Partial Transient Liquid Phase Research Articles

Effect of Ni interlayer on partial transient liquid phase bonding of Zr–Sn–Nb alloy and 304 stainless steel

Zr–Sn–Nb alloy and 304 stainless steel were joined by means of partial transient liquid phase bonding. The effects of Ni interlayer on the microstructure and properties of the joints were investigated. The reaction layers are formed in both joints and which are mainly composed of σ-FeCr layer, Zr(Cr, Fe)2+α-Zr layer and α-Zr+Zr2(Ni, Fe) layer. The intermetallic compounds are compact relatively and cracks are formed in the reaction layer of the direct bonded joint. In the joint with Ni interlayer, many α-Zr phases dispersedly exist in the reaction layer and the thickness of the reaction layer is distinctly larger than that without Ni interlayer. As a result of lower residual stresses and wider crack-free reaction layer, the bonding strength of the joint increases by using Ni interlayer.

Microstructure and mechanical properties of partial transient liquid phase bonded Si3N4–DZ483 superalloy joints

Partial transient liquid phase bonding (PTLPB) was applied to silicon nitride/nickel-based superalloy (DZ483) joints using Ti/Cu/Ni interlayers. Microstructure examination and mechanical properties evaluation of the joints show that bonding of Si3N4 to superalloy was successful. A uniform compact reaction layer about 2.7μm thickness was found at the Si3N4/Ti interface, which was formed by the reaction between Ti and Si3N4 substrate. With joining temperature rising, the flexural strength of the joining samples increased initially and then decreased. When the joining temperature was 1323K, the flexural strength of the joints reached to 170MPa. The fracture behavior of the joints was also discussed, with the ceramic reaction layer being the region where all failures occurred.

Partial Transient Liquid Phase Metals Layer-Surface Coating for Improved Oxidation Resistance and Low Cycle Fatigue Crack Initiation Life at 1073K in Air of TiAl Alloy

The partial transient liquid phase PTLP metals layer technique for ceramic-metal bonding was applied to surface coating of TiAl alloy. Ni/Al/Ni and Ni/Ti/Ni foils (10μm) layers were coated on flat surface of oxidation specimen OS and on notch root surface of notched compact tension specimen NCT of a TiAl alloy. It is shown that the oxidation resistance is significantly improved and that the resistance to the low cycle fatigue LCF crack initiation life is improved. A procedure of application of the present technique for three dimensional surface coating is proposed.

Partial Transient Liquid-Phase Bonding, Part I: A Novel Selection Procedure for Determining Ideal Interlayer Combinations, Validated Against Al2O3 PTLP Bonding Experience

Partial transient liquid-phase (PTLP) bonding is a bonding process that can bond hard-to-join materials, such as ceramics. The process uses a multi-layer interlayer composed of a thick refractory core and thin diffusant layers on each side. Upon heating, the diffusant material melts, and diffusion occurs until the liquid isothermally solidifies. Selecting interlayer materials is a key problem in producing strong, reliable PTLP bonds; materials are usually selected empirically or system by system. This article presents a novel selection procedure that provides a generalized, comprehensive, first-principles-based approach. Components of the selection procedure are linked directly to key characteristics of PTLP bonding. A filtering routine that provides structure for the selection procedure is summarized in this article and detailed in a companion article. Specific capabilities of the routine, such as non-symmetric bonds, add to its effectiveness in identifying additional PTLP bond candidates. By way of example, output from the selection procedure, in conjunction with sessile drop data, is used to analyze all Al2O3 PTLP bonds in the current literature. All analyzed bonds are included in various outputs from the selection procedure, validating its comprehensiveness. Also, Al2O3 PTLP bonds are analyzed as a whole, leading to the identification of important trends that result in increased bond strength. Finally, additional interlayer combinations for PTLP bonding of Al2O3 are presented based on output from the selection procedure and existing sessile drop data.

Partial Transient Liquid-Phase Bonding, Part II: A Filtering Routine for Determining All Possible Interlayer Combinations

Partial transient liquid-phase (PTLP) bonding is currently an esoteric joining process with limited applications. However, it has preferable advantages compared with typical joining techniques and is the best joining technique for certain applications. Specifically, it can bond hard-to-join materials as well as dissimilar material types, and bonding is performed at comparatively low temperatures. Part of the difficulty in applying PTLP bonding is finding suitable interlayer combinations (ICs). A novel interlayer selection procedure has been developed to facilitate the identification of ICs that will create successful PTLP bonds and is explained in a companion article. An integral part of the selection procedure is a filtering routine that identifies all possible ICs for a given application. This routine utilizes a set of customizable parameters that are based on key characteristics of PTLP bonding. These parameters include important design considerations such as bonding temperature, target remelting temperature, bond solid type, and interlayer thicknesses. The output from this routine provides a detailed view of each candidate IC along with a broad view of the entire candidate set, greatly facilitating the selection of ideal ICs. This routine provides a new perspective on the PTLP bonding process. In addition, the use of this routine, by way of the accompanying selection procedure, will expand PTLP bonding as a viable joining process.

Partial transient liquid phase bonding of carbon/carbon composites using Ti–Ni–Al2O3–Si compound as interlayer

Partial transient liquid phase (PTLP) bonding has been successfully developed to join carbon/carbon (C/C) composites using Ti–Ni–Al2O3–Si compound as interlayer. Gradient interface and core interlayer were formed in the C/C joints by element diffusions, chemical reactions and hot-press sintering. Partial liquid phase infiltrated into C/C matrix and formed ‘nail effect’, which was favorable to improve the mechanical properties of C/C joints. Shear strength and thermal shock resistance of the joints were investigated. The results indicated that the average joint shear strength reached 21.30MPa at room temperature (RT) and nearly did not reduce up to 1273K. The shear strength decreased slowly with increasing thermal cycles from RT to 1373K. After 30 thermal cycles, the strength retention ratio still achieved 73.10%. The excellent thermal shock resistance and high strength retention up to 1373K make the joints to be potentially used in a broad temperature ranging from RT to 1373K.

Partial transient liquid phase diffusion bonding of zirconium alloy (Zr–2.5Nb) to stainless steel 321

Partial transient liquid phase diffusion bonding was applied for bonding zirconium alloy (Zr–2.5Nb) to stainless steel 321 using one active titanium based interlayer and two zirconium based interlayers. Specimens were joined in a vacuum furnace at different temperatures under 0.5MPa dynamic pressure of contact. The influence of different bonding temperatures and bonding times on the microstructure, microindentation hardness, shear strength and interlayer thickness has been studied. The diffusion of Fe, Cr, Ni, Nb and Zr has been investigated by scanning electron microscopy and energy dispersive spectroscopy elemental analyses. The wettability of the interlayers on the zirconium alloy and stainless steel 321 was studied. Sessile drop test was performed for the specimens before the bonding operation at a temperature range between 820 and 865°C for 5, 10 and 15min. It is found that the titanium based interlayer with higher content of titanium has better wetting behaviour on the surface of the zirconium alloy at 850°C. Further studies showed that the increase in the bonding temperature caused significant reduction in the contact angle, spread ratio, spread factor and radius of the wetting. However, the height of the interlayer was decreased on the surface of the substrates by increasing the bonding temperature. Results indicated that the bonds prepared at 850°C for 15min for all the interlayers give suitable wetting behaviour, but due to the effect of bonding temperature the mechanical properties of the joints were reduced and brittle intermetallic compounds were formed at the interface of the joints. The titanium based interlayer operates as a barrier for diffusion of Fe and Cr and prevents the formation of brittle intermetallic compounds like Zr3Fe2, Zr2Ni and Zr3Fe.

The study on joining carbon/carbon composites using Ti–Ni–Si compound

2D carbon/carbon (C/C) composites have been successfully joined by partial transient liquid phase (PTLP) bonding using Ti–Ni–Si compound as interlayer. The shear strengths of C/C joints were found to be affected observably by joining temperature, joining pressure and holding time. The optimum process parameters were determined at 1150 °C, 30 MPa, 45 min, and the maximum joint shear strength was obtained under this optimum process condition with an average value of 23.58 MPa. Microstructures and compositions of joints were analyzed by scanning electronic microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). Results showed that element interdiffusions and chemical reactions took place in the joining zone and various compounds including Ni4Si7Ti4, TiSi2, SiC and TiC were produced, by which compact interlayer and strong interface were formed in C/C joints. The shear morphology indicated there were three fracture modes in C/C joints and the fracture was apt to occur through interlayer, interface and C/C matrix in strong joints. Thermal shock resistance experimental results revealed that joint shear strength has a rapid drop after 5 thermal cycles and then reduces gradually with the increase of thermal cycles between room temperature and 1000 °C.

Partial Transient Liquid Phase Diffusion Bonding of Zircaloy-4 to Stabilized Austenitic Stainless Steel 321 Using Titanium Interlayer

In this study, an innovative method was applied for bonding Zircaloy-4 to stabilized austenitic stainless steel 321 using an active titanium interlayer. Specimens were joined by partial transient liquid phase diffusion bonding method in a vacuum furnace at different temperatures under 1 MPa dynamic pressure of contact. The influence of different bonding temperatures on the microstructure, microindentation hardness, joint strength, and interlayer thickness has been studied. Additionally, a simple numerical model was developed to predict the evolution of interlayer during partial transient liquid phase diffusion bonding. Diffusion of Fe, Cr, Ni, and Zr has been investigated by scanning electron microscopy examinations and energy dispersive spectroscopy elemental analyses. Results showed that control of heating and cooling rate and 20 min soaking at 1223 K produces a perfect joint. However, solid state diffusion of the melting point depressant elements into the joint metal causes the solid/liquid interface to advance until the joint is solidified. The tensile strength values of all bonded specimens were found around 480–670 MPa. Energy dispersive spectroscopy studies indicated that the melting occurred along the interface of bonded specimens as a result of transfer of atoms between the interlayer and the matrix during bonding. The evolution of interlayer film thickness indicates a good agreement between the calculation and experimental measurement. This technique provides a reliable method of bonding zirconium alloy to stainless steel.

Overview of transient liquid phase and partial transient liquid phase bonding

AbstractTransient liquid phase (TLP) bonding is a relatively new bonding process that joins materials using an interlayer. On heating, the interlayer melts and the interlayer element (or a constituent of an alloy interlayer) diffuses into the substrate materials, causing isothermal solidification. The result of this process is a bond that has a higher melting point than the bonding temperature. This bonding process has found many applications, most notably the joining and repair of Ni-based superalloy components. This article reviews important aspects of TLP bonding, such as kinetics of the process, experimental details (bonding time, interlayer thickness and format, and optimal bonding temperature), and advantages and disadvantages of the process. A wide range of materials that TLP bonding has been applied to is also presented. Partial transient liquid phase (PTLP) bonding is a variant of TLP bonding that is typically used to join ceramics. PTLP bonding requires an interlayer composed of multiple layers; the most common bond setup consists of a thick refractory core sandwiched by thin, lower-melting layers on each side. This article explains how the experimental details and bonding kinetics of PTLP bonding differ from TLP bonding. Also, a range of materials that have been joined by PTLP bonding is presented.

Low-temperature partial transient liquid phase diffusion bonding of Al/Mg 2Si metal matrix composite to AZ91D using Al-based interlayer

Partial transient liquid phase diffusion bonding of an aluminium metal matrix composite (Al/Mg 2Si) to magnesium alloy (AZ91D) was performed using two heating rates. The influence of different heating rates on the microstructure, microhardness and shear strength has been studied. With a decrease in heating rate from 20 to 2 °C/min, the Mg content in the bond line decreased and the microstructure was altered. The composition and microstructure of the joined areas were examined by X-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDS). It was found that a heating rate of 2 °C/min resulted in an increasing in the shear strength of the joints. The kinetics of the bonding process accelerated due to the increase of solute diffusivity through grain boundaries of the metal matrix composite. Results suggest that Mg and Si contained in the interlayer favours the partial disruption of oxide films, facilitating the bonding process.

Microstructural evolution in the partial transient liquid phase diffusion bonding of Zircaloy-4 to stainless steel 321 using active titanium filler metal

Microstructural evolution of the partial transient liquid phase diffusion bonded Zircaloy-4 and stainless steel 321 using an active Ti-base interlayer were studied at different temperatures. Additionally, simple analytical models were developed to predict the evolution of the interlayer and intermetallics during the bonding operation. Bonds were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Precision measurement of the interlayer width was made as a function of the bonding temperature. The liquid film migration occurred as a result of chemical solubility differences between the stable and metastable phases. The formation and growth model of the intermetallic compounds at the interfaces of Zircaloy-4/Ti-base interlayer and stainless steel 321/Ti-base interlayer for controlling the bonding process was studied considering the diffusion kinetics and the thermodynamics. The evolution of the interlayer thickness indicated a good agreement between the calculation and experimental measurement. It was also demonstrated that the low isothermal solidification kinetic was not only due to the enrichment of the liquid phase with the base alloying elements such as Ti and Zr, but also the reduction of solid solubility limit of Cu in the base alloys contributed to the reduction of isothermal solidification kinetic.

Partial transient liquid phase diffusion bonding of Zircaloy-4 to stabilized austenitic stainless steel 321

An innovative method was applied for bonding Zircaloy-4 to stabilized austenitic stainless steel 321 using an active titanium interlayer. Specimens were joined by a partial transient liquid phase diffusion bonding method in a vacuum furnace at different temperatures under 1 MPa dynamic pressure of contact. The influence of different bonding temperatures on the microstructure, microindentation hardness, joint strength and interlayer thickness has been studied. The diffusion of Fe, Cr, Ni and Zr has been investigated by scanning electron microscopy and energy dispersive spectroscopy elemental analyses. Results showed that control of the heating and cooling rate and 20 min soaking at 1223 K produces a perfect joint. However, solid-state diffusion of the melting point depressant elements into the joint metal causes the solid/liquid interface to advance until the joint is solidified. The tensile strength of all the bonded specimens was found around 480–670 MPa. Energy dispersive spectroscopy studies indicated that the melting occurred along the interface of the bonded specimens as a result of the transfer of atoms between the interlayer and the matrix during bonding. This technique provides a reliable method of bonding zirconium alloy to stainless steel.

High-temperature variable melting point Sn-Sb lead-free solder pastes using transient liquid-phase powder processing

During this investigation, a high-temperature, variable melting point (VMP) Sn-Sb solder paste was developed. The solder was created by mixing pure Sn and Sb powders together with a flux to form a paste. The proper choice of flux composition and Sn powder size resulted in a Sn-10wt.%Sb solder paste that had an initial melting point of 232°C and solder ball formation at peak temperatures as low as 241°C. This represents a significant reduction in the process temperature that would normally be required for a prealloyed solder with a melting point of 250°C. When this solder paste is reheated, significant remelting does not take place until a temperature above 241°C is reached. In this way, the solder exhibits a VMP. Experiments indicate that this VMP behavior is due to isothermal solidification (or freezing) at the solder temperature owing to the partial transient liquid-phase (TLP) behavior of the solder powder paste.

Interfacial microstructure and strength of partial transient liquid-phase bonding of silicon nitride with Ti/Ni multi-interlayer

Abstract Partial transient liquid-phase bonding (PTLP bonding) of silicon nitride (Si 3 N 4 ) ceramic has been performed using Ti/Ni multi-interlayer in vacuum at 1273–1423 K. Interfacial microstructures were examined by scanning electron microscope, electron probe micro-analysis, and X-ray diffraction. The joint strength has been measured by four-point bending tests from room temperature up to 1000 °C. Interfacial structure of Si 3 N 4 /TiN/Ti 5 Si 3 + Ti 5 Si 4 + Ni 3 Si/(NiTi)/Ni 3 Ti/Ni is formed after bonding process. The NiTi layer is gradually consumed with simultaneous growth of the reaction layer and the Ni 3 Ti layer. The room temperature joint strength is significantly affected by the reaction layer thickness, whereas the elevated temperature joint strength significantly depends on whether the low melting point NiTi layer exists in the joint. The joint strength of more than 100 MPa is retained up to 800 °C as the NiTi layer is completely consumed. A model is proposed to optimize the PTLP bonding parameters for optimizing joint strength at both room temperature and elevated temperature.

PTLPB of Si3N4 to FA-129 using nickel as a core interlayer

Partial transient liquid phase bonding was applied to a silicon nitride/iron aluminide alloy (FA-129) joint. This joint was composed of two independent joining systems. The joint configuration was Si 3 N 4 /75Cu–25Ti/Cu/Ni/Al/FA-129. The results demonstrate that homogenization has no effect on the kinetic of the reaction layer formation between the ceramic and the nickel core due to a previous dissolution reaction. The reaction layer composition evolves from a TiN–Ti 5 Si 3 layer system after reaction during the first soaking time, to a single TiN layer after the complete cycle. The dissolution of the Ti 5 Si 3 layer in the Ni core becomes the driving factor influencing the properties of the joint. The composition of the copper–nickel alloy interlayer changes with homogenization treatment, passing from a maximum of 70–20 wt% Cu, depending on the conditions. NiAl and Ni 3 Al intermetallics were observed at the interface between the nickel and the FA-129 and their thicknesses varies with the homogenization conditions. The strength values obtained were within the range of 80 MPa, with the ceramic reaction layer being the region where all failures occurred.

PTLPB of Si 3N 4 to FA-129 using nickel as a core interlayer

Partial transient liquid phase bonding was applied to a silicon nitride/iron aluminide alloy (FA-129) joint. This joint was composed of two independent joining systems. The joint configuration was Si 3N 4/75Cu–25Ti/Cu/Ni/Al/FA-129. The results demonstrate that homogenization has no effect on the kinetic of the reaction layer formation between the ceramic and the nickel core due to a previous dissolution reaction. The reaction layer composition evolves from a TiN–Ti 5Si 3 layer system after reaction during the first soaking time, to a single TiN layer after the complete cycle. The dissolution of the Ti 5Si 3 layer in the Ni core becomes the driving factor influencing the properties of the joint. The composition of the copper–nickel alloy interlayer changes with homogenization treatment, passing from a maximum of 70–20 wt% Cu, depending on the conditions. NiAl and Ni 3Al intermetallics were observed at the interface between the nickel and the FA-129 and their thicknesses varies with the homogenization conditions. The strength values obtained were within the range of 80 MPa, with the ceramic reaction layer being the region where all failures occurred.

Interfacial microstructure of partial transient liquid phase bonded Si3N4-to-Inconel 718 joints

This work presents transmission electron microscopy (TEM) analysis of the interfacial microstructure in Si3N4-to-Inconel 718 joints with Ni interlayers produced by partial transient liquid phase bonding (PTLPB). Ti and Cu microfoils have been inserted between Si3N4 and the Ni interlayer and joining has been performed at lower temperatures than previous PTLPBs of Si3N4 with the same insert metals. The TEM work is focused on phase identification of the reaction layers between the Si3N4 and the Ni interlayer. According to the TEM analysis, most of the Cu precipitates without reacting with Ti and Ni. Si diffused in the filler metal and thin reaction layer formed at the interface between Si3N4 and the filler metal producing good bond-formation and hence, high interfacial strength. No interfacial fractures occurred after cooling from the bonding temperature of 900°C, which supports the results observed in the TEM analysis. This work confirms that this joining process can produce a more heat resistant Si3N4-to-Inconel 718 joint than active brazing using Ag–Cu–Ti alloys.

Active brazing of pure alumina to Kovar alloy based on the partial transient liquid phase (PTLP) technique with Ni–Ti interlayer

Pure alumina (99.9% grade compositions) was brazed to 4J33-Kovar alloy based on PTLP technique with nickel and titanium foils interlayer. The solder formed a sandwich microstructure: an α-Ti solid solution belt at mid part and Ti2Ni intermetallics belts at two sides. This structure accounts for the good property of the joint. Microanalysis identified a reaction product at the alumina-braze interface as Ni2Ti4O phase. The special properties and structural compatibility of Ni2Ti4O contributed to the firm joint. The effects of brazing conditions on the joint properties were investigated. The joint shear strength showed the highest value of about 65MPa and did not monotonously increase with the brazing temperature ascending. It was shown that extending of brazing time gave thicker reaction layer and higher joint strength.

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.