Brazing Parameters Research Articles

Microstructure, mechanical properties and chemical degradation of brazed AISI 316 stainless steel/alumina systems

The main aims of the present study are simultaneously to relate the brazing parameters with: (i) the correspondent interfacial microstructure, (ii) the resultant mechanical properties and (iii) the electrochemical degradation behaviour of AISI 316 stainless steel/alumina brazed joints. Filler metals on such as Ag–26.5Cu–3Ti and Ag–34.5Cu–1.5Ti were used to produce the joints. Three different brazing temperatures (850, 900 and 950 °C), keeping a constant holding time of 20 min, were tested. The objective was to understand the influence of the brazing temperature on the final microstructure and properties of the joints. The mechanical properties of the metal/ceramic (M/C) joints were assessed from bond strength tests carried out using a shear solicitation loading scheme. The fracture surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques. It was found that using a Ag–26.5Cu–3Ti brazing alloy and a brazing temperature of 850 °C, produces the best results in terms of bond strength, 234 ± 18 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, the use of the Ag–34.5Cu–1.5Ti brazing alloy and a brazing temperature of 850 °C produces the best results in terms of corrosion rates (lower corrosion current density), 0.76 ± 0.21 μA cm −2. Nevertheless, the joints produced at 850 °C using a Ag–26.5Cu–3Ti brazing alloy present the best compromise between mechanical properties and degradation behaviour, 234 ± 18 MPa and 1.26 ± 0.58 μA cm −2, respectively. The role of Ti diffusion is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ag and Cu distribution along the brazed interface seem to play the most relevant role in the metal/ceramic joints electrochemical performance.

Fast brazing development for the joining of the beryllium armour layer for the ITER first wall panels

This paper describes the development of a flat pancake inductor for brazing beryllium tiles on a primary first wall (PFW) panel heat sink as well as the development of the brazing parameters. Two main variables were tested: brazing filler metal on one hand and PVD coating material on beryllium tiles on the other hand. The nickel coating and silver base brazing filler metal was the best couple and obtained shear values higher than 100 MPa. The inductor design and the choice of materials were applied to the brazing of a mock-up for high heat flux testing. Some tiles sustained 1000 cycles at 1.5 MW.

Microstructure and mechanical performance of brazed joints of Cf/SiC composite and Ti alloy using Ag–Cu–Ti–W

Cf/SiC composite was brazed to Ti alloy using interlayer of Ag–Cu–Ti–W mixed powder. The effects of W content and brazing parameters on the microstructure and properties of the brazed joints were investigated. The results show that W grains mainly distribute in Ag phase in the brazing layer and provide the effects of reinforcement and lowering residual thermal stress on the joint. The room temperature and 500°C shear strengths of the joints performed at 500°C for 30 min with Ag–Cu–Ti–50W (vol.-%) are remarkably higher than the optimal strengths of the joints brazed with Ag–Cu–Ti.

Study on brazing of TiNi shape memory alloy with stainless steels

TiNi shape memory alloy (TiNi SMA) and stainless steel (SS) were brazed by using silver-base filler metal with Ag 50–68 mass%, Cu 10–30 mass%, Zn 12–20 mass% and Sn 0–10 mass%. The results showed that properties and microstructures of the inhomogeneous joint depend on brazing heat input (laser output power and brazing time). Higher and lower heat inputs result in decreasing the joint strength due to low metallurgical bonding force between TiNi SMA and filler metal and structure coarsing in TiNi SMA heat affected zone. At proper brazing parameters, the joint strength can reach 320–360 MPa. The superelasticity loss of TiNi SMA heat affected zone increases with increasing brazing heat input, which is mainly attributed with structure coarsing and B19′ phase partly transforming into B2 phase in this zone. It is necessary to select proper brazing parameters for obtaining satisfactory joint properties.

Interface structure and mechanical properties of the TiAl/42CrMo steel joint vacuum brazed with Ag–Cu/Ti/Ag–Cu filler metal

TiAl and 42CrMo steel were vacuum brazed with Ag–Cu/Ti/Ag–Cu filler metal. The joint interface was divided into three distinct zones, including the reaction layer near TiAl, the central zone, and the TiC reaction layer adjacent to the steel. During brazing, AlCu2Ti, AlCuTi and TiC phase formed quickly with an increase in brazing temperature or brazing time. By comparing the brazing conditions and joint strengths, the optimum brazing parameters were obtained. When brazed at 900 °C for 5 min, the room temperature tensile strength and shear strength of the joint were 347 MPa and 229 MPa, respectively.

Effects of laser brazing parameters on microstructure and properties of TiNi shape memory alloy and stainless steel joint

Laser brazing has been applied for joining TiNi shape memory alloy (SMA) and stainless steel (SS) using the silver-based filler metal with composition of 52%Ag, 22%Cu, 18%Zn and 8%Sn (wt.%) and effects of laser brazing parameters has been investigated. The filler metal has good wettability on both TiNi SMA and SS. The brazing seam metal consists of α-Ag solid solution, α′-Cu solid solution surrounded by the α-Ag and eutectic structures. Heat affected zones (HAZs) of TiNi SMA and SS are comprised of B 2 and B ′ 19 phases and austenite phase, respectively. Increasing laser output power and brazing time resulted in the grain coarsening and reducing the microhardness value in the HAZs. The laser output power and brazing time have effects on the superelasticity (SE) and shape memory effect (SME) of the TiNi SMA HAZ. With increasing laser output power and brazing time from 50 W/10 s to 70 W/20 s, the residual strain ( ɛ u) at room temperature in the HAZ increased from 0.37% to 2.22% and the shape recovery rate ( ψ) at 100 °C decreased from 91.6% to 62.1%. The deterioration of SE and SME in TiNi SMA HAZ could be attributed to the coarse-grained structures. It is favourable to decrease laser output power and brazing time for improving both SE and SME of TiNi SMA HAZ.

Mechanical property of induction brazing TiAl-based intermetallics to steel 35CrMo using AgCuTi filler metal

TiAl-based intermetallics joined by vacuum induction brazing using Ag–Cu35.2–Ti1.8 filler alloy at 850–970 °C for 1–10 min was investigated. The optimum brazing parameters are as follows: brazing temperature is 870–880 °C, brazing time is 4–6 min. The maximum tensile strength of the joint is 320 MPa for the specimen induction brazed at for 870 °C for 5 min, and at this time, the thickness of Al–Cu–Ti intermetallic compound layer is about one third of that of the whole interface. Interfacial microstructure of TiAl/Ag–Cu–Ti/35CrMo joint brazed at 870 °C for 5 min is instable at 400 °C. The instantaneous high temperature strength is 248 MPa at 400 °C, the fracture location of joint is mainly at Al–Cu–Ti intermetallic compound layer, the fracture pattern of brazed joint deviate from transcrystalline crack at room temperature into intergranular crack.

Mechanical property and fracture characteristic of induction brazed joints of TiAl-based intermetallics to steel 35CrMo with Ag–Cu–Ni–Li filler

TiAl-based intermetallics joined by vacuum induction brazing using Ag–Cu–Ni–Li filler at 850–970 °C for 1–10 min was investigated. The interfacial microstructure and strength of the brazed joints were comprehensively evaluated, and the optimum brazing parameters were obtained. Comparing the high-temperature–short time conditions and the low temperature–longtime conditions, the interfacial microstructure under high-temperature–short time conditions is more appropriate, whose interfacial microstructure is mostly non-equilibrium crystal, and it has fine mechanical properties. The optimum brazing parameters are as follows: brazing temperature is 920–930 °C, brazing time is 1–2 min, the largest tensile strength is 324 MPa.

Microstructure and strength of brazed joints of Ti3Al base alloy with AgCuZn filler metal

Brazing Ti3Al alloys with filler metal Ag–Cu34–Zn16 was carried out at 1073–1173 K for 60–1200 s. The relationship between brazing parameters and shear strength of the joints was investigated, and optimum brazing parameters obtained as follows: brazing temperature 1073–1083 K, brazing time 250–300 s. The maximum shear strength obtained for joints was 160–170 MPa. The reaction products and the interface structure of the joints were investigated by SEM, EPMA, and XRD. Three kinds of reaction product were observed to have formed during the brazing of Ti3Al alloys with Ag–Cu34–Zn16 filler metal: namely Ti(Cu, Al)2+TiCu intermetallic compounds formed close to the Ti3Al alloy, and Ag solid solution formed in the middle of the joint. The interfacial structure of brazed Ti3Al alloy joints with Ag–Cu34–Zn16 filler metal was Ti3Al/Ti(Cu, Al)2+TiCu/Ag solid solution/Ti(Cu, Al)2+TiCu /Ti3Al, and this structure does not change with brazing time once it forms. The formation of intermetallic compounds Ti(Cu, Al)2+TiCu results in embrittlement of the joint and poor joint properties. The thickness of Ti(Cu, Al)2+TiCu intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K0 of the Ti(Cu, Al)2+TiCu reaction layer in the brazed joints of Ti3 Al alloys with Ag–Cu34–Zn16 filler metal were 170 kJ mol–1 and 2·31 × 10−5 m2 s−1 respectively. The growth formula was y2=2·13 × 10−5exp(−20447.44/T)t. Careful control of the growth of the reaction layer Ti(Cu, Al)2+TiCu can influence the final joint strength.

Microstructure and strength of TiAl/steel joint induction brazed with Ag-Cu-Ti filler metal

Intermetallic TiAl was induction brazed to steel in an induction furnace with Ag-Cu-Ti filler metal at 1143 K for 0·2–2·4 ks. Microstructural analysis indicates that Ti, Al, and C atoms in base metal diffuse to the interface and react strongly with the filler metal during brazing. The interface structure of the joint can be divided into three distinct zones: the reaction layer near TiAl, composed of Cu-Al-Ti compounds and Ag based solid solutions; the central zone of the interface, consisting of Ag based solid solutions in which Ag-Cu eutectic phases are dispersed; a TiC reaction layer adjacent to the steel. The relationship between brazing parameters and tensile strength of the joints is discussed, and the optimum induction brazing parameters obtained. When brazed at 1143 K for 0.9 ks, the tensile strength of the joint is 298 MPa.

Microstructure and strength of brazed joints of Ti 3Al-base alloy with different filler metals

The interfacial microstructure and properties of brazed joints of a Ti 3Al-based alloy were investigated in this paper to meet the requirements of the use of Ti 3Al-based alloy in the aeronautic and space industries. The effects of different brazing fillers on the interfacial microstructure and shear strength were studied. The relationship between brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. The brazed joints were qualitatively and quantitatively analyzed by means of EPMA, SEM and XRD. The results showed that using a AgCuZn brazing filler, TiCu, Ti(Cu,Al) 2 and Ag[s,s] were formed, the shear strength of the joint was decreased because of the formation of TiCu and Ti(Cu,Al) 2; using a CuP brazing filler, Cu 3P, TiCu and Cu[s,s] were formed at the interface of the joint, the former two intermetallic compounds decreased the shear strength. The analysis also indicated that using the TiZrNiCu brazing filler, the optimum parameters were temperature T=1323 K, joining time t=5 min, and the maximum shear strength was 259.6 MPa. For the AgCuZn brazing filler, the optimum parameters were joining temperature T=1073 K, joining time t=5 min, and the maximum shear strength was 165.4 MPa. To the CuP brazing filler, the optimum parameters were joining temperature T=1223 K, joining time t=5 min, and the maximum shear strength is 98.6 MPa. Consulting the results of P. He, J.C. Feng and H. Zhou [Microstructure and strength of brazed joints of Ti 3Al-base alloy with NiCrSiB, Mater. Charact., 52(8) (2004) 309–318], relative to the other brazing fillers, TiZrNiCu is the optimum brazing filler for brazing Ti 3Al-based alloy.

Microstructure and strength of brazed joints of Ti 3Al-base alloy with TiZrNiCu filler metal

Brazing of Ti 3Al alloys with the filler metal TiZrNiCu was carried out at 1173–1373 K for 60–1200 s. The relationship of brazing parameters and shear strength of the joints was discussed and the optimum brazing parameters were obtained. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1273–1323 K, brazing time is 250–300 s. The maximum shear strength of the joint is 250–260 MPa. Four kinds of reaction products were observed to have formed during the brazing of Ti 3Al alloys with the filler metal TiZrNiCu, namely Ti 2Ni + TiCu intermetallic compounds formed close to the Ti 3Al alloy. TiNi 2Cu intermetallic compounds layer formed between Ti 2Ni + TiCu intermetallic compounds and the filler metal and a Ti[s,s] (here s,s means super saturation) solid solution formed with the dispersed TiNi 2Cu in the middle of the joint. The interfacial structure of brazed Ti 3Al alloys joints with the filler metal TiZrNiCu is Ti 3Al/Ti 2Ni + TiCu/TiNi 2Cu/Ti[s,s] solid solution + TiNi 2Cu/TiNi 2Cu/TiCu + Ti 2Ni/Ti 3Al and this structure will not change with brazing time once it forms. The formation of over many intermetallic compounds Ti 2Ni + TiCu + TiNi 2Cu results in embrittlement of the joint and poor joint properties. The thickness of Ti 2Ni + TiCu + TiNi 2Cu intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K 0 of the reaction layer Ti 2Ni + TiCu + TiNi 2Cu in the brazed joints of Ti 3Al alloys with the filler metal TiZrNiCu are 261 kJ/mol and 0.0434 mm 2/s, respectively and the growth formula was y 2 = 0.0434 exp(−31392.83/ T) t. Careful control of the growth of the reaction layer Ti 2Ni + TiCu + TiNi 2Cu can influence the final joint strength.

Joint evolution and strengthening mechanisms in arc brazed galvanised steels with Cu97Si3 filler

Galvanised steel sheets have been joined using an arc brazing processing technique with Cu97Si3 as the filler metal. Gas metal arc (GMA) brazing and gas tungsten arc (GTA) brazing tests were conducted in flowing argon and with varying process parameters. Excellent wetting between base material and filler was observed in all samples. Tensile specimens fractured at the base material in samples prepared using optimal brazing parameters. Microhardness tests performed on the cross-sections of joined samples indicated that joint zone hardness is higher than base material or copper filler. Examination using energy dispersive X-ray analysis revealed the presence of intermetallic compound Fe5Si3(Cu) in the joint as well as a small amount of copper inside the base material. The dispersal of fine Fe5Si3(Cu) particles in the joint is the main strengthening factor. The Fe5Si3(Cu) particles were determined to arise from three sorces: whiskerlike fragmentation, dissolve-separation, and anode spot action.

Microstructure and strength of brazed joints of Ti 3Al-base alloy with NiCrSiB

Brazing of Ti 3Al alloys with the filler metal NiCrSiB was carried out at 1273–1373 K for 60–1800 s. The relationship of brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1323–1373 K, brazing time is 250–300 s. The maximum shear strength of the joint is 240–250 MPa. Three kinds of reaction products were observed to have formed during the brazing of Ti 3Al alloys with the filler metal NiCrSiB, namely, TiAl 3 (TiB 2) intermetallic compounds formed close to the Ti 3Al alloy. TiAl 3+AlNi 2Ti (TiB 2) intermetallic compounds layer formed between TiAl 3 (TiB 2) intermetallic compounds and the filler metal and a Ni[s,s] solid solution formed in the middle of the joint. The interfacial structure of brazed Ti 3Al alloy joints with the filler metal NiCrSiB is Ti 3Al/TiAl 3 (TiB 2)/TiAl 3+AlNi 2Ti (TiB 2)/Ni[s,s] solid solution/TiAl 3+AlNi 2Ti (TiB 2)/TiAl 3 (TiB 2)/Ti 3Al, and this structure will not change with brazing time once it forms. The formation of over many intermetallic compounds TiAl 3+AlNi 2Ti (TiB 2) results in embrittlement of the joint and poor joint properties. The thickness of TiAl 3+AlNi 2Ti (TiB 2) intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K 0 of the reaction layer TiAl 3+AlNi 2Ti (TiB 2) in the brazed joints of Ti 3Al alloys with the filler metal NiCrSiB are 349 kJ/mol and 24.02 mm 2/s, respectively, and the growth formula was y 2=24.04exp(−41977.39/ T) t. Careful control of the growth of the reaction layer TiAl 3+AlNi 2Ti (TiB 2) can influence the final joint strength.

Effect of gap size and process parameters on diffusion brazing of Inconel 738

The influence of gap size and brazing parameters (temperature and time), on the microstructure and properties of diffusion-brazed Inconel 738 (IN-738) superalloy, was investigated using two commercial brazing alloys, Amdry 'DF3' and Nicrobraz 150. The residual liquid present at brazing temperature was observed to transform on cooling into centreline eutectic constituents in 'NB 150' brazement while three different dispersed intermetallic phases were observed in the 'DF3' joint. The volume fraction of the second phases increased with gap size in both 'NB 150' and 'DF3' brazements. In addition to the centreline eutectic constituents, nickel and chromium rich borides were observed at the melt back zone in samples brazed below the Ni3B eutectic temperature of 1093°C, and above this temperature only chromium rich borides were observed. Joints containing the second phase intermetallics in 'NB 150' and 'DF3' brazed materials were found to exhibit tensile properties inferior to that of the base alloy.

Joining silicon nitride ceramic using a composite powder as active brazing alloy

The aim of this study was to join silicon nitride ceramic using a Cu–Ti bi-metallic composite powder. The microstructure and mechanical properties obtained were similar to results obtained with conventional active brazing alloys but with different kinetics. The experimental results obtained show the potential in using the composite powder as a brazing alloy. The reaction layer produced at the ceramic/filler metal interface was composed mainly of TiN and Ti5Si3. Similar to many active ceramic brazing processes, the reaction layer was formed in two stages, where the initial step was controlled by a liquid/solid reaction, followed by diffusion controlled growth. Depending on the brazing parameter, the reaction layer thickness ranged between 4 and 12 μm. Reaction layer growth was modeled and the effective activation energy was found to be 64 kJ/mole. The four-point bending strength varied between 250 and 400 MPa, depending on joining conditions. The crack propagation mode was through the interface for low strength joints and through the ceramic for high strength joints.

Effect of residual stress on the strength of an alumina–steel joint by partial transient liquid phase (PTLP) brazing

The effect of residual stress on the strength of joints made between alumina and stainless using partial transient liquid phase (PTLP) brazing with the Ni of an 80Ni20Cr core interlayer was studied. It was found that the residual stress caused by the thermal expansion mismatch between alumina (Al 2O 3) and stainless steel-304 (SS304) deteriorated the Al 2O 3–SS304 joints severely compared to Al 2O 3–Al 2O 3 joints with the same brazing parameters. The high residual stress zones obtained through finite element method (FEM) simulation corresponded well to the fractographic observation of the Al 2O 3–SS304 joints. FEM simulation also demonstrated that Ni and Ni–Cr filler metals are compliant layers that are suitable to relieve thermal residual stress in the Al 2O 3–SS304 joints.

A study on microstructure in the brazing interface of WC–TiC–Co hard alloys

The brazing parameters and microstructure in the interface of WC–TiC–Co hard alloy and the brazing filler were investigated by means of inside-furnace brazing, scanning electron microscopy (SEM) and X-ray diffraction. Test results indicated that the brazing joint with which the interface combines excellently can be obtained by using Cu–Zn–Ni brazing filler alloy and controlling the heating temperature 940–960 °C, the heat preservation time 10–15 min and a suitable cooling. The crystal microstructure of the brazing filler alloy is α+β eutectic. The interface microstructure of the hard alloy and the brazing filler alloy distribute evenly. The interface zone consists of WC, TiC, CuZn (α-phase). There are no microcracks, inclusions, etc. nearby the interface. The interface zone is formed by mutual diffusion of the hard alloy and the brazing filler alloy under high temperature.

Brazing parameters determine the degradation and mechanical behaviour of alumina/titanium brazed joints

The main aims of the present study are simultaneously to relate the brazing parameters with the correspondent interfacial microstructure, the resultant mechanical properties and the electrochemical degradation behaviour of commercially pure titanium/alumina brazed joints. A filler metal on the Ag-26.5Cu-3Ti system has been used. Three different brazing temperatures (850, 900 and 950°C) and three holding times (0.3, 1.2, 2.4 ks) were tested, in order to understand the influence of each combination of brazing temperature holding times, over the final microstructure and properties of the joints. The mechanical properties of the M/C joints were assessed on the basis of bond strength tests carried out using a shear solicitation scheme. The fracture surfaces were studied morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques. It was found that a brazing temperature of 850°C and a holding time of 2.4 ks, produces the best results in terms of bond strength, 130 ± 16 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, a brazing temperature of 950°C produces the best results in terms of corrosion rates (lower corrosion current), 3.44 ± 0.73 μA cm−2. However, the joints produced at 850°C using a holding time of 1.2 ks present the best compromise between mechanical properties and degradation behaviour, 122 ± 12 MPa and 7.59 ± 1.47 μA cm−2 respectively. The role of Ti diffusion from the metallic Ti to the Al2O3 surface is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ti distribution along the brazed interface does not seem to play any relevant role in the M/C joints electrochemical performance.

Preliminary investigation on joining performance of SiCp-reinforced aluminium metal matrix composite (Al/SiCp–MMC) by vacuum brazing

The present study has investigated the joining performance of SiC particulate reinforced aluminium metal matrix composite (Al/SiCp–MMC) by vacuum brazing process. After the joints brazed with Al–Si–Mg foil brazing filler metal at different brazing batches, both the mechanical properties and the microstructures of brazed joints were estimated. Moreover, the influence of SiCp size, SiCp volume percentage and the brazing parameters on bonding quality of the joints have also been discussed in detail. The results have revealed that the bonding quality either in SiCp/Al interface or in SiCp/SiCp interface belongs to weak bonding, and the results also show that under the same brazing parameters condition, the strength of brazed joints decreases along with increasing the SiCp volume percentage. In addition, the results also indicate that for a constant SiCp volume percentage the strength of brazed joints decreases when SiCp size increases. These results are very useful for the joining design of discontinuously reinforced metal matrix composites and further for the optimum design of composition of composites.