Precipitates In Matrix Research Articles

Precipitation size and strain rate dependence of dislocation-amorphous nanopillar interaction mechanism in magnesium

Introducing amorphous phases into the crystalline matrix is a new design strategy to improve the mechanical properties of Mg alloys. In this work, the effects of strain rate and amorphous nanopillar size on the interaction mechanism between the dislocation and precipitation in the Mg matrix were investigated by molecular dynamics simulation. The results show that the interaction mechanism between dislocation and amorphous precipitation depends on strain rate and amorphous nanopillar size. At strain rates of 5 × 107/s and 5 × 108/s, the amorphous precipitation strengthens the Mg matrix due to the pinning effect of the amorphous precipitation relative to the dislocation. The interaction mechanism changes from merging and canceling of dislocation to the cross-slip mechanism with the increase of precipitation size. Moreover, the strengthening effect of the large-sized amorphous phase on the dislocation is noticeable. However, the amorphous precipitation softens the Mg matrix at strain rates of 5 × 109/s and 1 × 1010/s. The underlying mechanism varies from the dislocation shearing mechanism to the generation of dislocation loops with the increase of the amorphous precipitation size. This research can provide theoretical guidance for developing and designing new high-performance Mg alloys.

Effects of deep cryogenic treatment on microstructure, mechanical, and corrosion of ZK60 Mg alloy

This study aims to investigate the effects of deep cryogenic treatment combined with traditional heat treatment on the microstructural characteristics, mechanical properties, and corrosion performance of ZK60 magnesium alloy. Quasi-in-situ TEM testing also indicates that deep cryogenic treatment induces the formation of ultra-fine zinc-rich precipitates in the magnesium matrix. After solid solution treatment, materials with cryogenic treatment will retain significant internal stress, which promotes the subsequent precipitation of rod-like β′1 during aging. Microstructural analysis reveals that deep cryogenic treatment before solution treatment and artificial aging can significantly enhance the length and density of rod-like β′1 precipitates. The treated material shows improved strength while maintaining its original elongation rate. Due to the nanoscale precipitation-induced micro galvanic effect, the aged samples exhibit a higher corrosion rate. The abundance of micrometer-sized second phases in the untreated sample does not significantly accelerate the material's corrosion rate. The solution-treated samples show the weakest micro galvanic effect and the best corrosion resistance.

Effect of Nb addition on the microstructure and martensitic transformation of NiTiHfScNb high temperature shape memory alloys

In the present work, the effects of Nb addition and aging on the microstructure evolution and martensitic transformation of (Ni50.3Ti28.7Hf20.0Sc1.0)100-xNbx (x = 0, 5, 10, 15 at.%) high temperature shape memory alloys were investigated. The addition of Nb results in the formation of the eutectic β-Nb phase along with martensite and Sc2O3 at room temperature. Aging at 550 °C for 3 h leads to the formation of nanoscale H-phase. The surface area fraction of the H-phase decreases with increasing Nb content to 10 at.%. As the Nb content increases, the transformation temperatures of the solution-treated NiTiHfScNb alloy increase and then decrease due to the variation of Ni content in the matrix. The aged samples show a smaller transformation hysteresis in comparison with the solution-treated samples. The difference of thermal hysteresis between the solution-treated and the aged samples increases with increasing Nb content because of the H-phase precipitation and Nb solution in matrix.

Application of the stereomicrophotogrammetric method for the complex study of the Al-Cu-Mg alloys system

Purpose. To combine the stereophotogrammetric method for processing fracture surface images at the micro level with the results of a series of mechanical and metal fractographic studies with precision methods for scanning electron microscopy (SEM) and energy dispersive analysis (EDX) in order to determine the peculiarities and general laws of the fracture process of Al-Cu-Mg test samples. Methodology. In this work, the mechanical properties of Al-Cu-Mg samples after mild (recrystallization) annealing and subsequent natural aging and a sample without heat treatment were experimentally determined. At the next stage, SEM-stereomicrofractographic research on fractures and their three-dimensional reconstruction from the obtained stereo images were performed. EDX studies have been performed on various parts of the samples to determine the distribution of mass percentages of elements in the study areas. A comprehensive methodology for experimental studies of Al-Cu-Mg alloys was used in this work to obtain qualitative and quantitative information on the microstructure of fractures, which consisted of the following steps: determination of the mechanical properties of samples by traditional methods of macro- and microanalysis; study on stereopairs of the microstructure of fractures by the stereophotogrammetric method; identification of the chemical composition and structure of matrix precipitation particles by energy dispersive X-ray spectroscopy (EDX analysis). Findings. Our experiments have shown that with an increase in the time of natural aging, the hardness increases slowly and reaches a maximum hardness of 127 Hv30 after 97 hours, which does not decrease subsequently. After natural hardening, the average fracture strength increases to Rm 440.3 with a relative elongation of 21.8 %. Mechanical tests have shown that the tensile strength increases with the hardness value and, in contrast, the toughness decreases. The energy required to fracture the sample is 16 J, followed by transcrystalline cellular fracture. The precipitates have a diameter of approximately 2.5–3 microns. Originality. Comparing the results of mechanical and metallographic studies, it can be argued that the desired properties of Al-Cu-Mg samples appear after dispersion hardening, which confirms the optimal hardening conditions. The results of the photogrammetric evaluation of samples in the micro range demonstrate the flexibility and accuracy potential of photogrammetric measurement methods and their subsequent processing, interpretation, and integration with EDX analysis to select optimal study sites. Practical value. An integrated approach to the analysis of materials using the SEM stereomicrophotogrammetric method, mechanical and metallographic studies, and EDX analysis was tested in this work.

Effect of various non-isothermal aging on properties and microstructure of 7055 aluminum alloy

This study investigated the effect of various non-isothermal aging processes on the mechanical properties and corrosion resistance of 7055 aluminum alloy extruded bars. The investigation utilized electrical conductivity, mechanical properties, local corrosion resistance and slow strain rate tensile test combined with microstructure characterization techniques such as metallographic microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the NIA-2 (120 °C→200 °C/30 min→120 °C, v = 30 °C/h) process significantly improves the strengths of the alloy compared to the T73 temper, the tensile strength and yield strength increase by 53.0 MPa–632.5 MPa and by 64.7 MPa–605.4 MPa respectively. Additionally, the maximum depths of intergranular corrosion (IGC) and exfoliation corrosion (EXCO) decrease from 80.6 μm to 97.7 μm–71.4 μm and 89.5 μm respectively. Therefore, the NIA-2 process can achieve both high strength and excellent corrosion resistance. Furthermore, the study shows that the sizes of grain boundary precipitates (GBPs) and matrix precipitates (MPs) increase with the sequence of NIA-1 (120 °C→200 °C→120 °C, v = 30 °C/h), NIA-2, and NIA-3 (120 °C→200 °C→120 °C, v = 20 °C/h) processes. The atomic percentages of Zn, Mg, and Cu in GBPs also vary with the different processes. The increases in the sizes of GBPs, MPs, and the widths of precipitation-free zones (PFZs), as well as the segregations of GBPs components, are primarily responsible for the improved mechanical properties and corrosion resistance of the alloy.

Effect of aging treatment on the mechanical property and precipitation transformation of Mg–Co–Y alloy

The strength and plasticity of magnesium (Mg) alloys have always been of significant concern. Here, it explores how the mechanical properties and precipitation transformation of the as-cast Mg-0.9Co-4.5Y (at.%) alloy are affected by aging hardening. The results demonstrate that the ultimate compressive strength (UCS) and compressive yield strength (CYS) of the as-cast Mg-0.9Co-4.5Y (at.%) alloy at peak hardness reach 604.8 MPa and 401.5 MPa respectively, while the compression rate (ε) of that after solution-treated reaches 21.9%. For the above changes in malleability and strength, we conduct an in-depth investigation of the impacts of phase composition, LPSO structure, and matrix precipitation. We find that the improvement of malleability is linked to the reduction of the volume fraction of LPSO phase after solution treatment, while the substantially increase of CYS after peak-aging is related to the dispersion strengthen of MgYCo4 phase and precipitation of β′ and β′′ phases, in which the precipitation of β′ and β′′ phases plays a leading role. This study uncovers the mechanical property and microstructure evolution of Mg-0.9Co-4.5Y (at.%) alloy in the aging response process and provides ideas for the performance regulation of Mg–Co–Y alloys.

In vitro and in vivo study on fine-grained Mg–Zn–RE–Zr alloy as a biodegradeable orthopedic implant produced by friction stir processing

Magnesium alloys containing biocompatible components show tremendous promise for applications as temporary biomedical devices. However, to ensure their safe use as biodegradeable implants, it is essential to control their corrosion rates. In concentrated Mg alloys, a microgalvanic coupling between the α-Mg matrix and secondary precipitates exists which results in increased corrosion rate. To address this challenge, we engineered the microstructure of a biodegradable Mg–Zn–RE–Zr alloy by friction stir processing (FSP), improving its corrosion resistance and mechanical properties simultaneously. The FS processed alloy with refined grains and broken and uniformly distributed secondary precipitates showed a relatively uniform corrosion morphology accompanied with the formation of a stable passive layer on the alloy surface. In vivo corrosion evaluation of the processed alloy in a small animal model showed that the material was well-tolerated with no signs of inflammation or harmful by-products. Remarkably, the processed alloy supported bone until it healed till eight weeks with a low in vivo corrosion rate of 0.7 mm/year. Moreover, we analyzed blood and histology of the critical organs such as liver and kidney, which showed normal functionality and consistent ion and enzyme levels, throughout the 12-week study period. These results demonstrate that the processed Mg–Zn–RE–Zr alloy offers promising potential for osseointegration in bone tissue healing while also exhibiting controlled biodegradability due to its engineered microstructure. The results from the present study will have profound benefit for bone fracture management, particularly in pediatric and elderly patients.

Effect of annealing treatment on the microstructure and mechanical properties of bulk nanostructured Ti/AZ61 composites prepared by hot pressing

Magnesium alloys, as the lightest structural alloys, provide the possibility of solving environmental problems by improving energy efficiency. Developing and maintaining nanocrystalline matrix is a huge challenge, and the key to achieving ultra-high strength. The nanocrystalline Ti/AZ61 composite prepared by hot pressing was annealed, and its microstructural evolution was characterized via SEM, XRD, and TEM, including the changes in magnesium matrix, Ti dispersions, and nano-scale precipitates. The density and mechanical properties of annealed composites were tested and analyzed. After annealing treatment at 623 K for 80 h, the average grain size of nanocrystalline Ti/AZ61 composites was 102 nm. 97% of Ti dispersions were submicron sized, and Ti3Al precipitates remained nanometer-sized. Ti dispersions and Ti3Al precipitates were uniformly distributed in the magnesium matrix. Compared with hot pressed composites, the crack that originated from the prior particle boundary (PPB) was restrained for annealed composites. The improved density and PPB bonding strength of annealed Ti/AZ61 composites had a positive impact on strength and plasticity. After annealing treatment for 40 h, the density increased from ∼2.041 g/cm3 to 2.066 g/cm3. The hardness, yield strength, and FFS were 146 HV, 493 MPa, and 5.6%, respectively, with corresponding increasing rates of 7%, 12%, and 65%, respectively.

Study on microstructure of rare earth Mg-9%Gd-2%Y-3%Nd -0.7%Zr alloy and properties of micro-arc oxidation films

The micro-arc oxidation protective film has been prepared on the surface of Mg-9%Gd -2%Y-3%Nd-0.7%Zr alloy by using the microarc oxidation technique of “step by step depressurization”. The microstructure of magnesium alloy substrate and micro-arc oxidation film were measured by OM, SEM and XRD, and the properties of the film were evaluated by electrochemical test of film thickness and surface morphology. The results show that the discontinuous network multiple eutectic phases are distributed in the grain boundary and there are dispersed-granular precipitates in the alloy matrix. After the micro-arc oxidation treatment, the thickness and corrosion resistance of the micro-arc oxidation film increased with the increase of oxidation time, and the surface micropore size increased first and then decreased, and the surface morphology of the micro-arc oxidation film changed from no micro-crack to micro-crack, and finally the micro-crack disappeared.

3D network-structured CoSb/P-CNFs@rGO as a highly conductive self-supporting anode material for lithium-ion batteries

CoSb particles have an extremely high specific capacity as anodes for Li-ion batteries, but the severe expansion during the reaction process makes their cycle stability very poor. In this study, a 3D CoSb/P-CNFs@rGO network structure has been successfully constructed by a simple electrospinning technique and hydrothermal treatment. 1D carbon nanofibers and 2D reduced graphene oxide network are intertwined and coated to create this 3D structure. In this ingenious strategy, CoSb particles are embedded in carbon nanofibers to restrain volume expansion. By encapsulating the nanoparticles in a graphene structural network, it is possible to stabilize the matrix structure and precipitate CoSb particles for secondary capture. In addition, the 3D network structure also builds a fast channel for 3D interaction electron/ion transfer. Benefiting from the above structural advantages, the CoSb/P-CNFs@rGO flexible self-supporting anode exhibits excellent electrochemical performance, including ultra-long cycling performance (870 mA h g−1 after 2000 cycles at a current density of 500 mA g−1). More importantly, the 3D structure design method may provide a simple and effective strategy to overcome the volume expansion of anode materials.

Precipitation transformation pathway and mechanical behavior of nanoprecipitation strengthened Fe–Mn–Al–C–Ni austenitic low-density steel

Precipitation strengthening has been widely adopted in austenitic low-density steel owing to excellent hardened effects. This approach generally employs the coherent κ′-carbides and non-coherent B2 particles. Revealing the precipitation transformation pathway is decisive for further optimizing the microstructures under specific engineering applications. Herein, the detailed precipitation sequence of Fe–28Mn–11Al–1C–5Ni (wt%) austenitic low-density steel as well as its influence on mechanical properties during aging process is systematically investigated. Our results reveal that nano-sized κ′-carbides domains (2 nm) exist in the solution-treated specimen. During aging at 500 °C for 1 h, the cuboidal κ′-carbides (15–20 nm) uniformly disperse in austenite matrix. However, after aging at 700 °C for 15 min, the coarsen κ′-carbides (30–35 nm) inhomogeneously distribute and align preferentially along the 〈1 0 0〉 directions. Further, extending the aging time to 60 min, the needle-type B2 particles replace the κ′-carbides due to the enrichment of Ni elements at the phase boundaries among the austenite and κ′-carbides. After aging at 900 °C, κ′-carbides entirely dissolve into the austenite matrix, and the intragranular B2 particles are the sole precipitates in the austenite matrix and follow the K-S orientation relationship with austenite. The work hardening capability seriously deteriorates due to the shearing of κ′-carbides by gliding dislocations. While the intragranular B2 particles preserve excellent work hardening rate by dislocations bow-out mechanism. The present work is meaningful for guiding the design of new generation dual-nano precipitation austenitic lightweight steel.

Interactions between clay minerals, bacteria growth and urease activity on biocementation of soils

Biocementation is a low carbon footprint soil improvement technique alternative to the use of hydraulic binders such as cement, mainly applied in sandy soils due to the need for vital room for bacteria and easy access for nutrient transport to feed them. This treatment is not suitable for natural clayey soils, however pore clogging caused by the presence of clay in low percentages may not be a problem, and clay minerals can be beneficial to increase the area for bacteria to attach and therefore to precipitate larger quantities of biocement. In addition, clay minerals can also have a positive influence on bacteria activity itself, and this is the novelty of this investigation. The influence of kaolin and bentonite clays on biocementation using Sporosarcina pasteurii was measured by (i) the amount of calcium carbonate precipitated in sandy soil prepared with known percentages of the two clays (1%, 5%, 10% and 20% in dry sand mass), relating it with unconfined compression strength, and (ii) evaluating bacteria growth and urease activity in liquid media with 1% and 5% of each clay. The best enhancement of biocementation was found for kaolin percentage between 5% and 10% and for 5% of bentonite, considering as reference the case where no clay was added. These relatively small percentages were linked to physical aspects related with the room occupied by the clay minerals causing dispersion of the precipitate in the clay matrix, although the presence of clay in the fluids of soil voids could contribute positively for bacteria growth and long-term survival. These results confirm that biocementation treatment may be effective on soils with relatively small clay percentages and opens the possibility that clay can be used in controlled fixed amounts to improve the efficiency of this treatment in clean sands.

Atomic-scale investigation of H-trapping by fine NbC precipitates in a low C ferritic steel

The origin of hydrogen trapping by the Nb-carbide precipitates in a ferritic steel was studied at the atomic scale with the help of HRTEM (high resolution transmission electron microscopy) and 3D-APT (atom probe tomography). A Nb-added ferritic steel was prepared in the laboratory and subjected to aging after solutionizing treatment to have fine Nb-carbide precipitates in ferrite matrix. The precipitation kinetics were simulated beforehand using TC-Prisma in Thermocalc software. A large number of nanometer-sized Nb-carbide precipitates were observed in the ferrite matrix using TEM. 3D-APT studies on the steel sample electrolytically charged with D (deuterium) showed that the D atoms are trapped more within the precipitates than at the precipitate-matrix interfaces. It has been argued that H atoms occupy the vacant lattice sites on carbon sub-lattice sites in non-stoichiometric NbC0.83.

SCC susceptibility of RRA treated high-zinc 7068 aluminum alloy

Stress corrosion cracking (SCC) behavior of various retrogression and re-ageing treated, high-zinc (> 7 wt%) 7068 alloys is examined. SCC and inter-granular corrosion resistance is correlated with microstructural and compositional heterogeneities. Specimens that were pre-aged at 100⁰C and retrogression treated at 180 °C exhibited retarded reduction reaction kinetics in polarization studies, and better SCC resistance. Besides the microchemistry of grain boundary precipitates, matrix precipitate size affected the oxygen reduction kinetics. An increase in copper content of discontinuous boundary precipitates did not monotonously lead to improved SCC resistance. 7068 alloy specimens pre-aged at lower temperature exhibited higher strength and SCC resistance.

High-temperature oxidation properties of economical and lightweight Fe-Cr-Ni-Al medium-entropy alloy

This study investigated the microstructure, high-temperature oxidation properties and mechanism of non-equiatomic Fe-Cr-Ni-Al medium entropy alloy (MEA). Microstructural observation of MEA identified coarse grains of mm scale, and cuboidal precipitates with an average size of 125 nm were evenly distributed within grains. Phase analysis confirmed that the alloy consisted of a Fe-Cr matrix (BCC structure) and B2 Ni-Al precipitate. High temperature isothermal oxidation tests measured oxidation weight of 0.08 mg/cm2 at 800 ℃, 0.17 mg/cm2 at 900 ℃, 0.22 mg/cm2 at 1000 ℃, and 0.47 mg/cm2 at 1100 ℃. Compared to other alloys tested with similar conditions, Fe-Cr-Ni-Al MEA presented by this study achieves economic benefits with relatively excellent high-temperature oxidation resistance. The outstanding high-temperature oxidation resistance of the MEA presented by this study is due to the evenly distributed dense stable Al2O3 layer formed regardless of temperature conditions. In addition, the alloy did not have breakaway oxidation, which can occur as oxidation progresses.

Performance assessment of gridded climatic data and modeling spatial accuracy ranking matrix for gridded precipitation using a new pixel-based approach: a district-wise case study of Punjab

Performance assessment of gridded climatic data and modeling spatial accuracy ranking matrix for gridded precipitation using a new pixel-based approach: a district-wise case study of Punjab

Thermal stability behaviors of ultrafine-grained Cu-Cr-Zr alloy processed by friction stir processing and rolling methods

In order to investigate the effect of different microstructures on thermal stability, the thermal stability behaviors of ultrafine-grained Cu-Cr-Zr alloy processed by friction stir processing (FSP) and cold rolling (CR) methods was contrastively investigated by comparing with pure copper in this study. In addition to the precipitate strengthening, the FSP and CR samples were mainly strengthened by high angle grain boundaries (HAGBs) and dislocations, respectively. When there were no precipitates in Cu matrix, the onset temperature of softening of CR sample was 50 °C higher than that of the FSP sample at the same strength increment. But the precipitates in the FSP and CR Cu-Cr-Zr samples stabilized the deformed microstructures and precipitate coarsening occurred before the recrystallization of deformed microstructures. Therefore, the thermal stability differences disappeared in the FSP and CR Cu-Cr-Zr samples with the same onset temperature of softening (400 °C). In Cu-Cr-Zr alloys, although the stored energy of the FSP sample (39.1 J/mol) was 17.1% higher than that of the CR sample, the activation energy (∼175 kJ/mol) for grain growth of FSP sample was the same as that for recrystallization of CR sample. The different decrease degrees of thermal stability caused by different stored energy are completely masked by the kinetic constraint of precipitates.

Structure Hardness and Elastic Modulus of Ti-Nb-Y Alloys

The effects of rare earth element Y addition on the structure, elastic modulus and hardness of Ti80Nb20-xYx (x =0, 1, 2) alloys were investigated experimentally. The results showed that the structure of Ti-Nb-Y ternary alloys consist of the Ti-Nb matrix and Y-rich precipitates. Increasing the Y content can significantly improve the hardness and elastic modulus decreases with of Ti-Nb-Y alloys.

Direct Shear Characteristics of Enzymatically Cemented Sands

A laboratory study was conducted to investigate the shear strength of bio cemented sands using enzyme-induced carbonate precipitation (EICP) via the direct shear test. Several specimens were prepared using four different application methods of EICP solution, namely spraying, mix-&-compact, percolation, and injection. Potential use of EICP for improving the sand-concrete interaction strength was also studied. Results indicated that the adopted application method of introducing the EICP solution to the soil affects the distribution pattern of CaCO3 precipitation in the soil matrix, thereby shear strength. Each method yielded a different response when sheared compared to untreated sand. The injection method was found to achieve higher shear strength and interparticle cementation under controlled rate and distribution followed by percolation. The spraying and mix-&-compact methods produced specimens with weaker particles' bond and lower shear strength measurement but still showed relatively better performance than the untreated sands. Better cementation of soil grains was achieved in medium sand and when fine and organic materials were removed. Sands response to EICP-treatment was inferred to vary depending on the geotechnical characteristic of the soils. Moreover, the interfacial strength between sand and concrete was found to be enhanced after applying the EICP treatment as it coarsened soil particles.

Microstructural evolution and superelastic properties of ultrafine-grained NiTi-based shape memory alloy via sintering of amorphous ribbon precursor

NiTi-based shape memory alloys (SMAs) are considered as cutting-edge intelligent functional materials. However, it remains a great challenge to obtain ultrafine-grained (UFGed) bulk materials with mm-scale size as well as outstanding superelastic properties. Here, UFGed bulk Ti35Zr15Ni35Cu15 NiTi-based SMA is successfully prepared via spark plasma sintering of amorphous ribbon precursor at different sintering temperatures, and microstructural evolution and superelastic properties are symmetrically investigated. It is found that its grain size ranges from UFG to micro-grain with increased sintering temperature regardless of the predominant B2 matrix in all bulk samples. Interestingly, the orientation relationships between B2 matrix and nano-scale fcc (Ti,Zr)2Ni precipitate evolve from coherent to incoherent. Consequently, the UFGed samples exhibit perfect superelasticity with the high recoverable strain of ∼5.8%, the stable recovery rate above 99%, and the great critical stress inducing martensitic transformation higher than 1 GPa, far superior to the corresponding ones of suction-cast micro-grained TiZrNiCu SMAs. Fundamentally, the perfect superelasticity is attributed to the good resistance to dislocation slip or grain boundary slip by residual nano-scale amorphous phase or secondary phase of coherent and semi-coherent fcc (Ti,Zr)2Ni precipitate. In addition, the gentle superelastic plateau is associated to the favorable transfer stress and the strong ability to accommodate dislocation movement, which is generated by the coherent interface between nano-scale fcc (Ti,Zr)2Ni and UFGed B2 matrix. These results suggest that spark plasma sintering of amorphous alloy precursor is a feasible route to obtaining excellent superelasticity in NiTi-based SMAs.