Formation Of Brittle Phases Research Articles

Effect of Ni interlayer on microstructure and mechanical properties of Sn-based alloy/steel bimetallic materials via liquid-solid compound casting

Tin-based alloys have been widely used as an excellent bearing material. However, preparing of Tin/steel bimetallic materials with sound metallurgical interfaces has proven challenging. Importantly, a large number of brittle intermetallic compounds inevitably form at the interface, affecting the material's bonding properties. In this study, an electroplated Ni layer was used for the first time as an intermediate layer in Tin/steel bimetallic composites. It solves the problems of steel surface oxidation and poor wettability. Additionally, the introduction of the electroplated Ni layer impedes the formation of brittle phases, thereby improving interfacial bond strength. The results show that the Tin/steel interface of the Ni interlayer consists mainly of a large number of Ni3Sn4 phases rather than the commonly known FeSn2 phase. A thin layer of residual Ni plating also exists between the steel and the diffusion layer. Furthermore, the properties of Ni3Sn4 and FeSn2 phases were calculated using first-principles calculations. A Tin/steel bimetallic interface achieved a maximum shear strength of 58.63 MPa in the presence of the Ni intermediate layer. At that time, the residual thickness of the Ni layer was 1.5 μm, and the thickness of the diffusion layer was 4.8 μm.

Crack suppression in directed energy deposition of molybdenum

Additive manufacturing (AM) is a valuable tool for the fabrication and repair of refractory parts such as molybdenum alloys. Cracking is a common defect encountered during AM processing of refractory parts, that is generally associated with the segregation of light elements to grain boundaries which affect grain boundary cohesion and, ultimately, affect the final performance of the part. Similarly, because of the high melting points of refractory metals, lack-of-fusion defects are also common. The effect of build substrate and small alloying additions on suppression of defects during multilayer builds was investigated using directed energy deposition (DED) printing. Identical sample matrices were printed on three different build substrates: molybdenum (Mo), commercially pure titanium (Cp-Ti), and 316 stainless steel (316). Twenty-six usable samples were produced. Samples were cross sectioned, polished, and were characterized for total cross-section defect area. Additionally, samples from each substrate material were analyzed for grain boundary oxygen content. The strongest defect suppression, producing crack free material, was observed in samples printed on a Cp-Ti build substrate with a ten atomic percent addition of titanium in the molybdenum powder feed. The part quality was enhanced due to three factors: 1) the moderation of thermal diffusivity through a change in build plate material, 2) the suppression of light element segregation via increased solubility through titanium addition, and 3) a lack of brittle phase formation due to metallurgical compatibility of the build material with the build substrate. Analysis of defect area versus dimensionless number, π1, shows that increasing π1 reduced defects throughout the part.

First Principles Calculation of the Effect of Cu Doping on the Mechanical and Thermodynamic Properties of Au-2.0Ni Solder.

To meet the demands for high-temperature performance and lightweight materials in aerospace engineering, the Au-Ni solder is often utilized for joining dissimilar materials, such as Ti3Al-based alloys and Ni-based high-temperature alloys. However, the interaction between Ti and Ni can lead to the formation of brittle phases, like Ti2Ni, TiNi, and TiNi3, which diminish the mechanical properties of the joint and increase the risk of crack formation during the welding process. Cu doping has been shown to enhance the mechanical properties and high-temperature stability of the Au-Ni brazed joint's central area. Due to the difficulty in accurately controlling the solid solution content of Cu in the Au-Ni alloy, along with the high cost of Au, traditional experimental trial-and-error methods are insufficient for the development of Au-based solders. In this study, first principles calculations based on density functional theory were employed to analyze the effect of Cu content on the stability of the Au-2.0Ni-xCu (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) alloy phase structure. The thermal properties of the alloy were determined using Gibbs software fitting. The results indicate that the Au-2.0Ni-0.25Cu alloy exhibits the highest plastic toughness (B/G = 5.601, ν = 0.416, Cauchy pressure = 73.676 GPa) and a hardness of 1.17 GPa, which is 80% higher than that of Au-2.0Ni. This alloy balances excellent strength and plastic toughness, meeting the mechanical performance requirements of brazed joints. The constant pressure specific heat capacity (Cp) of the Au-2.0Ni-xCu alloy is higher than that of Au-2.0Ni and increases with Cu content. At 1000 K, the Cp of the Au-2.0Ni-0.25Cu alloy is 35.606 J·mol-1·K-1, which is 5.88% higher than that of Au-2.0Ni. The higher Cp contributes to enhanced high-temperature stability. Moreover, the linear expansion coefficient (CTE) of the Au-2.0Ni-0.25Cu alloy at 1000 K is 8.76 × 10-5·K-1, only 0.68% higher than Au-2.0Ni. The lower CTE helps to reduce the risk of solder damage caused by thermal stress. Therefore, the Au-2.0Ni-0.25Cu alloy is more suitable for brazing applications in high-temperature environments due to its excellent mechanical properties and thermal stability. This study provides a theoretical basis for the performance optimization and engineering application of the Au-2.0Ni-xCu alloy as a gold-based solder.

Microstructural, tribological, and corrosion behavior of B4C-added TiO2 coatings applied on 316 L stainless steel via sol-gel method

Corrosion protection of metals is essential for a wide range of technological applications, and coating metal surfaces with protective materials is a commonly employed method to achieve this. Among these, TiO2 coatings are extensively used due to their excellent photocatalytic properties, their applications in sensing and solar cells, and enhancing the corrosion and wear resistance of metal surfaces. Recent advancements have focused on the incorporation of carbide particles, such as B4C, to further improve the performance of TiO2 coatings. In this study, TiO2 coatings containing 0–3.25 wt% B4C were applied to a 316 L stainless steel substrates using the sol-gel method. The coatings were characterized by XRD and SEM-EDS analyses, and their wear and corrosion properties were evaluated using ball-on-disc wear tests and corrosion tests in NaCl solutions. The results demonstrated that lower concentrations of B4C led to improved wear resistance, likely due to the formation of a durable tribolayer, while higher concentrations reduced the wear resistance, attributed to increased oxidation and the formation of brittle phases. Corrosion resistance was enhanced in coatings containing 0.25 wt% and 1.25 wt% B4C, which can be attributed to the formation of protective B2O3 phases. However, at higher B4C concentrations, the corrosion rate increased, primarily due to the presence of cracks in the coating structure. Overall, the addition of 0.25 wt% B4C to the TiO2 coating significantly improved wear and corrosion resistance, indicating its potential as an effective additive for protective coatings.

Influence of added La2O3 on the microstructure, mechanical properties, and tribocorrosion resistance of TiB2–Ni plasma-sprayed coatings

To enhance the tribocorrosion resistance of 7075-T6 aluminum alloy in deep sea environments, TiB2–Ni coatings with varying La2O3 content were deposited on 7075-T6 aluminum alloy substrates using plasma spray technology. The effects of different La2O3 contents on the organization, structure, and properties of the coatings were analyzed. The results indicated that La2O3 incorporation suppressed brittle phase formation such as Ni3B; 1.0 wt% La2O3 addition reduced Ni3B by 16.9%. The coating's corrosion resistance significantly improved with La2O3 doping - the self-corrosion current density of the 1.0 wt% La2O3-doped coating decreased from 71.2 nA/cm2 to 30.2 nA/cm2.

Fabrication and evaluation of Ti6Al4V /NiCrBSi bimetallic structure with Nb/Cu bilayer by laser melting deposition

The fabrication of high-quality bimetallic structures using titanium and nickel alloys is a desirable integration for fully leveraging their remarkable properties. This study is dedicated to the surface modification of titanium brake discs, using laser melting deposition to produce the Ti6Al4V/NiCrBSi bimetallic structure and inhibition of brittle phase formation by Nb/Cu bilayer. The results showed the generation of brittle intermetallic compound phases was effectively resisted using Nb/Cu bilayer, thus preventing cracking and peeling of the Ti6Al4V substrate and NiCrBSi coatings. Moreover, the bimetallic structure fractured at the weakest position, i.e. at the Nb/Cu interface, with a maximum strength of 243.20 ± 55.16 MPa during the tensile testing, exhibiting brittle-like failure behaviour. Additionally, the friction and wear properties of the Ti6Al4V substrate and NiCrBSi coatings were evaluated at both room temperature and elevated temperature (600 °C). The results reveal that the NiCrBSi coatings effectively improved the friction and wear properties of the Ti6Al4V.

EFFECT OF ELECTRODE ON JOINING TWO DISSIMILAR METALS (SS & MS

This study examines the challenges associated with joining dissimilar metals, specifically stainless steel and mild steel, and investigates the impact of electrode selection on joint quality and characteristics. Various welding processes, including shielded metal arc welding (SMAW), is explored. Experimental findings indicate that electrode choice significantly influences the formation of intermetallic compounds, fusion zone morphology, and mechanical strength of the joint. Alloying elements in electrodes are found to enhance weldability and performance by facilitating metallurgical bonding and reducing the formation of brittle phases. Furthermore, the study explores variations in welding parameters to optimize the process for desirable joint properties. By deepening our understanding of electrode roles in welding dissimilar metals, this research offers insights crucial for selecting appropriate techniques and parameters, ensuring reliable joints. These insights have broad applicability across industries such as automotive, aerospace, construction, and manufacturing, where dissimilar metal joining is common. Key Words: dissimilar metals, intermetallic compounds, Weldability, morphology, mechanical strength.

Use of molybdenum in Ni 620 filler metal to influence the microstructure of brazed hot work steel

AbstractBrazing of hot work steel with nickel‐based filler metals is a widely used process for manufacturing casting tools. However, the formation of brittle phases in the joint impairs its mechanical properties. Reducing these intermetallic phases is an important aspect. Thermodynamic equilibrium calculations are used to estimate the change in melting range and apearance of intermetallic phases by adding different amounts of molybdenum to Ni 620. The filler metals are then produced and their solidus and liquidus temperatures are investigated using differential scanning calorimetry. Specimens of X37CrMoV5‐1 are then brazed in a vacuum furnace and their microstructure is analysed by scanning electron microscopy/electron dispersive spectroscopy and their hardness properties by nanoindentation. The addition of molybdenum to the Ni 620 filler metal leads to the formation of chromium molybdenum boride rich phases and reduced hardness values in brazed joints. Manipulation of Ni 620 by molybdenum helps to improve relevant properties in brazing hot work steel.

Review on Laser Welding Technology on Aluminum and Copper Dissimilar Materials for Secondary Batteries Assembly

Electric vehicles have recently taken center stage, driven by growing environmental concerns, with a key focus on ensuring the reliability of their batteries. The materials used in the electrical connections of secondary batteries predominantly consist of Al and Cu alloys, necessitating the joining of both similar and dissimilar materials. This paper presents a technical review on laser welding technology applied to the challenging Al/Cu dissimilar metal combination. The complexity arises from the formation of brittle phases in intermetallic compounds and the low absorption of laser beams by the base materials. The characteristics of various laser welding modes and their effective monitoring through deep learning are explained in detail. The development of real-time laser welding monitoring technology is crucial to increase productivity and enable the mass production of reliable electric vehicle battery systems.

Ultrastrong and ductile steel welds achieved by fine interlocking microstructures with film-like retained austenite

The degradation of mechanical properties caused by grain coarsening or the formation of brittle phases during welding reduces the longevity of products. Here, we report advances in the weld quality of ultra-high strength steels by utilizing Nb and Cr instead of Ni. Sole addition of Cr, as an alternative to Ni, has limitations in developing fine weld microstructure, while it is revealed that the coupling effects of Nb and Cr additions make a finer interlocking weld microstructures with a higher fraction of retained austenite due to the decrease in austenite to acicular ferrite and bainite transformation temperature and carbon activity. As a result, an alloying design with Nb and Cr creates ultrastrong and ductile steel welds with enhanced tensile properties, impact toughness, and fatigue strength, at 45% lower material costs and lower environmental impact by removing Ni.

Designing brazing filler metal for heat-resistant nickel alloys of new generation marine gas turbines

The object of research is the processes of the formation of brazed joints and the stressed state. The subject of research is structure, chemical composition, long-term high-temperature strength at a temperature of 900 °C, speed of high-temperature salt corrosion. Existing brazing filler metals have a high-temperature performance of 40–50 % of the performance of the SM93-VI and SM96-VI alloys. Despite this, brazing is the main technique of joining modern heat-resistant cast alloys. Therefore, the development of new brazing filler metals that ensure the formation of joints with increased long-term high-temperature strength is relevant. Ship gas turbine blades operate at a temperature of 900 °C. The purpose of the development of the new SBM-4 brazing filler metal is to achieve long-term high-temperature strength of brazed joints at a temperature of 900 °C at the level of 85–90 % of the strength of heat-resistant alloys SM93-VI and SM96-VI. A two-stage method was used in the development of SBM-4 brazing filler metal. At the first stage, the chemical composition of the brazing filler metal base was determined, taking into account the peculiarities of operating conditions of the blades of marine gas turbine engines and the achievements of materials science of heat-resistant alloys. At the second stage, the depressant and its necessary content were selected. Computer software was used to determine the distribution between the γ- and γ'-phases, taking into account the participation of each element in both dispersion and solid-solution strengthening. Rational limits of concentrations of alloying elements were determined. The criterion was the minimum susceptibility of brazing filler metal to the formation of brittle phases, taking into account the influence of chromium, rhenium, and tantalum concentrations on resistance to high-temperature salt corrosion and high-temperature performance. The long-term strength of SM93-VI and CM96-VI alloys brazed with SBM-4 brazing filler metal is 89–91 % of the strength of the base metal. Technologies of brazing and correction of casting defects have been introduced into production.

Aluminium foil-aided ultrasonic welding of NiTi and 304 stainless steel: a study of mechanical properties and interface microstructure

The achievement of an effective connection between superelastic NiTi and 304 stainless steel (304 SS) using ultrasonic welding with varying welding energy inputs has been studied. It has been observed that the addition of aluminium foil serves to a tight joint, which displays two kinds of interfaces where no defects were observed. With the increase in input energy, the peak load exhibits an initial growth phase followed by a decrement phase, and the interfacial heat production intensifies gradually, leading to subsequent interfacial oxidation. When the input energy is 750 J, the joint peak load reaches its maximum at 890 N. The fracture pattern of the joint exhibited both interfacial fracture and edge fracture. In high welding energy situations, Fe4Al13 (a brittle phase) is produced, which deleteriously impact on the joint's performance. Conversely, low welding energy results in the absence of any brittle phase formation.

Improving the strength-ductility synergy and corrosion resistance of Inconel 718/316L dissimilar laser beam welding joint via post-weld heat treatment

Inconel 718/316L dissimilar welding is widely used in nuclear power plants, which suffers from the deterioration of mechanical properties and corrosion resistance after welding, attributed to the formation of brittle phase and the existence of residual stress. In this paper, the impact of post-weld heat treatment (PWHT) on Inconel 718/316L welding joints is systematically investigated. By conducting PWHT after welding, notable reductions in residual stress in as-welded joints are significantly reduced and the microstructure is improved, resulting in an enhanced strength-ductility synergy and corrosion resistance. The as-welded joints exhibit the generation of brittle Laves phase and welding residual stress in the fusion zone. After PWHT at 650 °C, a substantial increase in the quantity of fine-scale γ″ strengthening phases with a uniform dispersion distribution in weldment is observed, along with the release of residual stress. This combination yields an optimal strength-ductility synergy and corrosion resistance of the joint. However, the δ phase precipitates along in Laves phase boundary after PWHT at 850 °C, which exhibits a semi-coherent interface with γ matrix, and a non-coherent interface with the Laves phase, leading to severe stress concentration at the δ phase interface. This severe stress concentration could be a preferred location for crack initiation and propagation, resulting in a substantial loss in mechanical behavior. Additionally, the increase in the phase boundary of γ/γ″, γ/Laves, Laves/δ and γ/δ reduces the corrosion resistance of the joint. The findings of this study provide an effective strategy for improving the performance of Inconel 718/316L dissimilar laser beam welding joint.

Impact of thermal oxidation parameters on micro-hardness and hot corrosion of Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr alloy

Protective oxide layers on Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr (TC21) alloy with equiaxed microstructure considerably influence micro-hardness and hot corrosion resistance. The present work’s thermal oxidation of TC21 alloy was performed at 600, 700, and 800 °C for 5, 20, and 50 h durations. Hot corrosion methods in NaCl and NaCl + Na2SO4 salt media were applied to raw (unoxidized) and oxidized samples at 600 and 800 °C for 50 h. Hot corrosion was conducted at 600 °C for 5 cycles with 10-h steps. The best oxide layer thickness was observed at 800 °C, which increased with increased oxidation time and temperature. The surface hardness of the oxide layer at 800 °C was 900 ± 60 HV0.05 owing to the formation of TiO2 and Al2O3 phases. Raw material hardness was 342 ± 20 HV0.05, increasing threefold due to thermal oxidation. In the case of NaCl, weight loss dominated all samples except at 800 °C for 5 h. In the case of NaCl + Na2SO4, weight gain occurred at 600 and 800 °C for 5 h. Weight loss occurred for the raw samples and those processed at 800 °C for 20 and 50 h, where the oxide layer flaked off. Surface hardness increased upon hot corrosion testing because of the formation of brittle phases, such as TiO2 and Na4Ti5O12. Samples that oxidized at 800 °C for 5 h had the highest hardness and corrosion resistance.

Study on Laser Overlap Welding of Titanium/Aluminum Dissimilar Metals Based on Niobium Microalloying

Brittle intermetallic compounds, formed during the welding process of titanium/aluminum (Ti/Al), lead to a significant reduction in joint mechanical properties. The purpose of this study is to mitigate the formation of brittle phases during the laser welding of dissimilar Ti/Al metals, thereby enhancing the mechanical properties of the joints. In this investigation, an innovative approach is adopted, utilizing Nb foil as an interlayer to effectively minimize the formation of brittle intermetallic phases during dissimilar welding. A comprehensive analysis of the microstructure of the transition layer was conducted using material characterization methods, including scanning electron microscope equipped with an energy dispersive X-ray spectrometer. The mechanical performance of the welded joints was assessed using tensile testing. The results indicate that the effective welding width and joint penetration depth at the joint interface were reduced in Ti/Al dissimilar metals when Nb was added as an intermediate layer, under the same welding process parameters, when compared to unalloyed weld seams. Furthermore, the utilization of a 0.05 mm Nb foil as the intermediate layer results in a significant 25% increase in the average shear strength compared to the other condition, with the average shear strength of the joint reaching its peak value at 192 N/mm. The unalloyed Ti/Al weld joint usually fractured along the melting zone, displaying complete brittle fracture characteristics. After Nb microalloying, the joint typically fractures along the transition zone and interface, exhibiting both cleavage and ductile fracture characteristics, indicating the combination of a brittle and toughness fracture. This study provides experimental evidence and new insights for welding Ti/Al composite structures, with significant theoretical and practical applications.

Achieving excellent strength-ductility synergy via cold rolling-annealing in Al-containing refractory high-entropy alloys

Most refractory high-entropy alloys (RHEAs) with Al possess excellent strength but low elongation. Low ductility is generally induced by the formation of brittle phases after long-term heat treatment. Here, we demonstrate a new strategy to optimize strength-ductility in RHEAs through cold rolling-annealing treatments. The Zr35Ti30Nb20Al10Ta5 RHEA was cold rolled followed by annealing. A high tensile yield strength of ∼997 MPa with an elongation of ∼20% was obtained. Several factors together optimize the mechanical properties. First, the high-density dislocation entanglements introduced by cold rolling and short-time annealing are beneficial to uniform strain hardening and ductility. Second, short-term annealing can prevent the generation of the brittle LAVES phase in Al-containing RHEAs. Third, the B2 nanoprecipitates are dispersed in the BCC matrix phase, strengthening the alloys. Fourth, the fine grain size induced by cold rolling and short annealing times contributes to the strength.

The impact of structure and temperature on the mechanical properties and radiopacity of Ta-W coatings for tiny endovascular medical implants

The trackability of tiny endovascular medical implants (TEMIs) during and after surgery is a crucial parameter for their accurate implantation and after surgery follow-ups. In this work, novel radiopaque Ta-W coatings were produced by magnetron sputtering deposition and further investigated with the aim to improve X-ray visibility of TEMIs under fluoroscopy imaging. Different deposition strategies, named micro-multilayer (Micro-ML), nano-multilayer (Nano-ML) and co-deposition (Co-dep), and different substrate temperatures (25 °C and 600 °C) were implemented which allowed to tune the morphology, mechanical properties and radiopacity of the coatings, while avoiding the formation of brittle phases, such as β-Ta and β-W. Ta-W coatings produced at high temperature (600 °C) contained stable phases such as α-Ta (bcc) and α-W (bcc), without brittle phases such as β-Ta and β-W. However, traces of β-W and β-Ta were detected in the group of samples produced at low substrate temperature (25 °C). The elastic modulus and the hardness of Micro-ML and Nano-ML were found to increase with increasing temperature, whereas they decreased in the case of samples produced by the Co-dep condition. The chemical state of Ta as well as the proportion of oxidized Ta (Ta-O) detected on all coatings were found to change as a function of the substrate temperature and deposition strategy. Samples with the highest amount of Ta-O at their surfaces showed the lowest corrosion potential. Finally, the samples produced by Micro-ML strategies performed on 600 °C substrates and irradiated according to radiographic imaging of conditions comparable to that of fluoroscopy, exhibited an X-ray contrast improvement of 82%/μm, which was higher than what was found in all other samples. Higher volume fractions of α-W in the coatings resulted in higher X-ray attenuation potential for photons in the energy range typical of fluoroscopy. Overall, the production of Ta-W coatings by the Micro-ML strategy and performed with a substrate temperature of 600 °C seems an optimal approach for the production of highly visible TEMIs in X-ray imaging.

Direct energy deposition of Cu–Nb functionally graded layers for dissimilar joining titanium alloys and steels

The heterogeneous compounds of titanium and iron steel are of wide interest in additive manufacturing. To prevent the formation of brittle intermetallic compounds, a layer of Nb and Cu was used. The use of the Nb and Cu interlayer successfully prevents the mixing of Ti and Fe, thus avoiding the formation of FexTiy brittle phases. In the Ti–Nb–(Nb + Cu–10Al) transition interlayer, it was possible to achieve the interlayer without the formation of brittle phases. The static tensile strength of the Grade1/316 L compounds with Nb–(Nb + Cu–10Al) interlayer is 335.5 MPa, the compounds exhibit ductile–brittle fracture.

Microstructure Evolution and Mechanical Properties of 20%SiCp/Al Joint Prepared via Laser Welding.

SiC particles-reinforced Al matrix composites (SiCp/AMCs) have been widely used in the aerospace structural components. In this work, 20 vol% SiCp/2A14 joint was fabricated by laser welding technology. The effects of different laser power/welding velocity on the 20 vol% SiCp/2A14 joint forming, microstructure evolution and mechanical properties were studied in detail. The results showed that, under the same heat input, the high power/high welding velocity was beneficial to reduce the porosity of SiCp/2A14 joint and inhibited the formation of brittle phase of Al4C3. At 8 kW-133 mm/s welding parameters, the maximum tensile strength of the SiCp/2A14 joint reached 199 MPa, which is ~64% higher than that of the SiCp/2A14 joint prepared at 4 kW-66 mm/s welding parameters. By analyzing the fracture morphology and SEM image of SiCp/2A14 joint section, it is was found that the porosity of weld and Al4C3 brittle phase were the important factors limiting the strength of SiCp/2A14 joint. This work provides a reference for the process window design of laser welding SiCp/2A14 composites.

Fabrication and joining of NiAl and TiAl intermetallics by additive sintering

To manufacture hard-to-deform intermetallics and their components at high temperatures and for a short-time, a novel additive sintering method based on solid-state powder densification is proposed, which aims to achieve the fabrication and joining of intermetallics. In this study, the sintering and joining of NiAl/NiAl and NiAl/TiAl alloys were conducted using this method. The results show that good bonding was achieved between similar intermetallics of NiAl/NiAl. Nevertheless, due to the formation of brittle phases, defects were observed in the bonding interface of the NiAl/TiAl alloy. An interlayer of V was employed to optimize the microstructure of the interface, which can prevent the formation of the brittle phase and improve the property of the interface.