Types Of Precipitates Research Articles

Generating Mechanism of Large Heterogeneous Carbonitrides with Multiple Layers in H13 + Nb Bar

The characteristics and generating mechanism of heterogeneous carbonitride with micron size in H13 + Nb bar are studied. Three types of precipitates are observed according to the number of layers, that is, two-layer ones, three-layer ones, and four-layer ones. Two-layer precipitate contains the oxide core and the outer Ti–V-rich carbonitride, while three-layer precipitate has one more Nb-rich carbonitride at the outside. Four-layer precipitate has a V-rich carbonitride at the outmost layer besides the inner three types of phases similar to that in the three-layer precipitate. The size of these large precipitates can be even up to tens of microns. The oxide cores are mainly stoichiometric spinel MgAl2O4 and generated in the liquid steel before solidification. The compositional characteristics and precipitating sequence of carbonitride can be well explained through calculation by Scheil–Gulliver model in Thermo-Calc. Ti–V-rich phase precipitates first during solidification, after which Nb-rich phase and V-rich phase precipitates successively. Some dissolution occurs between the different layers during the following temperature reducing and heating treatment process.

Selective evolution of secondary γ′ precipitation in a Ni-based single crystal superalloy both in the γ matrix and at the dislocation nodes

Two distinct evolutionary processes of secondary γ′ precipitates in a Ni-based single crystal superalloy were revealed by means of Cs-corrected high-resolution transmission electron microscopy (HRTEM) and corresponding X-ray energy dispersive spectroscopy analyses. Upon creep testing at elevated temperatures, it was determined that large quantities of secondary γ′ precipitates were formed. The precipitates were found to select two distinctive forms and routes: one randomly dispersed in the γ matrix (2nd γ′γ), and the other formed at nodes of dislocation networks (2nd γ′d) in regular arrays. These two types of secondary γ′ precipitates exhibited different evolutionary morphologies and mechanisms. The 2nd γ′γ precipitates progressively evolved in shape from spherical to cuboidal and then to butterfly-like shapes, and the mean size also increased gradually from 11 nm to 34 nm. The 2nd γ′d precipitates exhibited stable cuboidal morphology and a mean size of ∼30 nm. These differences are attributable to the different element transport conditions for the two types of precipitates, i.e., an uphill diffusion for the 2nd γ′γ precipitates and a dislocation network pipe transportation for the 2nd γ′d precipitates. The 2nd γ′γ precipitates show severe segregation of γ′-rich elements of Ni and Al and deficiency of γ′-poor elements of Cr compared with the 2nd γ′d precipitates.

The effect of topical application of 0.15% ganciclovir gel on cytomegalovirus corneal endotheliitis

Background/aimsThe aim of this study was to evaluate the therapeutic efficacy and drug transfer of topical application of 0.15% ganciclovir (GCV) gel on cytomegalovirus (CMV) corneal endotheliitis.MethodsThis study is a...

Effect of β heat treatment on phase transformations of TC21 during rolling

Phase transformations during hot rolling is determined for the forged and β heat treated TC21 titanium alloys. The results show that β heat treatment has a great effect on phase constitution. Three types of precipitates, namely, α2, ω and (Ti, Zr)5Si3 phase is observed in the rolled forged materials, whereas the rolled β heat treated materials exhibites the presence of lamellar α and type 2α precipitate. The influence of β heat treatment on the phase transformations has been discussed on the basis of alloying elements, and β heat treatment can eliminate or decrease elemental segregation.

Precipitation Hardening and Statistical Modeling of the Aging Parameters and Alloy Compositions in Al-Cu-Mg-Ag Alloys

The addition of Ag to Al-Cu-Mg systems has been proposed to replace the existing high-strength 2xxx and 7xxx Al alloys. The aged Al-Cu-Mg-Ag alloys exhibited promising properties, due to special type of precipitates named Ω, which cooperate with other precipitates to enhance the mechanical properties significantly. In the present investigation, the effect of changing percentages of alloying elements, aging time, and aging temperature on the hardness values was studied based on a factorial design. According to this design of experiments (DOE)—23 factorial design, eight alloys were cast and hot rolled, where (Cu, Mg, and Ag) were added to aluminum with two different levels for each alloying element. These alloys were aged at different temperatures (160, 190, and 220 °C) over a wide range of time intervals from 10 min. to 64 h. The resulting hardness data were used as an input for Minitab software to model and relate the process variables with hardness through a regression analysis. Modifying the alloying elements’ weight percentages to the high level enhanced the hardness of the alloy with about 40% as compared to the alloy containing the low level of all alloying elements. Through analysis of variance (ANOVA), it was figured out that altering the fraction of Cu had the greatest effect on the hardness values with a contribution of about 49%. Also, second-level interaction terms had about 21% of impact on the hardness values. Aging time, quadratic terms, and third-level interaction terms had almost the same level of influence on hardness values (about 10% contribution). Furthermore, the results have shown that small addition of Mg and Ag was enough to improve the mechanical properties of the alloy significantly. The statistical model formulated interpreted about 80% of the variation in hardness values.

HRTEM studies of aging precipitate phases in the Mg-10Gd-3Y-0.4Zr alloy

Rare-earth (RE) element addition can remarkably improve the mechanical properties of magnesium alloys through precipitation hardening. The morphology, distribution and crystal structure of precipitates are regarded as major strengthening mechanisms in the Mg-RE alloys. In order to understand the formation of precipitates during aging at 225 °C in a Mg-10Gd-3Y-0.4Zr alloy (GW103K) with high strength and heat resistance, a high-resolution transmission electron microscopy (HRTEM) was employed to characterize the microstructural evolution. It was found that three types of precipitates were observed in the alloy at the early stage, named as: single layer D019 structure, one single layer D019 structure and one layer of Mg, two parallel single layers (containing RE) and Mg layer in between, which was regarded as ordered segregation of RE, precursors to form β″ and β′ phase, respectively. Both of β″ and β′ phase were transformed from the precursors. It was also found that large size of β′ phase and the small size of β″ phase were constantly existent in the whole aging process. β′ phase played a major role in the strengthening of the GW103K alloys and the decrease of the hardness was caused by the coarsening of β′ phase.

A microstructure-based yield stress and work-hardening model for textured 6xxx aluminium alloys

The plastic properties of an aluminium alloy are defined by its microstructure. The most important factors are the presence of alloying elements in the form of solid solution and precipitates of various sizes, and the crystallographic texture. A nanoscale model that predicts the work-hardening curves of 6xxx aluminium alloys was proposed by Myhr et al. The model predicts the solid solution concentration and the particle size distributions of different types of metastable precipitates from the chemical composition and thermal history of the alloy. The yield stress and the work hardening of the alloy are then determined from dislocation mechanics. The model was largely used for non-textured materials in previous studies. In this work, a crystal plasticity-based approach is proposed for the work hardening part of the nanoscale model, which allows including the influence of the crystallographic texture. The model is evaluated by comparison with experimental data from uniaxial tensile tests on two textured 6xxx alloys in five temper conditions.

Characterization of Microstructure and Mechanical Properties of 9.2Cr0.45V0.7C Heat-Resistant Steel

Microstructure and mechanical properties of 9.2Cr0.45V0.7C steel have been evaluated in this work. Differential scanning calorimetry study indicating the various phase changes during heating and cooling is consistent with high-temperature XRD analysis. Carbide precipitates are observed during tempering in the temperature range of 750–800 °C. Two types of precipitates are identified, MC-type precipitates with an average size of 50 ± 15 nm and M23C6-type precipitates with an average size of 150 ± 50 nm. The tensile properties of the steel are dependent on tempering and processing conditions. Room-temperature tensile properties increase with tempering temperature. The hot rolling is more effective than hot forging to improve tensile properties of the steel at room temperature. High-temperature tensile strength decreases, whereas elongation increases with increasing temperature. Conventional creep curve shows three stages of behavior for this steel at 60 MPa and 600 °C.

Complex Precipitation Sequences of Al-Cu-Li-(Mg) Alloys Characterized in Relation to Thermal Ageing Processes

The Al-Cu-Li-(Mg) alloy is a high-performance lightweight material strengthened by complex coexisting precipitates that form in the alloy upon thermal ageing. Using high-resolution (scanning) transmission electron microscopy in association with first-principles energy calculations, we systematically studied the complex coexisting precipitates in the alloys and correlated their precipitation sequences with thermal ageing processes applied. The principal results are the following: (1) eight types of precipitates can be observed in the alloy; (2) of these precipitates, the T 1-phase is most stable. The S-phase precipitates with segregated Li atoms at their interfacial edges are unexpectedly more stable than the σ-phase; (3) the T 1-phase has a characteristic precursor that plays the key role in its nucleation and growth.

Inter- and intragranular delta phase quantitative characterization in Inconel 718 by means of image analysis.

This paper describes an image processing method for discriminating the inter- and intragranular delta phase precipitates in Inconel 718 (IN 718). The successive practical operations and the motivations of their choices are presented in detail. The method was applied to IN 718 specimens heat treated with different parameters to produce microstructures containing various amounts of both types of precipitates. They were characterized by electron microscopy in backscattered electron imaging. The main difficulty arose from the fact that the brightness distributions of inter- and intragranular precipitates partially overlap. Additional information on their morphology and their spatial distribution had to be exploited in order to differentiate them. The shape and the orientation of the precipitates were evaluated using the structure tensor, an operator that quantifies the directionality of the intensity distribution in an image. The distance between parallel precipitates was also used as an additional property to identify clusters of intragranular precipitates.

Surface adsorption and precipitation of inositol hexakisphosphate on calcite: A comparison with orthophosphate

Unraveling the processes of adsorption–precipitation of organic phosphates (OPs) on calcite is important for understanding the transformation, mobility and bioavailability of phosphorus (P) in calcareous soils. To elucidate these processes, the interaction between myo-inositol hexakisphosphate (IHP) and calcite was studied using macroscopic sorption experiments and a variety of analytical approaches. The experiments were also conducted with orthophosphate (Pi) for comparison. Calcite presented a similar sorption capability for IHP and Pi through the rapid formation of surface precipitates based on sorption experiments and the results of Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. After interacting with IHP/Pi, two different types of precipitates on a calcite surface could be directly observed by SEM images and analyzed by energy dispersive spectroscopy (EDS): a sphere-shaped precipitate considered typical for the poorly crystallized calcium phytate and a plate-shaped precipitate considered typical for the crystalline hydroxylapatite. This study suggests that active calcite strongly influences the species and behavior of IHP via a rapid surface precipitation reaction in a natural environment and advances our knowledge for predicting the fate of dissolved OP species in a variety of calcareous soils and geological settings enriched with calcite.

Microstructure and mechanical properties of friction spot welding aluminium–lithium 2A97 alloy

Abstract In this study, we investigated the microstructure and mechanical properties in different regions of the friction spot welded 2A97 aluminium–lithium alloy subjected to different heat treatment processes. The 2.0 mm thick hot-rolled sheet of 2A97 alloy was successfully welded using friction spot welding method with optimised welding parameters. Afterwards, the as-welded 2A97 joints experienced two subsequent heat treatment procedures: solution and ageing; directly ageing. The corresponding microstructure and mechanical properties of the heat-treated specimens were studied by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), hardness test and tensile test. The results show that the mechanical properties of the 2A97 joints before and after heat treatment were significantly modified, which was mainly related to fine-grained microstructure, size and type of precipitates, and dislocation density. Compared to the base material and the material that only experienced direct ageing, the whole friction spot welded 2A97 joint after solution and ageing treatment delivered better mechanical properties.

Mechanical and Wear Properties of Sb- and Y-Added Mg-9Al-1Zn (AZ91) Alloy

This paper studies the effect of Sb and Y additions on the microstructure and mechanical properties of the AZ91 alloy. The results indicate that the Sb and Y additions lead to the formation of Mg3Sb2 and Al2Y phases. These phases modify the morphology of the β-Mg17Al12 phase, and hence refine the microstructure. The effects of Sb and Y additions on the aging behavior have also been investigated. Aging of the AZ91 alloy results in the formation of continuous and discontinuous types of precipitates. Whereas Sb and Y additions to AZ91 alloy suppresses the formation of discontinuous precipitate. The paper also reports the mechanical properties of as-cast and aged Sb-added AZ91-xY alloys for room and high temperatures. The optimum tensile properties are obtained with the alloy having the combined addition of 0.5 wt pct Sb and 0.6 wt pct Y. The fracture surface of AZ91-0.5Sb-0.6Y alloy reveals more quasi-cleavage type of failure with a cleavage fracture than the base alloy. At HT, the AZ91-0.5Sb-0.6Y alloy displays more cleavage facets connected with tearing ridges and shallow dimples than AZ91 alloy. Furthermore, it observed the improvement in wear resistance through the addition of Y. The worn surface reveals abrasion, oxidation, delamination, and plastic deformation wear mechanisms.

Dependence of tensile and compressive deformation behavior on aging precipitation in rolled ZK60 alloys

Reducing serious tension–compression yield asymmetry is one important concern for wrought Mg alloys. This study aims to exploit the influence of aging time on tensile and compressive deformation behaviors in rolled ZK60 alloy sheets. The experimental results show that the type and amount of precipitates are greatly dependent on aging time at 175°C. A number of disk-like β′2 precipitates are present after aged for 10h. However, rod-like β′1 precipitates are observed after 30h and the amount of disk-like precipitates reduces. The tension–compression yield asymmetry of the as-solution ZK60 specimens is very serious. It is significantly improved with the formation of disk-like precipitates, while becomes worse with the presence of rod-like precipitates and the reduction of disk-like precipitates. This should be attributed to the disk-like and rod-like precipitates have different hardening effects on the main deformation modes of tension and compression deformations in the present ZK60 alloys.

Formation and evolution of precipitates in high Cr ferritic heat-resistant steels

For high Cr ferritic heat-resistant steels, dispersion hardening has played a vital role in improving creep strength at high temperatures. In this paper, the various types of precipitates in high Cr ferritic steels are reviewed, concerning M3C, M23C6, MX, M2X, Laves phase and Z phase. The evolution of these precipitates is a complicated process, since the dissolution of one type of precipitate may be overlapped with the precipitation of another type or other types. The composition of some precipitations varies towards the equilibrium composition under certain conditions, which is relevant to the solubility and diffusivity of the alloying element, while the composition of some other precipitates changes slightly. For the precipitates in high Cr ferritic steels, the preferred nucleation sites involve prior austenite grain boundaries, lath boundaries, dislocations and the interfaces between the precipitates and the matrix.

Retraction Note: Dislocation-particle interaction in precipitation strengthened Ll2-ordered Ni3Al

Transmission electron microscope investigation has been performed on the particle-dislocation interactions in Ni3Al-based intermetallics containing various types of fine precipitates. In an Ll2-ordered Ni3Al alloy with 4 mol.% of chromium and 0.2–0.5 mol.% of carbon, fine octahedral precipitates of M23C6 type carbide, which has a cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops are formed in Ni3Al containing fine dispersions of M23C6 particles. In the alloys with appropriate titanium content, fine precipitates of coherent disordered γ are formed during aging. The γ precipitates are initially spherical or rounded cubic in shape and grow into platelets as aging proceeds. Loss of coherency is initiated by the introduction of dislocations at the γ/γ′ interface and results in step formation at the dislocations. The γ precipitates become globular after the loss of coherency. In the γ′ phase hardened by the precipitation of the disordered γ phase, dislocations are attracted into the disordered γ phase and cut through the particles during deformation at any stage of aging. In Ni3Al containing a fine dispersion of disordered γ, superdislocations are strongly attracted to the disordered particles and dissociate on the (111) plane in the γ particles, while they dissociate on the (010) plane in the matrix. It is shown by comparison that the strengthening due to attractive interaction is more effective than that due to repulsive interaction. The roles of the variation of the interaction modes and of the dissociation of superdislocations in the matrix and particles are discussed in connection with the optimum microstructures of Ll2-ordered intermetallics as high temperature structural materials.

RETRACTED: Microstructure study of alloy to enhance safety and reduce adverse environmental effects of future fusion power plants

Reduced-activation steels were developed to enhance safety and reduce adverse environmental effects of future fusion power plants. Martensitic and bainitic steels were developed during the 1985–90 timeframe, and the feasibility of their use for fusion was investigated in an international collaboration from 1994 to present. This work continues to improve the steels and the formation of very small nano-metric precipitates through standardized heat treatments in Cr–W–V alloy system using the microscopic observations. Metallography studies have revealed that the microstructure of alloy after tempering has been tempered martensite. Also after tempering, the matrix structure of alloy and the formation of nano-scale precipitates on grain and lath boundaries were confirmed by SEM observations. By the application of XRD spectra analysis and TEM electron diffraction patterns, it was shown that the type of precipitates extracted from alloy, would be M23C6 and M7C3that include a cubic and trigonal crystal structure, respectively.

Mechanical properties and corrosion behavior of Mg–Gd–Ca–Zr alloys for medical applications

Magnesium alloys are promising candidates for biomedical applications. In this work, influences of composition and heat treatment on the microstructure, the mechanical properties and the corrosion behavior of Mg–Gd–Ca–Zr alloys as potential biomedical implant candidates were investigated. Mg5Gd phase was observed at the grain boundaries of Mg–10Gd–xCa–0.5Zr (x=0, 0.3, 1.2wt%) alloys. Increase in the Ca content led to the formation of additional Mg2Ca phase. The Ca additions increased both the compressive and the tensile yield strengths, but reduced the ductility and the corrosion resistance in cell culture medium. After solution heat treatment, the Mg5Gd particles dissolved in the Mg matrix. The compressive strength decreased, while the corrosion resistance improved in the solution treated alloys. After ageing at 200°C, metastable β′ phase formed on prismatic planes and a new type of basal precipitates have been observed, which improved the compressive and tensile ultimate strength, but decreased the ductility.

Grain boundary diffusion and precipitates in B2 Ti−50.2 at.% Ni alloy

Grain boundary diffusion of 44Ti and 63Ni in the B2 Ti−50.2 at.% Ni polycrystalline alloy was measured in Harrison's B regime (573−923 K) using the radiotracer technique. The triple product P = sδDgb (s is the segregation factor, δ the grain boundary width, and Dgb the corresponding grain diffusion coefficient) for Ti and Ni was determined. Although the absolute values of the triple products P are typical for the B2-ordered alloys, both Ti and Ni GB diffusion in NiTi reveals a unique behavior with significant deviations from a linear Arrhenius-type temperature dependence. Transmission electron microscopy analysis of GB structures at 673 K and 923 K substantiated the occurrence of different interface types which may provide the slower and faster grain boundary diffusion paths in agreement with the experimental data. The influence of different types of precipitates on grain boundary diffusion and possible diffusion mechanisms in the different regimes are discussed.

Dynamic nanomechanical properties of novel Si-rich intermetallic coatings growth on a medical 316 LVM steel by hot dipping in a hypereutectic Al–25Si alloy

This aim of this study is to determine the elastoplastic properties of Ni-free Al3FeSi2 intermetallic coatings grown on medical stainless steel under different experimental conditions. Elastoplastic properties are defined by the plasticity index (PI), which correlates the hardness and the Young׳s modulus. Special emphasis is devoted to correlate the PI with the wear resistance under sliding contact, determined by scratch testing, and fracture toughness, determined by using a novel method based on successive impacts with small loads. With regard to the substrate, the developed coatings are harder and exhibit a lower Young׳s reduced modulus, irrespective of the experimental conditions. It has been shown that preheating of the samples prior to hot dipping and immersion influences the type and volume fraction of precipitates, which in turn also affect the nanomechanical properties. The higher the preheating temperature is, the greater the Young׳s reduced modulus is. For a given preheating condition, an increase of the immersion time yields a decrease in hardness. Although apparent friction coefficients of coated specimens are smaller than those obtained on AISI 316 LVM, they increase when using preheating or higher immersion times during processing, which correlates with the PI. The presence of precipitates produces an increase in fracture toughness, with values greater than those presented by samples processed on melted AlSi alloys with lower Si content (12wt%). Therefore, these intermetallic coatings could be considered “hard but tough”, suitable to enhance the wear resistance, especially when using short periods of immersion.