Precipitation Behavior Research Articles

Effect of Sulfur Content on Precipitation Behavior of Dendrite Sulfide Inclusion in Continuous Casted 20CrMnTi Gear Steel

The effect of sulfur content on sulfide inclusion and dendrite MnS in continuous casted 20CrMnTi gear steel is investigated. There are two main types of sulfides in 20CrMnTi steel: pure MnS and TiN–MnS composite inclusions. The number of TiN–MnS is higher than MnS, especially in the edge of the billet. TiN–MnS is smaller both in area and size than pure MnS. The statistical results of dendrite MnS show that the increase of S content decreases the average size of sulfides, whereas raises the number and the maximum size of sulfides. With the S content increasing, the proportion of large‐sized dendrite MnS in steel decreases, but the amount of large‐sized dendrite MnS increases, which results in the increase of number of large‐sized dendrite MnS. The average area of dendrite MnS inclusions first increased and then decreased from the edge to the center of billet, and the maximum area appeared at about 1/2 radius of the billet. Comparison with the microstructure of the two billets, the proportion of ferrite increased with the increase of S content.

Surface morphologic changes and mineral transformation mechanisms after CO2-brine-rock reaction in organic matter-rich ferroan shale

Sequestrating CO2 in shale reservoirs can not only reduce CO2 emission, and enhance oil and gas recovery. Nevertheless, shale reservoirs were normally formed in reducing environments, and are abundant in Fe2+ and organic matter. Fe2+ influence the dissolution and precipitation behavior of minerals within the reservoir. Simultaneously, organic matter occupies the pore spaces within the reservoir, thereby affecting the reservoir physical properties. The CO2-brine-rock reaction experiment was carried out using organic matter-rich ferroan shale in this study. The changes in surface morphology of minerals and organic matter utilizing X-ray Diffraction localization monitoring techniques. Based on the TOUGHREACT, a quantitative analysis was conducted on the dissolution and precipitation of individual components. The results suggest that the carbonates preferentially dissolved at the early stage, resulting in a rougher surface morphology andthe formation ofcracks. During the early stage, ankerite transformed into pyrite and chlorite. As the reaction progresses, an elevation in the solution’s acidity facilitates converts chlorite to pyrite and kaolinite. After the dissolution of dolomite, calcite is the primary secondary mineral. The formation of clay minerals consumes Mg2+, resulting in minimal magnesite. The dissolution of feldspar was weaker than carbonate minerals. Dissolution of plagioclase results in the formation of dawsonite in solution. The dissolution of K-feldspar induces the transformation of smectite to illite. In addition, as the reaction solution acid escalated, the soluble mineral components in the large-particle polymer dissolved and dispersed into small-particle organic matter. The small-particle organic matter absorbs secondary minerals generated to form a cake-like polymer.

Relationship of litterfall anomalies with climatic anomalies in a mangrove swamp of the Yucatan Peninsula, Mexico.

Among the set of phenological traits featuring mangrove ecosystems, litterfall production stands out with marked intra-annual and longer-term variation. Furthermore, mangrove forests resilience is one of the most important ecological attribute, reconciling the juxtaposed terrestrial and marine environment such transitional systems occupy. However, world's mangroves are nowadays facing recurrent climatic events, reflected in anomalies depicted by major drivers, including temperature and precipitation. This physical-environmental setting may either constrain or favor overall forest productivity. A combination of time series analysis (spectral density and cross-correlation techniques) and statistical model fitting (General additive model) was implemented to explore trends in total litterfall of a well-developed mangrove forest in southeastern Gulf of Mexico (Celestun Lagoon, SE Mexico) and potential association with the varying behavior of temperature (°C) and precipitation (mm month-1), highlighting their anomalies. The results are consistent with a synchronous response between litterfall production and climatic variables (mean monthly temperature and total monthly precipitation). Concurrent peak litterfall production in Celestun lagoon with high temperatures and precipitation occurred during June and October, featuring a two-month time lag for the response time. More than half of the litterfall anomalies (53.5%) could be reflecting either multiple sources of climatic anomalies (maximum, minimum, and monthly average temperature and monthly total precipitation) or single point events (cyclone landfall). This relationship dynamics showed an interannual persistence (1999-2010). The structure portrayed by the litterfall time-series was not unequivocally related to climatic anomalies. Arguably, climatic anomalies behave with different intensities and even may exhibit complex interactions among them. The study of anomalies provides a baseline for a better grasp of: i) mangrove anomalies responses and ii) their vulnerability to these extremes.

Achieving high strength and high-electrical-conductivity of Cu-Ni-Si alloys via regulating nanoprecipitation behavior through simplified process

Overcoming the tradeoff between mechanical strength and electrical conductivity is a long-standing challenge in developing advanced copper alloys for industrial applications. Herein, we report a new strategy to obtain high strength and good conductivity of Cu-Ni-Si-Ca alloy by introducing and regulating the discontinuous precipitation (DP) and continuous precipitation (CP) behaviors. The DP process combined with thermomechanical treatment was exploited to expedite the precipitation kinetics, whilst the competition between DP and CP was utilized to inhibit the nucleation and growth of continuous precipitation phase (CPP). The resultant copper alloy exhibits superior comprehensive properties with a yield strength of 956 MPa, fracture strength of 989 MPa, and electrical conductivity of 34.1 % IACS. The improved electrical conductivity is attributed to the heterogeneous-nucleation dominant DP, while the high strength stems from the combination of strain hardening and precipitation strengthening of δ-Ni2Si and t-Ni3Si precipitates. Notably, the precipitation strengthening arises from both the dislocation passing and cutting mechanisms, with the strongly ordered DO22-type (t-Ni3Si) phase contributing approximately 202 MPa to the overall strength through the cutting mechanism. This work offers a new pathway for alloy design of high-strength and high-electrical-conductivity copper alloys, by regulating coherent ordered nanoprecipitates through DP and CP.

Structural modulation and frictional, antibacterial and biocompatible properties of Ag-incorporated DLC films: Dependence on Ag precipitation behavior

Ag-incorporated DLC (Ag-DLC) film attracted widespread attention in the bio-alloy implants field due to its excellent mechanical, biocompatible, and antibacterial properties. However, how to balance the short-term efficient antibacterial and biocompatibility of films, and the correlation between Ag precipitation and structural properties are still unclear. Hence, Ag-DLC films with different Ag contents were deposited by modulating Ag target current, focusing on the influence of Ag precipitation behavior. Results show that Ag dopants exist in the form of Ag crystals rather than bond with carbon matrix, which can easily precipitate and aggregate to film surface. The precipitated Ag amount with Ag target current enhances from 2.75% to 35.04% while promotes the formation of sp2 carbon structure catalyzed by Ag, corresponding to decreased mechanical property. Interestingly, a small number of Ag dopants could effectively improve the friction behavior due to the lubrication effect of soft metal Ag and the friction interface transformation. Importantly, the best antibacterial property of film is obtained at high Ag precipitation content, while the surfaces with low Ag precipitation content are more favorable for cell adhesion and cytotoxicity reduction. Therefore, the Ag target current for better comprehensive performance is suggested within the range of 0.4 to 0.6 A.

Solidification precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys

AlN inclusions are the major inclusions in FeCrAl alloys and precipitate during solidification. The precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys were theoretically calculated based on the Clyne–Kurz model and a diffusion-controlled growth model. The results indicated that AlN inclusions precipitated at a solid fraction of 0.45. Following precipitation, the Al concentration exhibited a slight decrease compared to scenarios where AlN inclusion precipitation was not considered, although it still showed an increasing trend. Conversely, the N concentration exhibited a significant turnaround, gradually dropping below its initial value. In addition, varying the cooling rate to 0.17, 0.83, 1.67, and 16.67 K/s, the final sizes of AlN inclusions were 46.5, 21.1, 14.8, and 4.7 μm, respectively. Fixing other factors, the solid fractions for AlN precipitation at initial Al concentrations of 4.19, 4.69, and 5.19 wt% were 0.535, 0.45, and 0.365, respectively, and the final sizes of AlN inclusions were 16.2, 14.8, and 13.6 μm, respectively. Similarly fixing the other factors and varying the initial N concentrations to 0.0045, 0.0053, and 0.0060 wt%, the solid fractions of AlN were 0.515, 0.45, and 0.40, respectively, and the final sizes of AlN inclusions were 14.6, 14.8, and 15.0 μm, respectively. This indicates that increasing the cooling rate, increasing the initial Al concentration, and decreasing the initial N concentration could effectively reduce the precipitation size of AlN inclusions. This work provides guidance for the investigation of the precipitation and growth kinetics of AlN inclusions in FeCrAl alloys.

Studying the effect of Cr content on microstructure and deformation behavior of (NiCo)88-xCrxAl10Ta2 medium-entropy alloy through L-DED gradient material

Optimization of Cr content is crucial for γ'-strengthened NiCoCr-based medium entropy alloys, influencing the stacking fault energy, deformation behavior and the precipitation of brittle σ phase. In this study, (NiCo)88-xCrxAl10Ta2 gradient materials were prepared by L-DED, and the influence of Cr content on the phase precipitation and tensile deformation behavior was investigated. As the Cr content decreases from 24.1 at% to 13.9 at%, the aging time for σ phase precipitation at the grain boundaries at 750°C increases from 100 hours to 215 hours. Meanwhile, the coarsening rate of γ' phase at 750°C are found to be 7.84×10−28 m3/s and 13.6×10−28 m3/s for the Cr content of 24.1 at% and 18.7 at%, respectively. It suggests that the reduction in Cr content notably suppresses the precipitation of σ phase, and accelerates the coarsening rate of γ' phase. Tensile testing of the gradient material reveals that the lower Cr content region exhibits fewer and shorter stacking faults during tensile deformation due to its higher stacking fault energy, leading to the rapid development of local strain, subsequent necking, and eventual fracture. Taking into account the evolution of microstructure, hardness, and deformation substructure with varying Cr content, the appropriate Cr content in (NiCo)88-xCrxAl10Ta2 medium entropy alloy is 17–24 at%.

The effect of cooling rate on the precipitation behavior and fracture toughness of the η phase in LDED CoCrFeNiTi high-entropy alloy

Precipitation strengthening is recognized as an effective method for strengthening high-entropy alloys (HEAs) or medium-entropy alloys (MEAs), especially the recently developed CoCrFeNiTi HEA. The η phase plays a crucial role in strengthening CoCrFeNiTix HEAs, though it remains relatively understudied. In this study, CoCrFeNiTi HEA was fabricated by laser directed energy deposition (LDED). The research investigated the effect of cooling rate on the precipitation behavior and fracture toughness of the η phase in non-equilibrium solidified CoCrFeNiTi HEA. The findings revealed that the precipitation of the η phase in the as-deposited LDED sample was restrained, resulting in a very low volume fraction. However, a high-volume-fraction η phase was achieved through annealing at 900 °C for 6 h, followed by air cooling. This approach not only maintained the desired ∼6.2 % volume fraction of the η phase but also prevented its growth and coarsening (∼403 nm), resulting in an optimal combination of microstructure and mechanical properties. The η phase exhibited the Blackburn type orientation relationship with the FCC phase: <11 2‾ 0>η//<1 1‾ 0>FCC and {0001}η//{111}FCC. The L interface of the η phase demonstrated a coherent relationship with the FCC phase ({0001}η//{111}FCC), while the W interface was incoherent with the FCC phase ({11 2‾ 0}η//{1 1‾ 0}FCC). The unique interface characteristics promoted a higher growth rate at the W interface compared to the L interface, leading to the preferred growth of the η phase. The chemical compositions of both the FCC phase and η phase were accurately predicted by experiments and simulations, elucidating the precipitation kinetics of the η phase. When v ≥ vWC, the nucleation and precipitation of the η phase were inhibited. Conversely, when v ≤ vFC, significant coarsening of the η phase occurred. However, when v ≈ vAC, the AC sample exhibited superior mechanical properties, with a microhardness of ∼860 HV and excellent fracture toughness. These findings provide valuable insights and guidance for further enhancement and optimization of HEAs/MEAs strengthened by the η phase.

Mechanism and kinetics of ultrasound-enhanced CaCO3 precipitation for indium enrichment in zinc oxide dust leaching solution

In this study, ultrasound-enhanced calcium carbonate precipitation was used to enrich indium in zinc oxide dust leachate, and the effects of precipitation endpoint pH and ultrasound power on the indium precipitation behaviour were investigated, and the optimal conditions of ultrasound-enhanced precipitation were obtained to be the precipitation endpoint pH of 4.0 and the ultrasound power of 200 W. The precipitation rate of indium under these conditions was 99.79 %. At the same time, the effects of ultrasonication and conventional stirring on the indium precipitation kinetics were compared, which proved that ultrasound can shorten the time for precipitation to reach equilibrium and reduce the amount of calcium carbonate used, and the theory of ultrasonication activation energy was put forward. The activation energy of ultrasonication was Eu-a = 2.63 KJ/mol, and that of conventional precipitation was 9.78KJ/mol, which proved that ultrasonication could reduce the activation energy of the precipitation reaction, and promote the rapid precipitation reaction. The kinetic model of ultrasound-enhanced indium precipitation is lnC0-lnCt = exp(0.11339–318.54/W).t + A. In addition, the mechanism of ultrasound-enhanced calcium carbonate precipitation of indium was revealed by XRD, SEM-EDS, XPS and TEM analyses of the precipitated residue, it was demonstrated that ultrasound can inhibit the precipitation of zinc, and the ZnCO3 phase was found in the ultrasonically precipitated residue. This study provides a new idea for indium enrichment, and the future focus will be on the scale-up of the ultrasound-enhanced precipitation device.

Precipitation behavior and strengthening mechanism in a Cu-3.5Ti-0.1 Tm alloy

The study investigates the complex relationship between precipitation patterns, microstructural evolution, and mechanical properties in a Cu-3.5Ti-0.1 Tm alloy subjected to isothermal ageing. The results reveal that ageing at 450 °C leads to the formation of nanoscale β′-Cu4Ti phase particles within the grains and fibrous β-Cu4Ti precipitates along the grain boundaries. The precipitation microstructure of this aged alloy is predominantly characterised by tetragonal β′-Cu4Ti precipitates. During spinodal decomposition, Ti atoms segregate in rod-like Ti-rich Cu phases, facilitating their conversion into β′-Cu4Ti phase. The β′-Cu4Ti precipitates remain fully coherent with the Cu matrix, exhibiting a crystallographic orientation relationship of (001)Cu//(001)β′ and [100]Cu//[130]β′. As the precipitate radius exceeds approximately 11 nm, the elastic strain energy surpasses the energy at the precipitate/matrix interface. This leads to a shape transition from spherical to cuboidal for the β′-Cu4Ti precipitates. Moreover, the Ti solute atoms contribute significantly to the alloy's strength through solid solution hardening, with the dissolution of 1 at.% Ti solute increases the yield strength by 46.2 MPa. However, as ageing progresses from 1 to 20 h, the effect of solid solution strengthening decreases, while precipitation strengthening becomes more dominant, mainly due to the Orowan bypass mechanism. After 20 h of ageing, precipitation strengthening significantly increases the yield strength by about 436 MPa, exceeding the contributions from solid solution strengthening (78 MPa) and grain-boundary strengthening (14 MPa).

Unveiling the precipitation behavior and mechanical properties in G-phase strengthened CrFe2Ni2Ti0.2Six multi-principal element alloys

In order to develop Co-free CrFeNi based multi-principal element alloys (MPEAs) with good synergies between strength and plasticity, the effects of Si content on the microstructures and mechanical properties of CrFe2Ni2Ti0.2Six (x = 0, 0.125, 0.25, 0.375, 0.5 and 0.625) MPEAs are studied in this work. The results show that the addition of Si induces a phase transformation from a single-phase face-centered cubic (FCC) structure to a dual-phase structure, comprising an FCC solid solution phase and G-phase. The outcomes from phase formation theory and phase diagram calculations (CALPHAD) also confirm that CrFe2Ni2Ti0.2Six MPEAs are prone to form dual-phase structures. With increasing Si content, the yield strength and hardness of the alloys increase by 47.2 % and 57.3 %, respectively, while still maintaining a strain of 34.2 %, which is indicative of commendable overall mechanical properties. This is ascribed to the coherence between FCC matrix and G-phase, enabling an enhancement in strength concurrently with the retention of considerable plasticity. Moreover, grain boundary strengthening and precipitation strengthening play a dominant role in the strengthening of CrFe2Ni2Ti0.2Six MPEAs. The present work offers new insights for the further development of high-performance non-metallic MPEAs, so as to achieve a combination of targeted microstructures and excellent properties.

Strengthening behavior and microstructure of 2195 Al-Cu-Li alloy under cycling loading

Cyclic strengthening process, as a newly developed aluminum alloy strengthening technique, has garnered significant attention due to its advantages of rapidity, efficiency, and superior mechanical properties. This study investigated the effects of strain amplitude and loading frequency on cyclic strengthening, including mechanical properties and microstructural evolution. At room temperature, the cyclic strengthening effect of the 2195 alloy increases with increasing strain amplitude, while the influence of loading frequency is pronounced within the elastic range but nearly negligible within the plastic range. Microstructural analysis reveals that cyclic strengthening behavior within the elastic range is attributed to the precipitation of clusters, whereas within the plastic range, it is attributed to the precipitation of clusters and dislocation multiplication. Unlike other plastic deformations, cyclic plastic loading generates dislocations primarily in the form of dislocation loops. The dynamic precipitation of clusters and the diffuse distribution of dislocation loops significantly enhance the alloy's strength with minimal sacrifice of elongation. Experimental investigations on the influence of loading frequency on these precipitation behaviors demonstrate a positive correlation with dislocation generation and a negative correlation with cluster precipitation. Comparison of specimens with different strain amplitudes reveals that larger strain amplitudes provide more energy for cluster precipitation, thereby promoting precipitation. However, excessively large strain amplitudes lead to the annihilation of vacancies due to the introduction of more dislocations, thus inhibiting cluster precipitation. This indicates that the precipitation of clusters during cyclic deformation is profoundly influenced by dislocation behavior. This study deepens the understanding of cyclic strengthening mechanisms and provides support for subsequent development of cyclic strengthening processes in other materials design.

Characterizing Short-Time Aging Precipitation Behavior of a Novel Nickel-Iron-Based Alloy via Electrical Performance.

In this paper, the precipitation behavior and its effect on resistivity in a new type of nickel-iron-based alloy during short-term aging were investigated. During the aging process, the γ' phase increases in average size and decreases in number, with its area fraction fluctuating over time. This fluctuation is caused by the mismatch in the redissolution and growth rates of the γ' phase. As the area fraction of the γ' phase increases, the content of solute atoms in the matrix that scatter electrons decreases, lowering the resistivity of the alloy. Additionally, the continuous precipitation of M23C6 at grain boundaries during aging causes the resistivity to gradually increase. This paper explains the fluctuation in the total amount of γ' phase during short-term aging and proposes a new method for characterizing the precipitation behavior of the γ' phase in the novel alloy using the relative trend of resistivity changes.

Influence of microalloying on precipitation behavior and notch impact toughness of welded high-strength structural steels

Microalloying elements such as Nb and Ti are essential to increase the strength of quenched and tempered high-strength low alloy (HSLA) structural steels with nominal yield strength ≥ 690 MPa and their welded joints. Standards such as EN 10025–6 only specify limits or ranges for chemical composition, which leads to variations in specific compositions between steel manufacturers. These standards do not address the mechanical properties of the material, and even small variations in alloy content can significantly affect these properties. This makes it difficult to predict the weldability and integrity of welded joints, with potential problems such as softening or excessive hardening of the heat-affected zone (HAZ). To understand these metallurgical effects, previous studies have investigated different microalloying routes with varying Ti and Nb contents using test alloys. The high-strength quenched and tempered fine-grained structural steel S690QL is the basic grade regarding chemical composition and heat treatment. To evaluate weldability, three-layer welds were made using high-performance MAG welding. HAZ formation was investigated, and critical microstructural areas were identified, focusing on phase transformations during cooling and metallurgical precipitation behavior. Isothermal thermodynamic calculations for different precipitations were also carried out. Mechanical properties, especially Charpy notch impact toughness, were evaluated to understand the influence of different microalloys on the microstructure of the HAZ and mechanical properties.

Synergistic optimization of microstructure and mechanical properties of AISI 430 ferritic stainless steel via dual-phase zone annealing process

This study systematically evaluated the impact of dual-phase zone annealing on the microstructure and mechanical properties of cold-rolled 430 Ferritic Stainless Steel (FSS), focusing on the phase transformation process from ferrite to austenite and the dissolution and precipitation behavior of the M23C6 phase. The annealing process significantly affects the microstructural characteristics of ferrite and martensite, including grain size, the distribution of grains of various sizes, aspect ratio, and phase content. The amount of martensite first increased and then decreased with rising annealing temperatures. The sample annealed at 1050 °C exhibited the highest martensite content of 29.5%. The variation in martensite content reflects the complex interplay between phase transformation kinetics and thermodynamic equilibrium. As the annealing time increased or temperature rose, the M23C6 phase at ferrite grain boundaries gradually dissolved and re-precipitated at higher temperatures. At lower temperatures, the M23C6 phase precipitated within martensite, but as the temperature increased, the precipitated phase diminished until it disappeared. Temperature changes affect the solubility of precipitates, atomic diffusion rates, and the uniform distribution of atoms across different phases. Appropriately increasing annealing temperature or extending annealing duration enhances the strength and hardness of 430 FSS. However, excessively high annealing temperatures lead to a decline in mechanical properties. The sample annealed at 1000 °C demonstrated the best mechanical properties, achieving a tensile strength of 783 MPa and an elongation of 16.0%. Furthermore, the analysis of fracture morphology and yield behavior in stress-strain curves further elucidated the macroscopic mechanical performance of the material.

Microstructural evolution and precipitation behavior of multicomponent Al83Mg5Si5Cu5Li2 alloy

We investigated the microstructural evolution and precipitation behavior of a new multicomponent Al83Mg5Si5Cu5Li2 alloy using transmission electron microscopy and atom-probe tomography. As-cast alloy consists of θ-Al2Cu, Mg2Si, Q-Al5Cu2Mg8Si6, and AlLiSi phases. Solution treatment causes the formation of the Q-Al5Cu2Mg8Si6 phase, and slow furnace cooling causes the formation of θ-Al2Cu particles in the Al matrix, which depletes solute atoms. Nanoscale Cu/Si/Mg-rich solute clusters are formed during natural aging, contributing to an excellent age-hardening response.

Understanding process parameter-induced variability for tailoring precipitation behavior, grain structure, and mechanical properties of Al-Mg-Si-Mn alloy during solid-state additive manufacturing

Additive friction stir deposition (AFSD), a solid-state additive manufacturing technique, has excellent industrial application potential, particularly for Al alloys. However, in-depth process parameter-microstructure-property correlations are lacking, especially regarding precipitation behavior. In this work, AFSD of Al-Mg-Si-Mn alloy with various process parameter combinations was performed to understand the variation (by ∼ 70 %) in the nano/microhardness, concerning the precipitation behavior. The low nano/microhardness sample exhibited dissolution of the β” strengthening phase. However, higher nano/microhardness samples showed varying microstructural features with high dislocation density owing to fine-scale pre-β” precipitation and another sample possessed inhomogeneous β” phase distribution and β’ precipitation at the grain boundaries, thus exhibiting reprecipitation during AFSD. The variation in the grain structure was such that the high nano/microhardness samples exhibited large, elongated grains (∼11 to 13 µm) and low recrystallization fractions (∼16 –18 %) suggesting a predominantly non-recrystallized microstructure. Conversely, the lowest nano/microhardness sample exhibited the smallest grain size (∼5 µm) and, a higher recrystallization fraction (∼42 %). These findings demonstrate extensive variation in the precipitation behavior, grain structure, and mechanical properties due to the process parameters. Future applications can leverage this knowledge to tailor the microstructure and mechanical properties based on the identified process parameter combinations.

Manipulation of the α-phase precipitation behavior through dual-aging treatment and its correlation with mechanical properties in a metastable β titanium alloy

The precipitation behavior of α-phase and its crucial impact on the mechanical properties have been investigated in a metastable β-type Ti-4Al-6V-5Mo-3Cr-1Zr (wt%, Ti-46531) alloy. Through dedicated design of dual-step aging conditions, the nucleation mechanism, number density and morphology of the secondary α-phase precipitates can be modulated. After the first-step aging treatment at 300 °C for 5−100 h, isothermal ω-phase (ωiso) particles precipitate and are uniformly dispersed in the β-phase matrix, with their number density gradually increasing with aging time. The subsequent second-step aging treatment at 600 °C for 2 h leads to the rapid dissolution of ωiso and the precipitation of α-phase through the classical nucleation process with a steady number density. Lowering the second-step aging temperature to 520 °C promotes the heterogeneous nucleation of the α-phase with the assistance of uniformly dispersed ωiso particles. This leads to a significant increase in the number density of α-phase precipitates. Consequently, the maximum yield strength increases from 1296 MPa for samples aged at 600 °C to 1623 MPa for samples aged at 520 °C. The precipitation of α-phase serves a dual role in enhancing the yield strength, both by providing precipitation strengthening and by increasing dislocation density. The contribution to yield strength enhancement from the former effect is considerably more substantial than the latter. This work underscores the crucial role of α-phase number density in determining the strength of metastable β titanium alloys, offering new insights into the tailoring of microstructures and mechanical properties through dual-aging treatments.

Evolution of inclusions in DH36 grade ship plate steel during high heat input welding

In this paper, the solid solution and precipitation behavior of inclusions on the surface and 1/2 thickness of the tested steel plate under the condition of welding heat input of 400 kJ/cm is investigated by using laser confocal experiments with hot-rolled state DH36 ship plate steel as the research object, and the mechanism of the effect of inclusions on the phase transformation of an acicular ferrite is revealed. The results show that the inclusions of the tested steel are mainly composed of Oxide-MnS, MnS, Oxide, TiN, Spinel, etc. The amount of inclusions on the surface of the tested steel plate is significantly higher than that at the 1/2 thickness position. During the heating stage, the small inclusions on the surface immediately disappeared, and the large inclusions gradually solidified in the matrix; atomic diffusion occurred at the bond between the inclusions and the matrix; while the small inclusions at the 1/2 thickness position gradually disappeared at the beginning of the heating stage, and the inclusions began to precipitate and grow when the temperature was increased to 990 °C. The acicular ferrite preferentially nucleates and grows near the boundary of the inclusions during the post-weld cooling stage, and its growth ends when two acicular ferrites cross.

Grain-refined metastable β titanium alloy with suppressed ω-assisted nucleation and enhanced mechanical properties

The mechanical characteristics of metastable β titanium alloys are related to the α precipitates that form during aging. Although precipitation behavior can be modulated by ω-assisted nucleation, the influence of grain size (GS) on this process has not been fully considered. In this study, the effects of grain refinement on mechanical properties and ω-assisted nucleation were investigated by aging the Ti-5.3Cr-4.9Mo-4.9 V-4.3Al-0.9 Nb-0.3Fe (TB18) alloy with coarse grains (87 μm) or fine grains (25 μm) at different heating rates (RH). It was found that ω-assisted nucleation depends on the RH, with a lower RH promoting the processes of ω-assisted nucleation and the precipitation of finer secondary α (αs) plates. The vacancy concentration after annealing reduced with decreasing GS, indicating that ω-assisted nucleation is suppressed by grain refinement. Additionally, grain refinement significantly improved the ductility of the TB18 alloy. This effect was attributed to enhanced homogeneous plastic deformation and an increase in slip systems, such as pyramidal <c+a> slip on αs plates. At ultimate tensile strengths of 1300–1550 MPa, the elongation of the fine-grained specimens was typically 2–3 times greater than that of the coarse-grained specimens. Furthermore, the corresponding mixed fracture mode involved a greater extent of ductile fracture. Therefore, the mechanical properties of metastable β titanium alloys are primarily limited by coarse β grains.