Amorphous Filler Metal Research Articles

Superior shear strength subject to the regulation of plastic toughness in K4169 alloy/TiAl intermetallic joints vacuum brazed with gradient composite amorphous filler metals

The concept of gradient composite amorphous filler metal (GAFM) was utilized to solve the scientific problem of low strength caused by excessive Ti-containing brittle-hard intermetallic compounds (IMCs) generated in Ni/TiAl brazed joints through interfacial hysteresis reaction. Based on the cluster-plus-glue-atom model, the GAFMs (Zr25Ti21.25Ni25Cu18.75/Zr31.25-XVXCu50Ni18.75) were designed for vacuum brazing of K4169 alloy with TiAl intermetallic. And the shear strength of the joint brazed with (Ti21.25Zr25Ni25Cu18.75/Zr25V6.25Cu50Ni18.75) GAFM reached 344 MPa. The relation between grain boundary, solution, dislocation and strength was established. The cracks initiated from the (Ti,Zr)(Ni,Cu)+(Cr,Fe,Ni) brittle-hard phase and the plastic-tough phase (Zr,Ti)(Ni,Cu) interface in Zone II with (Ti21.25Zr25Ni25Cu18.75/Zr31.25-XVXCu50Ni18.75) GAFMs at 1040 °C/10 min, and then extended to the (Ti,Zr)(Al,Ni,Cu)3[010]/(Ti,Zr)(Ni,Cu,Al)3[0-10] non-coherent interface. To regulate the distribution of the plastic-tough phase in Zone II, raising brazing temperature could promote the dissolution of Zone I into Zone II. The addition of V to the GAFMs, εG and εα mismatches increased and prompted the Niss[00-1]+TiAl[010] phase, (Cr,Fe,Ni)ss[00-1] phase with a-value lattice distortion of 21.38%, (Ni,Cr,Fe) and ZrNi3[0-2-1] grains refinement in Zone II, where KIC*/KIC>1, the brazed joint strengthening effect was enhanced. The columnar grains were transformed into grains with reticulated cladding characteristics. The percentage of substructured grains increased from 46.6% to 56.3%, and the percentage of HAGBs rose to 84.7%, which inhibited dislocation migration. Therefore, the ZrNi3 plastic-tough phase, prohibited the expansion of the major crack generated from the (Cr,Fe,Ni) brittle-hard phase. The major crack extended to the Ti(Ni,Cu,Al)3 [1–10]/Ti(Al,Cu,Ni)2[0-10] semi-coherent interface and then to the TiAl substrate, resulting in a zigzag crack expansion.

Microstructure and properties of the TiAl/GH3030 dissimilar joints vacuum-brazed with a Ti-based amorphous filler metal

TiAl intermetallic was vacuum brazed to GH3030 alloy with a Ti-based amorphous filler metal (Ti33.3Zr16.7Cu39Ni11, at.%). The effect of the brazing temperature on the microstructural evolution and mechanical properties of the brazed joints was investigated. Ti3Al and Al(Cu, Ni)2Ti phases composed the diffusion zone I at the TiAl side resulting from the diffusion of Cu and Ni into TiAl intermetallic, and the diffusion zone III at GH3030 side consisted of α-Ni and α-Cr solid-solution phases and a TiNi3 intermetallic phase, which rooted in the diffusion of Ti into GH3030 alloy. Increasing the brazing temperature accelerated the diffusion and migration of the constituents, and further thickened all reaction zones. The growth rate of zones I and III was wzoneI = 0.0789 μm/oC and wzoneIII = 0.0833 μm/oC, respectively. The formation of zone III was more difficult than that of zone I with the growth activation energy (Q) of QzoneI = 101.96 kJ·mol−1 and QzoneIII = 165.58 kJ mol−1. The maximum shear strength was 260 MPa obtained at 960 °C/10 min. All brazed joints fractured at the interface of Al3(Cu, Ni)Ti2/Al(Cu, Ni)2Ti, because of the mismatch of their lattice structure and hardness, and all failed joints demonstrated zonal and brittle features.

Phase diagram-guided composition design and property investigation of Ni-based filler metals

The fundamental mechanism underlying the formation of brazed joints involves the diffusion of elements between the base metal (BM) and the brazing filler metal (FM). The formation of brittle compounds in FM during the brazing process frequently results in a significant deterioration of the mechanical properties of the brazed joints. Ni and Cu elements exhibit infinite solubility, and the incorporation of Cu element results in a decrease in the liquidus temperature of FM, thereby enhancing its surface wettability on the BM. The present investigation involves the preparation of as-cast and amorphous FMs with varying Cu element concentrations to examine their material properties, such as weldability, wettability, thermophysical behavior, and creep resistance. The thermophysical and mechanical properties of the nickel-based filler metal BNi-2 were evaluated using the JMatPro software for material thermodynamic simulation and compared with data obtained from existing literatures. An analysis is conducted on the creep properties of a novel FM comprising of Ni, Cr, Fe, Si, B, and Cu. The results suggest that the thermophysical properties of BNi-2 filler are minimally impacted by the presence of Cr (6–8 wt%), Fe (2.5–3.5 wt%), Si (4–5 wt%), and B (2.75–3.5 wt%). Furthermore, alterations in the composition of Si and B elements have a significant impact on the distribution of γ and γ′ phases, consequently influencing the creep properties of the material. At 25 °C, the equilibrium phase of BNi-2 with different Cu contents indicates a gradual decrease in the content of γ phase, while the content of γ′ and Cu–Ni phases increases with an increase in Cu content. The BNi-2 filler with 3 % Cu exhibits the most favorable properties in terms of steady creep rate and fracture life compared to other fillers. This is attributed to the competitive equilibrium between the γ phase and Cu–Ni phase. The addition of 6 % Cu element results in the optimal wettability of the filler metal and creep resistance of the brazed joints. It is also observed that as the concentration of Cu reaches 9 %, there is a gradual increase in the FeB phase, a rise in the proportion of brittle compounds, and a decline in the amorphous forming ability.

Multiscale microstructural consideration of enhanced shear strength in TiAl intermetallic/K4169 alloy composite joints prepared by vacuum brazing with (Ti, Zr)-Ni-based amorphous filler metal

TiAl intermetallic could be used to replace Ni-based alloy in assemblies to generate excellent specific strength. A (Ti,Zr)-Ni-based amorphous filler metal Ti21.25Zr25Ni25Cu18.75 (at.%) was designed using a cluster-plus-glue-atom model to successfully vacuum braze K4169 and TiAl bimetallic assemblies. At various brazing temperatures and holding time, the quantitative relationships between lattice distortion, grain boundary, dislocation density, and hardness, elastic modulus, shear strength of the joints were investigated. Meanwhile, the fracture mechanism of the joints was revealed. The brazed seam mainly consisted of solid diffusion reaction layers (Zones I and III) and filler metal residue zone (Zone II). When the brazing temperature increased to 1030 °C, grain refinement occurred in the brazed seam. Zone I was primarily composed of (Ni)ss[0-11]+TiNi[011]/(Cr,Fe,Ni)ss[0-11]/(Ti,Zr)Ni[0-1-1]+(Cr,Fe,Ni)ss[0-11]. The (Ti,Zr)(Ni,Cu)[001] and (Ti,Zr)(Ni,Cu)[101] intermetallic compound-based solid solutions were formed in Zone II. And the lattice distortion of (Ti,Zr)(Ni,Cu)[101] and (Ti,Zr)(Ni,Cu)[001] was 32.05% and 14.82%, respectively. As a result, the proportion of low angle grain boundaries (LAGBs) and deformed grains in Zone II rose to 38.6% and 38.7%. In Zones I and III, the proportion of LAGBs reduced to 8% and 3.4%, respectively. As the holding time increased, the long-range diffusion of Al in Zone II caused the (Ti,Zr)(Ni,Cu)[001] with cubic structure to transform into (Ti,Zr)(Ni,Cu,Al)[00-1] with hexagonal crystal system structure, where the lattice distortion was 4.42% and 10.49% for a and c. At 1030 °C/10 min, the average geometrically necessary dislocation densities (GNDs) in Zones I, II and III were 9.87 × 1014 m−2, 8.55 × 1014 m−2 and 11.4 × 1014 m−2, respectively. Therefore, the shear strength of joints reached 322 MPa due to the lattice distortion, dislocation strengthening and fine grain strengthening. Meanwhile, the plastic and brittle hard phases were generated in Zone II and displayed a mechanical interlocking structure that contributed to the performance of the joint. Both (Ti,Zr)(Ni,Cu)[001] and (Ti,Zr)(Ni,Cu)[101] in Zone II formed along different low-index cleavage planes during transgranular fracture. The cracks initiated in this region extended to the interface between Zones I and II and exhibited bimodal grain characteristics.

Microstructure and mechanical properties of TLP-bonded 9CrMoCoB heat-resistant steel with Ni–Cr–B interlayer

9CrMoCoB heat-resistant steel was transient liquid phase (TLP) bonded by using a Ni–Cr–B amorphous filler metal. Results indicated that the TLP-bonded joint was composed of three feature regions, and the precipitates in the diffusion affected zone (DAZ) were M23(C,B)6-type carboborides and M3B2-type borides with different morphologies and locations. Fine granular Fe2Mo-type Laves phases and MX-type carbides that existed in the original base metal were found in the grain. The carboborides and borides in the DAZ that grew with the increase in bonding time and temperature were reduced or completely dissolved after post weld heat treatment (PWHT). The joints without PWHT showed high strength and low elongation due to the high hardness and high hardenability of the matrix. The initiation of cracks occurred on borides in the athermal solidification zone and carboborides in the Ni-DAZ and passed through in the bonded seam, resulting in the reduction in the tensile strength of the bonded joints. The hardness of the joints was obviously reduced, and their toughness was obviously improved after PWHT. The highest tensile strength reached to 744 MPa when the TLP joints were bonded at 1150 °C for 30 min, which was comparable with the original base metal.

Microstructure evolution and mechanical properties of TiAl/GH536 joints vacuum brazed with Ti–Zr–Cu–Ni filler metal

In this study, a novel Ti–Zr–Cu–Ni amorphous filler metal was fabricated and applied to vacuum brazing of TiAl alloy and Ni-based superalloy (GH536). The effects of brazing temperature on the interfacial microstructure and mechanical properties of the joints were analyzed. Three different regions, the isothermal solidification layer Ⅰ, continuous reaction layer Ⅱ and continuous diffusion layer Ⅲ, were formed in the joints after brazing. The SEM and EDS results show that brazing temperature plays an important role in element diffusion, microstructure evolution and metallurgical quality of brazed joints, while the thickness of layer Ⅱ and Ⅲ was basically not affected by brazing temperature. The obtained joints showed excellent shear strength both at room temperature and elevated temperature. With the increase of brazing temperature, the shear strength of joints at room temperature firstly increased and then decreased. The optimal shear strength of 279 MPa was obtained after brazing at 1100 °C for 10 min. With the increase of test temperature, the shear strength of joints obtained at 1110 °C/10 min firstly decreased, then increased, and decreased again, with the maximum value of 156 MPa at 600 °C. The shear fracture mainly occurred in the thinnest layer Ⅱ and the fracture morphology exhibited typical cleavage fracture characteristics.

Brazing of Porous Copper Foam with Copper Sheet Using CuNiSnP Amorphous Filler Metal

This research studies effects of the brazing time on interfacial microstructure of brazed joint between the porous copper foam (PCF) and Cu substrate using CuNiSnP amorphous filler metal. To examine the interfacial microstructure and its properties, an assessment of PCF/CuNiSnP/Cu brazed joints was conducted after electric furnace brazing under hydrogen (H2) atmosphere. The results showed that the interfacial microstructure was thick for short brazing time specimens and thin for prolonged brazing time specimens. The interfacial microstructures consisted of Cu-rich solid solution, (Cu, Ni)3P, and Cu3P as a eutectic structure discovered in the brazing region at different brazing times of 5, 10, and 20 min. Only the Cu-rich solid solution and (Cu, Ni)3P were found in the specimen with brazing time of 30 min. indicating that different brazing times affected interfacial microstructures and therefore reliability of the brazed joints.

Vacuum brazing TiAl intermetallics to GH3030 alloy with a multi-component Ti-based filler metal

TiAl intermetallics was vacuum-brazed to GH3030 alloy with multi-component Ti-based amorphous filler metal (Ti 36.1 Zr 11.1 V 2.8 Cu 38.9 Ni 5.6 Al 2.8 Co 2.8 , at.%). The effect of brazing temperature on the microstructure evaluation and shear strength of TiAl/GH3030 brazed joint was studied. The brazed seam presented sectionalized feature with the formation of four reaction zones. Two transition zones with linear growth formed respectively adjacent to two base metals due to elemental solid-state diffusion from the filler metal to base metals. Increasing the brazing temperature accelerated the diffusion between the filler metal and base metals. And those two transition zones thickened, as well as the middle zone composed of primary phase and (Ti, Zr)(Al, Cu, Ni) matrix. Blocky primary phase Ti(Al, Cu, Ni) 3 in middle brazed seam increased, thinning the Ti(Ni, Cu) reaction layer. The maximum shear strength of the brazed joint was obtained at 990 °C. During the shear test, the cracks of the brazed joint propagated along the interface of the transition zone/middle brazed seam at TiAl base metal side on account of the stress concentration and the formation of Ti(Al, Cu, Ni) and Ti(Al, Cu, Ni) 3 at two sides of the fractured interface. And the failed joint exhibited layered fracture surfaces and brittle fracture feature.

Microstructure evolution and mechanical properties of high Nb–TiAl alloy/GH4169 joints brazed using CuTiZrNi amorphous filler alloy

A CuTiZrNi amorphous filler metal was fabricated and utilized for brazing high Nb–TiAl alloys and GH4169 superalloys. The microstructure and mechanical properties of the high Nb–TiAl/GH4169 joints brazed from 900 °C to 1020 °C temperature range were studied. Results showed that the high Nb–TiAl/GH4169 joints consisted of three zones. The interfacial microstructure of the joints was high Nb–TiAl alloy/Ti3Al + Al3(Ni, Cu)Ti2 + Al(Ni, Cu)2Ti/AlCu2(Ti, Zr) + (Ti, Zr)(Ni, Cu) + Ti2(Ni, Cu)/Cr-rich (Cr, Ni, Fe)ss + Ni-rich (Ni, Cr, Fe)ss/GH4169 alloy. The element diffusion between the substrates and the filler alloy was intensified as the brazing temperature increased, and the interfacial reaction layer thickened. At 960 °C, the joint exhibited a maximum shear strength which was approximately 241.9 MPa. At higher brazing temperatures, the excessive AlCu2(Ti, Zr) phase and coarse Ti2(Ni, Cu) deteriorated the joint properties due to their inherent brittleness.

Interface behaviour of brazing seam of contact-reaction brazing an AZ31 magnesium with amorphous filler metal

In order to achieve brazing of magnesium alloy without brazing flux, a new AlSiCu amorphous alloy was designed as an intermediate layer. The contact reaction brazing method was used to brazing AZ31 magnesium alloy with AlSiCu amorphous alloy as an intermediate layer. The SEM and OM methods were used to analyze the structure of the brazing seam, and it was found that there were block, granular, and dendritic alloy phases in the brazing seam. The composition of the alloy phases in the brazing seam was measured by EDS analysis, and the intermetallic compounds of Mg Al were found. Unfixed micro-holes were found in the brazing seam held at 450 °C for 15 min, and these micro-holes disappeared and a complete interface connection was formed in the brazing seam when the holding time increased to 20 min. With the increase of brazing time, the brazing seam became wider and the dendrite in the brazing seam began to spread towards the base metal and gradually decreased after holding for 25 min. After holding for 30 min, the dendrite disappeared and the second phase appeared as granular and short rod distribution, and the number decreased significantly. The joint strength increases significantly with the increase of holding time, and the tensile shear strength of the lap joint is 110 MPa. The average hardness of the brazing seam is 94.2 HV, the hardness values of the matrix phase and the second phase are different greatly. The probe was used to analyze the microstructure and morphology of the shear fracture, and it was found that cleavage patterns and dimples existed on the fracture surface at the same time. • The contact reaction brazing method is used to achieve the brazing connection of the AZ31 magnesium alloy. • The AlSiCu amorphous alloy is used as the intermediate layer, and the tissue performance of the joint is improved. • By means of diffusion and differentiation, the shape of the MgAl compound in brazing seam is changed.

Microstructure evolution and mechanical properties of vacuum brazed ZrO2/Ti–6Al–4V joint utilizing a low-melting-point amorphous filler metal

The shear strength of ZrO2 and TC4 brazed joint is usually controlled by the oxide reaction layer adjacent to the ZrO2 ceramic. However, there are few studies of the formation and growth mechanism of this reaction layer at present. And the relationship between brazing parameters, joint strength and thickness of the oxide reaction layer also needs further study. In this study, the ZrO2 and TC4 were brazed using a low-melting-point Ti35Zr25Be30Co10 amorphous filler at different brazing parameters. The microstructure and mechanical performance of the joints were studied by SEM, EPMA, XRD, TEM as well as shear tests. The results revealed that the TiO layer was formed on the surface of ZrO2 ceramic, and the joint strength reached the highest value of 180 MPa at 810 °C for 10 min. The formation of the TiO layer is a typical reaction-diffusion process and its growth process exhibits characteristics of an island growth mode. Furthermore, the quantitative relationships between the brazing parameters and the thickness of the TiO layer were established, which paves an innovative way for improving the strength of the joint by controlling the thickness of the TiO layer.

Interfacial features of TiAl alloy/316L stainless steel joint brazed with Zr−Cu−Ni−Al amorphous filler metal

TiAl alloy and 316L stainless steel were vacuum-brazed with Zr−50.0Cu−7.1Ni−7.1Al (at.%) amorphous filler metal. The influence of brazing time and temperature on the interfacial microstructure and shear strength of the resultant joints was investigated. The brazed seam consisted of three layers, including two diffusion layers and one residual filler metal layer. The typical microstructure of brazed TiAl alloy/316L stainless steel joint was TiAl alloy substrate/α2-(Ti3Al)/AlCuTi/residual filler metal/Cu9Zr11+Fe23Zr6/Laves-Fe2Zr/α-(Fe,Cr)/316L stainless steel substrate. Discontinuous brittle Fe2Zr layer formed near the interface between the residual filler metal layer and α-(Fe,Cr) layer. The maximum shear strength of brazed joints reached 129 MPa when brazed at 1020 °C for 10 min. The diffusion activation energies of α2-(Ti3Al) and α-(Fe,Cr) phases were −195.769 and −112.420 kJ/mol, respectively, the diffusion constants for these two phases were 3.639×10−6 and 7.502×10−10 μm2/s, respectively. Cracks initiated at Fe2Zr layer and propagated into the residual filler metal layer during the shear test. The Laves-Fe2Zr phase existing on the fracture surface suggested the brittle fracture mode of the brazed joints.

Microstructure and Mechanical Properties of Commercially Pure Ti/Steel Joint Brazed by Zr-Ti-Ni Amorphous Filler Metal.

In this study, the characteristics of commercially pure titanium (hereinafter referred as CP-Ti)/Steel joints, brazed with Zr-Ti-Ni amorphous filler metal were analyzed. The effects of brazing temperature and time on the microstructure and joining strength of the CP-Ti/Steel joints were investigated. It was observed that Ti diffused into stainless steel substrate formed a brittle reaction zone, which contained intermetallic compounds, such as τ (Ti5Cr7Fe17), (Fe, -Ni)Ti, and FeTi, observed at the joint interface. As the brazing temperature and time increased, the width of the reaction layer in the joint was observed to increase. To suppress the oxidation of the substrates, the experiment was conducted at a cooling and heating speed of 100 °C/min, under a vacuum of 5×10-5 torr. The joining strength was observed to be significantly affected by the brazing conditions, such as temperature and duration time. The shear strength test showed that the strength increased for 15 min and then sharply decreased. This was attributed to the formation of brittle intermetallic compounds, like (Fe, Ni)Ti. The joint brazed at 880 °C for 15 min showed the maximum joining strength, of 216 MPa.

Phase transformation study during diffusion brazing of γ-TiAl intermetallic using amorphous Ni-based filler metals

The paper aims at understanding the microstructure evolution of the diffusion brazing of γ-TiAl intermetallic compound using two Ni-based filler metals, a ternary Ni-Si-B, and a quinary Ni-Cr-Fe-Si-B. It was found that the joint region comprised of two distinct zones: analogous reaction layers adjacent to the TiAl substrates and a solidified zone at the middle of the joint region. The reaction layers consisted of separate intermetallic phases regions including ternary and binary Ti-Ni-Al intermetallic compounds. The solidified zone mainly composed of the Al1-xNi3Six isostructural solid solution and athermally Ni-boride or Ni-Cr rich borides containing eutectic microstructures at the joint centerline. The maximum shear strength was 240 MPa, and obtained by using Ni-Cr-Fe-Si-B filler metal. Fracture of the joint with Ni-Cr-Fe-Si-B filler occurred in the reaction layer/solidified zone interface, but joint with Ni-Si-B filler was fractured at solidified zone.

Brazing TC4 titanium alloy/316L stainless steel joint with Ti50-xZrxCu39Ni11 amorphous filler metals

TC4 titanium alloy was brazed to 316L stainless steel with newly designed TixZr50-xCu39Ni11 amorphous filler metals. The effect of Zr content on the wettability of filler metals, interfacial microstructure and shear strength of the brazed joints was investigated. Precipitation behavior of submicron phase and fracture behavior of the brazed joints were analyzed. Increasing Zr content in filler metals first increased and then decreased the spreading area of filler metals on both TC4 titanium alloy and 316L steel substrates, and changed the primary phase in filler drops. Besides, residual filler metal layer was thickened due to the reduction of filler metal flowability. But the thickness of the transition zone decreased, particularly the α-Fe reaction layer, attributed to the attenuation of Ti diffusion from filler metal to 316L steel substrate. Submicron β-Ti phase precipitated near the FeTi/Fe2Ti interface, and there were orientation relationships among the submicron β-Ti phase, FeTi and Fe2Ti as follows: (110)FeTi||(110)β-Ti/[1(_)11]FeTi||[1(_)11]β-Ti and (100)FeTi||(100)β-Ti/[001]FeTi||[001]β-Ti. The shear strength of brazed joints first increased and then decreased with the peak value of 238 MPa at 22.2 at.% Zr. Stress concentration at FeTi/Fe2Ti interface and impossible orientation relationship between FeTi and Fe2Ti phases resulted in the brittle fracture at FeTi/Fe2Ti interface of the brazed joint.

Investigation on Strength and Microstructural Evolution of Porous Cu/Cu Brazed Joints Using Cu-Ni-Sn-P Filler

Porous Copper (Cu) was brazed to Cu plates using Cu-9.7Sn-5.7Ni-7P amorphous filler metal. The effects of brazing parameters on the porous Cu and brazed joints were investigated. The furnace brazing temperatures employed were 660 °C and 680 °C, and the holding times were 10 and 15 min. After brazing, the microstructure was analyzed using Scanning Electron Microscope (SEM) equipped with Electron Dispersive X-ray Spectroscope (EDS). SEM results showed that the thickness of the brazed seam at the base joint decreased with increasing temperature and time. At low brazing temperature, microvoids and cracks were observed at the joint interface. The microvoids and cracks disappeared in the sample brazed at 680 °C for 15 min, and higher diffusion of the filler was noted in the overall bonded region. The formation of Cu-P, Cu-Ni, and Ni-Sn phases at the joint interface was validated using X-ray diffraction. The phases formed increased the hardness of the brazed joints and porous Copper. It was observed that the rigidity of porous Copper tends to increase due to surface hardening effects. The rigidity of porous Cu after brazing is important in ensuring minimal deformation during cooling device servicing, which is an integral feature of prospect product development.

Interfacial microstructure and shear strength of Ti6Al4V alloy/316 L stainless steel joint brazed with Ti33.3Zr16.7Cu50−xNix amorphous filler metals

Ti33.3Zr16.7Cu50-xNix (x = 0–16.5, at.%) amorphous filler metals were designed to braze Ti6Al4V alloy and 316 L stainless steel (SS). The effect of Ni addition in filler metals on the wettability, joint microstructure evolution and shear strength were investigated. The reaction phase identification and crack initiation mechanism were analyzed in depth. Ni addition weakened the wettability of the filler metal and thickened the brazed seam. The filler metal with 11 at.% Ni was optimized for brazing of Ti6Al4V alloy/316 L SS with the maximum joint shear strength of 318 MPa. FeTi, Fe2Ti, FeCr, and α-Fe phases formed around the transition zone close to 316 L SS substrate, which was the weak part of the brazed joints. The interface between FeTi and Fe2Ti phases was non-coherent with the lattice mismatch of 61.4%, initiating the crack at (β-Ti + FeTi)/Fe2Ti interface. The initiative cracks mainly propagated along the Fe2Ti and FeCr layers with brittle feature. Optimizing the constituents and alloying process for Ti-Cu-based filler metal has huge potential in improving the performance of titanium alloy/steel joint.

A high-strength vacuum-brazed TiAl/Ni joint at room temperature and high temperature with an amorphous foil Zr-Al-Ni-Co filler metal

An amorphous Zr58.6Al15.4Ni20Co6 foil was fabricated and applied as the filler metal to vacuum braze TiAl- and Ni-based alloys. The obtained joint has high strength both at room temperature (RT) and high temperature (HT). To investigate the effect of the brazing temperature and holding time on the joint strength, experiments were performed at different temperatures and held for different time. Five different regions derived from the interfacial atomic diffusion and crystallization of the amorphous filler metal were formed after brazing. The energy dispersive spectrometer (EDS) results indicated that sufficient interdiffusion occurred between the filler metal and base alloys after brazing. As a result, fine phases that were different from the base alloys were formed and dispersively distributed in the joint. Shear tests were performed at 30℃ and 600℃ and the results show that the joint strength first increased and then decreased with increases in holding time and heating temperature. The maximum shear strength of the joint at 30℃ and 600℃ were 353 MPa and 214 MPa respectively.

Brazing of curved copper sheets using CuNiSnP amorphous filler metal

This research investigates the effect of bending stress using furnace brazing on the interfacial layer between curved copper sheets and CuNiSnP amorphous filler metal. Copper sheet curvatures were varied between 5, 10, 15, 20, and ∞ mm to manipulate the bending stress of the base metal. The thermal behaviors and phase transformations of CuNiSnP amorphous filler metal were also characterized. The results showed that crystallization of the filler metal started at 200 °C, with multiple phases formed over the course of thermal treatment. The curved radius and bending stress were inversely correlated, while the interfacial layer of brazed joints and copper sheet curvatures were positively correlated. The interfacial layer was thin in small curvature specimens and thick in large radius specimens, indicating that the bending stress in the base metal affected the reliability of brazed joints.

Microstructure evolution of TC4 titanium alloy/316L stainless steel dissimilar joint vacuum-brazed with Ti-Zr-Cu amorphous filler metal

TC4 titanium alloy was vacuum-brazed to 316L stainless steel (SS) with Ti-Zr-Cu amorphous filler metal. The effect of brazing time and temperature on the interfacial microstructure and mechanical properties of joints was investigated. Electron probe micro-analyzer (EPMA) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) were used to study the joint microstructure; meanwhile, the reaction phases on fracture surfaces were identified by X-ray diffraction (XRD). The results show that all joints had similar interfacial microstructure of TC4 titanium substrate/Widmanstatten/β-Ti + Ti2Cu/(α-Ti + λ-Cu2TiZr) + Ti2Cu/Ti-Fe-Cu/TiFe/(Fe, Cr)2Ti/σ-phase + Fess/316L stainless steel substrate. Three reaction layers TiFe/(Fe, Cr)2Ti/σ-phase + Fess formed close to 316L stainless steel substrate and could benefit the mechanical properties of joints. The maximum shear strength of 65 MPa was obtained at 950 °C for 10 min. During shear test, cracks initiated at the interface of Ti-Cu-Fe layer/TiFe layer and propagated along the brazed seam/316L interface with a large amount of cleavage facets existing on the fracture surface.