Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.     

Joining of C/C composite to TC4 using SiC particle-reinforced brazing alloy

Silicon carbide particles were used as reinforcement in the Ag-26.7Cu-4.6Ti (wt.%) brazing alloy for joining C/C composite to TC4 (Ti-6Al-4V, wt.%). The mechanical properties of the brazed joints were measured by shear strength testing. The effects of the volume percentage of SiC particles on the microstructures of the brazed joints were investigated. It is shown that the maximum shear strength of the joints is 29 MPa using 15 vol.% SiC in the brazing alloy which is greater than that with Ag-26.7Cu-4.6Ti brazing alloy alone (22 MPa). Ti is reacted with SiC particles, forming Ti–Si–C compound in the particle-reinforced brazing alloy. Due to this, more SiC particles in the brazing alloy, the thickness of TiC/TiCu reaction layer near C/C composite decreases. Moreover, SiC particles added to the brazing alloy can reduce the CTE of the brazing alloy which results in lower residual stress in the C/C composite-to-metal joint. Both of the above reasons lead to the increasing of the shear strength of the brazed joints. But excessive SiC particles added to the brazing alloy lead to pores which results in poor strength of the brazed joint.     

Brazing continuous carbon fiber reinforced Li2O–Al2O3–SiO2 ceramic matrix composites to Ti–6Al–4V alloy using Ag–Cu–Ti active filler metal

C_f/LAS composites and TC4 alloy were brazed successfully by vacuum brazing using Ag–Cu–Ti active filler metal. The interfacial microstructure was characterized by a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction. The effects of brazing temperature on the interfacial microstructure and joint properties were investigated in details. Various phases including TiC, TiSi₂, Ti₃Cu₄, Cu (s,s), Ag (s,s), TiCu and Ti₂Cu were formed in the brazed joints. Interfacial microstructure varies greatly with the increase of brazing temperature, while the amount of Ti₂Cu reduced, but no new phase is generated. The optimal shear strength of the joint is 26.4 MPa when brazed at 890 °C for 10 min. Shear test indicated that the fracture of the brazed joints went through the TiSi₂ + TiC layer close to the C_f/LAS composites interface.     

Microstructure and brazing mechanism of porous Si3N4/Invar joint brazed with Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler

Porous Si_3N_4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe_2Ti and Ni_3Ti intermetallic compounds. The effects of the brazing temperature and the thickness of Cu interlayer on the microstructure and mechanical properties of brazed joints were investigated. The typical microstructure of the joint brazed with multi-layered filler was porous Si_3N_4/TiN + Ti_5Si_3/Ag-Cu eutectic/Cu/Ag-Cu eutectic/Cu-rich layer + diffusion layer/Invar. When the brazing temperature increased, the reaction layer at the ceramic/filler interface grew thicker and the Cu interlayer turned thinner. As the thickness of Cu interlayer increased from 50 to 150μm, the joint strength first increased and then decreased. In this research, the maximum shear strength(73 MPa) was obtained when being brazed at 1173 K with a 100μm Cu interlayer applied in the filler, which was 55% higher than that brazed with single Ag-Cu-Ti brazing alloy and had reached 86% of the ceramic. The release of residual stress and the barrier effect of Cu interlayer to inhibit the formation of Fe_2Ti and Ni_3Ti intermetallics played the major role in the improvement of joint strength.     

Effect of calcium on the microstructure and mechanical properties of brazed joint using Ag–Cu–Zn brazing filler metal

The induction brazing of 316LN stainless steel using Ag–Cu–Zn filler metal containing various content of Ca was carried out to investigate the influence of impurity element Ca on the microstructure and mechanical properties of the brazed joint. The results showed that Ca additions caused the coarser of the grains and their irregular distribution. Increase of the Ca content resulted in the formations of brittle intermetallic compounds (IMCs) CaCu which perhaps lead to the formations of voids. All of the calcium-containing brazed joints performed better in microhardness than calcium-free ones and brazed joints containing 0.003 wt.% Ca showed the highest microhardness of 203HV. While the tensile strength decreased with the increment of Ca, from 460 MPa to 400 MPa. The combination effects of coarser grains, brittle IMCs and voids conduced to the reduction of tensile strength and microhardness of the brazed joints.     

Characteristics of dissimilar laser-brazed joints of isotropic graphite to WC–Co alloy

The effect of Ti serving as an activator in a eutectic Ag–Cu alloy filler metal in dissimilar laser-brazed joints of isotropic graphite and a WC–Co alloy on the joint strength and the interface structure of the joint is investigated in this study. To evaluate the joint characteristics, the Ti content in the filler metal was increased from 0 to 2.8 mass%. The laser brazing was carried out by irradiating a laser beam selectively on the WC–Co alloy plate in Ar atmosphere. The threshold content of Ti required to join isotropic graphite to WC–Co alloy was 0.4 mass%. The shear strength at the brazed joint increased rapidly with increasing Ti content up to 1.7 mass%, and a higher Ti content was found to be likely to saturate the shear strength to a constant value of about 14 MPa. The isotropic graphite blocks also fractured at this content. The concentration of Ti observed at the interface between isotropic graphite and the filler metal indicates the formation of an intermetallic layer of TiC.     

Study on cold metal transfer welding–brazing of titanium to copper

3 mm Pure titanium TA2 was joined to 3 mm pure copper T2 by Cold Metal Transfer (CMT) welding–brazing process in the form of butt joint with a 1.2 mm diameter ERCuNiAl copper wire. The welding–brazing joint between Ti and Cu base metals is composed of Cu–Cu welding joint and Cu–Ti brazing joint. Cu–Cu welding joint can be formed between the Cu weld metal and the Cu groove surface, and the Cu–Ti brazing interface can be formed between Cu weld metal and Ti groove surface. The microstructure and the intermetallic compounds distribution were observed and analyzed in details. Interfacial reaction layers of brazing joint were composed of Ti₂Cu, TiCu and AlCu₂Ti. Furthermore, crystallization behavior of welding joint and bonding mechanism of brazing interfacial reaction were also discussed. The effects of wire feed speed and groove angle on the joint features and mechanical properties of the joints were investigated. Three different fracture modes were observed: at the Cu interface, the Ti interface, and the Cu heat affected zone (HAZ). The joints fractured at the Cu HAZ had higher tensile load than the others. The lower tensile load fractured at the Cu interface or Ti interface was attributed to the weaker bonding degree at the Cu interface or Ti interface.     

Vacuum brazing of sapphire with Inconel 600 using Cu/Ni porous composite interlayer for gas pressure sensor application

In this research, sapphire as a ceramic was brazed to Inconel 600 as a metal with a commercially available Cusil ABA (63Ag–1.75Ti–35.25Cu) filler foil as braze alloy where Cu/Ni porous composite introduced as an interlayer so it could be used in a particular gas pressure sensor application. Several brazing processes were carried out in a high vacuum furnace in order to investigate the effects of brazing parameters on the joint interface and mechanical properties. The common brazing temperature and time were in the ranges of 830–900 °C and 15–30 min respectively, while vacuum pressure was remained constant at 1 × 10⁻⁴ Pa. SEM-EDS and XRD analyses of the joint microstructure and interface composition revealed five distinct phases; Ni₃Ti, AlNi, Cr_1.97Ti_1.07, Fe_0.2Ni_4.8Ti_5, (TiO_1.06)_3.32. The brazing area formed two “ocean” structures near to Inconel and sapphire interfaces whereas a reaction layer was developed at the surface of Inconel 600. Under the mechanical property analyses the brazed joint at 900 °C for 30 min obtained the maximum shear strength of 58.5 MPa which is adequate for particular gas pressure sensor application.     

Microstructure and mechanical properties of MoSi2–MoSi2 joints brazed by Ag–Cu–Zr interlayer

The present work investigates joining of two MoSi₂ parts through Cusil/Zr/Cusil interlayer with Cusil being a commercial eutectic of Cu–Ag alloy. The joining operation was implemented in an inert gas tube furnace by brazing. The brazing temperature ranged from 800 to 930 °C while the operation lasted for 60 min. Evaluation of joints strength through shear loading identified the maximum strength 60.31 MPa for the brazed sample at 830 °C. Interfacial microstructure was studied by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) techniques. Applying the temperature of 830 °C was led to a uniform dense joint consisting of various phases with excellent bonding within the interfaces. XRD and EDS results revealed different phases such as Mo₅Si₃, Ag-rich solid solution and Cu₁₀Zr₇ at the interface. At higher brazing temperatures the amount of intemetallic compounds and residual stresses increased and therefore, mechanical properties of the joint degraded. The fracture analysis by SEM revealed various fracture path and morphology for different brazing temperatures.     

Study on vacuum brazing of high purity alumina for application in proton synchrotron

The paper describes an experimental study to evaluate two different vacuum brazing processes to obtain high purity alumina (99.7%) joints suitable for application in rapid cycle proton synchrotron. Two different brazing routes, adopted for making alumina–alumina brazed joints, included (i) multi-step Mo–Mn metallization, followed by brazing with BVAg-8 alloy and (ii) advanced single-step active brazing with CuSil-ABA® alloy. Both the brazing routes yielded helium leak tight and ultra-high vacuum (pressure < 10⁻⁹ mbar) compatible joints. Active-brazed specimens exhibited tensile and mean flexural strengths of 62 and 110 MPa, respectively. Metallized-brazed specimens, although associated with relatively lower tensile strength (35 MPa) than the targeted value (>50 MPa), displayed higher mean flexural strength of 149 MPa. The results of the study demonstrated that active brazing is a simple and cost effective alternative to conventional multi-step metallization route for producing quality joints of high purity alumina for application in rapid cycle proton synchrotron machine.     

Thermodynamic and kinetic analysis of interfacial reaction between CBN and titanium activated Ag–Cu alloy

Abstract

Thermodynamic and kinetic analysis was performed in order to study the interfacial reaction mechanism of cubic boron nitride (CBN) abrasive grains and Ti activated Ag–Cu filler alloy during high temperature brazing. Meanwhile, microstructure of the interfacial layer was experimentally detected using scanning electron microscope (SEM), energy dispersion spectrometer (EDS) and X-ray diffraction (XRD) in the present paper. The results indicate that according to the thermodynamic theory, the interfacial reaction has been proved feasible, and during brazing the special active element Ti concentrated to and reacted with the CBN abrasive to form TiB₂ and TiN, which joined hard the abrasive grain and steel substrate. Furthermore, the diffusion activation energy of the growing process in the interfacial reaction layer has discovered that the layer growth largely depends on the new formed TiN under conditions of 1153–1193 K and 5–30 min.     

Brazing of SiO2f/SiO2 composite modified with few-layer graphene and Invar using AgCuTi alloy

Due to the poor wettability of the AgCuTi alloy on the SiO_2f/SiO₂ composite, direct brazing of the composite with an Invar alloy could hardly achieve a reliable joint. To overcome that, the SiO_2f/SiO₂ composite was decorated with few-layer graphene (FLG) by a plasma enhanced chemical vapor deposition (PECVD) method. Sessile drop experiments indicate that the contact angle dropped from 123.8° to 50.7° after FLG was grown on the surface of the SiO_2f/SiO₂ composite. Afterwards, the effects of brazing temperature and Ti contents on the microstructure evolution and mechanical properties of joints (Invar/SiO_2f–SiO₂ modified with FLG) were investigated. The typical interface structure of the joint is SiO_2f–SiO₂/Ti₅Si₃ + TiO₂ + Cu_xTi_6 − xO(x = 2,3)/Ag(s,s) + Cu(s,s) + Cu–Ti blocks/wave-like Fe₂Ti + Ni₃Ti/Ag(s,s) + Cu(s,s) + Fe₂Ti + Ni₃Ti blocks/Invar. As the brazing temperature and Ti contents increase, the reaction layer on the SiO_2f/SiO₂ side becomes thicker and cracks gradually propagate. Meanwhile, a few dispersive Fe₂Ti + Ni₃Ti phases change into large-area wave-like compounds and more Cu–Ti compounds form with the increase of the Ti content. The microstructure evolution significantly affects the shear strength of the brazed joints. The highest shear strength is 26 MPa brazed at 860 °C for 10 min with 4.5 wt.% Ti content.     

Ultrasound-assisted brazing of Cu/Al dissimilar metals using a Zn–3Al filler metal

Ultrasound-assisted brazing of Cu/Al dissimilar metals was performed using a Zn–3Al filler metal. The effects of brazing temperature on the microstructure and mechanical properties of Cu/Al joints were investigated. Results showed that excellent metallurgic bonding could be obtained in the fluxless brazed Cu/Al joints with the assistance of ultrasonic vibration. In the joint brazed at 400 °C, the filler metal layer showed a non-uniform microstructure and a thick CuZn₅ IMC layer was found on the Cu interface. Increasing the brazing temperature to 440 °C, however, leaded to a refined and dispersed microstructure of the filler metal layer and to a thin Al_4.2Cu_3.2Zn_0.7 serrate structure in the Cu interfacial IMC layer. Further increasing the brazing temperature to 480 °C resulted in the coarsening of the filler metal and the significantly growth of the Al_4.2Cu_3.2Zn_0.7 IMC layer into a dendrite structure. Nanoindentation tests showed that the hardness of the Al_4.2Cu_3.2Zn_0.7 and CuZn₅ phase was 11.4 and 4.65 GPa, respectively. Tensile strength tests showed that all the Cu/Al joints were failed in the Cu interfacial regions. The joint brazed at 440 °C exhibited the highest tensile strength of 78.93 MPa.     

Investigation of the effect of Al–5Ti–1B grain refiner on dry sliding wear behavior of an Al–Zn–Mg–Cu alloy formed by strain-induced melt activation process

This study was undertaken to investigate the influence of Al–5Ti–1B master alloy and modified strain-induced melt activation process on the structural characteristics, mechanical properties and dry sliding wear behavior of Al–12Zn–3Mg–2.5Cu aluminum alloy. The optimum amount of Ti containing master alloy for proper grain refining was selected as 2 wt.%. The alloy was produced by modified strain-induced melt activation (SIMA) process. Reheating condition to obtain a fine globular microstructure was optimized. The optimum temperature and time in strain-induced melt activation process are 575 °C and 20 min, respectively. T6 heat treatment was applied for all specimens before tensile testing. Significant improvements in mechanical properties were obtained with the addition of grain refiner combined with T6 heat treatment. After the T6 heat treatment, the average tensile strength increased from 283 MPa to 587 MPa and 252 MPa to 564 MPa for samples refined with 2 wt.% Al–5Ti–1B before and after strain-induced melt activation process, respectively. Dry sliding wear performance of the alloy was examined in normal atmospheric conditions. The experimental results showed that the T6 heat treatment considerably improved the resistance of Al–12Zn–3Mg–2.5Cu aluminum alloy to the dry sliding wear.The results showed that ultimate strength and dry sliding wear performance of globular microstructure specimens was a lower value than that of Ti-refined specimens without strain-induced melt activation process.     

Study on the microstructure and mechanical properties of diffusion brazing joint of C17200 Copper Beryllium alloy

In order to study the microstructure and mechanical properties of Copper Beryllium alloy, spreadability test was carried out at two temperatures under Argon atmosphere for different filler metals of Ag content. The results show that BAg2a (Ag–26Cu–21Zn–19Cd) and BAg1a (Ag–18.5Cu–17Zn–14.5Cd) are the best choice for brazing of Copper Beryllium. Zn affects the wetting of interlayer because it spreads preferentially. The bonding process was carried out at a temperature ranging of 650–800 °C for various times under Argon atmosphere using of BAg2a (Ag–26Cu–21Zn–19Cd) film with 100 μm thickness as interlayer.Interfacial microstructures were examined by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The eutectic and intermetallic compounds such as CuZn, AgZn3 and AgCd3 were formed at the interfaces between the interlayer and substrate. Microhardness and tensile tests were used for evaluating the mechanical properties. Average of hardness at the center of brazed seam decreased with increasing time and temperature that associated with diffusion of main elements to substrate and intermetallic formation at the interface. Maximum tensile strength of 170 MPa was obtained at 750 °C for 20 min for filler metal BAg2a without heat treatment and 227 MPa with heat treatment.     

Microstructural and mechanical properties of jointed ZrO2/Ti–6Al–4V alloy using Ti33Zr17Cu50 amorphous brazing filler

Ceramic ZrO₂ and metallic Ti–6Al–4V alloy are jointed by using a Ti₃₃Zr₁₇Cu₅₀ (at.%) amorphous alloy as a solder at 1123–1273 K in a high vacuum. It is demonstrated that the microstructure and mechanical properties are significantly influenced by the brazing temperature, the heat time and the cooling rate. The brazing seam jointing ZrO₂ with Ti–6Al–4V is composed of ZrO₂/Cu₂Ti₄O, (Ti,Zr)₂Cu/TiO, Ti₂O/CuTi₂, (Ti,Zr)₂Cu/CuTi₂/Ti–6Al–4V alloys and compounds, of which the increasing thickness weakens the shear strength as the brazing temperature, the heat time the cooling rate increase. The maximum shear strength of the brazing joints reaches 162 MPa with the optimal technical parameters: the brazing temperature of 1173 K, the heat time of 10 min and the cooling rate of 5 K/min. The fracture of the joint occurs in the brittle seam layer nearby the side of ZrO₂.     

Reliability studies of Cu/Al joints brazed with Zn–Al–Ce filler metals

This paper examines the effect of different Ce content on the properties and microstructures of Zn–22Al filler metals and Cu/Al brazing joints. The results indicate that, the spreading area on Cu substrates of Zn–22Al filler metal could be improved by 29.7% with the addition of 0.03 wt% Ce, whereas the oxidation resistance of the alloy increased significantly. The thermal behaviors of Zn–22Al filler metals were minimally influenced by the addition of Ce. The Zn–22Al–xCe filler metals show finer and more uniform microstructures when the added Ce content is in the range 0.03–0.05 wt%. Particularly, the addition of trace Ce into the Zn–22Al filler metal can refine the microstructures and decrease the thickness of the layer of intermetallic compounds produced in the Cu/Al brazing joints. Some bright (Zn,Al)–Ce intermetallic compounds particles were observed in the alloy when the Ce content exceeds 0.08 wt%. The results also indicate that the shear strength of Cu/Al joint brazed with Zn–22Al–0.05Ce is 30.3% higher than that of the Zn–22Al filler metal. Some hard and brittle Ce-bearing intermetallic compounds particles appear in the fracture surface when the Ce content is 0.25 wt%, which resulted in the weakening of the mechanical properties of Cu/Al brazing joints.     

Effect of stress peening on surface layer characteristics of (TiB + TiC)/Ti–6Al–4V composite

Residual stresses and microstructure on surface layer of (TiB + TiC)/Ti–6Al–4V are investigated after stress peening. The values of domain sizes and microstrain of surface deformation layers are calculated from the integral breadth of diffractive peaks via Voigt method. The results show that the compressive residual stresses and microhardness are improved significantly after stress peening, and the variations of residual stresses are affected by both the prestresses and the directions of measurement. Microstructure investigations reveal that, the deformation amount increase after stress peening, and smaller domain grain sizes and higher density dislocations are introduced. The changes of microstructures are mainly influenced by the values of prestresses. According to these investigations, it is can be found that the stress peening is superior to the conventional shot peening treatments and it is an effective method to improve the surface properties of (TiB + TiC)/Ti–6Al–4V composite.     

Effects of rare earth La on microstructure and properties of Ag–21Cu–25Sn alloy ribbon prepared by melt spinning

Ag–21Cu–25Sn alloy ribbon as a promising intermediate temperature alloy solder (400–600 °C) was prepared by melt spinning technique in this paper. Rare earth La was added into Ag–21Cu–25Sn alloy to refine the microstructures and improve the wettabilities of as-prepared alloy solders. The phase constitutions, microstructures, melting temperatures and wettabilities of selected specimens were respectively tested. The results showed that the dominant phase constitutions of Ag–21Cu–25Sn–xLa alloy ribbons were Ag₃Sn and Cu₃Sn. The grain size of Ag–21Cu–25Sn–xLa alloy decreased with the addition of La increasing. La addition reduced the melting temperatures of Ag–21Cu–25Sn–xLa alloy ribbons, and effectively improved the wettabilities of the alloy ribbons. When the addition of La was 0.5 wt%, the wettability of as-prepared alloy solder achieved the optimal value of 158 cm² g⁻¹ under brazing temperature 600 °C and dwell time 15 min. In addition, raising brazing temperature and prolonging dwell time could improve the wettability of Ag–21Cu–25Sn–xLa alloy ribbon.     

Hot deformation behavior of spray-deposited Al–Zn–Mg–Cu alloy

The flow behavior of spray-deposited Al–10.21Zn–2.76Mg–1.45Cu–0.16Zr (wt.%) alloy has been systematically investigated by thermal compression tests with temperature and strain rate ranging from 613 K to 733 K and 0.001–1 s⁻¹, respectively. Microstructural observations revealed that the average grain size of spray-deposited alloy was below 25 μm due to the high cooling rate. Both relatively high temperature and low strain rate could promote the formation of dynamic recrystallization (DRX). The stress level of the alloy decreased with increasing deformation temperature and decreasing strain rate, which could be characterized by a Zener–Hollomon parameter in the hyperbolic-sine equation. Furthermore, the strain-dependent constitutive equation could lead to a good agreement between the calculated and measured flow stresses in the elevated temperature range for spray-deposited alloy. The deformation activation energy for spray-deposited alloy was relatively lower than that of the as-cast alloy owing to ultrafine grains and high supersaturated solid solubility.