Microstructure Inspection Research Articles

The effect of gold additions on the ageing behaviour and creep properties of the magnesium alloy AZ91E

Trace amounts of gold have been added to AZ91E, and the effects of this addition on the ageing behaviour, the T6 microstructure after ageing at 473 K and the creep performance are reported. T6 ageing was carried out at 373, 423 and 473 K. At the lowest temperature the T6 ageing behaviour was unaffected by the addition of gold. At the highest temperature, however, the ageing kinetics were affected by the presence of gold. Inspection of the aged microstructures showed that, in the presence of gold, the level of discontinuously precipitated Mg 17Al 12 usually seen in AZ91E was significantly reduced. Growth of discontinuous precipitation was suppressed at the majority of the grain boundaries and, where present, typically extended less than 10 μm into the grains upon ageing at 473 K. The precipitation of platelets of Mg 17Al 12 within the grains was not significantly affected by the presence of gold. Nuclear magnetic resonance showed that there were some differences in the ageing behaviour at 473 K during the time of most rapid hardness increase, consistent with the ageing proceeding at a slower rate in the alloy containing gold. The constant load creep behaviour was determined at 393 and 423 K and stresses between 50 and 100 MPa. The gold-containing alloy showed a prolonged period of steady state creep compared to the standard AZ91E, and slightly reduced minimum creep rates. A conventional power law equation was applied to the creep data and, at stresses below that leading to power law breakdown, the stress exponent for AZ91E was found to be 3 and 2.5 for the gold-containing alloy. The activation energy was reduced from 140 for AZ91E to 117 kJ mol −1 for the gold-containing alloy.

Microstructural stability of reduced activation ferritic/martensitic steels under high temperature and stress cycling

Reduced activation ferritic/martensitic steels are leading candidates for blanket/first-wall structures of the D-T fusion reactors. In fusion application, structural materials will suffer cyclic stresses caused by repeated changes of temperature and electromagnetic forces according to reactor operation scenarios. Therefore, creep–fatigue behaviors are extremely important to qualify reduced activation steels as fusion structural materials. In this work, microstructural stability of reduced activation ferritic/martensitic steels under various external stresses, such as constant stress cyclic stress, was studied. The materials used are JLF-1 steel (9Cr–2W–V,Ta) and JLS-2 steel (9Cr–3W–V,Ta). The microstructure inspection by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) was performed following creep rupture tests, fatigue and creep–fatigue tests at elevated temperatures. In order to examine precipitation morphology in detail, the improved extracted residue and extracted replica methods were applied. From the microstructural observation of creep rupture-tested specimen, intergranular precipitates such as M 23C 6 and Laves phase coarsened by applying the static stress.

Verbessertes Umformverhalten durch serielle induktive Nachwärmung von Laserstrahlschweißnähten

Tailored Blanks are used in car body manufacturing to meet increasing demands in light weight construction with increasing stiffness and passive safety. Due to its high seam quality, laser beam welding is commonly used for the production of these blanks. As the seam has to be deformed as a part of the blank, the hard welded zone limits the deformability and therefore the possibilities of shaping. Inductive post-heating of the welded zone from the welding heat can temper the martensite in the welded zone or increase the T 8/5 -time being important for the formation of the microstructure. This reduces the martensite content in the seam and the heat affected zone and combines high strength and high deformability. The potential of this method will be demonstrated in tensile testing, Erichsen testing as well as in microstructural inspections.

Contactless excitation and measurement method for inspection of microstructures and thin films

A specially designed resonator to avoid the change of the resonance characteristics by thermal influences of the laser beam was fabricated on a silicon on insulator wafer. This resonator design enables one to apply a lateral driving force to generate lateral vibration. The resonator was excited using a laser diode which was driven with sinusoidal current, and the vibration was detected by measuring intensity fluctuation of the He–Ne laser beam reflected on the resonator mass. Four evident resonance frequencies were successfully observed in the range from 100 Hz to 100 kHz.

Optical problems of wafer inspection with DUV microscopy for structures of about 0.1 μm

Abstract The inspection of small micro and nano structures involves the use of optical imaging below the resolution limit. Using classical microscopes up to these regions, one has to consider the three dimensional character of the structures and the partial coherence of the illumination light. To get an idea about the resolution limit’s dependence on microscope parameters one can use the Rayleigh criterion, which is valid for incoherent illumination only. On the other hand, with the inspection of structures generated lithographically, one also has to consider the influence of the height of the structures (topography). It can be shown that the imaging behaviour of the 3D-structures is greatly different from that given by the plane objects.

"In situ" Preparation of Replica for Microstructural Observation of Plant Components by Micro-sputtering Technique.

Metallic microstructure inspection is essential in assuring long-life operation of steam power stations. In common chemical etching methods for microstructure observation, the etching conditions are not readily specifiable and delicate handling techniques are required. To overcome this difficulty a physical etching method is employed with micro-sputtering technique where an inner-magnet is provided with a portable evacuation system and a movable power supply. A specimen taken from the main Y-shaped steam pipe of a disassembled power plant was etched using this new apparatus and a replica of the pipe surface was observed by optical microscopy. The result of observation was as good as that obtained by the chemical etching performed under the most favorable condition.

Topograph for inspection of engine cylinder walls

The microstructural inspection of engine cylinder walls is an important task for quality management in the automotive industry. Until recently, mainly tactile methods were used for this purpose. We present an optical instrument based on microscopic fringe projection that permits fast, reliable, and nondestructive measurements of microstructure. The field of view is 0.8 mm x 1.2 mm, with a spatial sampling of 1100 x 700 pixels. In contrast to conventional tactile sensors, the optical method provides fast in situ three-dimensional surface characterizations that provide more information about the surface than do line profiles. Measurements are presented, and advantages of this instrument for characterization of a surface are discussed.

Manufacture of Unidirectional Carbon Fiber Reinforced Carbon Composites by Preformed-Yarn Method

A bundle of polyacrylonitrile-based carbon fibers was included in a matrix precursor composed of fine pitchcoke and mesophase pitch, and was coated with polypropylene, resulting in a preformed yarn (PY). Unidirectional (UD) PY sheets, prepared by aligning the PYs, were stacked. Hot press molding of the staked UD-PY sheets at 600°C and heat treatment up to 2000°C were performed to manufacture a UD-C/C composite. Density, porosity, flexuralstrength and modulus of the resulting UD-C/C composite test pieces were measured. Flexural strength and modulusof the UD-C/C composite test pieces manufactured from PY with 40wt% pitch coke in its matrix precursor were487.3MPa and 125.4GPa, respectively. Even without impregnation, these value were superior by a factor of about 1.3than the UD-C/C composites manufactured by conventional method using phenol resin as a main component of matrixprecursor. Microstructural inspections of cross sections of the test pieces were also carried out. Any kind of pore werehardly recognized and a good fiber/matrix bonding was formed in the matrix of the UD-C/C composites manufactured from PY with 40wt% pitch coke in its matrix precursor.

Microstructural simulation and imaging of granular flows in two- and three-dimensional hoppers

Abstract Distinct element simulations of granular flows in two- and three-dimensional hoppers are compared with imaging data from conventional photography and gamma-ray tomography where information of the order of the particle size can be extracted. A novel feature of these comparisons is that both particle and vessel dimensions are matched exactly between the experiments and the computer simulations, thereby leaving little scope for speculation regarding śscale effects’ which are often used to justify scepticism over the validity of simulation predictions. Another novel feature of the work is that quantitative comparisons are provided during the entire period of filling and discharge events rather than selecting an arbitrary ‘snapshot’ in time, as is often the case in such simulation studies. Microstructural inspection of two-dimensional photographs of systems with large disc particles provides quantitative information which shows good agreement with simulation in terms of packing height, static and flowing voidage, stagnant/flow boundaries in funnel flow and heap/repose angles. Three-dimensional solids fraction data from packed beds of 7 mm diameter maple peas obtained by transmission gamma-ray tomography show encouraging agreement with simulation. An important result of these investigations is the degree of correlation between the flowing voidage and flow velocity of particles which are individually both affected by variations in particle size and shape but are mutually compensating in their effects on the simulated and measured discharge rates. In general, the simulations produce a less dilated assembly moving at smaller velocities.

Microstructure Inspection by Means of Mechanical Barchausen Effect Analysis

Microstructure Inspection by Means of Mechanical Barchausen Effect Analysis

A modeling of radiation induced microstructural evolution under applied stress in austenitic alloys

Effects of applied stress on interstitial type Frank loop evolution at early stages of irradiation were investigated by both numerical calculation and irradiation experiments. In the experimental part of this work, microstructural inspection has been made by transmission electron microscopy with a special emphasis on Frank loops and perfect loops on every {111} plane. The results of the TEM observation revealed that Frank loop concentration on a {111} plane increased as the resolved normal stress to a {111} plane increased and that small perfect loops were more likely produced on {111} planes where larger resolved shear stress was applied. The model of a stress effect on Frank loop unfolding was provided, which is triggered by nucleation of a Shockley partial dislocation loop in a Frank loop, was proposed. The results of the numerical calculation was successful to predict the strong dependence of Frank loop concentration on the resolved normal stress to {111} plane, which was the characteristic feature seen in the irradiation experiments.

部分オーステンパ処理による球状黒鉛鋳鉄の静的強度と疲労き裂進展抵抗の改善

In the previous study on the fatigue crack propagation characteristics of ductile cast iron, it was found that the propagation resistance could be improved by austempering from (α+γ) phase region (partial-austempering) without decreasing static strength, especially in the low ΔK region. In this paper, to improve the static strength in addition to the propagation resistance without decreasing ductility, the influence of treating temperture in (α+γ) phase region was examined. Microstructure inspection, tensile tests, fatigue tests (stress ratio, R=0.1) and fractography were carried out on the ductile cast iron specimens which were partial-austempered at four different treating temperatures (800°C, 815°C, 830°C and 840°C). The results obtained were compared with those of the as-cast material whose matrix-structure consisted of ferrite (about 60%) and pearlite (about 40%) and the materials whose matrix-structures were changed into ferrite (about 100%) or bainite (about 100%) by heat-treating.The matrix-structure of the partial-austempered materials consisted of ferrite and bainite. When partial-austempered at 800°C, 815°C, 830°C and 840°C, the ratio of bainite became approximately 20%, 40%, 80% and 90%, respectively. The static strength (0.2% proof stress and tensile strength) was improved with an increase of the ratio of bainite, but the ductility and propagation resistance decreased except the propagation resistance in the material whose matrix-structure was ferrite. The reasons were discussed in terms of fractography. The most effective treating temperature to improve the static strength and propagation resistance without decreasing ductility was 830°C for the ductile cast iron used in this study.

The Role of Grain Boundaries in the Deformation and Failure of a Superplastic Al-Li Alloy

The large elongations associated with superplasticity are observed only in materials with fine grain sizes. An Al-Li alloy processed thermomechanically to develop a fine grain size exhibits superplastic characteristics and large elongations to failure of up to about 900 percent. Measurements at large elongations reveal that the grain boundary sliding contribution to superplastic deformation is about 75 percent. Microstructural inspection of superplastically deformed specimens reveals also the occurrence of extensive cavitation.

Design and Application of a Quadrupole Detector for Low‐Voltage Scanning Electron Microscopy

AbstractScanning electron microscopes operated at low voltages are applied in the inspection and metrology of microstructures as well as in the testing of integrated circuits. The efficiency of a conventional Everhart‐Thornley‐detector is poor in this application, especially if large samples, e.g. wafers, are inspected or tested at small working distances. In addition, the primary beam is deflected and aberrations are added by the extraction field of this detector. A new type of detector for secondary electron recording in low‐voltage scanning electron microscopy was, therefore, designed, built and tested. It utilizes crossed electric and magnetic quadrupoles to compensate for each other in their effect on the primary beam. On the other hand, both fields support the extraction and collection of the secondary electrons. During the test application, the detector showed high efficiency resulting in low‐noise images without any negative effect on the resolution.

Effect of Bending by Line Heating Method on Brittle-Fracture Propagation Characteristics of Steel Plates

One of the authors has previously published the detailed procedures for plate bending by Line Heating Method, and showed its great promises for bending the steel ship hull plates. This method, which is consisted of heating and subsequently water-cooling a steel plate, has been suspected by not few concerned as possessing harmful effects on material properties. However, it was then proved by various tests such as static-tension, bending, V-notch Charpy and hardness tests or microstructure inspection, that the effect on material is as slight as that caused by press-bending in, either cold or hot state, because the heating in this process is duly controlled so as not to heat the plate beyond A-1 transformation point of steel.Recently, a number of large-scale brittle fracture tests, which is believed to have good correlation with brittle fracture of actual steel structures, has been developed. A Double-Tension test is one of the most representative of these large-scale tests, and the brittle-fracture properties of steel plates bent by Line Heating Method was investigated with this test by the present authors, the resultls of which are reported in this paper. It was revealed that the heated zone of steel plates becomes indeed more brittle than the original material, but the degree of deterioration is almost same as that caused by press-bending ; in other words, Line Heating Method can safely be used for ship hull steel plates from the viewpoint of brittle fracture.It was also found that the shear-fracture transition-temperature by Pressed-notch Charpy test is 'highly correlated with the arresting-temperature obtained by the Double-Tension test, if the applied stress is nearly as high as the yield point of the material.