Cu-rich Clusters Research Articles

Atomic-scale three-dimensional irradiation-induced defect kinetics models for bcc Fe-based alloys

The interaction between irradiation defects and dislocations could lead to macroscopic hardening and embrittlement. In this study, molecular dynamics (MD) and machine learning were conducted to study three-dimensional void- and Cu-cluster-induced kinetics models under interaction with dislocations in body-centered cubic Fe-based alloys. MD Results show that dislocation climb and shear are two types of interaction mechanism based on the defect size. Combined MD results and machine learning, it was found that the dislocation length increased linearly with an increase in the size of the defects after the interaction. In addition, the number of atoms in the Cu-rich cluster and the reduced number of vacancies in the voids had a square relationship with the defect size where 0.85D2 is for Cu-rich cluster and 0.50D2 is for void. Furthermore, atomic-scale three-dimensional irradiation-induced defect kinetics models were developed and incorporated into the crystal plasticity finite element model (CPFEM). We also analyzed the contributions of various defects to the increase in the yield stress during CPFEM simulation. Compared with DBH model, the prediction of MD data-driven CPFEM matches better with the experimental data. Cluster contributed the most to hardening with low obstacle strength due to the higher number density compared with dislocation loops and voids. The loops also contributed to hardening; however, their contribution was smaller than that of the clusters. Although the number density and size of voids were minimized, they may have contributed because of the high obstacle strengths. This work can indeed deepen the understanding of irradiation effect in Fe-based alloys.

TiC-induced nanoscale Cu-rich re-precipitation mechanism under welding thermal cycles and its effect on the strength-toughness of heat affected zones

In order to solve the softening problem of welding heat affected zone (HAZ) for Cu-bearing steel caused by the dissolution of Cu-rich particles, TiC was utilized to induce the Cu-rich re-precipitation. With the peak temperature increased from 780 °C (ICHAZ) to 950 °C (FGHAZ), the size of 9R–Cu increases from 4 nm to 5 nm, accompanied with the increment of volume fraction from 0.6% to 1.0%. Phase field simulations indicate that TiC repels Cu atoms into γ-Fe matrix and promotes the formation of Cu-rich clusters. Then, Cu-rich clusters provide more nucleation sites for Cu-rich particles, which contributed to the re-precipitation of refined 9R–Cu. Due to the disappearance of coarse grain boundary Cu-rich particles and formation of fresh lath bainite, re-precipitated Cu-rich particles provided precipitation strengthening value of 237 MPa and 298 MPa without decreasing the low temperature toughness for ICHAZ and FGHAZ. The yield strength and absorbed energy at −40 °C of HAZs exceed 1000 MPa and 120J, respectively.

A multiscale study on the microstructure and hardening models of the irradiation defects on reactor pressure vessel steels: Modelling and experiment

Irradiation defects are known to impede the dislocation motion in irradiated reactor pressure vessel (RPV) steels. However, consistent experimental studies of the respective irradiation defects and relevant theoretical studies of the interaction mechanism and hardening model are still lacking. In this study, the microstructure and irradiation-induced hardening of RPV steels are investigated using transmission electron microscopy (TEM)/energy-dispersive X-ray spectrometry (EDS) and molecular dynamics (MD) simulations. In A508-Ⅲ steel, 9R, twinned fcc, and other typical Cu-rich cluster structures are observed using TEM after the irradiation experiment. Based on the experimental results, MD simulations are performed to study the interactions between the dislocations and Cu clusters or voids. A mechanism diagram of the interaction mechanism coupling the effects of temperature and defect size is shown for both the Cu clusters and voids. A relevant hardening model is proposed based on the MD data, which is further discussed in relation to the macroscopic mechanical properties. Furthermore, the irradiation-induced hardening of the RPV steel is successfully predicted, which further demonstrates the reliability of the proposed unified hardening model.

Tailoring microstructure and mechanical properties of 17-4PH steel fabricated by wire-arc directed energy deposition via a combination of intrinsic and post-processing heat treatments

This paper examines the effect of intrinsic heat treatment, i.e., multiple transient heating from subsequent passes, and post-processing heat treatment on the microstructure and mechanical properties of 17–4PH stainless steel fabricated by wire-arc directed energy deposition. By carefully controlling the interpass temperature to remain below the martensite start (Ms) temperature, intrinsic heat treatment effectively triggers the formation of Cu-rich clusters and the reversion of austenite. This approach results in a concurrent enhancement in the ultimate tensile strength, increasing from 1036 MPa to 1128 MPa, and elongation, increasing from 13.2% to 18.5%, for the as-built part. During post-processing heat treatment, the microstructural response to direct aging treatment hinges on the initial microstructure induced by intrinsic heat treatment. Notably, direct aging treatment significantly enhances the hardness and ultimate tensile strength of the as-built part created at an interpass temperature surpassing the Ms temperature. Conversely, its influence on the mechanical properties of the as-built component, fabricated at an interpass temperature lower than the Ms temperature, remains minimal. Additionally, the application of a solution treatment effectively eradicates the inherent microstructural characteristics, regardless of the initial fabrication conditions. Nonetheless, the grain size of the solution-treated specimen is markedly influenced by the as-built microstructure. Ultimately, a judicious amalgamation of intrinsic and post-processing heat treatments yields an exceptional combination of properties, including high hardness (465 HV), ultimate tensile strength (1437 MPa), and elongation (14.5%). These results underscore the significance of a comprehensive consideration of intrinsic and post-processing heat treatments to tailor the microstructure and mechanical properties of 17–4PH steel fabricated by wire-arc directed energy deposition.

Achieving ultra-high flow stress and hardness in a medium Mn stainless steel by the formation of strain-induced martensite and G-phase precipitates

This work demonstrates how the deformation of a medium Mn austenitic stainless steel and its subsequent thermal treatment results in the steel having an ultra-high flow stress, and with a microstructure containing strain-induced martensite (α′) and G-phase precipitates. A 14 wt.%Cr-8 wt.%Mn-1 wt.%Ni austenitic stainless steel was uniaxially compressed at room temperature and quasi-static strain rates to determine the evolution of strain-induced martensite with strain. Uniaxial compression resulted in a sigmoidal stress-strain curve (enhanced work-hardening) with the flow stress reaching ∼2.2 GPa, and the α′ fraction saturating at 0.8 true strain. Atom-probe tomography showed that aging at 400 °C for 72 h formed 2–3 nm sized G-phase precipitates containing Cu-rich clusters and having a nominal composition of Ni8Si2Mn20Cu17Cr8Fe44. Such a microstructure resulted in a steel with an ultra-high tensile strength and a compressive flow stress of around 2 GPa. Though the tensile ductility was low, there was sufficient flowability in compression.

Single crystal synthesis, structure, and magnetism of Pb10−xCux(PO4)6O

The recent claim of superconductivity above room temperature in Pb10−xCux(PO4)6O with 0.9 < x < 1 (referred to as LK-99) has sparked considerable interest. To minimize the influence of structural defects and impurity phases on the physical properties, we have synthesized phase-pure single crystals with a copper doping level of x ∼ 1. We find that the crystals are highly insulating and optically transparent. X-ray analysis reveals an uneven distribution of the substituted Cu throughout the sample. Temperature (T) dependent magnetic susceptibility measurements for 2 ≤ T ≤ 800 K reveal the diamagnetic response characteristic of a non-magnetic insulator, as well as a small ferromagnetic component, possibly originating from frustrated exchange interactions in Cu-rich clusters in the Pb10−xCux(PO4)6O structure. No anomalies indicative of phase transitions are observed. We, therefore, rule out the presence of superconductivity in Pb9Cu(PO4)6O crystals and provide some considerations on the origin of anomalies previously reported in experiments on polycrystalline specimens.

Thermal ageing effect on solute segregation and precipitation in the heat-affected-zone of dissimilar metal welds for nuclear power plants

Solute segregation in the carbon-depleted (CDZ) heat-affected zone of dissimilar metal welds (DMW) designed for nuclear power plant EPRTM reactors has been investigated by atom probe tomography (APT) and related to the mechanical properties (toughness test). The analysis of grain boundaries (GBs) by APT allowed the quantification of the P segregation and other solute elements, in all the analyzed samples, before and after long-term ageing heat treatments. The post-weld stress-relief heat treatment applied to the samples before the ageing heat treatments leads to important GBs segregation levels. Following thermal ageing treatments allow a relative increase of GB segregation. P segregation increases with the various thermal ageing conditions. The experimental data were used to model P segregation in high-angle GBs. The simulations show that P segregation is kinetically limited by bulk diffusion, explaining the observed P segregation increase with temperature. P segregation in GBs in the CDZ of the DMW should remain low compared to the expected equilibrium segregation level during the entire reactor service. In addition to solute segregation in extended defects, APT measurements revealed the presence of Cu-rich clusters in GBs, dislocations, and grains in all the aged samples. These clusters were not observed in the sample before ageing.

Optimized rolling processes to balance magnetic and mechanical properties of high-strength non-oriented silicon steels

A bottleneck in the development of high-strength non-oriented silicon steels for drive motors of new energy vehicles is the balance of strength and magnetic properties. This paper successfully tackled this problem through the optimization of thickness reduction for hot and cold rolling and the formation of coherent precipitates using a Cu-alloyed non-oriented silicon steel. More specifically, a thickness reduction of 96% in the course of hot rolling promoted the homogenization of microstructure during the following normalization treatment. Subsequently, a deformation degree of 80% during cold rolling ensured the inheritance of the uniform microstructure and inhibited the abnormal growth of recrystallized grains during annealing, thereby suppressing the iron loss to a value as low as 15.6 W/kg. At the meantime, this combined process promoted the inheritance of λ-fibers and the formation of {114}〈481〉 texture in the annealed sheet, improving the magnetic induction intensity B50 to 1.606 T. In addition, under the joint effect of a variety of strengthening mechanisms, the yield strength of this annealed sheet reached 668 MPa. A pronounced increase in strength, about 207 MPa, was derived from precipitation hardening by the great difference in the modulus between coherent Cu-rich clusters and the α-Fe matrix.

High-entropy Fe-Cr-Ni-Co-(Cu) coatings produced by vacuum electro-spark deposition for marine and coastal applications

High-entropy coatings (HECs) are of a great interest for the protection of structural steels and alloys used in the costal and offshore areas. Here, thick, dense, and uniform Fe-Cr-Ni-Co-(Cu) coatings with a crack-free surface have been successfully deposited on AISI 420S steel by vacuum electro-spark deposition using CrNiCo and CrNiCoCu electrodes. The coatings consist of columnar grains (approximately 300 nm in diameter) and subgrains (10–50 nm thick) of an fcc phase and spherical inclusions of mixed SiO2 + (Cr,Ti)2O3 oxide, 30–50 nm in size. Although Cu is an element prone to segregation, the experimental results show that Cu does not form its own phase and is in the metal solid solution. Molecular dynamics simulation shows that Cu has a slight tendency to self-clustering and form Cu-rich clusters in FeCrNiCo-Cu HECs. However, several regions enriched in Cu are observed in the FeCrNiCo-Cu samples. FeCrNiCo coatings tested in artificial seawater and the Black Sea exhibited enhanced corrosion resistance. In tribocorrosion tests, FeCrNiCo-(Cu) coatings performed better than steel substrate due to faster recovery of a passive film. The addition of Cu has a positive effect on the antibacterial activity of FeCrNiCo coatings against Gram-positive B. cereus Arc30 and B. cereus F strains.

Effect of Cu on the Microstructure and Mechanical Properties of a Low-Carbon Martensitic Stainless Steel.

Reversed austenite is of vital importance in low-carbon martensitic stainless steel because it improves impact toughness. However, a proper amount of reversed austenite is obtained by tempering at a critical temperature, which reduces the strength of the steel. Therefore, how to improve strength-toughness matching is an important problem. Copper (Cu) is an effective strengthening element in steels. However, there is little in-depth discussion on the role of Cu on the microstructure and mechanical properties of low-carbon martensite steel. In this work, the effect of different Cu content on the reversed austenite formation, tensile strength, and impact toughness of a low-carbon martensitic stainless steel (0Cr13Ni4Mo) was systematically investigated through use of a transmission electron microscope (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT), and other characterization methods and mechanical property tests. The results showed that the addition of Cu decreased the phase transition temperatures of martensite and austenite and increased the volume fraction of the reversed austenite. APT results indicated that Cu-rich clusters first formed with alloying elements such as ferrum (Fe) and nickel (Ni) and then grew to be precipitates through rejection of the alloying elements. The Ni atoms diffused towards the interface between the precipitates and the martensite matrix, which provided heterogeneous nucleation sites for the reversed austenite. Cu precipitations strengthened tensile strength during tempering. However, it generated temper brittleness in the steel at a tempering temperature of 450 °C, resulting in the impact energy of the 3Cu-steel being only 7 J. A good combination with higher tensile strength (863 MPa) and ductility (192 J) was obtained when tempering at 600 °C in the presence of Cu-rich precipitates and a sufficient volume fraction of the reversed austenite. The results provide guidance for the design of steels with reversed austenite and Cu and promote the development of high-strength and high-toughness steels.

Fast hardening response of martensitic stainless steel by copper-rich cluster formation under pulsed electric current

The pursuit of excellent comprehensive mechanical properties using a rapid aging process is of practical significance in the field of aging strengthening. A pulsed electric current assisted aging process can effectively accelerate aging and reduce the energy consumption caused by long-term thermal aging. The mechanism of a Cu-rich cluster formation promoted by a pulsed electric current was investigated to better understand the fast-hardening response process. The size and structure of the Cu-rich cluster were characterized using transmission electron microscopy (TEM); the results indicated that the pulsed electric current did not change the mechanism of aging strengthening but accelerated the process. The time required to achieve peak aging decreased owing to the athermal effect (interaction between atoms and electrons) induced by the pulsed electric current. The athermal effect decreased as the temperature increased, and a relationship between the athermal effect and temperature was obtained. When a current density of 7 × 107 A/m2 was applied, the precipitation activation energy of the Cu-rich clusters decreased by 91 kJ mol−1; this was owing to the following two aspects. (1) The pulsed electric current lowered the vacancy formation energy and resulted in an increase in vacancy concentration and (2) the current density gradient caused by the difference in conductivity between the matrix and Cu-rich clusters accelerated the substitution of the Cu atoms and vacancies and reduced the atomic migration energy. These results provide insights into the effect of a pulsed electric current on the kinetics of precipitation in the martensitic stainless steel and a deduction for the mechanism of the rapid growth of Cu-rich clusters.

Recent Advances on Composition-Microstructure-Properties Relationships of Precipitation Hardening Stainless Steel.

Precipitation hardening stainless steels have attracted extensive interest due to their distinguished mechanical properties. However, it is necessary to further uncover the internal quantitative relationship from the traditional standpoint based on the statistical perspective. In this review, we summarize the latest research progress on the relationships among the composition, microstructure, and properties of precipitation hardened stainless steels. First, the influence of general chemical composition and its fluctuation on the microstructure and properties of PHSS are elaborated. Then, the microstructure and properties under a typical heat treatment regime are discussed, including the precipitation of B2-NiAl particles, Cu-rich clusters, Ni3Ti precipitates, and other co-existing precipitates in PHSS and the hierarchical microstructural features are presented. Next, the microstructure and properties after the selective laser melting fabricating process which act as an emerging technology compared to conventional manufacturing techniques are also enlightened. Thereafter, the development of multi-scale simulation and machine learning (ML) in material design is illustrated with typical examples and the great concerns in PHSS research are presented, with a focus on the precipitation techniques, effect of composition, and microstructure. Finally, promising directions for future precipitation hardening stainless steel development combined with multi-scale simulation and ML methods are prospected, offering extensive insight into the innovation of novel precipitation hardening stainless steels.

Enhanced cryogenic and ambient temperature mechanical properties of CoCuFeMnNi high entropy alloy through controlled heat treatment

Dedicated thermal treatments can improve the mechanical behaviour of high entropy alloys (HEAs) by producing nanostructured microstructures with improved characteristics. Herein, the inherent metastability of an equiatomic CoCuFeMnNi alloy was exploited to induce the formation of secondary phases upon ageing treatment. Advanced characterization techniques, namely high resolution synchrotron X-ray diffraction and aberration corrected scanning transmission electron microscopy, allowed to describe the decomposition of the supersaturated solid solution. Nanometric rounded Cu-rich clusters in the solution-treated alloy and coherent, regularly oriented Cu-rich discs in the peak-aged condition were possibly produced by spinodal decomposition. An almost 100% enhancement of mechanical strength was obtained thanks to the modulation of composition. Moreover, mechanical behaviour at cryogenic temperature was improved by ageing, both in terms of strength and ductility. Plastic deformation took place by dislocation slip, regardless of the testing temperature. • CoCuFeMnNi high entropy alloy was subjected to solution treatment and ageing • The alloy’s inherent instability leads to decomposition of the supersaturated matrix. • The nanostructured microstructure led to improved mechanical behaviour.

Evidence of in-situ Cu clustering as a function of laser power during laser powder bed fusion of 17–4 PH stainless steel

The use of intrinsic heat treatments to control the microstructural evolution during additive manufacturing could eliminate the need for costly post-build processing. Using atom probe microscopy and cluster search algorithms, this study investigates the degree of Cu clustering and precipitation in 17–4 precipitate hardening (PH) stainless steel fabricated by laser powder bed fusion (LPBF). It was found that LPBF samples exhibit a greater than random degree of Cu clustering, irrespective of the laser power during fabrication. It is further shown that using a higher laser power (161.5 W rather than 127.5 W) led to a higher number density of Cu clusters, Cu precipitates, and higher hardness due to the greater heat input. The observations of Cu-rich clusters and precipitates within as-printed LPBF samples and its laser power dependence are novel and show potential for inducing desired strengthening phases directly during LPBF, mitigating the need for post-fabrication heat treatments.

Concurrent (Fe,Mo)2C carbides and Cu-rich clusters precipitation in ferritic steel containing copper during aging

ABSTRACT The concurrent (Fe,Mo)2C carbides and Cu-rich clusters precipitation in the ferritic steel containing copper after aging at 400°C for 4000 h have been investigated using transmission electron microscopy (TEM) and atom probe tomography (APT). The results show that spinodal decomposition and an atomic ordering reaction occur in the ferritic steel containing copper. After aging, the retained austenite decomposed by the spinodal mechanism into C-rich and C-lean regions. The C-rich phase transforms into the (Fe,Mo)2C carbides via the ordering reaction, while Cu-rich clusters formed in the C-lean regions. The experimental results can be interpreted on the basis of phase separation via spinodal decomposition followed by chemical ordering. The small size of Cu-rich clusters can be attributed to the lower diffusion coefficient of Cu in the retained austenite.

Microstructure, Inclusions, and Elemental Distribution of a Compacted Graphite Iron Alloyed by Ce and La Rare Earth (RE) Elements

This work investigates the microstructure and inclusions of a compacted graphite iron (CGI) alloyed by Ce and La rare earth (RE) elements. In our study, alloying elemental distribution and solute segregation were characterized by methods of secondary ion mass spectrometry (SIMS) and a three-dimensional atom probe (3DAP) with high sensitivity and spatial resolution. RE sulfide, MgS, carbide, and composite inclusions formed during solidification and provided heterogeneous nucleation cores for the nucleation of the graphite. Significant solute clustering in the matrix, coupled with the segregation of solute to grain boundaries, was observed. C, Mn, Cr, and V were soluted in cementite and promoted the precipitation of cementite, while Si was found to be soluted in ferrite. Cu is usually distributed uniformly in ferrite, but some Cu-rich atom clusters were observed to segregate towards the interface between the ferrite and cementite, stabilizing the pearlite. In addition, P, as a segregation element, was enriched along the boundaries continuously. The RE elements participated in the formation of inclusions, consuming harmful elements such as As and P, and also promoted the heterogeneous nucleation of the graphite and segregated, in the form of solute atoms, at its interfaces.

Direct Observation of Cu Clusters and Dislocation Loops by Cs-Corrected STEM in Fe-0.6wt%Cu Alloy Irradiated in BR2

The neutron irradiation of Fe-based fusion and fission reactor materials leads to an increase in ductile-to-brittle transition temperature with a decrease in upper shelf energy. It is well known that Cu content has a strong influence on the embrittlement phenomenon, as Cu-rich clusters (CRPs) are thought to be directly responsible for embrittlement. In contrast, mechanical property studies for steels with different Cu levels exhibit dominant matrix defects in the embrittlement of both low-Cu steels and high-Cu steels at high fluences. To determine the effects of dislocation loops and CRPs on radiation hardening in those steels, neutron irradiation was conducted on Fe-0.6wt%Cu alloy. The neutron irradiation was performed in BR2 at 290 °C up to a dose of 4.1 × 1024 n/m2. After irradiation, the microstructure was observed and analyzed by spherical aberration-corrected transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) combined with X-ray energy-dispersive spectroscopy, using a JEOL ARM200FC. This technique enabled simultaneous observation of ~10 nm CRPs and dislocation loops. Additional high-voltage electron irradiation was performed at room temperature, and the dislocation loops were identified as interstitial-type dislocation loops. Radiation-induced hardening due to neutron irradiation was estimated by measuring the size and density of the dislocation loops and the CRPs. These results suggest that simultaneous observation of dislocation loops and CRPs using the Cs-corrected STEM with EDS analysis is essential for the study of radiation-induced hardening in Fe-based alloys.

Phase instabilities in austenitic steels during particle bombardment at high and low dose rates

Disruption of phase stability by energetic particle bombardment is a major challenge in designing advanced radiation-tolerant alloys and ion beam processing of nanocomposites. Particularly, ballistic dissolution susceptibility of different solute nanocluster species in alloys is poorly understood. Here, low dose rate neutron irradiations were conducted on a Fe-Cr-Ni based austenitic steel in the BOR-60 reactor (9.4 × 10−7 dpa/s, 318 °C) followed by accelerated dose rate ion irradiations at multiple temperatures (~ 10−3 dpa/s, 380 – 420 °C). Using atom probe tomography, the stability of radiation-enhanced Cu-rich and radiation-induced Ni-Si-Mn-rich nanoclusters was evaluated. During neutron irradiation, Cu-rich clusters nucleated with their core concentrations progressively increasing with dose, while Ni-Si-Mn-rich clusters formed and evolved into G-phase precipitates. Ion irradiations dramatically altered the nanoclusters. Cu-rich clusters were ballistically dissolved, but Ni-Si-Mn-rich clusters remained stable and coarsened with dose at 400 and 420 °C, highlighting that different nanocluster species in a single microstructure can have innately distinct ballistic dissolution susceptibilities. Solute-specific recoil rates were incorporated into the Heinig precipitate stability model, which shows that in addition to radiation-enhanced diffusion, recovery from ballistic dissolution depends on solute concentration gradient near cluster interfaces. The combined experimental-modeling study quantified the critical temperatures and damage rates where ballistic dissolution dominates for each cluster species.

Microchemical evolution of irradiated additive-manufactured HT9

The microstructural responses under 5 MeV Fe2+ single-ion-beam irradiation of three conditions of additive-manufactured (AM) HT9 steel using a powder-based directed energy deposition (DED) technique with and without postbuild heat treatments were investigated. Besides the observed dislocation loop formation and the absence of cavities at the irradiation condition of 50 dpa at 460 °C, Ni/Si/Mn-rich precipitates are found to form in all three conditions of AM-HT9, whereas Cu-rich clusters that arise from Cu uptake from the DED process are only observed in the heat-treated conditions, and not in the as-built (ASB) condition. Coprecipitation of the Cu- and Ni/Si/Mn-rich clusters occur near defect sinks such as line dislocations and grain boundaries in the heat-treated AM-HT9. The variation in microchemical evolution can be directly linked to the starting sink strength of the 3 AM-HT9 conditions, and the ASB condition with higher sink strength suppressed the responses observed in the postbuild heat-treated specimens.

Evolution of nanosized Cu-rich clusters in a Fe–15Cu–15Ni alloy produced by laser powder bed fusion

Designing a metastable microstructure with a coherent nano-sized precipitation phase in the matrix is an effective strategy in improving the strength of materials. Recently, the rapid fusion and solidification cycle associated with laser-based additive manufacturing (AM) has emerged as a promising strategy to design unique microstructures with lattice distortion, solute segregation, and nano-sized precipitations. In this study, the evolution of nano-sized Cu-rich clusters in an AM-processed Fe–15Cu–15Ni alloy (wt.%) was investigated by conducting multiscale microstructural characterization. The results reveal that nano-sized Cu-rich clusters were generated inside the matrix due to a phase decomposition induced by the intrinsic heat treatment during the AM process. The heat energy generated by the laser beam not only initiated Cu-rich cluster formation, but also induced precipitation growth. Therefore, the average Cu-rich cluster size increased with an increase in the volumetric energy density. The hardness of the AM-processed Fe–15Cu–15Ni alloy at first increased with an increase in the energy density until a medium energy density level (140 J/mm3), due to formation of Cu-rich clusters. The hardness decreased with further increase in energy density (185 J/mm3), due to the Cu-rich cluster growth and retained austenite. The results reveal that laser-based AM successfully induces nano-cluster without the need for post-treatment and that the mechanical properties of materials can be optimized by adjusting the processing parameters in a way to enable nano-sized cluster and phase formation.