Types Of Precipitates Research Articles

Effects of Fe self-ion irradiation on a low carbon MX-ODS steel at 550°C

Oxide Dispersion Strengthened (ODS) steels with nano-scale oxides have become one of the candidate materials used in advanced nuclear reactor systems. A novel MX-ODS steel with extremely low carbon content was irradiated with 3 MeV Fe ions at 550°C up to peak damage of 70 dpa. The steel contains uniformly distributed Y2O3 nano-precipitates with an average size of 3.5 nm and a number density of 5 × 1022/m3. A V-rich shell was found surrounding the core of Y, O, and Si at some particles. Two types of large precipitates, Y-Ta-Si oxides, and VN, were observed in the steel instead of carbides. Voids of very small size are present due to irradiation and the calculated void swelling was only 0.004%, suggesting good irradiation tolerance of the MX-ODS steel in this study. Fine and dense oxide nano-precipitates and their shell-core structure remained stable while the shape of large precipitates changed after irradiation.

Effect of Heat Treatment on Osteoblast Performance and Bactericidal Behavior of Ti6Al4V(ELI)-3at.%Cu Fabricated by Laser Powder Bed Fusion.

Cu addition to alloys for biomedical applications has been of great interest to reduce bacterial growth. In situ-alloyed Ti6Al4V(ELI)-3at.%Cu was successfully manufactured by laser powder bed fusion (L-PBF). Even so, post-heat treatments are required to avoid distortions and/or achieve required/desired mechanical and fatigue properties. The present study is focused on the investigation of microstructural changes in L-PBF Ti6Al4V(ELI)-3at.%Cu after stress relieving and annealing treatments, as well as their influence on osteoblast and bactericidal behavior. After the stress relieving treatment, a homogenously distributed β phase and CuTi2 intermetallic precipitates were observed over the α' matrix. The annealing treatment led to the increase in amount and size of both types of precipitates, but also to phase redistribution along α lamellas. Although microstructural changes were not statistically significant, such increase in β and CuTi2 content resulted in an increase in osteoblast proliferation after 14 days of cell culture. A significant bactericidal behavior of L-PBF Ti6Al4V(ELI)-3at.%Cu by means of ion release was found after the annealing treatment, provably due to the easier release of Cu ions from β phase. Biofilm formation was inhibited in all on Cu-alloyed specimens with stress relieving but also annealing treatment.

Doubled strength and ductility via maraging effect and dynamic precipitate transformation in ultrastrong medium-entropy alloy

Demands for ultrahigh strength in structural materials have been steadily increasing in response to environmental issues. Maraging alloys offer a high tensile strength and fracture toughness through a reduction of lattice defects and formation of intermetallic precipitates. The semi-coherent precipitates are crucial for exhibiting ultrahigh strength; however, they still result in limited work hardening and uniform ductility. Here, we demonstrate a strategy involving deformable semi-coherent precipitates and their dynamic phase transformation based on a narrow stability gap between two kinds of ordered phases. In a model medium-entropy alloy, the matrix precipitate acts as a dislocation barrier and also dislocation glide media; the grain-boundary precipitate further contributes to a significant work-hardening via dynamic precipitate transformation into the type of matrix precipitate. This combination results in a twofold enhancement of strength and uniform ductility, thus suggesting a promising alloy design concept for enhanced mechanical properties in developing various ultrastrong metallic materials.

Microstructures and mechanical properties of the precipitation strengthened Al0.4Cr0.7FexNi2V0.2 high entropy alloys

In this study, a series of Al0.4Cr0.7FexNi2V0.2 (x: molar ratio, x = 0.5, 1, 2) high entropy alloys were cold-rolled and annealed. The microstructures and mechanical properties of the alloys were systematically investigated. The results revealed that all the solution-treated alloys with different Fe contents exhibited solo FCC phase. After annealing, the coherent L12 phases and hard BCC phases were formed in the Fe0.5 and Fe1 alloys, while the Fe2 alloy only contained the L12 phases. The precipitation of L12 and BCC phases increased the hardness of the alloys. The volume fraction of BCC phase was found to decrease as the Fe content increased, the excessive BCC phases led to the decrease of plasticity. The mechanical properties of alloys were mostly determined by the degree of recrystallization and the amount and type of precipitates. The precipitation of the second phase was regulated by tailoring the alloy composition, so that the AN Fe1 alloy can obtain excellent mechanical properties.

Microstructure and Mechanical Properties of Autogeneous GTA Weldments of Reduced-Activation Ferritic/Martensitic Steel and the Effects of Alloying Elements

Five reduced-activation ferritic/martensitic (RAFM) steels containing different contents of Cr, Ta, and Ti were prepared and the weldability of these alloys were evaluated by autogeneous gas tungsten arc (GTA) welding. After welding, post weld heat treatment (PWHT) was performed at temperatures of approximately 730-750 ℃. The microstructures of all alloys after PWHT consisted of a tempered martensite matrix and two types of precipitates, namely, M<sub>23</sub>C<sub>6</sub> and MX. Both the tensile and yield strength of the GTA welds increased with an increase in Cr and Ta contents due to the enhanced solid solution and precipitation strengthening. An increase in Ti content promoted the precipitation of fine MX particles and thereby suppressed the precipitation of M<sub>23</sub>C<sub>6</sub> carbide. This improved the impact toughness without a considerable loss of strength.

Origin of the nucleation preference of coherent and semicoherent nanoprecipitates in Al–Cu alloys based on atomistically informed classical nucleation theory

The age-hardening response during the heat-treatment process of Al–Cu alloys is significantly and nonlinearly influenced by the type and size of metastable precipitates formed. In Al–Cu alloys, a semicoherent θ′ phase, usually observed after the formation of coherent Guinier–Preston (GP) zones during aging, is the key strengthening precipitate. Thus, identifying the energetics of preferential nucleation of these precipitates is essential for clarifying the optimal conditions for the formation of precipitates that effectively contribute to hardening. In this study, using classical nucleation theory (CNT) along with a recently developed machine-learning-based interatomic potential with near first-principles accuracy, we characterized the nucleation preference of coherent GP zones and semicoherent θ′ nanoprecipitates in Al–Cu alloys at various temperatures and solute concentrations. Our atomistically informed CNT model revealed the overall temperature and solute-concentration dependencies of the nucleation barriers of the nanoprecipitates, which determine the crossover temperatures at which the ease of formation of each precipitate alternates at the solute concentration of interest. The predicted results were in good agreement with the previous experimental observations. The findings of this study contribute to furthering the understanding of the driving forces for nucleation of precipitates in Al–Cu alloys at an atomic level and provide theoretical guidance for identifying the optimal age-hardening response.

Interphase and fibrous precipitation in a thermomechanically processed V–Nb–Mo microalloyed steel

A novel V–Nb–Mo steel was thermomechanically processed to promote ferrite grain refinement and precipitation during the austenite to ferrite transformation. Transmission electron microscopy and three-dimensional atom probe tomography confirmed the formation of two main types of precipitates: nano-scale interphase precipitates and fibrous precipitates (FP). Both the precipitates had a Baker–Nutting orientation relationship with the ferrite matrix, but with different variants. Interphase precipitates exhibited a disc shape with an average distance between precipitate rows of 15 ± 2 nm and an average Guinier radius of 3.9 ± 1.7 nm, whereas FP had a rod-shape 2.5 ± 0.5 nm in radius and 8–25 nm in length. It appeared that the FP are formed along the plane perpendicular to the interphase precipitates plane.

Microstructure and corrosion behavior of Y-modified ZK60 Mg alloy prepared by laser powder bed fusion

The microstructure and corrosion behavior of Y-modified ZK60 Mg alloy prepared by laser powder bed fusion (LPBF) are studied. By controlling the content of Y, the quantity, distribution, and type of precipitates are regulated, and the corrosion resistance is improved. Specifically, the ZK60 alloy with 1 wt% Y exhibits excellent corrosion resistance, which is mainly due to the formation of a continuous network of rare earth-containing precipitates at the grain boundaries that form corrosion barriers to impede corrosion and induce grain refinement. In addition, the passivation and stability of the surface film are improved after the addition of Y.

Microstructure changes and enhanced properties of an automotive AlMgSi alloy improved by micro-alloying La-addition

Micro-alloying of rare earth elements can improve the properties of Al alloys, but the mechanisms how they change the microstructures and therefore the properties of the alloys are still generally unclear. Using scanning electron microscopy and atomic-resolution transmission electron microscopy, here we have revealed the microstructural differences between two AlMgSi alloys with and without La-addition, and investigated the impacts of La-addition on specific microstructure-property relationships of the material. It is shown that La-addition has three significant effects on the microstructures and the properties of AlMgSi alloys. Firstly, La-addition changes the types of precipitates formed during aging. Most of β“ precipitates formed in the peak-aged alloy with La-addition are polycrystalline β” precipitates. In the over-aging stage of this alloy, the dominant precipitates formed are the β”/U2, β”/β’ and β’/U2 composite precipitates, rather than the expected β’ precipitates. Secondly, La-addition induces the formation of numerous FCC AlSiLa intermetallics, which significantly refine the grain size and enhance the strength and the ductility of the alloy. Thirdly, La-addition may enhance the electrical conductivity of the age-hardened alloy by reducing the solute atoms in the Al-matrix.

Precipitation sequence in Al-Sc-Zr alloys revisited

Sc and Zr additions to Al provide significant strengthening through the formation of Al3(Sc,Zr) L12 dispersoids. Fe impurities are always present in commercial Al alloys and the effect of these impurities on precipitation mechanisms in Al-Sc-Zr alloys remain poorly understood. This is particularly relevant when considering recycled aluminium as recycling results in the build-up of impurities. We used a combination of resistivity and thermo-electric power (TEP) measurements to monitor the evolution of solid solution during ageing of an Al-Sc, Al-Zr and Al-Sc-Zr alloy. Sc first comes out of solution to form Al3Sc dispersoids, followed by Zr to form Al3Zr. A range of Al3Sc-core/Al3Zr-shell faceted morphologies were observed with high angular annular dark field scanning transmission electron microscopy (HAADF-STEM). The presence of a new class of Fe-rich plate-like precipitates in the {100}Al was revealed via HAADF-STEM. The ordered positions of the precipitate and matrix reflections in the selected area diffraction pattern and in high-resolution TEM images reveal that these precipitates display a multi-layered structure. The centre of the plates is pseudo-icosahedral with apparent five-fold symmetry, and is rich in Fe. The outside layer has a L12 structure and is rich in Sc and Zr. The layered structure allows complete coherency with the aluminium matrix. These precipitates are highly anisotropic with a thickness of 5-10 nm and a length up to ∼1000 nm. This is the first report of the formation of this type of coherent pseudo-icosahedral precipitates in isothermal conditions which is named the D-phase.

Discontinuous precipitation in a Cu-10Ni-1Si alloy with ultra-high strength, high shock absorption, and good stress relaxation resistance

The discontinuous precipitation in a Cu-10Ni-1Si alloy aged at 500 °C and 550 °C was studied to clarify the types of discontinuous precipitates, and the crystal relationships between precipitates and the matrix. The continuous δ-Ni2Si precipitates were detected in the initial aging stage, then discontinuous β-Ni3Si and continuous δ-Ni2Si precipitates were detected simultaneously. The crystal relationship between discontinuous β-Ni3Si precipitates and the copper matrix at the beginning of aging was that: (1̅11̅)Cu//(111̅)β, [011]Cu//[011]β. The lamellar discontinuous β-Ni3Si precipitates significantly improve stress relaxation resistance and damping properties, which are attributed to the interaction between lamellar structure and dislocation motion. These findings indicated that the formation of the lamellar discontinuous precipitates tends to prevent dislocation slip and promote precipitation, resulting in enhanced mechanical properties and conductivity properties simultaneously.

An analytical model of grain growth considering the conjoint effects of precipitate pinning and solute drag in steel

ABSTRACT An analytical model is developed to explain the kinetics of grain growth in steel that takes into account all feasible prime phenomena; namely, surface energy reduction, precipitate pinning effect and solute drag effect. The shapes of matrix grains and the precipitates are assumed to be tetrakeidecahedron and spherical, respectively. A single solute and a single type of precipitate are further assumed to be responsible for the solute drag and the precipitate pinning, respectively. An explanation of drag energy is provided in terms of Gibbs free energy change for solute segregation that eventually merges to the well-known Langmuir–McLean relationship. The developed model is validated in view of the existing database in available literature. A new methodology of grain growth analysis is accordingly proposed on the basis of the conceptualised ‘effective migration coefficient’ of the system.

Microstructure characteristics and mechanical performance of Fe-Cr-Ni-Al-Ti superalloy fabricated by powder metallurgy

Fe-Cr-Ni-Al-Ti ferritic superalloy was fabricated by hot isostatic pressing (HIP) of Fe-Cr-Ni-Al-Ti gas-atomized powders. Three types of precipitates with difference in particle size, composition and morphologies have been identified in the as-HIPed ferritic alloy. Micron-sized B2-NiAl distributed in the bulk together with L2 1 -Ni 2 TiAl and Fe(Cr) sub-precipitations are the dominant precipitates. Submicron-sized B2/L2 1 composite precipitates with Fe(Cr)-enriched outer layer and nano-scaled single B2 particles are distributed around the micron-sized B2/ L2 1 / Fe(Cr) composite precipitates. After solution treatment at 1100 °C, various types of precipitates in as-HIPed alloy can be completely dissolved, while dense spherical B2/L2 1 particles are precipitated rapidly even upon water quenching. During aging at 700 °C, the spherical particles evolve into cuboidal morphology and then coarsen and coalesce into large plates. The loss of coherency between the particle and the matrix would produce dense dislocation network at the particle/matrix interface. The measured tensile strength of as-HIPed ferritic superalloy at 700 °C is up to 198 MPa with a total elongation of 47.6%, and the cracks are found to be initiated at the prior particle boundaries, which leads to the failure. To fabricate the high-performance Fe-Cr-Ni-Al-Ti superalloy by powder metallurgy, we suggest that the prior particle boundaries should be avoided during consolidation process. • L2 1 -Ni 2 TiAl and Fe(Cr) sub-precipitations are formed within micron-sized B2-NiAl precipitates. • Outer layer of submicron-sized B2/L2 1 precipitates is enriched in Fe(Cr). • During aging at 700 °C, dense dislocation network is formed at the particle/matrix interface. • Cracks are initiated at prior particle boundaries upon tensile deformation of HIPed Fe-Cr-Ni-Al-Ti superalloy.

Evolution of discontinuous/continuous Al3(Sc,Zr) precipitation in Al-Mg-Mn 5083 alloy during thermomechanical process and its impact on tensile properties

The evolution of discontinuous and continuous Al3(Sc,Zr) precipitation in an Al-Mg-Mn AA5083 alloy during heat treatment and hot rolling was investigated. The results showed that, at a high Sc content (0.43 wt%), a large number of line/fan-shaped structures were formed as discontinuous Al3(Sc,Zr) precipitation during solidification, while no such discontinuous precipitation was observed when the amount of Sc added was low (0.15 wt%). During the three-step heat treatment (275 °C /12 h + 375 °C/48 h + 425 °C/12 h), two types of precipitates — Mn-bearing dispersoids and spherical Al3(Sc,Zr) precipitates — were formed as the main strengthening phases. In the high-Sc alloy, the discontinuous Al3(Sc,Zr) precipitates dissolved partially. However, the quantity of the spherical Al3(Sc,Zr) precipitates in the high-Sc alloy was much lower than that in the low-Sc alloy, which degraded its aging hardening response. During hot rolling, although the discontinuous precipitates were completely dissolved, the number density of the spherical Al3(Sc,Zr) precipitates in the high-Sc alloy was still lower than that in the low-Sc alloy. The tensile properties of the Sc-containing alloys improved significantly compared with those of the base alloy. However, the yield and ultimate tensile strengths of the high-Sc alloy were lower than those of the low-Sc alloy. This indicates that the discontinuous precipitation had a deleterious effect on the mechanical properties of the alloy.

Effects of Ti microalloying on the microstructure and mechanical properties of acicular ferrite casting steel for high-speed railway brake discs

Owing to the continuous interest on high-speed railway trains, research on the brake disc made of ferritic cast steel with high strength and toughness, and the manufacturability of complicated cooling fins has been conducted. In acicular ferrite, Ti is a major element; however, studies on the effect of Ti composition on the mechanical and impact properties are limited to a Ti content of up to 0.05 wt%. In this study, the microstructure and mechanical properties of high-speed railway brake disc steel material with 0–0.12 wt% Ti were investigated. The specimens were subjected to the same quenching–tempering heat treatment, in which acicular ferrite formation was observed by optical microscopy, scanning electron microscopy, electron backscatter diffraction (EBSD), electron probe microanalyzer, and transmission electron microscopy. Ferrite blocks, such as acicular ferrite, granular bainite, bainitic ferrite, and polygonal ferrite, were characterized in detail and quantitatively analyzed by EBSD. For different Ti contents, ferrites of various morphologies were noted. Moreover, the types of precipitates were determined to be cementite, Cr-rich carbide, V-rich carbide, and Ti-rich carbide. The highest hardness, impact toughness, and strength were measured with the addition of 0.06 wt% Ti. The crack propagation mode in the impact specimen was observed using fracture surface analysis. In addition, the relationship between the microstructure and mechanical properties, such as strength, toughness, and hardness, was discussed based on the alloying Ti content. In this study, the effect of acicular ferrite and precipitates on toughness in ferrite casting steel was confirmed, and the optimal Ti content was confirmed.

Achieving superior strength and ductility in 7075 aluminum alloy through the design of multi-gradient nanostructure by ultrasonic surface rolling and aging

Aluminum alloys were used in various fields due to their high specific strength and low density. However, the disadvantage of low strength limits its wider application. In this work, the effect of ultrasonic surface rolling process (USRP) and artificial aging on microstructure and mechanical properties of 7075 aluminum alloy were investigated in detail. The results indicated that a multi-gradient nanostructure (MGNS) layer, i.e., grain gradient and precipitation gradient, was generated on the surface of the alloy. The tensile strength of the aged-USRP sample (692 MPa) was about 63 % higher than that of the coarse-grained sample (425 MPa), and the plasticity was comparable to that of the coarse-grained specimen. The underlying mechanisms of grain refinements, precipitation behavior and their effects on tensile properties were quantitatively analyzed. The high strength of the aged-USRP sample originated from grain boundary strengthening, precipitation strengthening, dislocation strengthening and synergistic strengthening. The activation of geometrically necessary dislocations (GNDs) during tensile deformation improved the plastic coordination ability of different microstructures. Thus, excellent strength-ductility synergy of 7075 aluminum alloy was obtained. • Multi-gradient nanostructure was formed on the surface of 7075 Aluminum Alloy. • Gradient nanostructure of type and number density of precipitates formed. • The multi-gradient nanostructure enhanced strength-ductility synergy of the alloy.

Effect of ageing on precipitation evolution and corrosion behaviour of Al–Zn–Mg–Cu alloy

The Al–Zn–Mg–Cu alloy was subjected to 4 passes equal channel angular pressing (ECAP) at 400°C, followed by different solutions and ageing treatments. The size, type and distribution of precipitates in aluminium matrix are different in different ageing treatments. In single-stage ageing, a large number of η′ precipitates and Guinier-Preston-II (GP-II) zones are generated in the aluminium matrix. The precipitates are mainly MgZn2 (η) precipitates and η′ precipitates during the double-stage ageing. The size and type of precipitates in three-stage ageing are similar to those in two-stage ageing. Simultaneously, the single-stage ageing sample has poor corrosion resistance and good hardness. Two-stage ageing and three-stage ageing samples have better corrosion resistance, but their hardness is lower than that of single-stage ageing.

Microstructural and residual stress analysis of functionally graded friction surfaced Al-Cu-Mg-Ag alloy

This study analyzed the microstructure and residual stress of a functionally graded friction surfaced Al-Cu-Mg-Ag alloy. To prepare a multilayer material using the friction surfacing process, different layers of Al-Cu-Mg alloy containing 3, 7, and 12 wt% of silver powder were deposited on the Al-Cu-Mg alloy substrate. After homogenization and aging heat treatment, a functionally graded structure with different silver weight percentages in different layers was obtained. The results showed that silver powder reduces the dimensions of the clad layers compared to the sample without silver. After homogenization and artificial aging treatment, a bimodal microstructure formed in the silver-containing sample. It was determined that two types of spherical (S-Al 2 CuMg) and rod-shaped precipitates (Ω precipitates) are formed in the microstructure of different layers. By moving from the first layer to the third layer, the concentration of Ω precipitates increases as the weight percentage of silver added to the microstructure increases. After aging heat treatment, it is observed that the hardness changes are mild, and the average hardness increases from the substrate (134 HV0.1) to the third layer (165 HV0.1).

Nanomechanical Characterization of Enzyme Induced Carbonate Precipitates

The mechanical properties of calcium carbonate minerals formed by enzyme-induced carbonate precipitation (EICP) were studied using nanoindentation. Two types of precipitates were considered: (i) a “baseline” precipitate, synthesized via urea hydrolysis in an aqueous solution of urease enzyme, urea, and calcium chloride; and (ii) a “modified” precipitate, synthesized from a similar solution, but with the inclusion of nonfat dry milk. While both precipitates predominantly comprised calcite, X-ray diffraction and Raman spectroscopy indicated broader peaks in the modified precipitate, implying differences in the crystal structure of the two precipitates. Both precipitates were polycrystalline and had a higher average indentation hardness (H) and a lower indentation modulus (M) compared with the values for single calcite crystals reported in the literature. The ductility of the precipitates was quantified by the ratio M/H. The modified precipitate had a higher average M/H, implying greater ductility. The increased ductility of the modified precipitate results in higher resistance to crack propagation. In sands biocemented using the modified EICP solution, the increased ductility of the precipitate, in addition to preferential precipitation at interparticle contacts, may contribute to relatively high unconfined compressive strengths at low carbonate contents.

Influence of Forging Parameters on Microstructure and Properties of En AW-6082 Alloy

Aluminum alloys are widely used in automotive industry due to their low density and good corrosion resistance. This category includes alloys based on AlSiMg which are suitable for load bearing parts operating under higher temperatures. This paper deals with analysis of influence of deformation parameters and heat treatment on structure and mechanical properties of EN AW-6082 (AlSi1MgMn) alloy manufactured by horizontal cast module technology. Casted rods were used as a billet, which was formed to defined height by hot open-die forging. Subsequently the precipitation hardening was used as heat treatment. Changes in microstructure were evaluated based on the metallographic analyzes performed by light optical microscopy and scanning electron microscopy using an energy dispersive X-ray spectrometry and electron backscatter diffraction. Mechanical properties were determined by uniaxial tensile test and hardness testing. The results showed, that due to the process parameters, no significant structural changes were observed in the surface layer of forging. However, microstructure is significantly inhomogeneous in the core due to the dynamic softening processes. Mechanical properties are increasing which is significantly influenced by the type and distribution of precipitates emerging during the artificial aging.