Dissimilar Transient Liquid Phase Research Articles

Kinetics of initial diffusion solidification during continuous heating in term of IN718 superalloy / 316LN steel TLP bonding system

In this work, the effect of heating rate on the solidification kinetics of the dissimilar transient liquid phase (TLP) bonding joint of IN718 superalloy / 316LN steel was investigated. It was determined that the initial diffusion solidification (IDS) during continuous heating, accompanied by the melting of interlayer, plays an important role on the formation of TLP bonding joint. The lower heating rate results in the more sufficient IDS and thus the shorter time needed for isothermal solidification. This overturns the conventional view that the solidification behavior in TLP bonding joints mainly occurs at the stage of isothermal holding. Additionally, the IDS process is modeled using diffusion-based concepts under varying heating rates. The proposed model is more applicable for the prediction of solidification time in TLP bonding joint than the classic models only on the consideration of isothermal solidification.

High temperature shear and thermal aging behavior of dissimilar transient liquid phase bonded Hastelloy X to Ni3Al intermetallic compound

Nickel super alloys and intermetallic compounds (IMCs) are candidate as strategic materials for turbine industry, because of its excellent high temperature properties. In this study, mechanical properties and thermal aging behavior (post thermal exposure) of the transient liquid phase (TLP) bonds between Hastelloy X to Ni3Al IMC at temperature range of 800–900 °C were investigated. The microstructure and fracture surfaces of the joints were examined by optical and scanning electron microscopes as well as XRD analysis. The optimum joint bonding strength was achieved for the sample treated at 1100 °C–180 min equaling to 355 ± 4.5 MPa. XRD patterns of semi-cleavage fracture surfaces revealed nickel solid solution matrix containing BNi3 and Ni3Si compounds generated at ASZ/ISA interface. The ultimate tensile strength reaches 36.5 ± 1 and 20.5 ± 1 MPa at temperatures of 800 °C and 900 °C, respectively. Fracture occurred in the IMC substrates for both temperatures were due to shrinkage porosity during solidification of IMC and mismatch of crystal lattice constants with the matrix. The thermal aging process at 900 °C for 50–500 h had a minor effect on the joint microstructure but generated TCP phases in the Hastelloy X.

Microstructure Evolution of Athermal Solidification Zone and Its Effect on Mechanical Properties in Dissimilar Transient Liquid Phase Bonded Joint of IN718 Ni-Based Alloy/316LN Steel

Microstructure Evolution of Athermal Solidification Zone and Its Effect on Mechanical Properties in Dissimilar Transient Liquid Phase Bonded Joint of IN718 Ni-Based Alloy/316LN Steel

Effect of bonding temperature and bonding time on microstructure of dissimilar transient liquid phase bonding of GTD111/BNi-2/IN718 system

The effect of bonding temperature and bonding time on the microstructure of transient liquid phase (TLP) bonding named GTD111 and IN718 superalloys, using a commercial Ni–B–Cr filler alloy (BNi-2) interlayer were evaluated. The sandwich assembly was kept in a vacuum furnace at temperatures of 1050, 1100, and 1150 °C for 1, 15, 30, 45, 60, and 80 min until the TLP process occurred. Microstructural characterization was carried out via optical microscopy, scanning electron microscopy (SEM) equipped with field emission energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Microstructural assessments displayed those in little bonding times, the joint microstructure includes continuous eutectic intermetallic phases and longer times cause eutectic free microstructure. The bonding temperature affects the isothermal solidification rate, while, at low bonding temperatures microstructure of the joint centerline is controlled by diffusion of melting point depressant (MPD) elements. Despite, at high bonding temperature effect of base metal alloying elements on the joint microstructure development was more marked. The results showed that athermally solidified zone (ASZ) size reduces with increasing bonding temperature and time due to diffusion of boron into the base metal.

Comprehensive microstructural investigation during dissimilar transient liquid phase bonding cobalt-based superalloys by BNi-9 amorphous interlayer foil

Cobalt-based X-45 and FSX-414 superalloys with interlayer BNi-9 have been bonded by a transient liquid phase bonding process at a constant temperature of 1150 °C with the holding times of 1, 10, 60, 120, 180 and 240 min. Microstructural changes of base metals showed that the conditions of 1150 °C/240 min can be used to joint base metals, in such a way that the primary carbides of M 6 C and M 23 C 6 are significantly dissolved in the matrix, forming a supersaturated solid solution. Examination of the bonded specimens showed that during heating up to the bonding stage, Nickel-rich carbo-boride deposits are formed at the interface between the filler metal and the base alloys due to the solid-state diffusion of boron element. The next generation of carbo-borides is formed in the diffusion affected zone of the base metals, which are also Cobalt–Chromium–Tungsten–Molybdenum-rich carbo-borides. Bonding at 1150 °C/1 min resulted in lack of complete diffusion of boron element into the base metals; quasi-eutectic compounds γ, Ni 3 B and CrB were formed in the centerline of the bond and, increasing the holding time causes the interdiffusion of alloying elements of base metals and the interlayer and leads to the uniformity of the chemical composition along the joint. Bonding under standard solution heat treatment condition (1150 °C/240 min) completely removes the diffusion affected zone on the 45-X side.

Effect of Bonding Time on Dissimilar Transient Liquid Phase (TLP) Bonding of IN939 to IN625 Superalloys: Microstructural Characterization and Mechanical Properties

Effect of Bonding Time on Dissimilar Transient Liquid Phase (TLP) Bonding of IN939 to IN625 Superalloys: Microstructural Characterization and Mechanical Properties

The effect of bonding time on the microstructure and mechanical properties of dissimilar transient liquid phase bonding between UNS N08825 alloy and UNS S32750 super duplex stainless steel using the BNi-2 interlayer

• The dissimilar transient liquid phase (TLP) bonding of the UNS N08825 alloy to UNS S32750super duplex stainless steel was successfully accomplished using the BNi-2 interlayer. • The complete isothermal solidification occurred at 1050 °C and the bonding time of 300 s. • Shear strength of the TLP joints improved by increasing the holding time. In this study, the microstructure and mechanical properties of transient liquid phase, dissimilar joints between UNS N08825 alloy and UNS S32750super duplex stainless steel was investigated. The joining process was carried out at 1050 °C for 0, 60, 120, and 300 s using an BNi-2 interlayer. The transient liquid phase bonding area was divided into three zones: (i) the isothermal solidification zone which contained γ-Ni solid solution, (ii) the a-thermal solidification zone which consisted of Ni- and Cr-rich borides and Ni 3 Si precipitates, (iii) and the diffusion affected zone in which Cr-Ni-Fe-Mo-Cu-rich borides constituents existed. The hard and brittle eutectic compounds in the bonding zone posed deleterious effects on the mechanical properties of the joints. By increasing the holding time, the amount of these detrimental phases in the bonding zone decreased before finally a eutectic-free joint was achieved at the bonding time of 300 s, which was notably low as compared to the previous studies. The joint held for 0 s had the widest a-thermal solidification zone and the highest hardness was measured at the center of it (546 Hv). The average hardness of the diffusion affected zone on the UNS S3750 super duplex stainless steel side was approximately 450 Hv, which was markedly higher than that of the diffusion affected zone on the UNS N08825 side (302 Hv). The joint held for 0 s showed the lowest shear strength (239 MPa), while the maximum shear strength was obtained for the joint with a holding time of 300 s, approximately 487 MPa. Moreover, it was demonstrated that eutectic compounds were the principal cause of the brittle fracture in the joints containing the a-thermal solidification zone, whereas the joint with a complete isothermal solidification experienced a brittle fracture that occurred at the diffusion-affected zone of UNS N08825 alloy.

EBSD study of dissimilar transient liquid phase joining of duplex stainless steel SAF 2205 to nickel-based superalloy IN X-750

SAF 2205 and IN X-750 were joined using the TLP method. The joining process was carried out at 1100 °C for different times using BNi-3 interlayer. Microstructural study and identification of the present phases in the bonding regions were performed using optical microscopy and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and electron backscatter diffraction technique. Microhardness and shear strength tests were done to measure the mechanical properties. Different phases such as BN, Ni3B, Ni2B, CrB, Cr2B, and Ni2Si were formed in the bonding area. EBSD analysis results showed that the amount of the formed phases in the bonding area is a function of the bonding time. As the holding time increased, the amount of created phases in the bonding area increased from about 8 to 11 wt.%. The microhardness profile of the joining area also behaved differently as the bonding time changed. The maximum measured microhardness was about 850 HV which appeared in the athermally solidified zone of the bonded sample for 1 min. The maximum shear strength was observed in the bonded sample with complete isothermal solidification, approximately 72% of the shear strength of SAF 2205 and 85% of IN X-750.

Evolution of microstructure and mechanical properties on dissimilar transient liquid phase (TLP) bonding of GTD-111 and IN-718 by BNi-9 (AWS A5.8/A5.8M) interlayer

Dissimilar transient liquid phase (TLP) bonding of GTD-111 and IN-718 nickel-based superalloys was investigated using BNi-9 (AWS A5.8/A5.8M) as an interlayer. The effect of the bonding time on the microstructure and mechanical properties of the TLP-bonded specimens was studied at 1100 °C using optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy-dispersive spectrometry (EDS), and micro-hardness and shear strength analyses. Joint microstructural studies revealed that at the bonding times shorter than 75 min, nickel- and chromium-rich borides were formed with the joint centerline. The volume fraction of intermetallic compounds decreased with the increase of the bonding time and the diffusion of boron element whereby the isothermal solidification eventually completed after 75 min. Micro-hardness investigations along the bonding joint showed that the hardness of an isothermal solidification zone (ISZ) decreased with the completion of isothermal solidification. The hardest zone in the joint structure belonged to the athermal solidification zone (ASZ). The shear strength test results showed that incrementing the bonding time increased the shear strength where the shear strength value at 1 min/1100 °C (320 MPa) raised to 590 MPa after the completion of isothermal solidification.

Dissimilar transient liquid phase bonding of Ti–6Al–4V and Co–Cr–Mo biomaterials using a Cu interlayer: Microstructure and mechanical properties

In order to construct a bimetallic device for the medical application, the selection of the joining process is essential. Transient liquid phase (TLP) bonding of two biomaterials of Ti–6Al–4V and Co–Cr–Mo (ASTM F-75) alloys with a Cu interlayer was investigated at the bonding time of 5, 15, 30, and 45 min at the bonding temperature of 920 °C. To evaluate the microstructure, the interfacial brazing zone (IBZ) was studied using an optical microscope (OM), field emission scanning electron microscope (FE-SEM), and energy dispersive spectroscopy (EDS). The results showed that the microstructure of Ti–6Al–4V/Cu/Co–Cr–Mo was composed of CoCr(Ti, Mo), Ti(Cu, Co), Ti2Cu, α-Ti, and β-Ti. By raising the bonding time and increasing the diffusion of Cu into base metals, the transformation of Ti(Cu, Co) into Ti2Cu was done. Then, the thickness of the Ti(Cu, Co) intermetallic compound (IMC) reduced. With increasing bonding time from 30 to 45 min, the morphology of Ti2Cu IMC changed from tiny to blocky. Shear strength, microhardness, and fractographic assessment were used to investigate the mechanical properties of the bonding zone. It is found that with increasing the bonding time, the shear strength of the brazed joints increased. The maximum shear strength of 316 MPa occurred at 45 min. The microhardness test also demonstrated that the CoCr(Ti, Mo) in the diffusion layer with the hardness value of 839 HV was the hardest phase. The formation of IMCs changed the fracture mode.

Microstructural Evaluation during dissimilar transient liquid phase bonding of TiAl/Ni-based superalloy

The paper aims at understanding solidification phenomena and solid state precipitations during dissimilar transient liquid phase bonding of γ-TiAl intermetallic compound to IN718 Ni-based superalloy using a quinary Ni–7Cr–3Fe–4.5Si–3.2B (wt%) filler metal. The mechanisms of intermetallic formation via solidification and solid state reactions are discussed. The joint is featured by the formation of Ni-rich solid solution in an isothermal solidification zone near to IN718, Ni-rich solid solution and isostructural binary phases solid solution designated as Al1-xNi3Six in an isothermal solidification zone near to TiAl, boride/silicide and boro-silicide formation during binary and ternary eutectic-type solidification in an athermal solidification zone, fine nickel silicide precipitation during cooling in the joint centerline, and in-situ precipitation of Cr–Mo–Nb rich borides in a diffusion affected zone. On the other hand, Ni from the filler metal reacted with γ-TiAl base metal, leading to the formation of Ti2Ni, τ2-Al2TiNi and τ4-AlNi2Ti compounds on the reaction layer adjacent to TiAl substrate. The evaluation of different zones of the bond region showed that some brittle phases with high hardness are formed in the bond region. It was identified that the presence of the eutectic gamma solid solution between boride phases within the joint centerline can decrease the detrimental effect of the intermetallic phases on the joint toughness.

Evaluation of microstructure and mechanical properties of transient liquid phase bonding of Inconel 718 and nano/ultrafine-grained 304L stainless steel

In this research, dissimilar transient liquid phase (TLP) bonding of the nano/ultrafine-grained 304L stainless steel to the Inconel 718 superalloy was studied using a BNi2 interlayer. The bimodal stainless steel was produced by a thermomechanical martensitic method consisting of 80 % cold rolling and reversion annealing. The bonding processes were carried out at 1050 °C for 5, 15 and 60 min. The microstructural evaluation of the 304L/IN718 joints revealed that the isothermal solidification was completed at the bonding time of 60 min. The Cr-Fe-Nb-borides and Fe-Ni-borides were observed in the diffusion affected zone (DAZ) of IN718 and 304L, respectively. The average microhardness values of the ASZ and DAZ, were markedly higher than those of the ISZ and the base metals. The 5-min and 60-min joints exhibited the lowest and highest amounts of shear strength, respectively. Evaluation of the fracture surface of the 5-min sample indicated a brittle fracture while the 60-min joint was pronouncedly ductile. Cross-section of the fractured samples implied that the 5-min bond fractured through the ASZ while the failure of the 60-min joint happened at the interface of 304L/joint zone. In addition to the dissimilar bonding, similar TLP bonding of 304L stainless steel was evaluated. The 304L nano/ultrafine-grained bonded samples indicated high density of the DAZ precipitates and shear strength compared to the 304L coarse-grained TLP bonded sample.

Thermal processing strategies enabling boride dissolution and gamma prime precipitation in dissimilar nickel-based superalloys transient liquid phase bond

The microstructure of dissimilar transient liquid phase bond between Hastelloy X and IN792 nickel-based superalloys is featured by lack of sufficient formation of γ′ precipitates in the bond-centerline and extensive in-situ precipitation of boride second phases in the diffusion affected zones (DAZ). This paper investigates the impact of two thermal processing strategies, using standard solution treatment and aging of IN792 (STA strategy) and using solution treatment of IN792 followed by a post-bond heat treatment utilizing solution treatment of Hastelloy X and aging treatment of IN792 (SPTA strategy) on the joint microstructure and mechanical properties. The boride precipitates in the DAZ of Hastelloy X showed higher resistance to dissolution rather than those in IN792 which can be attributed to the higher content of the boride former elements in Hastelloy X. Both thermal processing routs resulted in the formation of γ′ strengthened bonds with overmatched hardness compared to the Hastelloy X. However, STPA strategy enabled complete dissolution of borides in DAZ of IN792, significant dissolution of borides in DAZ of Hastelloy X, and development of bimodal γ′ distribution in the IN792 base material. Nevertheless, the grain growth in the Hastelloy X after STPA strategy limits the achievable joint shear strength.

Phase formation during dissimilar transient liquid phase (TLP) bonding of IN939 to IN625 using a Ni-Cr-Fe-Si-B interlayer

An effort was made to assess the applicability of using transient liquid phase bonding technique to join a nickel-based precipitation-hardened superalloy (Inconel 939) to a solid-solution-hardened one (Inconel 625) to avoid the limitations of other joining techniques such as fusion welding. Microstructural development and phase formation mechanism of the joint region were studied in Inconel 939/Ni-Cr-B-Fe-Si/Inconel 625 system. The chemical composition of the isothermally solidified zone in each side of the joint was governed by the chemical composition of the adjacent base alloy. Eutectic-γ solid solution, chromium-rich boride and nickel-rich boride phases were formed at the centerline of the joints with insufficient holding times due to the segregation of chromium and boron elements during the athermal solidification. Increasing the holding time resulted in the decrement of athermally solidified zone width. In the holding time of 30 min, the isothermal solidification was finished and a bond without detrimental centerline-eutectics was produced. Hard and brittle chromium-rich and chromium-molybdenum-rich boride particles were formed by a solid-state precipitation phenomenon in the diffusion affected zone of Inconel 939 and Inconel 625, respectively. Chromium depletion was observed in the vicinity of these precipitates. The holding time had almost no influence on the width of the joint area. However, higher concentrations of solute elements were detected at the joints’ centerline in longer holding times.

Effect of bonding time and homogenization heat treatment on the microstructure and mechanical properties of the transient liquid phase bonded dissimilar GTD-111/FSX-414 TLP superalloys

Dissimilar transient liquid phase joints were fabricated between Ni-based GTD-111 and Co-based FSX-414 superalloys using a 50 μm thick amorphous NiSiB interlayer. The athermally solidified zone in the middle of joint contained the ternary eutectic of γ/Ni3B/Ni6Si2B and few amounts of Ni3Si. The amount of eutectic phase was decreased by increasing the bonding time. The complete isothermal solidification was obtained at the joining time of 100 min. The completion of isothermal solidification was controlled by several factors including the diffusion of Si and B from the bonding zone into the base metals, the diffusion of Ti, Al, Co and Cr from the base metals into the bonding zone and proportional re-distribution of them throughout the joint. The width of bonded zone (about 80 μm) was greater than the thickness of interlayer due to the coupled diffusion and dissolution phenomena. After the homogenization heat treatment, an increase of 34% in shear strength of the joint was observed due to the uniform distribution of strengthening precipitates across the bonding area.

TLP bonding of dissimilar FSX-414/IN738 system with MBF80 interlayer: Prediction of solid/liquid interface location

Isothermal solidification process of a dissimilar transient liquid phase (TLP) bonding of FSX-414/MBF80/IN738 system was simulated by finite difference method. The TLP joint model was divided into two parts and a moving liquid/solid interface model was used for the parts. Diffusion equations were solved for each half of the joints simultaneously up to the end of isothermal solidification. The completion time of isothermal solidification, concentration profiles and position of the solid/liquid interface for each half were calculated. The intersection of the solid/liquid interfaces of two halves was considered the end of isothermal solidification. To obtain some required diffusion data, TLP bonding of FSX-414/MBF80/IN738 was performed at different temperature and time under vacuum atmosphere. The calculated results show good agreement with the experimental results.