Nanostructure characterisation of flow-formed Cr–Mo–V steel using transmission Kikuchi diffraction technique

Birosca, S.; Ding, Rengen; Ooi, S. W.; Buckingham, R. C.; Coleman, Costa; Dicks, Keith

doi:10.1016/j.ultramic.2015.02.001

Cited by 16 publications

(11 citation statements)

References 27 publications

(45 reference statements)

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“…All TKD and EBSD scans were performed using a Jeol JSM-7800F Field Emission Gun Scanning Electron Microscope (FEG-SEM) with Nordlys Nano hardware and AZtec 2.1 software package that acquire TKD, EBSD and Energy Dispersive X-ray Spectroscopy (EDS) data. The same TKD procedure, detailed in Birosca et al, 2015, was used here. TEM foil was mounted using a microclamp SEM sub-stage which was fixed to a standard 70º tilted EBSD sample holder.…”

Section: Transmission Kikuchi Diffraction (Tkd)mentioning

confidence: 99%

“…However, the DP quality and indexing rate reduced to less than 50% beyond 7.2 microns and 0% after 8.6 microns away from TEM foil perforation edge, see the distorted and diffused diffraction pattern at 8.6 micron in the same figure. Birosca et al, 2015, reported that the sharpest DPs can be obtained where the TEM foil thickness was ~100 nm. It seems that the thickness of TEM foil at 8.6 microns was much thicker than 100 nm in the current study.…”

Section: Transmission Kikuchi Diffraction (Tkd) Characterisationsmentioning

confidence: 99%

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The dislocation behaviour and GND development in a nickel based superalloy during creep

Birosca

Liu

Ding

et al. 2019

International Journal of Plasticity

144

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In the current study, dislocation activity and storage during creep deformation in a nickel based superalloy (Waspaloy) was investigated, focussing on the storage of geometrically necessary (GND) and statistically stored (SSD) dislocations. Two methods of GND density calculations were used, namely; EBSD Hough Transformation and HR-EBSD Cross Correlation based methods. The storage of dislocations, including SSDs, was investigated by means of TEM imaging. Here, the concept of GND accumulation in soft and hard grains and the effect of neighbouring grain orientation on total dislocation density was examined. Furthermore, the influence of applied stress (below and above Waspaloy yield stress) during creep on deformation micro-mechanism and dislocation density was studied. It was demonstrated that soft grains provided pure shear conditions at least on two octahedral (111) slips for easy dislocation movement reaching the grain boundary without significant geometrically necessary accumulation in the centre of the grain. Hence, the majority of the soft grains appeared to have minimum GND density in the centre of the grain with high GND accumulation in the vicinity of the grain boundaries. However, the values and width of accumulated GND depended on the surrounding grain orientations. Furthermore, it was shown that the hard grains were not favourably oriented for octahedral slip system activation leading to a grain rotation in order to activate any of the available slip systems. Eventually, (i) the hard grain resistance to deformation and (ii) neighbouring grain resistance for the hard grain reorientation caused high GND density on a number of octahedral (111) slip systems. The results also showed that during creep below the yield stress of Waspaloy (500 MPa/700C), the GND accumulation was relatively low due to insufficient microscopic stress level. However, the regions near grain boundaries showed high GND density.Whereas, in addition to the movement of pre-existing dislocations (SSD and GND) at higher mobility rate under 800 MPa/700C above yield creep condition, large numbers of dislocations were generated and moved toward the grain boundaries. This resulted in much higher GND density but narrower width of high intensity GND near the grain boundaries. It is concluded that although GND measurement by means of EBSD can provide a great insight of dislocation accumulation and its behaviour, it is critical however to consider SSD type which is also contributes to the strain hardening of the materials.

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Section: Transmission Kikuchi Diffraction (Tkd)mentioning

confidence: 99%

Section: Transmission Kikuchi Diffraction (Tkd) Characterisationsmentioning

confidence: 99%

The dislocation behaviour and GND development in a nickel based superalloy during creep

Birosca

Liu

Ding

et al. 2019

International Journal of Plasticity

144

View full text Add to dashboard Cite

show abstract

“…Tempered lath martensite and deformed microstructures were obtained after the heat treatment. In the case of tempering, the austenite phase transformation does not occur, so some deformed microstructure remains [21]. On the other hand, the deformed microstructure transforms into an austenitic structure by heating at the phase transformation temperature (Ac 3 , the temperature at which the α-to-γ transformation commences) or higher temperatures under the normalized condition [22].…”

Section: Discussionmentioning

confidence: 99%

Influence of Heat Treatment on the Workability of Modified 9Cr-2W Steel with Higher B Content

Heo

Kim

et al. 2019

Metals

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In this study, the effect of heat treatment on the fracture behavior of alloy B steel with boron (B) contents as high as 130 ppm was investigated. The Alloy B are derived from Gr.92 steel with outstanding creep characteristics. The amounts of minor alloying elements such as B, N, Nb, Ta, and C were optimized to achieve better mechanical properties at high temperatures. Hence, workability of the alloy B and Gr.92 were compared. An increase in the B content affected the phase transformation temperature and texture of the steel. The development of the {111}<uvw> components in γ-fibers depended on the austenite fraction of the steel after the phase transformation. An increase in the B content of the steel increased its α-to-γ phase transformation temperature, thus preventing the occurrence of sufficient transformation under the normalizing condition. Cracks occurred at the point of the elastic-to-plastic deformation transition in the normal direction during the rolling process, thereby resulting in failure. Therefore, it is necessary to avoid intermediate heat treatment conditions, in which γ-fibers do not fully develop, i.e., to avoid an imperfect normalization.

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“…As shown in Figures 3 and 4 Morpholoiges after the different heat treatment conditions are classified into tempered lath martensite structure and deformed structure. Since the morphologies of tempering heat treatment conditions that the austenite phase transformation did not occur, the deformed structure was remained [20]. On the other hand, the deformed microstructure was transformed into an austenitic structure by heating at the Ar3 (the temperature at which the α to γ transformation commences on heating) transformation point or higher in the normalized condition [21].…”

Section: Discussionmentioning

confidence: 99%

Influence of Heat Treatment on the Workability of Modified 9Cr-2W Steel with Higher B Content

Heo¹,

Kim²,

Kim³

et al. 2019

Preprint

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In this study, the effect of heat treatment was investigated to influence the occurrence of fracture during manufacturing process of Alloy B steel with boron contents as high as 130 ppm. As the content of boron increases, it affects the phase transformation temperature and texture. The development of {111} components in the γ-fiber is affected depending on the austenite fraction after phase transformation. The Alloy B steel indicated that the increase in the boron content increased the α to γ phase transformation temperature such that sufficient transformation did not occur in the normalizing condition. The cracks occurred at the point of the transition from elastic to plastic deformation in the ND direction during the rolling process, thereby resulting in failure.Therefore, it is necessary to avoid the intermediate heat treatment condition in which γ-fiber does not fully develop, i.e., an imperfect normalization. IntroductionNuclear power generation plays a key role in the Korea energy with low costs of raw materials and excellent base load capacity, however its enlargement is limited due to problem of spent nuclear fuel after operation. To solve these problems, it is necessary to develop an innovative nuclear power plant which can contribute to sustainable development, environmental protection and preparation for rapidly increasing energy consumption [1,2].Recently, research has carried out to develop sodium cooled fast reactor (SFR) because it has many advantages in terms of economic efficiency, stability, nuclear non-proliferation and reducing the emission of spent nuclear fuel. It is designed to operate at temperature much higher than those in light water reactors and to improve thermal efficiency [3][4][5][6][7]. Nuclear fuel cladding tube which transfers efficient the fission energy and confines nuclear fuel rod and fissile material is a main component. Hence, the development of fuel cladding tube is essential as it is the most important component directly related to the safety of nuclear reactor.Ferritic-martensitic (FM) steels have been considered as fuel cladding and duct materials for a SFR owing to their high thermal conductivities, low expansion coefficients and superior irradiation swelling compared to austenitic steel [8][9][10]. However, the creep rupture strength of FM steels abruptly decreases during long term creep exposure at high temperature [11]. An advanced FM steel alloy was developed on the basis of Gr.92 steel. Minor alloying elements such as B, N, Nb, Ta, and C Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 16

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Nanostructure characterisation of flow-formed Cr–Mo–V steel using transmission Kikuchi diffraction technique

Cited by 16 publications

References 27 publications

The dislocation behaviour and GND development in a nickel based superalloy during creep

The dislocation behaviour and GND development in a nickel based superalloy during creep

Influence of Heat Treatment on the Workability of Modified 9Cr-2W Steel with Higher B Content

Influence of Heat Treatment on the Workability of Modified 9Cr-2W Steel with Higher B Content

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