In the present study, the effect of time and base metal microstructure on the Transient Liquid Phase (TLP) bonding of 304L stainless steel was studied. TLP was performed at 1050 0C for 5 and 60 minutes on the coarse grain austenitic and martensitic microstructure using BNi-2 interlayer. To prepare martensitic microstructure, as-received 304L was rolled at-15 0C up to 80% rolling reduction. TEM analysis was proved that the microstructure of 80% rolled samples consisted of two different morphologies of martensite namely as lath-type and dislocation cell type martensite. It was observed that the structure of bonded zone after 5 min has consisted of isothermally solidified zone (ISZ) containing γ solid solution and athermally solidified zone (ASZ) containing complex boride phases. Meanwhile, after 60 min of heating, the structure of bonded zone completely solidifies isothermally. The obtained results also showed that the martensitic microstructure considerably effect on the width of diffusion affected zone (DAZ) which was related to the reversion of martensite to ultrafine grain austenite during heating.

AISI 304 stainless steel is joined by transient liquid phase diffusion bonding, using an amorphous base nickel interlayer with a thickness of 50fLm. The bonding process was carried out at 1100°C under different atmospheres, air, argon and vacuum, at different bonding times of 30 to 180 min. The joints were then homogenized at 1150°C for 120 min. Microstructure studies showed that voids and cavities were formed at the joint region and the joint/parent alloy interface of bonds made under air and argon gas. The formation of these voids and cavities was related to the oxidation of the interlayer and joint/parent alloy interface during the bonding process. But, there were no voids or cavities at the bond region and joint/parent alloy interface when the bonding process was carried out in vacuum. Shear test results showed that the shear strength of bonds made under vacuum and then homogenized is very close to the shear strength of the parent alloy.

Due to their superior properties such as high specific strength, high creep resistance and high strength at elevated temperatures, aluminum composites reinforced with alumina nano particles are widely used for advanced purposes such as aerospace and auto industries. Lack of an appropriate welding process limits their applications. Transient liquid phase (TLP) bonding is one of the state-of-the-art joining processes. It is used for welding composites and advanced materials. Microstructure and mechanical properties of TLP bonding depend on the bonding time and temperature. In the current study, the effect of bonding time on the microstructure and bonding strength of the TLP diffusion bonded of Al2O3 p/Al nanocomposite was investigated. A thin layer of copper deposited by electroplating was used as an interlayer. The bonding times of 20 and 40 min were not sufficient for completing the isothermal solidification, and the bonding strengths were not satisfactory. By increasing the bonding time to 60 min at constant bonding temperature of 580oC, the isothermal solidification was completed and the final joint microstructure consisted of softα-Al phase with dispersed CuAl2 precipitated particles. Decreasing the amount of brittle eutectic structures in the joint seam by increasing the bonding time was the main reason for improvement of the joint shear strength. The maximum joint shear strength was achieved at 580oC for 60 min which was about 85% of the shear strength of the base material.

In this research, the effect of bonding temperature on the microstructure and mechanical properties of Inconel 939 super alloy by transient liquid phase bonding method. For this purpose, the middle layer of MBF20 with a thickness of 50 microns and three temperatures of 1060 °C, 1120 °C, 1180 °C and a time of 45 minutes have been used. In order to evaluate the microstructure, a scanning electron microscope equipped with an elemental analysis system has been used. Vickers hardness test and shear strength test have been used to evaluate the mechanical properties. The research findings showed that with increasing temperature from 1060 °C to 1120 °C, the width of the athermal solidification zonedecreased from 38µm to 35µm and with increasing temperature at 1180 °C, the athermal solidification zone was completely removed and isothermal solidification zone was replaced. In addition, with increasing temperature, the hardness in the joint center decreases and the shear strength increases.

In this paper, transient liquid phase (TLP) bonding process between Inconel 718 alloy and Inconel 600 alloy using a BNi-2 interlayer with 50 mm thickness was investigated. Transient liquid phase bonding process was performed at 1050oC for 5, 25 and 45 min. Microstructure evaluation was carried out through optical microscopy, field emission scanning electron microscopy (FE-SEM). Also, bonding shear strength was measured. The results showed that the joint microstructure was formed of three zones including isothermal solidification zone (ISZ), thermal solidification zone (ASZ) and diffusion affected zone (DAZ). At the time of 5 min, boride intermetallic compounds in thermal solidification zone were formed. Isothermal solidification was completed and thermal solidification zone vanished by increasing the bonding time from 5 to 45 min. Diffusion affected zone of the Inconel 718 alloy was persistent and expanded by increasing the time and diffusion of B element to parent metals, but this region in Inconel 600 alloy vanished and the homogenization process occurred by increasing the bonding time. Also, because of the removal of boride intermetallic compounds, changes in hardness in the joint region were smoother and the hardness value of joint region was about 280 HV. The results of shear strength showed that the bonding strength was increased from 250 MPa to 410 MPa with increasing the bonding time from 5 to 45 min, respectively.

Transient liquid phase (TLP) bonding of two dissimilar alloys Al 2024 and Ti-6Al-4V was carried out at 580 and 600 ° C for 45 min bonding time using a 30-μ m-thick pure silver (Ag) foil interlayer. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the phase structure and compositional changes across the joint region. Mechanical properties of the joints were investigated through shear strength and hardness tests. The joint formation was due to the solid-state diffusion of Ag and Cu into Al and Ti alloys, followed by eutectic formation, isothermal solidification, and formation of various intermetallic compounds such as Ag2Al, Al2Cu and Al2CuMg along the Ag/Al2024 interface. Moreover, the interdiffusion of titanium and aluminum led to the formation of Al3Ti intermetallic compounds. These types of intermetallics produced a metallurgical bond at Al 2024 interface. The study showed that the shear strength of the joint reaches a high value of 176. 11 MPa obtained at the higher bonding temperature of 600 ° C. It was also observed that the sample failed away from the base metal.

Despite rapid advancement of additive manufacturing methods in recent years, sufficient research on bonding of additively manufactured materials to conventional alloys has not been conducted. This study evaluates the bonding between austenitic stainless steel L316 and Ti-6242 alloy, fabricated by electron beam melting, using the transient liquid phase (TLP) bonding method. The TLP bonding was achieved using a copper interlayer and processing in a vacuum furnace, examining the effects of process time and surface roughness on bond quality. The samples were characterized by optical and scanning electron microscopy, X-ray diffraction, shear strength testing, and surface roughness measurement. Results showed that reducing the surface roughness increased the shear strength. Additionally, processing time significantly affected the element diffusion, formation of intermetallic compounds like FeTi and TiCu, and the shear strength of the joints. The highest shear strength of 200 MPa was obtained with surface preparation by grinding and polishing and bonding at 980°C for 120 minutes.

In this paper, the effect of bonding temperature and time on the microstructure of transient liquid phase bonding of GTD-111 nickel-based superalloy was studied. The bonding process was performed at temperatures of 1080, 1120 and 1160 ° C at different times and the microstructure of the various bonding regions was analyzed by light and scanning electron microscopy. The results show that by increasing the bonding temperature from 1080 to 1160 ° C, solidification time was reduced from 195 to 90 min and the dissolution rate of the base metal and the bonding width increased. Also, at all holding times, the bonding zone containing secondary phases included nickel-rich and chromium-rich borides and nickel silicide in a  matrix. These phases were observed in the centerline and adjacent of the interface. By increasing the bonding time, the volume fraction of the precipitates in the bonding zone decreased and the brittle boride phases were completely removed. This process is due to the strong dependence of the diffusional behavior of the TLP-joint on temperature and time. It was observed that with increasing the bonding temperature, the bonding width and the rate of dissolution of the base metal increase. The results showed that with increasing holding time at all three bonding temperatures, the thickness of the ASZ zone and the volume fraction of precipitates in the bonding area decreased and the DAZ width increased.

According to the industry’s need to an appropriate bonding process for components made of AISI 321 austenitic stainless steel, which is used in power-plant parts such as turbines, transient liquid phase (TLP) bonding of AISI 321 steel using MBF-30 and MBF-20 interlayers was studied in this research. TLP bonding was performed in a vacuum furnace at 1050, 1100 and 1150oC for 30-120 minutes. The microstructural studies were conducted on the joints using an optical microscope and an scanning electron microscope (SEM). Phase analysis of the joints was also performed a SEM/EDS and XRD system. To investigate the distribution of elements across the joints, line scan analysis was used. The shear strength test and the microhardness measurement test were conducted on the joints, in order to study the joints’ mechanical properties. The minimum time or complete isothermal solidification at 1050, 1100 and 1150oC was obtained as 75, 45 and 30 minutes, respectively. At the incomplete isothermal solidification condition, Fe-B, Cr-B, Ni-Si and Ni-B phases were observed at the joint centerline and diffusion affected zone (DAZ). With increasing bonding temperature and time, more homogenous joint, lower hardness at the different zones of the joints and higher shear strength were obtained. The maximum shear strength for MBF-30 interlayer was obtained as 99 and 98 percent of that of the base metal, and for MBF-20 interlayer was obtained as 95 and 94 percent of that of the base metal, respectively.