Fe-based Alloys Research Articles

Mn content optimum on microstructures and mechanical behavior of Fe-based medium entropy alloys

Fe-XMn-5Si-10Cr-0.9C (X = 10, 15, 20, and 25 wt%) medium entropy alloys (MEAs) with different Mn contents were prepared by magnetic suspension melting in a water-cooled copper crucible, and casted in a negative pressure suction copper mould. The modified Warren–Averbach equation and the thermodynamic model were used to calculate the alloy dislocation density and stacking faults, respectively. The effects of the Mn content on the phase structure, stacking fault energy (SFE), dislocation density, and mechanical properties of the alloy were investigated. The results indicate that the MEAs possess a low stacking fault energy (∼8.50–14.44 mJ/m2) and a unique high as-cast dislocation density (up to 4.8 × 1015 m−2). The microstructure of the as-cast alloys consisted of austenite phase. As loading, the γ → ε martensite transformation occurs and is accompanied by obvious work-hardening behaviour. A low SFE and high ΔSmix improved the storage capacity of the dislocation density, promoted the formation of ε-martensite, and improve the strength and plasticity. Both the SFE and ΔSmix increased with an increase in the Mn content, and the dislocation density initially increased and then decreased. Optimising the Mn content and coordinating the balance between the SFE and ΔSmix can regulate the optimal dislocation density.

Preparation, characterization and dynamic mechanical analysis of CuZnAl shape memory alloys

Shape-memory alloys (SMAs) are metallic materials that, after undergoing temperature or stress cycling, regain their original shape. Although Ni-Ti is widely commercialized, it is seen as a costly alternative. Therefore, cost-effective and easy-to-process alloys such as Fe- and Cu-based alloys are being explored nowadays. Fe-based alloys have serious processing difficulties and have texture-dependent properties. Therefore, Copper based SMAs are seen as potential alternatives. Cu-based SMAs are High-Temperature SMAs, Cu-Zn-Al, in particular, operates at higher temperature while showing good SME properties. In this present study, Cu-Zn-Al were manufactured by induction melting process, hot rolled, and then homogenized. The phase transformation behavior was investigated by Differential Scanning Calorimetry (DSC) and their phase composition was investigated by X-ray Diffraction (XRD). Dynamic mechanical analysis (DMA) was performed to study the damping behavior of the alloy. The findings revealed that Cu-Zn-Al has the highest damping capacity, which makes them desirable for particular applications.

Study on sintering mechanism for extrusion-based additive manufacturing of stainless steel through molecular dynamics simulation

Unlike conventional metal powder based additive manufacturing (AM) technology, a Printing-Debinding-Sintering (PDS) process that adopts polymer-based filaments with highly filled metal particles can be employed as an economical approach to create metal parts at high fabrication rate and a low manufacturing cost. To achieve dense metal parts, the underlying sintering mechanism should be well understood, which has not yet been documented. In this study, molecular dynamics (MD) simulation was conducted to comprehensively unveil the sintering mechanisms during PDS of stainless steel 316L using a novel Fe-Ni-Cr three-element, three-particle sintering configuration. The mechanism of Cr element aggregation at the grain boundaries was revealed by analyzing the evolution of particle structure, diffusion activation energy, and interactions among solute elements during the unique heating process of PDS. In addition, the microstructure of the PDS-built 316L samples was characterized to verify such an aggregation phenomenon. It was found that the self-diffusion coefficient of Cr element increased substantially at the 1600 K holding stage. Meanwhile, Cr element was diffused to grain boundary and formed severe grain boundary aggregation due to its lower diffusion activation energy and stronger interactions between atoms. Moreover, the extra energy released due to this aggregation phenomenon promoted a further coalescence of particles. This study provides an atomic-scale understanding of sintering behavior of PDS-built Fe-based alloys, which paves a way for the multiscale modeling of the sintering process in PDS of other alloy systems.

Corrosion and Mechanical Properties of Novel Fe-Based Bulk Amorphous Alloys

Corrosion and Mechanical Properties of Novel Fe-Based Bulk Amorphous Alloys

Effectiveness of Ni-based and Fe-based cladding alloys in delaying hydrogen generation for small modular reactors with increased accident tolerance

This study investigates the high temperature oxidation behaviour of a Ni–20Cr-1.2Si (wt.%) alloy in steam from 1200 °C to 1350 °C by Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD). The results demonstrate that exposed Ni-based alloy developed a thin oxide scale, consisted mainly of Cr2O3. The oxidation kinetics obtained from the experimental results was applied to evaluate the hydrogen generation considering a simplified reactor core model with different cladding alloys following an unmitigated Loss-Of-Coolant Accident (LOCA) scenario in a hypothetical Small Modular Reactor (SMR). Overall, experimental data and simulations results show that both Fe-based and Ni-based alloys may enhance cladding survivability, delaying its melting, as well as reducing hydrogen generation under accident conditions compared to Zr-based alloys. However, a substantial neutron absorption occurs when Ni-based alloys are used as cladding for current uranium-dioxide fuel systems, even when compared to Fe-based alloys.

Effect of P addition on soft magnetic properties of Fe–Si–B–P–Cu–C nano-crystalline alloys

The effect of P addition on the nano-crystallization of Fe81.5Si0.5B15.5-xPxCu0.5C2 (x = 0, 4.5, 7.5, 11 at.%) amorphous alloys under various heating rates has been studied. Appropriate P addition enhanced the thermal stability of Fe–Si–B–P–Cu–C amorphous alloys. The results also revealed that P addition could decrease the required critical heating rate for the low coercivity and improve the magnetic softness of annealed samples. Although as commonly found in most Fe-based nano-crystalline alloys, a small amount of P addition (4.5 at.%) could effectively help reduce the coercivity when a high heating rate was applied during nano-crystallization, the high heating rate failed to decrease the coercivity in 7.5 at.% P-added alloys and even reversely caused the deterioration of magnetic softness for excessive P addition (11 at.%). The unusual phenomenon in the alloy with 11 at.% P addition lies in the fast increase of diffusion rate with rising temperature and delayed nucleation, which are caused by the weakened bond energy and increased segregation energy, respectively. The results suggest that the improvement of magnetic softness for Fe-based nano-crystalline alloys through simply increasing the P addition would meet its ceiling, due to the limited decrease in coercivity and even increase through applying high heating rate with excessive P concentration. The understanding of P role on the nano-crystallization mechanism could contribute to the compositional design of high-performance soft magnetic Fe-based alloys with an acceptable heating rate in industry.

New evaluation of the thermodynamics stability for bcc-Fe

The thermodynamic properties for bcc-Fe were predicted by combination of the first-principles calculations, the quasiharmonic approximation, the CALPHAD method and the Weiss molecular field theory. The hybrid method considers the effects of the lattice vibration, electron, intrinsic magnetism and external magnetic fields on the thermodynamic properties at finite temperature. Combined with experimental data, the calculated heat capacity without external magnetic fields was used to verify the validity of the hybrid method. Close to the Fermi level the high electronic density of states leads to a significant electronic contribution to free energy. Near the Curie temperature lattice vibrations dominant the Gibbs free energy. The order of the other three excitation contributions to Gibbs free energy from high to low is: intrinsic magnetism > electron > external magnetic fields. The investigation suggests that all the excitation contributions to Gibbs free energy are not negligible which provides a correct direction for tuning the thermodynamic properties for Fe-based alloy.

Microstructural evolution of Fe-based amorphous alloy coatings via ultrasonic vibration-assisted laser cladding

• The coatings have a four-layer structure from the crystal to the amorphous phase. • The crystallisation width increases by 35 μm due to ultrasonic energy. • The formed columnar dendrites break and recrystallise due to ultrasonic streaming. Fe-based amorphous coatings were fabricated using laser cladding with and without ultrasonic vibration. The effect of ultrasonic vibration on microstructural evolution was studied in this paper. When compared with Fe-based amorphous coatings fabricated via laser cladding without ultrasonic vibration, the crystallisation zone at the bottom of the coating increases from 46 μm to 81 μm. It has a wavy distribution that is produced via the thermal effect and high-frequency disturbances due to ultrasonic vibration. The formed columnar dendrites break and recrystallise to form equiaxed crystals as a result of the stirring caused by ultrasonic-vibration induced streaming. However, the amorphous phase still dominates the top zone of the coating, which is less affected by ultrasonic vibration. The entire coating has a four-layer gradient microstructure from the crystalline phase to the amorphous phase, which is instrumental in reducing stress in the bonding area between the coating and substrate.

Microstructure, magnetic domain and dynamic loss of surface-textured Fe-based nanocrystalline alloy

1 DO 3 dendritic-crystallites bear <001>-oriented fiber texture at free surface. 2 TFA slightly weakens the fiber texture and induces magnetic rotation process. 3 The surface-textured alloy after TFA exhibits low dynamic loss. 4 A correlation mechanism between microstructure, domain and loss was obtained. Heterogeneous coarse surface crystallites induced in the industrial Fe-rich nanocrystalline alloy is an obstacle for high-frequency and high-power commercial applications. Herein, the phase, crystal orientation, nanostructure and magnetic domain evolution of the surface-crystallized Fe-rich alloy were systematically investigated. Microstructure and inverse pole figures analysis confirms that the DO 3 ordered dendritic-crystallites bear <001>-oriented fiber texture before and after annealing at the free surface, while ultrafine nanocrystals are randomly oriented in the interior and wheel surface after annealing. As compared to zero magnetic-field-annealing, the transverse magnetic-field-annealing induces weakly oriented fiber texture and relatively uniform dendritic-crystallites at the surface, and uniform anisotropy in the interior and surface, which promotes smooth wall motion at the surface and magnetization rotation in the interior. This synergetic effect reduces the excess loss and leads reduction in dynamic loss at 1.0 T and 10 kHz by 36%.

Influence of Surfacing Fe-Based Alloy Layers on Wire Arc Additive Manufactured Ni-Based Superalloys Material on Its Microstructure and Wear Properties.

Wire arc additively manufactured (WAAM) Ni-based materials have good properties but are costly and hard to cut, leading to difficulties in machining after welding and wasting the materials. To overcome these shortcomings, this work proposes a method of surfacing Fe-based alloy layers on WAAM Ni-based material. The effect of this method on the microstructure and wear properties of WAAM Ni-based materials is discussed. In this work, a Fe-based alloy (JX103) was welded as the last layers of the WAAM Ni-based superalloy (JX201) material. The hardness, microstructure, and wear behavior of the material with different residual Fe-based materials were tested and analyzed. Our results indicate that the surface hardness was smoothly increased from HV350 to HV400 by overlaying Fe-based alloy layers. Microstructure analysis shows that γ-Fe gradually disappears, and the carbide form changes from WAAM Ni-based superalloys to Fe-based alloys. In the fusion boundary, the occurrence of cellular dendritic growth, a type -Ⅱ boundary, and low dilution indicate good crack resistance and good connection performance between these two materials. The wear test showed that the wear resistance of JX201 was decreased by changing the last layer to JX103. However, as the residual thickness of JX103 decreased, the influence gradually reduced. Meanwhile, the wear mechanism changed from severe abrasive and adhesive wear to light abrasive wear. When the thickness is less than 0.5 mm, the wear weight per minute is at the same level as the sample without JX103.

In vitro cytocompatibility and antibacterial studies on biodegradable Zn alloys supplemented by a critical assessment of direct contact cytotoxicity assay.

In vitro cytotoxicity assessment is indispensable in developing new biodegradable implant materials. Zn, which demonstrates an ideal corrosion rate between Mg- and Fe-based alloys, has been reported to have excellent in vivo biocompatibility. Therefore, modifications aimed at improving Zn's mechanical properties should not degrade its biological response. As sufficient strength, ductility and corrosion behavior required of load-bearing implants has been obtained in plastically deformed Zn-3Ag-0.5Mg, the effect of simultaneous Ag and Mg additions on in vitro cytocompatibility and antibacterial properties was studied, in relation to Zn and Zn-3Ag. Direct cell culture on samples and indirect extract-based tests showed almost no significant differences between the tested Zn-based materials. The diluted extracts of Zn, Zn-3Ag, and Zn-3Ag-0.5Mg showed no cytotoxicity toward MG-63 cells at a concentration of ≤12.5%. The cytotoxic effect was observed only at high Zn2+ ion concentrations and when in direct contact with metallic samples. The highest LD50 (lethal dose killing 50% of cells) of 13.4mg/L of Zn2+ ions were determined for the Zn-3Ag-0.5Mg. Similar antibacterial activity against Escherichia coli and Staphylococcus aureus was observed for Zn and Zn alloys, so the effect is attributed mainly to the released Zn2+ ions exhibiting bactericidal properties. Most importantly, our experiments indicated the limitations of water-soluble tetrazolium salt-based cytotoxicity assays for direct tests on Zn-based materials. The discrepancies between the WST-8 assay and SEM observations are attributed to the interference of Zn2+ ions with tetrazolium salt, therefore favoring its transformation into formazan, giving false cell viability quantitative results.

A laser-shock-enabled hybrid additive manufacturing strategy with molten pool modulation of Fe-based alloy

A novel hybrid laser additive manufacturing (LAM) process based on laser shock modulation of molten pool (LSMMP) is proposed in this work. By using a combination of experiment and simulation, the residual stress, heat transfer, and mass transfer behaviors are comprehensively studied. Also, microstructure evolution behavior is analyzed. The relationship between the convection behavior, the evolution of microstructure and the enhancement of residual stress induced by LSMMP is established. Compared with the traditional post-treatment process, the LSMMP assisted LAM process exhibits higher efficiency in residual stress control with the same pulsed laser energy input. The hidden mechanism in microstructure evolution and residual stress enhancement is expected to be possible related to intensified molten pool convection, uniform solute distribution and improved cooling rate induced by LSMMP. The hybrid LAM process strategy based on LSMMP provides a new approach for the application of short pulse laser in hybrid manufacturing.

Creep deformation behavior of the Ni–Fe-based GH984G alloy

The creep deformation behavior and microstructure evolution of the Ni–Fe-based GH984G alloy were investigated at temperatures of 700 °C–775 °C, with the stress ranging from 150 MPa to 400 MPa. The results demonstrate that the apparent stress exponent and apparent creep activation energy are 6.53 ± 0.74 and 546.7 ± 6.8 kJ/mol, respectively. The creep activation energy is higher than that of lattice self-diffusion, which is related to the interaction between dislocation and γ′ precipitates and can be corrected by threshold stress. The threshold stresses are 109.1 MPa, 51.5 MPa and 24.8 MPa at 700 °C, 750 °C and 775 °C, respectively. The true stress exponent is 4.95 ± 0.14 and the true creep activation energy is determined to be 288.3 ± 4.3 kJ/mol. The microstructure analysis demonstrates that the climbing of a/2 <110> perfect dislocation is the primary mechanism of creep at 700 °C. The dislocation climbing and a/6 <112> partial dislocation shearing into γ′ are both significant factors during creep deformation at 750 °C. The creep damage tolerance of 6.4 ± 1.1 indicates that microstructural degradation, including γ′ and M23C6 coarsening, is the primary creep damage mechanism for the GH984G alloy. The deformation mechanism map for GH984G alloy is established and the creep mechanism within the investigated conditions locates in the power-law creep domain controlled by dislocation climbing.

Reinforced mechanical properties of plasma-sprayed Fe-based amorphous composite coatings by in-situ TiNx/TiOy

Ceramic particle-reinforced Fe-based amorphous coatings have received extensive attention due to their excellent strength and wear resistance. In this paper, TiNx/TiOy -enhanced Fe-based amorphous coatings were prepared by reactive plasma spraying technology, and the effect of eggshell-like TiNx/TiOy on the comprehensive mechanical properties of Fe-based amorphous coatings was systematically studied. The results showed that the hardness of the composite coating was significantly higher than that of the amorphous single-phase coating. Moreover, indentation experiments showed that TiNx/TiOy effectively confined crack growth in the amorphous phase. Though the bonding strength of the composite coating was lower than that of the pure amorphous coating, but still maintained a high bonding force of 20.68 MPa. Through the wear experiment, it was found that the wear scar of the composite coatings appeared plastic deformation, the friction coefficient and wear mass loss were both greatly reduced, and the optimal wear performance appeared in the composite coating with 15% Ti addition. In addition, SEM, EDS analysis, and the first-principles simulation results demonstrated the good bonding between Ti-containing compounds and Fe-based alloys.

STUDY ON MICROSTRUCTURE AND CORROSION RESISTANCE OF LASER CLADDING FE BASED ALLOY COATING

In order to improve the corrosion resistance of 45 steel surface, fe-based alloy coating was prepared on the surface of 45 steel by laser cladding technology and the microstructure of Fe-based alloy coating was observed.Corrosion resistance test of Fe-based alloy coating and 45 steel in 3.5wt.% NaCl solution and 1mol/L HCl solution.The results show that the coating structure of the laser cladding Fe-based alloy is uniformly dense, and there are no obvious cracks, porosity and other defects on the surface of the coating.The self-corrosion potential (Ecorr) of the coating and 45 steel in 3.5wt.% NaCl solution was -570.96mV and -831.15mV, and the self-corrosion current density (icorr) was 12.13uA·cm-2 and 13.70uA·cm-2, respectively.The Ecorr of the coating and 45 steel in the 1mol/L HCl solution were -453.45mV and -497.00mV, respectively, and the icorr of the coating and 45 steel was 297.78uA·cm-2 and 379.31uA·cm-2, respectively.The coating has a greater arc capacitive than 45 steel, has a larger impedance modulus, and has better corrosion resistance.

Magnetostriction and damping of forced vibrations in Fe-Mo single and polycrystal alloys

Magnetostriction and damping of forced vibrations in Fe-Mo single and polycrystal alloys is studied and analyzed with respect to existing approaches and experimental data. Our data suggest that a more complex dependence (compared with linear dependence predicted by Smith and Birchak) between damping capacity and magnetostriction takes place for this and possibly other Fe-based ferromagnetic alloys. We believe that more factors related to the structural changes, brought about by the additions (elements added to Fe), which can affect phase stability as well as magnetic and electric contributions influencing property response, should be considered to provide a better correlation between the magnetic and magnetomechanical characteristics of this alloy.

Investigation of glass forming ability, crystallization behavior, and soft magnetic properties of Fe–B–P–C–Cu alloy ribbons

The effect of Cu content on GFA, crystallization behavior, and soft magnetic properties in high P Fe84+xB6P6C3Cu1−x (x = 0, 0.2, 0.4, 0.6, and 1.0 at. %) alloy ribbons were systematically investigated to balance the relationship between glass forming ability (GFA), heat treatment window, and soft magnetic properties of high saturation magnetic flux density (Bs) Fe-based nanocrystalline alloys. It was discovered that lowering Cu promotes the formation of an amorphous structure. The GFA of alloys rises from 23 μm for Fe84B6P6C3Cu1 to 29 μm for Fe84.4B6P6C3Cu0.6. Analysis of thermal physical properties shows that when Cu content is between 1.0 at. % and 0.6 at. %, reducing Cu in the alloys does not affect the onset temperature of the first crystallization peak (Tx1), the second one (Tx2), and ΔT (ΔT = Tx2 − Tx1), whereas when Cu content is less than 0.6 at. %, reducing Cu leads to an increase in Tx1 and a decrease in Tx2 and ΔT, which is not conducive to obtaining a wide temperature range of precipitation of a single α-Fe phase. The alloys have a wide range of crystallization annealing temperature (693–753 K) and annealing time (60–6 min) to obtain a low coercivity (Hc) of about 8.0 A/m, high Bs of about 1.80 T, and high effective magnetic permeability (μe) of about 10000 when Cu is between 1.0 at. % and 0.6 at. %. The Bs, Hc, and μe of Fe84.4B6P6C3Cu0.6 alloy annealed at 723 K for 30 min are 1.82 T, 8.1 A/m, and 10820, respectively.

Evolution and Removal of Inclusions in Fe-Based Amorphous Alloys

Evolution and Removal of Inclusions in Fe-Based Amorphous Alloys

Improvements in Hot Corrosion Behavior of CO2 Laser-Welded Fe-Based A-286 Alloy in an Aggressive Salt Environment by High-Velocity Oxy-Fuel Coating

Improvements in Hot Corrosion Behavior of CO2 Laser-Welded Fe-Based A-286 Alloy in an Aggressive Salt Environment by High-Velocity Oxy-Fuel Coating

Development of Fe-based amorphous alloy with high iron content for room-temperature magnetic refrigeration application

In this work, in order to develop new Fe-based amorphous alloys with room-temperature magnetocaloric effect and good magnetocaloric performance, high iron content Fe-based amorphous alloys were designed, and their Curie temperatures were adjusted to room temperature through the addition of Mo. As a result, a new Fe83Mo6Si1B7P2C1 amorphous alloy with room-temperature magnetocaloric effect was successfully prepared by melt-spinning technique, and it has the Curie temperature of 300 K, the maximum isothermal magnetic entropy change of 2.74 J kg−1 K−1 and the refrigerant capacity of 485.2 J kg−1 under an applied magnetic field of 5 T. Combining with the advantages of excellent magnetocaloric properties, negligible hysteresis loss, and low material cost, the present Fe83Mo6Si1B7P2C1 amorphous alloy should be a promising candidate as room-temperature magnetic refrigerants.