Ni-based Filler Metal Research Articles

Taguchi Analysis of Relation Between Tensile Strength and Interfacial Phases Quantified via Image Processing

Quantitative analysis was performed via image processing to identify the relationship between the tensile strength and the thickness of the CrxBy phase layer at the interface of brazed 304 stainless steel with Ni-based filler metal (MBF20). The experimental design was based on the Taguchi method to determine the relative contributions of the processing conditions, including the brazing temperature, heating rate, holding time, and filler metal thickness. The CrxBy phase at the brazement interface was extracted by an image-processing method from backscattered electron imaging; the numerically defined thicknesses of the CrxBy phase layers developed under varied processing conditions were calculated. The tensile strengths at temperatures of 25 °C and 650 °C were measured for specimens brazed under identical experimental conditions based on the Taguchi method and the post-tensile testing fracture surfaces were analyzed. Regarding the relationship between the thickness of the CrxBy phase layer, as determined through the image processing of the microstructure, and the tensile strength at 25 °C, thicker CrxBy layers deteriorated the tensile strength of the brazement interfaces. Although a slight discrepancy occurred in the brazement tensile strengths between the testing temperatures of 25 °C and 650 °C, the elevated temperature during tensile testing affected the brazed interface microstructure; with this consideration, the overall results for both tensile strength tests corresponded to the quantitatively analyzed CrxBy phase layer thicknesses. From the relationship between CrxBy layer thickness and tensile strength, the heating rate is the most effective processing condition to achieve high bonding strength, because changes in heating rate compared to those of other processing conditions have the greatest effect in changing the CrxBy phase layer thicknesses and tensile strength. Therefore, the results confirmed that the image-processing method enabled accurate quantitative analysis of the microstructure, permitting prediction of the mechanical strength of the joint.

Effect of Silicon on the Microstructure and Performance of the New Binary Deep Eutectic Ti–Cu–Zr–Ni-Based Filler Metal

This study designed (Ti0.55Cu0.20Zr0.15Ni0.10)1−xSix amorphous alloys based on binary deep eutectics and examined the effect of silicon (Si) on the amorphous forming ability of the filler alloys. The results show that a certain amount of Si added to the filler metals could improve the amorphous forming ability of the alloys. Under the same experimental conditions, the Ti0.55Cu0.20Zr0.15Ni0.10 filler metal with 0.5 wt % Si had the strongest amorphous forming ability compared to the other filler alloys containing different amounts of Si; its reduced glass transition temperature (Trg) was 0.5554, and its supercooled liquid phase region width (∆Tx) reached 60 °C. The (Ti0.55Cu0.20Zr0.15Ni0.10)99.5%Si0.5% filler metal designed in these experiments presented good amorphous forming ability and wettability. The brazed joint of SiC and TC4 obtained with this amorphous filler metal showed a shear strength of 102 MPa, indicating an increase of 122% compared to the brazed joint obtained with the filler metal without Si.

Effect of Ni-Ti filler on brazed W-Cu/18-8 joints

W-Cu composite and 18-8 stainless steel were vacuum brazed with an improved Ni-based filler metal, with varying Ti content. The microstructure, element distribution, phase composition, and fracture mechanism of the brazed joints were investigated. The improved NiCrSiBFe-Ti quench filler metal showed good wettability on the W-Cu composite and 18-8 stainless steel. Enhanced diffusion and metallurgical reactions between the filler metal and base metal were observed. The addition of Ti not only optimized the structure, but also reduced the formation of brittle intermetallic compounds, which is important for significantly improving the brazed-joint strength. The highest brazed-joint shear strength (381 MPa) was observed when the Ti content was 1.6%.

Corrosion behaviors of the iron-based and Ni-based brazing filler metals brazed on the stainless steels in a solution of 3.5MASS% NaCl

<p class="AMSmaintext"><span lang="EN-GB">The corrosion resistance was studied electrochemically for an iron-based brazing filler metal F300 and a Ni-based brazing filler metal Ni613. Both austenitic stainless steel SUS316 and ferritic stainless steel SUS444 were used as base metals for these brazing filling metals. F300 showed a higher corrosion rate than those of Ni613 and both base metals and was less corrosion-resistive. While Ni613 showed a stronger depression effect of an anodic reaction than those of base metals, F300 showed little depression effect of the reaction. As an Fe-Ni phase dissolved preferentially in F300 and a finite laminated corrosive morphology was observed, the corrosion progression along a depth direction was suggested. These corrosion behaviors depend on the difference of chemical composition of these brazing filler metals.</span></p>

Characterisation of PTA processed overlays without and with WC nanoparticles

ABSTRACTMixtures of Ni-based filler metal without and with 0.5, 1, and 2% WC nanoparticles (NPs) were methodologically tested in order to improve the wear behaviour of WC/Ni-based overlays deposited on low carbon steel by the plasma transferred arc (PTA) process. On adding 2% WC NPs, the longitudinal direction overlay microstructure was modified to have a fibrous appearance. The mechanism to improve WC particle distribution and thus prevent microcrack propagation in the overlays implies a liquid-phase viscosity change. Results of pin-on-disk tests in the overlay using filler metal with 2% WC NPs show that the combined effect of fibrous microstructure and W-rich phases in the overlay, decreases the volume loss by 76% and 78% in comparison with overlays without WC NPs for a 1 and 5 N load, respectively. These outcomes might be of interest for the mining industry, where machinery and equipment are exposed to extreme wear conditions.

Image processing-based analysis of interfacial phases in brazed stainless steel with Ni-based filler metal

This work presents an image processing method to identify the distribution of CrxBy in a brazed joint of SUS304/MBF20/SUS304. Although the chemical compositions at designated locations on such joints can be measured through electron-probe microanalysis (EPMA) and transmission electron microscopy (TEM), determining the overall distribution of CrxBy and quantitatively describing this phase is difficult. Therefore, an image-processing algorithm was developed using material-specific intensity differences in backscattered electron images. The image-processing algorithm was verified and validated by EPMA and TEM measurements. Based on the developed image processing method, the effects of the brazing temperature on the CrxBy layer thickness were quantitatively analyzed.

Vacuum Brazing Diamond Grits with Cu-based or Ni-based Filler Metal

Diamond grits were brazed using Cu-Sn-Cr and Ni-Cr-B-Si filler metals, and the brazed grits were examined for microstructure (SEM, EDS, XRD), microhardness, and compression strength. Results showed that the microstructure of the Cu-based filler metal was uniform and consisted of α-Cu + (α-Cu + δ). Its wettability to the diamond was better than Ni-based filler due to the formation of a thin carbide reaction layer that improved the bond strength between the diamond and steel. The Cu-based filler led to reduced thermal damage to the diamond. The Cr in the filler metal diffused to the steel substrate to form a reaction layer at the filler/steel substrate interface. The microhardness of the Ni filler metal (810-830 HV0.3) was significantly higher than that of Cu filler metal (170-230 HV0.3). The compressive load values of the diamond grits brazed with Cu-based or Ni-based filler metal were 93.7 and 49.2% of the original diamond, and the TI values were 83.7 and 59.8% of the original diamond. Grinding experiments for failure mode in monolayer tools revealed that the tools brazed with Cu-based filler metal had a lower macro-fracture ratio than those brazed using the Ni-based filler.

The Microstructural Evolution of Vacuum Brazed 1Cr18Ni9Ti Using Various Filler Metals.

The microstructures and weldability of a brazed joint of 1Cr18Ni9Ti austenitic stainless steel with BNi-2, BNi82CrSiBFe and BMn50NiCuCrCo filler metals in vacuum were investigated. It can be observed that an interdiffusion region existed between the filler metal and the base metal for the brazed joint of Ni-based filler metals. The width of the interdiffusion region was about 10 μm, and the microstructure of the brazed joint of BNi-2 filler metal was dense and free of obvious defects. In the case of the brazed joint of BMn50NiCuCrCo filler metal, there were pits, pores and crack defects in the brazing joint due to insufficient wettability of the filler metal. Crack defects can also be observed in the brazed joint of BNi82CrSiBFe filler metal. Compared with BMn50NiCuCrCo and BNi82CrSiBFe filler metals, BNi-2 filler metal is the best material for 1Cr18Ni9Ti austenitic stainless steel vacuum brazing because of its distinct weldability.

Development and testing of a high-chromium, Ni-based filler metal resistant to ductility dip cracking and solidification cracking

Ni-based filler metals for repair and construction of nuclear reactor components require 30 wt% Cr to insure resistance to primary water stress corrosion cracking (PWSCC). Current generation alloys can be susceptible to solidification cracking and ductility dip cracking, depending on Nb content and the amount of eutectic that forms during weld solidification. Computational thermodynamic modeling was used to identify alternative eutectic-forming elements to Nb, such as Hf and Ta. Previous work has utilized a design of experiment methodology (DOE) in conjunction with computational and experimental techniques to optimize a new filler metal composition that should be resistant to weld cracking. In this paper, the optimized compositions were subjected to further weldability testing, namely the cast pin tear test (CPTT) and the strain-to-fracture (STF) test. An optimized Ta-bearing composition was found to be crack resistant, while an optimized Hf-bearing composition was highly susceptible to solidification cracking. Differences may be related to the nature of the eutectic constituents that form at the end of solidification. The Hf-bearing composition did not form Laves phase as its final eutectic constituent, while Laves is present in both the Nb- and Ta-bearing systems.

The influence of isothermal ageing and subsequent hydrogen charging at room temperature on local mechanical properties and fracture characteristics of martensitic-bainitic weldments for power engineering

The present study deals with the effects of high temperature expositions and subsequent cathodic hydrogen charging of dissimilar martensitic/bainitic weldment on its local mechanical properties and fracture behaviour at room temperature. Circumferential welded joint under investigation was produced by tungsten inert gas welding of X10CrWMoVNb9-2 martensitic and 7CrMoVTiB10-10 bainitic steels tubes with Ni-based filler metal and the application of subcritical postweld heat treatment. Hardness profile measurements revealed pronounced hardness peaks in over-heated regions of the individual steels heat-affected zones which remained preserved also during subsequent expositions at 600?C for up to 5000 hours. Gradual microstructural degradation of these regions included precipitate coarsening and the formation of new secondary phases during thermal exposure. The combined effects of thermal and hydrogen embrittlement of the studied weldment resulted in deleterious effects on its tensile and fracture behaviour.

Microstructure transformation and crack sensitivity of WC-Co/steel joint welded by electron beam

The 30 mm thick WC-Co cemented carbide and AISI 1045 steel were electron beam welded (EBW) with and without Ni-based filler metal. Welding-brazing joints of WC-Co and steel were obtained as the molten pool wet and spread on the unmelted WC-Co base metal. The WC loose areas formed at the WC-Co interface have guaranteed the effective metallurgical bonding. According to simulation results, the thickness of filler metal should be less than 1 mm to avoid unbonding. The direct EBW WC-Co/steel joint was mainly composed of martensite, residual austensite and herringbone M6C carbides. The bulk brittle phases η-Fe3W3C increased the joint brittleness and crack sensitivity. With Ni-based filler metal, the microstructure of the joint was mainly composed of γ-Fe and herringbone carbides FeW3C. No η-Fe3W3C formed at WC-Co interface because of the metallurgical blocking effect. The plastic property of the joint was improved, and WC-Co/filler metal/steel EBW joints with no crack were obtained.

Microstructure and properties of W-Cu/1Cr18Ni9 steel brazed joint with different Ni-based filler metals

Abstract W-Cu alloy and 1Cr18Ni9 steel were brazed with NiCrSiBFeTi and NiMnSiCuZr filler metals in a vacuum furnace. The main microstructure of the NiCrSiBFeTi brazing seam region was a Ni-based solid solution of W, Cu, Cr, and Fe dissolved in the Ni phase and intermetallic compounds CrB and TiCr2. The main microstructure of the NiMnSiCuZr brazing seam region was a Ni-based solid solution of Cu, Cr, and Fe dissolved in the Ni phase Fe-based solid solution of Ni, Cu, and Cr dissolved in the Fe phase and intermetallic compounds Mn5Si3, Ni3Si, and Ni7Zr2. The elements Ni, Si, and Ti contained in the NiCrSiBFeTi filler metal and the elements Ni, Mn, and Si contained in the NiMnSiCuZr filler metal were more easily diffused into the interface of W-Cu alloy compared with that of 1Cr18Ni9 steel. The shear strength values of NiCrSiBFeTi joint and NiMnSiCuZr joint were approximately 285 and 249 MPa, respectively, and fracture of the two joints occurred at the interface near the W-Cu alloy side. The fracture morphology of the former was identified as cleavage brittle fracture, and the latter was identified as intergranular brittle fracture.

Deformation Mechanism and Microstructure Evolution of T92/S30432 Dissimilar Welded Joint During Creep

The cross dissimilar welds between T92 martensitic steel and S30432 austenitic steel were crept at 625 °C with different applied stresses, and the creep deformation and microstructure behaviors were characterized. The results revealed that the creep deformation behavior of dissimilar weld joint was controlled by its martensitic T92 part due to the Ni-based filler metal employed. The fracture positions of crept dissimilar welded joints were located in base metal of T92 steel as the applied stress over than 140 MPa. The fracture type was mainly caused by plastic deformation and characterized by dimples and surface necking. In contrast, as applied stress was <140 MPa, fractured location was transferred into the fine-grained heat-affected zone of T92 part identified to be the intergranular brittle fracture. This phenomenon was controlled by creep deformation and related to undissolved carbides, fine grain size and constraint effect induced by creep deformation inconsistent in this zone.

Development of rapidly quenched nickel-based non-boron filler metals for brazing corrosion resistant steels

Corrosion-resistant steels are stably applied in modern rocket and nuclear technology. Creating of permanent joints of these steels is a difficult task that can be solved by means of welding or brazing. Recently, the use rapidly quenched boron-containing filler metals is perspective. However, the use of such alloys leads to the formation of brittle borides in brazing zone, which degrades the corrosion resistance and mechanical properties of the compounds. Therefore, the development of non-boron alloys for brazing stainless steels is important task. The study of binary systems Ni-Be and Ni-Si revealed the perspective of replacing boron in Ni-based filler metals by beryllium, so there was the objective of studying of phase equilibrium in the system Ni-Be-Si. The alloys of the Ni-Si-Be with different contents of Si and Be are considered in this paper. The presence of two low-melting components is revealed during of their studying by methods of metallography analysis and DTA. Microhardness is measured and X-ray diffraction analysis is conducted for a number of alloys of Ni-Si-Be. The compositions are developed on the basis of these data. Rapidly quenched brazing alloys can be prepared from these compositions, and they are suitable for high temperature brazing of steels.

Low-cycle fatigue behaviors of a new type of 10% Cr martensitic steel and welded joint with Ni-based weld metal

In the present work, Ni-based filler metal was used to weld a new type of 10% Cr martensitic steel. Due to the microstructure and chemical composition difference between martensitic steel and the Ni-based weld metal, a clear interface existed in the dissimilar welded joint. At the region of the interface, the microstructure was physically connected and an element transition layer was formed. Low-cycle fatigue (LCF) results showed that the welded joint was not fractured at the interface. Meanwhile, the martensitic steel and Ni-based weld metal exhibited cyclic softening and cyclic hardening behaviors, respectively. For martensitic steel, the width of the laths increased and the dislocation density decreased after the fatigue test, whereas in the fatigue-tested Ni-based weld metal, the dislocation density increased. The continuous connection and composition transition at the region of interface, combined with the high ductility and cyclic hardening behavior of Ni-based weld metal, is beneficial for the LCF properties of the welded joint.

Experimental investigation on interface phenomena involving spreading of Fe–Cr based filler metal

Fe–Cr based alloy emerges as an economic alternative to Ni based filler metal applied in brazing of steels and high temperature alloys; however, its spreadability and interface microstructure have been very poorly studied. In the present study, wettability and interface microstructure of new type Fe–Cr–Ni–Cu–P–Si filler metal are investigated at different pressures. The molten Fe–Cr–Ni–Cu–P–Si filler metal demonstrated good spreadability both in vacuum and in air. Fingering phenomenon at the spreading edge indicated the dissolution of base metal during spreading and insufficient diffusion. Reactions promoted the fragmentation and removal of the oxide film, and the dissolution of oxide and base metal further improved the spreadability. These mechanisms indicate potential for an excellent brazeability of Fe–Cr–Ni-Cu–P–Si filler metal.

Investigation of the Repair Welding Technology Using Ni Base Electrode

Metal materials are subjected to innumerable time-dependent degradation mechanisms when operate in power, petrochemical and refinery plant. These materials are subjected to multiaxial stresses, creep, fatigue, corrosion and abrasion. As a result of service especially at high temperatures and high pressures, can lead to forming cracks, damages or failures. In situation of breakdown in such systems there is a need for weld repair on plant components and repair work can be expensive and time-consuming. Most weld repairs of low alloy steels require high-temperature post weld heat treatment (PWHT); but in certain repairs, however, this is not always possible. Expenses of the repair work could be reduced if the weld repairing is performed on site. Application of the nickel based filler metal can be alternative to performing PWHT. These repair welding procedures with Ni based filler metal could be categorized as cold repair welding. Purpose of presented investigation was to compare a repair welding technology with filler austenite material based on Ni and without application of the PWHT, with a classical repair welding procedure with preheating and PWHT and using a filler metal with chemical composition similar to parent metal. Properties comparison of the welded joints obtained by these two repair welding technologies was performed for the Cr-Mo steel (13CrMo4-5) by the metal arc welding procedure with covered electrode (MMA - 111). Weldability analysis by the analytical equations and technological tests for determination of the sensitivity to crack forming for cold and hot cracks by the CTS and Y tests, were performed for both repair welding technologies. Tensile tests, absorbed energies tests, banding tests and hardness measurements were performed on trial joins. Light optical microscopy (LOM) was applied for microstructure analysis. The fracture toughness for both technologies, were estimated by the calculated stress intensity factor KIc and dynamic stress intensity factor KId for weld metal and heat affected zone. All of the obtained results were analyzed and discussed. It was concluded that repair welding technology with Ni base filler material without PWHT, enables welded joints without the appearance of cracks, with a good mechanical properties, slightly higher hardness in the HAZ, but with lower expenses compared to standard repair welding technology. In applying this technology in emergency welding repairing on-site, on the equipment and industrial facilities with high security requirements, inspection using non destructive technique has to be frequently applied compared to standard procedures.

Use of the cast pin tear test to study solidification cracking

The cast pin tear test (CPTT) was originally developed by F.C. Hull in the 1960s to study solidification cracking in austenitic stainless steels. Over a past 5 years, researchers at the Ohio State University have modified the original test and apparatus design to study solidification cracking in a range of Ni-base alloys and stainless steels. This paper describes the development of the test apparatus, the techniques that are used, and results from the testing of several alloy systems. It is shown that the CPTT closely reproduced the trends in solidification cracking behavior determined by the Transvarestraint test and experienced in actual welds. Very good correlation is found between rankings of the solidification cracking susceptibility in various high-alloy stainless steels and high-Cr Ni-base filler metals generated using the CPTT and other solidification cracking tests. In addition, the application of the CPTT to study dilution effects in dissimilar material combinations is described.

Microstructure and properties degradation of P/T 91, 92 steels weldments in creep conditions

The studies were performed on dissimilar ferritic/austenitic weldments between 9Cr tempered martensitic steels of the grades either P/T 91 or 92 and unstabilised AISI316H austenitic steel. The welded joints were fabricated using the fusion welding by tungsten inert gas (TIG) method with Ni-based filler metal. Microstructural analyses were performed using light and electron microscopy. Microstructural gradient in heat-affected zone (HAZ) of 9Cr steels remained preserved during creep exposure. All weldments fractured by the type IV failure within their intercritical HAZ (ICHAZ) regions. The most remarkable microstructural change during creep was the precipitation of intermetallic Laves phase. Experimentally determined phases of the samples after creep exposure are in good agreement with equilibrium thermodynamic calculations.

Weldability Studies of High-Cr, Ni-Base filler metals for power generation applications

The solidification behaviour and weld solidification cracking susceptibility of high-Cr, Ni-base filler metals that are widely used, or proposed for use, in the nuclear power industry have been investigated. Two heats of ERNiCrFe-13 (filler metal 52MSS), one heat of ERNiCrFe-7A (filler metal 52M), and one heat of a modified ERNiCr-3 (filler metal 82 with higher Cr content, designated here as filler metal 52i) have been tested using both the Transvarestraint test and the Cast Pin Tear test (CPTT). The solidification behaviour in these alloys has been studied by a newly developed procedure that accurately replicates the solidification process in fusion welds of Ni-base alloys and is based on the patented technique for Single Sensor Differential Thermal Analysis (SS DTA™). Results of the solidification studies showed that filler metal 52i has the widest solidification range, followed by the two heats of filler metal 52MSS, and filler metal 52M. The filler metal 52i also has the widest eutectic temperature range. The interdendritic eutectic constituent formed in weld metal of this filler metal and filler metal 52MSS is enriched in Nb and results from the eutectic reaction of γ + L → γ + NbC at the end of solidification. Both the CPTT and the Transvarestraint test provided the same ranking of solidification cracking susceptibility among these filler metals. Both heats of 52MSS and the heat of 52i were found to be more susceptible to solidification cracking than filler metal 52M. The slightly higher resistance to solidification cracking of filler metal 52i relative to the 52MSS filler metals is attributed to crack “healing” during the final stages of solidification. This is the result of the higher fraction of eutectic liquid of filler metal 52i, as confirmed by metallographic studies. The results of this study confirm the higher solidification cracking susceptibility of high-Cr, Ni-base filler metals that contain higher Nb levels to counteract ductility-dip cracking, relative to filler metals that are Nb-free. This study has also shown that the CPTT can be used as an alternative, and reliable, tool for ranking the solidification cracking susceptibility of high-Cr, Ni-base filler metals proposed for use in nuclear power plants and other applications.