Intermetallic Zone Research Articles

The influence of weld fluid flow on the formation mechanism of intermetallics and HfO2 precipitates in dissimilar electron beam welding of C-103 niobium alloy to nickel

In this research, the effect of weld fluid flow in molten pool on the formation and behavior of intermetallic compounds NbNi3 and Nb7Ni6 and HfO2 precipitates in dissimilar electron beam welding of niobium base alloy C-103 to nickel was investigated. It was observed that due to the large difference in the melting temperature of the base metals, nickel contributed 82% by volume and C-103 contributed 18% by volume in weld zone. In the weld zone and attached to the C-103 base metal, a thin and continuous intermetallic zone was formed, including the initial phase of NbNi3 and the eutectic structure of NbNi3+Nb7Ni6. In the areas after the continuous intermetallic layer in welding, the initial phase of NbNi3 and the eutectic structure of NbNi3+γ-Ni are formed. During welding, HfO2 particles in the C-103 base metal enter the molten pool due to the weld fluid flow and remain as white precipitates in the welding zone and close to C-103. In addition to these precipitates, nanometer precipitates of HfO2 are also observed in the weld, which are formed in-situ in the weld due to the reaction of hafnium with dissolved oxygen in the melt. In the central zone of the weld, continuous band-shaped intermetallic layers can be observed which have been removed from the wall of C-103 due to the fluid flow of the molten pool and moved towards the central zone of the weld. These layers act as nucleus in the center of the molten pool and solidification occurs from their surface. At first, solidification begins with the planar growth of the initial phase of NbNi3, and then cellular and columnar dendritic growth occurs. At the end of solidification, the eutectic structure of NbNi3+γ-Ni forms between cells and dendritic branches. Due to the presence of intermetallic compounds NbNi3 and Nb7Ni6 as well as HfO2 nanometer precipitates in the weld, the hardness of the weld zone was higher than that of the base metals.

Finite element based 3-D modelling of residual stress in high vacuum actively brazed diamond/Ni-Cr filler/C45 steel joint

In active brazing of diamonds, high brazing temperature and difference in the thermo-mechanical properties of the diamond grain, filler alloy, and substrate lead to the development of unfavorable residual stresses in the bonding region. This residual stress can potentially cause initiation of cracks within the interfacial reaction layer formed between diamond and filler-alloy, weakening the joint. Since the diamond particles used in diamond grinding tools are micro-sized and complex in shape, it is experimentally difficult to measure residual stress at the grit-filler interface. In the present investigation, a coupled thermo-mechanical three-dimensional finite element model has been developed to predict, map, and analyse the formation of residual stresses in diamond-bond-substrate systems. The presented model uniquely differs from those in literature, which are mostly 2-D type and did not consider the presence of interfacial reaction layer between diamond and filler. A Ni-Cr-Fe-B active brazing alloy has been selected as the filler and C45 steel as the substrate in the current simulation. Chromium carbide has been considered to be the interfacial compound. The numerical simulation suggests that the maximum value of residual stresses, predominantly tensile in nature, gets shifted from the diamond to the intermetallic zone at the bond level when the interfacial reaction compound is introduced between the diamond and filler. It also establishes that orientations of diamond during its placement on substrate for brazing have significant influence on the magnitude of induced residual stress. Approximately 40 % reduction has been observed in case of hexagon-base brazed diamonds when compared to that (1620 MPa) developed on square-base brazed diamonds. Raman spectral analysis of brazed specimen was conducted to experimentally validate the numerical simulation results. Residual stress was estimated from the peak shift of D-band in the spectra. The numerically computed residual stresses were found to deviate within the range of 3–15 % of the experimentally determined values.

Reverse cladding of 304 stainless steel to LM25 aluminium alloy through die-casting

Stainless steel (SS) coatings/claddings over aluminium alloy (AA) substrates have been practiced through friction surfacing, thermal and cold gas spraying, laser coating, and diffusion bonding. In this work, 304-grade SS is reverse-cladded to an LM25 AA through die-casting using a surface-prepared sheet insert. The clad-substrate interface was characterized micrographically and compositionally through optical and electronic microscopic techniques. Micrographs revealed that reverse cladding was achieved successfully by forming an intermetallic zone (IMZ). The IMZ contains four intermetallic layers (IMLs) of varying thickness with 6.42 ± 2.04 µm near the central region. Electron probe microanalysis showed Fe3(Al, Si), Fe3(Si, Al), Fe(Al, Si), and Fe3Al15Si2 are the associated phases with four IMLs from the SS to AA side, respectively.

Mechanical properties, corrosion behavior and biocompatibility of orthopedic pure titanium−magnesium alloy screw prepared by friction welding

Abstract The dissimilar joining of biodegradable magnesium alloy to pure commercial titanium by rotational friction welding with rotational speeds of 1100, 1200 and 1300 r/min for the production of bio-screw was investigated. The metallographic analysis revealed that a good joining was obtained at the Ti/Mg alloy joint. On the magnesium alloy side, various regions such as the weld center zone (WCZ), dynamic recrystallization zone (DRX), thermo-mechanically affected zone (TMAZ) and partially deformed zone (PDZ) were observed. The highest tensile and shear strengths were 173 and 103.2 MPa, respectively at a rotational speed of 1300 r/min. The Ti/Mg alloy dissimilar friction welded joint failed at the vicinity of the intermetallic zone containing Ti3Al phase. The hardness values from the base metal magnesium alloy to the joining point increased mainly due to grain refinement (8.57 μm in diameter) and the presence of titanium particles, while the hardness values were constant on the titanium side. It was also found that the corrosion rate of the Ti/Mg alloy joint was higher compared with that of the Ti and Mg alloy from the immersion studies. Additionally, the sample with a rotational speed of 1300 r/min showed better biocompatibility and a cell viability of 98.12% due to better corrosion resistance.

Evolution of the mechanical properties of Ti-based intermetallic thin films doped with different metals to be used as biomedical devices

This study reports the assessment of the mechanical properties of intermetallic titanium thin films, doped with different amounts of aluminium, copper, silver, and gold, aiming their use as biopotential electrodes for non-invasive physiological monitoring. The four binary thin film systems, Ti-Me (Me = Al, Cu, Ag, Au), were prepared by DC magnetron sputtering, placing different number of Me pellets on a pure Ti target. The use of a Ti-composed target gave rise to a wide range of compositions, resulting in three distinctive zones of (micro)structural features, identified in all the prepared systems. In the first zone, a Ti-rich one, the films behaved like solid solutions, developing Ti-like microstructures. As the Me/Ti atomic ratio increased, the formation of intermetallic phases played the leading role and it became possible to observe two different microstructural trends, clearly related to the Me type. This zone was identified as an intermetallic region. In the third zone, a Me-rich one, the microstructures displayed by the different films (Me/Ti > 1.0) showed to be dependent on the Ti solubility into Me. The assessment of the mechanical properties revealed an improved hardness and stiffness with the Me addition, directly related to the formation of intermetallic compounds in different degrees of crystallinity. Moreover, the adhesive strength between the substrate and the coating was higher for the films deposited in the intermetallic zone, more evident in the films prepared with Au, Cu and Ag, in this order. The hardness enhancement was especially evident for the thin films presenting microstructures typical of thin film metallic glasses (TFMGs), Ti-Au and Ti-Cu, about twice the values exhibited by the Ti-Al and Ti-Ag ones. Furthermore, the toughness of these metallic glass-like thin film systems was remarkable, more evident within the Ti-rich zone, presenting H/E ratios close to 0.1 and good elastic recoveries. In contrast, the typical columnar morphologies, combined with the brittle intermetallic structures of the Ti-Ag and Ti-Al films, proved to be less resistant to the plastic deformation (H/E ≤ 0.04), despite the improved elasticity presented by the Ag-rich films.

Microstructure, mechanical and electrical properties of laser-welded overlap joint of CP Ti and AA2024

The study results of an overlap welded joint of Commercially Pure Titanium Grade 4 (CP Ti) and Aluminum-Copper Alloy 2XXX series (AA2024) obtained by laser welding without defects in the form of pores and cracks are presented. A microstructure using optical and scanning electron microscopes, a phase composition using X-Ray Diffraction, an electrical resistivity of welded joints were studied. It was found that at tensile shear strength (TSS) testing, failure occurs not only in the brittle intermetallic zone of the welded joint but also in the columnar heat affected zone (HAZ) of aluminum. A 1% of titanium does not have time to diffuse from the HAZ of aluminum at a higher welding speed (150 mm/s), whereas, at a speed of 20% less titanium is not observed in the HAZ of aluminum. The tensile shear strength of samples welded on the titanium side is in the range of 80–120 MPa, depending on the rate of input energy.

Effects of the process parameters on the formability of the intermetallic zone in two-layer Mg/Al materials

This paper discusses experimental results concerning the plastic deformation of the bonding zone in a two-layer AZ31/Al material subjected to compression loads. The specimens were fabricated by diffusion bonding method. The 50μm thick transition zone at the AZ31/Al interface contained Mg–Al intermetallic phases. The physical modelling of the deformation behaviour of the intermetallic zone was performed using a Gleeble 3800 system. The compression tests were carried out at two temperatures (300 and 400°C), two strain rates (0.1 and 1.0s−1) and a true strain of 0.15 applied in one or two stages. The metallographic examinations and microhardness measurements were performed to assess the influence of the selected process parameters on the forming behaviour of the intermetallic zone. The experiments revealed that the main factors affecting the formability of the intermetallic zone in the two-layer AZ31/Al material were the strain rate and the temperature. It was found that when the deformation occurred at a strain rate of 0.1s−1 and a temperature of 400°C, there was no loss of continuity of the intermetallic transition zone; such conditions induced its plasticization.

Microstructure and Mechanical Properties of Explosive Weld Copper-Mild Steel Joint

Mild steel and copper was joined with explosive welding using suitable parameters to obtain a copper-mild steel joint of high integrity. There was no diffusion, melting and formation of intermetallic zone between the bonded plates. An inter-mixed zone of the base materials is observed with a span of 1300 μm around the interface. Significant hardening and softening of the microstructure was observed on the copper and steel sides around the interface respectively by inter-mixing effect arising out of mechanical inter-locking. Shear strength of the joint (260 MPa) was quite higher with respect to that of the copper, the weaker metal of the copper-mild steel bimetal combination. Reasonably ductile shear failure occurred in the copper plate, and no failure was observed along the interface.

Microstructure evolution and bonding mechanism of Ti2SnC-Ti6Al4V joint by using Cu pure foil interlayer

Ti2SnC, as one of functional ceramics with self-healing ability, was studied in welding with Ti6Al4V (TC4) through Cu interlayer under an applied mechanical pressure 10MPa in Ar atmosphere. Electron probe microanalyses indicated that the outward diffusion of Sn from Ti2SnC played a critical role in the chemical composition of the joining interface. After 60min, the reaction layers consisted of five zones: an interleaved zone (V) of β-Cu(Sn) and α-Cu(Sn), an enriched zone (IV) of Sn and intermetallic CuTi0.5Sn0.5 phase, the intermetallic zones (III) and (II) composed of TiCu4 and Ti3Cu4, a zone (I) consisting of β-Ti (Cu) phase. After shear tests, the corresponding fractographs indicated that the cracks mainly propagated in the Ti2SnC matrix with an intergranular fracture mode.

Effect of bonding temperature on the microstructure and mechanical properties of Ti-6Al-4V to AISI 304 transient liquid phase bonded joint

Transient liquid phase (TLP) bonding process was performed to join Ti–6Al–4V and AISI 304 austenitic stainless steel using a copper interlayer. The effect of the bonding temperature on the microstructure and mechanical properties was studied in the range of 870–960°C. Microstructural characterization was carried out through optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the rate of isothermal solidification was increased by increasing the bonding temperature. In addition, when the bonding temperature was increased to 960°C, the width of the eutectic and intermetallic zones was completely removed, leading to complete isothermal solidification. According to the results, a minimum hardness value of 216VHN was measured in the joint zones and the highest shear strength was 374MPa, as obtained for the sample joined at 960°C. The fracture analysis showed different fracture morphologies for different bonding temperatures.

Recent Developments for Ultrasonic-Assisted Friction Stir Welding: Joining, Testing, Corrosion - an Overview

Due to the steadily increasing demand on innovative manufacturing processes, modern lightweight construction concepts become more and more important. Especially joints of dissimilar metals offer a variety of advantages due to their high potential for lightweight construction. The focus of the investigations was Al/Mg-joints. Friction Stir Welding (FSW) is an efficient process to realize high strength joints between these materials in ductile condition. Furthermore, for a simultaneous transmission of power ultrasound during the FSW-process (US-FSW) a positive effect on the achievable tensile strength of the Al/Mg-joints was proven.In the present work the industrial used die cast alloys EN AC-48000 (AlSi12CuNiMg) and AZ80 (MgAl8Zn) were joined by a machining center modified especially for Ultrasound Supported Friction Stir Welding. The appearing welding zone and the formation of intermetallic phases under the influence of power ultrasound were examined in particular. In order to identify optimal process parameters extensive preliminary process analyzes have been carried out. Following this, an ultrasound-induced more intensive stirring of the joining zone and as a result of this a considerably modified intermetallic zone was detected. At the same time an increase of the tensile strength of about 25% for US-FSW-joints and for fatigue an up to three times higher number of cycles to failure in comparison to a conventional welding process was observed. Moreover, detailed corrosion analyzes have shown that especially the welding zone was influenced by the corrosive attack. To expand and deepen the knowledge of the US-FSW-process further material combinations such as Ti/Steel and Al/Steel will be considered in future.

Amino Acid Interleaved Layered Double Hydroxides as Promising Hybrid Materials for AA2024 Corrosion Inhibition

AbstractVarious α‐amino acid (αAA) molecules were screened for their ability to retard the corrosion of AA2024 aluminum alloy substrate. The αAAs screened were L‐arginine (L‐Arg), L‐asparagine (L‐Asn), L‐cysteine (L‐Cys), L‐cystine, L‐histidine (L‐His), L‐methionine (L‐Met), L‐phenylalanine (L‐Phe), L‐serine (L‐ser), L‐tryptophan (L‐Trp), and L‐tyrosine (L‐Tyr). From their performances compared with that of the reference additives chromate and 2‐mercaptobenzothiazolate (MBT), L‐Cys and L‐Phe were selected, and their layered double hydroxide (LDH) interleaved derivatives were further scrutinized. Different LDH phases, namely, LiAl2, Mg2Al, MgZnAl, and Zn2Al, were tested as hosts for the inhibitor αAA substances, and the materials were characterized by XRD, FTIR spectroscopy, and SEM. The efficiencies and durable performances of the hybrid materials as an anticorrosion agents for aluminum alloy 2024 (AA2024) were demonstrated through direct current (DC) polarization measurements, and the evolution of the polarization resistance was recorded. The mechanism of inhibition focused on the most promising hybrid material LDH/L‐Cys and was tentatively explained as anion exchange and dissolution of the inorganic framework at the cathodic and anodic corrosion zones, respectively, with the particular occurrence of Cu‐rich intermetallic zones. The obtained results evidence that the LDH/L‐CYS assembly embedded in the polymer coating retards the corrosion process of the AA2024 substrate after a prolonged immersion time.

In-situ investigation of microcrack formation and strains in Ag–Cu-based multi-metal matrix composites analysed by synchrotron radiation

In this study, multi-metal matrix composites based on SiC fibres coated with titanium alloys are investigated. In contrast to ordinary titanium matrix composites, the consolidation was realised by an infiltration process using a silver-based filler material in order to avoid shrinkage, distortion or fibre breakage. During the infiltration process, a transition zone between the titanium coating and the filler material developed consisting of several intermetallic phases. The behaviour of this intermetallic reaction zone under stepwise increased tensile stresses was investigated in-situ by synchrotron radiation using computer tomography and X-ray diffraction. Multiple cracks were observed already at the lowest investigated load level. Depending on the titanium alloy, different types of fracture occurred within the intermetallic transition zones with limited elastic strains in the predominant intermetallic phase TiCu.

Partially degradable friction-welded pure iron-stainless steel 316L bone pin.

This article describes the development of a partially degradable metal bone pin, proposed to minimize the occurrence of bone refracture by avoiding the creation of holes in the bone after pin removal procedure. The pin was made by friction welding and composed of two parts: the degradable part that remains in the bone and the nondegradable part that will be removed as usual. Rods of stainless steel 316L (nondegradable) and pure iron (degradable) were friction welded at the optimum parameters: forging pressure = 33.2 kPa, friction time = 25 s, burn-off length = 15 mm, and heat input = 4.58 J/s. The optimum tensile strength and elongation was registered at 666 MPa and 13%, respectively. A spiral defect formation was identified as the cause for the ductile fracture of the weld joint. A 40-µm wide intermetallic zone was identified along the fusion line having a distinct composition of Cr, Ni, and Mo. The corrosion rate of the pin gradually decreased from the undeformed zone of pure iron to the undeformed zone of stainless steel 316L. All metallurgical zones of the pin showed no toxic effect toward normal human osteoblast cells, confirming the ppb level of released Cr and Ni detected in the cell media were tolerable.

Impact of temperature on shear strength of single lap Al–Cu bimetallic joint

The paper presents the results of experimental investigations concerning the mechanical properties of aluminium–copper bimetal (Al–Cu) obtained by rolling. The basic mechanical properties of Al–Cu bimetal were determined, anisotropy of mechanical properties was examined, and hardening process was analysed and described. The analysis was also related to each component (layer) of bimetal, for which similar tests were conducted. The essential studies of aluminium–copper bimetal included shear strength tests of single lap joint under uniaxial tension. The tests analysed the effect of temperature of annealing and time on the maximum values of shear stresses (average), which occurred in the course of shearing of the adhesive layer connecting the components of bimetal. Microanalysis of the chemical composition at the border of phase separation was carried out, and thickness of diffusion layer generated at different temperature conditions was measured. The mechanism of joints failure was analysed, depending on the influence of temperature factors. It was found that the intermetallic zone was formed at the boundary of bimetal phase joint during structural changes. This zone was responsible for the change of mechanical properties of bimetallic lap joint and had a significant effect on its operating ability.

Hierarchical microstructure of explosive joints: Example of titanium to steel cladding

The microstructure of explosive cladding joints formed among parallel Ti and steel plates was examined by electron microscopy. The bonding interface and the bulk materials around it form pronounced hierarchical microstructures. This hierarchy is characterized by the following features: at the mesoscopic scale of the hierarchy a wavy course of the interface characterizes the interface zone. This microstructure level is formed by heavy plastic shear waves (wavelength≈0.5mm) which expand within the two metal plates during the explosion parallel to the bonding interface. At the micro-scale range, intermetallic inclusions (size≈100–200μm) are formed just behind the wave crests on the steel side as a result of partial melting. Electron diffraction revealed FeTi and metastable Fe9.64Ti0.36. Most of the observed phases do not appear in the equilibrium Fe–Ti phase diagram. These intermetallic inclusions are often accompanied by micro-cracks of similar dimension. At the smallest hierarchy level we observe a reaction layer of about 100–300nm thickness consisting of nano-sized grains formed along the entire bonding interface. Within that complex hierarchical micro- and nanostructure, the mesoscopic regime, more precisely the type and brittleness of the intermetallic zones, seems to play the dominant role for the mechanical behavior of the entire compound.

High effective organic corrosion inhibitors for 2024 aluminium alloy

Abstract The inhibiting effect of several organic compounds on the corrosion of 2024 aluminium alloy in neutral chloride solution was investigated in the present work. The candidates were selected based on the assumption that effective inhibitors should form highly insoluble complexes with components of AA2024. Along with organic complexing agents, the salts of rare-earth elements were included into screening electrochemical impedance spectroscopy (EIS) test for getting comparative data. Results of EIS analysis revealed three most effective organic inhibitors: salicylaldoxime, 8-hydroxyquinoline and quinaldic acid. Their anti-corrosion performance was additionally investigated via dc polarization, as well as localized techniques: scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy coupled with scanning Kelvin probe (SKPFM). Localized measurements at exactly the same microdimensional zones of the alloy before and after immersion into 0.05 M sodium chloride solution allowed tracing the evolution of the Volta potential, chemical composition, surface topography and formation of corrosion products on the surface and intermetallic inclusions during the corrosion tests. The results show that the quinaldic acid, salicylaldoxime and 8-hydroxyquinoline provide anti-corrosion protection for AA2024 forming a thin organic layer of insoluble complexes on the surface of the alloy. Inhibiting action is the consequence of suppression of dissolution of Mg, Al and Cu from the corrosion active intermetallic zones.

Untersuchungen zum Gefügezustand von Verbunden aus Kohlenstofffasern (T 800H) und der Magnesiumlegierung AZ91 / Investigations into the Microstructures of Carbon Fibre (T 800H)/ Magnesium Alloy (AZ91) Composites

Composites of T 800H carbon fibres and the Magnesium alloy AZ91 were produced by Squeeze Casting. As a result of this method of casting and the presence of the carbon fibres, segregation of the Magnesium alloy occurs whereby an intermetallic zone of Mg 17 AL 12 is precipitated around the carbon fibres. Electron beam microscopic investigations confirm the formation of needle-like phases of different morphology at the fibre-matrix interface, which differ from one another in their geometry and orientation. Needle-like phases with a length to diameter ratio UD of between 4 and 6 are found orientated parallel to the surface of the T 800H fibres, whilst needles with an UD ratio of between 20 and 25 are found positioned at angles between 45 and 135° to the fibre surface.

Kinetics of the isothermal spreading of tin on the air-passivated copper surface in the absence of a fluxing agent

A specially designed ultrahigh vacuum in situ surface analysis and wetting system has been constructed to study the spreading of liquid metal solders on carefully prepared and well-characterized solid substrates. Initial studies have been completed for the spreading of pure Sn solder on Cu substrates in the absence of any fluxing agent. Surface chemical analysis by X-ray photoelectron spectroscopy showed the as-received surface consisted of about 8 nm of Cu 2O. Solder spreading was performed under 50 Torr of highly purified He gas to allow for adequate thermal coupling between the solder and the substrate. Isothermal spreading experiments were performed on the as-received Cu surface in the temperature range between 262 and 372°C. Measurable solder spreading was observed on this surface even at temperatures only 30°C above the melting temperature of the pure Sn solder (232°C). The results of the isothermal experiments show that solder spreading on the as-received Cu surface is an activated process with an activation energy of 39.9±3.1 kcal mol −1 in the range of 262 to 327°C, and a 1/3-order dependence on spreading time. Between 327°C and 330°C, a discontinuity in the Arrhenius plot is observed. At 330°C and above, the spreading process is non-activated and shows a 1/5-order dependence on spreading time. It is believed that this discontinuity in spreading rates is a direct result of vacuum-assisted decomposition of the surface Cu 2O, with retention of a subsurface oxide. Similar experiments in an inert atmosphere glove box at atmospheric pressure do not show the spreading rate discontinuity, although overall spreading rates and kinetics are similar. The overall spreading process is believed to be facilitated through an oxide displacement reaction, where the spreading Sn reduces the surface Cu 2O to Cu and captures the oxygen to form SnO 2 as spreading proceeds. Metallurgical cross-section analysis after spreading on the as-received surface shows the expected formation of Cu–Sn intermetallic zones and a microstructure with no gaps at the Cu–Sn interface due to remaining patches of Cu oxide.

Intermetallic zone growth during MA of aluminium-titanium-silicon carbide composites: F.E. Wawner and T.D. Bayha (Lockheed Aero Systems Co, USA)

Intermetallic zone growth during MA of aluminium-titanium-silicon carbide composites: F.E. Wawner and T.D. Bayha (Lockheed Aero Systems Co, USA)