Extraction Replica Technique Research Articles

Revisiting the applications of the extraction replica sample preparation technique for analysis of precipitates in engineering alloys

The extraction replica technique is a useful sample preparation method to fabricate transmission electron microscopy samples for subsequent studies of small particles, such as precipitates, in different types of alloys. With other sample preparation methods, such as thin foil fabrication, the surrounding matrix might influence compositional or crystallographic analysis in the TEM. The extraction replica technique omits that problem, as the precipitates are extracted onto a thin, amorphous film (most commonly carbon) and the influence of the matrix is thus eliminated. The replica can be produced in a direct manner, by a two stage-method or in certain cases by the oxide replica method. A variety of precipitates from common engineering alloys including carbides, nitrides, oxides and various intermetallic phases in steels, nickel-, zirconium-, aluminium-, copper-, and magnesium-based alloys, can be extracted and the techniques are summarized in this work. The choice of etchant is crucial for the end result, as is also showcased experimentally in this work. Furthermore, the direct replica and two-stage replica method are directly compared with each other by new experiments on a low alloyed steel and a zirconium alloy. There are indications that the direct method has a greater particle extraction efficiency of smaller particles compared to the two-stage method. Moreover, the direct method also facilitates the analysis of other features, such as grain boundaries, in special cases. • Extraction replicas are used to characterize a variety of particles in engineering materials. • The direct, and two-stage, carbon replica is the most common and versatile type. • The direct replica tends to have a better extraction of small particles. • The direct replica can also reproduce other features, such as grain boundaries. • The choice of etchant is crucial for the end result.

Transmission electron microscopy of precipitation in fine-grained heat-affected zone of Grade91 steel weld during creep exposure

Precipitation during creep exposure at 550 °C in the fine grain heat-affected zone of a Grade91 steel weld produced by gas tungsten arc welding with no filler and post-weld heat treatment at 760 °C for 30 min. has been investigated. The applied tension load during creep testing was 165 MPa, the creep rupture time was 1138 hrs. (100% creep aging), and the creep exposure times were 911, 569, 341, 223 and 114 hrs. for 80%, 50%, 30%, 20% and 10% creep aging, respectively. Light microscopy and scanning electron microscopy were used to examine the heat-affected zone in the steel weld. Grain size in the fine grain heat-affected zone was measured by a circular intercept method on secondary electron images from scanning electron microscopy. Precipitates were detached from the fine grain heat-affected zone by a carbon-film extraction replica technique and investigated by transmission electron microscopy. During creep, a continual increase in grain size was observed in the fine grain heat-affected zone, starting from about 1.70 µm after post-weld heat treatment to about 2.30 µm at 100% creep aging. Precipitates found during creep were M23C6, M7C3, M6C, MX, M2X and high-Si Laves phase. M23C6 was found in all creep conditions until rupture, mainly at prior austenite grain boundaries and sub-boundaries. M7C3, M6C and high-Si Laves phase were observed during creep aging, mainly nearby grain boundaries and sub-boundaries. Relatively fine MX and M2X were found after 20% creep aging until rupture, mainly within grain interiors. Detailed criteria for identification of these precipitate phases, based mainly on energy dispersive X-ray spectrometry and selected area electron diffraction using transmission electron microscopy, is given and a major cause of premature loss of creep strength in Grade91 steel weld is discussed. This is important in understanding creep behavior of steel parts used for boiler tubing, heat exchangers, and steam piping systems in fossil-fuel power plants.

TEM replica analysis of particle phases in a tempered martensite ferritic Cr steel after long term creep

Tempered martensite ferritic steels (TMFSs) have been and are being used for critical components in high temperature plant operating in the 600 °C range. They are exposed to creep conditions for long time periods, exceeding 100,000 h. In the present study we investigate a 12% Cr TMFS, after creep-testing at 550 °C at 120 MPa for 139,000 h. We had previously investigated this material in the TEM using thin foils. We now use an extraction replica technique to analyze four particle families: M23C6, MX, Laves-phase and Z-phase, considering statistically relevant numbers of particles (between 120 and 720). We show how EELS mapping can help in identifying Z-phase particles and use Cr-V-maps to differentiate between the four particle families. The chemical evolution of particles is investigated. The experimental results are discussed in the light of previous thin foil data and with respect to predictions from computational thermodynamics. The strength and weakness of thin foil and replica procedures are compared. Improvements for thermodynamic databases are suggested.

Spectrum imaging of complex nanostructures using DualEELS: I. Digital extraction replicas.

This paper shows how it is possible to use Dual Electron Energy Loss Spectroscopy (DualEELS) to digitally extract spectrum images for one phase of interest in a complex nanostructured specimen. The specific cases studied here concern Nb or V precipitates, a few nanometres in size, in high manganese steels. The procedures outlined allow the extraction of the precipitate signal from the Fe-Mn matrix, as well as correction for surface oxide and any surface carbon contamination. The resulting precipitate-only spectrum images are then suitable for quantitative analysis of the precipitate chemistry. This procedure results in much improved background shapes under all edges of interest, mainly as a result of the removal of the extended electron loss fine structure (EXELFS) from the elements in the matrix. This allows the reliable extraction of even tiny quantities of elements, such as low levels of nitrogen in some carbide precipitates. As well as being relevant to precipitation in steels, these techniques will be widely applicable to the separation of chemically-distinct phases in complex nanostructured samples, and can be viewed as a digital version of the extraction replica technique.

The Study on the Precipitation Behavior of the Second Phase Particles for Fine Grain and High Strength IF Steel

The new type SFG HSS (super fine grain, high strength steel sheet) has been developed by adding solid-solution strengthening elements to conventional IF steel such as Si, Mn. The precipitation behavior of the second phase particles was observed and studied by a carbon extraction replica technique used transmission electron microscopy (TEM). The shape of the small second particles is similar to spherical and ellipse, the sizes of which are 10~30nm. It is seen that the particles are dispersed on the matrix. The precipitate composition of small particles is Nb (CN) and the precipitate composition of large particles is NbC examined by energy dispersive X-ray (EDX). It is noted that the yield strength is low as well as the tensile strength is high by the PFZ which is free of precipitate called precipitated free zone on the one side of the grain boundary. The results of microstructure shows that the second phase particles pinned on grain boundary not only can inhibit the grain growth, but also the grain can be fined.

Evolution of microstructure and precipitation state during thermomechanical processing of a X80 microalloyed steel

A series of anisothermal hot torsion tests were carried out to simulate hot rolling on a high-strength low-carbon CMnNbMoTi microalloyed steel corresponding to an industrial X80 grade for pipeline construction. Mean Flow Stress was graphically represented against the inverse of temperature to characterize the evolution of austenite microstructure during rolling, which was also studied by optical microscopy and SEM on samples quenched from several temperatures. On the other hand, particles precipitated at different temperatures during rolling were analyzed by means of TEM using the carbon extraction replica technique and their size distribution and mean size were determined, as well as their morphology, nature and chemical composition. The effect of rolling temperature and austenite strengthening obtained at the end of thermomechanical processing on final microstructure and precipitation state was studied. Austenite strengthening was characterized by means of the parameter known as accumulated stress (Δ σ). It was found that ferrite grains are finer and more equiaxed when the austenite is more severely deformed during finishing (higher values of Δ σ) but lower values of Δ σ generate a higher density of acicular structures after cooling, which should improve the balance of mechanical properties. The increase in strength associated to acicular ferrite compared to polygonal ferrite is revealed by the higher values of Vickers microhardness measured on samples corresponding to low Δ σ. On the other hand, (Ti, Nb)-rich carbonitrides can be found from reheating and their size keeps a constant value near 20–30 nm during thermomechanical processing. A second population of much finer (Nb, Mo)-rich carbonitrides whose size is close to 5 nm forms from lower temperatures, near 1000 °C. The accomplishment of two different levels of Δ σ at the end of hot rolling schedule does not seem to introduce major differences in precipitation state before final cooling.

Effect of Rare Earth (RE) La on Solid Solution of Second Phase Particle and Austenite Grain Growth in Steel Containing High Niobium

The solid solution of the second phase particle and austenite grain growth behavior of the high niobium-containing RE steel was studied by mathematical calculation and extraction replica technique. The purpose of the study was to investigate the effects of Rare Earth La on austenite grain growth and propose an empirical equation for predicting the austenite grain size of RE steel. Austenite grain grows in an exponential law with the increase of heating temperature, while approximately in a parabolic law with the increase of holding time. Results show that the RE steel has good anti-coarsening ability at elevated temperatures. When soaking temperature is lower than 1250°C , AGS and growth rate are small for high niobium steel, but soaking temperature is lower than 1220°C , AGS and growth rate are small for RE steel. RE La can promote solid solution of second-phase particles Nb(C, N), the solution temperature decrease 30°C than high niobium steel.

The Study on the Precipitation Behavior of the Second Phase Particles for As-Hot Rolled Dual-Phase Nb-Bearing Steel

The precipitation behavior of the second phase particles was observed and studied by a carbon extraction replica technique used transmission electron microscopy (TEM) for Nb-bearing dual-phase steel. It is found that there are more second phase particles on the surface than that of in the center of sample. The mainly smaller particle which sizes of is below 20nm show the shape of spherical and ellipse. The sizes of larger particles are range of 20nm~40nm and the shape of them present rectangle or ellipse. The particles are dispersed on the matrix and the particle boundary is clear. The precipitate composition of particles are all Nb(C、N) examined by energy dispersive X-ray (EDX). The results of microstructure shows that the second phase particles pinned on grain boundary not only can inhibited the grain growth, but also the grain can be fined during the heating and cooling course.

Influence of deep cryogenic treatment on microstructure and evaluation by internal friction of a tool steel

The Influence of deep cryogenic treatment (DCT) on microstructure of a tool steel was studied by means of in situ obviation and carbon extraction replica technique. The results obtained have been shown that the retained austenite is present in a thin film between the laths of martensite and stably exists even during prolonged soaking time in liquid nitrogen. The in situ obviation and carbon extraction replica shows the carbides were not precipitated directly in the process of deep cryogenic treatment. The internal friction indicates the carbon atoms segregate to nearby dislocations and produced strong interactions, including interstitial carbon atoms themselves and between the interstitial carbon atoms with time-dependent strain field of dislocations. The cluster of carbon atoms nearby the dislocations either act as or grow into nuclei for the formation of carbide on subsequent during tempering.

Evolution of Carbide Precipitates in 2.25Cr-1Mo Steel during Long-Term Service in a Power Plant

Carbide precipitation from the steel matrix during long-term high-temperature exposure can adversely affect the fracture toughness and high-temperature creep resistance of materials with implications on the performance of power plant components. In the present work, carbide evolution in 2.25Cr-1Mo steel after long-term aging during service was investigated. Boiler pipe samples of this steel were removed from a supercritical water-cooled coal-fired power plant after service times of 17 and 28 years and a mean operational temperature of 810 K (537 °C). The carbide precipitation and coarsening effects were studied using the carbon extraction replica technique followed by analysis using transmission electron microscopy and energy dispersive X-ray spectroscopy. The carbides extracted using an electrolytic technique were also analyzed using X-ray diffraction to evaluate phase transformations of the carbides during long-term service. Small ball punch and Vickers hardness were used to evaluate the changes in mechanical performance after long-term aging during service.

Abnormal growth of austenite grain of low-carbon steel

Niobium is an important alloying element for the steel. To know further the effect of Nb in the steel, the contrast experiments on the austenite grain growth of the 0.015%Nb and free Nb steels were carried out using Gleeble 1500 thermomechanical simulator. The experimental results indicate that the austenite grain of 0.015%Nb steel is finer than that of Nb free steel at 1150–1230°C. And when the heating temperature arrives the critical temperature 1240°C, the austenite grain of Nb steel suddenly grows up, while the austenite grain of Nb free steel changes little. Finally, the austenite grain of Nb steel is obviously coarser than that of Nb free steel. By transmission electron microscopy (TEM) using a carbon extraction replica technique, the precipitates of Nb(C,N) were not observed in the 0.015%Nb steel. It is concluded that the grain-boundary internal adsorption of Nb atoms leads to the result.

Oxide coarsening and its influence on recrystallization in a mechanically alloyed Fe-base oxide-dispersion-strengthened alloy

Analytical transmission electron microscopy has been used to determine whether yttria particles readily coarsen in oxide-dispersion-strengthened ferritic stainless alloy (PM2000), in an attempt to contribute to a model that explains the directionality of the microstructure observed when this material undergoes recrystallization under isothermal conditions. Likewise, the role of Al2O3 particles in the recrystallization processes of alumina-enriched PM2000 alloy has been studied via the addition of 1 wt pct Al2O3 particles as dispersoids. A carbon extraction replica technique was used to show that no coarsening of the yttria dispersion occurred even under exaggerated heat treatment at 1380 °C for 1 hour. By contrast, a significant ripening of alumina particles occurred apparently without influence on the recrystallization processes.

Caustic stress corrosion cracking of a spheroidal graphite cast iron: characterisation of ex-service component

This paper discusses observations of features suggesting grain boundary embrittlement ahead of stress corrosion crack tips in ex-service cast iron components exposed to strong caustic environments during Bayers process for alumina processing. The cracks and the neighbouring areas in the ex-service specimens were examined using conventional metallography, SEM, the extraction replica technique in the TEM and Auger electron spectroscopy. In all cases, the cracking was initiated at the surface of the steel exposed to the corrosive environment and it appeared that crack nucleation may have been aided by local stress concentrations and/or zones of local residual stress concentration. The fracture mode was almost exclusively intergranular and the crack path followed ferrite grain boundaries. There was clear evidence of a local zone of grain boundary embrittlement extending ahead of the tip of the major cracks examined. The phenomenon was established by investigating the fresh fracture surfaces produced by extending pre-existing cracks under impact loading at liquid nitrogen temperature. Auger electron spectroscopy of the fresh intergranular fracture surface failed to reveal any evidence of local elemental grain boundary segregation that might account for the observed embrittlement. In the absence of evidence of any other embrittling species on the exposed intergranular facets, there arises the possibility of hydrogen being involved in the embrittlement. The paper discusses hydrogen assisted intergranular cracking, as observed in the case of similar materials, to be the possible mechanism.

Caustic stress corrosion cracking of a graphite cast iron component

This paper presents failure analysis of an ex-service cast iron component exposed to aggressive caustic solutions during Bayers process for alumina processing. The cracks and the neighbouring areas in the ex-service samples were examined using conventional metallography, scanning electron microscopy (SEM), the extraction replica technique in the transmission electron microscope (TEM) and Auger electron spectroscopy (AES). The features include intergranular stress corrosion cracking and grain boundary embrittlement ahead of the crack-tips. The paper also argues the possibility of hydrogen-assisted crack propagation.

Evolution of Austenite Microstructure and Precipitation State during Hot Rolling of a Nb-Microalloyed Steel

Evolution of Austenite Microstructure and Precipitation State during Hot Rolling of a Nb-Microalloyed Steel

Comparison between precipitation kinetics of manganese sulfide during hot compression process with one and two holding time in grain-oriented electrical steel

The aim of this work is the study of manganese sulfide particles precipitation (Fe-3%Si) after one and two holding time during hot compression process. Samples were heated at 1573K for 1800s. After the specimens were cooled down to 1373 and 1173K, hold for 32, 60 and 338s and the compression of 50% is applied during the holding time and then water quenched, in the process with two holding time, the first holding time is-60s (50% is applied), then the compression of 30% is applied (second holding time: 32, 60 and 338s), then water quenched. Grain size characterization was carried out using OM. The study of comparison precipitation has been carried out on the surface and the center of each sample. For TEM characterization of MnS particles an extraction replica technique has been used. Image analyzer measured the particle diameter. Optical micrographs showed that the grain size decreases with the second holding time process for the two temperatures on the two studied regions. Hot compression process with two holding time provides more dislocation and defects increasing the possibility of MnS particles precipitate and providing higher MnS particle density.

Assessment of material thermal history in elevated temperature components

The extraction replica technique provides a valuable nondestructive metallographic tool both for monitoring microstructural changes caused by material aging and for quantitatively assessing the thermal history of material in components operating in creep regime. It has been, in fact, verified that the chemical composition of carbides collected on replicas is correlated both to temperature and to time of exposure of the material. In this report, the infield application of the replica technique is described, focusing on the quantitative evaluation of exposure temperature of a 2 1 4 Cr1Mo steel. The validity of the technique has also been verified for 9–12% Cr ferritic steels after long-term creep exposure in laboratory tests; also in this case, on the basis of the available data, a correlation between the Cr Fe ratio in M 23C 6 carbide and the Larson-Miller parameter appears promising.

Observations on the precipitates in steels by extraction replica technique using the potentiostatic etching method with a non-aqueous electrolyte

Quantitative analysis of the precipitates of the steel is necessary in order to improve mechanical properties of the steel, because the precipitates in steels play an important role on the grain growth, recrystallization, and precipitation hardening. Recently, in-situ scanning electron microscope(SEM) observations on the precipitates with potentiostatic etching method in non-aqueous electrolyte have been reported. We applied the potentiostatic etching method for the preparation of the extraction replica.

High-voltage and high-resolution TEM in materials research: Penetration and Resolution Issues

Transmission electron microscopy has produced most of what is known about the microstructures of inorganic materials. Although some internal structures can be seen on etched surfaces using replicas or the SEM, the lack of electron diffraction data eliminates the availability of crystallographic information so that the identity and habit plane of precipitates or characteristics of lattice defects cannot be determined. However, the old extraction replica technique has come back into vogue for analytical microscopy because matrix effects in X-ray or ELS spectra can be eliminated. Extraction replicas can also be used for HREM studies of small constituents in multi-phase materials when standard specimen thinning techniques are inapplicable.

Precipitation behavior in austenitic and ferritic steels during fast neutron irradiation and thermal aging

Precipitation behavior has been studied using a carbon extraction replica technique in Ti-modified Type 316 stainless steels (JPCA-2) and 9Cr-2Mo ferritic/martensitic steels (JFMS) irradiated to 8.1 × 1024 n/m2 at 873 and 673 K, respectively, in the experimental fast breeder reactor JOYO. Precipitate identification and compositional analysis were carried out on extracted replicas. The results were compared to those from the as-received steel and a control which had been given the same thermal as-treatment as the specimens received during irradiations. Carbides, Ti-sulphides and phosphides were precipitated in JPCA-2. Precipitate observed in JFMS included carbides, Laves-phases and phosphides. The precipitates in both steels were concluded to be stable under irradiation except for MC and M6C in JPCA-2. Small MC particles were found precipitated in JPCA-2 during both irradiation and aging. Irradiation proved to promote the precipitation of M6C in JPCA-2.