Quantitative Microstructural Analysis Research Articles

Nucleation kinetics of the α→ γM massive transformation in a Ti-47.5 at.% Al alloy

Continuous cooling experiments, utilizing in situ, high-speed computer-controlled temperature and electrical resistivity measurements and quantitative stereological analysis of microstructures, coupled with calculations based on the classical theory of nucleation, were performed to study the nucleation kinetics of the α→γ M massive transformation in a Ti-47.5 at.% Al alloy. Using previously determined thermodynamic data on the reaction temperature, time, undercooling and driving force for the massive transformation, the free energies for critical nucleus formation and the nucleation rates were computed for different nucleus shape models, including incoherent grain face, edge and corner nuclei and faceted grain face nuclei, and compared with experimentally determined nucleation rates. The results indicate that nucleation of singly faceted grain face nuclei and incoherent grain corner and grain edge nuclei are highly likely. Good agreement was also obtained between the calculated and experimental nucleation rates at these various sites. Based on these results, possible nucleation mechanisms during the massive transformation are discussed in light of current thinking on the nature of this transformation.

Local chain‐configuration dependence of the mechanisms of the chemical reaction of poly(vinyl chloride). IX. Novel results on stereoselectivity of chlorination reaction

AbstractA poly(vinyl chloride) (PVC) sample was chlorinated in solution in the presence of 2,2′‐azobisisobutyronitrile and by the fluid‐bed method. The aim was to evaluate the scope of the stereoselectivity of the chlorination reaction. The quantitative microstructural analysis of the residual PVC with a degree of chlorination was followed by 13C NMR spectroscopy. From the evolution of the content of isotactic (mm), heterotactic (mr), and syndiotactic (rr) triads and of mmmm, mmmr, and rmmr isotactic pentads in the unchlorinated parts of the polymer, it was unambiguously inferred that the chlorination reaction proceeds by a stereoselective mechanism in that the mr heterotactic triads are the most reactive structures followed by the isotactic triad at mmmr and rmmr pentads. This conclusion was confirmed on the basis of the Fourier transform infrared results. The results provide valuable information regarding the effect of tacticity and related local conformations in the chemical reactions of PVC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 508–519, 2003

Analytical modeling of the electrical conductivity of metal matrix composites: application to Ag–Cu and Cu–Nb

Modeling the electrical conductivity of composite materials is a complex matter, particularly if microstructural features lead to a size effect in electronic conduction or create an anisotropy. The method described in this article accounts for these circumstances by incorporation of appropriate phenomenological models. It provides a means to analyze and estimate the resistive behavior of two-phase or multi-phase micro-composites and nano-composites. A comparison with experimental data is carried out for two high-strength conductors, Ag–Cu and Cu–Nb, both of which have undergone extensive quantitative microstructure analysis to provide the required input for the model.

Mechanical properties of microwave sintered Si3N4-based ceramics

The mechanical properties and microstructure formation processes in Si3N4+3% AI2O3+5% Y2O3(Yb2O3) ceramic compacts sintered under microwave heating (MWH) and under traditional heating (TH) were investigated. The initial ceramic materials were powder blends of silicon nitride with oxides. The mean powder particle sizes were 0.5-1.0 mim. The content of alfa-phase in the Si3N4 powder was more than 95 %. The samples were sintered at 1800BC in nitrogen at normal pressure, the heating rate in all experiments was 60BC/min. The Vickers hardness (HV), fracture toughness (K1C) and bending strength (on) were determined. The microstructures of fracture surfaces of samples were studied by SEM. Quantitative microstructure analysis was carried out. It was shown that the values of HV and Kic of ceramic samples sintered under MWH at 1800BC rose steadily with the sintering time. This caused an increase in density, which reached maximum as fast as after 30 min of the MWH sintering; the mass loss at that time amounted to 3-4 %. The porosity of sintered samples with an addition of yttria was less than 1 %, that of ytterbia was greater, 2.4 %. For similar values of relative density, the hardness and fracture toughness of ceramic samples produced under MWH were higher as compared with those of samples sintered under TH. The microstructure of samples had the form of elongated grains in a matrix of polyhedral grains of the beta-Si3N4 phase. Measurements showed the mean size of grains in samples produced by MWH to be greater that in samples produced by TH. A larger number of elongated grains were formed. It was concluded that for sintering under MWH of Si3N4-based ceramics the growth of elongated beta-Si3N4 grains and formation of a "reinforced" microstructure were promoted and thereby improved the mechanical properties of such ceramics.

Modern quantitative microstructure analysis on the example of aicu5mg1 alloys

Using an automatic, QUANTIMET 500 MC, device for quantitative picture analysis and applying linear method of measurement on the example of AlCu5Mg1 alloys, the grain size (min, max and medium values), as well as relative standard measuring errors (RSE), dendrite arm spacing (DAS) and length eutectic (Le) and also distribution by size (histogram) and volume participation of ?-hard solution and eutectic have been determined. We have also studied the influence of grain-refining additives AlTi5B1 for the same chemical composition of the aluminium-capper-magnesium alloy. It has been concluded that with the increase of titanium content, the mean value of grain size decreases. We have also examined hardness and pressure strength.

Local chain configuration dependence of the mechanisms of chemical reactions of PVC. 8. New results from the reductive dechlorination reaction

The reductive dechlorination of poly(vinyl chloride) (PVC) with lithium aluminium hydride, tri- n-butyl tin hydride and lithium triethyl borohydride as reducing agents has been performed in the solution of tetrahydrofuran. A comparative study of the microstructural evolution with conversion using the three different reducing agents was carried out. The quantitative microstructural analysis with conversion has been followed by 13C NMR spectroscopy. From the evolution of the content of isotactic ( mm), heterotactic ( mr) and syndiotactic ( rr) triads, and of mmmm, mmmr and rmmr isotactic pentads in the unmodified parts of the polymer, it is unambiguously inferred that only the central chlorine atoms of isotactic triads in mmr tetrads or heterotactic triads in rmmr pentads are reactive. This conclusion was confirmed on the basis of FTIR results. The results provide valuable information regarding the effect of tacticity and the related local conformations in the chemical reactions of PVC.

Stereoselective Nature of Graft Copolymers Based on Poly(vinyl chloride): Synthesis of PVC-g-PMMA and PVC-g-PIB

Graft polymers from poly(vinyl chloride) with side chains of poly(methyl methacrylate) and poly(isobutylene) obtained by free radical and cationic techniques, respectively, were synthesized. The graft products were separated from the resulting mixtures of homo- and copolymers by fractional precipitation or extraction. The graft copolymers were characterized by infrared spectra, elemental analysis, NMR, and osmometric determinations. The quantitative microstructural analysis after grafting reaction has been followed by 13C NMR spectroscopy. From the results it is concluded that the modification of PVC by graft reactions through free radical and cationic polymerization proceeds by a stereoselective mechanism in that a fraction of isotactic triads is involved. Comparing the results obtained herein and those previously obtained in the nucleophilic substitution on PVC it is concluded that the highly reactive GTTG– isotactic triad conformation which is likely only at mmr tetrad has an apparent implication on the reactivity of the graft reaction. This conclusion was confirmed on the basis of the FT-IR and the thermal stability of the graft copolymers. This work provides some new insight into the prominent role of the microstructure-dependent local conformation on the polymer properties.

Some microstructural aspects of strength variation in rocks

The experimental study of rock strength revealed a remarkable mechanical variation in closely related rocks. This variation is explained through a quantitative analysis of microstructures. The oriented dry rock specimens were loaded at a constant stress rate and the uniaxial compressive strength with deformation, was recorded together. Microstructures were analysed in thin sections using petrographic image analysis, making it possible to determine size, shape and the shape-preferred orientation of individual grains, grain size distribution and modal composition. The typical grain size has been found to be the main microstructural factor controlling strength variation in groups of rocks which are closely related mineralogically. The increase of strength anisotropy is connected with an increasing degree of shape-preferred orientation of rock-forming minerals.

Mustererkennung in der quantitativen Gefügeanalyse am Beispiel von Stahlgefügen / Textural Identification in the Quantitative Analysis of Steel Microstructures

Computer aided quantitative microstructural analysis is becoming increasingly more significant in the field of metallography. One particular problem of the technique is the identification of individual microstructural constituents which differ in their grey scale values only slightly from the surrounding microstructure or have very fine structures. With such types of microstructures, since no quantitative determinations can be made, no correlation can be made to the mechanical properties of the material. One possible way of circumventing these problems is by making use of the global characteristics of the material in the evaluation. Instead of segmenting and evaluating the individual constituents, the pattern made by the constituent is quantified directly as part of the overall image. The main characteristic of such images is their image analytical texture or grey scale structure. Using suitable parameters for the analysis, images of the different types of microstructures found in a C45 steel, from martensite to Ferrite/Pearlite are quantified using textural analysis. A neuronal grid is trained to identify the relationship between information gained from the image and the hardness of the material. The system is currently capable of predicting the hardness of C45 steels to an acceptable practical accuracy.

The effect of particle structure on apparent density of electrolytic copper powder

The quantitative microstructural analysis and the sieve analysis of copper powder as well as the scanning electron microscopy analysis of the copper powders particles were performed. It was found that the structure of the copper powder particles determines the apparent density of copper powder. The powder particles from the same fractions of different powders occupy approximately the same volume, but the structure of metallic copper is very different. This causes the difference in apparent densities of copper powder obtained under different conditions. The more dendritic is the structure of powder particles the smaller is the apparent density of copper powder.

Microstructure and strength of nickel at large strains

A quantitative microstructural analysis is presented for pure polycrystalline nickel (99.99%) cold rolled to reductions from 70 to 98% ( ε vM 1.4–4.5). Applying transmission electron microscopy (TEM) techniques, key structural parameters, such as spacing between dislocation boundaries and high angle boundaries, as well as the misorientations across their boundaries, have been measured and analyzed. Application of scaling and similitude hypotheses to these microstructural parameters and their distributions revealed that the structures maintain a similar character with increasing strain. This similarity indicates that the measured parameters capture the important features of the structure. Scaling and similitude provide governing principles for structure formation. Based on this structural information and a detailed description of the morphology, structural parameters are identified, strength determining parameters chosen, and strength–structural relationships discussed. The suggestion is then made that two strengthening contributions should be considered: (i) dislocation strengthening due to the presence of low angle boundaries and (ii) grain boundary strengthening due to medium to high angle boundaries. The calculated individual strength contributions evolve differently with the strain and their addition leads to flow stress values and hardening rates in good agreement with those observed experimentally. No saturation of the calculated or experimental flow stress was observed.

Quantitative analysis of experimental and synthetic microstructures for sedimentary rock

A quantitative comparison between the experimental microstructure of a sedimentary rock and three theoretical models for the same rock is presented. The microstructure of the rock sample (Fontainebleau sandstone) was obtained by microtomography. Two of the models are stochastic models based on correlation function reconstruction, and one model is based on sedimentation, compaction and diagenesis combined with input from petrographic analysis. The porosity of all models closely match that of the experimental sample and two models have also the same two point correlation function as the experimental sample. We compute quantitative differences and similarities between the various microstructures by a method based on local porosity theory. Differences are found in the degree of anisotropy, and in fluctuations of porosity and connectivity. The stochastic models differ strongly from the real sandstone in their connectivity properties, and hence need further refinement when used to model transport.

Local chain configuration dependence of the mechanisms of analogous reactions of PVC. 6. The influence of the nucleophile nature

The nucleophilic substitution reactions on poly(vinyl chloride) (PVC) with sodium benzenethiolate, sodium thiobenzoate and sodium 2-mercaptobenzothiazolate have been carried out in solution of cyclohexanone. The aim was to study from a comparative point of view the influence of nucleophile characteristics, in particular bulkiness, on the reaction mechanisms through the microstructural evolution with degree of substitution of the same PVC sample with the three kinds of nucleophile in the same experimental conditions. The quantitative microstructural analysis with conversion has been followed by 13C NMR spectroscopy. Owing to steric hindrance of 2-mercaptobenzenethiolate the stereoselective nature of the reaction is enhanced making the reaction through the mr triads of mmr inoperative in practice unlike the other nucleophiles. This conclusion was confirmed on the basis of the FTIR results.

Particulate refinement and redistribution during the axisymmetric compression of an Al/SiCp metal matrix composite

Abstract Previous investigations have shown that the thermomechanical processing of Al/SiCp metal matrix composites (MMC) can reduce the size of SiC particles and yield a more homogeneous spatial distribution of particles. Both of the above microstructural features are conducive to improvements in the ductility and fracture toughness of MMC. This research was designed to measure the effectiveness of thermomechanical processing on the microstructure of an MMC by monitoring the change in SiC particle size and spatial distribution during the course of deformation processing. The MMC used in this investigation was the Al alloy 2618 reinforced with 14 vol% SiCp. Continuous and discontinuous axisymmetric compression tests were conducted, both at room and elevated temperatures. Optical and quantitative microstructural analysis was performed over many fields from each as-deformed specimen. This study finds that at elevated temperatures, a large number of fractured SiC particles corresponded with the macroscopic peak flow stress of the composite. Furthermore, the propensity for particulate fracture was most pronounced when specimens were deformed at room temperature, diminishing somewhat when specimens were deformed at elevated temperatures. However, deformation at elevated temperatures resulted in a more uniform spatial distribution of SiC particles within the matrix.

A methodology for automated quantitative microstructural analysis of transmission electron micrographs

It is generally recognized that proper quantification of microstructural behavior is necessary for the optimization of materials properties. In the specific case of polycrystalline thin films, transmission electron microscopy (TEM) is required for microstructural interrogation due to the small (nm–μm) inherent length scales in these systems. While a meaningful study requires large grain populations, typical data sets are relatively small due to the need for human interpretation of the contrast in TEM micrographs. To overcome this limitation, a general methodology has been developed to fully automate the grain boundary identification procedure by using a combination of both conventional and newly developed image processing algorithms to extract and combine information from multiple, optimized TEM micrographs. This technique has been validated by systematically analyzing microstructures of thin Al films, as obtained from TEM micrographs, and comparing these results with those obtained by a conventional, manual approach. Indeed, a statistical analysis shows that the agreement between these two methods is quite good. We further show that based upon a large population (8185 grains) one can estimate the number of grains required to draw meaningful conclusions about this microstructure. While the emphasis of this work is on TEM image processing, the techniques developed here are expected to be sufficiently general and flexible so as to be applicable to other (e.g., focused-ion beam) microscopies.

Quantitative microstructural analysis of M2 grade high speed steel during high temperature treatment

The microstructural changes of M2 grade high speed steel were examined quantitatively to identify the mechanisms responsible for changes during high temperature treatment. Reheating at high temperature leads to major microstructural changes involving phase transformation, spheroidization and coarsening of carbides formed in the as-cast M2 grade high speed steel. The M 2C carbide decomposes rapidly to form MC and M 6C in less than 1h after attaining the reheating temperatures of 1150 or 1200°C. Further reheating brings about the eutectic M 6C carbide spheroidization and general coarsening of both M 6C and MC. Carbide particles situated at the original austenite grain boundaries grow preferentially until impingement of carbides along these boundaries takes place. It is the diffusion of tungsten in γ-Fe which controls spheroidization rate of M 6C carbides, while diffusion of vanadium and tungsten in γ-Fe is the rate controlling mechanism for coarsening of MC and M 6C carbides, respectively. The process of spheroidization of alloy carbides such as M 6C, is somewhat different from that of cementite where impingement of the already spheroidized carbide particles make the analysis more difficult.

Quantitative analysis of microstructures produced by creep of Ti–48Al–2Cr–2Nb–1B: Thermal and athermal mechanisms

A γ-based TiAl alloy with equiaxed microstructure and fine grain size has been studied to analyze the deformation mechanisms responsible for the creep behavior. The microstructures produced by creep and high temperature deformation have been examined by TEM to obtain information about the different aspects characterizing the primary and secondary stages of creep. Mechanical twinning has been confirmed to occur in a fraction of the grains that never exceeds 50% while 1/2 ‹110› dislocations are active within all the γ grains. The twins are only responsible for a small amount of strain, but they lead to a subdivision of the microstructure and determine (directly or indirectly) the hardening process observed during the primary stage of creep. We have proposed that during the secondary stage the creep rate is determined by the unblocking of pinned dislocations by processes such as a pipe diffusion or cross slip that allow thermally activated glide of 1/2‹110› dislocations on (001) planes.

Dislocation structures and flow stress

The relation between polycrystal deformation and single crystal deformation has been studied for pure aluminium deformed in tension. A quantitative microstructural analysis has shown a significant effect of grain orientation on the microstructural evolution of grains in the polycrystal. This analysis has made it possible to estimate the flow stress of grains embedded in a polycrystal allowing a comparison with the deformation behaviour of single crystals.

Microstructures and yield strength of nitrogen alloyed super duplex steels

Ferritic-austenitic duplex steels combine high mechanical strength with acceptable corrosion resistance and are attractive for applications in the chemical and petrochemical industries. Alloying with nitrogen increases further both strength and corrosion resistance. In this work attention is paid to the influence of nitrogen and the constituents' spatial arrangement in the microstructure on the yield strength σ d y of the compound. The matrix-inclusion character of ferrite and austenite, which can be quantified by the parameters contiguity C and fraction of clusters r, markedly influences σ d y. Besides the topology of the microstructure, the yield strengths of the single phases ferrite and austenite, σ α y and σ γ y, affect σ d y. σ γ y is calculated from the austenite's nitrogen content and the mean grain size of the austenite. σ α y is calculated in two ways: One method considers the ferrite mean grain size, the nitrogen content in the ferritic phase and the coherent α′-particles. In a second approach, σ α y is calculated from σ γ y and the microhardness ratio of ferrite to austenite. An extensive quantitative analysis of various duplex microstructures reveals that r is much more sensitive to variations in the topology than the contiguity. Therefore, it is sensible to establish a relationship for σ d y, which incorporates the yield strengths of the single phases and the parameter fraction of clusters of ferrite and austenite. For this purpose a non-linear rule of mixture-type equation for σ d y is proposed showing excellent agreement with experimentally obtained strength values.

Qualitative and quantitative analysis of microstructures in Polish glacial tills with respect to their age: J. Trzcinski, Kwartalnik Geologiczny, 39(3), 1995, pp 403–421

A new method has been applied in the course of analysis of glacial tills, in areas glaciated during the North Polish, Middle Polish, and South Polish Glaciations. The method has not yet been commonly employed for assessing engineering-geological characteristics of soils. This study has allowed for determination that matrix microstructure is the most common in glacial tills. Among all tills in Poland the youngest tills have maximum porosity, but contacts and structural ties in these tills are loose. The older the glacial tills, the less porosity and closer contacts and ties they have.