Transient Liquid Phase Diffusion Research Articles

Investigation on microstructure and mechanical properties of GH5188 superalloy TLP joints using nickel based alloy interlayer

GH5188 was bonded successfully with a commercial BNi-2 interlayer through transient liquid phase (TLP) diffusion bonding. The characteristic bonded joint was formed by following three characteristic zones: diffusion affected zone (DAZ) mainly consisting of boride precipitates, athermal solidification zone (ASZ) composed of multiple silica-boride phases and isothermal solidification zone (ISZ) containing γ solid solution phases. As the holding time increases, ISZ gradually replaced ASZ and a defect-free joints was obtained then. However, excessive holding time can cause ASZ to reappear because of the extravagant dissolution of the base metal. The joints’ shear strength from 574 MPa (1190 °C/5 min) increased to 777 MPa (1190 °C/60 min), and the fracture location shifted from ASZ to DAZ with the fracture mode transferred from cleavage fracture to mixed fracture.

Effect of bonding temperature on microstructure and properties of TLP joined Q355 steel with Cu interlayer

Abstract Q355 steel with Cu interlayer was bonded by transient liquid phase diffusion bonding (TLP-DB) at different bonding temperatures, and good bonding joints were obtained. The joints were characterized by optical microscopy, scanning electron microscopy and mechanical properties. The results show that there is a bending phenomenon caused by the difference of element diffusion at the bonding interface at the bonding temperature of 1050 °C. With the increase of the bonding temperature, the diffusion of Cu element plays a role in refining the grain, but with the increase of the bonding temperature, it will also lead to the overgrowth of the grain; At the bonding temperature of 1050 °C, there are obvious mutations in the diffusion of Cu and Fe elements, but the increase of the bonding temperature has a good effect on the interdiffusion of the elements. The mechanical properties test showed that with the increase of the bonding temperature, the hardness, shear strength, and impact toughness at the center of the joint increased first and then decreased, and all reached the maximum at 1100 °C. The electrochemical performance test showed that with the increase of temperature, the corrosion resistance of the joint also increased first and then decreased.

The influence of holding time on the microstructure and properties of TLP joints of Q355 steel

Using BNi as the interlayer material, transient liquid phase diffusion welding experiments were conducted on Q355 steel at a welding temperature of 1050 °C under different holding times (10, 15, 20, 25 min). The welded joint microstructure, element diffusion migration, and phase composition were analyzed by using modern analytical testing instruments such as optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The mechanical properties of the joint were tested and analyzed by using a microhardness tester, universal testing machine, and impact testing machine. The electrochemical corrosion property of the welded joint was analyzed and studied by using an electrochemical workstation. The results showed that under the conditions of 1050 °C and 6 MPa pressure, the Q355 steel TLP welded joint with better property could be obtained with a 20-min holding time. With the increase of holding time, the width of the bonding interface layer increased first and then decreased, and the microstructure tended to be more uniform. The shear strength gradually increased, reaching a maximum of 496.7 MPa (25 min), but the impact toughness increased first and then decreased, with a maximum of 250.61 J/cm2 (20 min). The corrosion resistance of the joint also improved first and then weakened.

Rapidly achieving high-performance joining of single crystal superalloy and powder metallurgy superalloy via partial transient liquid phase diffusion bonding

A rapid and high-performance partial transient liquid phase diffusion bonding process has been proposed for the DD5 single crystal superalloy and the FGH96 P/M superalloy via a mixture of NiTi alloy and FGH96 P/M superalloy powders as interlayer. During the bonding process, isothermal solidification and homogenization of the joint were achieved through a rapid diffusion mechanism of short-range and large-area between the liquid phase of NiTi and the FGH96 particles and the base material. When bonded at 1170 °C only for 60 min of the holding time, isothermal solidification and homogenization of the joints were completed. The isothermal solidification joint consisted of a polycrystalline zone with γ/γ′ structure similar to that of FGH96 and an epitaxial growth zone (EGZ) derived from DD5. Compared with traditional brazing and transient liquid diffusion bonding process (TLP), no brittle compounds and eutectics of Si and B were presented in the joint, which ensured the joint with excellent mechanical properties. With the increase of holding time, both the tensile strength and elongation was significantly increased on account of the reduction of η-Ni3Ti. When the joints were bonded at 1170 °C for 60 min, the elevated temperature strength of 650 °C reached 880.7 MPa, which was more than 80 % and 60 %o that of the DD5 and FGH96, respectively.

The Liquid Fraction of ZA27 Zinc Alloy from TLP Diffusion Bonding Affecting Mechanical Properties and Microstructural Characterizations of SSC-ADC12 Aluminum Alloy

This work investigated liquid fraction in ZA27 zinc alloy interlayered with SSC-ADC12 aluminum alloy workpieces for Transient Liquid Phase (TLP) diffusion bonding. The results clearly indicated that liquid fraction had a necessary influence on TLP diffusion bonding. In other words, the high liquid fraction and bonding time tends to produce excellent bond strength. The maximum bond strength at 27.21 MPa was from 100% liquid fraction and 90 min from bonding time. The hardness increased by approximately 23.36% comparing to SSC-ADC12 aluminum alloy and by 11.18% comparing to the ZA27 zinc alloy. The microstructure was homogeneous in the bond line and formed to MgZn2 and CuZn4 intermetallic compound under Scanning Electron Microscope. According to Energy Dispersive X-Ray Spectrometer analysis, Zn atoms had the ability to move about 4.381 mm from the bond line and the elements' uniform distribution.

Effect of Brazing Temperature on Microstructure, Tensile Strength, and Oxide Film-Breaking Synergy of 5A06 Aluminum Alloy Welded by TG-TLP

5A06 aluminum alloy bar was brazed by temperature gradient transient liquid phase diffusion welding (TG-TLP). The effects of brazing temperature on the microstructure and the tensile strength of the brazing joints were investigated. Three typical brazing filler alloys (1# Al-20Cu-6Si-2Ni, 2# Al-10Cu-10Si-3Mg-1Ga, and 3# Al-6Cu-10Si-2Mg-10Zn) were prepared by smelting, and TG-TLP diffusion bonding was carried out at different brazing temperatures (550 °C~590 °C). The results show that with the increase in brazing temperature, the oxide films at the brazing junction are easier to be broken and dispersed, but the oxidation extent will also increase. The oxidation products enriched were mainly Al2O3 and SiO2 at the brazing junction. There are different optimal brazing temperatures corresponding to the different filler alloys. For 1#, the optimal temperature is 570 °C; for 2# is 580 °C; for 3# is 580 °C. For 1# brazing joints, the maximum tensile strength was 113 MPa, and for 2# was 122.4 MPa. Under the experimental conditions of this study, the maximum tensile strength of the TG-TLP joint is 147.4 MPa of 3# brazing sample (at 580 °C), which has increased by 30% and 20% compared to 1# and 2# respectively. The nickel-rich phase at the interface (of 1# brazing filler) could form a brittle fracture, which was unfavorable for interface bonding. For TG-TLP brazing of 5A06, the filler alloy with high Al:Cu ratio (12:1 wt.%) needs a sufficient temperature gradient to exert the film-breaking effect, while the filler alloy with low Al:Cu ratio (3.6:1 wt.%) needs to accurately control its brazing temperature to avoid excessive oxidation. There are many research gaps in the influence of brazing material composition and brazing temperature on the microstructure and mechanical properties of 5A06 aluminum alloy TG-TLP joints. The research results can provide a theoretical basis for formulating the TG-TLP brazing specification of 5A06 aluminum alloy.

Transient Liquid Phase Diffusion Bonding of Ni3Al Superalloy with Low-Boron Nickel-Base Powder Interlayer

As a technology for micro-deformed solid-phase connection, transient liquid phase (TLP) diffusion bonding plays a key role in the manufacture of heating components of aero engines. However, the harmful brittle phase and high hardness limit the application of TLP diffusion bonding in nickel-based superalloys. In this paper, a new strategy in which a low-boron and high-titanium interlayer can restrain the brittle phase and reduce the hardness of the TLP-diffusion-bonded joint is proposed. With this strategy, the Ni3Al joint can achieve a high strength of 860.84 ± 26.9 MPa under conditions of 1250 °C, 6 h and 5 MPa. The microhardness results show that the average microhardness of the joint area is 420.33 ± 3.15 HV and is only 4.3% higher than that of the Ni3Al base material, which proves that this strategy can effectively inhibit the formation of the harmful brittle phase in the joint area. The results of EBSD show that 7.7% of the twin boundaries exist in the isothermal solidification zone, and only small amounts of secondary precipitates are observed at the grain boundaries in the joint, which indicates that twin boundaries may play a dominant role in crack initiation. This study provides a feasible avenue to suppress the brittle phase in TLP-diffusion-bonded joints.

Investigation on hybrid bonding of tungsten/steel with in-situ formed composites interlayer

Hybrid bonding between steel and W using 88(97W-2.7Cu-0.3Ni)−12Ni powder mixtures sandwiched between Ni and Cu foils was carried out in vacuum for 60 min at 1120 ℃ with a pressure of 5 MPa. The assembly sequence of bonding specimens was steel/Ni/Cu/88(97W-2.7Cu-0.3Ni)−12Ni powder mixtures/Cu/Ni/Cu/W. The microstructures and composition distribution of the joint were studied by SEM and EDS. Joint properties were evaluated by shear experiment tests, and the fracture characteristics of the shear samples for the joints were also determined by SEM. The results showed that the joints comprised steel/Ni/composites/Cu-Ni/W, wherein the composites interlayer consisting of tungsten heavy alloy and irregular Ni agglomerate in-situ formed by the combined sintering of 88(97W-2.7Cu-0.3Ni)−12Ni powder mixtures. The hybrid bonding mechanisms of the interfaces in the joint include solid-phase diffusion bonding and transient liquid phase diffusion bonding. An additional hot-dip experiment found that obvious solid-liquid interface diffusion and Ni segregation occurred under the bonding conditions, and a large number of W atoms diffused into the Cu-Ni liquid phase. In the Cu-Ni alloy layer, the content of element W is more than 4.22% (at.%). The average shear strength of W/steel joints was 263 ± 7 MPa and all the shear samples were fractured in the W near the bonding interface.

Ti/Cu/Kovar Multilayer Interlayer PTLP Diffusion Bonding Si3N4/Ht250

In this paper, partial transient liquid phase (PTLP) diffusion bonding between Si3N4 ceramics and Ht250 cast iron was carried out by using an Ti/Cu/Kovar/Cu/Ti interlayer. The effects of the heating temperature and holding time on the microstructure, formation mechanism, and mechanical properties of Si3N4/Ht250 cast iron joints were studied. The results show that the maximum shear strength of the joint is 112 MPa when the welding temperature is 1000 °C and the holding time is 1 h. In addition, the problems of Ti/Cu/Ti intermetallic compound formation and Cu/Si3N4 ceramic residual thermal stress in the joint can be effectively alleviated.

Effect of micro-oxidation and Cu modification of C/C composite on microstructure and mechanical properties of C/C|Ti3Al joints

In order to form the strong mechanical interlocking and improve the compatibility between interlayer and C/C composite, a porous structure with a series of annular gaps and Cu coating on C/C composite surface were designed and prepared by micro oxidation in the muffle furnace and magnetron sputtering, respectively. The C/C composite |Ti3Al joints were prepared by transient liquid phase (TLP) diffusion bonding. During the bonding process, the liquid phase flowed into the gaps, and the infiltration layer is formed between C/C composite and core interlayer. The infiltration layer mainly consists of C/C matrix, TiC and Ag (s, s), and the CTE of infiltration layer between that of C/C composite and interlayer. Therefore, the mismatch of thermal deformation between C/C composite and interlayer can be reduced, which can avoid high stress in the joint. After surface modification of C/C composite with micro-oxidation at 630 °C for 30min and Cu film, the wettability of liquid phase on C/C composite increased, and Ti–Cu phase formed in the core interlayer of the corresponded joints, which consumes the Ti atoms in liquid phase and causes a thin TiC layer. The shear strength of the joints increases from 34.58 MPa (the original joints) to 44.23 MPa (the pretreated C/C|Ti3Al joints) under optimized process (i.e. 880 °C, 10min), and the fracture not occurs in C/C composite but in joint area after pretreatment of C/C composite.

Partial transient liquid phase diffusion bonding of ZrC-SiC and 304 stainless steel by Ti/Ni interlayer: Microstructure and properties

The ZrC-SiC ceramic (ZS) was joined to 304 stainless steel (304SS) by using Ti/Ni interlayer. The joining process involves a transient liquid phase bonding at the ZS interface and a diffusion bonding at the 304SS interface. It is found TiCx grew fast on ZS interface or precipitated as particles in certain region of transient liquid, and its distribution and morphology were controlled by Ti gradient. Small amount of Si dissolved into liquid and then precipitated as Ti3Ni2Si with similar lattice structure to Ti2Ni. During solid-state diffusion, the TiNi reaction layer quickly transformed to refractory TiNi3 layer with a small number of Kirkendall pores and Ni5Zr phase at the TiNi3/Ni boundary. The underlying mechanism of interfacial reactions and microstructure evolution were proposed. The maximum shear strength of 97 ± 10 MPa was achieved when joining at 960 °C for 3 h. The failure mainly occurred along TiNi3/Ni boundary due to the presence of Kirkendall pores.

TLP diffusion bonding of C–C composite and TC4 alloy using AgCuNiLi alloy as joining material

Abstract In this study, AgCuNiLi alloy was successfully used as the intermediate layer to join Ti-6Al-4V (TC4) alloy and silicon carbide (SiC) coated carbon–carbon (C–C) composites by transient liquid phase diffusion bonding (TLP). Through the characterization and analysis of microstructure, element distribution, phases and fracture behavior of as-prepared joints by optical microscopy, scanning electron microscope, energy dispersive X-ray spectrometry, X-ray diffraction, mechanical testing etc., the influences of the SiC coating on the surface of C–C composites on the microstructure and mechanical properties of the joints were studied. Experimental results indicate that joints with a gradient structure of “C–C|SiC coating|Ti–Cu intermetallic|Ag-based solid solution|Ti–Cu intermetallic|diffusion layer|TC4” can be formed during the bonding procedure. The presence of SiC coating greatly improves the continuity and density of the interfacial layer adjacent C–C composites, which is beneficial to the overall performance of the joint. The average shear strength of as-prepared joint achieves 26.5 MPa, and the fracture tends to occur along the interface of C–C|SiC and adjacent areas.

Stable bonding of W and ODS steel fabricated by TLP diffusion technology through inserting a novel composite interlayer Zr/Cu

Bonding of tungsten (W) with oxide dispersion strengthened (ODS) steel is an urgent challenge during the practical manufacturing process in many applications, including advanced nuclear reactor systems, military equipment, etc. To eliminate the generation of brittle intermetallic compounds Fe-W and relieve the residual thermal stresses, a novel composite interlayer Zr/Cu, for bonding W with ODS steel using the transient liquid phase (TLP) diffusion technology, was designed in this work. The bonding materials were prepared as a sandwiched structure of W/Zr-Cu/ODS steel in a vacuum diffusion bonding device. Interfacial structure and tensile strength of the bonded joints were investigated, and the processing parameters were optimized. After the bonding process, a reliable Cu/ODS steel interface could be built at all applied temperatures or holding times. Nevertheless, only as the bonding temperature was 1000 °C or even higher, the inserted Zr foil could be completely consumed and a stable W/Cu interface free from intermetallic compounds and micro-cracks was built. Additionally, the bonding ratio was gradually improved with increasing the bonding temperature or holding time. As a result, a high-strength W/Cu/ODS steel joint of ∼430.4 MPa could be fabricated at 1000 °C for a holding time of 60 min, and the bonding ratio was as high as 98 %, which provided a significant guide for the assembly of plasma facing components (PFCs).

Fabrication of porous forsterite-spinel-periclase ceramics by transient liquid phase diffusion process for high-temperature thermal isolation

Porous forsterite-spinel-periclase ceramics with low thermal conductivity were synthesized via a transient liquid phase diffusion process by using pre-synthesized pellets and fused magnesia powder. The effects of sintering temperature on the pore formation, phase composition, sintering behavior, and properties of the resulting porous ceramics were investigated. The pre-synthesized pellets had a porous structure and contained a large amount of cordierite and enstatite. During the sintering progress, the pellets were converted into a transient liquid phase, which diffused into the solid MgO matrix. The liquid phase diffusion reaction promoted forsterite and spinel formation, which resulted in the in-situ formation of large pores. At elevated temperatures, the liquid phase disappeared and a large number of well-developed grains were simultaneously precipitated from the liquid phase. Porous ceramics with thermal conductivities of 0.42–0.48 W/(m·K) and refractoriness under load values of 1588 °C and 1624 °C were obtained after sintering at 1600 °C for 3 h.

Effect of mechanically alloyed sintering aid on sinterability of TiB2

High-melting-point borides are attractive for structural and functional materials used in extreme environments. However, their poor sinterability due to their high melting point and strong covalent bonding have prevented their further applications. In this study, a new sintering process, called transient liquid-phase diffusion sintering (TLPDS), has been developed for high-melting-point borides. TiB2 compacts were fabricated by spark plasma sintering at 50 MPa for 15 min at temperatures of 1300 and 1600 °C via TLPDS of TiB2 powder with a eutectic TiB–Ti powder as the sintering aid, prepared via mechanical alloying (MA). Differential scanning calorimetry results indicated that the melting temperature of the obtained sintering aid was lower than its equilibrium melting point. MA of the sintering aid suppressed the open pore fraction to one-third of that in the compact sintered with the aid prepared without MA when sintering at 1300 °C. We also propose a possible mechanism for TLPDS of TiB2.

Experimental and Numerical Study of Transient Liquid Phase Diffusion Bonded DZ40M Superalloys

Transient liquid phase (TLP) diffusion bonding of DZ40M cobalt-based superalloy was carried out using a self-made NiCrCoWB intermediate layer. The typical microstructure of the joint was investigated. The effect of holding time on the microstructural evolution and the tensile strength of the brazed joints was studied. The tensile strength of the joints TLP bonded at 1160 °C for 60 min reached the maximum value of 487 MPa, which was 88.6% of the base metal strength. The diffusion of boron and the evolution of the eutectic zone were numerically studied. The time needed for isothermal solidification completion was calculated and predicted, which was well in accordance with the experimental results.

A Novel Rapid Manufacturing Process for Metal Lattice Structure.

A novel lattice structure manufacturing process is proposed in this article, which has the potential to overcome the manufacturing shortcomings of small-scale metal lattice structure. The proposed hierarchical process has four segments: Design, Bending, Dip, and Join (DBDJ). The proposed research use one-dimensional metallic wires/rods instead of powder, two-dimensional sheet, or liquid metal, which is highly transformative than the status quo. The topology-based design technique is focused to construct the lattice structure using a continuous thin rod. The layers are stacked in an additive manner to construct the three-dimensional lattice structure. The dip-coating meditate material transfer facilitates the node joining using transient liquid phase diffusion bonding, and hence, the manufacturing of the complex lattice structure is performed. The research framework provides a unique and holistic approach from design to manufacturing for realizing small-scale metallic lattice structure. A range of multiscale lattice structure is manufactured with the proposed DBDJ process. Very low relative density (∼3.8%) unit cell is achieved, and compressive tests demonstrate no failure at the joining node, which is reported in this article.

The microstructure and mechanical properties of YT5 cemented carbide/carbon-carbon composite joints prepared by transient liquid phase diffusion bonding using Ni/Cu/Ti multiple foils as joining materials

YT5 cemented carbides have been successfully joined to carbon-carbon (C–C) composites by transient liquid phase (TLP) diffusion bonding technique using Ni/Cu/Ti multiple foils as joining materials. The microstructure and mechanical properties of YT5/C–C composite joints are characterized and analyzed by electronic microscopy (SEM) with an energy disperse spectroscopy (EDS), X-ray diffraction (XRD) and general mechanical testing method. The results showed that multilayer gradient structure, i.e. YT5/Ti–C compounds/Ti–Ni + Ti–Cu compounds/C–Ti–W solid solution/C–C, was formed in the joints prepared by TLP diffusion bonding with the joining temperature changing from 960 to 1020 °C. There are various compounds including TiC, Ni2Ti, Cu4Ti3, Cu3Ti2 and Ti8C5 in the joints, and all interfaces were continuous and dense by element diffusion and chemical reactions during joining process. The average shear strength of joints prepared under 990 °C, 30 min achieves 21.4 MPa. Combined with shear morphology, load-displacement curves and phases on fracture surface, it can be inferred that fracture occurs in the interface region adjacent C/C composites side and presents a brittle fracture mode.

Wettability, Diffusion Behaviors, and Modeling of Ni Nanoparticles and Nanowires in Brazing Inconel 718

Ni nanoparticles (NPs) and nanowires (NWs) are compared as brazing filler metals for joining Inconel 718. NWs significantly enhance the strength of brazed joints compared to NP joints (270 MPa). Herein, joints formed with a pure NW pellet and a NW–NP mixed pellet yield average lap shear bonding strengths of 319.2 and 370 MPa, respectively. The experiment displays that the contact angle in brazing with NPs is higher than that with NWs. A modified Hart's equation is also proposed for predicting the effective interdiffusion coefficients of nanomaterials that account for surface diffusion in addition to lattice and grain boundary diffusion. The diffusion coefficients calculated by the modified Hart's equation are consistent with the values determined by Sauer–Friese analysis for NPs, but for NWs, the diffusion coefficients determined by Sauer–Friese are mainly controlled by grain boundary diffusion, significantly higher than those predicted by the modified Hart's equation due to size‐dependent transient liquid phase diffusion. This explains the enhanced brazing strength with NW fillers.

Diffusion brazing of stainless steels influence of Ni-B filler alloy composition

Stainless austenitic (0.12C-18Cr-10Ni-Ti, wt-%) and ferritic-martensitic (0.16C-12Cr-Mo-Si-V-Nb-B, wt-%) steels were joined by transient liquid phase diffusion bonding (also called diffusion brazing) with the filler metals based on Ni-Cr-Si-(Fe)-B at 1160 °C for different bonding times from 15 to 40 min. It is shown that the braze joints have a heterogeneous diffusion zone with a boride network which is formed during isothermal solidification. The influence of the filler metals composition on the joint microstructure and tensile strength was studied. It is established that the initial concentration of boron and chromium in the filler metal plays an important role in the formation of the microstructure. It is shown that the use of the filler metal with the optimized composition of Ni-20Cr-7.5Si-4.5Fe-1.5B makes it possible to obtain the most homogeneous structure, leading to the best tensile strength of the joint of about 500 ± 40 MPa.