Precipitation Behavior Research Articles

Precipitation Behavior and Phase Stability in Al-Cu-Mg-Li-Sc Alloy During Aging

Precipitation Behavior and Phase Stability in Al-Cu-Mg-Li-Sc Alloy During Aging

Precipitation behavior and strengthening mechanism of Q420 grade hot rolled V microalloyed ultra large H-beam

This study investigates the precipitation characteristics, precipitation kinetics, and strengthening mechanisms of Q420 grade hot-rolled ultra-large H-beams, focusing on three representative sites: the web center (W), flange quarter (F), and R-angle (R). Experimental results reveal nano-scale V(C, N) precipitation at all three sites, primarily featuring random and interphase precipitation, along with a small amount of austenite region precipitates and fibrous precipitates (FB). The average particle diameters are similar across sites: 8.2 ± 0.1nm (W), 8.8 ± 0.2 nm (F), and 8.1 ± 0.1nm (R). Calculations of precipitation-time-temperature (PTT) and nucleation-rate-temperature (NrT) curves indicate that precipitates nucleate uniformly during cooling, consistent with transmission electron microscope (TEM) observations, which reveal minimal precipitation at grain boundaries (GB) and dislocations. Strengthening contributions from precipitation are calculated at 87 MPa for W, 50 MPa for F, and 56 MPa for R. The low contributions can be attributed to the presence of numerous FB and precipitation-free zones (PFZ) at these sites. Among the three sites, W exhibits the highest strengthening due to its smallest interphase precipitation spacing. The F site, characterized by the highest dislocation density, has the largest average precipitate size and least interphase precipitation, resulting in the lowest contribution to precipitation strengthening.

Direct observation of the evolution behavior of micro to nanoscale precipitates in austenitic heat-resistant steel via electron channeling contrast imaging

Precipitation directly determines the high-temperature properties of the austenitic heat-resistant steels. The precipitations of MX, Z-phase, M23C6 and σ-phase, ranging from micrometers to nanometers, are commonly characterized using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). However, details of their evolution behavior are still unclear due to the limited SEM resolution using the traditional sampling method and the limited spatial resolution of TEM. In this work, field emission SEM-based electron channel contrast imaging (ECCI) techniques with flexible sampling routes were introduced to observe the precipitation evolution behavior of HR3C steel after aging at 700 °C for 8095 h. We showed that the coarse primary-MX and Z-phase in the as-received steel are relatively stable during aging. The coarse M23C6 and tiny secondary Z-phase dispersions were rapidly formed along the grain/twin boundaries and within dislocation arrays inside the grain interior, respectively. We further found that the M23C6 at grain boundaries would change from continuous to semi-continuous due to the formation of σ-phases, while in twin boundaries, it would become continuous over aging. Moreover, we showed that the σ-phases were in-situ transformed from M23C6 at the grain boundaries via its dissolution, facilitating the nucleation of tiny Z-phase inside the σ-phase grains, and this phenomenon has not been reported so far. We have demonstrated that ECCI with an electrolytic-polishing-based sampling route is effective in revealing multi-scale precipitation with high-throughput efficiency, and it allows the direct observation of the complex behavior of precipitates down to the nanoscale using a bulk sample. This method can be used as an efficient way for the quantitative microstructure study.

The control of fully equiaxed microstructure in laser welding Al-mg-Er-Zr alloy

The Al-Mg-Er-Zr alloy with higher strength and thermal stability was focused on as promising candidate in shipbuilding field. However, when this material was joined and manufactured with high-efficiency laser welding technology, the unmelted strengthening Al3(Er,Zr) particles segregated in weld bead and formed the discontinuous fine equiaxed and column grain zone simultaneously which decreased the joint strength. In order to solve the segregation behavior of precipitates and obtain the fully equiaxed microstructure of weld seam, the transverse scanning adjustable-ring-mode laser technology was employed. The stirring effect in the molten pool pushed the unmolten Al3(Er,Zr) dispersoids from the fusion line to the weld center. At the same time, the temperature distribution of weld seam was more homogeneous as inhibited the growth of column grain. Finally, the homogeneously distributed Al3(Er,Zr) particles as well as higher supercooling degree in the molten pool refined the microstructure. The optimal weld joint was obtained, which displayed remarkable mechanical performance with tensile strength of 389 ± 1 MPa, up to 93.3 % of base metal.

Roles of Al/Ni ratio and solidification cooling rate in grain boundary engineering of AlxCrFeMnNi(2-x) high entropy alloy

In this work, the roles of Al/Ni ratio and solidification cooling rate in grain size, dendrite morphology and grain boundary characteristic of the AlxCrFeMnNi(2-x) (x = 0.3, 0.7 and1.0) high-entropy alloys (HEAs) were investigated. The results show that the increasing of Al/Ni ratio results in a transition from single-phase FCC to dual-phase BCC + B2 along with the reverse precipitation behavior of BCC phase. While the phase composition is not affected by solidification cooling rate. With the increasing of Al/Ni ratio and solidification cooling rate, a significant columnar-to-equiaxed transition (CET) behavior can be observed. That is, grain refinement and transition from columnar dendrites to equiaxial and cellular dendrites. This is mainly attributed to the constitutional supercooling (CS) caused by the solute interaction effect of Al and Ni, and which can be evaluated by P and Q parameters. In addition, in-situ formation of serrated grain boundaries (SGBs) can be also observed in solidification microstructures, and with the increasing of Al/Ni ratio, the proportion of SGBs increases gradually. Whether the B2 precipitated phase is present or not, the formation mechanism of SGBs is mainly attributed to the lattice strain energy caused by the segregation of Al and Ni. The strategy simultaneously achieving grain refinement, CET and in-situ forming SGBs during solidification by tailoring Al/Ni ratio opens new perspectives for grain boundary engineering.

Collaborative improvement of mechanical and electrical properties of Cu–Ni–Co–P alloys via regulation of nanophase precipitation behavior

Owing to their excellent strength and electrical conductivity, Cu–Ni–Co–P alloys present strong potential as next-generation materials for integrated circuits in electronic information systems. However, these outstanding properties are closely tied to the precise control of nanophase precipitation behavior within Cu-based alloy systems. Herein, the design of alloy composition was combined with aging treatment to regulate the nanoprecipitation process. Furthermore, the effects of P content and aging treatment conditions, including temperature and duration, on the microstructure and the mechanical, and electrical properties of Cu–Ni–Co–P alloys were systematically investigated. The findings reveal that Cu–0.3Ni–0.3Co–0.16P alloys, when aged at 500 °C for 4 h, primarily consist of a Cu-rich matrix interspersed with numerous nanoprecipitates. These nanoprecipitates were identified as the hexagonal CoNiP phase, precipitating in Guinier–Preston (GP) zones and maintaining a coherent relationship with the Cu matrix. The as-annealed Cu–0.3Ni–0.3Co–0.16P alloys demonstrated a tensile strength of 652.9 MPa, a yield strength of 631.2 MPa, a Vickers hardness of 203.2 HV, and an electrical conductivity of 66.4 %IACS. Aberration-corrected scanning transmission electron microscopy revealed that G.P. zones suppressed the coarsening of the CoNiP phase, thereby enhancing the mechanical strength of the Cu–Ni–Co–P alloys. The strength analysis calculations suggest that fine-grain and precipitation strengthening mechanisms are the predominant factors in improving the mechanical strength of these alloys. This study provides valuable insights into the development and manufacturing of high-performance Cu-based alloys for advanced applications in the electronics industry.

Influence of particle deformation zone (PDZ) size on dynamic recrystallization and precipitation behavior of SiCp/Mg-5Zn material during hot compression

The influence of particle deformation zone (PDZ) size on dynamic recrystallization (DRX) and precipitation behavior of SiCp/Mg-5Zn material was investigated through the hot compression. First, the microstructure and microhardness of matrix in PDZ were characterized for SiCp/Mg after compression at room temperature. Then, the microstructure evolution of SiCp/Mg-5Zn materials with different PDZ size was analyzed by optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) after compressing different strains. The results show that a significant misorientation gradient was formed near the particle for SiCp/Mg after compression at room temperature, but which is smaller than that around the grain boundary. The addition of SiCp can promote DRX nucleation of Mg matrix, but the promotion effect of particles on DRX nucleation is less than that of grain boundaries for SiCp/Mg-5Zn material during the hot compression, which causes a decrease in the DRXed ratio of SiCp/Mg-5Zn material with increasing PDZ size. Moreover, the volume fraction and size of precipitated phase both decrease with increasing the PDZ size. The aim of this work is to provide a strategy to acquire Mg alloys with excellent mechanical performance by regulating the microstructure of Mg matrix.

Precipitation behavior of G-phase and its effect on mechanical properties of 30Cr2Ni4MoV steel

Precipitation behavior of G-phase and its effect on mechanical properties of 30Cr2Ni4MoV steel during thermal aging at 350–600 °C for 0–10,000 h are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atom probe tomography (APT), hardness and impact tests. Aging at 500 °C, the martensitic matrix of 30Cr2Ni4MoV steel basically keeps stable. With the lath width almost remaining unchanged, carbides coarsen to a slight degree, but G-phase will precipitate at grain boundary (GB). The G-phase is Ni16Mn6Si7 and its “nose” temperature is around 500–550 °C. Due to relatively high enrichment level of forming elements including Ni, Mn and Si at GB, the G-phase can nucleate at triple junction or adjacent to M23C6 at GB. Subsequently, the G-phase grows along GB until contacts with M23C6, and then coarsens along the width direction, which results in alternating distribution morphology of G-phase and M23C6 at GB. The Vickers hardness results show that the hardness remains stable due to the relatively stable microstructure after aging. After aging for 10,000 h, the hardness undergoes little decrease due to the slight coarsening of M23C6 and G-phase. Interestingly, the impact energy drops obviously after the precipitation of G-phase. The reason is that the G-phase at GB promotes the initiation and propagation of cracks during the impact process, leading to intergranular fracture (IGF).

The hot deformation behavior of a L12 precipitation strengthened face centered cubic high entropy alloy

In this work, the hot compressive deformation behavior of a homogenized Ni45Co15Cr15Fe15Al8Ti2 high entropy alloy was investigated at deformation temperatures of 900–1200°C and strain rates of 10−3-1 s−1. Initially, combined the true stress-strain curves and hyperbolic sine function model, the constitutive equation for the flow stress of the alloy during the hot deformation process was established. Additionally, the hot processing map of the alloy at a true strain of ε = 0.5 was plotted based on the DMM model. Coupled with microstructural observations, the optimal hot processing parameters for the alloy were determined to be T = 1070–1200 °C and ε̇= 0.001–0.05 s−1. Finally, the deformed microstructure of the alloy under different temperatures and strain rates was characterized using EBSD, and the dynamic recrystallization mechanisms was revealed. The flow stress decreases with the increasing deformation temperature and decreasing strain rate. As the deformation temperature increases from 900°C to 1200°C, the dynamic recrystallization mechanism transitions from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX). The findings of this study will provide valuable guidance for the development of hot forging parameters of the L12 strengthened FCC high-entropy alloys.

Microstructure, precipitates and mechanical properties of Cu-3Ni-1Ti alloy by two-stage cold rolling and aging treatment

The effects of two-stage cold rolling and aging treatment on the mechanical and electrical properties of Cu-Ni-Ti alloy were investigated. The microstructure evolution, precipitation behavior, and strengthening mechanism of the alloy after two-stage cold rolling and aging treatment were analyzed using microhardness, tensile strength, and electrical performance tests, combined with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. The research results show that the alloy after two-stage cold rolling and aging treatment exhibits excellent comprehensive properties, tensile strength reaches 635 MPa, yield strength is 597 MPa, hardness is 182 HV, conductivity is 62.1 % IACS, and elongation is 14.5 %. This processing method facilitates the precipitation of more nanoscale Ni3Ti phases and the formation of smaller cellular substructures. Consequently, the alloy maintains its exceptional mechanical properties through the combined effects of dislocation and precipitation strengthening. This study provides a novel preparation process and a solid theoretical foundation for enhancing the mechanical and electrical properties of Cu-Ni-Ti alloys.

The precipitation behavior of natural aging for Al-Cu-Li alloy after homogenization

The effects of natural aging (NA) on microstructure and mechanical properties of as-homogenized Al-4.1Cu-1.3Li-0.4Mg-0.4Ag-0.3Mn-0.5Zn-0.1Zr alloy are investigated in this work. The results show that the alloy exhibits a strong NA response attributed to a plethora of GP-Li zones and δ′ precipitated during the initial 3 days which provides nucleation sites for the T1 phase. After 15 days, the mechanical properties dramatically enhance due to the precipitation of the saturated GP-Li zones, δ′, and T1 phases. The yield strength, ultimate tensile strength, and fracture elongation reach 316 MPa, 469 MPa, and 14 % after NA for 15 days, respectively.

Effect of Pre-Rolling Strategy and Aging Precipitation Behaviors on Mechanical Properties and Wear Resistance of Biomedical Ti-15Mo Alloy

Effect of Pre-Rolling Strategy and Aging Precipitation Behaviors on Mechanical Properties and Wear Resistance of Biomedical Ti-15Mo Alloy

Influence of solid solution time on microstructure and precipitation strengthening of novel maraging steels

Effective subsequent heat treatment is crucial for achieving the desired microstructure and excellent mechanical properties in laser-deposited high-performance maraging steel. In this paper, we systematically investigate the synergistic relationship and tuning mechanism of different solution treatment times on the microstructure-property synergy of new maraging steels fabricated using laser direct energy deposition (LDED). To determine the optimal heat treatment process, solution treatment was conducted at 840 °C for varying durations, followed by aging at 530 °C for 2 h to induce precipitation strengthening. The results indicate that after 2 h of solution treatment, the alloy exhibits optimal ductility with an elongation of 7.90 % ± 0.15 %, attributed to the refinement of the martensitic matrix and precipitated phases, along with the formation of a small amount of residual austenite. When the solution treatment time is extended to 4 h, the alloy achieves its highest tensile strength, reaching 1958 ± 24 MPa. However, the elongation decreases to 7.31 % ± 0.12 % due to the coarsening of the martensite and secondary phase particles. After 6 h of solution treatment, significant coarsening and aggregation of the martensite and Fe2Mo intermetallic compounds markedly reduce the hardness, strength, and toughness of the alloy. By adjusting the solution treatment time, the size, morphology, and distribution of the martensitic matrix, Fe2Mo, and nanoscale precipitated phases play a critical role in the strengthening and fracture processes. Therefore, optimizing the precipitation behavior of the martensitic matrix and Fe2Mo intermetallic compounds through rational solution heat treatment is key to enhancing the mechanical properties of laser-deposited new maraging steels.

Coupled Precipitation Behavior of MnS–Nb(C, N) Composite Inclusion in Medium Carbon Micro-alloyed Steel

Coupled Precipitation Behavior of MnS–Nb(C, N) Composite Inclusion in Medium Carbon Micro-alloyed Steel

Comparison of Novel 1 GPa Low‐Carbon, Low‐Alloyed Steel Produced with Simulated and Laboratory‐Scale Thermomechanical Controlled Processes

A laboratory‐scale hot‐rolled Ti–Mo–V–Nb steel with 1 GPa tensile strength is produced, and its microstructure and tensile properties are characterized using advanced analysis techniques and uniaxial tensile testing. A Gleeble 3800 thermomechanical simulator is used to determine a process window for the thermomechanical controlled processing (TMCP) procedure. Although the simulated TMCP specimens are fully ferritic at coiling temperatures (CT) of 590 and 630 °C, the bainitic and mixed (bainitic + ferritic) microstructure is formed in the hot‐rolled steels. The variation in the microstructure causes variations in the dislocation density through the sheet thickness, which significantly reduces the steel's ductility properties, whereas a 16% elongation is achieved with the fully bainitic microstructure. Another significant difference between the simulated TMCP and hot‐rolled specimens is the precipitation behavior. No nanosized interphase‐precipitated (IP) carbides are formed in the hot‐rolled steel during the austenite‐to‐ferrite phase transformation, although the formation of the nanosized spherical IPs is observed within the polygonal ferrite grains of the simulated TMCP specimens at the CT of 630 °C. Relatively coarse (5–20 nm) spherical (V,Mo,Ti,Nb)C carbides do not strongly affect the tensile properties of the hot‐rolled Ti–Mo–V–Nb steel. The results show that the dislocation and grain boundary strengthening mainly contribute to the strength properties of this steel.

Microstructure instability of additively manufactured alloy 718 fabricated by laser powder bed fusion during thermal exposure at 600–1000 ℃

Microstructure and precipitation behavior of alloy 718 produced by laser powder bed fusion (L-PBF) and its recrystallized counterpart were evaluated after thermal exposure at a temperature range of 600–1000 ℃ for up to 1000 h. The as-built 718 featured a microstructure of columnar grains, and dislocation cell structures (DCSs) with chemical segregations (rich in Nb, Ti, Mo and depleted in Cr, Fe) and precipitates (Laves phase and carbonitride). The DCSs remained thermally stable for up to 1000 h at 600 ℃ or 100 h at 700 ℃, but only 10 h at 800 ℃. With the temperature increasing to 900 ℃ and 1000 ℃ for 1 h duration, the DCSs tended to partially disassemble, and the chemical segregations were removed. The chemical segregations at cell boundaries of the as-built 718 promoted the formation of γ′, γ″ and δ phases during aging, leading to a spatially heterogeneous distribution of γ′ and γ″ phases between the cell boundaries and interiors during short exposure time or at lower temperatures. Meanwhile, the coarsening of γ′ and γ″ phases and the phase transformation of γ″ to δ at 700–800 ℃ were facilitated in the as-built 718 compared to the recrystallized ones. A unique precipitation distribution was observed at 700 ℃ that γ′ and γ″ phases precipitated both at the cell boundaries and within cell interiors, while only γ′ formed in the vicinity of cell boundaries. Time-temperature-transformation curves for additively manufactured and recrystallized 718 were constructed based on the microstructure analyses. This study indicates that conventional heat treatment procedures may be suboptimized for additively manufactured 718 in high temperature applications.

Effect of wall thickness on the precipitation behavior, microstructure, electrical conductivity and mechanical properties of copper alloy prepared by electron beam powder bed fusion

Electron beam powder bed fusion (EB-PBF) is one of the most promising technologies for preparing thin-walled copper alloy, because copper alloy have a high energy absorption rate for electron beam, and high preheating temperature can reduce the solidification temperature gradient and reduce the deformation of thin-walled parts. At present, there are few reports on the systematic research work on the EB-PBF of thin-walled CuCrZr alloy parts, and it's impossible to effectively supervise the production of complex thin-walled CuCrZr alloy parts. This work aims to investigate the effect of thickness on the microstructure and mechanical properties of CuCrZr alloy produced by EB-PBF. As the wall thickness decreases from 5.0 mm to 0.3 mm, the grain sizes of the XY and YZ planes decreased from 20.4 μm and 43.1 μm to 14.5 μm and 21.5 μm respectively, and the texture intensity decreased from 16.04 and 23.57 to 7.62 and 10.99. The analysis showed that Cr2O3 nanoprecipitates were precipitated in situ in the sample, and their average size decreased from 65.8 nm to 21.6 nm. Due to the reduction in grain and nanoprecipitate size, the performance of thin-walled samples is significantly enhanced, with yield strength (YS) increasing from 112 MPa to 165 MPa and conductivity increasing from 71.7 %IACS to 86.1 %IACS. Finally, the main contributions to the YS of specimens with different wall thicknesses was discussed. Precipitation strengthening and dislocation strengthening are the main strengthening mechanisms in thin-walled samples, and the gradual refinement of nano-precipitates is the main reason for the improvement of mechanical properties as the wall thickness decreases.

CuCrZr alloy obtained via electron-beam powder bed fusion: Microstructural insights and precipitation behaviour

An in-depth characterization of microstructure and mechanical properties of CuCrZr alloy processed by electron beam powder bed fusion (EB-PBF) additive manufacturing technology was performed with the aim to investigate the effect the thermal history of the material during the building process has on the properties of printed parts. Fully dense samples with a relative density up to 99.77 ± 0.04 % were successfully obtained in optimized conditions. The samples in the as-built condition exhibit an anisotropic microstructure dependent on the energetic input. An extensive microstructural transformation occurs alongside the precipitation and segregation of chromium-rich species, driven by the elevated thermal conditions during the deposition process. This unique thermal evolution can be properly investigated and exploited to eliminate the need for further post-processing heat treatments. To identify and quantify the precipitations within the microstructure, scanning and transmission electron microscopy together with electron backscattered diffraction were used.

Synergistic inhibition to dissolution corrosion by de-twinning and precipitation in alumina-forming austenitic steel exposed to lead-bismuth eutectic with 10-8 wt.% oxygen at 600°C

This work investigated the original microstructure of cold-worked alumina-forming austenitic steel, along with its precipitation and dissolution corrosion behaviors in lead-bismuth eutectic with 10-8 wt.% oxygen at 600°C, using solution-annealed steel for comparison. Anomalously, cold-worked steel presented milder corrosion compared to solution-annealed steel, with average corrosion depths of 314.3 and 401.0 μm after 1700 h exposure. Cold working-induced de-twinning transformed the annealing twin boundaries into normal high-angle grain boundaries (NGBs), increasing NGBs proportion from 36% to 89%. The increased NGBs provided more nucleation sites for intergranular barriers composed of alternate NiAl and M23C6 precipitates, thus better obstructing the dissolution attack.

Achieving strength-ductility synergy in Mg-1.1Gd-0.6Zn-0.3Mn alloy by regulating precipitation behavior via stress aging strategy

Regulating the precipitation behavior of Mg alloys to overcome the strength-ductility trade-off puzzle is a long-thought pursuit in the materials community. With this purpose, external stress has been recently applied during aging and shows immense potential in affecting atomic diffusion, and regulating the coherence of the phase boundaries. In this study, elastic tensile (TSA) and compressive stress aging (CSA) of Mg-1.1Gd-0.6Zn-0.3Mn alloy are carried out and the competition of precipitation between multiple precipitates occurs during stress aging. A significant quantity of β’ precipitates primarily distribute along grain boundaries in conventional peak aging alloy. Whereas high density of γ’ phases rather than β’ phase precipitate in both TSA and CSA alloys. The first-principle calculations reveal that the application of external stress introduces shear strain, which decreases unstable stacking fault energies, and thereby promoting the precipitation of γ’ phase and impeding the precipitation of β’ phase. Furthermore, the sequential transformation from γ’ phase to Long Period Stacking Ordered (LPSO) phase occurs in CSA sample, due to the release of elastic local strain at phase boundaries. After subjected to TSA treatment, the sample possesses an ultimate tensile strength of 356 MPa, a yield strength of 294 MPa, and a total elongation of ∼14.3 %. The excellent strength-ductility synergy of TSA sample is primarily contributed to the profuse γ’ precipitates hindering the motion of large number of pyramidal 〈c + a〉 dislocations during tensile deformation. This study offers new insights on regulating the precipitation behavior of Mg alloys containing multiple types of precipitates through the application of external stress, and extends the potential window for obtaining an excellent strength-ductility synergy in age-hardenable Mg alloys.