Interdendritic Zones Research Articles

Achieving high strength-ductility synergy in Mg-Gd-Zn-Zr alloy by controlling extrusion processes parameters

The high rare earth content in current magnesium alloys poses environmental and economic challenges. To address this issue, this study designs a Mg-7.5Gd-6Zn-0.5Zr alloy (GZ76, wt.%) with low rare earth content, high strength, and excellent ductility. The morphology of the as-cast GZ76 alloy is characterized by a dendritic structure consisting of an α-Mg matrix and interdendritic zones comprising W+I phases, interspersed with fragmentary Zn-Zr phases. Furthermore, the extrusion process is employed to meticulously control the microstructure and enhance the mechanical properties of the alloy. This research focuses on investigating the effects of extrusion parameters on magnesium alloys to optimize their extrusion processing conditions. Through systematic manipulation of the extrusion ratio and extrusion speed, a comprehensive analysis is conducted to examine their impacts on grain refinement, texture evolution, distribution of second phase, and mechanical properties of extruded magnesium alloys. The results indicate that due to the insufficient recrystallization process, the microstructure of the as-extruded GZ76 alloys exhibits a bimodal structure, encompassing both fine recrystallized grains and coarse unrecrystallized grains. At larger extrusion ratio, a faster extrusion speed leads to superior mechanical properties of the alloy. Conversely, at smaller extrusion ratio, a slower extrusion speed is more favorable for achieving higher strength. These findings provide valuable insights into optimizing the extrusion parameters for enhancing the performance of magnesium alloys in engineering applications.

Effect of Ce and solidification cooling rate on the microstructure and mechanical properties of AA2017 aluminum alloy

Controlling dendritic growth and grain size in new Ce-containing Al-based alloys becomes crucial due to new envisioned applications and Ce rising demand in casting processes. In the present work Ce effect on the 2xxx Al series microstructures at various industrial-scale solidification cooling rates was investigated. The directional solidification technique is crucial in this endeavor since can generate several solidified samples related to several cooling rates. The AA2017 alloy and a modified version containing 3 wt % of Ce were both produced under directional solidification and various microstructure aspects were characterized. The mechanical behavior was analyzed by microhardness and compression tests. The Ce addition reduced primary and secondary dendritic spacing without impacting grain size. Cells were only observed to form on the Ce-containing alloy at cooling rates of approximately 19 °C/s; while dendritic configurations dominated all other conditions. While round pockets composed of Al+Al2Cu+Mg2Si ternary eutectic formed the interdendritic zones in the AA2017 alloy, the AA2017-Ce alloy microstructure was mainly constituted by elongated AlCeSi + Al8CeCu4 interdendritic phases. Finally, the addition of Ce favored an increase in the microhardness and compressive strength values of the AA2017 alloy, which is attributed to the refinement of the solidification structure, as well as the formation of a greater fraction of secondary reinforcement phases.

Influence of Al addition on microstructure and electrochemical behaviour of CrMnFeCoNi high-entropy alloy

To develop new corrosion-resistant materials for structural applications, CrMnFeCoNiAlx high-entropy alloys (HEAs) are produced via semi-industrial induction casting. The study aimed to investigate the influence of Al content (x = 0–0.3) on both microstructure evolution and corrosion properties of the alloys. X-ray diffraction and scanning electron microscopy (SEM) analysis revealed that all the alloys exhibited a single-phase face-centered cubic structure, with dendritic (Fe, Co, Cr-rich) and interdendritic (Mn, Ni, Al-rich) regions distinguished by elemental segregations. Furthermore, the incorporation of Al atoms into the solid solution led to an increase in the lattice parameter, indicating alloy strengthening. The corrosion resistance of the CrMnFeCoNiAlx alloy improved with higher Al addition. Electrochemical polarisation tests demonstrated a slight increase in the corrosion potential (Ecorr) and a significant decrease in the corrosion current density (icorr) upon Al addition. Additionally, slower kinetics for pit nucleation (higher E'corr) were observed, particularly notable for x = 0.3. Analysis of the corroded surfaces revealed a mixed degradation mechanism, involving pitting corrosion and selective dissolution of the interdendritic zone, which decreased as the Al content of the HEA increased. These findings underscore the effectiveness of Al addition in not only enhancing the mechanical properties of the Cantor alloy through solid solution strengthening, but also improving its corrosion resistance.

Thermal cycling effects on the local microstructure and mechanical properties in wire-based directed energy deposition of nickel-based superalloy

In additive manufacturing, intrinsic heat treatments take place during deposition that affect the properties of AM-structures. In this work, the influence of thermal cycling on the local microstructure and mechanical properties of nickel-based superalloy in wire-based electron beam directed energy deposition (EB-DED) was investigated. Structures were fabricated using a continuous deposition strategy (CDS) and discontinuous interpass cooling strategy (ICS) revealing changes in thermal profiles, time-temperature history, and microstructure. An altered morphology along the build-up height and interdendritic zones enriched in Nb are formed. Nb and Mo did not show a clear trend of segregation along the build-up height. Lower fractions of the Laves phase and MCs are found for both configurations. Differences between deposition strategies and locations within AM-structures are found for the γ" and δ phase. The higher Nb content in the interdendritic zone promotes the precipitation of γ" and δ phase by shortening the aging times compared to wrought materials. The longer deposition times of ICS favour the precipitation of fine γ" in the interdendritic zone throughout the deposition height. In contrast, the short deposition time of CDS leads to an increase in temperature and a heterogeneous distribution of γ" along the height, i.e. coarsening of the γ" followed by a dissolution along the built-up height. The microstructural changes correlate with the mechanical properties. Structures fabricated with ICS exhibit homogeneous mechanical properties throughout, while the graded microstructure of CDS results in graded mechanical properties and decreasing strength throughout.

Study on the microstructure and wear resistance of AlCrCuFeNiTix high entropy alloys for surfacing welding

In order to investigate the effect of Ti element content on the microstructure and wear resistance of AlCrCuFeNiTix (x = 0, 0.3, 0.6, 0.9) high entropy surfacing alloy, a melting electrode gas shielded welding technology was used to prepare AlCrCuFeNiTix high entropy surfacing alloy on the surface of carbon steel plates. The microstructure, phase composition, and wear resistance of the alloy were analyzed. The results show that the phase composition of the surfacing alloy becomes a BCC+FCC solid solution phase, with a much higher content of BCC phase than FCC phase. The microstructure consists of disordered BCC phase rich in Fe and Cr, ordered BCC phase rich in Al and Ni, and FCC phase rich in Cu. The microstructure exhibits typical dendritic (DR) and interdendritic (ID) structures. With the increase of Ti element, hard Fe2Ti phase precipitates in the interdendritic zone, and the micro hardness of the alloy shows an increasing trend. The maximum hardness can reach 636 HV, which is 2.4 times that of the base material. With the increase of Ti element, the friction coefficient of the alloy shows a trend of first decreasing and then increasing, and the wear amount first decreases and then increases. When Ti is 0.6, the wear resistance of the high entropy surfacing alloy reaches its best.

A novel prediction model of the freckle defects for single-crystal superalloy blades

The freckle is a typical surface defect formed during the directional solidification of SC (single crystal) components of Ni-based superalloys. It generally appears as a long and narrow trail of equiaxed grains aligned roughly parallel to the direction of gravity, which breaks the integrity. Once appears, the freckle can never be avoided by further treatment. With the turbine blade requirements increasing, the state-of-the-art methods include adding more refractory elements into Ni-based SC superalloys, and the design of blades with a more complex geometric shape make the freckle defects grow easier at the special surface zones. This leads to a significant challenge in controlling grain defect formation in SC blades and vanes for freckles. The current consensus to freckle formation is described as the Rayleigh-Taylor instability (RTI) flow that occurred in the interdendritic zone. During solidification, the compositional segregation (CS) occurred as soon as the solid interface forwarding led to the density changes between the interdendritic melting phases and the residual liquids. For nickel-based superalloys, the enrichment of low-density solutes like Al, and Ti at the interdendritic zone will make the liquid lighter. However, the widely used Ra model can’t correctly match the freckle tendency of the components with complex shapes (called geometrical effects of freckles), especially for blades. Recent reports indicate that the freckles occur at the preferred positions in the casting. In this work, a novel model is designed to quantitatively discuss the geometrical effects on freckle formation and to combine existing Ra number models with solidification models to enable freckle predictions at a smaller scale. The proceeding of this work can make the design of complex blades easier.

Microstructure evolution and mechanical properties of wire-fed electron beam directed energy deposition repaired GH4169 superalloy

In this paper, the microstructural evolution and failure behavior of GH4169 superalloy repaired using wire-fed electron beam directed energy deposition (EB-DED) are investigated in detail. Results show that in the deposited zone (DZ), the Laves phase is formed in the interdendritic zone, and the γ'' phase and γ′ phase precipitate around the Laves phase and are distributed gradiently along the building direction. In contrast, the substrate zone (SZ) is composed of fine equiaxed grains and uniform distributed γ'' and γ′ phases. Direct aging heat treatment cannot effectively dissolve the Laves phase, but can further precipitate the γ'' and γ′ phases, resulting in an increase in yield strength and ultimate tensile strength and a decrease in elongation. During the plastic deformation process, dislocation activity preferentially occurs in the γ matrix and forms accumulation at the Laves/γ interface, leading to the formation of cracks in the DZ, so that all tensile samples fail in the DZ. In addition, this study further elucidates the fracture mechanism of the Laves phase within grains and at grain boundaries.

Experimental and Numerical Investigations of the Fatigue Life of AA2024 Aluminium Alloy-Based Nanocomposite Reinforced by TiO2 Nanoparticles Under the Effect of Heat Treatment

Using aluminium metal matrix nanocomposites has recently gained increased attention in the industry due to their high strength and ductility. In this paper, TiO2 nanoparticles in volume percentages of 5 wt. % were added to the AA2024 alloy using the stir casting method. Using a novel powder injection system, TiO2 nanoparticles with an average particle size of 30 ± 5 nm was added to the matrix. The influence of TiO2 content on the fatigue life before and after heat treatment was studied. The results showed the fatigue properties of AA2024 with TiO2 nanoparticles increased after heat treatment. The optimum improvement in fatigue properties was obtained at 5 wt. % TiO2 after heat treatment, with an improving fatigue life in 14.71% compared with sample based. This is due to an increased number of fine precipitates besides its uniformly distributed after heat treatment. The fatigue life of the composite materials with added nanoparticles was investigated using a finite element-based ANSYS workbench. There was a good match between what happened in the experiments and what happened to the numerical fatigue strength. For the composite materials, the difference between the experimental and numerical values of fatigue strength was not greater than 4% for the matrix. The results also, indicated that, after ageing, the precipitate-free zone at the inter-dendritic zone disappeared or became smaller. However, after adding 5 wt. % of titanium and, also, performing heat treatment, it is not possible to precipitate the Al2CuMg precipitates, and, instead of it, the Al3TiCu and Al7TiCu phases precipitates have been formed.

Exploring the potential of Mg-Zn-Mn-Ca/ZnO composites as a biodegradable alternative for fracture fixation: microstructural, mechanical, and in-vitro biocompatibility analysis

The current research investigates the microstructural, mechanical, in vitro degradation, biocompatibility, and in silico biomechanical behaviour of highly alloyed Mg-Zn-Mn-Ca quaternary system reinforced with ZnO nanopowder as candidate material for resorbable fixation devices. The as-cast composite materials showed dendritic microstructure comprising of α-Mg as major constituent and Mg7Zn3 and Ca2Mg6Zn3 phases distributed in interdendritic zones, as revealed by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The addition of ZnO led to a 17% and 22% increase in ultimate and yield strengths in tension and a 24% and 27% enhancement in ultimate compressive and compressive yield strengths, respectively. The mechanical strengthening and observed tension–compression reversed yield asymmetry strongly correlated with the lattice distortion (c/a ratio) resulting from the macroalloying. The amplitude-dependent internal friction confirmed the presence of immobile obstacles to dislocations and their role through their hysteretic-type anelastic response. The in vitro degradation results revealed corrosion barrier effect of secondary phases. The cell adhesion, viability, and cytoskeleton observations favoured their biocompatibility except for hemolysis rate. The finite element results showed reduced stress-shielded zone for developed materials indicating the favourable mechanical environment for peri-implant tissues at fracture interface required for faster fracture healing.

Effect of Mo on high entropy Ti-Nb-Zr-Ta alloy: Phase equilibria, microstructure and mechanical properties

Thermal and mechanical properties of Ti-Nb-Ta-Zr high entropy alloys are often influenced by element content and manufacturing routes, producing significant differences between mechanical properties and microstructure. This work presents a Ti-Nb-Ta-Zr alloy in which Mo is added by adjusting the composition with phase equilibria simulation, improving the mechanical properties based on a mixture of two chemically different solid solutions (BCC1 and BCC2). The materials were produced by arc-melting suction casting. Characterization of the dendritic and interdendritic zones was carried out by means of X-ray spectroscopy, indicating the segregation of Ta and Nb in BCC1 and Zr and Ti in BCC2 phases. The dislocation density increased preferentially in the interdendritic Zr-Ti rich zones. The mechanical properties results were related to the chemical differences between the BCC1 and BCC2 lattice parameters induced by the Mo addition. With Mo segregating between both BCC cells, the resulting microstructure increased the yield strength, being confirmed with the kernel average maps, which showed that, after compression tests, the interdendritic zone accumulated a high density of dislocations, resulting in the segregation of Ti and Zr, affecting the mechanical response of Mo containing alloy.

Studies on the Effect of Substrate Preheating, Interlayer Dwell, and Heat Treatment on Microstructure, Residual Stress, and Mechanical Properties of IN625 Superalloy Built by Direct Metal Deposition

Abstract In this investigation, IN625 alloy samples were processed by the directed energy deposition (DED) approach under various metal deposition strategies such as substrate preheating, interlayer dwell and with combined substrate preheating, interlayer dwell, as well as postheat treatment. The processed sample’s microstructural characteristics, residual stress, microhardness, and tensile properties are assessed in comparison to the manufacturing strategies. Rapid heat dissipation caused finer microstructure near the substrate. There is a growth of columnar grain structure epitaxially in the build direction. The progressive microstructure change seen in the build direction across the cross section was due to the gradual rise of heat accumulation between subsequent layers. The interdendritic zones contained Laves phases. Laves phases have a high Nb, Mo, as well as Si content, according to the energy-dispersive spectroscope (EDS) spectrum. The field emission scanning microscopy (FESEM) microstructural morphology of the deposited samples after their postheat treatment has shown a new microstructure with the combination of equiaxed (recrystallized) and columnar dendritic structure with the reconstruction of columnar dendritic solidification microstructure into equiaxed grains. Heat treatment caused the Laves phases to dissolve in the matrix of IN625 alloy, which led to the precipitation of nanometric γ″ phases. The deposition strategies with substrate preheating significantly decreased the residual stress with moderately improved mechanical properties. The combination of substrate preheating, interlayer dwell, and postheat treatment has shown an outstanding reduction of residual stress along with a remarkable improvement in tensile strength with the retainment of an equivalent ductility compared with other strategies.

Microstructure evolution and high temperature wear resistance of in-situ synthesized carbides reinforced NiCoFeCrSiMo high entropy alloy coatings fabricated by laser cladding

In this work, we reported a novel strengthening strategy of NiCoFeCrSiMo high entropy alloy by high density in-situ synthesized carbides. The external WC particles were introduced into the laser molten pool and basically dissolved which facilitate the in-situ reactions of carbides. The microstructure of composite coatings consists of high-density carbides which formed dendrites, while the FCC based solid solution matrix of high entropy alloy filled the inter-dendritic zone. The original added WC particles were almost dissolved in the laser pool and M6C type carbides or M2C carbides were in-situ synthesized. The composite coating was strengthened by dislocation pinning and plugging effects. Notably, the average microhardness of the composite coating can reach as high as 947 HV, while the friction coefficient of high entropy alloy coatings with 50 % WC addition could be as lower as 0.2 at 600 °C. The wear surface morphology analysis shows that the wear mechanism of M6C/FCC composite coating was adhesive wear and abrasive wear. The results in this work may provide some new thoughts for the design of ceramic particles reinforced HEA composite coatings.

Elucidating laser directed energy deposition based additive manufacturing of copper-stainless steel functionally graded material: Processing and material behavior

Copper (Cu)-stainless steel (SS 304L) multi-material is enduring research topic for various engineering applications such as tooling industry, aerospace, power-generation and cryogenic applications. Laser directed energy deposition (LDED) based additive manufacturing is a one of the promising technologies for fabricating Cu-SS multi-material component. However, LDED of Cu-SS is difficult due to the significant difference in thermo-physical properties and poor solubility of Cu and Fe. One of the methods to overcome this issue is adopting a functionally graded material (FGM) approach. In this pretext, the fabrication of Cu-SS FGM using the LDED process is taken up in the present study with three different Cu compositional grading approaches, such as direct (GD100Cu), 50 % (GD50Cu) and 20 % (GD20Cu). The LDED process windows for single tracks and bulk deposition of Cu-SS FGM are identified by varying the laser power, scan speed and composition of Cu and SS304L. Subsequently, the identified process window is used to deposit bulk structures of Cu-SS FGM. The LDED-built Cu-SS FGMs are characterized in terms of build quality, chemical composition, microstructural evolution and mechanical behavior. Microscopic analysis reveals, the defect-free deposition of GD100Cu and GD50Cu, at identified process parameters. For GD20Cu, the micro-crack formation in the graded region and inter-layer porosity in the Cu-rich region are two competing phenomenon, and it is observed that layer-wise increase in laser power and interlayer delay leads to minimum crack density and lower porosity. Further, increase in Cu content leads to significant change in microstructural morphology from columnar dendrites to fine cellular morphology. In Cu-SS FG structures, the chemical composition and mechanical properties are found to be changing gradually. Further, obtained ultimate tensile strength (UTS) of GD100Cu and GD50Cu is found higher than GD20Cu and the mode of failure is found to be ductile. The improved UTS in GD100Cu and GD50Cu in comparison with pure Cu arises due to formation of nano precipitate of Cu in the inter-dendritic zone of Fe rich phase. This establishes the suitability of LDED for building FG Cu-SS components at GD50Cu over GD20Cu.

Design of Fe36.29Cr28.9Ni26.15Cu4.17Ti1.67V2.48C0.46 HEA using a new criterion based on VEC: Microstructural study and multiscale mechanical response

The present work updated empirical parameter ranges with a high adjustment to the experimental results as obtained by the means of the exploratory data analysis (EDA) method. A new high entropy alloy with FCC structure reinforced by precipitation of intermetallic phases fabricated by vacuum-argon induction melting was designed and modeled. The main results showed that the valence electron concentration (VEC) is the predominant empirical phase prediction parameter in high entropy alloys and that the lattice packing factor is necessary to determine the presence of intermetallic phases effectively. Phase stability ranges based on VEC associated with the base crystal structures and the presence of intermetallics corroborated computationally by CALPHAD and experimentally were reported. The interdendritic zone proved to be a preferential precipitation zone with precipitates of σ, TiC, and γ' phases. The γ' phase showed a size difference between the dendritic and interdendritic zone associated with diffusive Ti mechanisms. The nanoscale mechanical response determined that dislocation creep and reinforcement in the interdendritic zone are predominant creep mechanisms that obtained an effective entanglement of the dislocations increasing the strain hardening coefficient. The mechanical response of the alloy obtained is superior to the average of the alloys with FCC structure. It maintains a high ductility that allows reaching an energy absorption and damage tolerance of 43.56 GPa% showing severe plastic slip lines being in the range of use for aerospace applications and hydrogen tanks.

Формирование биметаллического материала Ti–Al методом проволочного электронно-лучевого аддитивного производства

Currently, there is a request from aerospace and aircraft for the construction materials with sufficiently high mechanical strength, thermal creep, corrosion and oxidation resistance. The conventional alloys used for these purposes are too heavy. At the same time, alternative light materials such as Ti–Al-based alloys have many flaws, when they are produced by conventional methods. This work considers the possibility to produce the Ti–Al-based alloys by the method of a wire-feed electron-beam additive manufacturing (EBAM). We study the chemical and phase compositions, microstructure and microhardness of a bimetallic Ti–Al alloy, obtained by this method. It is found the formation of five characteristic regions between titanium and aluminum parts of the bimetallic billet. The mixing zone consists of TiAl and TiAl3 intermetallics, that is confirmed by the investigation of microstructure, chemical and phase compositions. According to XRD (X-ray diffraction) and EDS (energy-dispersive X-ray spectroscopy) analyses, it can be assumed that TiAl intermetallic prevails over TiAl3 one. The average microhardness of the mixing zone equals to 450 HV (≈4.4 GPa). This zone has developed dendritic microstructure, and even distribution of the phases without link to dendritic and inter-dendritic zones. The cracks appearing in this area are filled with the material of the upper layers, so the whole material is poreless and defect-free. Thus, the results of this work have shown a fundamental possibility to produce the intermetallic Ti–Al alloys with the use of the EBAM.

ИССЛЕДОВАНИЕ СВОЙСТВ И СТРУКТУРЫ АЛЮМОМАТРИЧНЫХ КОМПОЗИТОВ, АРМИРОВАННЫХ ЧАСТИЦАМИ TiO2

Alumina-matrix composite materials based on the AA2024 alloy and TiO2 nanoparticles varying from 0 to 7.5 wt. % have been obtained. A study of hardness and wear was carried out and it was found that increasing the content of titanium oxide nanoparticles from 0 to 5 wt.% leads to an increase in hardness from 39 to 64 HRB, with a further decrease to 38 HRB while the wear rate decreases in reverse order. The structure of the material and the wear surface were studied by optical and scanning electron microscopy. It is shown that the wear surfaces have an uneven structure, which indicates that the wear rate is the result of various failure mechanisms. It has been established that the structure of the alloy consists of numerous interdendritic matrix composites and fine precipitates scattered throughout the volume. It is shown that the interdendritic zone is bordered by Al7Cu2Fe and Al(Cu, Mn, Fe, Si). Intermetallic composites Al3TiCu and Al9TiFe have been revealed

Effects of Metal and Fluoride Powders Deposition on Hot-Cracking Susceptibility of 316L Stainless Steel in TIG Welding

This study aims to investigate the effects on the hot cracking susceptibility of fluoride powders such as CaF2, NaF, LiF, and metal powders such as Mn, Ti, Nb and mixed Ti-Nb deposited on the 316L stainless steel during the TIG (Tungsten Inert Gas) welding process. A self-restraint hot cracking bench test using specimens of trapezoidal shape and 3 mm of thickness was selected. The obtained results of the weldability with the different powders were compared with those obtained with the conventional TIG parent-metal weld. The susceptibility to hot cracking was evaluated by the length of the crack and by the critical width at the end of the crack propagation. The formed cracks were first revealed by the liquid penetrant test, and then the surfaces of cracks were observed and analyzed by SEM-EDS-XRD tools. Among the powders tested, single Nb powder and the mixed flux of 80% Nb + 20% Ti exhibited the lowest crack length. The crack propagation ended at 22 mm of length and 30.8 mm of width. The analyses of the fracture surfaces of cracks revealed the presence of Niobium carbide (Nb2C), titanium, chromium, niobium oxide (TiO0.6Cr0.2Nb0.0202) complex compounds and cementite (Fe3C) at the interdendritic zones.

Effects of Ti content on the microstructure, mechanical properties and corrosion behavior of TixZrNb alloys

The study reports the effects of Ti content on microstructures, mechanical properties and corrosion behavior of the TixZrNb alloys. The BCC phase TixZrNb (x = 1, 1.5 and 2 mol) alloys have a typical dendritic morphology. With the increase of Ti content, the dendrite arms grow up, and the area of the inter-dendritic zone decreases. Furthermore, the segregation of Zr elements forms the βZr phase. Ti1ZrNb alloy has the highest yield strength of 516 MPa and hardness of 254 HV, and the Ti1.5ZrNb alloy shows the best elastic deformation performance (n = 0.46). The potentiodynamic polarization curve and electrochemical impedance spectroscopy show that Ti1.5ZrNb alloy has better electrochemical corrosion behavior than other alloys in 3.5 wt.% NaCl solution at 25 °C. The cyclic polarisation curve shows that Ti2ZrNb alloy is more prone to pitting corrosion in 3.5 wt.% NaCl solution.

Insight into the passivation and corrosion behavior of additive manufacturing repaired single crystal superalloy

The passivation and corrosion behaviors of additive manufacturing repaired Ni-based single crystal superalloy were analyzed by comparison with the substrate. We found that the cladding layer is comprised of fine cellular dendrites (FDs) and fine cellular interdendritic zones (FIDZs) with abundant nano particles of γ′(Ni3Al) phase. The cladding layer possesses thicker passive film which gives better protection to the cladded component. The FIDZs are more sensitive to corrosion because of the dissolution of Nb-rich and Cr-Mo depleted zones in FIDZs. The γ/γ′ couples in the substrate tend to form mesh-like corrosion morphologies due to the selective dissolution of γ′ phases.

Primary microstructure characterization of Co-20Ni-9Al-7W-3Re-2ti superalloy

The characterization of the primary microstructure of the new Co-based superalloy of Co-20Ni-9Al-7W-3Re-2Ti type was shown in this article. The investigated alloy was manufactured by induction melting process from pure feedstock materials. The fundamental technological problem related to Co-Al-W-X multicomponent alloys casting process is a strong susceptibility to interdendritic segregation of alloying elements, especially tungsten and rhenium. The performed analysis revealed that the observed effect of alloying elements segregation was detectable and much stronger than for Co-9Al-9W and Co-20Ni-7Al-7W alloys, related to titanium, nickel, and aluminium migration to inter-dendritic spaces. Consequently, the tungsten concentration gradient between dendritic and interdendritic zones was higher than for Co-9Al-9W and Co- 20Ni-7Al-7W alloys. The same situation was in the case of rhenium and cobalt, but Co concentration in the interdendritic zone was only slightly lower.