FeNi-based Alloys Research Articles

Ultrastrong and ductile FeNi-based alloys through Pd-containing multicomponent L12-type precipitates

Precipitation strengthening stands as a paramount strategy for enhancing the mechanical properties of FeNi-based alloys. Conventional precipitates used for strengthening typically contain only two major constituent elements selected from Ni, Al, and Ti. However, knowledge about the intrinsic properties and strengthening mechanisms of multicomponent precipitates remains limited. Here, we propose introducing novel multicomponent L12-type precipitates containing palladium (Pd) to strengthen FeNi-based alloys. The strengthened FeNi alloy achieves an eightfold increase in strength compared to the FeNi matrix while maintaining good ductility. Using meticulous micro-characterization and energy-dispersive X-ray spectroscopy (EDS) techniques, in conjunction with first-principles calculations, this study investigated the effects of Pd addition on the thermodynamic stability, morphology, coherency, and strengthening mechanisms of the precipitates. Results indicate that the addition of Pd induces the nucleation of L12-type precipitates, increases their ductility, and eliminates anisotropy in the shear modulus of the precipitates. Excessive Pd content can alter the shape of precipitates from spherical to acicular due to increased interfacial mismatch between the precipitates and the FeNi matrix. These insights shed light on the impact of Pd addition on the intrinsic properties of L12-type precipitates, offering a promising pathway for the design of advanced FeNi-based alloys with optimized mechanical performance.

A novel under-aging design to improve the creep rupture life of a precipitation-strengthened Fe–Ni-based superalloy

The under-aging, peak-aging, and over-aging microstructures of a precipitation-strengthened Fe–Ni-based alloy were designed by applying different heat treatment procedures. Tensile creep tests were conducted at 700 °C and 250 MPa on samples exhibiting different strengthening γ′ precipitate volume fractions and diameters. The creep life of the alloy in the under-aged state was increased by more than 10% compared to the peak-aged condition, which provided a new approach to designing the heat treatment regime that improve the creep rupture life and plasticity of precipitation-strengthened alloys. The improvement in creep properties of the under-aged state was attributed to the transition from shearing to Orowan looping of γ′ particles by matrix dislocations during the dynamic precipitation and coarsening of γ′ phase, increasing intragranular deformation resistance. The under-aged microstructure design allowed reducing the grain boundary sliding contribution to overall strain during creep. As a result, the steady-state creep stage of the alloy in the under-aged state was extended. Additionally, relationships between applied stress and nucleation, growth, and coarsening of the γ′ phase have been evidenced.

Development of an interatomic potential for L12 precipitates in Fe–Ni–Al alloys

Fe–Ni-based alloys have been considered as candidate structural materials for advanced nuclear reactors, and some of their excellent properties are particularly associated with L12 precipitates dispersed in the alloys. For a better understanding of the irradiation response, classical molecular dynamics is an essential tool to simulate the irradiation-induced defect formation and subsequent microstructural evolution. We here develop an interatomic potential for L12(Ni,Fe)3Al precipitates in the ternary Fe–Ni–Al system. The fitting parameters are tuned to describe the lattice and elastic constants of NiFe solid solutions and defect formation/vacancy migration energies in the fcc matrix. Furthermore, the lattice properties and defect energies of L12(Ni,Fe)3Al are considered for the fitting. We demonstrate the developed potential reproduces the lattice and defect properties with reasonable accuracy by comparison with density functional theory calculations, existing empirical potentials, and experimental data. This potential will be useful to investigate the defect formation and evolution of (Ni,Fe)3Al precipitates in the alloys under irradiation, which would provide critical insights into the materials design strategy to achieve enhanced properties.

The Stress-Controlled Low Cycle Fatigue Properties of HK40 and HP40 Heat-Resistant Fe–Ni Base Alloys

The Stress-Controlled Low Cycle Fatigue Properties of HK40 and HP40 Heat-Resistant Fe–Ni Base Alloys

The formation of structural disorder in FeNi-based alloys – Theoretical approach

• Positive values of enthalpy of formation of amorphous phase in Fe-Ni system confirmed on the basis of Miedema’s model. • Insignificant influence of Co doping on the enthalpies of formation in FeNi system. • Promotion of amorphous phase and solid solution formation ability depending on Cu substitution. • Cu as promising candidate when aiming destabilization of FeNi crystalline structure. FeNi-based alloys are known to crystallize in bcc or fcc-structures depending on their composition. In many slowly cooled objects, like meteorites, L 1 0 -type phase (tetrataenite) with its characteristic layered Fe/Ni structure has been found. Nevertheless, the synthesis of L 1 0 FeNi phase in industrial amount in a bulk form has not been possible, mainly due to sluggish diffusion and low order/disorder temperature of this phase. We present results of the calculations of formation enthalpies for solid solution and amorphous phase in Fe-Ni system. Additionally, we performed calculations for Co and Cu substitutions (found in meteoritic matter). Our calculations confirm poor glass forming ability of FeNi system and limited influence of Co in this aspect. In contrast, Cu is a promising candidate when aiming at destabilization of FeNi solid solution, as a starting point in L 1 0 phase formation. Formation enthalpy for some Cu-substituted compositions reaches highly negative values. It is expected that at least local chemical segregation should be facilitated by the presence of Cu atoms (attributed mainly to different values of Cu-Co and Cu-Ni interfacial enthalpies).

Effect of Si addition on the magnetic properties of FeNi-based alloys with L10 phase through annealing amorphous precursor

As a promising candidate of rare-earth free hard magnetic materials, L1 0 -FeNi has been paid much attention in the last decades. However, it is difficult to be artificially fabricated due to its low thermal stability and sluggish diffusion ability of atoms below the crucial temperature of 320 °C. In this study, a promising method of annealing amorphous precursor was extensively developed through (Fe 50 Ni 50 ) 84−x Si x P 16 (x = 0, 4 at%) and (Fe 50 Ni 50 ) 86−x Si x P 14 (x = 2, 4, 8 at%) alloys. Especially, the effect of Si on the formation of L1 0 phase in annealed FeNi-based alloys was investigated and clarified. It is found Fe 42 Ni 42 P 16 with a much low crystallization temperature could be an appropriate basic amorphous alloy for the formation of L1 0 phase. The addition of Si enhanced the thermal stability of Fe-Ni-P amorphous alloys. Interestingly, Si could stabilize the L1 0 phase in annealed samples and increase its disordering temperature above which L1 0 -FeNi phase could deteriorate into soft magnetic phase. As expected, appropriate Si addition indeed improved the hard magnetic properties of the annealed alloys and samples with high coercivity above 900 Oe was obtained. Further Si addition would deteriorate the magnetic-crystalline anisotropy of L1 0 phase and decrease the coercivity of annealed Fe-Ni-Si-P alloys. Nevertheless, the results indicate that increasing the order-disorder transition temperature through element doping in L1 0 lattice would be a promising strategy for the massive formation of L1 0 -FeNi like other ordered phases (i.e. L1 2 -FeNi, L1 0 -CoPt), and could substantively contribute to the artificial fabrication of FeNi-based rare-earth free magnets in future. • Sample with the high coercivity above 900 Oe is obtained by annealing Fe-Ni-Si-P amorphous alloy. • The addition of Si increases the crystallization temperatures and thermal stability of Fe-Ni-P amorphous alloys. • Si could enhance the thermal stability and the disordering temperature of L1 0 phase. • Excessive Si addition would deteriorate the intrinsic magnetic hardness of L1 0 phase.

Effect of long-term aging on microstructural stability and tensile deformation of a Fe–Ni-based superalloy

The microstructural evolution, tensile behavior and deformation mechanism of a Fe–Ni-based superalloy for advanced ultra-supercritical coal-fired power plant during long-term isothermal exposure at 700–800 °C for 500–3000 h were investigated. The coarsening rate constant of γ′ phase in the alloy exposured at 700 °C, 750 °C and 800 °C were about 47.543 nm3/h, 277.963 nm3/h and 2201.937 nm3/h, respectively. The activation energy for γ′ growing is around 250.24 kJ/mol. The results showed Al, Ti and Ni elements primarily gathered into γ′ precipitates, while Cr and Fe mainly partitioned into γ matrix in Fe–Ni base alloy. After long-term aging, there was no precipitation of harmful phases such as the η and σ phases, but the decomposition of MC + γ → M23C6 + γ′ was observed. The microcracks were prone to initiate and propagate around pores formed by MC decomposition and lamellar M23C6 carbide, which might result in the premature fracture failure of the alloy. The yield strength first remained stable with a slight increase in the γ′ phase diameter and then decreased after further thermal exposure. The variation of tensile strength with precipitate size could be rationalized by the transformation between shearing model and Orowan looping mechanism of γ′ precipitates with increasing the γ′ precipitate size.

Deoxidation and inclusion evolution of FeNi-based expansion alloy smelted by slagging method

ABSTRACT The composition of CaO-SiO2-MgO-Al2O3-CaF2 slag was designed by thermodynamic calculation of [Al]-[O] equilibrium of FeNi-based expansion alloy. On this basis, the deoxidation and inclusion evolution in the process of slagging and smelting FeNi-based expansion alloy in the medium frequency induction furnace were investigated. The results show that the oxygen content in the alloy melt is mainly controlled by the [Fe]-[O] equilibrium, and the change trend of the equilibrium oxygen content calculated by [Fe]-[O] equilibrium is consistent with the actual oxygen content. The total oxygen content of the final ingot is 45 ppm. After Al deoxidation in the melting process, the inclusions in the alloy are transformed into composite oxide inclusions rich in Al2O3 and MgO. After final deoxidation with Si-Ca alloy, the contents of Al2O3 and MgO in the inclusions decreased significantly, while the CaO content increased. And there are mainly CaO-SiO2-MgO-Al2O3 composite oxide inclusions in the ingot.

Effect of in-situ TiB2 particles on microstructure and mechanical properties of Al–Fe–Ni manufactured by selective laser melting

To simultaneously enhance the strength and ductility of novel heat-resistant Al–Fe–Ni alloy manufactured by selective laser melting (SLM), nano-TiB2 particles are introduced to break the strength-ductility trade-off. In this study, in-situ TiB2 decorated Al–Fe–Ni composite and Al–Fe–Ni base alloy have been successfully fabricated by SLM to investigate the effects of TiB2 particles on the microstructure and mechanical properties. The results showed that broader SLM process windows and higher relative densities (better SLM processability) were achieved in the composite. The introduced TiB2 particles transformed the large elongated grains with a strong {100} texture in the Al–Fe–Ni alloy to fine equiaxed grains with random orientation in the TiB2/Al–Fe–Ni composite. The morphology and distribution of Al9FeNi phases were also changed due to the existence of particles. The stress-strain curves obtained from tensile tests showed that the strength and ductility were improved simultaneously in the composite compared with those in the alloy. The underlying mechanisms of strengthening and enhancing ductility are preliminarily elucidated.

Effects of P addition on the glass forming ability, crystallization behaviour and soft magnetic properties of FeNi-based amorphous alloy

In this work, the effects of P substitution on the thermal stability, crystallization behavior, and magnetic properties of melt-spun and annealed (Fe40Ni40Si9.5B9.5-xPxCu1)0.97Nb0.03 (x = 0, 1, 2, 3 and 4) alloy ribbons the have been explored. All alloys can be readily fabricated into completely amorphous structures with good surface quality by the melt-spinning method. Thermodynamic investigation reveals that proper P addition not only favors the amorphous formation but also enhance anti-crystallization ability. These alloys show excellent magnetic properties after optimal annealing, i.e., low coercivity (Hc) of 0.06–1.16 A/m, high permeability (μe) of 11680–17100 and moderate saturation magnetization (Ms) of 85.4–97.6 Am2/kg. Besides, the substitution of minor P metalloids facilitates homogeneous precipitation of α-Fe nanocrystals. This work helps us to develop a novel the FeNi-based alloy is vital important for achieving excellent soft magnetic properties.

Effect of Si Addition on the Magnetic Properties of Feni-Based Alloys with L10 Phase Through Annealing Amorphous Precursor

Effect of Si Addition on the Magnetic Properties of Feni-Based Alloys with L10 Phase Through Annealing Amorphous Precursor

High-temperature corrosion of an Fe–Ni-based alloy HR6W under various conditions at 750 °C and 810 °C: Effect of the temperature, water vapor, simulated ash and SO2

The influences of temperature, SO2, water vapor and simulated ash on the high-temperature corrosion of an Fe–Ni-based alloy HR6W at 750 °C and 810 °C for 1000 h was systematically investigated. The weight gains and characterization of the corrosion products formed on the HR6W alloy in various environments were used to obtain the high-temperature corrosion behaviors of the alloy. The results show that weight gains of alloy HR6W under various gas conditions at 750 °C and 810 °C was much lower than that of the samples coated with salt, indicating that alloy HR6W exhibited excellent corrosion resistance due to a Cr2O3-rich scale. The SO2 promoted crackings of the Cr-rich oxide scales at 750 °C and 810 °C. After exposure to air containing water vapor and SO2, the corrosion products were mainly composed of an outer layer of Fe2O3, a small amount of NiO and an inner layer of Cr2O3. Sulfidation of alloy HR6W underneath the Cr-rich oxide scale was clearly observed on the samples exposed to SO2 and on all samples coated with salt. Additional NiO was found on the samples coated with salt exposed to air containing SO2. Alloy HR6W coated with salt exposed to air containing SO2 at 750 °C and 810 °C experienced the most severe corrosion among all samples herein due to the high causticity of the alkali-iron-tri-sulfates. The key elements affecting the high-temperature corrosion of alloy HR6W in the various gas environments were temperature > SO2>water vapor, in the order. Under the gas-molten salt conditions, the SO2 played the most important role in determining the corrosion rate. The key elements were SO2> temperature > water vapor, in that order.

Structural transformations and magnetic properties of plastically deformed FeNi-based alloys synthesized from meteoritic matter

In this work we investigated FeNi-based alloys synthesized from the cosmic matter of Morasko Meteorite (MM). The fall of Morasko iron meteorite is one of the biggest known in Central Europe and it has been dated to take place about five thousand years ago. It is known that iron meteorites contain hard magnetic tetrataenite phase (L10 FeNi), which has not been synthesized on the Earth in significant amount in the bulk form yet, because of very sluggish diffusion of Fe and Ni atoms below the disorder-order temperature of 320 °C. Firstly we doped the metallic part of Morasko Meteorite with Ni to obtain nearly equiatomic composition Fe51Ni49, which is the composition of pure tetrataenite.Further synthesis steps (melt-spinning, high pressure torsion, isothermal annealing at Ta = 320 °C for τa = 720 h) were undertaken to induce structural disorder and to observe changes in the structure/microstructure of the meteorite melt with nickel and its magnetic behavior. The presence of fcc FeNi with slightly varying lattice constant was confirmed at each step of the treatment. It evolved from the initial value of a = 3.589 ± 0.001 Å in the as-quenched state, through 3.591 ± 0.001 Å after 10 revolutions in the high pressure torsion process, to the maximum value of 3.593 ± 0.001 Å after 30 revolutions of anvils. No significant impact of further application of stress (50 revolutions) was noted, as the lattice parameter changed within the uncertainty limit. After annealing, the lattice parameter decreased to the initial value of the as-quenched sample (a = 3.589 ± 0.001 Å). The observed broadening of the peaks in the X-ray diffraction patterns may be attributed to the presence of microstrains and refinement of crystallites. Both contributions were determined using the Williamson-Hall method. In the initial state, the domain sizes were of about 100 ± 17 nm and diminished to 36 ± 11 nm after application of stress. Further isothermal annealing did not change the crystallites size, which was evaluated to be 35 ± 9 nm. Microstrains in the initial state were determined as (0.039 ± 0.017)10−3 and increased significantly to (0.562 ± 0.060)10−3 after 30 revolutions of anvils. Isothermal annealing decreased microstrains to (0.215 ± 0.071)10−3. After application of stress, the coercivity and remanence were enhanced, while subsequent isothermal annealing caused their decrease. Moreover, severe plastic deformation facilitated saturation of magnetization. As-quenched sample reached saturation at a magnetic field of about 2 T, while for high pressure torsion processed alloy this value was significantly reduced.

Design of wear and corrosion resistant FeNi-graphite composites by laser cladding

Friction and wear can cause severe surface damage of machine elements and result in their complete failure. Of the several ways to limit/control friction and wear, a measure to counter the potential damage is to apply a layer of a material with more desirable surface properties, which also provides the flexibility to use cost-efficient bulk materials. In systems under dry sliding conditions, such as railway switches, replacing the components cost considerable time and money. In the current study, laser cladding, a well-known powerful process for repair engineering, was used to fabricate new innovative low friction materials for dry sliding contacts that are exposed to corrosive attacks. The successful implementation of graphite as a solid lubricant in dry sliding conditions is well-known. A homogenous coating with an austenitic FeNi-based alloy containing different percentages of graphite was applied by means of laser cladding using preplaced powder method. The effect of graphite content and its lateral distribution on the friction and wear properties is investigated using a modified ASTM G65 test rig in two-body sliding configuration. Tribological results showed that increasing graphite content in the clads significantly reduces wear, but the level of the coefficient of friction appears to be determined mainly by the composition of the matrix. The wear resistance can be further increased by maximising the inter-particle distances. On the whole, clads of all compositions had superior wear resistance compared to reference materials such as stainless steel XNi22 and cast iron GJL250. The clads were further classified in terms of corrosion resistance against synthetic sea water in a modified potentiodynamic setup. The resistance to wear and corrosion improve with graphite content.

Correlating the lattice parameter and Curie temperature of γ-Ni in Fe-Ni-base alloys

We report a correlation between the Curie temperature (TC) and lattice parameter (a) of γ-Ni phase in Fe-Ni-base alloys. The Bethe-Slater curve represents the dependence of exchange integral (J) on the ratio of the interatomic spacing (D) to the diameter of 3d orbital (d) of an element. According to the mean field model, the exchange integral J is directly proportional to the TC. A large number of Fe-Ni base alloys were surveyed to establish a mathematical relationship between TC and D/d, as well as to predict the TC of FCC γ-Ni phase by estimating its lattice parameter.

Microstructure Evolution of Fe–Ni-Based Alloy HR6W during Isothermal Aging

Microstructure Evolution of Fe–Ni-Based Alloy HR6W during Isothermal Aging

The Study on Welding Technology of 9Ni Steel

9Ni steel is a low temperature serving ferrite steel, providing high strength and excellent low temperature toughness, which could serve well at-196°C. Therefore 9Ni steel is widely used in storage tanks and transport ships for liquefied natural gas (LNG). Nevertheless there are some challenges in the industrial application, such as hot cracking, cold cracking, magnetic arc blow, etc.. In this paper, the study on the welding technology of 9Ni steel developed by Baosteel is carried out. Firstly the weldability is analyzed through welding thermal simulation using Gleeble 3500 system, Y-groove cracking test, maximum hardness in weld heat-affected zone test. The results prove that 9Ni steel could be welded without preheating. The welding consumables have also significant influence on the performance of the welded joints. In this paper the characteristics of different types of welding consumables, including ferrite base type, austenitic stainless steel type, Ni-base alloy type and Fe-Ni base alloy type are analyzed, then the selecting principle for welding consumables is proposed. Furthermore welding process experiments are undertaken using various welding procedures such as SMAW, GTAW, FCAW and SAW. The results indicate that heat input and interpass temperature should be controlled to ensure a sound weld joint. Finally fracture toughness at-196°C of 9Ni steel and its joint is studied using CTOD test. In conclusion, 9Ni steel developed by Baosteel has good weldability and can meet the requirements of industrial application.

Formation and Magnetic Properties of Nanocomposites in Rapidly Solidified Fe42Ni41.7C7Si4.5B3.9P0.9 (at%) Ribbons

A novel nanocomposite structure comprising ~ 20-nm face-centered cubic Fe50Ni50 nanocrystals embedded within an amorphous matrix has been developed directly from a liquid alloy of Fe42Ni41.7C7Si4.5B3.9P0.9 (at%) through melt-spinning. Grain growth kinetics was significantly limited by the amorphous phase formed between nanocrystals. Glass forming elements rejected from nanocrystals stabilize the amorphous phase restricting further growth of nanocrystals. The nanocomposite ribbon exhibits excellent soft magnetic properties compared to those of the conventional micron-scale microstructured Fe50Ni50 alloy known as 50 Permalloy. When the as-melt spun ribbon was heated to 600 °C, two exothermic events occurred. The formation of metastable C-rich Fe3Ni and Si- and P-rich FeNi phases at low temperatures was confirmed by detailed transmission electron microscopy analysis. The hard magnetic behaviors of these metastable phases were estimated based on the hysteresis curve analysis results obtained from a ribbon heated to 600 °C. Through proper addition of glass-forming elements to FeNi-based alloys, nanocomposites with superior soft magnetic properties were effectively fabricated for massive practical soft magnetic applications.

Effects of Corrosion in Supercritical CO2 on the Microstructural Evolution in 800H Alloy

This study investigates corrosion of Fe–Ni-based alloy 800H that were exposed to supercritical CO2 (sCO2), ambient air and argon gas at pressures up to 20 MPa, at 650 and 750 °C for up to 1000 h. This alloy and other comparable metal alloys are expected to be used in sCO2 heat exchanger cycles as proposed in the DOE Advanced Ultra-Supercritical program. Alloy 800H is considered for this application, because it meets the high-temperature strength and creep rupture requirements and is a lower cost alternative to other Ni-based alloys. The oxidation performance and microstructural changes due to exposure in sCO2 have been evaluated and compared with exposures in air and Ar. The 800H alloy showed similar oxide scale thicknesses in sCO2 as in air. A recrystallized zone was observed beneath the oxide formed in air and sCO2. No such zone was observed after exposure to Ar, suggesting this recrystallization was associated with the oxidation process and not simply an effect of surface finishing. A wider recrystallized zone was observed underneath the oxide formed in sCO2 than in air. The effect of air and sCO2 on internal oxidation and carburization was investigated as well, showing that air led to more internal oxidation but less internal carburization than sCO2. It was concluded that the carbon species provided by the sCO2 atmosphere in conjunction with the increased grain boundary density in the recrystallized zone allowed for more ingress of carbon into the base metal, which resulted in a higher densities of carbides beneath the oxide scale.

High temperature oxidation of Fe–Ni-base alloy HR120 and Ni-base alloy HAYNES 282 in steam

High temperature oxidation of Fe–Ni-base alloy HR120 and Ni-base alloy HAYNES 282 in steam at 800–1000 °C was investigated and compared. Results show that the oxidation kinetics of HAYNES 282 and HR120 followed a parabolic law. Temperature affected the stability of formed chromia, leading to the observation of (Fe, Cr)2O3, Fe2NiO4 on the surface of Fe–Ni-base alloy, which is not the case for Ni-base alloy. The strengthening element titanium accelerated the growth of chromia formed on the Ni-base alloy. It is concluded that the resistance of high temperature oxidation of HR120 is superior to HAYNES 282.