Fe Cr Ni Alloys Research Articles

Additively Manufactured Stainless Steel Wind Tunnel Model Support Featuring Honeycomb Structures for Vibration Attenuation

Wind tunnel model support (WTMS) is an indispensable component of wind tunnel testing. However, the presence of vibrations within the model‐support system can compromise the accuracy of data and give rise to significant safety hazards. In this study, an approach for vibration attenuation by incorporating honeycomb structures into the design of the WTMS is proposed. To this end, stainless steel WTMSs with integrated honeycomb structures are fabricated by selective laser melting (SLM). Results showed that stainless steels prepared under optimized SLM processing parameters exhibit high crystallinity and consist of single‐phase Fe–Cr–Ni alloy. The stainless steels exhibited robust mechanical properties, including a tensile strength of ≈1 GPa, an elongation of ≈8%, and a compressive strength of ≈1.4 GPa. These exceptional mechanical properties can be attributed to the formation of a cellular structure and tangled dislocations. The first‐order and the third‐order resonant response of WTMS honeycomb structures can be effectively reduced. The vibration reduction mechanism can be attributed to the occurrence of local resonance when the natural frequency of the internal periodic unit of the WTMS closely matched the vibration frequency of the model. The utilization of honeycomb structures holds significant potential for achieving vibration attenuation in WTMS.

Mechanical properties, nano-tribological behavior and deformation mechanism of FeCrNi MEA with the addition of Co/Cu: Molecular dynamics simulation

During manufacturing processes, alloys face increasingly demanding requirements for their mechanical and tribological properties, underscoring the importance of revealing their deformation mechanisms. This study employed molecular dynamics simulation to construct models of FeCrNi (C1), FeCoCrNi (C2), FeCrNiCu (C3), and FeCoCrNiCu (C4), investigating the tribological properties of C1 alloy under various conditions and the mechanical properties across a wide temperature range (223–1073 K). The results indicate that the elastic modulus of the alloys follows the order C2 > C4 > C3 > C1 across the temperature range of 223 K to 1073 K. The elastic modulus increases with rising temperatures and decreases before rising once again as temperatures decrease. The phase transitions become more pronounced below 300 K. The addition of Co elements to the FeCrNi alloy contributes to fine-grain strengthening, uniform distribution of internal stress and strain, reduction in local stress concentration, and improvement of the alloy ductility and tensile strength. Compared to sliding friction, rolling friction reduces the number of worn atoms; however, the tensile and shear effects cause an increase in the stress gradient, leading to more severe subsurface damage and shear deformation. Temperature significantly affects the tribological properties of the alloys: phase transitions at high temperatures promote dislocation slip and plastic deformation, while at low temperatures, higher hardness and strength are observed. The roughness of stacking faults is greatly influenced by temperature, with an increase at the low-temperature range (223–273 K), a decrease in the mid-temperature range (273–673 K), and a smoother surface at the high-temperature range (673–1073 K). The research aims to provide a deeper understanding of the excellent mechanical and tribological properties of FeCrNi alloy at the micro/nano scales, thereby advancing their application and development in manufacturing processes.

High-strength WC-Co/Low carbon steel connected by Ni–Cr–Fe alloy through brazing for roller sleeves

Enhancing the bond strength between WC-Co and steel is crucial for broadening its applications. In this study, WC-Co was bonded to low-carbon steel (LCS) using a Ni–Fe–Cr alloy at 1180 °C in an argon atmosphere furnace. The WC-Co/LCS (WL) interface was characterized by XRD, SEM, and EPMA, revealing no cracks or pores and confirming robust metallurgical bonding. The bonded material's shear strength reached approximately 321–328 MPa, significantly exceeding that achieved with Ag–Cu–Zn–Cd, Cu–Zn, Cu–Ni–Al, Ag–Cu–Zn + Ni/Mn, and Ag–Cu–In–Ti filler materials in the welding process. EPMA analysis showed that Fe, Cr, and Ni from the Ni–Fe–Cr alloy diffused into the WC-Co over distances of approximately 802–815 μm, 803–817 μm, and 632–641 μm, respectively. Initially, WC decomposed at sharp corners to form W₂C, which subsequently reacted with Fe and Cr to form M₆C and M₇C₃. This methodology was also applied to producing roller sleeves for vertical mills, increasing their lifespan by 1.9 times.

The influence of Nickel on the corrosion protection of FeCrNi alloys after breakaway corrosion at 600 °C

Breakaway corrosion of stainless steels remains a challenge for many industrial applications operating in harsh conditions. The lifetimes of metallic components are often determined by the corrosion propagation after breakaway. Nevertheless, studies on the protective properties of the Fe-rich oxides formed after breakaway are scarce. This study investigates the influence of Ni on the protection after breakaway on a broad range of Fe18CrxNi model alloys, by systematically inducing breakaway of the initially formed protective, Cr-rich oxides. The results clearly demonstrate an improved protection after breakaway for higher Ni-contents, explained by the alloys’ ability to avoid internal oxidation involving Fe-rich BCC and spinel.

Phase-field modeling of interdiffusion between dissimilar Fe-Cr-Ni alloys during non-isothermal hot isostatic pressing

Powder metallurgy hot isostatic pressing (PM-HIP) has emerged as a promising alternative to welding for joining dissimilar metals. During HIP, interfacial bonding is mediated by solid state diffusion. The interdiffusion zone across the interface depends on processing conditions, calling for the need for accurate numerical tools capable of simulating interdiffusion and possible phase transformation in order to optimize processing parameters. Here, a phase-field (PF) model based on CALPHAD-based free energy functionals is developed to simulate the interdiffusion and phase evolution between dissimilar Fe–Cr–Ni based steels undergoing HIP and is demonstrated using the interface between 316L and SA508 steels. To overcome the numerical challenges caused by the singular magnetic and entropy terms in the CALPHAD free energy models in the Fe–Cr-Ni system, polynomial functions are fitted with temperature dependent coefficients represented by Fourier series to accurately describe the phase stability of both fcc and bcc phases in the composition and temperature space. This enables simulations of non-isothermal HIP cycles. Diffusivity data from commercial software and literature are taken to parameterize the kinetic parameters. A discrete nucleation model is incorporated for possible phase transformation. The modified thermodynamic models are validated against previous experiments at 923 K and 1273 K. The interdiffusion kinetics are benchmarked against new HIP experiments joining powder and bulk 316L to bulk SA508 with three different HIP cycles. The good agreement between simulations and experiments on both phase stability and interdiffusion indicate that the model is suitable for simulating interdiffusion between Fe–Cr–Ni alloys during HIP cycles. It is also found that using powder and bulk 316L gives similar interdiffusion profiles at elevated temperature when a dense interface forms during HIP.

Atomistic analysis of the mechanisms underlying irradiation-hardening in Fe–Ni–Cr alloys

This work presents a comprehensive examination of the physical mechanisms driving hardening in irradiated face-centered cubic FeNiCr alloys. The evolution of irradiation-induced defects during shear deformation is modeled by atomistic simulations through overlapping cascade simulations, where the nucleation and evolution of dislocation loops is validated by transmission electron microscopy images obtained from irradiated FeNiCr alloys using tandem accelerator. The effect of different shear rates on the microstructure of irradiated materials with a specific focus on the changes in the density of voids and dislocation loops induced by irradiation was analyzed. Additionally, the fundamental interaction processes between single irradiation-induced defects contributing to irradiation hardening, such as voids and dislocation loops in the alloy are explained. The analysis at atomic level indicates that both the dislocation loops and the voids exhibit strengthening effects. Furthermore, the nanometric voids are much stronger obstacles than dislocation loops of comparable size. The mechanism of cutting the voids leads to an increase of voids density and thus contributes to an increase in irradiation hardening. The mechanism of collapse of small voids into dislocation loops leads to decrease of voids density and at the same time increase of loops density. The coupling effect between the density of voids and dislocation loops is determined. Finally, the novel, physical mechanisms-based model of irradiation hardening and dislocation-radiation defect reaction kinetics are developed, which consider the mechanisms of void cutting, void shrink and void collapse to dislocation loop.

The Impact of HCl on Alkali-Induced Corrosion of Stainless Steels/FeCrAl Alloy at 600 °C: The Story After Breakaway

The impact of Cl on alkali-induced high-temperature corrosion of stainless steels/FeCrAl alloys after breakaway oxidation was investigated in a simulated biomass- and waste-fired boiler environment at 600 °C. For this investigation, three alloys were exposed to low Cl load environment (H2O+KCl) and to high Cl load (H2O+KCl+HCl). Post-exposure analysis showed that the stainless steel SVM12 experiences fast oxidation and forms thick double-layered Fe-rich oxide scales. The corrosion attack is further accelerated with addition of HCl for this material with the effect being more pronounced in the inward-growing scale. The FeCrAl and FeCrNi alloys exhibit slower oxidation kinetics after the breakaway corrosion compared to SVM12 in the H2O+KCl exposure. Furthermore, in contrast with SVM12, the addition of HCl did not accelerate the corrosion attack on these alloys. It is argued that the properties of the secondary oxide layer formed after breakaway corrosion are important in the continued corrosion resistance against chlorine-induced corrosion attack. Especially, the Cr content in the inner scales is suggested to be important in corrosion mitigation.

Sliding wear behavior of a Laves phase-strengthened CrFeNiNb0.158 alloy at room and elevated temperatures

Face-centered-cubic (FCC) compositionally complex alloys (CCAs) are recognized for their exceptional mechanical properties, rendering them promising candidates for demanding engineering applications. However, a significant challenge faced by these alloys is their limited wear resistance. In this study, we addressed this issue by introducing 5 at.% Nb into an equiatomic FCC CrFeNi alloy, thereby creating a Laves phase-strengthened CrFeNiNb0.158 alloy, and investigated its sliding wear behavior at both room and elevated temperatures. Our findings reveal a substantial improvement in the wear performance of the Laves phase-strengthened CrFeNiNb0.158 alloy. Specifically, at room temperature (RT), the alloy exhibited a remarkable 62 % reduction in wear rate compared to the CrFeNi alloy. Furthermore, at an elevated temperature of 600 °C, the wear rate decreased by approximately 95 %, primarily attributed to the formation of a lubricating (Cr, Fe)2O3 oxide layer. Through detailed analysis, we identified the wear modes as abrasive wear at RT and oxidative wear at elevated temperatures. These results provide valuable insights for designing wear-resistant FCC CCAs by utilizing Laves phase strengthening and incorporating elements prone to oxidation to facilitate the formation of a protective oxide layer at elevated temperatures.

Strengthening CrFeNi multi-principal element alloy through grain refinement, introducing partially recrystallized structure, and constructing fine heterostructures

The excellent corrosion resistance exhibited by CrFeNi multi-principal element alloys makes them highly desirable for the development of novel stainless alloys, but they exhibit a low strength. This work explores a simple processing route to enhance the strength by cold-rolling and annealing a CrFeNi alloy to introduce a partially recrystallized structure, refine its grain, and construct fine heterostructures. These changes increased the yield strength from 402 MPa to 1025 MPa while maintaining acceptable ductility. Dislocation strengthening, grain boundary strengthening, and hetero-deformation-induced strengthening were responsible for the strength enhancement. A smaller soft phase in the heterostructure enhanced the effectiveness of hetero-deformation-induced strengthening. The findings presented in this article offer additional strengthening methods for CrFeNi multi-principal element alloys.

Mechanical and surface characteristics in laser-assisted machining of NiFeCr alloy: An atomic-scale understanding

This investigation explores mechanical characteristics and subsurface damage of NiFeCr alloy in laser-assisted machining through molecular dynamics simulation. The results of machining force, friction coefficient, local strain/stress, temperature distribution, subsurface damage, surface morphology, and worn volume are comprehensively explored, thereby revealing the mechanism of laser-assisted machining under different working conditions. Compared to conventional processing, average machining force, shear strain, subsurface damage, and dislocated length are all reduced in laser-assisted machining, which improves surface finish quality. Amorphization of removed chips in laser-assisted machining enhances the material removal efficiency. Analysis of various laser powers shows a decreased machining force with increasing laser power. However, residual stress and temperature rise, potentially impacting surface integrity. The subsurface damage depth exhibits nonlinearity with increasing laser energy, highlighting the competition between mechanical stress and thermal effect. The surface morphology and atomic flow demonstrate effective material removal with increasing laser power. The average machining force, friction coefficient, and subsurface damage depth show nonlinear relationships with cutting speed. The number of worn atoms is proportional to machining length and cutting speed, indicating enhanced material removal during high-speed machining.

First-principles and cluster expansion study of the effect of magnetism on short-range order in Fe–Ni–Cr austenitic stainless steels

Short-range order (SRO), the regular and predictable arrangement of atoms over short distances, alters the mechanical properties of technologically relevant structural materials such as medium/high entropy alloys and austenitic stainless steels. In this study, we present a generalized spin cluster expansion (CE) model and show that magnetism is a primary factor influencing the level of SRO present in austenitic Fe–Ni–Cr alloys. The spin CE consists of a chemical cluster expansion combined with an Ising model for Fe–Ni–Cr austenitic alloys. It explicitly accounts for local magnetic exchange interactions, thereby capturing the effects of finite temperature magnetism on SRO. Model parameters are obtained by fitting to a first-principles data set comprising both chemically and magnetically diverse face-centered cubic configurations. The magnitude of the magnetic exchange interactions are found to be comparable to the chemical interactions. Compared to a conventional implicit magnetism CE built from only magnetic ground state configurations, the spin CE shows improved performance on several experimental benchmarks over a broad spectrum of compositions, particularly at higher temperatures due to the explicit treatment of magnetic disorder. We find that SRO is strongly influenced by alloy Cr content, since Cr atoms prefer to align antiferromagnetically with nearest neighbors but become magnetically frustrated with increasing Cr concentration. Using the spin CE, we predict that increasing the Cr concentration in typical austenitic stainless steels promotes the formation of SRO and increases order–disorder transition temperatures. This study underscores the significance of considering magnetic interactions explicitly when exploring the thermodynamic properties of complex transition metal alloys. It also highlights guidelines for customizing SRO through adjustments of alloy composition.

The deformation and friction mechanisms of NiFeCr alloys based on molecular dynamics simulations

NiFeCr alloys are widely used in aerospace, marine and power equipment due to their good mechanical properties and wear resistance. At present, the relevant research on NiFeCr alloys mainly focuses on the design and preparation of the alloys, and there are relatively few studies on their mechanical behaviour and scratch deformation. In this paper, the effect of strain rate on the mechanical behaviour and scratch deformation of NiFeCr alloys is investigated using the molecular dynamics method. The results of tensile deformation under different strain rates show that when the strain rate increases from 2.5 × 109/s to 5.0 × 109/s, multiple slip systems are initiated simultaneously, and the entanglement of dislocations in different slip systems leads to dislocation stacking, and the strain rate enhancement effect is significant. When the strain rate is from 5 × 109/s to 7.5 × 109/s, the strain rate enhancement effect is not obvious. Further molecular dynamics scratching studies were carried out, and the results showed that as the scratching rate increased, the strain rate increased, the total number and length of dislocations increased, and the scratching force increased.

Weakening the mechanical property anisotropy of additively manufactured medium entropy alloy by controlling the cellular structure

Cellular structure is a unique microstructure characteristic of the additively manufactured face-centered cubic phase metallic materials. It typically grows preferentially along the temperature gradient, leading to anisotropy in mechanical properties and restricting the practical application. Herein, we adopted a discontinuous laser scanning strategy for fabricating the face-centered cubic FeCrNi alloy. The scanning layer is divided into nine discontinuous equal-width regions along which the laser beam prints discontinuously. This strategy can increase the temperature gradient in the melt pool by weakening the thermal influence between the adjacent scanning regions, which helps to suppress cellular structure growth along the temperature gradient. Compared with the sample prepared by the conventional continuous laser scanning strategy, the sample printed using the discontinuous laser scanning strategy exhibits finer cellular structures with a significantly shorter length along the growth direction, and the anisotropy of mechanical properties is weakened. The in-plane anisotropy of ultimate tensile strength decreases from 21.6 to 6.4. This study presents a novel approach to optimize the mechanical properties of additively manufactured face-centered cubic phase metallic materials.

Origins of twin boundaries in additive manufactured stainless steels

316L and 304L stainless steels and a compositional gradient of both are fabricated using the same processing parameters via laser directed energy deposition additive manufacturing. In those alloys, the increase in chromium-to-nickel ratio is accompanied with grain refinement and formation of a high density of twin boundaries, i.e. Σ3 boundaries. By means of electron microscopy, crystallographic and thermodynamic calculations, we demonstrate that two mechanisms arising from the ferrite-to-austenite solidification mode are at the origin of twin boundary formation and grain refinement: (1) inter-variant boundaries emerging from the encounter of pairs of austenite grains formed from a common ferrite orientation with Kurdjumov–Sachs orientation relationship; (2) icosahedral short-range-ordering-induced (ISRO) nucleation of twin-related γ grains directly from the solidifying liquid. These findings define new routes to achieve grain boundary engineering in a single step in FeCrNi alloys, by tailoring the solidification pathway during the AM process, enabling the design of functionally graded materials with site-specific properties.

Nanoindentation creep mechanism of gradient ultrafine lamellar γ+Ni5Zr eutectic using electromagnetic levitation coupled with fall casting

A quaternary Ni50Fe20Cr20Zr10 eutectic alloy was designed based on the Ni–Fe–Cr alloy, and the gradient ultrafine lamellar γ+Ni5Zr eutectic was achieved by means of electromagnetic levitation coupled with fall casting (EML-FC). The temperature field, the process of interface migration, microstructural characteristics and the nanoindentation creep property of the alloy were systematically analyzed. During the rapid solidification, since the conical surface served as the main heat dissipation channel, the solid-liquid interface moved from the conical surface towards the top of the cone axis. The gradual decrease in cooling rate from 105 to 103 K s−1 along this direction led to the formation of the gradient ultrafine lamellar γ + Ni5Zr eutectic with the size from 59 ± 12 to 140 ± 36 nm. The nanoindentation creep behavior and mechanism were analyzed by estimating the strain rate sensitivity and activation volume. As the interlamellar spacing of the eutectic decreased, the nanohardness and creep resistance of the alloy gradually increased owing to an increase in grain boundary density and the enhancement of coupling effect between dislocation and grain boundary. In addition, the creep behavior of alloy was sensitive to the loading rate. Increasing the loading rate led to an increase in strain rate sensitivity from 7.69 × 10−3 to 18.89 × 10−3 and a decrease in activation volume from 29 to 12 b3. This special eutectic structure and its improved nanohardness and creep resistance properties offered a potential opportunity to explore a new generation of alloys for the hot-end components of 972 K ultra-supercritical fossil-fired power plants.

Effects of Mo and C addition on the microstructure and corrosion behavior of FeNiCrAl duplex alloy

Effects of Mo and C addition on the microstructural evolution and corrosion resistance in chloride solution of FeNiCrAl duplex alloy were investigated. The results showed that α phase stabilizing element Mo increased the α/γ volume ratio and γ phase stabilizing element C decreased its ratio in FeNiCrAl alloy, and the chemical composition of α and γ phases was changed by Mo and C addition, which affected the corrosion resistance of FeNiCrAl alloy. Pitting corrosion mainly occurred in α phase around NbC precipitated at α/γ interface due to the micro-galvanic corrosion (MGC) effect between α (anode), γ (cathode) and NbC (cathode) phases. The pitting corrosion resistance was improved by Mo and C addition, resulting from that Mo and C enhanced the passivity of passive films and decreased the MGC effect between α, γ and NbC phases.

Stacking fault energy, thermal expansion behavior, and elastic coefficients of a single-crystalline CrFeNi medium-entropy alloy

The equiatomic CrFeNi alloy is considered to be a model single-phase face-centered cubic medium-entropy alloy. The Bridgman technique was employed to grow a single crystal of this alloy and its dilatation behavior and elastic properties were measured in the temperature range: 100 K–673 K. Based on transmission electron microscopy investigations, plastic deformation is initially caused by the glide of dissociated dislocations (Shockley pairs bounded by a stacking fault ribbon). From their dissociated widths, a stacking fault energy of 36 mJ∙m-2 was determined.

Synergic investigation of microstructure, precipitation, and micro-segregation on Inconel 825 weldments: A comparative study between GTAW and EBW

Inconel 825, a Ni–Fe–Cr alloy highly regarded for its exceptional corrosion resistance and high-temperature strength. This investigation studies the effect of heat input, precipitation, and micro segregation of Inconel 825 weldments and compares the effectiveness of two welding techniques: gas tungsten arc welding (GTAW) and electron beam welding (EBW). The findings indicate that increasing heat input generally enhances weldment quality by reducing the lack of penetration. However excessive heat input in GTAW leads to root cracking and solidification cracking; while EBW demonstrates better control over undercut and maintains consistent weld quality even at higher heat inputs. Both GTAW and EBW samples exhibit dendritic grain morphologies with distinctive grain boundaries. Precipitates, such as Al4C3 and TiN, are observed in both processes, contributing to improved mechanical properties. While GTAW weldments show some degree of segregation for Mo, Cu, Ti, and Al, EBW weldments demonstrate negligible segregation for major alloying elements but micro-segregation of Ti and Al. EBW weldments additionally showcase higher average hardness, superior tensile strength, and ductility compared to GTAW weldments. This can be attributed to lower heat input, faster cooling rates, and a reduced rate of elemental segregation. Fractographic analysis reveals the presence of voids and micro-voids, indicating a ductile mode of failure for both GTAW and EBW samples. These void characteristics vary based on the heat input and microstructural features.

Effects of in situ composite ceramics on the mechanical properties and microstructure of Fe–Cr–Ni alloys

Fe–Cr–Ni composites reinforced with Al2O3–MgO composite ceramics were prepared via reactive hot pressing at 800 °C for 2 h under 30 MPa. The composites primarily comprised Cr0.19Fe0.7Ni0.11, Fe–Cr, magnesium aluminate spinel, Al2O3, and MgO phases. The mechanical properties and microstructure of the metal matrix composites changed with the changing in situ Al2O3–MgO content. The composite ceramic exhibited excellent mechanical properties (Vickers hardness = 5.59 GPa, bending strength = 244.59 MPa, and fracture toughness = 11.66 MPa·m1/2) when Al2O3/(MgO + Al2O3) (mol/mol) was 0.6371 owing to the difference in the residual stress at the interface between the ceramic particles and metal matrix.

Microstructure and mechanical properties of CrFeNi high-entropy alloy reinforced by Al and Ti elements

Developing high entropy alloys (HEAs) that possess both superior mechanical properties and low cost is a classic challenge in the design of alloys used in engineering applications. In this work, a series of Co-free Al x Ti(9–x)(CrFeNi)91(x = 0, 3, 6, and 9 at%, denoted as AlxTi(9-x) hereafter) HEAs were designed to investigate the influence of Al and Ti elements on the microstructure and mechanical properties of the FCC-structured CrFeNi alloy and pursue a considerable strength-plasticity balance. Massive precipitates with a nano-scale but different morphology and/or structure formed in the inter-dendritic region of alloys. The morphology of precipitates was strongly linked with the variation in the relative content of Al and Ti elements, which varied from a granular shape (ordered BCC structure) in Al9 and Al6Ti3 alloys to a strip shape (HCP structure) in Al3Ti6 alloy. With an increase (decrease) in Ti (Al) content, the yield strength of alloy significantly improved, which benefited from the combined effect of solution strengthening and precipitation strengthening, but the elongation dropped sharply. Compared to the same amount of Al element, Ti element contributed to the improvement of strength but deteriorated the plasticity of alloy. Thereinto, Al6Ti3 alloy presented a relatively favorable strength-plasticity balance with a yield strength of 768 MPa and an elongation of 10.2%. Apparently, only the moderate amount of Al and Ti elements helps to the favorable configuration of strength and plasticity. The findings in this work provide a distinct insight into the design and optimization of Co-free HEAs as the structural applications.