Filler Metal Research Articles

Heat Treatment Optimisation of Electron Beam Welded Reactor Pressure Vessel Steel

AbstractElectron beam welding (EBW) is a promising technology for the joining of large steel components such as pressure vessels. Notably, EBW does not use a filler metal, meaning that the weld and parent material (PM) should have the same composition. Accordingly, it may be possible to homogenise microstructure and properties across the weld given a suitable post-weld heat treatment (PWHT), essentially making the weld ‘disappear’. To investigate this possibility, three different PWHTs were applied to an SA508 Grade 4N weld. A stress-relief PWHT only had a relatively minor impact on the variations in microstructure and hardness across the fusion zone (FZ), heat-affected zone (HAZ) and PM versus the as-welded state, and compositional microsegregation in the FZ was unchanged. Hardness was successfully homogenised across the parent and weld in heat treatments involving a traditional 860 °C austenitisation, quench and temper, but compositional microsegregation persisted in the FZ. The addition of a homogenisation step at 1200 °C eliminated this microsegregation, with the weld area only remaining visible owing to the presence of compositional banding in the PM. However, homogenisation also led to the formation of undesirable prior austenite grain structures following subsequent re-austenitisation at 860 °C. Nevertheless, the application of PWHTs involving a full re-austenitisation seems promising for future applications.

Hf-doped amorphous filler metal towards high-performance TC4/SS316L brazed joints

Conventional welding poses significant challenges when directly joining titanium alloys and stainless steels due to their inherent physical and metallurgical properties variances. The primary challenge in achieving durable joints is to avoid the formation of brittle Ti–Fe intermetallic compounds (IMCs). In this study, Hf-doped amorphous filler material was employed to join TC4/SS316L dissimilar metals by vacuum brazing, achieving a maximum shear strength of 380 MPa under 910 °C/10 min at 1.25 at.% Hf. The interfacial microstructures consisted of the sequence: β-Ti/α-Ti/β-Ti + Ti2(Cu, Ni)/Ti2(Cu, Ni)/Ti2(Zr, Ni)+TiCu/Ti2(Ni, Cu, Fe)/γ-(Fe, Ni) + σ. This study presents a successful approach for the brazing of titanium alloy with stainless-steel alloy for high-precision components in the field of aerospace and nuclear sectors.

The Effect of Post Weld Heat Treatment in Multi Layer Welding on Tensile Strength and Hardness

Post weld heat treatment is heating objects in the furnace to certain temperatures and times after the object has been welded. PWHT is expected to reduce residual stress on objects due to the welding process. In this case, we warm up annealing (holding in a furnace) at a temperature of 750 °C with a heating time of 40 minutes. We use MIG welding (metal inert gas) and a metal filler FS 705-6 with a diameter of 0.8 mm, with a total of 3 layers. First, the object will be formed according to the standard and welded in three layers with MIG welding. Then, the object will be cut and formed according to the tensile test standards, after which the tensile test and hardness test will test it to determine the mechanical characteristics of the object. From the testing that has been carried out, it is known that objects without PWHT have a higher stress and hardness value than objects with PWHT, with a stress value of 346.57 MPa and the highest hardness value of 93.5 HRB at the 3rd welding point. However, objects with PWHT have higher elasticity and strain values, with an elasticity value of 3.32 MPa, and the strain value of objects with PWHT is 13.1.

Змочування ZnO-кераміки сплавами системи срібло—олово у вакуумі

ZnO is interesting as a promising material for use in various industries; in these applications there it is a need for metallization of ZnO-based materials, as well as their joining. For these purposes the using of liquid metal fillers is effective. Despite this, there are only a few single works that investigate issues related to the wetting and adhesion of metallic melts on the surface of zinc oxide or materials based on it. Therefore, the wetting of zinc oxide was investigated by Ag—Sn melts. intered ceramics made of pure ZnO without additions with porosity of 15%, silver and tin high purity were studied. Silver-tin alloys were prepared by previous melting in a vacuum. The wetting experiments were performed by the sessile drop method in vacuum. Addition of tin to silver can very significantly improve the wetting of the ZnO melt; there is a clear concentration dependence. The smallest of the contact angle is 57°. For the con¬centration of tin 5% at., when wetting has not yet been reached, a transition layer is observed between ceramics and metal. It is noticeable that lines, both between the ZnO substrate and the transition layer, and between the transitional layer and the frozen drop, are very uneven. Therefore, it can be concluded that the transition layer was not appeared due to adsorption, but formed as a result of the interaction of Ag—5Sn with ZnO, in particular uneven dissolution of the components of the substrate, possibly with the formation of a non-stoichiometric zinc oxide. In the case of tin concentration 10% (at.), when the melt wet the substrate, there is a zone containing two phases, dark and light (metal) in the ceramics under the drop. This two-phase area is obviously formed as a result of the impregnation of the melt in the pores in ceramic.Therefore, increasing the concentration of tin in Ag—Sn melts significantly improves the wetting of ZnO-ceramic by these systems, but the formation of developed transitional layers, as well as intensive impregnation of the melt deep into the ceramics complicates the use of these alloys for brazing or metallization of materials based on ZnO. Keywords: zinc oxide, wetting with metals, contact interaction, microstructure, transition layer

Study on the Microstructure and Properties of Al Alloy/Steel CMT Welding–Brazing Joints Under Different Pulse Magnetic Field Intensities

Butt welding experiments on 6061 Al alloy and Q235B steel of 2 mm thickness were conducted using an ER4047F flux-cored wire as the filler metal, after adding a pulsed magnetic field into the process of cold metal transfer (CMT) welding. The effect of the pulsed magnetic field intensity on the macro morphology, microstructure, tensile strength and corrosion resistance of the welding–brazing joint was analyzed. The results showed that when the pulsed magnetic field intensity increased from 0 to 60 mT, the wettability and spreadability of the liquid metal were improved. As a result, the appearance of the Al alloy/steel joint was nice. However, when the pulsed magnetic field intensity was 80 mT, the stability of the arc and the forming quality of the joint decreased, which resulted in a deterioration in the appearance of the joint. A pulsed magnetic field with different intensities did not alter the microstructure of the joint. All of the joint was composed of θ-Fe2(Al,Si)5 and τ5-Al7.2Fe1.8Si at the interface and Al-Si eutectic phase and α-Al solid solution at the weld seam zone. Actually, with the pulsed magnetic field intensity increasing from 0 mT to 60 mT, the IMC thickness in the interfacial layer gradually reduced under the action of electromagnetic stirring. Also, the grain in the weld seam was refined, and elements were distributed uniformly. But when the pulsed magnetic field intensity was 80 mT, the grain in the weld seam began to coarsen, and the intermetallic compound (IMC) thickness was too small, which was unfavorable for the metallurgical bonding of Al alloy and steel. Therefore, with the increase in pulsed magnetic field intensity, the tensile strength of the joints first increased and then decreased, and it reached its maximum of 187.7 MPa with a pulsed magnetic field intensity of 60 mT. Similarly, the corrosion resistance of the joint first increased and then decreased, and it was best when the pulse magnetic field intensity was 60 mT. The Nyquist plot and Bode plot confirmed this result. The addition of a pulsed magnetic field caused less fluctuation in the anode current density, resulting in less localized corrosion of the joint using the scanning vibrating electrode technique (SVET). The XPS analysis showed the Al-Fe-Si compounds replacing the Fe-Al compounds in the joint was the main reason for improving its corrosion resistance under the action of a pulsed magnetic field.

A Comparison Study of High-Temperature Low-Cycle Fatigue Behaviour and Deformation Mechanisms Between Incoloy 800H and Its Weldments

The high-temperature low-cycle fatigue (LCF) behaviour of Incoloy 800H and its weldments with Haynes 230 and Inconel 82 filler metals, which were fabricated with the gas tungsten arc welding (GTAW) technique, was investigated and compared at 760 °C. The results revealed that the Incoloy 800H weldments showed lower fatigue lifetimes compared to the base metal. However, the weldments with the Haynes 230 filler metal demonstrated an improved fatigue life at the low strain amplitude compared to both Incoloy 800H and the weldment with the Inconel 82 filler metal. The Incoloy 800H base metal showed pronounced initial cyclic hardening with hardening factors increasing with strain amplitudes. In contrast, the weldments with Haynes 230 and Inconel 82 filler metals displayed short initial cyclic hardening and saturation stages, followed by long continuous cyclic softening. The fractography and microstructure after LCF the tests were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Transgranular fracture with multiple crack initiations was the predominant failure mode on the fracture surfaces of both Incoloy 800 base metal and the weldments. TEM examination revealed that planar dislocation slips at the low strain amplitude evolved to wavy slips, eventually forming a cell structure at high strain amplitudes in the Incoloy 800H material as the strain amplitudes increased. However, the weld metal exhibited a planar slip mode deformation mechanism regardless of cyclic strain amplitude in the weldment specimens. The differing cyclic hardening and softening behaviours between Incoloy 800H and its weldments are attributed to the higher strength of the weldment specimens compared to the base metal. In the Incoloy 800H base material specimens, the reverse strains during LCF created wavy dislocation structures, which could not fully recover due to the non-reversible nature of the microstructure. As a result, cells or subgrains formed within the microstructure once created. In contrast, the higher strength of the weld metal in the weldment specimens significantly suppressed the formation of wavy dislocation structures, and deformation primarily manifested as planar arrays of dislocations.

Microstructure degradation and creep failure study of the dissimilar metal welded joint of heat-resistant steel and Inconel 617 alloy tested at 650 °C and applied stress range of 100–150 MPa

The advanced ultra-supercritical (A-USC) power plant system is anticipated to become India's next-generation base-load power station. To adopt AUSC technology, dissimilar welded joints (DWJs) between heat-resistant steels and the nickel-based alloys, using the nickel-based fillers, will need to be implemented. However, failure of dissimilar welded joints from P92 steel base metal or the heat affected zone (HAZ) has been commonly observed under high-temperature creep conditions. In the present study, the creep rupture behaviours and rupture mechanisms of DWJ between the Ni-based alloy Inconel 617 and heat-resistant P92 steel with Inconel 617 (ERNiCrCoMo-1) filler metal were investigated. Creep tests were conducted at 650 °C in the stress range of 100–150 MPa. To examine the creep rupture behaviour of the DWJ samples, optical microscopy (OM), scanning electron microscopy (SEM) and microhardness tests were performed. Cross-sectional images of the fractured creep specimens tested under various operating conditions revealed failures originating from distinct locations, including the P92 base metal and the inter-critical heat affected zone (HAZ). The specimen tested at 650 °C/150 MPa exhibited failure originating from the P92 base metal, whereas the specimen tested at 650 °C under the stress range of 100–130 MPa showed failure from the inter-critical heat affected zone (ICHAZ). The failure from P92 BM was primarily governed by plastic deformation, with the growth and coalescence of dimples ultimately resulting in trans-granular fracture. The specimens tested at 650 °C/100–130 MPa, which failed from the ICHAZ, exhibited a typical Type IV inter-granular failure. This failure mode is primarily attributed to matrix softening in HAZ, weakening of the boundaries, coarsening of the precipitates, and the evolution of intermetallic Laves phases. The specimen that failed in the stress range of 100–130 MPa exhibited a high density of microvoids in the ICHAZ, along with a few microvoids in the FGHAZ. The weld metal showed negligible degradation in microstructure, while the hardness study revealed a significant increase in hardness with an increase in rupture time, i.e., a decrease in applied stress and it was attributed to evolution of the new carbide phases in weld metal. Coarsening of the carbide precipitates was observed in each zone of the HAZ of P92 steel as well as in the base metal. The EDS study of the fracture tip and the FGHAZ/ICHAZ of the specimen that failed under stresses of 100 MPa and 120 MPa confirmed the evolution of intermetallic Laves phases. High magnification SEM images confirmed that triple boundaries are preferential locations for microvoid nucleation. The failed specimen showed the presence of microvoids near the carbide precipitates, with a large density of both coarse and fine precipitates confirmed all around and inside the microvoids. The ICHAZ and FGHAZ confirmed the formation of fine prior austenite grain boundaries (PAGBs) during the welding thermal cycle, which exhibited a lower density of carbide precipitates and this played a major role in Type IV failure.

Precipitation reconstruction of a diffusion brazed austenite joint with Ni-filler

Abstract The paper will explain the formation and effects of brittle precipitates in form of borides and silicides during high-temperature vacuum diffusion brazing on the example of a nickel-based filler metal from the NiCrSiB system. This filler metal foil was used to braze butt joints of the metastable austenite AISI 304L. Energy and wavelength dispersive X-ray spectroscopy was applied to identify the precipitates. Using a focused ion beam in scanning electron microscopy, the brazed joint was removed layer by layer over a large area to gain insights into the 3D structure of the precipitates. Subsequently, a methodology will be presented on how to reconstruct a 3D model from the image data using deep learning-based image segmentation. The final model unravels the complex morphology of these precipitates and thus contributes to a better understanding of the solidification and precipitation mechanisms in diffusion brazing.

High-strength stainless steel joints achieved by co-regulation mechanism of phosphide dispersed distribution and γ-phase generation

A novel iron-based filler FeCr18Ni10Si6P6 was designed to address the inherent limitations of joint strength reduction caused by the formation of the continuous brittle phase in the diffusion affected zone (DAZ) during traditional iron-based filler joints. The influence of process parameters on the microstructure evolution and mechanical properties of the joints was subjected to a comprehensive examination. The results indicated that the diffusion of Cr would result in the formation of α-phase in DAZ of the joints, which predominantly solidified most of the P atoms. This ultimately led to the precipitation of phosphide in the form of fine needles, enhancing the strength of the joints and altering the joint fracture region from DAZ to athermal solidified zone (ASZ). The joint strength peaked at 177 MPa when brazed at 1120 °C for 15 min, which is 2.6 times higher than that of traditional iron-based filler metals used in bonding. This filler metal presents a novel approach to the low-cost and high-quality joining of stainless steel.

Vertically aligned liquid metal thermal pad with excellent electromagnetic shielding and ultra-high compressibility

With the increasing integration level of modern electronics, flexible highly thermally conductive and electromagnetic interference shielding (EMI) materials were urgently demanded in electronic devices. Traditionally carbon or solid metal fillers are widely used as a reinforcement to fabricate a flexible thermally conductive and EMI shielding materials. However Due to the trade-off between mechanical and thermal properties, it is difficult to further improve the performance of solid filler/polymer composites. Here in this work based on the intrinsic excellent electrical and thermal conductivity of liquid metal (LM), we embedded the LM network structure vertically in the silicone gel and fabricated a vertically aligned LM(VALM) composites. Compared to the randomly dispersed LM composites, VALM composite exhibits high through plane thermal conductivity (κ⊥: 6.08 W/m·K) and excellent EMI shielding efficiency (SE) (minimum and maximum EMI SE for VALM2 were 33.2 dB and 39.5 dB). In addition, due to the fluidic nature of LM, composite materials exhibit excellent softness and flexibility (compression modulus of 0.56 MPa). Practical heat dissipation test results and EMIS efficiencies demonstrate usefulness of VALM composite in next-generation electronics.

Development of a Mathematical Model of the Self-Shielded Flux-Cored Arc Surfacing Process for the Determination of Deposition Rate.

The article presents a method of developing a mathematical model of the arc surfacing process performed using the self-shielded flux-cored filler metal wire with the chromium cast iron (Fe15) weld deposit. A three-level design (static, determined, and complete) was used to determine the function of the test object, thus enabling the simulation of deposition rate in relation to wire feed speed and electrode extension. The deposition rate for the specified set of surfacing parameters amounted to between 4.31 kg/h and 11.25 kg/h. The study was also concerned with identifying the effect of the significance level of test factors and interactions between them on the resultant factor, as well as an assessment of the adequacy of the test object function. In relation to significance level α = 0.01, regression coefficients b0, b1, b2, and b11 significantly affected the deposition rate of the surfacing process. Coefficient b22 was significant at a level of 0.40, whereas coefficient b12 was significant at a level of 0.15. The mathematical model presenting the effect of wire feed speed and electrode extension, as well as interactions between them on the deposition rate of the surfacing process, was adequate for the adopted level of significance α = 0.05.

Steel Chips as a Raw Material for MEX

In recent years, metal chip powders obtained from solid-state processes have shown great potential as a sustainable raw material for powder technologies. The material and fragmentation process of the chips has a significant role in the final characteristics of the powder particles, such as size and particle size distribution, shape, surface, and structure, which are essential parameters to consider when converting chips to powder for applications. However, tool steel chips as a powder raw material have not yet been significantly studied. In this study, the steel chips were from machining AISI H13 steel and the milling process used a ball mill, and the challenge was to obtain powder particle sizes of around 20 µm with suitable properties from the application of envisaged material extrusion (MEX). A comparison study with the commercial raw material for MEX, such as powder metal filament extrusion, was performed. This study highlights the behaviors of chip powders during all steps of MEX, namely, feedstock and filament production, 3D object shaping, thermal de-binding, and sintering. A comparison of the mixture based on powder from chips and commercial powders for MEX was performed after evaluating the mixing torque of the powder and the system of binders and additives suitable for the rheological characteristics required for an extrusion mixture, and optimizing the binder removal and the sintering conditions. The 3D objects resulting from chip powders had a refined microstructure, showing an increase of 15% in the microhardness when compared with the those resulting from commercial powders.

Performance of the GH4169 Joint Using a Novel Ni-Based Amorphous Brazing Filler Metal

A novel Ni-Cr-Si-B filler metal (JNi-5) was designed and further fabricated into the amorphous brazing filler metal for joining the GH4169 alloy. The effect of brazing temperature on the microstructure and mechanical properties of GH4169 joints was investigated. The typical microstructure of the joint at 1030 °C is composed of four specific zones: the base metal (BM), heat-affected zone (HAZ), isothermal solidification zone (ISZ), and athermal solidification zone (ASZ). The typical microstructure of the joint is GH4169/(Nb, Mo)-rich boride+(Cr, Nb, Mo)-rich boride/γ(Ni)/Ni-rich boride+γ(Ni)/γ(Ni)/(Cr, Nb, Mo)-rich boride+(Nb, Mo)-rich boride/GH4169. As the temperature increased, the HAZ continued to widen and the ASZ depleted at 1090 °C and 1120 °C. Additionally, the borides within the HAZ coarsened at temperatures of 1090 °C and 1120 °C. At 1030 °C, the fracture path is in the ASZ, and the existence of the brittle phase in the ASZ provides the potential origin for crack growth. The fracture mode is a quasi-cleavage fracture. At 1060 °C, 1090 °C, and 1120 °C, the fracture behavior mainly happened in the HAZ, and the existence of borides in the HAZ provides the potential origin for crack growth. Namely, the shear strength of joints was principally dominated by the brittle precipitations in the HAZ. The fracture mode of these joints is the hybrid ductile. At 1060 °C, the shear strength of the obtained joint is the highest value (693.78 MPa) due to the volume fraction increase in the Ni-based solid solution. Finally, the optimized brazing parameter of 1060 °C/10 min was determined, and the corresponding highest shear strength of 693.78 MPa was obtained owing to the increased content of the Ni-based solid solution in the joint.

Microstructure, mechanical properties, and corrosion resistance of dissimilar weld joints between SS304 and Inconel 600 welded using gas tungsten arc welding

The microstructure, mechanical characteristics, and corrosion resistance of dissimilar gas tungsten arc welding (GTAW) joints of 304 stainless steel (SS304) to Inconel 600 (IN600) with Inconel 600, using ERNiCr-3 and ERSS308 filler metals were investigated. The welding process was executed at a current of 110 Amps under argon shielding gas, and all fabricated welds successfully joined SS304 to Inconel 600 without visible cracks or porosity at the weld metal interface. Microstructural analysis with optical and scanning electron microscopy revealed a mix of columnar and equiaxed dendritic structures in the weld zone for all samples. An unmixed zone was noted at the interface on the SS304 side when welded with Inconel 600 and ERNiCr-3, attributed to the differing melting points and chemical compositions of these fillers compared to SS304. The presence of Nb and Ti in the ERNiCr-3 filler facilitated the formation of TiC and NbC carbides in the welded metal structure, resulting in higher hardness compared to other specimens. Mechanically, the ERNiCr-3 welded sample exhibited superior hardness, with the highest microhardness values recorded in the ERNiCr-3 weld metal (197–207 HV) and higher values on the SS304 side (176–194 HV) compared to the IN600 side (164–176 HV). Corrosion tests, including Tafel and Electrochemical Impedance Spectroscopy, indicated that the ERNiCr-3 weld metal had better corrosion resistance than the IN600 weld metal. Due to the differences in chemical compositions of the base metals SS304 and IN600, it is necessary to consider an appropriate filler for welding these materials. ERNiCr-3 demonstrated increased hardness due to the formation of TiC and NbC carbides, along with enhanced corrosion resistance. These properties make it a promising material for industrial applications that require durability, strength, and resistance to corrosion, particularly in high-temperature or corrosive environments.

Enhanced vacuum brazing joining between Ti–48Al–2Cr–2Nb/Ti–22Al–25Nb intermetallic alloys by Zr-free Ti-based filler

This study investigates the microstructure and tensile properties of vacuum-brazed joints of Ti–48Al–2Cr–2Nb (Ti4822) and Ti–22Al–25Nb (Ti2AlNb) intermetallic alloys using Ti-based filler metals, with and without the addition of Zr element. Detailed microstructural characterization of the brazed joints was conducted using Electron Backscatter Diffraction and Transmission Electron Microscopy, identifying various phases and their distributions. The tensile properties were tested at room temperature and at 650 °C, revealing the influence of Zr on the mechanical performance of the joints. The results demonstrated that the microstructure of joints brazed with Zr-containing filler metals exhibited a layered structure with brittle Zr-enriched intermetallic compounds, limiting their mechanical properties. Conversely, Zr-free filler metals yielded more homogeneous and ductile microstructures, significantly improving tensile strength and elongation. The Zr-free joints obtained after holding at 980 °C for 60 min exhibits the highest tensile strength, reaching 368.23 MPa at room-temperature and 293.46 MPa at 650 °C, respectively. These findings provide valuable insights for optimizing brazing processes and filler metal compositions to enhance the performance of TiAl-based intermetallic alloy joints.

Effect of SiC particles on microstructure and mechanical properties of SiCp/AZ91 magnesium matrix composite brazed joint

The impact of SiC particles on the microstructure, mechanical properties, and fracture morphology of magnesium alloy brazed joints was investigated. The brazing experiments of AZ91+AZ91, AZ91+SiCp/AZ91, and SiCp/AZ91+SiCp/AZ91 were carried out under the same technological conditions by using the self-designed special filler metal for magnesium matrix composites. The impact of SiC particles on the microstructure and mechanical properties of brazed joints was analyzed. The addition of Ti can effectively enhance the wettability of filler metal on SiC particles. The shear strength of SiCp/AZ91+SiCp/AZ91 joints is 76.0MPa. The shear strength of the joint is 43.4% higher than that of AZ91+ AZ91.

Corrosion behaviour of medium entropy alloy deposited on low carbon steel substrate by innovative welding method

In recent decades, thanks to the advancements within materials science and engineering, a novel class of metallic compounds, named high and medium-entropy alloys, has begun to capture the attention of researchers worldwide. Despite their excellent mechanical and anticorrosive properties, the widespread usage of these materials in industrial applications still remains a challenge and a subject worthy of investigation. In the present work, an innovative concept of developing high and medium-entropy alloys by deposition welding technique is presented and analysed in detail. Melting a bundle of rods by the Gas Tungsten Arc Welding (GTAW) method, in the same molten pool, a medium-entropy alloy (MEA) from the AlCrFeNi system is deposited on a low carbon steel substrate. In order to increase the chemical homogenization of the deposited material and to eliminate or reduce the eventual defects that may occur, electric arc remelting without using filler metal was performed in transverse, longitudinal, or combined (transverse and longitudinal) direction relative to the initial deposition welding direction. The assessment of the resistance to corrosion, modifications of microstructure, chemical composition and hardness have revealed that the medium-entropy alloy, obtained by melting in the same welding pool of several common welding rods with various chemical compositions, is an innovative, sustainable, and advantageous alternative to stainless steel materials.

Research on the Strengthening Mechanism of MWCNTs-Cuf Composite Interlayer for Si3N4/TC4 Brazed Joints

With the rapid development of aerospace technology, the high-quality brazing connection between Si3N4 ceramic and TC4 titanium alloy has become a key factor in advancing the development of aircraft antenna covers. To improve the mechanical strength of the joints, this study used the electrophoretic deposition method to prepare a multi-walled carbon nanotubes-foam copper (MWCNTs-Cuf) composite interlayer and selected the optimal deposition parameters. The most suitable brazing parameters under this interlayer were also determined. The joints’ formation mechanism and fracture mode were revealed to elucidate the synergistic strengthening mechanism of the composite interlayer. The results showed that MWCNTs, based on their phase characteristics, produced high-density dislocations and fine crystal strengthening effects during the brazing cooling process. This effectively resisted the corrosion of the brazing material on the foam copper (Cuf), protected the integrity of the foam copper framework, and exerted the excellent plastic deformation ability of foam copper (Cuf). It reduced the residual stress in the joints, resulting in the highest shear strength of the MWCNTs- Cuf composite interlayer, reaching 96.23 MPa. Compared with only adding Ag-Cu-Ti active brazing filler metal and adding ordinary foam copper interlayer, the shear strength increased by 78.2% and 44.7%, respectively.

Microstructure evolution and shear strength in CoCrFeNi/AISI 304 joint by vacuum brazing with BNi-2 filler metal

Microstructure evolution and shear strength in CoCrFeNi/AISI 304 joint by vacuum brazing with BNi-2 filler metal

Disclosing Connection Links between Microstructure and Mechanical Performance in Pulsating Current Gas Tungsten Arc Welding of Hastelloy B-2 Superalloy

In this study, welding a Ni-Mo-based superalloy (Hastelloy B-2) was examined in order to characterize the microstructure and mechanical performance of joints along with assessing the effects of current intensity on the microstructure and mechanical responses of different weld zones. The gas tungsten arc welding (GTAW) process was used to weld the samples using ERNiCrMo-2 filler metal. The pulsed current GTAW process was used to weld the superalloy sheets of thickness of 1 mm with background current (Ib) of 20 A and 40 A and peak current (Ip) of 80 A and 60 A. Tensile and Vickers microhardness tests were conducted to evaluate the effect of pulsed current on mechanical properties of the welds along with chemistry and microstructure characterizations. Finally, the fracture surfaces after the tensile test were studied using SEM fractography analysis. The results indicated that increasing Ib and decreasing Ip led to low heat input and high cooling rate resulting in a high thermal gradient. This caused microstructure transition from the columnar dendrites to the coaxial ones in the weld zone; molten metal convection in the fusion zone led to fine grains in the weld zone during welding time. Moreover, a significant decrease in the amount of molybdenum carbides at the interdendritic regions of the weld metal was observed under these conditions. The tensile strength of the weld metal was higher than that of the base metal resulting in the fracture of all welds from the base metal. Additionally, the microhardness results indicated a significant increase for the weld metal compared to both heat-affected zone (HAZ) and base metal. The higher mechanical properties of the weld metal is attributed to the increase in background current and decrease in peak current leading to a fine grain microstructure. Fractography following the tensile test showed a completely ductile fracture.