Precipitation Of Phase Research Articles

The Impact of Multiple Thermal Cycles Using CMT® on Microstructure Evolution in WAAM of Thin Walls Made of AlMg5

Wire Arc Additive Manufacturing (WAAM) of thin walls is an adequate technology for producing functional components made with aluminium alloys. The AlMg5 family is one of the most applicable alloys for WAAM. However, WAAM differs from traditional fabrication routes by imposing multiple thermal cycles on the material, leading the alloy to undergo cyclic thermal treatments. Depending on the heat source used, thermal fluctuation can also impact the microstructure of the builds and, consequently, the mechanical properties. No known publications discuss the effects of these two WAAM characteristics on the built microstructure. To study the influence of multiple thermal cycles and heat source-related thermal fluctuations, a thin wall was built using CMT-WAAM on a laboratory scale. Cross-sections of the wall were metallographically analysed, at the centre of a layer that was re-treated, and a region at the transition between two layers. The focus was the solidification modes and solubilisation and precipitations of secondary phases. Samples from the wall were post-heat treated in-furnace with different soaking temperatures and cooling, to support the results. Using numerical simulations, the progressive thermal cycles acting on the HAZ of one layer were simplified by a temperature sequence with a range of peak temperatures. The results showed that different zones are formed along the layers, either as a result of the imposed thermal cycling or the solidification mode resulting from CMT-WAAM deposition. In the zones, a band composed of coarse dendrites and an interdendritic phase and another band formed by alternating sizes of cells coexisted with the fusion and heat-affected zones. The numerical simulation revealed that the thermal cycling did not significantly promote the precipitation of second-phase particles.

Study on hardenability of 2050 Al–Cu–Li alloy ultra-thick plate

The hardenability of the 2050 Al–Li alloy ultra-thick plate was evaluated by end quenching and interrupted quench methods. Microstructural investigation at different thickness positions after quenching and aging were conducted using optical microscopy, scanning electron microscope, and transmission electron microscope. The factors affecting the hardenability were discussed in combination with cooling rate and composition examination using energy dispersive spectroscopy. The results indicated that the tensile strength of different thickness positions decreased as the distance from the quenching end increases. Coarse Cu-rich phase particles, formed at the grain and grain boundaries during the end quenching process, lead to solute depletion around the grain boundaries, causing a precipitate-free zone. This zone obstructs the formation of the T1 phase, thereby reducing strength. At identical distances from the quenching end, the tensile strength at the mid-thickness (T/2) location consistently exceeds that at the quarter-thickness (T/4) location. This is due to the original microstructural differences, where the T/2 position experiences a slower cooling rate, has a lower copper content, and shows an increase in the number but a decrease in the size of precipitated coarse Cu-rich phase particles from the supersaturated solution, with the solute consumption remaining relatively constant. Consequently, the tensile strength variation at equal distances from the quenching end is minimal.

Numerical simulation and experimental study on effect of cooling rate on microstructure and strength of nanostructured materials

In this study, by numerical simulation (finite element method, FEM) and experimental, the cooling rate was investigated by changing the product thickness (20, 3, 2, 1, 0.5 and 0.3) mm of Al based two-phase nanostructured materials casted through a copper mold. The effect of cooling rate on the microstructure and strength of the alloy was studied. The Experimental results showed that the precipitated intermetallic phases have a decreasing size corresponding to the increasing cooling rates by simulation from ~102 K/s to ~104 K/s. The results show that an appropriate cooling rate can improve the microstructure and properties of the alloy. The Abaqus/Standard capability for uncoupled heat transfer analysis was intended to model solid body heat conduction with general, temperature-dependent conductivity; internal energy (including latent heat effects); and quite general convection and radiation boundary conditions. This study describes the basic energy balance, constitutive models, boundary conditions, finite element discretization, and time integration procedures used. The time step used an automatic algorithm through the smallest tolerance. The maximum temperature change was allowed over a period and the increment was adjusted for this parameter, as was the rate of convergence in the non-linear cases. First-order heat transfer elements used the rule of numerical integration with integrated stations located at the corners of the element for thermal capacitance terms. (Jacobian terminology). This approach is particularly effective when there is a strong latent thermal effect. Thus, first - order elements were used in the case of latent heat. The HEATCAP element is available for single - point pooled thermal capacitance modeling. Centralized film loading options between the mold and the casting were specified by the user.

Evidence for Ge2Sb2Te5 phase formation upon crystallization of Ge-doped Sb2Te3 phase change films

In this work, we investigated the phase transition characteristics of Ge-doped Sb2Te3 phase change films prepared by the magnetron sputtering method. During the crystallization process of Ge-doped Sb2Te3 films, we observed a metastable phase and identified its crystal structure as the face-centered cubic Ge2Sb2Te5, a previously uncharacterized phenomenon. The Te phase precipitated upon crystallization of Sb2Te3 films, while the Te phase disappeared and the Ge2Sb2Te5 phase appeared upon crystallization of Ge-doped Sb2Te3 films, resulting in the coexistence of Ge2Sb2Te5 and Sb2Te3 phases in the single-layer Ge-doped Sb2Te3 films. The appearance of the Ge2Sb2Te5 phase resulted from the formation of Ge–Te bonds due to the combination of the precipitated Te phase with the incorporated Ge. Furthermore, the formation of the Ge2Sb2Te5 phase was mainly responsible for the increased crystalline resistance and crystallization temperature of Sb2Te3 films. The surface roughness of Ge-doped Sb2Te3 films was significantly reduced, exhibiting good potential for improving the contact performance between the films and electrodes. Our findings contribute to enhancing the understanding of Ge-doped Sb2Te3 films and their role in phase change memory technology.

A novel alloy design approach in developing CoNi-based high entropy superalloy using high entropy alloys thermodynamic and spark plasma sintering

This study introduces an innovative alloy design strategy by integrating HEAs principles to develop CoNi-based high entropy superalloys (HESAs). The powder of designed HESA produced using gas atomization and consolidated using spark plasma sintering (SPS). The alloy design strategy validated by CALPHAD to mitigate detrimental phase precipitation and segregation during powder production, material consolidation, and post-processing heat treatments. CoNi-HESA powder with a calculated mixing entropy of 1.568R was successfully developed and consolidated using SPS. Optimization of SPS parameters at 1175 °C, 10 min, and 100 °C/min achieved a relative density of 99.9 %. Subsequent heat treatments further improved the material's characteristics. Solutionizing at 1190 ± 10 °C for 2 h with water quenching resulted in a fine grain structure of ∼7 μm grain size. Aging at 900 °C for 24 h, followed by water quenching, yielded uniformly distributed fine γ′ precipitates comprising approximately 65 % of the γ matrix, without unwanted secondary precipitates or TCP phases. This study demonstrates the effectiveness of the novel approach in designing CoNi-based HESAs and optimizing their properties through careful process parameter selection and post-heat treatment cycles. The combination of thermodynamic calculations, HEA principles, and powder metallurgy techniques offers a promising approach for developing advanced high entropy superalloys with tailored microstructures.

Influence of GH4169 addition on cracking control, microstructure and mechanical properties of GH4169/K465 composite material manufactured by selective laser melting

In the process of additive manufacturing, K465 nickel-based superalloy tends to form a eutectic structure with a low melting point. Subsequently, rapid cooling leads to the formation of significant residual tensile stress. This tensile stress makes the prepared sample susceptible to cracking. The research explored the susceptibility to cracking of the alloy material and analyzed the microstructure and properties of GH4169/K465 alloy obtained. The generation of cracks can be managed by decreasing the concentration of Al and Ti elements. The microstructure of GH4169/K465 alloy consists of a matrix phase γ, a white Laves precipitated phase, and spherical particle precipitated phase NbTi4. The mechanical properties of samples 1GH1K, 7GH5K, and 3GH1K were analyzed. The results indicated an elongation exceeding 20 %, a tensile strength exceeding 1000 MPa, and a reduction in hardness from 329 HV to 285 HV. The powder mixing process has been demonstrated to effectively address the shortcomings of individual materials by combining the strengths of different alloy materials to produce a hybrid material with excellent comprehensive performance.

Stress-induced intersecting stacking faults and shear antiphase boundary in Zr5Ge4 second phase precipitate embedded in Ge-modified Zircaloy-4

Secondary phase precipitates are vital to control mechanical, corrosion and irradiation response of the multiphase alloy systems. This work reports the mechanical response of an ordered complex intermetallic Zr5Ge4 precipitate during hot working of the experimental Zircaloy-4 modified with dilute Ge addition. Atomic scale insight is provided into the formation mechanism of straight and circular stacking faults and shear antiphase boundary in Zr5Ge4 precipitate. Two types of stacking faults, having displacement vectors 1/3[100] and 1/3[110] with small components along the c-axis, come across and form a distinct region on the (001) surface composed of a zigzag atomic arrangement different from the parent crystal. Besides this, a shear antiphase boundary along the Zr5Ge4/fcc-Zr interface is analysed and concomitant generation of nanotwins is evidenced by the streaking effect in the associated fast Fourier transform (FFT) pattern. By analysing the distortion and stacking faults in the surrounding fcc-Zr phase, comments are made on the role of external stresses in generating the aforementioned planar defects. The relative activity of two types of displacement vectors observed in Zr5Ge4 precipitate is discussed on the basis of the nature of the atomic bond.

Understanding the impacts of L12 nanoprecipitates on the electrochemical and passive behavior of CoCrNiAlTi-type high-entropy alloys

This work investigated the effects of L12 nanoprecipitates on the electrochemical corrosion behavior and passive film characteristics of CoCrNiAlTi-type high-entropy alloys (HEAs) in chloride-containing solutions. Compared with the single-phase recrystallized alloys, the precipitation of the L12 phase destabilized surface passive films, thus deteriorating the localized corrosion resistance and increasing the metastable pitting activities of the L12-strengthened HEA. Influenced by the L12-induced chemical inhomogeneities, the increase of Cr(OH)3 content in passive films together with the high galvanic corrosion tendency between the two phases was considered as the main reason for the increased susceptibility of the L12-strengthened alloys to localized corrosion attacks.

Microstructure, phase evolution and mechanical properties of nickel-silicon carbide reinforced Ti6Al4V alloy processed by pulsed electric current sintering

In this work, fully densified Ni–SiC reinforced Ti6Al4V matrix composites were consolidated by pulsed electric current sintering (PECS) technique. The microstructural evolution and mechanical properties of the developed composites with varying SiC contents were investigated. The microstructural study revealed in-situ precipitation of TiC, Ti5Si3 and Ti3SiC2 strengthening phases within the composites. The α colony size in the composites was notably reduced compared to the fabricated SiC-deficient samples due to the addition of SiC additive into the Ti6Al4V alloy matrix. The in-situ precipitated phases enhanced the mechanical properties of the composites. Composite reinforced with 10 wt% SiC (TNi10SiC) displayed the highest hardness value of 609.8 ± 50.9 HV0.5 among the sintered samples, translating to an increment of about 88 % compared to the unreinforced sample T. Among the sintered samples, the highest flexural strength of 2094.32 ± 97.67 MPa was obtained for the TNi5SiC composite, after which the flexural strength deteriorates with increasing SiC content as witnessed in TNi10SiC composite with the least flexural strength of 863.67 ± 71.57 MPa due to agglomeration of the reinforcement phases within the composite. Samples reinforced with 0 wt% SiC experienced a ductile fracture, and the composites containing 2.5 wt% - 5 wt% SiC content witnessed intergranular and interlamellar fractures. However, at higher SiC content, reinforcement pull-out and debonding of the agglomerated reinforcement phases predominates, and composites fail by brittle fracture.

Roles of micro-alloyed Y and Gd in improving the corrosion resistance and mechanical properties of pure Mg

The microstructure, corrosion resistance and mechanical properties of extruded pure Mg, Mg–2Y and Mg-2Gd were studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), scanning probe microscope (SPM), immersion test, electrochemical test and tensile test. The results demonstrated that Mg–2Y and Mg-2Gd were composed of Mg, Mg24Y5, and Mg5Gd phases with the addition of Y and Gd. The addition of Y and Gd to pure Mg noticeably reduced the grain size and textural strength of the alloy. Mg-2Gd alloy had the smallest grain size and the lowest textural strength. The corrosion rate of Mg-2Gd was the slowest due to the influence of grain size. Y slowed the corrosion of pure Mg in the early stages due to the grain refinement, but speeded up the corrosion because of the galvanic corrosion produced by the precipitation of the second phase in the latter stages. The elongation of pure Mg, Mg–2Y, and Mg-2Gd were 16.5 %, 38.67 %, and 48.67 %, respectively. The inclusion of Y and Gd refined the grain, softened the texture strength, and activated basal slip, which improved the elasticity of alloys. Gd was more significant than Y in improving the corrosion resistance and mechanical properties of pure Mg.

Multi-year evaluation of CloudSat, ERA5, and IMERG global snowfall products

Snowfall products derived from satellite-based radar observations, reanalysis products and phase-classified precipitation products are the three primary sources of information on surface snowfall. This study compares snowfall rate products from CloudSat, ERA5 and IMERG using the Triple Collocation (TC) method on a global scale covering almost the entire period of CloudSat cloud-profiling radar (CPR) 2C products from 2006 to 2019, especially considering the precipitation phase classification field of IMERG (probability of Liquid Precipitation, pLP). The main conclusions include but are not limited to the following: (1) The pLP threshold significantly impacts the ability of IMERG to identify snowfall from precipitation, with an optimal pLP threshold of 25 percent determined by matching IMERG with CloudSat and ERA5 snowfall events globally. (2) CloudSat presents the highest performance and stability on a global scale, with average TC-estimated CC and RMSE of 0.472 and 1.465, respectively. (3) The TC-estimated CC of IMERG exhibit significant spatiotemporal heterogeneities, but IMERG product with the optimal pLP threshold show comparable performance with CloudSat, with an average TC-estimated RMSE of ∼ 1.533. (4) ERA5 performed worse than the other two products, except in some high-latitude and high-altitude areas. This study provides novel insights into the performances of snowfall rate products from different sources at the global scales and provides a foundation for improving satellite- and model-based snowfall rate retrievals.

Achievement of heat treatment strengthening in phosphor bronze through semi-coherent precipitation

Traditional phosphor bronzes have faced difficulties in terms of strengthening via heat treatment. In this study, a Cu-Sn-P-Ni-Si alloy with capability of precipitation strengthening was designed based on phase diagram calculations. After direct aging treatment, the mechanical properties of the Cu-8Sn-0.1P alloy exhibit minimal changes. However, significant strengthening was achieved in the Cu-Sn-P-Ni-Si alloy. Experimental results demonstrate that during the direct aging process, semi-coherent interfaces are formed between the precipitate phases and the matrix in Cu-8Sn-0.1P-1Ni-0.227Si alloy, resulting in significant performance enhancement. Specifically, the yield strength of the alloy was increased by approximately 39% after aging treatment. Crucially, the strengthening mechanism of the Cu-Sn-P-Ni-Si alloy and the formation mechanism of semi-coherent interfaces were elucidated. This work provides a method to significantly enhance the comprehensive performance of phosphor bronze without requiring any special additional manufacturing processes. The achievement of heat treatment strengthening of phosphor bronze without undergoing deformation processing will enhance its potential for application.

High-temperature tensile properties of Cu-modified AlSi10Mg alloy fabricated by selective laser melting

In this study, an AlSi10Cu4Mg alloy was prepared by selective laser melting (SLM) using a mixture of pre-alloyed AlSi10Mg and elemental Cu powders, followed by aging at 180 ℃ for 2 h. The high-temperature tensile properties of both the SLMed and SLM-aged samples were tested in the temperature range of 200–400 ℃, and the microstructure changes during deformation were compared. At the temperature of 200 ℃, the SLMed sample exhibits outstanding tensile properties with an ultimate tensile strength (UTS) of 327±2 MPa and an elongation (EL) of 25.5±0.5 %. This is mainly related to the strain hardening that caused by the accumulation of anomalous dislocations near the high-volume fraction of Si nano-particles within the grains. For the SLM-aged sample, the aging treatment is found to further increase the strength, yielding a UTS of 381±3 MPa. The metastable transition of the Al2Cu phase indirectly promotes the precipitation of the nano-sized Si phase during the aging process. As the testing temperature increases, the strength increment of the SLM-aged sample gradually diminishes, while the elongation increment increases. Due to the limited intrinsic thermal stability of Si nano-particles and θ′ phase, the coarsening of the precipitates can weaken the strengthening effect. The dynamic recrystallization process can be accelerated by the aging treatment, thereby helping to improve the elongation.

Near-surface self-resistance hydrogen effect of eutectic high-entropy alloy AlCoCrFeNi2.1

A series of engineering application studies related to hydrogen damage has been carried out for the eutectic high-entropy alloy (HEA) AlCoCrFeNi2.1 with excellent comprehensive properties. This work mainly introduces the element segregation and microstructure evolution phenomenon near the surface phase boundary and around the precipitated phase found in the hydrogen damage experiment of the material. Studies have shown that the evolution of the near-surface phase boundary microstructure of HEAs caused by hydrogen charging has a great influence on the hydrogen trap density inside the alloy. The “self-resistance hydrogen effect” is produced, that is, hydrogen-induced microstructure evolution causes the effect of delayed hydrogen diffusion. In this phenomenon, the synergy between hydrogen atoms and vacancies and dislocations on the alloy surface is crucial.

Enhanced age hardening response of a Mg-Y alloy by Ca addition at an elevated temperature

The effect of Ca addition on the age hardening response and precipitation behavior of a Mg-7Y-0.5Zr (wt%) alloy during isothermal aging at 350 ℃ has been studied by hardness test and high-angle annular dark-field scanning transmission electron microscopy. The addition of 0.6 wt% Ca can effectively enhance the age hardening response of Mg-7Y-0.5Zr alloy at 350 ℃, and the enhanced hardness is mostly attributed to the uniform precipitation of a novel strengthening precipitate phase, designated βp. The βp phase forms as plates on {101̅0}α planes. It has a Cd45Sm11-type structure (space group F4̅3m, lattice parameter a = 2.24 nm) and a composition of Mg5Y0.8Ca0.2. Its orientation relationship with the α-Mg matrix phase is such that [1̅11]βp // [21̅1̅0]α and (110)βp // (0001)α. After prolonged aging at 350 ℃, the metastable phase βp can transform in-situ to the equilibrium phase β-Mg24Y5 with a cube-to-cube orientation relationship. The βp → β phase transformation is associated with the transition of constituent atomic clusters and the re-distribution of selected atoms within clusters.

Innovative design of heterogeneous structures in Cu-containing titanium alloys to enhance mechanical properties, abrasion resistance, and antibacterial performance

How to precisely modulate the morphology and distribution of precipitated phases to have long-term antibacterial activity and outstanding strength-ductility has slowed the overall development and engineering applications of Cu-bearing biomedical titanium alloys. For the first time, the electron beam powder bed fusion (EBPBF) was employed to design titanium alloys with a completely solid solution, and containing fine Ti2Cu precipitates in both uniform and layered structures. The mechanical properties of the designed alloy with the layered (α-Ti and Ti2Cu) structure are superior to the other structures, especially with an outstanding compressive yield strength of 1221.9 MPa. Simultaneously, the wear resistance of the heterogeneous structures containing Ti2Cu precipitates was significantly improved, with a specific wear rate only half of that of the EBPBF-fabricated Ti6Al4V alloy. The compact arrangement of Ti2Cu phases created a large number of interfaces conducive to the formation of corrosion channels, which provided the capacity of continuous Cu2+ release. This work comprehensively analyzes the effects of heterogeneous structures on enhancing the sustained antibacterial capacity and optimizing the mechanical properties of a Cu-containing titanium alloy, laying a good foundation for their application in clinical and implantable devices.

Effect of pulse current density on creep ageing behavior of 2195 Al-Li alloy

Electrical pulse-assisted creep ageing forming can effectively improve the mechanical properties and forming efficiency of large aluminum components. However, it is difficult to achieve uniform and consistent current density at different positions in complex components. Thus, the creep behavior, mechanical properties, and microstructure evolution of 2195 Al-Li alloy under three pulse current densities (0A/mm2, 3A/mm2 and 8A/mm2) was systematically studied. The experimental results showed that the creep deformation increases with increasing current density during the 1st hour stage of electric pulse-assisted creep ageing process. However, the total creep strain of 8 h shows a trend of decreasing and then increasing. Low density pulsed currents (non-thermal effect) can promote the precipitation of the T1 phases and θ′ phases, and narrow the precipitates free zone compared to conventional creep aged sample (0A/mm2). High density (Both of non-thermal effect and Joule heating effect) pulsed currents can promote the precipitation of T1 phases, inhibit θ′ phases and form the precipitated phase penetrate the grain boundaries. A gratifying finding is that an increase in current density accelerates the aging hardening process, but the peak strength after creep ageing is the same for different current densities. This indicates that high pulse current density can improve creep ageing forming efficiency and ageing hardening process, and can use non-uniform current densities to solve the problem of significant differences in overall structural component formability while maintaining final performance consistency.

Effect of Nb content and cooling rate on the microstructure transformation and mechanical properties of hot-rolled rebar

In this study, the synergistic effect of the Nb content and cooling rate on the microstructural transformation, precipitation behavior, and mechanical properties of hot-rolled rebar was studied using a Gleeble-3800 thermal simulation machine, scanning electron microscopy, transmission electron microscopy, and a universal tensile testing machine. The results showed that the synergistic effect of Nb content and cooling rate could optimize the microstructure and precipitation behavior of rebar, promote ferrite and pearlite transformation, and reduce the ferrite grain size, pearlite lamellar spacing, and precipitated phase size, thereby improving the strength and plasticity of Nb-containing rebar. When the cooling rate was 3 °C/s and the Nb content was 0.035 wt%, the ferrite grain size decreased to 21.45 μm, the pearlite lamellar spacing refined to 0.222 μm, and the particle size of the (Nb, Ti, V) C precipitates reduced to 5 nm. Accordingly, the yield and tensile strength increased to 779 ± 6 MPa and 973 ± 8 MPa, respectively, the elongation at fracture increased to 16.35%, and the microhardness increased to 311.39 ± 8.0 HV.

Achieving high strength and fatigue performance of wire-arc additive manufactured 6061 aluminum alloy via interlayer friction stir processing and heat treatment

Interlayer friction stir processing (IFSP) has been proved to be an effective method for addressing metallurgical defects and modifying the microstructure of 6061 aluminum alloy produced by wire-arc additive manufacturing (WAAM). In this study, the effect of T6 post-heat-treatment on the microstructure, tensile properties and fatigue behavior were systematically investigated. The results show that the WAAM + IFSP-T6 component has excellent mechanical properties matching wrought counterparts, despite the abnormal grain growth in the stir zone, but there are no defects and a large number of nanometer β'' phases precipitate within the grains in the component. The mechanical properties of WAAM + IFSP-T6 component are isotropic, and the average yield strength, ultimate tensile strength, elongation and fatigue strength are 314 MPa, 336 MPa, 13% and 127 MPa, respectively.

Effect of Inconel 718 Filler on the Microstructure and Mechanical Properties of Inconel 690 Joint by Ultrasonic Frequency Pulse Assisted TIG Welding.

Ultrasonic frequency pulse assisted TIG welding (UFP-TIG) experiments were conducted to join Inconel 690 alloy (IN690) by adding Inconel 718 alloy (IN718) as the filler. The effect of the filler on the microstructure, mechanical properties, and ductility dip cracking (DDC) susceptibility of IN690 joints were investigated. The results show that a variety of precipitates, including MC-type carbide and Laves phases, are formed in the weld zone (WZ), which are uniformly dispersed in the interdendritic region and grain boundaries (GBs). The increase in the thickness of the IN718 filler facilitates the precipitation and growth of Laves phases and MC carbides. However, the formation of Laves phases in the WZ exhibits a lower bonding force with the matrix and deteriorates the tensile strength of IN690 joints. Due to the moderate content of Laves phases in the WZ, the IN690 joint with 1.0 mm filler reaches the maximum tensile strength (627 MPa), which is about 96.5% of that of the base metal (BM). The joint with 1.0 mm filler also achieves the highest elongation (35.4%). In addition, the strain-to-fracture tests indicate that the total length of cracks in the joint with the IN718 filler decreases by 66.49% under a 3.8% strain. As a result, the addition of the IN718 filler significantly improves the mechanical properties and DDC resistance of IN690 joints.