Melting Point Depressant Research Articles

Study on Ni3Al-Based Single Crystal Superalloy Joints Brazed by Vacuum Brazing with Zr-Containing Filler

Melting point depressants (MPDs) are required to lower the melting point of filler for brazing. In this study, Zr was used as the MPD, and powder filler was prepared by adjusting the Zr and Mo content referring to Thermo-Calc calculations. The prepared filler was used to braze a high-Mo Ni3Al-based single crystal superalloy, IC21, for 1200 °C/30 min. The effects of adjusting the Zr and Mo content on the microstructure and tensile properties of the joint were investigated. The increase in Zr content promotes the formation of Ni7Zr2 in the joint, leading to a decrease in the tensile strength of the joint. The increase in Mo content forms diffusion barriers between the BM and filler, resulting in an enhancement in the tensile strength of the joint. However, continued increases in Mo content leads to an increase in the P-topologically close packed phase, causing a decline in the tensile strength of the joint. When the Zr content was (11.8–12.2) wt.% and the Mo content was (7.3–7.7) wt.%, the tensile strength of the joint at 980 °C reached a maximum of 550 MPa. This study provides a potential direction for the design of brazing filler composition for high-Mo Ni3Al-based superalloys.

Microstructure evolution and mechanical properties of Cu-Ni-Ti transient liquid phase bonding for SiC-GH3536 joints

In this study, transient liquid-phase (TLP) bonding of SiC and GH3536 was employed using Cu80Ti15Ni5 (at%) mixed powder. The melting characteristics of the filler materials were analyzed, and the influence of holding time on the microstructure and mechanical properties of the joints was investigated. The formation mechanism of the joints was also explored. The results indicate that the filler materials completely melted at 970°C. In the liquid filler materials, high-melting-point intermetallic compounds (IMCs) can be formed in situ, thereby consuming the melting-point depressant element Ti. Isothermal solidification of the joints was achieved in a short period, and the joint consists of a Cu(ss) matrix and partial (CuₓNi1-x)2Ti ternary compounds and silicides. Cu(ss) exhibits good plasticity, and the in-situ generated (CuxNi1-x)2Ti helps reduce the coefficient of thermal expansion (CTE) of the joints. Therefore, the joining layer has a beneficial effect in alleviating residual stresses. After holding at 970°C for 15 minutes, the maximum shear strength reached 56.25 MPa. This work provides a new method for joining SiC ceramics and their composites with nickel-based alloys, offering innovative insights into the bonding of ceramics with metals.

Precipitation evolution of M5B3 boride in diffusion affected zone and its effect on mechanical properties of TLP bonded Mar-M247 superalloys

Boron is usually added in the bonding interlayer as the melting point depressant element in the transient liquid phase (TLP) bonding of Ni-based superalloys, which inevitably leads to the precipitation of borides and therefore has an important impact on the mechanical properties of the joints. M5B3-type borides (where M is a mixture of Cr, W and Mo) are the predominant borides in diffusion affected zone (DAZ) of the Mar-M247 bonded joints. In present work, the precipitation and evolution of M5B3 in the joints with different bonding time have been systematically investigated by multi-scale methods. Three kinds of crystallographic orientation relationships between M5B3 and matrix have been observed, and the morphologies and precipitation positions of M5B3 borides are found to have certain characteristics in specific bonding time joints. These crystallographic orientation relationships are consistent with the predictions based on calculations of coincidence of reciprocal lattice points (CRLP) model. The effect of the precipitation of borides on mechanical properties has been evaluated by means of microhardness and micropillar compression testing.

High-performance brazing of single crystal superalloys with Ni-Cr-Ta filler material

High-performance joining especially brazing has been highly expected in the manufacture or maintenance of single crystal blades. In this paper, a Ni-40Cr-10Ta (at.%) alloy was developed as filler material for single crystal superalloys. High-performance brazing of DD5 superalloy was achieved. The joints brazed at 1260 °C contained an isothermal solidification zone (ISZ) with “γ + γ′” structure and an athermal solidification zone (ASZ) composed of γ, γ', γ/γ′-eutectics, TaCr2 and TaC. Unlike the conventional filler materials with melting point depressants of B and Si, the Ni-Cr-Ta filler material was free of B and Si, and thus the resulting joints contained no B-rich and Si-rich compounds and eutectics with low melting points, which enhanced the brazed joint performance. The tensile strength at 980 ℃ of the heat-treated joints reached 654 MPa, which is 88.5 % that of the base metal.

Effects of Cu, Sn, and Ti doping on the interfacial properties of Ag-based filler metal/WC: First-principles study and experimental characterization

First-principles calculations were used to determine the formation energy, work of adhesion, and electronic structure of the interface of Ag-doped (Cu, Sn, and Ti)/WC, revealing the effect of doping atoms on the interfacial bonding behavior. Additionally, an active filler metal Ag–Cu–Sn–Ti was developed from the calculation results and applied to braze YG18 cemented carbide/40Cr steel joint. The interfacial structure and elemental diffusion behavior at the filler metal/WC interface were characterized. The doping of Cu and Ti at the interface contributes significantly to the stability of the interfacial structure and the improvement of the work of adhesion. The effect of doping of Sn atoms at different positions on interfacial stability and the work of adhesion is not obvious, and it can be doped into Ag alloys as a melting point depressant. The charge accumulation zone and atomic orbital hybridizations at the interface contributes to enhance the interface stability and the work of adhesion. The TEM analysis demonstrates that the diffusion behavior of Ti is particularly noticeable, aggregating at the Ag/WC interface and interacting with C to generate a TiC reaction layer, ultimately producing a WC/TiC/Ag interface structure.

A new low-temperature preparation technology of heat-resistant diamond/Cu joint using composite braze: microstructure evolution and mechanical properties strengthening

A low-temperature brazing method of diamond and Cu was proposed by using composite filler of Au-Si eutectic + NiTi particle. Prior to joining, diamond surface was modified by an active alloy of AgCu28 +TiH2, the resulting Ag-Cu coating could ensure the good wettability of Au-Si filler during brazing and formed TiC layer could ensure a tight interfacial bonding. In the brazing process, it was found that melting point depressant element of Si in Au-Si filler could be completely consumed by (i) reacted with NiTi alloy and formed NiTiSi whiskers and (ii) precipitation in form of Ti5Si3C and TiCuSi in modified layer, while the interdiffusion between Au and Cu substrate lead to a ductile seam matrix of heat-resistant (Au, Cu)ss. Attributed to the excellent plasticity and high melting temperature of (Au, Cu)ss and the strengthening effect of NiTiSi whiskers, the joint brazed at 600 ℃ not only have a high shear strength of 108 MPa at room temperature, but also exhibited a excellent heat-resistance, the joint showed a shear strength of 89 MPa and 28 MPa at 300 ℃ and 500 ℃, respectively.

Interfacial microstructure and mechanical properties of joints between ZrO2 ceramic and 316 stainless steel brazed using Ag–Cu–In–Ti filler

An active Ag-based filler containing the melting point depressant of In was used for brazing ZrO2 ceramic with 316 stainless steel (SS) at relatively low brazing temperatures. The brazing feasibility to obtain a robust joint was investigated via changing brazing temperatures from 740 to 820 °C with a holding time of 10–30 min. The typical microstructure of the ZrO2/316SS joint was ZrO2/TiO/Cu2Ti4O + Ag(s, s) + Cu(s, s)/Ag(s, s) + Cu(s, s) + Cu(Ti, In) + FeTi + Cu(Ti, Fe)/316SS. The type of reaction products primarily depended on the brazing temperature, and the TiO phase appeared only at 780 and 800 °C, while the FeTi formed at temperatures higher than 760 °C. Meanwhile, the blocky Cu(Ti, In) and Cu(Ti, Fe) compounds were gradually replaced by the FeTi phase due to the enhanced affinity of Ti and Fe in the liquid alloy. The maximum shear strength reached 308 MPa at 780°C-20 min, and the typical fracture occurred at the Ag-based solid solution and reaction bilayer bordering the ZrO2 ceramic. Notably, a shear strength of above 270 MPa was obtained at wide temperatures from 760 to 820 °C, higher than ZrO2/SS brazed joints using other Ag-based fillers.

First-Principles Study on Si Atom Diffusion Behavior in Ni-Based Superalloys.

The Si atom diffusion behavior in Ni-based superalloys was evaluated based on first-principles calculations. Also, the site occupation of Si atoms as the melting point depressant elements in Cr, Mo, and W atom doped γ-Ni and γ'-Ni3Fe supercells was discussed and Si atom diffusion behaviors between both adjacent octahedral interstices were analyzed. Calculation results indicated that formation enthalpy (∆Hf) was decreased, stability was improved by doping alloying elements Cr, Mo, and W in γ-Ni and γ'-Ni3Fe supercells, Si atoms were more inclined to occupy octahedral interstices and the diffusion energy barrier was increased by increasing the radius of the doped alloy element. Especially, two diffusion paths were available for Si atoms in the γ'-Ni3Fe and Si diffusion energy barrier around the shared Fe atoms between adjacent octahedral interstices and was significantly lower than that around the shared Ni atoms. The increase of interaction strength between the doped M atom/octahedron constituent atom and Si atom increased Si atom diffusion and decreased the diffusion energy barrier. The Si atom diffusion behavior provides a theoretical basis for the phase structure evolution in wide-gap brazed joints.

Effect of MBF-20 Interlayer on the Microstructure and Corrosion Behaviour of Inconel 625 Super Alloy after Diffusion Brazing.

The joining zone includes three main parts, which comprise an isothermal solidification zone (ISZ), the athermal solidification zone (ASZ), and a diffusion affected zone (DAZ). Field emission scanning electron microscopy (FESEM) was used here to observe the microstructure equipped with ultra-thin window energy dispersive X-ray spectrometer (EDS) system. Additionally, electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization tests were conducted to evaluate the effect of the DB process on the corrosion resistance of the Inconel 625 superalloy. In the bonding time period, some Mo- and Cr-rich boride precipitations and Ni-rich γ-solid solution phases with hardened alloy elements, such as Mo and Cr, formed in DAZ and ASZ, respectively, because of the inter-diffusion of melting point depressants (MPD). Moreover, during cooling cycles, Ni-Cr-B, Ni-Mo-B, Ni-Si-B, and Ni-Si phase compounds were formed in the ASZ area at 1110-850 °C. The DAZ area developed by borides compound with cubic, needle, and grain boundary morphologies. The corrosion tests indicated that the DB process led to a reduction in the passive region and increased the sensitivity to pitting corrosion.

Microstructural Modification by Redesigning the Chemical Composition of Ni 620 Filler Metal

Ni 620 is a widely used brazing alloy, especially in cases where high‐temperature strength and corrosion resistance are required. The formation of undesirable intermetallic phases in the brazing joint due to the addition of boron and silicon as melting point depressants affects the mechanical properties of the joint. Reducing the formation of intermetallic phases during brazing is an important issue in the application of Ni 620. In this study, two approaches, inoculation with Nb and variation of the B and Si content in Ni 620, are pursued to selectively influence the microstructure of the brazed joint. Therefore, the solidus and liquidus temperatures of the new brazing alloys are investigated by means of differential scanning calorimetry measurements. Also, the microstructure of brazed joints is analyzed and evaluated by scanning electron microscope/electron‐dispersive spectroscopy as well as the hardness properties using nanoindentaion. It is observed that the addition of Nb, as well as the variation of the B and Si content, leads to a change in the brittle phase band. Especially brittle borides can be reduced in this way. The results contribute to produce brazing joints with more adapted properties, despite low brazing temperatures and short holding times.

Tetraalkylammonium Chlorides as Melting Point Depressants of Ionic Liquids

Tetraalkylammonium Chlorides as Melting Point Depressants of Ionic Liquids

Effect of refractory elements M (=Re, W, Mo or Ta) on the diffusion properties of boron in nickel-based single crystal superalloys

Boron (B) is known as a melting-point depressant for the middle interlayer to transient liquid phase (TLP) bonding of the nickel-based single crystal superalloys (Ni-SCS). However, the mechanisms for the effect of refractory elements M (=Re, W, Mo or Ta) on B diffusion in Ni-SCS remain unclear till now. Thus, the refractory elements M (=Re, W, Mo or Ta)'s effects on the diffusion of B in Ni-SCS is investigated using the density functional theory in this paper. It is found that Mo and Re atoms are mainly distributed in the γ-Ni phase, while majority of W and Ta atoms are mostly located in the Al site in γ′-Ni3Al phase. The octahedral interstices of γ-Ni and γ′-Ni3Al are preferentially occupied by B atoms. The results indicate that the M (=Re, W, Mo or Ta) atoms doped in the structures prevent B diffusion, and the change trend of B diffusion E(BFP) follows Re < Mo < W < Ta. Electronic structure analysis shows that the different atomic radiuses from Re to Ta and different hybrid orbitals between M d and B 2p from Re to Ta play important roles in the diffusion properties of B in the nickel-based single crystal superalloys.

Mechanical Properties of Structural Components in Hastelloy X Joints Brazed with Ni-Pd-Cr-B-Si Alloy.

The brazing of structural high-temperature-resistant nickel alloys is a predominant method in manufacturing jet engines in the aircraft industry. Ni-Cr-base brazing filler metals (BFMs) containing B and Si as the melting point depressants are used for this purpose. The presence of the latter can lead to the formation of brittle constituents in the joints, decreasing their strength, toughness and creep resistance. The structures of Hastelloy X nickel superalloy joints brazed with Palnicro 36M BFM are presented in this paper along with the mechanical properties of their particular phases as a function of brazing time. Indentation hardness, Martens hardness, reduced modulus and creep coefficient were measured using the instrumented indentation method. The elastic part of the indentation work was also calculated. Pd forms an unlimited solution with Ni, but its high content in BFM does not fundamentally change the general joint structure known from other Ni-superalloy-Ni-BFM systems. However, new Pd-containing phases are emerging. The hardest components were Ni-B and Cr-B boride phases and Pd-Ni-Si phase in MZ and the boundary of DAZ and BM. MZ reduces the plasticity of a joint to the highest extent. The hardness of particular parts in the joints and the elastic portion of the indentation work decreased with the increase in brazing time, while the reduced modulus of the indentation contact and indentation creep increased. The results of indentation creep measurements indicate that all structural components of the joints were less susceptible to creep than the parent material at room temperature.

Application of nickel plating by galvanization on steel surface of brazed cemented carbide-maraging steel joints

Recently, the integration of a maraging steel heat treatment into a vacuum brazing has been conducted successfully to manufacture high-strength and sound cemented carbide-steel joints with elevated mechanical properties of the steel component. Besides the use of low-melting silver-based active filler alloys and cost-intensive palladium-containing filler alloys, the application of a nickel layer on the maraging steel surface by an arc-PVD process is an adequate approach to overcome the low wettability of those steels, which is caused by high fractions of elements with a high oxygen affinity like titanium and molybdenum. Though nickel plating by arc-PVD is an elaborate and time-consuming coating process, it is not suitable for industrial applications since a high vacuum is required in the specimen chamber and only a small number of specimens can be processed at the same time.Therefore, this publication evaluates the application of nickel galvanization by chemical plating and electroplating as an alternative nickel-coating method to manufacture a brazed joint between a cemented carbide and maraging steel (1.2709) component by using the copper filler metal Cu 110 (TM = 1085 °C). The electroplated and PVD-coated reference specimens featured a sound joint from a minimum nickel layer thickness of 7.0 µm with a similar microstructure consisting mainly of a copper-based fillet and a nickel-rich phase band at the maraging steel-fillet interface. The chemical-plated specimens showed excessive diffusion between the joining partners due to the presence of melting point depressant phosphor between 10.5 and 12.0 wt.-% in the applied characteristic nickel-phosphorus layer. Consequently, titanium migration occurred from the maraging steel surface to the cemented carbide-fillet interface, and columnar iron-cobalt phases formed originating from the cemented carbide into the copper-rich fillet. Except for the specimens coated with no nickel and a 2.5-µm PVD layer, all brazed joints featured a shear strength of at least 150.0 MPa. The maximum shear strength of 344.8 MPa was achieved by electroplating the maraging steel joining surface with a 20.0-µm-thick nickel layer. Moreover, the steel heat treatment was carried out successfully since an elevated and homogenous hardness of at least 648 HV1 was measured in all steel specimens after brazing.

The effect of melting point depressant elements B, Si, and P in Ni-based brazing filler metals on the formation of brazed joints

The effect of melting point depressant elements B, Si, and P in Ni-based brazing filler metals on the formation of brazed joints

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.

Effect of boron on the structural stability, mechanical properties, and electronic structures of γ′-Ni3Al in TLP joints of nickel-based single-crystal alloys

Boron (B) is known as a melting-point depressant for the middle interlayer to transient liquid phase (TLP) bonding of nickel-based single-crystal alloys. However, the mechanisms of B effects on structural stability, elasticity, and the electronic structures of γ′-Ni3Al remain unclear. In this work, the structural stability, mechanical properties and electronic structures of B-doped γ′-Ni3Al (the doping concentration was 0–20 at%) was investigated by employing the density functional theory. It is found that the Ni24Al8Bm (m = 0, 1, 2, 3, and 4) phases were steady-state structures, while the Ni24Al8Bm (m = 5, 6, 7, and 8) phases were non-steady-state structures. The calculated elastic constants indicated that the Ni24Al8Bm (m = 0, 1, 2, 3, and 4) phases exhibited some anisotropy, and anisotropy gradually decreased with increasing B content. Electronic structure analysis showed that the density of states and charge density were in accordance with the phonon spectra (PS) results. The changes of charge density of Ni-Al and Ni-B bonds with increasing B concentration were found to play important roles in the hardness and phase stability properties of the Ni24Al8Bm (m = 0, 1, 2, 3, 4, 5, 6, 7, and 8) phases.

Microstructure and mechanical properties of transient liquid phase bonding DD5 single-crystal superalloy to CrCoNi-based medium-entropy alloy

• The transient liquid phase bonding of DD5 single-crystal superalloy to CrCoNi-based medium-entropy alloy was achieved using a BNi-2 filler interlayer. • The M5B3-type boride (BCT) precipitated in the diffusion-affected zone exhibiting a coherent relationship of [ 2 4 0]BCT // [0 1 1]FCC and (0 0 2)BCT // (2 0 0)FCC with the FCC matrix. • The effect of the reaction phase properties on the joint performance was investigated. • The maximum shear strength of 752 MPa was obtained with the eutectic-free joint. This study focuses on the transient liquid phase (TLP) bonding of DD5 single-crystal superalloy to CrCoNi-based medium-entropy alloy (MEA) using a BNi-2 filler alloy. The microstructure and mechanical properties of the TLP-bonded DD5/MEA joint were evaluated, and the microstructural evolution mechanism was investigated. The formation of the isothermal solidification zone (ISZ) depended on the diffusion of the melting-point depressants (Si and B elements) from the liquid filler into the DD5 and MEA substrates, as well as the dissolution of the substrates. Boron diffused along the γ channel of DD5 and reacted to form M 5 B 3 boride, herein referred to as the diffusion-affected zone (DAZ I). Similarly, the Cr 5 B 3 boride precipitated in the Ni-rich MEA matrix adjacent to the MEA substrate (i.e., DAZ II). Additionally, a coherent orientation of [0] BCT // [0 1 1] FCC and (0 0 2) BCT // (2 0 0) FCC was detected between M 5 B 3 boride with a body-centered tetragonal (BCT) structure and the face-centered cubic (FCC) matrix. The performance of the joint was dominated by the properties of the bonding seam. As the bonding time increased from 20 to 80 min, the athermal solidification zone (including eutectic microstructure) was gradually replaced by the ISZ exhibiting excellent plastic deformation capability, and the shear strength of the joint was improved. The maximum shear strength (752 MPa) was achieved when the eutectic-free joint was bonded at 1050 °C for 80 min. The fracture morphology revealed a mixture mode, indicating the initiation of cracks in the DAZ II, mainly propagating in the ISZ, and passing through the DAZ I.

Microstructure, properties, and formation mechanisms of tungsten/steel hot isostatic pressing diffusion bonding joint utilizing a Ni-Si-B interlayer

In this study, tungsten and steel were successfully bonded utilizing hot isostatic pressing diffusion bonding with a Ni-Si-B interlayer. The interfacial structures and formation mechanisms of joints with interlayers of various thicknesses were systematically investigated. The results indicated that the interfacial structure of a joint with a thin (0.8 μm) Ni-Si-B interlayer is a W/Fe-W inter-metallic compound (IMC) reaction layer/(Fe,Ni) ss diffusion layer/steel structure, where through cracks appear at the interface of the W/reaction layer, leading to poor shear strength. As the interlayer thickness increases (3.2–22.9 μm), the brittle Fe-W IMC no longer appears and the interfacial structure is a W/Ni-W IMCs reaction layer/(Ni,Fe) ss diffusion layer/steel structure. When the interlayer thickness is 3.2 μm, there are many large voids in the diffusion layer. When the interlayer thickness increases to 5.3 μm, the most compact interfacial structure can be obtained with the maximum bonding strength of 363.5 MPa. However, when the interlayer thickness increases further to 12.6 and 22.9 μm, many voids appear in the reaction layer, leading to a decrease in bonding strength. The formation mechanism of a joint with a thin (0.8 μm) interlayer is a purely solid-solid reaction without the generation of a liquid phase. When the interlayer thickness is large (3.2–22.9 μm), the formation process of joints includes three stages: solid-solid reaction, remaining interlayer liquefaction, and solid-liquid reaction. Electron probe microanalysis results reveal that the melting-point depressant element Si is segregated in the reaction layer or diffusion layer depending on the interlayer thickness, which is precisely controlled by the staged formation mechanism of the joints.

Microstructure and mechanical properties in TLP joint of FeCoNiTiAl alloy and IC10 superalloy using Mn-Ni-Cr filler

A filler metal of Mn-Ni-Cr was used to transient liquid phase (TLP) bonding high-entropy alloy (HEA) of FeCoNiTiAl and Ni3Al base IC10 superalloy for 10 min ~ 120 min at 1150 °C and a pressure of 2 MPa. There was no diffusion affected zone (DAZ) existed in the bonded zone as the filler material Mn-Ni-Cr contained no conventional melting-point depressants (MDPs) of Si/B. Hence, the TLP joint was composed of two isothermally solidified zones (ISZs) and an athermally solidified zone (ASZ). The ISZ beside IC10 consisted of strip Ni(Al, Mn) phases, resulted from the diffusion of Al atoms, and only γ-(Ni, Mn) phases formed in another ISZ adjacent to HEA base metal (BM). Moreover, sluggish diffusion of HEA can prevent the BM from dissolving and formed a straight bond line consisting of “(Hf, Ta)C + Al0.89Mn1.1” compound in the interface between HEA and bonded zone. Furthermore, increase of bonding time can lead to enrichment of Al in the bonded zone and induce composition segregation during solidification. A compound of “Ni(Al, Mn) + Ni3Ta” formed in ASZ of joint bonded for 30 min ~ 120 min. Hardness results revealed that formations of Ni(Al, Mn) phases and the compounds in ASZ can cause the alternant hardness distribution of valley and peak across the joint and lead to the generation of stress concentration. Therefore, the maximum shear strength, 269.9 MPa, was achieved in the joint dwelled for a period of 10 min.