Base Filler Metal Research Articles

The effect of vacuum brazing time on the microstructure and mechanical properties of Ti-6Al-4 V to 316 L dissimilar joint using BNi-2 filler metal

Due to the distinct differences in physical and metallurgical properties, it is hard to join titanium alloys to stainless steels directly via conventional welding processes. In this research, the grade 5 titanium alloy was subjected to brazing with austenitic stainless steel through the vacuum furnace, and the process was conducted above the β transition temperature (BTT). In order to reduce brittle intermetallic formation, a nickel base filler metal (Ni-6.6Cr-4.5Si-3B) was employed under a vacuum condition, and the effect of time on the microstructure and mechanical properties of the joints was investigated. The brazing temperature led to the thickening of the interface to 400 µm, toward the titanium alloy, and the FeTi formed adjacent to the diffusion affected zone (DAZ). Moreover, the isothermal solidified zone (ISZ) widened during the whole process, which, led to higher dissolution of the titanium base metal in the ISZ. Because of the widening of the interfaces, there were no Ni-rich compounds or residual filler metal in this region. SEM result showed that TiB strengthening borides, which were distributed after 45 min, and this evolution caused an increase in the shear strength of the joint up to 67 MPa. Fractography analyses and XRD results of the fractured surfaces revealed that the Ti2Ni phase, which formed in the athermaly solidified zone (ASZ) during a two-step solidification reaction, caused the brittle fracture in all joints.

Effect of repair weld length on microstructure evolution and mechanical properties of 30CrMnSiNi2A ultra-high strength steel

OM, SEM, EBSD and a series of mechanical property tests were used to study the influence of different welding lengths on the original welded joints. The results show that the filler welding area is austenitic structure due to the introduction of nickel base alloy. There are martensite and ferrite at the bottom of both the original weld and the repair weld. With the increase of the repair weld length, the number of martensite decreases gradually. Weld length has little effect on the grain growth direction at the bottom of the weld. The grain size at the bottom of the weld is affected by the thermal cycle of the weld and the nickel base filler metal, and the number of large Angle grain boundaries with dislocation hindering effect decreases. In addition, the reason for microstructure change is explained by a mathematical model. The tensile strength and microhardness decreased continuously after the repair welding, and the impact toughness increased significantly due to the increase of the austenite structure.

Microstructure investigation on the fusion zone of steel/nickel-alloy dissimilar weld joint for nozzle buttering in nuclear power industry

Microstructure of the fusion zone of steel/nickel-alloy dissimilar metal welds (DMWs) for nozzle buttering was investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron back-scattered microscopy (EBSD). The results showed that the dissimilar joint was complete, without welding defects. The structures of the fusion zone included the beach structure along the fusion boundary, the peninsula structures connected with the fusion boundary, and the island structures in the weld. The distribution of these three types of structures near the fusion boundary was uneven. The beach structure was formed because of the insufficient mixing and solidification of the molten liquid base material and the filler metal, with the width ranging between 0 and 150 μm. The peninsula and island structures were formed by the undercooling of the insufficiently mixed liquid base material and filler metal that entered the weld because of the convection and scouring of the weld pool. The composition of the three structures depended on the degree of mixing of the liquid base material and the filler metal, with a dilution ratio between 40 and 60%. The degree of dilution for the beach, peninsula, and island structures decreased in turn. With an increase in the dilution ratio, the initial solidification temperature of the corresponding composition increased significantly. When the dilution ratio exceeded 94.5%, the initial solidification phase transformed from the face-centered cubic γ-austenite into a body-centered cubic ferrite, with island structures solidified in the form of ferrites in the weld near the fusion boundary. The austenite grain orientations at weld side are dispersed with 75% large (> 15°) misorientation in frequency and the overall texture orientation distributes dispersedly with deviating from the < 100 > direction.

Microstructure and phase analysis of brazing bonds for stainless steel (AISI 316L and 431) to carbon steel (A516 G70) using a Ni–Si–B filler metal alloy

Investigation the mechanism of brazing stainless steels (Austenitic stainless steel type 316L and martensitic stainless steel type 431) similar and dissimilar and also brazing them with carbon steel type A516 grade 70 to see the difference in bonding phases, the five specimen were brazed with Ni base filler metal with (4.5% Si and 3.2% B) using a furnace with protected gas (pure Argon) at constant holding time 10 min. The optical and scanning electron microscopy (SEM) are used to study the joint microstructure, also the interdiffusion of the elements was examined by energy dispersive spectroscopy analysis (EDS). While the reaction phases are identified by x-ray diffraction (XRD). The brazed joints showed continuous bonding between the filler alloy and the substrate, indicating to good wetting between the surfaces. EDS line and mapping scan shows The Nickel element which it’s at the filler metal alloy will be goes into the interface almost, because the stainless steels sides can handle it, also Cr element. While Si element will concentrate at the bond zone, finally Fe element Transfer through brazing zones easy. XRD test reveals that the bonding zone of the five specimen shows more the six types of phases which are Ni-Cr-Fe, Cr-Ni-Fe-C, SiC, Fe2B, Cr2B, and Cr-Fe-Ni-Mo.

Effects of dual-cracks on the creep crack growth behaviour of HastelloyC276-BNi2 brazed joints

ABSTRACT In this paper, the effects of dual-cracks on the CCG behaviour of Hastelloy C276-BNi2 brazed joints were investigated. And the effects of inner crack length, inner crack distance and mismatched material coefficients on the creep crack initiation (CCI) time, CCG rate and creep life were also discussed. The results show that the creep crack can across over the inner crack and propagates continuously. The brazing defects can accelerate the CCG rate, thus leading to the decrease in the creep life and CCG length. With the increases in inner crack length and the decreases in inner crack distance, the CCI time, creep life and CCG length decrease. Longer inner crack distance and shorter defect length can suppress creep crack initiation and propagation. Bigger mismatch factor between base metal and filler metal may avoid the weakening effects of brazing defect on creep life.

Al-Si-Zn Behaviouron Interface of AR500 Steel and AA7075 Aluminium Alloy BrazedJoint

The brazing of steel and aluminium alloy using low melting point aluminium based fillers has been extensively studied and the technique has been used in many industries, especially the automotive industry. The strength and failure mode of AR500 steel and AA7075 aluminium alloy brazing joint using the Al-Si-Zn filler metal will be measured and calculated in this paper. However, the adverse effect of intermetallic phases formation on the joint strength has limited the application of this joining method.These dissimilar metals possessing a high strength joint would be of benefit to industry especially in reducing the weight of products. The torch brazing method using Al-Si-Zn base filler metal wasused to join AR500 steel and AA7075 aluminium alloy in this study. The intermetallic phase formation of the brazing on was investigated by scanning electron microscopy and the mechanical strength of the joints was evaluated by shear testing, flexural testing and low velocity impact testing. A maximum shear load of 6460 N was obtained. The presence of intermetallic phases was found to have some effect on the strength of the brazed joint. However, overall, this brazing process using Al-Si-Zn filler metal facilitates the joining of these dissimilar metals to improve the mechanical properties of the joint

The effect of niobium and titanium in base metal and filler metal on intergranular corrosion of stainless steels

&#x0D; &#x0D; &#x0D; The article describes the effect of alloyed additives in base material and filler metal on intergranular corrosion. Steel 1.2 mm thick, titanium-stabilized ferritic stainless steel and titanium and niobium-stabilized ferritic stainless steel have been surfacing method MAG (135). The specimens received was subjected to macro and microscopic tests, hardness tests and the intergranular corrosion resistance test. The study showed a higher corrosion resistance of niobium and titanium stabilized steel from titanium-stabilized steel. In addition, a ferritic fine-grain structure was found in the padding axis made with the use of filler metal with titanium and niobium microadditives.&#x0D; &#x0D; &#x0D;

Chemical Characterization of the Crystalline Phases in Agglomerated Fluxes and Slags for Shielded Metal Arc Welding (SMAW)

The aim of this work is to study the difference between the crystalline phases of used fluxes and obtained slags after Shielded Metal Arc Welding (SMAW). It is well known that The weld pool solidifies into the weld metal while the lighter molten flux floats on the top surface and solidifies as a slag layer that can be easily removed .The effects of individual flux ingredients as well as their interaction effects on weld metal composition have been investigated in this paper. The mass concentrations between fluxes (FA, FB and FC) and slags (SA, SB and SC) summarize the physico-chemical behavior of elements transfer between base metal, filler metal, flux and slag forming during welding of pipelines by SMAW process. The analysis of different fluxes phases and slags by X-ray diffraction allowed to detect the presence of different crystalline phases, which were formed at low temperature (T &lt;1000°C) heat treatments, and during fluxes confection. As for the slags, the presence of new crystalline phases which have been formed at high temperatures.

Effect of weld metal ferrite content on mechanical properties and stress corrosion cracking resistance in 22 Cr 5 Ni duplex stainless steel

Welded 22 Cr 5 Ni duplex stainless steel is often used for chloride-containing environments and sour service applications. Chloride stress corrosion cracking (CSCC) during service poses a threat to the service life of the weldment. Yield strength and resistance to CSCC are considered to depend on the weld metal ferrite content, which is variously required to be 30 to 60%, 30 to 70 ferrite number, 35 to 75%, etc. Accordingly, the present work has been carried out in collaboration with a filler metal manufacturer to investigate the research gap pertaining to minimum ferrite content to obtain the required minimum weld metal yield strength and resistance to CSCC. In this study, 22 Cr 5 Ni weldments with weld metal ferrite content in the range of 14% to 30%, or 20 to 40 ferrite number, obtained by increasing the filler metal nickel content above the normal 9%, have been prepared and investigated. It was found that yield strength and tensile strength requirements of base metal and filler metal classifications were exceeded at all ferrite levels investigated and that no CSCC was observed after 1000-h exposure in the ASTM G 123 boiling 25% sodium chloride test.

Brazed Joint Interface Bonding Strength of AR500 Steel and AA7075 Aluminium Alloy

The joining of aluminium alloys to steels has been extensively studied, especially in the automotive sector. However, aluminium alloys are known to be difficult to join with steels when methods involving fusion welding are used because of the hot cracking problem. Hence, a high-strength joint between these dissimilar metals would be of benefit especially in reducing the weight of products. In this work, the torch-brazing method was applied to join AR500 steel with AA7075 aluminium alloy using Al–Si–Zn base filler metal at various flame times. The effects of the brazing work on the intermetallic phase formation and the mechanical strength of the joints were investigated. In this work, the maximum shear load obtained was 6460 N and the presence of the intermetallic phases had reduced the shear strength of the brazed joints. However, the torch-brazing process using Al–Si–Zn filler metal had successfully facilitated the joining of these dissimilar metals.

Microstructure and Mechanical Properties of Stainless Steel/Brass Joints Brazed by Sn-Electroplated Ag Brazing Filler Metals

To develop a high-Sn-content AgCuZnSn brazing filler metal, the BAg50CuZn was used as the base filler metal and a Sn layer was electroplated upon it. Then, the 304 stainless steel and the H62 brass were induction-brazed with the Sn-plated brazing filler metals. The microstructures of the joints were examined with an optical microscope, a scanning electron microscope and an x-ray diffractometer. The corresponding mechanical properties were obtained with a universal tensile testing machine. The results indicated that the induction brazed joints consisted of the Ag phase, the Cu phase and the CuZn phase. When the content of Sn in the Sn-plated Ag brazing filler metal was 6.0 or 7.2 wt.%, the Cu5Zn8, the Cu41Sn11 and the Ag3Sn phases appeared in the brazed joint. The tensile strength of the joints brazed with the Sn-plated filler metal was higher compared to the joints with the base filler metal. When the content of Sn was 6.0 wt.%, the highest tensile strength of the joint reached to 395 MPa. The joint fractures presented a brittle mode, mixed with a low amount of ductile fracture, when the content of Sn exceeded 6.0 wt.%.

Study on a novel Sn-electroplated silver brazing filler metal

Novel Sn-electroplated Ag brazing filler metal with a high tin content was prepared by combining the plating and thermal diffusion method. The BAg45CuZn alloy was used as a base filler metal, and a Sn layer was electroplated on it. Then the H62 brass was brazed with the Sn-plated brazing filler metal containing 6.2 wt% of Sn. The results showed that the microstructure of the brazed joints with the Sn-plated filler mainly consisted of the Ag phase, Cu phase, CuZn phase and Cu5Zn8 phase. The tensile strength of the joints brazed with the Sn-plated filler metal was 326 MPa, which was higher than that of the joints with the base filler metal. Fracture analysis showed that the fractures of the joints brazed by the Sn-plated filler metal was mainly ductile fracture mixed with a small quantity of brittle fracture.

Effect of Post-weld Thermal Treatment on Mechanical Properties of Welded Aluminum-Alloy Engine Head

The effect of post-weld thermal treatment has been investigated experimentally in an attempt to improve the mechanical properties of welded aluminum-alloy engine head. Welding of the locally damaged engine head is performed using two different filler metals—one is the commercial aluminum filler and the other base metal itself. Mechanical properties of the repaired engine head are analyzed before and after applying the thermal treatment in terms of measured values of micro-hardness, tensile strength, yield strength, percentage elongation at different zones of the welded samples. In order to realize the effect, microstructures of different welded samples are also observed through optical and scanning electron microscopes. Results of the present investigation show that the thermal treatment significantly improves the mechanical properties as well as microstructure of the welded region of Al-alloy engine head, especially those obtained by using the base filler metal.

INVESTIGATION ON BRAZING INTERFACE BONDING CHARACTERISTIC OF AA7075 AND AA6061 ALUMINUM ALLOY WITH AR500 STEEL USING Al-Si-Zn FILLER METAL

This paper presents the study on interface bonding characteristic of AA7075 and AA6061 aluminum alloy with AR500 steel by torch brazing bonding process. The weight reduction in vehicles component is required for energy saving in the automobile industry. Lightweight metals such as aluminum joining with other metal especially with steel, have started replaced steel parts in automobile structures but the effect of intermetallic compound (IMC) layer formation have limited the application in this industry due to strength matter. The torch brazing method was done to join the dissimilar metal with Al-Si-Zn base filler metal for the process. The shear strength of the AA6061/AR500 joint was higher than the AA7075/AR500 joint when the joining conditions were the same. The IMC formation was observed at the joint interface, and the joints mainly fractured at this region.

Interface and Bond Strength of Brazing Cemented Carbide K20 to Alloy Steel AISI 4140 by High-Frequency Induction

High-frequency induction brazing of cemented carbide (WC–Co, K20) and alloy steel (AISI 4140) using Cu–Zn base filler metal was carried out. The relationship between microstructure and performance of the welding joint was investigated. It was found that the filler metal exhibited excellent wettability and metallurgical bond in the welding surface. As the heating rate reduced, welding joint appeared smooth without any visible crack. In the diffusion layer, some intermetallic compounds were observed, which were produced by the reaction of diffusion atoms. The microhardness in the middle of the welding seam was 168 Hv and it increased gradually when approaching to the edge of welding seam. With brazing temperature increased or heating rate decreased, the shear strength of welding joint increased first and then decreased. The machining test clearly revealed that the cutting temperature and the flank wear increased with the cutting speed rose. The welding joint had good shear strength when the temperature was below 500°C and the shear strength decreased seriously when the temperature exceeded 500°C.

Microstructure and creep behaviour of pressure boundary welds from Grade 91 steel tee

New power generation equipment firing either coal or natural gas is required to operate at high levels of efficiency with greater operational flexibility than has been true for such equipment in the past. Because of their unique combination of superior creep strength and favourable thermal–physical properties, Grade 91 and the other creep strength enhanced ferritic (CSEF) steels are materials of choice for components operating in the elevated temperature sections of this equipment. To fully realise the benefits of these alloys, it is essential that careful control be maintained during all phases of processing of the material, from design, through material production, to fabrication and installation. Absent such control, rates of damage accumulation can be much greater than expected from ‘Code’ minimum data. Problems have been associated with incorrect heat treatment: failure to develop the necessary structure during the normalising heat treatment or breakdown of that structure during subsequent sub-critical heat treatments. Heat treating schedules must consider not only the specific chemical composition of the base and weld filler metal, but also the cumulative impact of multiple heat treatments on the final material structure and its properties. The present work has examined the performance of welds in an ex-service component. The results suggest that, even when less than optimal heat treatment is carried out, the susceptibility for Type IV cracking in weld heat affected zones may be the life limiting factor for most CSEF steel components.

Transient liquid phase diffusion bonding for micro PCD tool fabrication

In this study, K30 (W 90 wt%, Co 10 wt%) and DX5 (W 84 wt%, Co 16 wt%) tungsten carbide were used as base metals for transient liquid-phase diffusion bonding (TLPDB). The filler metal was MBF20, a type of nickel alloy used to minimize the residual stresses that occur due to the differences in the expansion coefficients of the metals. MBF20 contained B, Si, and Cr, which reduced the melting point of the nickel alloy and enhanced its mechanical properties. The base metal and filler metal surfaces were cleaned by mechanical polishing and cleaning. Diffusion bonding was performed under vacuum at 1,000–1,500 K under low pressure than buckling load conditions. The microstructure on the localized bonded surface was analyzed using scanning electron microscope (SEM) and optical microscopy. Result of no significant change was observed in the diffusion bonding in the low-to-mid temperature range due to insufficient filler metal or base metal dissolution at the bonding site. However, at high temperatures, the filler completely melted and bonded to the base metal on both sides. Our results showed that temperatures approaching the recrystallization temperature were required to provide high-quality welds for ultra-precision joints and micro polycrystalline diamond (PCD) tool fabrication.

Drawing Study of Sheet Bimetallic Brazed Parts

In this paper we propose to analyze drawing of bimetallic sheets joined by brazing. Drawing is the transformation of a plan workpiece to the drawn part or workpiece transformation with decreasing of depth corresponding transverse dimensions. The brazing process is based on the difference in the melting points of the base materials and filler metal. During the brazing process, the bimetallic sheets to be assembled are heated for at a temperature between the melting temperatures of the two alloys, this process tends to modify the geometry and the microstructure of the brazed sheets.

Fusion boundary microstructure evolution associated with embrittlement of Ni–base alloy overlays applied to carbon steel

The embrittlement of the fusion boundary region of Ni–base Alloy 625 overlay welds on AISI 8630 steel was evaluated. Metallurgical characterization, thermodynamic and kinetic simulations, and hydrogen charging experiments were conducted in an effort to identify the embrittlement mechanism and simulate the type of failures that occur in service under cathodic protection. Optical microscopy, scanning electron microscopy, electron backscattered diffraction, electron probe microanalysis, X-ray diffraction, and hardness mapping were all used to characterize the microstructure and assist in identifying the microstructural features in the transition region of this dissimilar alloy combination that can promote susceptibility to hydrogen-assisted cracking (HAC). A special low-angle sectioning technique was developed that expanded the very narrow transition zone between the Alloy 625 overlay and the heat-affected zone of the 8630 steel. Using this technique, a “featureless zone” resulting from planar solidification was evaluated. This was the region in which HAC was observed during service under cathodic protection. Carbon migration studies conducted using Dictra™ showed that considerable carbon buildup (over 1 wt.%) occurs in the transition zone during postweld heat treatment. This level of carbon was confirmed using electron probe microanalysis. The high carbon content stabilizes the austenite phase in this region and results in local hardness levels exceeding 500 VHN. Metallographic sections of samples that failed under cathodic charging revealed that cracking occurs preferentially within this hardened region. The paper describes the metallurgical basis for the formation of this transition zone in weld overlays of Ni–base filler metals on carbon steels.

More sophisticated thermodynamic designs of welds between dissimilar steels

In the present paper, steels that are mostly used in technical practice as base materials, filler metals and consumable electrodes in the design of dissimilar weld joints are studied. These steels differ mainly in the content of Cr, Mo, V, W and N. It is explained and emphasised in the present paper that the effect of thermodynamics, diffusion and phase transformations on the stability of dissimilar weld joints that are exposed to temperatures of over ∼500°C cannot be underrated during operation. For all the materials under study the carbon activity at 600°C is given as calculated by the CALPHAD method, and a correlation is shown to exist between the carbon activity and the total chromium content. This correlation can be used as a most general alternative in the selection of filler metals or consumable electrodes in the design of dissimilar weld joints. The primary goal of the present paper is, however, to present a more sophisticated alternative based on a mutual comparison of the temperature dependence of the carbon activities of the base alloys, filler metals and consumable electrodes under consideration. This alternative is suitable for routine engineering purposes. Attention is also drawn to the currently most advanced alternative, which enables the prediction of the redistribution of elements and phases after prolonged exposure.