Duplex Phase Research Articles

Remarkable cavitation erosion–corrosion resistance of CoCrFeNiTiMo high-entropy alloy coatings

A CoCrFeNiTiMo high entropy alloy (HEA) coating was prepared onto a Ti-6Al-4 V substrate using the double cathode glow discharge method. This innovative HEA coating exhibited a duplex phase microstructure, composed of a BCC-structure solid solution phase and a tetragonal structured intermetallic phase, Co2Mo3, and possessed high hardness, high load bearing capacity and strong adhesion to the substrate. The HEA coating underwent much less severe cavitation erosion damage in a 3.5 % NaCl solution relative to Ti-6Al-4 V according to the results of electrochemical measurements and the cumulative weight loss, because of its unique combination of excellent mechanical properties and high corrosion resistance.

Microstructure and tensile properties of duplex phase Al0.25FeMnNiCrCu0.5 high entropy alloy fabricated by laser melting deposition

Duplex phase Al0.25FeMnNiCrCu0.5 high entropy alloy (HEA) was fabricated successfully from elemental powder blends through a Laser Melting Deposition (LMD) process. The structural characteristics and tensile properties of the alloy have been studied by XRD, optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile test. The alloy consists of (FCC1 + FCC2 + BCC) phases with lattice parameters of 3.62 Å, 3.58 Å and 2.85 Å, respectively. The yield strength, tensile strength and elongation of LAM Al0.25FeMnNiCrCu0.5 at room temperature are 636 MPa, 1052 MPa and 24.5%, respectively. The LMD Al0.25FeMnNiCrCu0.5 alloy presents an outstanding combination of high tensile strength and good ductility.

Thermal stable hierarchical 3D nanolayered Zr-2.5Nb

Hierarchical 3D nanolayered Zr-2.5Nb has high strength, strain hardening and ductility because of the 3D α/β-Zr networks, which is a promising structural material for nuclear reactor. However, excellent thermal stability is of great importance for materials service in nuclear reactor. Here, we study thermal stability of the hierarchical 3D nanolayered Zr-2.5Nb. After 1 h annealing at various temperatures below 700 °C, α-Zr layer thickness only has a slightly increase. The hardness, yield strength and uniform elongation of the sample remain unchanged. Interface orientation relationship and layer morphology keep stable after annealing, indicating high thermal stability. The duplex phase structures coarsen quickly after annealing at 1000 °C. An obvious increase in hardness and yield strength was observed when sample annealed at 300 °C, which relates to the precipitation of ωiso phase in β-Zr. Controlling the number of ωiso phase is likely a strategy to further enhance the strength and ductility of the alloy.

Effects of Ag-Rich Nano-Precipitates on the Antibacterial Properties of 2205 Duplex Stainless Steel

The effects of the addition of silver on the microstructural variation and antibacterial performance of 2205 duplex stainless steel after solution and aging treatment were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, and antibacterial testing. The microstructure showed that 2205Ag is composed of a ferrite (α) + austenite (γ) duplex phase and Ag-rich nano-precipitates (Ag-NPs). The morphology of the Ag-NPs varied from spherical to polygonal after aging treatment at 450 °C for 4 h. These precipitates were identified as face-centered-cubic structures with a lattice parameter of a = 0.354 nm and a mismatch of δ = 0.84% relative to the austenite matrix. Notably, 2205Ag with polygonal Ag-NPs exhibited excellent antibacterial properties that were superior to those of 2205Ag with spherical Ag-NPs.

Remarkable bactericidal traits of a metal-ceramic composite coating elated by hierarchically structured surface.

SummaryA ceramic-based coating with a hierarchical surface structure was synthesized via solid-state reaction enabled by a double cathode glow discharge technique. This innovative coating comprises two distinct layers, specifically an outer layer with a well-aligned micro-pillar array and a dense inner layer. Both are composed of a face-centered cubic Cu(Co,Ni,Fe) solid solution phase together with a spinel-type Fe(Al,Cr)2O4 oxide. This coating exhibits superhydrophobicity and, yet, a very strong adhesion to water, i.e., the so-called “rose petal effect”. This coating also exhibits highly efficient antibacterial ability against both Staphylococcus aureus and Escherichia coli bacteria under both dark and visible light conditions. The excellent antibacterial property originates from the synergistic effects through the release of Cu ions coupled with photothermal activity upon light activation.

Fine-Grained FeCoNi(CuAl)x High Entropy Alloys: Phase Transformation, Microstructure Evolution and Mechanical Properties

A series of fine-grained FeCoNi(CuAl)x (x=0, 0.4, 0.6, 0.8, 1.0) medium-entropy alloy (MEA) and high-entropy alloys (HEAs) were fabricated by Mechanical Alloying (MA) and Spark Plasma Sintering (SPS). The effect of Al and Cu content (x) on phase composition, microstructure and mechanical properties of the alloys was investigated. Experimental results show that the crystal structure of FeCoNi(CuAl)x alloy transforms from single FCC phase for x=0 to FCC+BCC duplex phases for x=0.4~1.0, with the fraction of BCC phase gradually increasing with the increase of x. Adding a low content of Al and Cu elements to FeCoNi alloy can significantly hinder the grain growth during sintering process, the average grain size of FCC phase decreases from 0.95 to 0.30 µm at x=0.4. However, the grain sizes of FCC and BCC phases gradually grow up when x increases from 0.4 to 1.0. The variation in grain size indicates that the atomic diffusion rate of sintered alloy may be influenced by the sluggish diffusion effect in HEA as well as the content of Al and Cu with lower melting points. Mechanical properties of the HEAs are mainly affected by the volume fraction of BCC phase. The compressive yield strength and hardness of HEAs are improved at first and then slightly reduced, while the plasticity drops down continuously with the increase of x. The bulky HEA achieved excellent comprehensive mechanical properties with a compressive yield strength of 1467.7 MPa and plastic strain to failure of 24.9 % at x=0.6, due to the fine duplex microstructure.

Microstructure evolution and mechanical properties of AlxCoCrFeNi high-entropy alloys by laser melting deposition

AlxCoCrFeNi (x = 0, 0.2, 0.45, 0.7 and 1) high entropy alloys (HEAs) have been successfully synthesized by laser melting deposition (LMD). It is found that the microstructure of LMD-CoCrFeNi HEA with increasing the content of Al has been transformed from a single face-centered cubic (FCC) phase to mixture of FCC + BCC duplex phases, and then to body-centered cubic (BCC/B2) phases. The addition of Al (Al0.2, Al0.45 and Al0.7) remarkably improved the yield strength σ0.2 (from 138 MPa to 185 MPa, 262 MPa and 771 MPa) and the tensile strength σt (from 634 MPa to 675 MPa, 863 MPa and 1171 MPa) of the samples, with the prize of plasticity decrease from 46% to 45%, 41% and 11% in tension. This work provides an approach of LMD-fabricated CoCrFeNi-based HEAs with different Al addition to accommodate the microstructure and mechanical properties, and insights into the correlation of mechanical properties with the solid solution strengthening or/and the precipitation of hardening phase.

Microstructural evolution and mechanical behavior of a novel heterogeneous medium Mn cold-rolled steel

A novel heterogeneous medium Mn steel with a nominal composition of Fe-0.18C-7.8Mn-1.65Al-0.04Ce wt.% is successfully fabricated by introducing various nucleation energy barriers for reverse austenite in a cold-rolled specimen prior to final annealing. The obtained steel demonstrates a ferrite and austenite duplex phase with multiple morphologies (i.e., granular, block-shaped, and lath-like), dispersed grain size, and heterogeneous chemical components. The heterogeneous microstructure yields superior synergy of 1060 MPa yield strength, 1270 MPa tensile strength, and 54.5% total elongation. The tensile behavior and microstructural evolution of the fabricated heterogeneous steel are investigated in detail. The stacking fault and dislocation accumulations are found to dominate during the initial deformation stage, and granular austenite transforms into martensite in the intermediate strain stage. Finally, block-shaped and lath-like austenite undergoes a phase transformation. Moreover, the back stress caused by the heterogeneous microstructures significantly improves the yield strength and work hardening ability of the heterogeneous specimen. Therefore, the combination of successive transformation-induced plasticity (TRIP) effect, dislocation strengthening, and back stress hardening contributes to the outstanding mechanical properties of this steel.

Ultrasonic Cavitation Erosion Behavior of AlCoCrxCuFe High Entropy Alloy Coatings Synthesized by Laser Cladding.

Cavitation corrosion resistant coatings are an excellent solution to the cavitation corrosion problem. High entropy alloys provide a new possibility for cavitation resistant coatings due to their excellent comprehensive performance. Laser cladding was employed to synthesize AlCoCrxCuFe (x represents the Cr concentration, x = 0.5, 1.0, 1.5, 2.0) high entropy alloy coatings (HECs) on AISI 304 steel. The phase transformation, microstructure, micro-mechanical properties, and cavitation erosion performance of HECs were studied. Results showed that AlCoCrxCuFe HECs were composed of BCC and FCC duplex phase. The microstructure of HECs showed a typical dendritic structure. The composition segregation of interdendrite structures was observed. Cavitation erosion resistance represented by 20 h volume loss was decreased with the increase in Cr content. AlCoCrxCuFe HECs with the lowest chromium content (AlCoCr0.5CuFe) showed the best cavitation erosion resistance among all samples. The cavitation resistance of AlCoCrxCuFe HECs has good correlation with the mechanical parameter /( is nanohardness, is elastic modulus) and phase formation parameter δ (δ is atomic radius difference). The surface after 20 h of cavitation erosion testing exposed the dendritic structure of BCC phase, which was caused by the destruction of the interdendrite structure by cavitation impact.

Unveiling segregation-induced evolution in phase constitution of Cu-containing high-entropy alloys

A theoretical investigation of Cu segregation effect on phase constitution, magnetic, and mechanical properties of FeCoNi(CumAl)x high-entropy alloys is presented. Results show that the homogenous FeCoNi(Cu1.0Al)x only exists as a single face-centered cubic phase at arbitrary temperatures. The level of Cu-segregation determines the phase evolution amongst inhomogeneous single phase (0.75 ≤ m < 1.0), duplex phase (m « 0.75), and triple phase (m ≈ 0.75). Our results reproduce the observation. Only face-centered cubic phase can be formed for FeCoNi(CumAl)x with either rather low or extreme high content of (CumAl) even though the segregation occurred. The Cu addition lifts the total magnetic moments by enhancing the local magnetic moment of Fe, Co and Ni. The serious Cu segregation in the duplex-phase HEAs induces the decrease of ductility of fcc and bcc phases. The increasing Cu enhances the strength of Cu-rich fcc phase and the decreasing Cu weakens that of Cu-poor bcc phase.

Stress-assisted microbiologically influenced corrosion mechanism of 2205 duplex stainless steel caused by sulfate-reducing bacteria

In the present work, we studied the stress-assisted microbiologically influenced corrosion mechanism of 2205 duplex steel caused by sulfate-reducing bacteria (SRB) in simulated seawater environment. The results suggested that SRB have a significant influence on the pitting behavior of 2205 DSS, and stress promotes the MIC behavior. The mechanism proposes that the ferrite phases and high-residual stress regions manifest as the preferential anodic electron donor for SRB respiration due to the galvanic effect caused by the composing duplex phases, high-stress regions and low-stress regions; this outcome leads to the preferential dissolution of ferrite phases and high-stress regions.

Bioinspired design and toughening mechanism of the TC4-(γ-TiAl/α2-Ti3Al) laminated composite fabricated by spark plasma sintering

Inspired by nature, new bioinspired TC4-(γ-TiAl/α2-Ti3Al) laminated composite with nacre-mimetic lamellar and brick-and-mortar architectures was fabricated by spark plasma sintering for the first time. The results indicated that the composite displayed a unique micro-laminated structure, composing of alternating γ-TiAl/α2-Ti3Al duplex phase alloy layer and TC4 titanium alloy layer. The composite showed a significant increase in fracture toughness while maintaining appropriate flexural strength at room temperature. Bioinspired design played an important role in toughening by complicated crack propagation, interconnecting structure, and synergistic effects of layers.

Microstructure and mechanical properties of dissimilar friction stir welds in austenitic-duplex stainless steels

We produce defect-free dissimilar friction stir welds between 1.86 mm-thick 2205 duplex stainless steel (DSS) and 1.95 mm-thick 304 austenitic stainless steel (ASS). The refined grain structure in the stirring zone (SZ) has three typical regions. The duplex phase region (DPR) and the austenite phase region (APR) have similar microstructures as the SZ of 2205 DSS welds and 304 ASS welds, respectively. The mixed region (MXR) has a smaller ferrite volume fraction (less than 25%) than the 2205 base metal (BM, 46.0%), whereas the average grain size of ferrite (0.82 μm) and austenite (0.83 μm) in the MXR is significantly smaller than that of austenite grains (2.32 μm) in the APR. The evolution of the corresponding microstructure and the diffusion of elements within the typical regions are interpreted according to experimental observations and phase diagrams. Due to the grain refining, the MXR (287.5 Hv) and the DPR (298.5 Hv) both have a higher microhardness than 2205 BM (252.7 Hv). The APR (226.5 Hv) also has a higher microhardness than 304 BM (189.7 Hv). The tensile tests indicate that the dissimilar welds have a good ductility and a higher tensile strength (905 MPa) than the 304 BM (783 MPa).

Microstructure authentication on mechanical property of medium carbon Low alloy duplex steels

The present study emphasizes on the mechanical characterization of medium carbon AISI 1040 and 4140 duplex steels. AISI 1040 and 4140 steels are generally used as structural steels for varying applications, ranging from construction field material to heat resistant parts for moderate temperatures applications. The objective of the present work is to corroborate microstructure and mechanical properties by varying the intercritical temperature in duplex steels. The normalized specimens of as bought steel are heated to a different intercritical temperatures (750, 770, and 790 °C), followed by isothermal holding for 2 h and quenching to room temperature develops duplex phase structure. This treatment grows microstructure with a variable quantity of martensite embedded in a fine ferrite matrix. For the same carbon content in the duplex alloy steels, the addition of Cr, Mo, Si, and Mn, increases the tensile strength and hardness of the material but decreases the toughness and ductility. As the intercritical temperature varies, the amount of martensite and ferrite phases present in the duplex steel also varies, which intern alters the strength and hardness of the material. Duplex steels have higher strength and hardness than as bought, even though the impact strength and ductility are poor. Microhardness is used to identify the micro phases present in the material viz., ferrite and martensite. Microstructure shows the evidence of the formation of a duplex structure with a variation in the amount of aforesaid phases. The result obtained validates the influence of microstructure on mechanical properties of AISI 1040 and 4140 steels.

Thermoelectric behaviour with high lattice thermal conductivity of Nickel base Ni2CuCrFeAlx (x = 0.5, 1.0, 1.5 and 2.5) high entropy alloys

In this article, investigated Ni-based Ni2CuCrFeAlx (0.5 ≤ x ≤ 2.5) alloys were prepared by powder metallurgy route. On varying x, the alloy changes from single FCC to single BCC with a transition duplex in FCC/BCC region. The severe scattering effect of lattice in these high-entropy alloys was observed by weak x-ray diffraction intensities. Also, owing to this lattice effect, the observed electrical and thermal conductivity are much smaller than those of pure metal components. On a contrary, because of additional scattering effect of FCC/BCC phase boundaries in the alloys, both conductivity values are even higher than those in the duplex phase region. Present work explains the properties of temperature dependant High-Entropy alloys (HEA’s) as a potential new class of thermoelectric materials. The thermoelectric properties can be controlled significantly by changing the valence electron concentration via appropriate substitutional elements. Both the electrical and thermal properties were found to decrease with a lower VEC number. These findings highlight the possibility to exploit HEA’s as a new class of futuristic high temperature TE materials.

Static Recrystallization Behavior and Mechanical Properties of Heterogeneous Nanostructured Duplex Phase Stainless Steel

Static Recrystallization Behavior and Mechanical Properties of Heterogeneous Nanostructured Duplex Phase Stainless Steel

Simultaneously enhancing the strength and ductility of lamellar Ti–6Al–4V alloy via designing hierarchical 3D nanolayered structure

Ti–6Al–4V alloys with a hierarchical 3D nanolayered structure, comprised of nanoscale (α+β) duplex phases, were successfully produced by a conventional dynamic thermal–mechanical phase transformation (DTMPT) process. The Ti–6Al–4V alloys with hierarchical 3D nanolayered structure exhibited simultaneously enhanced strength and ductility as compared to the coarse-lamellar material of the same chemistry. The strength and ductility enhancement may derived from high interface density and unique interface structure. A formation mechanism of hierarchical 3D nanolayered structure has also been proposed based on the nucleation and coarsening of α phase.

Duplex phase hexagonal-cubic multi-principal element alloys with high hardness

We report on the influence of Mn additions on the microstructure and properties of (CoCrCuTi)100−xMnx multiprincipal element alloys (MPEAs) containing 5, 10, 15, and 20% Mn prepared by arc-melting. It was observed that the alloys containing less than 10 at.% Mn contained BCC dendrites and a Cu-rich face centered cubic (FCC) interdendritic matrix. In contrast, alloys containing Mn ≥ 10 at.%, consisted of a hexagonal dendritic Laves phase (C14, hexagonal, P63/mmc) with small amounts of Cr-rich and Ti-rich dendrites, and a Cu-rich FCC interdendritic matrix. Isopleths of the CoCrCuMnTi system were generated using the ThermoCalc software with TCHEA3 database in order to elucidate phase formation in these alloys. In addition, the particular composition Co22Cr18Cu20Mn16Ti24 was found to consist of Laves C14 phase hexagonal dendrites in a Cu-rich FCC interdendritic matrix with very small dispersed Ti-rich dendrites. Selected area electron diffraction of the dendritic phase in Co22Cr18Cu20Mn16Ti24 was found to have lattice parameters approximated to be a = 4.8Å and c = 7.5Å based on fitting the d-spacing of the indexed patterns to previously published data on the Cr2Ti intermetallic phase. The Vickers mircohardness of the hexagonal dendritic phase of Co22Cr18Cu20Mn16Ti24 was found to be 996.6 ± 57.2 HV 0.01, while the Cu-rich interdendritic matrix has hardness of 457.3 ± 7.0 HV 0.01 and overall hardness of both regions equaling 480.2 ± 21.4 HV 1. The overall Rockwell hardness was found to be 43 ± 2 HRC. The compressive strength of Co22Cr18Cu20Mn16Ti24 was measured to be 1430 MPa, while wear rate was measured as 2.64 × 10−5 mm3/m·N.

Developing Improved Mechanical Property and Corrosion Resistance of Mg-9Li Alloy via Solid-Solution Treatment

Cast Mg-9Li alloy was successfully solid-solution (SS) treated via heating at 575 °C for 4.5 h and rapidly quenched with ice-water mixture. The mechanical property and corrosion resistance of the SS alloy were simultaneously improved. Rapid bcc/hcp phase transition of the alloy occurred during the quenching process, creating the newly precipitated needle-like fine α-Mg phase, uniformly distributed in the β-Li phase matrix. Dramatic grain refinement and uniform distribution of the α-Mg phase, as well as the massively increased α/β phase interfaces, are factors leading to the improved mechanical property of the SS alloy. Meanwhile, due to the modified duplex-phase structure, the SS alloy has a uniform corrosion-resistant surface film on the β-Li phase, which completely covers the entire alloy surface and efficiently protects the substrate. In addition, the SS alloy has fewer difference in the elements concentration and corrosion activity of the duplex phases, which reduces the pitting sensitivity and improves the corrosion resistance of the alloy matrix. The findings in this binary Mg-Li alloy can also serve as a benchmark for other more practical and complicated Mg-Li alloys.

Ultrasonic machining and fretting wear of synthesized duplex brass metal matrix

Abstract In recent years, the budding researchers have an unquenchable desire to highlight the demand and properties of metal matrix by doing commendable researches. The demands of multipurpose metal matrixes are rapidly increasing due to its excellent properties. The phase structure plays an important role in metal matrix. The material properties and characterization is improving based on the phase structure of the material. The present work describes two phases namely soft and hard phase in brass metal matrix which has been fabricated through stir casting process. The material characterization and properties have been studied. The morphology of the material structure has been analyzed through Scanning Electron Microscope (SEM) and material composition has been proved by Energy Dispersive Analysis of X-rays (EDAX). The duplex phase in this metal matrix provides better material properties like strength, hardness, tensile strength and impact strength. Due to dual phase, it is difficult to machine by conventional machining process. Hence, ultrasonic machining process is used for machining this metal matrix. During machining, the various input parameters such as power rating, slurry concentration and grit size have been considered. The material removal rate (MRR) and surface roughness (SR) have been considered as output parameters. The wear properties have been also evaluated by tribometer. The most influential parameter for ultrasonic machining process and wear test has been confirmed through analysis of variance (ANOVA).