aluminum-silicon-flux (Al-Si-KxAlyFz) composite braze on a horizontal alumina (Al2O3) substrate (a non-wetting surface), and (2) capillary flow of the same braze alloy on an inclined aluminum-manganese (AA3003) substrate (a wetting surface). We vary the mass of the brazing liquid and the inclination of the substrate (i.e., the relative direction of gravity).In the composite metal/flux sessile drop experiments, we observe a secondary liquid flux meniscus forming at the contact line between the liquid Al-Si and the alumina substrate. We demonstrate that the equilibrium contact angle appears to be close to 180°, while the apparent contact angle depends on the mass of the braze. In the second set of experiments, we study the molten braze alloy on different inclinations of AA3003 in a wedge-T wetting/non-wetting assembly. As the inclination angle decreases, the wetting distance increases and the surface profile changes from a non-symmetric bag-like shape to a more symmetric pancake shape. With the mass decreasing, the surface profile on the vertical substrate approaches a symmetric shape when the wetting distance is equal or smaller than the capillary length. While the non-homogeneous melting and hence, the non-homogeneous microstructure of the melt, may prevent a full symmetry. Computational predictions of equilibrium shapes are in good agreement with experimental results.

Microstructure and properties analysis of the brazing alloy prepared from recycled E-waste.

In order to realize the efficient and comprehensive utilization of e-waste resources and short process preparation of alloy brazing materials, this study has analyzed the microstructure and properties of e-waste recycled brazing alloys by the analysis methods of inductively coupled plasma emission spectrometer, differential scanning calorimeter, scanning electron microscope, metalloscope, X-ray diffractometer, micro-hardness tester. Experimental results showed that phase compositions are significant differences between the alloys prepared by the recycled e-waste and the pure metals. The circuit board recycling alloy mainly consisted of α-Fe dendrites, (Cu, Sn) phases, Sn-rich phases and Cu matrix, while the alloy obtained by pure metals is composed of (Cu, Sn) phase, Sn-rich phase and Cu matrix. The melting temperature of alloy obtained by melting the circuit board is in the range of 985.3°C–1,053.0°C, which was wider and higher than that of alloy obtained by pure metal smelting. The shear strengths of the joints brazed by the brazing alloys prepared by the recycle e-waste and pure metals are 182.21 MPa and 277.02 MPa, respectively. There is little difference in hardness between the two types of brazed joints. In addition, there are a large number of precipitated phases in alloy obtained by the recycled circuit board, owing to the precipitation strengthening mechanism. The main strengthening mechanism of alloy obtained by pure metals is solid-solution strengthening. The paper focused primarily on alloy obtained by melting the circuit board and studying the specific composition, melting temperature, structure, and properties of alloys formed by melting the circuit board and pure metals. Meawhile, the size, morphology and other microstructure evolution of the second phase of brazing alloy were investigated to provide theoretical guidance for the brazing alloy in the subsequent actual production process.

Flux-Free Brazing of Aluminum Alloys under Ultra-Low Oxygen Partial Pressure through a Zirconia Oxygen Pump

Flux-Free Brazing of Aluminum Alloys under Ultra-Low Oxygen Partial Pressure through a Zirconia Oxygen Pump

Self-propagating exothermic reaction assisted Cu clip bonding for effective high-power electronics packaging

For the high-power modules packaging, Cu clip bonding has gained growing interest to replace the multiple wire-bonding for the benefits of lower resistance and improved thermal performance, which is especially beneficial for higher reliability. However, the current interconnection materials and bonding processes cannot fully meet the reliability requirements of the emerging Cu clip integrated structure. Brazing alloys can serve in high-temperature conditions, since they have the melting points above 450 °C. However, very limited brazing alloys have been applied in electronics packaging since the processing temperature is also high if needs to be melted. It is promising to develop the low-temperature bonding technology which can serve at high temperatures. In this study, incorporating with the Cu-15Ag-5P brazing alloy as the interconnection material, the self-propagating exothermic reaction (SPER) has been applied to assist the Cu clip bonding process, which provides intense local heating to achieve the interconnects in millisecond scale. The bonding mechanism between Cu-15Ag-5P and Cu substrate is examined and discussed. The research findings promise an effective assembly route viable for the application of high-power electronics packaging.

Microstructures, mechanical properties and formation mechanisms of tungsten heavy alloy brazed joints using Cu-Ti-Ni-Zr amorphous filler

Vacuum brazing of tungsten heavy alloys (WHAs) was conducted with a design of Cu-Ti-Ni-Zr amorphous filler. The effects of key brazing parameters (brazing temperature T, holding time t) on interfacial microstructures and mechanical properties were investigated. The typical microstructure of brazing seam was composed of CuTi eutectic, CuZr dendrites along with (Cu, Ti) (Ni, Zr) and (Cu, Ni) Ti2 phases. With the brazing temperature increased from 850 °C to 1000 °C, the phenomenon of “infiltration induced separation of adjacent W grains” was intensively expanded, which was addressed in view of the Marangoni convection effect, atom diffusion, internal reaction, and grain boundary wetting. The maximum shear strength of the joint brazed at 925 °C for 20 min reached 366.6 MPa. This first detailed study on wettability, interfacial microstructures, and joining mechanism of WHAs brazed joints can benefit an in-depth understanding in joining process of WHAs, which can also provide guidance for joining of sintered dual/multi-phase refractory composites.

Reduced strength degradation of reactive air brazed Ba0.5Sr0.5Co0.8Fe0.2O3-δ membranes by pre-oxidation of metallic components

Oxygen transport membranes can be joined leak-tight and high-temperature resistant to metal components by reactive air brazing. To overcome the typical strength degradation of these braze joints during aging at the application temperature of 850 °C, the diffusion-controlled growth of mixed oxide layers at the interface between metal and braze alloy has to be reduced. In this study, we investigated how a pre-oxidation of the chromia forming austenitic steel X15CrNiSi25-21 and alumina forming ferritic steel X8CrAl25-5 influences the bending strength of BSCF-Ag3CuO-steel joints. Brazed double joint specimens were aged for 1000 h at 850 °C in air prior to 4-point bending and subsequent macroscopic as well microscopic analyses.Pre-oxidation of steel X15CrNiSi25-21 reduced the strength degradation during aging from 75 to 59% and effectively suppressed chromium poisoning of BSCF. The minimum fracture stress was raised from 0 to 24 MPa which significantly increased the reliability. For the first time, it was possible to obtain mixed and ceramic fracture types in addition to poor-strength delamination fractures. The strength of pre-oxidized X8CrAl25-5 joints was affected by axial cracks and pores at the mixed oxide layer and lower compared to joints with pre-oxidized X15CrNiSi25-21. In contrast to pre-oxidized X15CrNiSi25-21, no acicular phases were identified in the BSCF. Nevertheless, the apparently dense Al2O3 layer could not avoid chromium diffusion, as Ba–Cr oxides were detected in the braze.

Effect of the Surface States of 1Cr18Ni9Ti Stainless Steel on Mn-Based Brazing Alloy Wetting

The wetting properties of the brazing filler on the substrates play an important role in achieving a reliable joint. In this work, the wetting behaviour of the Mn-based brazing alloy on the surface of 1Cr18Ni9Ti stainless steel is investigated. First, surface treatment was adopted to prepare four different surface states on the stainless steel, including polished, acid treatment, nickel coating, and sandblasting. The surface morphology with nickel coating shows micro-and nano-scale protrusions, forming a uniform 3D Ni layer. The surface roughness of substrates increases after sandblasting treatment. It is found that the wetting angle of brazing alloy on the Ni coated substrates decreases noticeably. After sandblasting, the high roughness speeds up the wetting spread of the brazing alloy at the initial stage. The effect of heating temperature and holding time is also studied systematically. With the increase in holding time, the height of the melting brazing alloy decreases slightly on the sample surfaces. Based on the characterization of the joint section, the Ni layer dissolves into the melting brazing alloy. The diffusion and dissolving are indicated between the brazing alloy and substrates, forming a reliable bond.

Microstructure and mechanical properties of TiAl/TiAl joints brazed with a newly developed Ti–Ni–Nb–Zr quaternary filler alloy

A novel Ti–Ni–Nb–Zr quaternary filler alloy with the composition of Ti-(19∼25)Ni-(15∼25)(Nb ​+ ​Zr) (wt.%) was designed. The filler alloy was composed of (Ti,Nb)ss, (Ti,Zr,Nb)ss ​+ ​(Ti,Zr)2Ni, α-Ti and Ti2Ni phases. It was fabricated into filler foil with a thickness of about 45 ​μm by a rapid solidification technique. The results indicate that the liquidus temperature of the Ti–Ni–Nb–Zr brazing alloy was about 978 oC, and the brazing alloy presented excellent wettability on TiAl substrate. The TiAl joint mainly consisted of β/B2 phase, Ti2Al, Ti2AlNi and α2-Ti3Al phases. The diffusion of Al atom from base metal to brazed seam led to the formation of Ti2Al and Ti2AlNi. Considering that no previously references on XRD pattern of Ti2AlNi compound can be found, Ti2AlNi cast alloy specimen was specially prepared and XRD peaks were specially labeled. The micro-hardness and bending strength tests of the Ti2AlNi phase were carried out, and the results were 761 HV and 192 ​MPa, respectively. The brazing parameters of 1010 oC/10 ​min offered the joint shear strength of 280 ​MPa at room temperature, and the joints exhibited tensile strength of 372 ​MPa at room temperature and 340 ​MPa at 750 oC, indicating that the newly developed filler alloy could offer a stable high-temperature strength.

Effect of welding time on the joint organization and mechanical properties of 6063 aluminum alloy

The 6063 Aluminum alloy brazing joint was prepared with the Al-Si12 solder. The effect of welding time on the structure and shear properties of brazing weld is studied and the interface is analyzed. The study shows that the spreading performance of brder gradually increases with the welding time, the shear strength of the 6063 aluminum alloy joint increase first and then decreases with the increase of the welding time. When the optimal brazing process is 605°C 15min, the interface between Al-Si12 solder and aluminum alloy is good, and the shear strength is 122.4MPa. To ensure the bonding strength of 6063 aluminum alloy, the optimal insulation time of brazing is 15min.

Analysis of the Wetting and Diffusion Processes Upon the Contact Alloying of Zn–Cu–Al and Mg–Al Brazing Alloys with AMg3 Alloy

Analysis of the Wetting and Diffusion Processes Upon the Contact Alloying of Zn–Cu–Al and Mg–Al Brazing Alloys with AMg3 Alloy

Challenges and Latest Developments in Diffusion Bonding of High-Magnesium Aluminium Alloy (Al-5056/Al-5A06) to Stainless Steels

The aim of this work was to investigate the challenges associated with bonding Al-Mg alloys and develop a new method for bonding these alloys to steels. During an extensive R&D project, over 80 attempts, using 11 methods, were made to bond Al-6 wt.% Mg alloy (Al-5056/Al-5A06) to two types of stainless steels (heat-resistant 1Cr18Ni9Ti and conventional 316). Wide ranges of temperature (500 °C to 580 °C), pressure (0.5 MPa to 10 MPa) and time (1 min to 2 h) were used when direct diffusion bonding of these alloys. Then, effects of using various interlayers and brazing foils were investigated. The interlayers used in this work were gallium, pure titanium, copper and aluminium foils, aluminium 6061 alloy sheets, aluminium-silicon brazing foils, zinc and zinc alloy foils as well as an active brazing foil (known as Incusil-ABA containing silver, copper, indium and titanium). Several complex and multi-stage processes, using up to 3 different interlayers in the same joint, were also developed and assessed. Examination and assessment of the bonded samples, including failed attempts, paved the way of developing new methods for bonding these dissimilar materials. A number of samples with tensile strengths from 200 MPa to 226 MPa were made by using complex combinations of 2 or 3 interlayers and triple-stage bonding cycles. The highest recorded bond strength was 226 MPa in the as-bonded condition. This value is above the measured yield strength (134 MPa) and about 93% of the measured ultimate strength (243 MPa) of the parent Al-Mg alloy after it was subjected to the same bonding cycle. Since the use of complex processes was not feasible for bonding large components, a simpler and more practical bonding cycle was also developed in the project. Using the simpler process, joints with tensile strengths around 90 MPa could be made. This article also sheds light on the difficulties associated with brazing and soldering aluminium alloys with a high magnesium content.

Microstructure coarsening in Ba0.5Sr0.5Co0.8Fe0.2O3-δ during reactive air brazing

Reactive air brazing of the ceramic oxygen transport membrane material BSCF causes microstructural modifications. The trend towards minimizing of membrane thicknesses requires a physical understanding of these modifications since they may influence both oxygen permeation and mechanical properties. To this purpose, wetting samples with variations in the Ag-xCuO braze alloy (1 < x < 25 at.-%) and the brazing time (0 < t < 120 min) were characterized by quantitative image analysis. We found that the pore size in reactive air brazed BSCF increases with increased brazing time as well as CuO-content in the braze. A local porosity minimum is always observed at the end of the reaction zone close to the unaffected bulk BSCF. Additionally, a zone with unidirectionally elongated grains at the end of which silver residues were found is observed. The observed coarsening effects are explained by liquid melt film penetration along the grain boundaries which increases the grain boundary mobility. Phase field simulations qualitatively confirmed the experimentally observed elongated grain structure.

Design CuZr alloy to control Ti diffusion and reaction layer thickness in C/C-TC4 joins

Brazing C/C composites and Ti6Al4V (TC4) can expand their practical applications, but the too much brittle TiC at C/C side is harmful to joint strength. The key to high-quality brazing joints is to control the excessive diffusion of Ti element from TC4 and TiC reaction layer at C/C. Herein, a new type of CuZr brazing alloy was designed, since Cu element can react with Ti, and Ti element are infinitely miscible in Zr. The interfacial microstructures showed that CuZr alloy reacted with Ti to form Ti 2 Cu + (Zr, Ti) 2 Cu, preventing diffusing Ti and optimizing reaction layer thickness. The effects of brazing temperature and holding time on microstructure changes were analyzed. When the temperature and holding time was insufficient, TiC+ZrC reaction layer was formed not well and inhomogeneous Ti(s, s) and Ti 2 Cu were dispersed in (Zr, Ti) 2 Cu, leading to a relatively low shear strength. Microstructures of continuous TiC+ZrC reaction layer and homogeneous (Zr, Ti) 2 Cu + Ti 2 Cu were optimized as temperature and holding time increased. Optimal microstructure of the joints was brazed at 970 °C for 10 min, which was C/C-TiC+ZrC/Ti 2 Cu + (Zr, Ti) 2 Cu/Ti(s, s)-TC4, and the joint reached the maximum shear strength about 54.2 MPa. • The design of CuZr alloy controls the diffusion of Ti interfacial reaction thickness. • Ti-Cu-Zr reaction phase was revealed by Gibbs free energy analysis method. • The effects of brazing temperature and holding time were investigated in detail. • The shear strength attained to 54.2 MPa by optimizing temperature and holding time.

Releasing the residual stress of Cf/SiC-GH3536 joint by designing an Ag-Cu-Ti + Sc2(WO4)3 composite filler metal

• The work is the first one to introduce Sc 2 (WO 4 ) 3 into brazing process. • The Sc 2 (WO 4 ) 3 maintains its negative thermal expansion effect in Ag-Cu-Ti system. • The residual stress releasing mechanism is revealed by finite element analysis method. • The shear strength improves 2.6 times by introducing Sc 2 (WO 4 ) 3 reinforcing phase. Due to native character of thermal expansion coefficient (CTE) mismatch between C f /SiC and GH3536, achieving high strength joint was a huge challenge for C f /SiC-GH3536 joints. Herein, a composite filler metal of Ag-Cu-Ti + Sc 2 (WO 4 ) 3 was developed to join C f /SiC and GH3536. This work introduced Sc 2 (WO 4 ) 3 to Ag-Cu-Ti system as a negative thermal expansion (NTE) reinforcing phase to release joint residual stress. Sc 2 (WO 4 ) 3 was evenly distributed in the brazing seam and reacted with Ti to form Ti 3 O 5 reaction layer. The results of finite element analysis showed that the residual stress of the joints was effectively released by introducing Sc 2 (WO 4 ) 3 reinforcing phase, and the mises stress was decreased from 447 to 401 MPa. The maximum shear strength of the C f /SiC-GH3536 joint brazed with Ag-Cu-Ti + 6 vol% Sc 2 (WO 4 ) 3 filler alloys was 64 MPa, which was about 2.6 times higher than that of Ag-Cu-Ti alloys. The results of this study provide a promising strategy for the introduction of new Sc 2 (WO 4 ) 3 reinforcing phase in Ag-Cu-Ti system, and improve the reliability and feasibility of composite brazing alloy in brazing filed.

Dissimilar joining of SS 321 – Alumina ceramic via metalized brazing alloy and investigation on its metallurgical and microstructural properties

The aim of this project is to brazing alumina ceramic to stainless steel 321L and investigating its strength and microstructure properties. The brazing process carried out at the temperature of 650 °C and 700 °C for 40 and 60 min in the controlled atmosphere furnace (tube furnace 1400 °C) using filler alloy (Ag45Cd) coated to a thickness of 100 nm by titanium via the Sputtering process. The mechanical and microstructural properties of join were observed by optical microscopy and scanning electron microscopy (SEM). Also, to evaluate mechanical properties, a shear test was performed in the section. Finally, to analyze fracture surfaces, X-ray diffraction analysis and SEM were used. The optimal temperature and time on this project were obtained at 700 °C and 60-min having shear bond strength of 98 MPa.

Brazing of TiAl and Ti2AlNb alloys using high-entropy braze fillers

To address the excessive formation of brittle compounds when brazing TiAl alloys, a TiZrHfCoNiCu high-entropy brazed filler was developed to realize the brazing of TiAl/Ti 2 AlNb couples. The TiAl/Ti 2 AlNb brazed joints can be divided into 4 zones, i.e., 2 diffusion zones at the TiAl/braze filler, Ti 2 AlNb/braze filler interfaces and 2 zones divided inside the brazed seam. α 2 + γ-TiAl were the main reaction products formed at the TiAl/braze filler interface and α 2 + Ti 0.5 Al 0.12 Nb 0.38 were the main reaction products at the Ti 2 AlNb/braze filler interface. Effects of brazing temperatures on the interfacial microstructure and mechanical properties of the TiAl/Ti 2 AlNb brazed joints were investigated. When brazing at 1100°C/15 min, the highest shear strength can reach 157 MPa (room temperature), and 123 MPa (650°C) respectively. The relationship between the microstructure and the corresponding mechanical response were discussed in detail. This research can offer new insights on developing desirable brazing filler when joining TiAl and TiAl based alloys. • A TiZrHfCoNiCu high-entropy alloy braze filler was developed to realize the brazing of TiAl/Ti2AlNb couples. • Ti 0.5 Al 0.12 Nb 0.38 and α 2 + γ-TiAl formed at the braze filler/base metal interfaces were the key to realize the joining. • The α 2 + γ-TiAl at the TiAl/braze filler interface was preferential to crack for the strongest brazed joints. • Highest shear strength of 157 MPa (room temperature) and 123 MPa (650°C) were achieved at 1100°C/15 min.

Laser beam brazing of aluminum alloys in XHV-adequate atmosphere with surface deoxidation by ns-pulsed laser radiation

Laser beam brazing is an established manufacturing process due to its low heat input and esthetically appealing seams. However, brazing of materials with high oxygen affinity, such as aluminum alloys, requires the removal of surface oxides prior to the brazing process, commonly through the application of chemical fluxes that may be harmful to the environment and to health. The approach presented here dispenses with the use of fluxes and involves oxide layer removal by means of ns-pulsed laser radiation within an atmosphere that is adequate to an extreme high vacuum (XHV) in regard to the oxygen content. By doping the process gas with monosilane (SiH4), an oxygen content equivalent to an extreme high vacuum with an oxygen partial pressure below 10−20 mbar is realized. Hence, a subsequent reoxidation is actively prevented so that wetting of the base material by the filler material and consequent diffusion processes are enabled. The wetting angle between filler material and material is used to evaluate the effectiveness of laser-based deoxidation under an XHV-adequate atmosphere.