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Local distribution of orientation relationship between austenite and martensite is quantitatively examined using lath martensite in an ultra-low-carbon steel. Orientation relationship is systematically deviated between near Greninger–Troiano and Nishiyama–Wasserman orientation relationships around variant boundaries of the smallest misorientation pair, which is observed as the most frequent variant pair in the steel. Misorientation between this variant pair is decreased at some boundaries of the pair. Formation mechanism of the pair is discussed using the observed boundary characters. Image, graphical abstract [ABSTRACT FROM AUTHOR]

ABSTRACT The copper electroplating stress measurement method uses the grain growth in the copper on a machine element that has been subjected to repeated loads. Because this growth is also caused by thermal energy, the effect of the ambient temperature on grain growth density and grain orientation was investigated. Cyclic torsion tests were carried out at temperatures from 293 to 353 K. The relationship among the grain growth density, maximum shear stress, number of cycles, and ambient temperature was formulated to measure the maximum shear stress occurring on the machine element. Moreover, cyclic bending-torsion tests were also performed, and the orientations of grown grains were analysed by electron backscatter diffraction. The slip directions of grown grains corresponded closely with the direction of shear stress in spite of the ambient temperatures. This means that principal stresses can be measured by using the pole figure or the inverse pole figure of grown grains at temperatures up to 353 K. [ABSTRACT FROM AUTHOR]

A cyclic biaxial stress measurement method using electrodeposited copper foil was examined. The crystallographic orientations of individual grains that undergo grain growth in copper foil subjected to cyclic loading were analyzed by electron backscatter diffraction (EBSD). One of the slip directions in most of the grains corresponded to the direction of maximum shear stress when the biaxial stress ratio was negative. However, the number of grains with other orientations gradually increased as the biaxial stress ratio approached zero. On the basis of these features, we propose biaxial stress measurement using EBSD analysis of grown grains in copper foil. Our new method has excellent resolution compared with other stress-strain measurement methods since it can measure the average biaxial stress ratios in an area of 500 μm × 500 μm. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the substructures of lenticular martensites with different martensite start temperatures (Ms) by transmission electron microscopy. Observation of Fe–33Ni revealed a substructural change from fine transformation twins in the midrib and twinned region to several sets of screw dislocations in the untwinned region during growth. Tangled and curved dislocations also appeared near the martensite–austenite interface of the untwinned region, as the martensite inherited the dislocations in the surrounding austenite. In contrast, curved and tangled dislocations appeared in the entire untwinned region in Fe–31Ni and in the whole martensite plate in Fe–20.5Ni–35Co, as the higher Ms temperatures facilitated the plastic deformation of the surrounding austenite. Thermally transformed thin plate martensite in Fe–31Ni–10Co–3Ti grew into a lenticular shape accompanied by a substructure with dislocations after deformation at temperatures above the Ms temperature. The change in the substructure of lenticular martensite presumably resulted from the local temperature rise in the martensite plate. [Copyright &y& Elsevier]

Abstract: The microstructure and the strength of the lath martensite in Fe–0.2C and Fe–0.2C–2Mn alloys were analyzed as a function of the prior austenite grain size. The size of martensite packets formed within individual austenite grains was controlled by the austenite grain size but not affected by the Mn addition. However, the further subdivision of packets into blocks differed significantly in the two alloys, and at a given austenite grain size a smaller block size was observed in the Mn containing alloy. The yield strength of the two alloys was related to the packet size and the block size, respectively, and the results suggested that the block size is the key structural parameter when analyzing the strength–structure relationship of lath martensite in low carbon steels. [Copyright &y& Elsevier]

Abstract: The morphology and crystallography of lath martensite in two Mn-containing interstitial free steels and a maraging steel were examined in detail by a combination of transmission electron microscopy, electron backscatter diffraction in a scanning electron microscope and optical microscopy. Indirect determination of the orientation relationship between the lath martensite and the austenite was made by analysis of misorientation distributions, and a similar orientation relationship was found for the three alloys in accordance with previous observations in low-carbon steels. Furthermore, the formation of six variants in a given packet and the preferential arrangement into blocks of low-misorientation variant pairs demonstrate a universality of morphology and crystallography of lath martensite. The presence of six variants in a packet can be accounted for by the minimization of the total shape strain introduced during the transformation. The lath boundaries developed within the volume of a certain variant show alternating misorientations and a mixed tilt and twist character characterizing these structures as low-energy dislocation structures. [Copyright &y& Elsevier]

Abstract: The orientation relationship of lenticular martensite (M) with respect to austenite (A) is nearly Greninger–Troiano at the midrib and twinned region but gradually deviates towards Kurdjumov–Sachs near the M/A interface. This change is related to the change in the substructure of martensite and also to the deformation in the surrounding austenite. [Copyright &y& Elsevier]

The morphology and crystallography of lath martensite in Fe-C alloys containing various carbon contents from 0.0026 to 0.61% were studied by analyzing electron back scattered diffraction patterns in scanning electron microscopy and Kikuchi diffraction patterns in transmission electron microscopy. As carbon content increases, the sizes of both packet and block decrease. In low carbon steels (0.0026–0.38%C), a block which is observed as having different contrasts under optical microscopy contains two groups (sub-blocks) of laths which are of two K-S variants with a misorientation of about 10 degrees. On the other hand, in the high carbon alloy (0.61%C), a block consists of laths of a single K-S variant. [Copyright &y& Elsevier]

Background: Measurement of local stress amplitude at the stress concentration point is a key component of mechanical design from the viewpoint of preventing metal fatigue. Copper electroplating method, which is a stress measurement method utilizing grains grown in a copper foil by cyclic loading, is suitable for such microscopic stress measurement. Reports have shown that the maximum shear stress and principal stress, which are important components in the evaluation of fatigue strength, can be measured by examining the density and crystallographic features of grown grains. Objective: Electron backscatter diffraction (EBSD) analysis of grown grains can be utilized to understand the crystallographic features of the grains, but EBSD equipment requires technical skill to operate, which makes it inconvenient. In this paper, we explore the feasibility of stress measurement by analyzing the crystallographic features of grown grains using the X-ray diffraction (XRD) method, which is more versatile than the EBSD method. Methods: Cyclic loading tests were conducted using smooth specimens with copper foil adhered under various biaxial stress conditions of bending and torsion. The surfaces of the grains-grown copper foil were then analyzed by the XRD method. Results: The peak of diffraction intensity tended to shift from the (220) plane to the (111) plane as the biaxial stress ratio increased. We quantified this tendency using the Lotgering factor and developed an empirical formula for determining the relationship between the Lotgering factor and the biaxial stress ratio. Conclusions: Our proposed empirical formula enables principal stress measurement within a biaxial stress ratio C ranging from –0.45 to 0, and the measurement accuracy is comparable to that of the conventional EBSD method. [ABSTRACT FROM AUTHOR]

Optical emission signals of a dc arc plasma system that was used for generating ZnO nanoparticles (NPs) have been investigated in gas phase as a function of chamber pressure and arc current. In this technique, a commercially available zinc 4N rod is used as a zinc source, as well as anode in the dc circuit and ambient air as an oxygen source. A carbon rod acts as the cathode. The optical transitions of Zn(I) and O(I) in addition, excitation of high energy states of N, CN, and atomic nitrogen lines were observed in OES due to increase of electron temperature than gas temperature ( T > T) by reducing the chamber pressure from 760 torr to lower pressures. The as-prepared NPs show good crystalline quality with hexagonal wurtzite structure and the particle size was ranging from few nm to 100 nm in the form of rod and spherical morphologies. The impurity nature and structural properties of as-prepared NPs by dc arc plasma experiments were correlated with OES and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: The upper bainite structures were investigated in Fe–9Ni–(0.15–0.5)C (mass%) alloys transformed at temperatures between 723 and 623K. A bainite packet similar to lath martensite is formed and is partitioned into blocks containing lath-shaped bainitic ferrite with the same parallel close-packed plane relationship of the K–S relationship. Its feature is categorized into three types: (A) a packet contains laths of two K–S variants with a small misorientation (sub-blocks), (B) a packet is divided by blocks largely misoriented and each block contains sub-blocks and (C) a packet is divided by blocks containing a single variant of laths. A packet of type (A) is formed at 723K in each alloy whereas the packet type becomes (B) or (C) at lower temperatures. As a result, bainite blocks are refined with decreases in transformation temperature and carbon content. In contrast, blocks and packets of lath martensite are refined with increasing carbon content. [Copyright &y& Elsevier]

Abstract: The corrosion behavior of 28Cr–7Ni–O–0.34N duplex stainless steels in air-saturated 3.5-wt% NaCl solution at pH 2, 7, 10 and 27 °C was studied by the potentiodynamic method. Two types of microstructures were investigated: the as-forged duplex and microduplex (average austenite grain size 5–16 μm) structures. The austenite volume fractions of the tested steels were between 0.35 and 0.64. The nitrogen effect on corrosion behaviors of both duplex and microduplex stainless steels were the same. At pH 2, the corrosion potential increased when the nitrogen content increased, however, corrosion current density as well as corrosion rate decreased. At pH 7 and 10, the effect of nitrogen on corrosion potential and corrosion rate could not be observed. Corrosion potential at pH 10 was lower than at pH 7. Pitting potential increased when the nitrogen content in the tested steels increased at all tested pH. For the nitrogen effect on the passive current density, it seemed that only at pH 2, the average passive current densities reduced when the nitrogen content increased. Nitrogen may have participated in the passive film or has been involved in the reaction to build up passive film. The ammonium formation and nitrogen enrichment at the interface metal/passive film with adsorption mechanism were discussed. The dissolute nitrogen might have combined with the hydrogen ions in solution to form ammonium ions, resulting in increasing solution pH. The steel could then easily repassivate, hence the corrosion potential and pitting potential would increase. However, the ammonium formation mechanism could not explain the decrease of corrosion potential in basic solution. Nitrogen enrichment at the metal/passive film interface with adsorption mechanism seemed to be an applicable consideration in increasing pitting potential. However, this mechanism did not involve the ammonium ion formation. In general, for the duplex and microduplex stainless steels tested, nitrogen increased the general corrosion resistances in acid solution and pitting corrosion resistance at all solution pH. Metallographic observation in both tested duplex and microduplex steels after pitting corrosion at all tested pH revealed that, the corroded structure in the tested steels without nitrogen alloying was austenite, but those with nitrogen alloying was ferrite. Even though ferrite had a higher chromium content than austenite but higher dissolved nitrogen in austenite than in ferrite may have increased the pitting resistance equivalent number (PRE) of austenite to be higher than that of ferrite. [Copyright &y& Elsevier]

The crystal orientation dependence on a surface damage in molybdenum mirror has been investigated under the irradiation with 3 keV helium ions to a fluence of 10 22 ions/m 2 . A strong correlation between the surface roughening and the grain orientation was confirmed from SEM–EBSD analysis. It was found that significant surface roughening including crater-like depressions is formed on the grain surfaces with crystalline planes close to (1 0 0), while relatively smooth surface remains on grains with the other directions. In contrast, the reflectivity measurement of the single crystal molybdenum with a spectroscopic ellipsometry showed smaller reduction in (1 0 0) sample than in (1 1 0) and (1 1 1) samples. The smallest helium desorption in (1 0 0) sample was also detected with thermal desorption spectroscopy in comparison with them in (1 1 0) and (1 1 1) samples, which indicates (1 1 0) and (1 1 1) samples include the large amount of defects acting as effective trapping site for He atoms. A cross-sectional TEM observation actually showed a relatively large bubbles at sub-surface regions of (1 1 0) sample. These results indicate that the optical reflectivity should be affected by not only a top surface profile but also internal radiation damages such as high density of helium bubbles. [ABSTRACT FROM AUTHOR]

Abstract: The change in morphology and substructure of α′ martensite with a volume change accompanying austenite (fcc) to martensite (bcc) transformation was studied using various Fe–Ni–Co alloys. The volume change accompanying martensitic transformation was decreased by the Invar effect of austenite with Co addition to the Fe–Ni binary alloys. In Fe–28Ni–20Co and Fe–24Ni–30Co (mass%) alloys, small and negative volume changes were established (−0.30% and −0.39%, respectively). With a decrease in volume change, the transition temperature of martensite morphology from lenticular to lath increases. The dislocation densities in martensite and austenite decrease as the volume change approaches zero. [Copyright &y& Elsevier]

Abstract: The effect of ausforming on formation of upper bainite structure was investigated in Fe–9Ni–(0.15–0.5)C (mass%) alloys, focusing on the crystallographic feature of bainitic ferrite. The specimens were ausformed at 1073 or 873K by 50% compressive reduction after austenitizing, and transformed at 623K. Lath-shaped upper bainite structures similar to lath martensite are formed at 623K. A bainite packet is partitioned into blocks of all the six variants of the K–S orientation relationship satisfying the same parallel close-packed plane relationship. In both of the non-ausformed and ausformed specimens, bainite blocks are coarsened with increasing carbon content. In the Fe–9Ni–0.15C alloy, the effect of ausforming on the bainite block width is small. For higher carbon alloys (Fe–9Ni–0.3C and 0.5C), bainite blocks are remarkably coarsened by the ausforming. In contrast, the ausforming refines lath martensite blocks in the Fe–9Ni–0.15C alloy but has a small effect in higher carbon alloys. [Copyright &y& Elsevier]