Kinds Of Precipitates Research Articles

Pseudo-equilibrium equations for calcium phosphate precipitation with multi-unit particles.

The chemistry underlying bone mineral formation in vertebrates is the reaction of calcium phosphate precipitation. In a near-neutral solution, an amorphous phase and hydroxyapatite nanoparticles appear successively, and the reaction system containing either of the two kinds of precipitates is in a non-equilibrium state. Here, we propose a pseudo-equilibrium approach to the solution chemistry of the precipitation reactions. We employed two series of reaction systems, collected samples at various stages, and analyzed the solution chemistry data on the basis of a simplified model of reaction. We derived two types of pseudo-equilibrium equations from the two series, respectively. These equations reveal the existence of multiple structural units in a precipitate particle and correlate the ionic product with the surface proportion per structural unit (m). The surface proportion, in turn, is related to the whole particle through a particle-surface equation. Notably, the two types of pseudo-equilibrium constants have the common expression of "Kd = ionic product" if the number of the structural units (u) is large enough. Together, these findings have revealed some aspects of the non-equilibrium thermodynamics of precipitation reactions, indicating the solution chemistry route to the equilibrium state. The concept of the multi-unit particle may shed new light on the study of precipitation reactions of other slightly soluble electrolytes. And the relationship between the ionic product and the surface proportion of a structural unit is not only fundamental in chemistry, but may also apply to non-equilibrium systems in nature and biology, such as marine sedimentation, human vascular calcification, and bone mineral metabolism.

A Yield Stress and Work Hardening Model of Al-Mg-Si Alloy Considering the Strengthening Effect of β" and β' Precipitates.

Precipitates are the primary source of strength for the Al-Mg-Si alloy. Aluminum alloy in the peak-aged state mainly contains β" and β' precipitates. Most of the literature has only considered the strengthening effect of β". Here, we develop a single-crystal intensity model including both precipitate enhancement effects for the first time. This model was subsequently implemented into a crystal plastic finite-element method to model the uniaxial tensile process of a polycrystalline aggregate model of Al-Mg-Si alloy. The simulation results for uniaxial stretching are in good agreement with the experimental results, confirming that the constitutive parameters used for the single-crystal strength model with two precipitates are based on realistic physical implications. Furthermore, by comparing the uniaxial tensile simulation results of a peak-aged alloy considering the actual precipitated phase composition of the alloy with those assuming that the precipitated phase is only the β" phase, the predicted tensile strength of the former is around 5.65% lower than that of the latter, suggesting that the two kinds of precipitation should be separately considered when simulating the mechanical response of Al-Mg-Si alloy. It is highly expected that the present simulation strategy is not limited to Al-Mg-Si alloys, and it can be equally applied to the other age-enhanced alloys.

Site-specific analysis of precipitates during the coiling of an HSLA steel containing V and Nb

Precipitation in a high-strength low-alloy steel containing V and Nb additions during coiling at 500 °C, was investigated by advanced characterization techniques including electron backscattered diffraction, focused ion beam, transmission electron microscopy and atom probe tomography. During coiling, nano precipitates were preferentially formed around dislocations and grain/sub-grain boundaries in the high Kernel Average Misorientation (KAM) areas associated with bainite. Precipitates were frequently observed around cementite in the low KAM areas with cementite which were identified as granular bainite. Interphase clusters were found in the low KAM areas associated with ferrite. The site-specific methods reveal the co-existence of different kinds of precipitates. Analysis of the results indicates that the precipitation of microalloy particles close to cementite could lower the precipitation hardening contribution that could be achieved through microalloying.

Influence of temperature on the precipitation phase transformation behavior of RR350 aluminum alloy during artificial aging and related mechanisms

This study investigates the influence of artificial aging temperature on the evolution of precipitation phases and age hardening behavior of the RR350 aluminum alloy. The manner of nucleation and growth of different kinds of precipitates and phase transformation between them are analyzed, along with the corresponding mechanisms are discussed. The results reveal that the aging temperature affects little the precipitation process of precipitates which still follows the sequence of GP zones - θ″- θ′ in the RR350 aluminum alloy during artificial aging, but influences significantly the precipitation speed and phase composition, morphology, size and size distribution of the resultant precipitates in the alloy. An imperceptible relationship between the hardness of the sample and the composition of the precipitates were discovered. As the artificial aging temperature (160–180–200 °C) increases, the peak-aging hardness of the samples decreases and the time for reaching the peak-aging status shortens gradually. When the temperature is low, 160 °C for example, the precipitates in the peak-aging status are mainly composed of θ″ phase and some minor θ′ phase. As the temperature increases to 200 °C θ′ phase becomes prevalent. As a result, the alloy shows lower peak-aging hardness since the strengthening effect of the finer θ″ phase is much stronger than that of the θ′ phase. Increasing the aging temperature accelerates the competitive processes of nucleation of GP zones, growth of all precipitates, and the phase transformation. At higher temperatures, phase transformation from θ″ to θ′ overweighs the formation of GP zones, growth of both θ″ and θ′ phases, resulting in more amount of θ′phase in the peak-aging and over-aging statuses.

Alloying element distributions of precipitates in Cu–Cr alloys aided by machine learning

The presence of the fcc Cr-rich precipitates is a significant factor for the excellent performance of Cu–Cr alloys. In this work, we proposed an efficient approach based on machine learning to study on the alloying element distributions of the fcc Cr-rich precipitates in Cu–Cr alloys. The random forest algorithm with lower mean absolute error was selected for the classification of alloying elements. The alloying elements Mg, Si, Sc, Ti, Co, Ni, Y, Nb, Ag, In and Sn were classified into two groups. Sc and Ni were located mainly on the periphery of the fcc Cr-rich precipitates, while others were distributed randomly in the fcc Cr-rich precipitates, which was basically consistent with the ab initio results. The distribution of V was also determined experimentally and predicted via machine learning, and excellent agreement was found among experiment, machine learning and ab initio calculation. This work can provide an effective way to investigate the distribution tendency of alloying elements for various kinds of precipitates.

Investigation on the precipitate morphology and fraction characterization by atomic force microscopy

Precipitate was typically characterized by the transmission electron microscopy (TEM) or scanning electron microscopy (SEM) to analyze the relationship between material property and precipitate fraction. However, these procedures tend to be are always time consuming because of the complicated sample preparation process involved and the observation course. Particularly, sometime the precipitate can't be highlighted solely from the images easily. In this study, atomic force microscopy (ATM) was performed to characterize the morphology and fraction of the precipitate in this paper. Five kinds of materials were selected and prepared by electropolishing or vibration polishing method to display the precipitates on the sample surface. The experiment results prove that different types of precipitates with higher values for height on a sample surface could be clearly observed by AFM, and the images quality is highly relied upon the surface quality. The precipitate fraction can be calculated using the AFM micrographs and image photo post treated software (IPP). It was turned out that AFM is found suitable for observation almost all kinds of precipitates, and the precipitates can be easily separated from the images. Not only vibration polishing but also electrolytic polishing could offer a smooth surface for observing nanosized precipitates by AFM. A comparison of the fraction result obtained by AFM and precise microchemical analysis proves that the fraction measurement result obtained by AFM is acceptable.

On the microstructure and mechanical behaviour of the Cr2Fe2NiCo0.67Cu0.67Ti0.33 alloy during homogenisation

The present study investigates the microstructure and mechanical properties of the Cr2Fe2NiCo0.67Cu0.67Ti0.33 high-entropy alloy after homogenisation. The results show that the as-cast microstructure consisted mainly of a dual-phase FCC + σ structure. By heat-treating, the microstructure changed from the FCC + σ to the mixed FCC + BCC solid solutions. The EDS and XRD analysis show that despite different crystal structures of the σ and BCC phases, their chemical composition is the same. In addition, two kinds of precipitations, enriched by Ti and Cu, are found in the microstructure. Formation of these precipitates beside hard σ-phase resulted in an increase in hardness. Additionally, higher elongation and strain hardening ability achieved in the specimen that σ → BCC transformation occurred.

Remarkable cryogenic strengthening and toughening in nano-coherent CoCrFeNiTi0.2 high-entropy alloys via energetically-tuning polymorphous precipitates

In the present work, three kinds of precipitates with different morphologies, structures, sizes, and volume fractions were obtained via energetically-tuning the microstructures of the nano-precipitated CoCrFeNiTi0.2 high-entropy alloy (HEA). Subjected to the heavy cold rolling immediately after homogeneous precipitation, L12 structured spherical nano-particles with an average size of 16.5 nm rapidly grow into 200 nm-sized spherical ones due to Ostwald ripening. On the other hand, superfluous mechanical energy storage energetically facilitates the phase transformation from spherical L12 to rod-shaped D024 structures for initially formed nano-precipitates. Besides, some other newly formed nano-precipitates with an average size of 6.5 nm are available, originating from heavily plastically deformed-induced nucleated sites. Multi-scale precipitates interact with dislocations in different ways. The strengthening provided by dislocations cutting through smaller nano-particles and bypassing grown ones account for 57.7% and 42.3% of precipitation strengthening, respectively, while rod-shaped precipitates can act as equivalent interfaces to hinder dislocation movement. Their synergistic effect has achieved remarkable strengthening and toughening. Specially, dislocation slips dominate at 298 K, while stacking faults (SFs) assist plastic deformation at 77 K. Compared with 298 K, the yield strength (YS) and ultimate tensile strength (UTS) of the current HEAs at 77 K are increased by 38.9% and 38.2% to 1 GPa and 1.5 GPa, respectively, and the tensile strain is slightly increased to 35% instead of loss, realizing excellent strength and plasticity combination. Theoretically established strengthening models agree well room-temperature and cryogenic yield strengths experimentally. Moreover, the tensile elongation is effectively predicted by the Whitehouse-Clyne model. This strengthening strategy of energetically-tuning polymorphous precipitates provides the basic guidance to develop high-performance nano-precipitated alloys. The current strengthening and plasticity models can be employed to well predict the mechanical properties of such kinds of alloys at cryogenic temperatures.

Effect of Zr on the microstructure and mechanical properties of 12Cr ferritic/martensitic steels

The effect of Zr in the range of 0–∼1.36 wt.% on the microstructure and mechanical properties of 12Cr ferritic/martensitic steels was investigated. The steels were prepared by melting and hot rolling, then normalized at 1050 °C for 30 min and tempered at 760 °C for 90 min. The steels with 0–∼0.11 wt.% Zr had a mixture of martensite and ferrite, while the steels with ∼1.36 wt.% Zr showed fully ferrite. The area fraction of the ferrite phase in steels increases as an increase in the Zr content, which indicates that Zr is a ferrite forming alloy element in steels. The precipitates in steels with 0–∼0.11 wt.% Zr were mainly distributed along martensitic lath boundary and ferritic/martensitic interface. The coarser precipitates distributed at the ferrite/martensite interface were M23C6 carbides and obey Kurdjumov-Sachs orientation relationship, namely (110)α-Fe//(111)M23C6 and [-111]α-Fe//[011]M23C6. There were two kinds of precipitates in the steels containing ∼1.36 wt.% Zr. The coarser precipitates, which distributed randomly, were Zr-rich (Fe, Zr) compounds. The Laves phases found in smaller precipitates were distributed at the grain boundary. Tensile tests showed that the strength decreased and the ductility increased as an increase in the Zr content. The steels with 0–∼0.11 wt.% Zr demonstrated a superior strength balance, of which the tensile strength and elongation at room temperature were 750–830 MPa and 19%–22%, respectively. At the elevated temperature (600 °C), the tensile strength of the steels decreased to 390–450 MPa and the elongation of steels increased to 27%–34%.

Microstructural characterisation of a Co–Cr–Mo laser clad applied on railway wheels

Abstract A Co – Cr –Mo laser cladding applied on railway wheels is characterised by a combination of EBSD and EDX. A complete pass of the cladding is investigated to achieve a better understanding of the microstructure evolution during laser cladding. A microstructure with columnar grains extending over the whole thickness of the cladding is observed. The grains have a <001>-fibre texture with the fibre axis parallel to the normal of the substrate surface, and a substructure consisting of cells/dendrites. During the cladding process, two different kinds of precipitates form in the cell walls, which can be identified as M6C and a non-equilibrium phase. Furthermore, stacking faults are observed to occur in the cladding grains and are discussed with respect to the laser cladding process.

Modeling Semiarid River–Aquifer Systems with Bayesian Networks and Artificial Neural Networks

In semiarid areas, precipitations usually appear in the form of big and brief floods, which affect the aquifer through water infiltration, causing groundwater temperature changes. These changes may have an impact on the physical, chemical and biological processes of the aquifer and, thus, modeling the groundwater temperature variations associated with stormy precipitation episodes is essential, especially since this kind of precipitation is becoming increasingly frequent in semiarid regions. In this paper, we compare the predictive performance of two popular tools in statistics and machine learning, namely Bayesian networks (BNs) and artificial neural networks (ANNs), in modeling groundwater temperature variation associated with precipitation events. More specifically, we trained a total of 2145 ANNs with different node configurations, from one to five layers. On the other hand, we trained three different BNs using different structure learning algorithms. We conclude that, while both tools are equivalent in terms of accuracy for predicting groundwater temperature drops, the computational cost associated with the estimation of Bayesian networks is significantly lower, and the resulting BN models are more versatile and allow a more detailed analysis.

An IoT based Low-cost Weather Monitoring System for Smart Farming

Background: Weather monitoring is an important aspect of crop cultivation for reducing economic loss while increasing productivity. Weather is the combination of current meteorological components, such as temperature, wind direction and speed, amount and kind of precipitation, sunshine hours and so on. The weather defines a time span ranging from a few hours to several days. The periodic or continuous surveillance or the analysis of the status of the atmosphere and the climate, including parameters such as temperature, moisture, wind velocity and barometric pressure, is known as weather monitoring. Because of the increased usage of the internet, weather monitoring has been upgraded to smart weather monitoring. The Internet of Things (IoT) is one of the new technology that can help with many precision farming operations. Smart weather monitoring is one of the precision agriculture technologies that use sensors to monitor correct weather. The main objective of the research is to design a smart weather monitoring and real-time alert system to overcome the issue of monitoring weather conditions in agricultural farms in order for farmers to make better decisions. Methods: Different sensors were used in this study to detect temperature and humidity, pressure, rain, light intensity, CO2 level, wind speed and direction in an agricultural farm and real time clock sensor was used to measured real time weather data. The major component of this system was an Arduino Uno microcontroller and the system ran according to a program written in the Arduino Uno software. Result: This is a low-cost smart weather monitoring system. This system’s output unit were a liquid crystal display and a GSM900A module. The weather data was displayed on a liquid crystal display and the GSM900A module was used to send the data to a mobile phone. This smart weather station was used to monitor real-time weather conditions while sending weather information to the farmer’s mobile phone, allowing him to make better decisions to increase yield.

1.7 Gpa tensile strength in ferrous medium entropy alloy via martensite and precipitation

A Fe50Co25Ni10Al5Ti5Mo5 medium entropy alloy was fabricated through the casting route and processed by hot rolling and heat treatment to achieve high strength via martensitic structure and precipitation. The hot-rolled plate heat-treated at 1000 °C for 10 min exhibited fine lath martensite structure, two kind of precipitates, retained FCC phase, and high dislocation density. The sample with this complex microstructure exhibited superior tensile properties with an extremely high tensile strength of ∼ 1.7 GPa and a good uniform elongation of ∼ 8%.

TH84. GENOME-WIDE ANALYSIS OF DNA METHYLATION IN 106 SCHIZOPHRENIA FAMILY TRIOS IN HAN CHINESE

A Fe50Co25Ni10Al5Ti5Mo5 medium entropy alloy was fabricated through the casting route and processed by hot rolling and heat treatment to achieve high strength via martensitic structure and precipitation. The hot-rolled plate heat-treated at 1000 °C for 10 min exhibited fine lath martensite structure, two kind of precipitates, retained FCC phase, and high dislocation density. The sample with this complex microstructure exhibited superior tensile properties with an extremely high tensile strength of ∼ 1.7 GPa and a good uniform elongation of ∼ 8%.

Microstructural Characterization and Mechanical Property of Al-Li Plate Produced by Centrifugal Casting Method

Using a centrifugal casting method, along with deformation and aging, we produced a high-strength, low-anisotropy Al-Li plate. The electron probe microanalysis, transmission electron microscope, differential scanning calorimetry, and X-ray diffraction were used to clarify the evolution of strengthening phases. Experimental results showed that centrifugal-cast Al-Li plate consisted of intragrain δ′—(Al,Cu)3Li precipitate and interdendritic θ′—Al2Cu particles. After cold-rolling to a reduction ratio of 60% and annealing at 800 K for 90 min, both primary θ′ and δ′ were dissolved in solid solution. Aging at 438 K for 60 h led to the formation of two kinds of precipitates (needle-like T1—Al2CuLi and spherical δ′ in two sizes), which acted as the main strengthening phases. The average values of ultimate tensile strength and yield strength for the anneal-aged plate reached 496 MPa and 408 MPa, with a total elongation of 3.9%. The anneal-aged plate showed mechanical anisotropy of less than 5%. The tensile fracture morphology indicated a typical intergranular fracture mode.

Responses of Spring Discharge to Different Rainfall Events for Single-Conduit Karst Aquifers in Western Hunan Province, China.

It is a challenge to describe the hydrogeological characteristics of karst aquifers due to the complex structure with extremely high heterogeneity. As the response of karst aquifers to rainfall events, spring discharge variations after precipitation can be used to identify the internal structure of karst systems. In this study, responses of spring discharge to different kinds of precipitations are investigated by continuously monitoring precipitation and karst spring flow at a single-conduit karst aquifer in western Hunan province, China. Recession curves were used to analyze hydrodynamic behaviors and separate recession stages. The results show that the shape of the recession curve was changed under different rainfall conditions. Recession processes can be divided in to three recession stages under heavy rain conditions due to water drainage mainly from conduits, fracture, and matrix at each stage, but only one recession stage representing drainage mainly from matrix in the case of light rain. With the change in amount and intensity of precipitation, the calculated recession coefficient at each stage changes in an order of magnitude. The influence of precipitation on the recharge coefficient and the discharge composition at each recession are discussed, and then the conceptual model diagram of water filling and releasing in the single-conduit karst aquifers is concluded. The findings provide more insight understand on hydraulic behaviors of karst spring under different types of rainfall events and provide support for water resource management in karst regions.

Effect of microstructure and precipitate formation on mechanical and corrosion behavior of friction stir processed AA6061 alloy using different cooling media

The present work studies the effect of microstructure and precipitate formation on mechanical and corrosion characteristics of friction stir processed AA6061 alloy using different cooling technologies (cryogenic and water cooling). The results revealed that recrystallized fine grains formed in all friction stir processing samples (grain size within a range of 2–6 µm) as a result of dynamic recovery and recrystallization, while samples processed in cooling-assisted friction stir processing resulted in better grain refinement in the stir zone than in air-cooled friction stir processing. Three kinds of precipitates (Fe-based needle-shaped precipitates, Si-based round-shaped precipitates, and chain of small round-shaped Si-based precipitates) were identified in base material and friction stir processing samples. Compared to air-cooled friction stir processing, in cooling-assisted friction stir processing, the hardness and tensile strength increased but remained lower than for the base alloy due to the presence of high density Fe-based needle-shaped precipitates. The ductility after friction stir processing greatly improved due to thermal softening and dissolution of precipitates. The corrosion results demonstrated that the corrosion resistance greatly enhanced after friction stir processing due to uniform distribution of grain structure and discontinuous chain of small round-shaped Si-based precipitates in stir zone. Moreover, cooling-assisted friction stir processing resulted in improved corrosion resistance compared to air-cooled friction stir processing due to the formation of fine precipitates.

Precipitation formation on ∑5 and ∑7 grain boundaries in 316L stainless steel and their roles on intergranular corrosion

In sensitized (700°C for 10 h) AISI 316L stainless steel samples attacked by an HF solution, coincidence site lattice (CSL) ∑7 grain boundaries (GBs) always show corrosion while ∑5 GBs never do. This distinct corrosion behaviour can be related to the distinct precipitation behaviour of the different GBs, which itself depends on the GB characters. It is found that ∑5 GBs, although being curved both macro- and microscopically, neither show facets nor precipitates. The amount of segregation is enhanced in sensitized ∑5 GBs compared to solution-annealed ones. In contrast, ∑7 GBs show clear faceting in both the solution-annealed and sensitized state, with one facet orientation showing strong segregation while the other not. GB energy anisotropy is applied to explain the faceting phenomenon. The formation of two kinds of precipitates, i.e., C14 Laves phase and M23C6 carbide, holding responsible for two distinct morphologies of corrosion, are believed to be both linked to intensive faceting and the anisotropic segregation of ∑7 GBs. For the carbide, a preferred {111} orientation out of all ∑7 facets measured by trace analyses is presumed to facilitate its nucleation.

Remarkable Cryogenic Strengthening and Toughening in Nano-Coherent CoCrFeNiTi <sub>0.2</sub> High-Entropy Alloys via Energetically-Tuning Polymorphous Precipitates

In the present work, three kinds of precipitates with different morphologies, structures, sizes, and volume fractions were obtained via energetically-tuning the microstructures of the nano-precipitated CoCrFeNiTi0.2 high-entropy alloy (HEA). Subjected to the heavy cold rolling immediately after homogeneous precipitation, L12 structured spherical nano-particles with an average size of 16.5 nm rapidly grow into 200 nm-sized spherical ones due to Ostwald ripening. On the other hand, superfluous mechanical energy storage energetically facilitates the phase transformation from spherical L12 to rod-shaped D024 structures for initially formed nano-precipitates. Besides, some other newly formed nano-precipitates with an average size of 6.5 nm are available, originating from heavily plastically deformed-induced nucleated sites. Multi-scale precipitates interact with dislocations in different ways. The strengthening provided by dislocations cutting through smaller nano-particles and bypassing grown ones account for 57.7% and 42.3% of precipitation strengthening, respectively, while rod-shaped precipitates can act as equivalent interfaces to hinder dislocation movement. Their synergistic effect has achieved remarkable strengthening and toughening. Specially, dislocation slips dominate at 298 K, while stacking faults (SFs) assist plastic deformation at 77 K. Compared with 298 K, the yield strength (YS) and ultimate tensile strength (UTS) of the current HEAs at 77 K are increased by 38.9% and 38.2% to 1 GPa and 1.5 GPa, respectively, and the tensile strain is slightly increased to 35% instead of loss, realizing excellent strength and plasticity combination. Theoretically established strengthening models agree well room-temperature and cryogenic yield strengths experimentally. Moreover, the tensile elongation is effectively predicted by the Whitehouse-Clyne model. This strengthening strategy of energetically-tuning polymorphous precipitates provides the basic guidance to develop high-performance nano-precipitated alloys. The current strengthening and plasticity models can be employed to well predict the mechanical properties of such kinds of alloys at cryogenic temperatures.

The role of trace Ag in controlling the precipitation and stress corrosion properties of aluminium alloy 7N01

The effect of trace Ag on the early precipitation and the resistance to stress corrosion cracking (SCC) of peak-aged 7N01 alloy (Al-4.5Zn-1.55Mg-0.12Cu) were investigated. A characterization method known as three-dimensional atom probe (3DAP) was used in this research to investigate the precipitation behaviors of the alloy. When 0.12 wt % Ag is present in the alloy, the solid solubility of the alloy increases after the solid-solution treatment at 485 °C and quenching in water. In the early stage when the alloy is aged at 120 °C, Ag atoms will enrich around the clusters (GPI zones and GPII zones) giving rise to more nucleation sites for them. As the ageing time goes on, these clusters will transform into high-density η′ phase and then the hardness and mechanical strength of the alloy will increase. Three kinds of precipitates with different sizes in the alloy after peaking ageing were found by high resolution transmission electron microscopy (HRTEM). The results obtained from the high angle annular dark field of scanning transmission electron microscope (HAADF-STEM) show that Ag atoms are distributed around η′ phase in the matrix and η phase in the grain boundaries, which significantly increases the corrosion resistance of the alloy in NaCl solution after peak ageing. The results from the slow strain rate test (SSRT) and the observation of fracture morphologies show that for the alloy with trace Ag addition and after peak ageing, the resistance to SCC is improved, as well as the size and the distribution distance of the precipitate (MgZn2) in the grain boundaries increase.