Types Of Precipitates Research Articles

The effect of Pd content on microstructure and shape-memory properties of Ti–Ni–Pd–Cu alloys

The effect of Pd content on the microstructure and high-temperature shape memory properties of Ti–Ni–Pd–Cu alloys was investigated. The increase in Pd content led to the increase of transformation temperatures. The volume fraction of two types of precipitates (i.e. TiPdCu and Ti2Pd) also increased with increasing Pd content. Although the formation of these precipitates resulted in an increased resistance against the plastic deformation, the amount of recovery strain decreased during thermal cycling tests at various stress levels. By adjusting the heat treatment time, a high transformation temperature and large amount of recovery strain could be achieved while keeping the enough resistance against the plastic deformation.

A comprehensive study on the microstructure of high strength low alloy pipeline welds

The microstructural characteristic of HSLA welds containing different amounts of titanium were evaluated carefully. It was observed that the microstructure of welds consisted of ferrite with mixed morphologies, and small amounts of pearlite and martensite–austenite micro-constituents. Because of insufficient time for diffusion of carbon, formation of pearlite lamellae could not be completed in the weld region. Martensite was formed from carbon enrichment of austenite during nucleation and growth of acicular ferrite and bainitic ferrite. While coarse manganese sulfide particles had weak interface strength with matrix and formed some micro-fissures; increasing titanium amount of welds dispersed different modified morphologies of inclusions in the microstructure. Several types of precipitates including spherical, cubical, fine and irregular titanium carbonitride were found in the microstructure and they were favorite sites for nucleation of acicular ferrite. The size of cubical/spherical and fine precipitates was measured between 70–100 and 10–20nm, respectively. Low energy interface of inclusion/matrix and the depletion of carbon in austenite were proposed as the nucleation mechanisms of acicular ferrite from nano-sized inclusions.

Computer simulation of phase transformation and plastic deformation in IN718 superalloy: Microstructural evolution during precipitation

Microstructural evolution during co-precipitation of γ′, γ″ and δ phases from a supersaturated γ matrix during aging of superalloy Inconel 718 (IN718) is investigated by computer simulation using the phase-field method. The precipitation model is quantitative, using as model inputs ab initio calculations of elastic constants, experimental data on lattice parameters, precipitate–matrix orientation relationship, interfacial energy of each individual precipitate phase and interdiffusivities, and a Ni–Nb–Al pseudo-ternary thermodynamic database specifically developed for IN718. In order to simulate statistically representative multiphase microstructures observed in the alloy, the Kim–Kim–Suzuki treatment of interfaces is employed. Simulation results show how alloy composition, lattice misfit, external stress, temperature and time affect precipitate microstructure and variant selection during isothermal aging, without any a priori assumptions about key microstructural features including size, shape, volume fraction and spatial distribution of different types of precipitates and different variants of the same precipitate phase. The shapes of precipitates and their coarsening kinetics are analyzed based on the two-dimensional moment invariant. The various multiphase microstructures generated by the simulations have been used as model inputs in a study to investigate how precipitate microstructure (in particular shape and spatial distribution) influences the strength of IN718.

Rapid Generation of Amyloid from Native Proteins <em>In vitro</em>

Proteins carry out crucial tasks in organisms by exerting functions elicited from their specific three dimensional folds. Although the native structures of polypeptides fulfill many purposes, it is now recognized that most proteins can adopt an alternative assembly of beta-sheet rich amyloid. Insoluble amyloid fibrils are initially associated with multiple human ailments, but they are increasingly shown as functional players participating in various important cellular processes. In addition, amyloid deposited in patient tissues contains nonproteinaceous components, such as nucleic acids and glycosaminoglycans (GAGs). These cofactors can facilitate the formation of amyloid, resulting in the generation of different types of insoluble precipitates. By taking advantage of our understanding how proteins misfold via an intermediate stage of soluble amyloid precursor, we have devised a method to convert native proteins to amyloid fibrils in vitro. This approach allows one to prepare amyloid in large quantities, examine the properties of amyloid generated from specific proteins, and evaluate the structural changes accompanying the conversion.

Effect of long-term aging on microstructure and local behavior in the heat-affected zone of a Ni–Cr–Mo–V steel welded joint

Evolution of microstructure, micro-hardness and micro-tensile strength behavior was investigated in the heat-affected zone of a Ni–Cr–Mo–V steel welded joint after the artificial aging at 350°C for 3000h. After detailed characterization of microstructures in optical microscopy, scanning electron microscopy and transmission electron microscopy, it is revealed that the change of martensite–bainite constituent promotes more homogeneous microstructure distribution. The aging treatment facilitates redistribution of carbon and chromium elements along the welded joint, and the micro-hardness is increased slightly through the welds due to enrichment of carbon. The types of precipitates in the weldment mainly include M3C, MC, M2C and M23C6. The carbides in base metal, weld metal and coarse-grained heat-affected zone are prone to change from ellipsoidal to platelet form whereas more uniform spherical carbides are observed in the fine-grained zone. Precipitation and coarsening of M23C6 near the fusion line, and formation of MC and M2C, are responsible for the tensile strength decrease and its smooth distribution in the aged heat-affected zone. This implies that the thermal aging can relieve strength mismatch in the weldments.

TEM analysis of 2205 duplex stainless steel to determine orientation relationship between M23C6 carbide and austenite matrix at 950 °C

Microstructures of 2205 duplex stainless steel were examined using transmission electron microscopy. During isothermal heating at 950 °C, M23C6 carbide was formed on the austenite grain boundaries with two types of morphologies: “larva” and “triangle”. The orientation relationship between the M23C6 carbide and the austenite matrix is cubic-to-cubic. In addition, these two types of precipitates have a twin relationship with each other. Based on the STEM-EDS data, the silicon content of triangle M23C6 carbide is higher than that of the larva M23C6 carbide, revealing that the silicon content in the M23C6 carbide plays an important role in determining the orientation relationship between the M23C6 carbide and the austenite matrix.

Aerobic and Anaerobic Ammonia-Oxidizing Microorganisms in Low-Temperature Hydrothermal Fe-Si-rich Precipitates of the Southwestern Pacific Ocean

Fe-Si-rich hydrothermal precipitates are distributed widely in low-temperature diffusing hydrothermal fields. Due to the significant contribution of Fe-oxidizing bacteria (FeOB) to the formation of this type of hydrothermal precipitates, previous studies focus mostly on investigating FeOB-related microbial populations, albeit these precipitates actually accommodate abundant other microbial communities, particularly those involved in marine nitrogen cycle. In this study, we investigated the composition, diversity, and abundance of aerobic and anaerobic ammonia-oxidizing microorganisms dwelling in low-temperature Fe-Si-rich hydrothermal precipitates of the Lau Integrated Study Site based on ammonia monooxygenase (amoA) gene and 16S rRNA gene. Phylogenetic analysis revealed the common presence of ammonia-oxidizing archaea (AOA), Nitrosospira-like ammonia-oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing anammox (bacteria) in the Fe-Si-rich hydrothermal precipitates. Quantitative PCR analysis showed that AOA dominated the whole microbial community and the abundance of archaeal amoA gene was 2–3 orders of magnitude higher than that of AOB and anammox bacteria. Result of glycerol dialkyl glycerol tetraether analysis confirmed the presence and abundance of AOA. Our results suggest that microbial ammonia oxidations, especially archaeal aerobic ammonia oxidation, are prevalent and pivotal processes in low-temperature diffusing hydrothermal fields. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.

Influences of Nitrogen Content and Aging Precipitates on Pitting Corrosion Resistance Properties of High Nitrogen Austenitic Stainless Steel

This study is concerning the influences of nitrogen content and aging precipitates on pitting corrosion resistance properties of high nitrogen austenitic stainless steel (HNS) through potentiodynamic polarization method. The microstructure of aged HNS is analized by scanning electron microscopy (SEM). The main results obtained are as follow: the formation of intergranular, cellular Cr2N and intermetallic χ precipitates makes the depletion of Cr and Mo in the matrix and deteriorates the resistance to pitting corrosion in aged specimens. Cr2N starts to precipitate in the form of lamellar structure to cellular precipitates, the pitting corrosion drops to about 0 VSCE. HNSs perform the same tendency that the pitting corrosion potential firstly decreases then increases and reduce to the minimum value at nose temperature. All the pitting corrosion potential of HNS-B aged for 2h at different temperature presents more than that of HNS-A. The pitting corrosion resistance is mainly controlled by nitrogen content before great precipitates of cellular Cr2N and intermetallic χ phase rich in Cr and Mo. It is also mainly controlled by the content and the type of precipitates after great precipitates of cellular Cr2N.

Transformation and precipitation behaviour of Ti–Mo bearing high strength medium-carbon steel

The authors describe here the transformation and precipitation behaviour of Ti–Mo bearing high-strength medium-carbon steel during continuous cooling, using a combination of thermo-simulation and microscopy approach. The study demonstrates that Ti and Mo carbides precipitate during austenite-to-ferrite, austenite-to-bainite and even during austenite-to-martensite transformations, contributing to precipitation strengthening. Four different types of precipitates in the size range of 3–200 nm were observed during the transformation. They are spherical (Ti,Mo)C and TiC, cuboidal (Ti,Mo)(C,N) and long thin strips of FexC. The size of the precipitates was large and the density was less during austenite transformation. However, the size decreased and density increased during the austenite-to-bainitic ferrite transformation. During the austenite-to-martensite transformation, a high density of fine and spherical-shaped precipitates comprising of Ti and Mo in the range of 3–10 nm were observed.

Alloying effect of Ni and Cr on irradiated microstructural evolution of type 304 stainless steels

Life extension of the existing nuclear power plants imposes significant challenges to core structural materials that suffer increased fluences. This paper presents the microstructural evolution of a type 304 stainless steel and its variants alloyed with extra Ni and Cr under neutron irradiation at ∼320°C for up to 10.2dpa. Similar to the reported data of type 304 variants, a large amount of Frank loops, ultrafine G-phase/M23C6 particles, and limited amount of cavities were observed in the irradiated samples. The irradiation promoted the growth of pre-existing M23C6 at grain boundaries and resulted in some phase transformation to CrC in the alloy with both extra Ni and Cr. A new type of ultrafine precipitates, possibly (Ti,Cr)N, was observed in all the samples, and its amount was increased by the irradiation. Additionally, α-ferrite was observed in the type 304 steel but not in the Ni or Ni+Cr alloyed variants. The effect of Ni and Cr alloying on the microstructural evolution is discussed.

Degradation of renovation layers deposited on continuous steel casting rollers by submerged arc welding

The factors that affect the life of continuous steel casting rollers were investigated. Rollers that were removed from a manufacturing line because they had failed were renovated by submerged arc welding and subjected to working conditions until they again failed. The welding parameters (welding current, welding voltage, welding speed, current polarity, preheating temperature, interpass, postheating, and cooling conditions of clad) and chemical reactions and compositions had important effects on roller lifetime. Chromium has a dominant influence on the abrasion resistance of hard martensitic structures of the roller. Cr produces several types of precipitates (M3C, M23C6, M7C3, and M3C2). Alloying elements Mo and V in welding wire form fine carbides Mo2C and VC in weld layers. In low-carbon welding wires, precipitation hardening by N2 is used, by formation of chromium nitrides CrN and Cr2N. This article analyzes the process of failure of the functional surfaces of the repaired roller, in order to identify the origin and propagation of the cracks and share of corrosive environment on the tribo-degradation processes.

Macro- and Microstructural Studies of Laser-Processed WE43 (Mg-Y-Nd) Magnesium Alloy

The macro- and microstructural changes in the fusion zone (FZ) of WE43 magnesium alloy processed by a diode-pumped ytterbium (IPG YLS-3000) continuous wave fiber laser for specified processing conditions (from 4.17 to 12.5 × 107 J/m2) were studied. With the aid of computational heat-transfer model, the temperature history and cooling rate were determined for different laser-processing conditions. The computational heat-transfer results of laser-processed samples were used to correlate with microstructures characterized using optical, scanning, and transmission electron microscopies, and electron backscatter and X-ray diffraction analyses. The microhardness measurement was carried out to establish the structure–property relationship, and the results indicated that the minimal hardness variation (1 pct) within laser FZ was due to a constant heat extraction time (0.1 second), narrow variation in grain size (4 to 7 μm), and the type of precipitate (β-phase) formation.

Crystal structure of ultrathin lamellar precipitates

The crystal structure of lamellar precipitates formed in alloys 1213 (Al-Cu-Ag), V-1461 (Al-Cu-Li) and V-1469 (Al-Cu-Li-Ag) has been studied during age hardening. The experimental studies have been performed using transmission electron microscopy. The precipitates have {111} habits and thicknesses of several atomic planes. In diffraction patterns, these plates give a system of diffuse streaks. These ultrathin plates scatter electrons similar to two-dimensional crystal lattices. It is shown that thin plates of precipitates in alloys 1213, V-1461, and V-1469 give identical systems of diffuse streaks. The two-dimensional crystal lattices that give the system of these streaks have a hexagonal symmetry with the following orientation relationship: {ie481-1} and the lattice parameter af = 0.495 nm (there is no lattice parameter cf for two-dimensional lattices). A sequence of the steps of reconstruction of the spatial structure of plane precipitates is proposed in terms of their thickness, structures of two-dimensional lattices, and type of precipitates (extrinsic or intrinsic). The influence of Ag on the structure of lamellar precipitates in the V-1469 alloy is discussed.

Guinier-preston zone, quasicrystal and long-period stacking ordered structure in Mg-based alloys, a review

Both the solid solution and precipitation are mainly strengthening mechanism for the magnesium-based alloys. A great number of alloying elements can be dissolved into the Mg matrix to form the solutes and precipitates. Moreover, the type of precipitates varies with different alloying elements and heat treatments, which makes it quite difficult to understand the formation mechanism of the precipitates in Mg-based alloys in depth. Thus, it is very hard to give a systematical regularity in precipitation process for the Mg-based alloys. This review is mainly focused on the formation and microstructural evolution of the precipitates, as a hot topic for the past few years, including Guinier-Preston Zones, quasicrystals and long-period stacking ordered phases formed in a number of Mg-TM-RE alloy systems, where TM = Al, Zn, Zr and RE = Y, Gd, Hd, Ce and La.

Butterfly-shaped distribution of SiNx precipitates in multi-crystalline Si for solar cells

This paper concerns the precipitation mechanism of SiNx impurities in multi-crystalline silicon grown with a directional solidification system. A butterfly-shaped precipitate region was found across the middle part of ingot. These precipitates showed filament-like and fiber-like shapes of several micrometers in diameter and up to several millimeters in length. These two types of precipitates exist in different areas, forming three distribution zones in the butterfly region. The precipitate growth periodically stopped at the last stage of the butterfly formation. A non-uniform convection flow model was proposed to explain the precipitation behavior at the butterfly.

In situ characterization of Grade 92 steel during tensile deformation using concurrent high energy X-ray diffraction and small angle X-ray scattering

Abstract The tensile deformation in Grade 92 steel was studied in situ using simultaneous high energy X-ray diffraction (HE-XRD), radiography, and small angle X-ray scattering (SAXS) at room temperature (RT), 400, and 650 °C. Temperature-dependent elastic properties, i.e. Young’s modulus and Poisson’s ratio, were measured for α-Fe matrix, M 23 C 6 and Nb(C,N) phases in various crystallographic orientation. Significant differences in the evolution of lattice strain, peak broadening/sharpening, and void development in the α-Fe matrix, M 23 C 6 and Nb(C,N) precipitates revealed markedly different deformation and damage mechanisms at low and high temperature in the alloy. The strengthening effect of each type of precipitates measured by lattice strain agrees with the dislocation pile-up model at room temperature, while a different dislocation behavior was observed at 650 °C. Void volume fraction as a function of strain measured by SAXS can be described by a classic void nucleation and growth model at room temperature but not at 650 °C, implying a different damage process at high temperature.

Characterisation of precipitates in a Mg–7Gd–5Y–1Nd–0.5Zr alloy aged to peak-ageing plateau

The precipitates in a Mg–7Gd–5Y–1Nd–0.5Zr alloy aged to peak-ageing plateau (aged at 210°C from 18h to 180h) were studied using transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Precipitation at the peak-ageing plateau involves the formation of the β′ phase and a new type of plate-shaped phase precipitated along the (0001)α habit plane. The ellipsoid morphology of β′ was illustrated according to [0001]α and [101¯0]α zone axes observations. The orientation relationship between the β′ precipitates and matrix satisfies [001]β′//[0001]α and (100)β′//(112¯0)α, respectively. The TEM and HRTEM results indicate that the β′ precipitates have a base-centred orthorhombic structure with lattice parameters a=0.64nm, b=2.22nm and c=0.52nm. Further, atomic-scaled HAADF-STEM observations suggest a Mg7RE-type and not a Mg15RE-type structure for the β′ phase. The positive thermal stability of the alloy at 210°C ageing is attributed to the coherent relationship with the matrix and the formation of an interlaced network of the β′ precipitates. Aside from the β′ phase, a large amount of precipitate particles were observed to form on the (0001)α habit plane in the peak-aged samples. The new type of precipitates have a plate shape, of approximately 5nm wide along the [101¯0]α direction of the matrix and approximately 5nm long along the [2¯110]α direction. A completely coherent relationship with the matrix can also be observed.

9Cr-3W 강의 크리프 특성에 미치는 Mo 첨가의 영향

The effect of the Mo addition on the high temperature creep properties of the 9Cr-3W steel was also evaluated. Two experimental steels, (9Cr-3W and 9Cr-3W-0.5Mo), were prepared using a vacuum induction melting process, followed by hot rolling and heat treatment processes. Three types of precipitates, (<TEX>$M_{23}C_6$</TEX>, Nb-rich MX and V-rich MX) were observed in a typical tempered martensitic matrix. Significant effects of the Mo addition on the tensile properties were not observed. However, the creep properties at <TEX>$650^{\circ}C$</TEX> under applied stresses of 140 and 150 MPa were considerably enhanced by the Mo addition. The microstructural observation after the creep test indicated that the addition of Mo could function to retain the recovery of the martensitic matrix, thus resulting in the enhanced creep properties of the 9Cr-3W-0.5Mo steel. Furthermore coarsening of the <TEX>$M_{23}C_6$</TEX> carbides and formation of Laves phases were observed in both samples after the creep tests.

Microstructure and Properties of a High-Strength Cu-Ni-Si-Co-Zr Alloy

A high-strength Cu-Ni-Si alloy was developed with the additions of Co and Zr. The aging curve for the alloy was generated using hardness. Electron microscopy studies were conducted to analyze the phases in the alloy. Two types of phases, one of copper matrix and the other of Ni-Si-Co-Zr intermetallic phase, could be identified using scanning electron microscopy. Transmission electron microscopy studies confirmed the presence of two types of precipitates in solution-treated and aged (STA) condition, i.e., Ni2Si and Co2Si. Mechanical properties and electrical conductivity were evaluated in solution-treated (ST) and STA conditions. Aging of the ST samples at 500 °C for 3 h has shown an increase of 72 and 15% in yield strength (YS) and electrical conductivity, respectively. This increase in YS and conductivity on aging is primarily attributed to the formation of fine Ni2Si and Co2Si precipitates.

Formation of (Fe,Cr) carbides and dislocation structures in low-chromium steel studiedin situusing synchrotron radiation

The evolution of the size distribution of (Fe,Cr) carbides and the dislocation structure in low-chromium steel is studied during quenching and rapid heating byin situsmall-angle X-ray scattering (SAXS). The two-dimensional SAXS patterns consist of streaks on top of an isotropic SAXS signal. The evolution of the size distribution of the (Fe,Cr) carbides during heat treatment is determined from the isotropic component of the SAXS patterns. The isotropic part of the SAXS patterns shows that, after austenitization and quenching to room temperature, the average precipitate radius is 4.74 nm and the dispersion parameter for the lognormal size distribution is 0.33. Subsequent rapid heating to 823 K results in an average precipitate size of 5.25 nm and a dispersion parameter of 0.26. Bright-field transmission electron microscopy and high-resolution transmission electron microscopy reveal the nearly spherical morphology of the precipitates. The microstructural evolution underlying the increase in the average precipitate size and the decrease in the dispersion parameter after heating to and annealing at 823 K is probably that at room temperature two types of precipitates are present,i.e.(Fe,Cr)23C6and (Fe,Cr)7C3precipitates according to thermodynamic calculations, and at 823 K only (Fe,Cr)7C3precipitates are present. Additional measurements have been carried out on a single crystal of ferrite containing (Fe,Cr) carbides by combining three-dimensional X-ray diffraction (3DXRD) and SAXS during rotation of the specimen at room temperature, in order to investigate the origin of the streaks at low angles in the SAXS pattern. From simulations based on the theory of SAXS from dislocations, it is shown that the measured streaks, including the spottiness, in the two-dimensional SAXS patterns correspond to a dislocation structure of symmetric low-angle tilt boundaries, which in turn corresponds to the crystallographic orientation gradient in the single crystal of ferrite as measured by 3DXRD microscopy.