Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/05/31 21:11:02」(JST)

wiki en

Metallography allows the metallurgist to study the microstructure of metals.

A micrograph of bronze revealing a cast dendritic structure

Al-Si microstructure

Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification.^[1] The microstructure of a material (which can be broadly classified into metallic, polymeric, ceramic and composite) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behavior, wear resistance, and so on, which in turn govern the application of these materials in industrial practice.

Methods

The concept of microstructure is perhaps more accessible to the casual observer through macrostructural features in commonplace objects. If one ever comes across a piece of galvanized steel, such as the casing of a lamp post or road divider, one observes that the surface is not uniformly colored, but is covered with a patchwork of interlocking polygons of different shades of grey or silver. Each polygon (the most frequently occurring would be hexagons) is a single crystal of zinc adhering to the surface of the steel beneath. Zinc and lead are two common metals which form large crystals visible to the naked eye. The metallic atoms in each crystal are well-organized into one of seven crystal lattice systems possible for metals (cubic, tetrahedral, hexagonal, monoclinic, triclinic, rhombohedral, orthorhombic); these systems dictate that the atoms are all lined up like points in a 3-D matrix. However, the direction of alignment of the matrices differ from crystal to adjacent crystal, leading to variance in the reflectivity of each presented face of the interlocked crystals on the galvanized surface. Symmetrical crystals are generally unstressed, unworked. They grow in all directions equally and were not subjected to deforming stresses either during or after. For large crystals, the ratio of crystal bulk to inter-crystal boundary (more properly, intergranullar boundary) is high. This indicates high ductility but correspondingly, lower strength (see Hall-Petch Strengthening), but a true study would take into quantitative account the relative strengths of the crystal and that of inter-crystal bonding.

Microscopy

Optical

When a polished flat sample reveals traces of its microstructure, it is normal to capture the image using macrophotography. More sophisticated microstructure examination involves higher powered instruments: optical microscopy, electron microscopy, X-ray diffraction and so on, some involving preparation of the material sample (cutting, microtomy, polishing, etching, vapor-deposition etc.). The methods are known collectively as metallography as applied to metals and alloys, and can be used in modified form for any other material, such as ceramics, glasses, composites, and polymers.

Two kinds of optical microscope are generally used to examine flat, polished and etched specimens: a reflection microscope and an inverted microscope. Recording the image is achieved using a digital camera working through the eyepiece.

X-Ray microtomographic

Nondestructive testing of microstructure for biological materials is a challenge and computer microtomography is the current solution. In fact, CMT can be used for the evaluation of microstructure of many other materials also. CMT can be very expensive though, and for research purposes, it is a necessity to generate a three-dimensional microstructure from two-dimensional cross-sectional images of the material. This is an area of active research and pursued by many scientists.

Electron microscopy

Aluminium copper (4 at% Cu) alloy showing copper precipitation within the aluminium matrix. The image is a projection through the metal where the dark regions are plate like copper precipitates

For high-resolution information on metallurgical microstructures, electron microscopic methods can be employed. This can allow for direct observation of atomic-scale features such as very fine precipitation reactions, dislocations or grain-boundary interfaces. Such methods may be critical in determining parameters such as solid state diffusivities.

References

^ Adapted from ASM Metals Handbook, Ninth Edition, v. 9, "Metallography and Microstructures", American Society for Metals, Metals Park, OH, 1985, p. 12.

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 消化管における光干渉断層撮影 optical coherence tomography in the gastrointestinal tract
2. 蛍光気管支鏡検査 fluorescence bronchoscopy
3. 睡眠不足：定義、影響およびマネージメント sleep insufficiency definition consequences and management
4. 思春期特発性側弯症：臨床的特徴、評価および診断 adolescent idiopathic scoliosis clinical features evaluation and diagnosis
5. 脳室周囲白質軟化症 periventricular leukomalacia

English Journal

Combined techniques for characterising pasta structure reveals how the gluten network slows enzymic digestion rate.

Zou W1, Sissons M2, Gidley MJ3, Gilbert RG1, Warren FJ4.
Food chemistry.Food Chem.2015 Dec 1;188:559-68. doi: 10.1016/j.foodchem.2015.05.032. Epub 2015 May 8.
The aim of the present study is to characterise the influence of gluten structure on the kinetics of starch hydrolysis in pasta. Spaghetti and powdered pasta were prepared from three different cultivars of durum semolina, and starch was also purified from each cultivar. Digestion kinetic parameters
PMID 26041231

Effect of mixing time on the structural characteristics of noodle dough under vacuum.

Liu R1, Xing Y1, Zhang Y1, Zhang B1, Jiang X2, Wei Y3.
Food chemistry.Food Chem.2015 Dec 1;188:328-36. doi: 10.1016/j.foodchem.2015.04.045. Epub 2015 Apr 22.
The structural characteristics of noodle dough under different vacuum mixing times were investigated using three flour samples by texture profile analysis (TPA), SEM, FTIR micro-imaging, and by measuring the glutenin macropolymer and free -SH content. The sheeted dough mixed for 8min presented bette
PMID 26041200

Highly-ordered silicon inverted nanocone arrays with broadband light antireflectance.

Zhang D1, Ren W2, Zhu Z2, Zhang H2, Liu B2, Shi W1, Qin X1, Cheng C2.
Nanoscale research letters.Nanoscale Res Lett.2015 Jan 22;10:9. doi: 10.1186/s11671-014-0718-x. eCollection 2015.
In this work, highly-ordered silicon inverted nanocone arrays are fabricated by integration of nanosphere lithography with reactive ion etching (RIE) method. The optical characteristics of as-prepared Si inverted nanocone arrays are investigated both by experiments and simulations. It is found that
PMID 25635178

Japanese Journal

Influence of Microstructure on Fatigue Fracture Characteristics of Al2O3

広島工業大学研究紀要 33, 67-74, 36192-00-00
NAID 120005403235

Nanocrystallization of Al Powder by Cryomilling Process

KONA Powder and Particle Journal advpub(0), 2017
NAID 130005150170

Microstructural Evaluation of ZrB<sub>2</sub>/ZrO<sub>2</sub> Ceramic Powders Prepared by Milling-Assisted Magnesiothermic Reduction of Oxide Raw Materials