Microstructural Evolution Research Articles

High temperature tensile creep behavior and microstructure evolution of Ti60 alloy rolled sheet

In this work, the high temperature tensile creep test of 2mm Ti60 alloy rolled sheet was carried out, and the creep behavior and microstructure evolution were studied. The initial microstructure of the 2mm Ti60 alloy rolled sheet is mainly composed of primary α phase and secondary α phase, and there are many dislocations and dynamic recrystallization (DRX) inside the rolled sheet. According to Norton-Bailey law, the creep stress exponent at 600 °C is calculated to be 3.6, and creep activation energy at 200MPa is calculated to be 286.4kJ/mol. It implies that the creep mechanism of the rolled sheet includes dislocation slip and dislocation climb. The initial Ti60 alloy rolled sheet has the {0001}<10-10>α texture. Stretching along the RD makes the texture direction gradually change from B-type (<0001>//ND) to T-type (<0001>//TD). Whether it is the B-type texture or T-type texture, the (0001) plane of the α phase always exhibits a basal texture state parallel to the tensile stress direction, contributing a good tensile creep property of this alloy sheet.

Real-time study of the interplay between phase formation and stress evolution at the W1−xSix/a−Si interface

Nanoscale W1−xSix layers with different Si content were deposited by magnetron sputtering on amorphous silicon layers. The structure and stress evolution during deposition were monitored and in real time. Thus, it was possible to disentangle different origins of stress built-up (interface formation, phase formation, grain growth, and texture) on the nanoscale. It was found that the bcc phase with a composition-dependent texture forms at low Si content (less than 10% Si), but only above a critical thickness. At intermediate Si content (13.9% and 16.5% Si), or low Si content and low thicknesses (≲4.5 nm), the β phase with A15 structure and coexisting phases (bcc or amorphous) form, while a single, amorphous phase is observed at high Si content (≳22% Si). An A15 formation driven by impurities (O,C,N) was excluded by combined x-ray photoelectron spectroscopy and x-ray diffraction measurements on a second sample series. calculations of substitutional bcc and A15 W1−xSix alloys support the formation of A15 at higher Si content. The A15-containing interlayer should be taken into account when discussing the superconductivity of W/Si multilayers. The stress evolution during deposition of W1−xSix was correlated with the microstructure evolution, and compared to similar observations for Mo1−xSix. Due to the crystalline phase (bcc/A15) and bcc texture ([111] and [110]) competition, the structure formation of W1−xSix shows a higher complexity. This explains the wide range of stress states (from tensile to compressive) observed after deposition of W1−xSix. Nanoscale W-Si based stress-compensation layers could be employed for tailoring the stress state of nonepitaxial semiconductor devices. Published by the American Physical Society 2024

Effect of laser remelting on microstructure evolution and high-temperature fretting wear resistance in a laser-cladding self-lubricating composite coating on titanium alloy substrate

TC21 titanium alloy possesses the advantage including high strength, low density, and great resistance to damage. Combining it with surface modification technology, it is expected to improve the performance of aviation structural components. This work applied laser remelting technology to realize surface modification, and the hardness and fretting wear properties of the coating were investigated. This research has found that laser remelting technology can effectively refine grain size and improve the performance of coatings. By exploring different laser remelting powers (600 W, 900 W, 1200 W) and the different diameters of laser beam (3 mm, 6 mm), the optimal laser process was obtained with laser power and spot diameter of 600 W and 6 mm, respectively. The average grain size is 2.1 μm. The laser remelting coating has an average microhardness about 980 HV0.2, and it is 2.5 times and 1.3 times higher than the substrate and laser cladding hardness, respectively. A minimum coefficient of friction (COF) about 0.5 was obtained by the laser remelting coating, and the wear rate reaches the lowest of 1.87 × 10−6 mm3/(N·m) at fretting temperature with 500 °C. The abrasive wear and adhesive wear were the main wear mechanisms, and accompanied by oxidative wear. This study provides important reference for improving the performance of high-strength titanium alloy to obtain low defect, high-performance coatings with stable quality.

Microstructure evolution and mechanical properties of tungsten alloy prepared by laser directed energy deposition

Tungsten heavy alloys (WHAs) are widely applied across military, medical, and other advanced industries. Laser-directed energy deposition (LDED) is an innovative approach to fabricate WHAs with intricate microstructures. This study explored the manufacturing processes and forming characteristics of three distinct tungsten alloy compositions to elucidate the microstructural formation mechanisms and performance evolution of WHAs prepared by LDED. Electron backscatter diffraction analysis revealed the occurrence of heterogeneous nucleation and dendritic precipitation in supersaturated solid phases across different alloy compositions. By applying the drag force equation derived from the two-phase flow theory, the Gaussian energy distribution inherent to the LDED process, and the low flowability of WHAs, this study reveals the microstructural layering mechanisms within LDED-produced samples. Through process optimization, 90W samples that exhibited an ultimate tensile strength of 1093MPa and elongation of 16.8% were obtained. In situ mechanical testing revealed that the reduced elongation of the WHAs produced by LDED is due to their unique fracture mechanism driven by the interconnection of cracks between fractured tungsten particles. However, by incorporating smaller W particles and optimizing the gap ratio, the stress concentration can be effectively mitigated and crack propagation can be curtailed, thereby significantly enhancing elongation.

Understanding the deformation creep and role of intermetallic compound-microstructure in Sn-Ag-Cu solders

Tin-based alloys are commonly used in lead-free solder joints in electronic interconnection applications, where creep can limit joint reliability. In this work, directionally solidified bulk solder alloys of different compositions (pure tin, SAC105 and SAC305) are mechanically tested under a constant load for each composition at room temperature to understand mechanical creep performance and quantify the role of different content of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in terms of secondary creep strain rate, microstructural evolution, and total amount of accumulated strain. In this work, microstructures are fabricated using directional solidification to promote a systematic variation in IMC sizes, shapes, and distributions within similar crystal orientations of the primary β-Sn matrix. Analysis of creep data indicates that secondary creep is dominated by obstacle-controlled dislocation motion. This is further confirmed by electron backscatter diffraction (EBSD) analysis, which reveals that the formation of subgrains and internal structure, correlating to the initial microstructure of the sample, i.e. changes in secondary dendrite arm spacing (λ2) and eutectic intermetallic spacing (λe). The experimental observations are supported further by crystal plasticity simulations that explicitly model the presence of IMCs within the Sn-based samples and show the dependence of the secondary creep rate upon the IMC content, and therefore be beneficial for the possible future composition design in solders.

The microstructure and mechanical property of W-TiC/Ti composites via chemical-mechanical milling method

Carbide dispersion strengthened W(CDS-W) has attracted much attention as a plasma-facing material (PFM). However, the carbide tends to segregate at W grain boundaries and has poor interface properties with W due to the large difference in the bond structure. In this work, nanometer Ti was added to improve the performance of the W/TiC interface, and nanoscaled W-TiC-x%Ti (x=0.1,0.5 and 1.0) composites were prepared by chemical-mechanical milling and ordinary sintering method. The effects of Ti on powder morphology, phase composition, microstructure and mechanical properties were systematically investigated using XRD, SEM, EDS, TEM and HADDF technologies. Simultaneously, the existence form and distribution of Ti elements, and W/TiC interface characteristics of powders and composites were analyzed. Moreover, the microstructure evolution and strengthening mechanism were preliminarily discussed. Results show that the W-TiC/Ti powder has an obvious core-shell multilayer structure with a particle size range of 50-120 nm. The addition of Ti exists in the forms of TiC, Ti, and TiO2, and has no effect on the morphology and phase composition. Besides, the phase transformation and solution-precipitation of the Ti-added occurs during the sintering process. Part of Ti precipitates on the W/TiC surface to form Ti rich region, which significantly promotes the dispersion of TiC and improves the W/TiC interface, as well as prevents the growth of W grains, and the average grain size is 2.90 μm. Moreover, the orientation relationship of [013]( 00)TiCFCC||[ 13]( 0)WBCC exists at the W/TiC interface, especially the coherent phase interface is formed. The tensile strength and microhardness at room temperature are 520 MPa and 850 HV0.2, respectively, which is attributed to the synergistic effect of fine-grained strengthening, dispersion strengthening and interface strengthening. This work can provide a new strategy and direction for preparing high-performance CDS-W materials.

Laser additive manufacturing of Ti and Ce co-modified 2195 difficult-to-process aluminum alloy: Grain refinement, cracking suppression and enhanced mechanical properties

High cracking susceptibility of Al-Li alloys with Ti/CeB6 addition is thoroughly suppressed in laser powder bed fusion (LPBF) processing of Ti/Ce co-modified 2195 alloys at relatively high scan speeds, while the cracking suppression mechanism and phase formation in these composites are not clarified. In this work, microstructure evolution and mechanical performance of the LPBF-fabricated Ti/Ce co-modified 2195 are investigated to reveal their cracking suppression and strengthening mechanisms. The results show that apparent grain refinement of the composites is ascribed to high supercooling from rapid formation of constitutional supercooling zone in front of solid–liquid interfaces by high-Q-value Ti solute, and heterogeneous nucleation of in situ formed Al3Ti and Al11Ce3 precipitates. Their synergistic interactions promote formation of fine equiaxed grains and thus inhibit crack initiation. The composites exhibit high microhardness of 100 ± 5 HV0.2, nano-hardness of 1.6 ± 0.1 GPa and elastic modulus of 97 ± 3 GPa, where the elastic modulus increases by ∼27% and ∼31% compared to those of LPBF-processed and conventionally manufactured 2195 alloys, respectively. A tensile strength of ∼336 MPa and an elongation of ∼3% are obtained from in-situ synchrotron X-ray diffraction measurement. The improved properties are derived from grain refinement and Orowan strengthening. Based on the optimal processing parameter and composition, a bracket component filled with lattice structures is designed and manufactured with good manufacturing quality and processing accuracy.

Enhancing machinability in free-cutting duplex brass alloys: Isotropic blocky α phase formation via optimized hot extrusion processing

Despite the active utilization of duplex brass alloys in the electronics and automotive industries, optimizing thermomechanical treatment conditions for achieving excellent machinability remains a subject of ongoing debate. In this study, to establish a strategy to achieve enhanced machinability via industrial-scale direct hot extrusion processing, we systematically investigated the effect of hot extrusion processing conditions on microstructural evolution, mechanical properties, and machinability of duplex brass alloys. In particular, the yield strength was effectively interpreted through the extended Hall-Petch relationship, and the machinability was further elucidated through the evaluation of rotational torque during the drilling test as well as the precise analysis of segmented chips produced in the drilling test. As a result, our microstructural analysis of the as-cast Cu58Zn39Pb3 alloy revealed that the cooling process during industrial-scale casting inevitably results in the formation of the Widmanstätten structured α phase and the heterogeneous dispersion of Pb particles. In contrast, 670 ℃ extruded lower part and 730 ℃ extrudates, which were extruded in the single β region that caused complete dynamic recrystallization behavior, exhibited a uniform and isotropic blocky α structure and uniformly redistributed Pb particles, ultimately leading to superior mechanical properties and machinability. Notably, our findings suggest that achieving an isotropic blocky α structure can be attained at temperatures up to 100 ℃ below the β-transus temperature by optimizing extrusion pressure conditions. This approach offers an efficient methodology for minimizing defects caused by high-temperature extrusion, such as surface oxidation and hot shortness cracking, while simultaneously minimizing processing costs.

Thermal profile modeling and microstructural evolution in laser processing of Inconel 625 plates by comparison of analytical and numerical methods

Microstructural evolution of materials under specified process conditions and parameters can be predicted by thermal modeling of additive manufacturing laser processes. The objective of this study was to develop, analyze and compare two methods for prediction: an analytical method and a numerical method for laser processing of Inconel 625 material. These methods were compared with experimental results for thermal profiling, and the effect of thermal profiles on microstructure of the experimental samples was explored. Maximum temperature and cooling rate of the numerical method were shown in good agreement, while the analytical method proved more challenging when compared to the experimental results for three laser parameters. Cooling curves were correlated with microstructure in terms of grain size, morphology, and orientation, with findings trending with parameter adjustments. This research supports the numerical modeling approach as a method for examining optimal laser processing conditions for Inconel 625 that is ideally suited for complex fluid flow analyses.

Microstructure evolution and oxidation resistance of plasma sprayed AlSi-doped AlCoCrFeNi coatings with post-annealing

High entropy alloy (HEA) coatings of equimolar AlCoCrFeNi typically exhibit a lower oxidation rate at high temperatures by forming a protective passivation film. However, the metal elements consumption during long-term oxidation limitted the application. In this work, AlCoCrFeNi HEA coatings doped by AlSi as a supplement to passivation elements were prepared by atmospheric plasma spraying (APS), and AlSi capsules were diffused uniformly into the coating through annealing treatment to offset the element consumption during high-temperature oxidation. Results showed that annealing promoted Al and Si atoms diffusing into the solid solution, which stabilized BCC and inhibited FCC formation. During the oxidation at 900 °C, a protective Al2O3 film was formed on the coating surface, and AlSi capsules continuously transported Al ions to the consumption zone and reduced oxidation rate to 0.0015 g/cm2. The HEA coating doped by passivation element capsules provided a new approach for the design of novel antioxidant coatings.

Achieving ultra-high strength in TiB/metastable-β composites via short-process technology

Lightweight titanium alloys with ultra-high strength and reasonable ductility are desirable for aerospace applications. However, titanium alloys typically require cumbersome heat treatment to achieve excellent mechanical properties. Here, ultra-high strength Ti-55531-based composites were fabricated by introducing TiB whiskers using a short process, i.e. melting and isothermal forging. The microstructure evolution during isothermal forging was investigated, TiB whiskers would promote the discontinuous dynamic recrystallization and impede abnormal grain growth, resulting in significant β grain refinement, equiaxialization, and crystal orientation randomization. In addition, uniformly distributed nano-scaled αs lamellae were formed. 2.5 vol% TiB/Ti-55531 achieved a superior strength-plasticity synergy with the ultra-high strength of 1525 ± 4 MPa and elongation of 6.4 %±0.2 %, which were 9.2 % and 12.3 % higher than that of Ti-55531, respectively. The strengthening mechanisms were thoroughly analyzed, providing further insight to simplify the preparation and advance the application of ultra-high strength TMCs via short-process technology.

Effects of cerium micro-alloying on microstructural evolution and dispersion strengthening in Al-Yb-Er-Zr alloy

This study investigates the impact of trace cerium (Ce) addition on the precipitation behavior of Al-0.03Yb-0.03Er-0.06Zr (at%) alloys, with a focus on the formation of eutectic phases and nanoscale dispersoids. Ce, known for its low solubility in Al, preferentially segregates at grain boundaries, leading to the formation of Ce-rich eutectic phases and significant grain refinement. Isochronal annealing experiments revealed a double-peak hardening pattern. The first peak, associated with Al3RE (RE= Yb, Er, Ce) precipitates, demonstrated minimal sensitivity to Ce addition. The second peak, related to core-shell L12-Al3(RE, Zr) precipitates, exhibited a notable increase in hardness in the Ce-added alloy. Isothermal annealing at 450 °C and 475 °C further demonstrated that Ce accelerates the annealing-hardening response and increases the number density of Al3(RE, Zr) dispersoids at elevated temperatures. This enhancement may be attributed to Ce serving as an effective inoculant element and significantly reducing the stacking fault energy, which facilitates easier nucleation of these particles.

Crystal structure, microwave dielectric properties, and far-infrared spectroscopy of a novel low-dielectric constant tremolite ceramic CaZnGe2O6

The diopside-structured CaZnGe2O6 ceramics were synthesized using the conventional solid-state reaction method in this study, and their crystal structure, microstructural evolution, and microwave dielectric properties were systematically investigated. The XRD and Rietveld refinement analyses confirmed that CaZnGe2O6 crystallizes in the monoclinic crystal system with a C2/c space group. The intrinsic microwave dielectric properties of the ceramics were evaluated using far-infrared spectroscopy. The ceramic structure exhibits high density and microstructural homogeneity after sintering at 1130 °C, resulting in exceptional microwave dielectric properties achieved at this optimal temperature (εr = 8.78 Q×f = 63,782 GHz, τf = −66.4 ppm/°C). These findings highlight the potential application of CaZnGe2O6 ceramics as low-permittivity materials suitable for microwave devices.

Influence of Cr inclusion on the microstructural evolutions and tensile properties of Sn-5 wt% Sb solder alloy

Influence of Cr inclusion on the microstructural evolutions and tensile properties of Sn-5 wt% Sb solder alloy

High temperature induced abundant closed nanopores for hard carbon as high-performance sodium-ion batteries anodes

Hard carbon (HC) stands out as the preeminent anode material for sodium-ion batteries (SIBs) which are deployed in expansive energy storage infrastructures. Herein, the large enough graphene nanosheets interlayer and abundant nanopores with a diameter of ∼2.1 nm induced by adjusting the pyrolysis temperature in the thermosetting phenolic resin-derived hard carbon matrix to augment the performance of the sodium ion storage. The presence of sufficiently large carbon interlayers has been proven to provide active sites for reversible adsorption, enabling effective storage of sodium ions in the high-voltage slope region, while also promoting rapid Na+ transport. Meanwhile, forming abundant closed nanopores with larger sizes helps sodium ion storage in the low-voltage plateau region. In the optimized samples, the formation of sufficient long graphene nanosheets with a perfect crystal lattice, which further shrinks to form enclosed nanopores, effectively reduces defective sites and specific surface area. Additionally, the appropriate content of C-O and C=O functional groups contributes to an exceptional initial Coulombic efficiency (ICE) of up to 93%. Simultaneously, the optimized sample HC-1500 contributes to a remarkable plateau capacity of 294 mAh g-1 during the charging process (high reversible capacity of 403 mAh g-1 at 0.1 C). Moreover, based on the microstructure evolution and Na storage behavior of hard carbon, an “adsorption (27%) – filling (73%)” sodium storage mechanism that the sodium storage as a quasi-metallic sodium state is demonstrated. Consequently, this study will offer valuable insights for the development of hard carbon anodes tailored for high-energy practical SIBs, while also advancing the understanding of sodium storage mechanisms.

Microstructure evolution and degradation process of AlCrTiSiN coatings with different Si contents at high temperatures

The microstructure evolution of AlCrTiN and AlCrTiSiN coatings containing 4, 6.8, and 10.6 at.% Si was studied at temperatures ranging from 800 to 1100 °C. The AlCrTiN coating exhibits a single-phase fcc-(Al,Cr,Ti)N structure, while the AlCrTiSiN coatings transition from a nanocomposite structure, composed of fcc-(Al,Cr,Ti)N and amorphous a-SixNy, to a fully amorphous structure as the Si content increases. The hardness and adhesion strength of coatings initially rise, peaking at 24 GPa and 44 N respectively, due to the formation of the nanocomposite structure. However, these properties decline as the coatings become fully amorphous. At elevated temperatures, severe oxidation leads to the gradual formation of layered oxides. Concurrently, phase transformation, spinodal decomposition, and crystallization occur within the nitride layer. The addition of Si enhances oxidation resistance by promoting the rapid formation of a dense and protective oxide layer, and by reducing nitrogen release and TiO2 formation. However, at 1000 and 1100 °C, the coating with 10 at.% Si exhibits slightly faster oxidation compared to the 6.8 at.% Si coating, as the increased Si content reduces the Al content, limiting the coating's ability to regenerate the protective oxide layer.

Effect of calcite on the thermal decomposition of pyrite: Thermodynamics, phase transformation, microstructure evolution and kinetics

Pyrite, a common iron mineral in refractory iron ores, emits SO2 during oxidative roasting, contributing to environmental pollution. This study investigated the effect of calcite on the thermal decomposition of pyrite, focusing on thermodynamics, phase transformation, microstructural evolution, and non-isothermal kinetics, with emphasis on SO2 formation inhibition. Results showed that pyrite decomposed first to pyrrhotite, then to magnetite and hematite, with SO2 as the primary gaseous product. Higher temperatures and lower oxygen concentrations favored S2 gas formation. Non-isothermal decomposition of pyrite occurred between 400–725°C, initiated at the particle surface, and significantly increased product porosity, resulting in butterfly-shaped hematite. The addition of calcite resulted in the reaction of SO2 with calcite to form anhydrite on the particle surface, inhibiting the release of SO2. Initially, the thermal decomposition of pyrite proceeded with a low apparent activation energy, making the reaction relatively easy. However, the presence of calcite significantly increased the apparent activation energy and inhibited the thermal decomposition reaction.

Microstructure evolution and mechanical properties of SrTiO3 ceramic joint brazed by SnO–ZnO–P2O5–SiO2 phosphate glass

The study uncovers the microstructure and mechanical properties of brazed joints between SrTiO3 ceramics and a phosphate glass with the composition 49SnO-19ZnO-32P2O5-3SiO2. The primary objective is to investigate the wettability of the phosphate glass on SrTiO3 ceramics and the evolution of joint strength over varying holding times. Key findings reveal that the phosphate glass exhibits favorable wettability on SrTiO3 ceramics. The formation of Zn2P2O7 and SnP2O7 phases in the joint microstructure and the amount of these two phases gradually increases with the holding time. The mechanical performance is highlighted by the achievement of a peak shear strength of 40.3 MPa after brazing at 560 °C for 10 min. Additionally, the hardness, elastic modulus, and plasticity of the Zn2P2O7 and SnP2O7 phases were found to be intermediate between those of the SrTiO3 matrix and the glass. The formation of these two phases significantly enhances the mechanical properties of the joint.

Deformation behavior and microstructure evolution of one novel superalloy with high rare earth gadolinium content: Multi-scale modeling and experimental study

It has been proved that rare earth elements have a positive effect on the performance of superalloys and steels at only trace levels, but rare earth phases are always tricky in the manufacturing process. In this work, one Ni–Mo–Cr-Gd alloy with ultrahigh rare earth Gd content (1.75 wt %) was designed to reveal the influence of hard and brittle Ni5Gd particles on hot deformation behavior and microstructure evolution. The Ni–Mo–Cr-Gd alloy exhibits higher deformation activation energy and smaller processable regions in the processing maps as compared with the Ni–Mo–Cr alloy. Combining electron back scatter diffraction and crystal plastic finite element method, it was found that strain concentrates around Ni5Gd particles, especially at grain boundaries, and rapidly reaches the critical value for recrystallization, which verifies particle stimulated nucleation. The recrystallization fraction decreases with strain rates from 0.01 to 1 s−1 but increases from 1 to 10 s−1, which is because meta-dynamic recrystallization occurs faster when the strain rate is greater than 1 s−1 and Ni5Gd particles promote the process indirectly by introducing more severely deformed matrix. Furthermore, the finite element modeling shows that plastic strain and temperature rise at the central region of samples increase with strain rate increasing, which can explain the unusual fragmentation of Ni5Gd at 1200 °C with the highest strain rate. Our results firstly reveal the evolution mechanism of Gd-containing superalloy during hot deformation, which can help to solve the manufacturing problems of similar alloys.

Effect of trace silver addition on microstructure and properties of Cu-0.45Cr-0.1Zr alloy

Cu-0.45Cr-0.1Zr-(0.3Ag) were produced and subjected to multistage thermo-mechanical treatment. The microstructure evolution and properties of the alloys during aging were investigated in detail and the effect of trace Ag on comprehensive properties of Cu-Cr-Zr alloy was discussed by kinetic and strength calculations. The results showed that Cu-0.45Cr-0.1Zr-0.3Ag alloy had a higher strength than Cu-0.45Cr-0.1Zr alloy while maintaining a high electrical conductivity. After multistage thermo-mechanical treatment, the tensile strength, yield strength and electrical conductivity of Cu-0.45Cr-0.1Zr-0.3Ag alloy reached 611MPa, 601MPa and 78.7 %IACS, respectively. The addition of Ag had little influence on the precipitation process of Cu-Cr-Zr alloy during aging: Cr particles transitioned from GP zones to face-centered cubic (fcc) structure and finally stabilized in body-centered cubic (bcc) structure, however, the composition of Zr precipitates changed after Ag doping. Most of Zr atoms segregated at grain boundaries in the form of Cu4AgZr in Cu-0.45Cr-0.1Zr-0.3Ag alloy instead of Cu5Zr in Cu-0.45Cr-0.1Zr alloy. The calculation results showed that the addition of Ag refined the size of Cr particle, increased the density of dislocations, enhanced the effect of dislocation strengthening.