Interstitial-free steel workpieces are deformed by equal-channel angular pressing (ECAP) for equivalent strain ε
vm
= 3 and ε
vm
= 21 followed by flash annealing. Microstructures are analyzed by ...optical microscopy, scanning electron microscopy and transmission electron microscopy. Mechanical properties are evaluated by hardness testing. Yield strength of materials is calculated from hardness values. Flash annealing (at 675 °C) of ECAPed samples for ε
vm
= 3 and ε
vm
= 21 results in abnormal subgrain growth and abnormal grain growth, respectively. Flash annealing at 700 °C of ECAPed (at ε
vm
= 3) IF steel converts abnormally grown subgrains to grains which serve as nuclei for recrystallization and that result in bimodal grain size distribution. Bimodal grain size distribution is also produced when ECAPed IF steel for ε
vm
= 21 is flash annealed at 675 °C due to abnormal grain growth or secondary recrystallization. Flash annealing of IF steel samples ECAPed for low ε
vm
, in the temperature range 600-675 °C, decreases the hardness continuously with increase in the annealing temperature but it increases at high ε
vm
. The former is due to annihilation of defects but the later is caused by ordering of nonequilibrium boundaries. The hardening and strengthening behaviors are similar.
In the present paper, the effect of symmetrical and asymmetrical bell-shaped stenoses on wall pressure drop, streamline contour, and rise in wall shear stress for the progression of the disease, ...atherosclerosis has been investigated numerically. The governing equations have been solved by finite volume method. Both steady and pulsatile flow at inlet is considered in our study. It is revealed from the study that the impact of wall pressure and peak wall shear stress on progression of disease are always high for asymmetrical shaped stenosis for both steady and pulsatile flow. The impact of asymmetrical shape on plaque deposition zone is less, if the aggravation changes the shape of stenosis due to change in stricture length only keeping percentage of restriction same. Whereas, the impact of asymmetrical shape on plaque deposition zone will be high, if shape of stenosis changes by increasing both stricture length and percentage of restriction for both steady and pulsatile flow. Impact of pulsatile nature of flow on the aggravation of disease is higher at some timesteps in comparison to steady flow.
Equal-channel angular pressing (ECAP) of interstitial-free (IF) steel at equivalent strain, ε
vm
= 12 has been employed to develop ultrafine-grained (UFG) microstructure with high fraction of low ...angle grain boundaries, that enhances strength significantly with reduced tensile ductility. ECAPed IF steel has been deformed further by cold rolling/cryorolling at −50 °C to >90 % reduction in area. It is observed that the UFG structure gets refined with an improvement in high angle grain boundary fraction and heavily stressed non-equilibrium grain boundaries in cryorolled state resulting in significant strengthening. However, the decrease in grain size to an ultrafine level with the increased lattice strain lowers the work hardening ability of the material that limits its ductility. Hence, the rolled samples are flash annealed at 675 °C in order to recover the ductility of the material by achieving partially recrystallized structures. Consequently, the increased subgrain size as well as the grain size, the reduced residual lattice strain, lower hardness and strength with marginal recovery of ductility is maintained in order to attain the yield strength 2–3 times compared to that of as-received coarse-grained IF steel.
A newly designed composition of non-equiatomic Fe.sub.40Cr.sub.25Ni.sub.15Al.sub.15Co.sub.5 medium-entropy alloy (MEA) was produced by induction melting (IM). The as-cast alloy was found to consist ...of a two-phase microstructure of BCC (2.87 + or - 0.01 A) and ordered B2 (2.88 + or - 0.02 A) type phases. The structures of these phases were confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It was observed that the Ni-Al-enriched ordered B2 phase of cuboidal shapes (~ 100 to 200 nm) is homogeneously distributed in Fe-Cr-rich BCC matrix with a cube-on-cube orientation relationship. The formation of the columnar dendrites (width 50 to 100 microm) was identified through optical microscopy (OM). The structural and microstructural stability of the alloy was investigated by heat-treating the alloy through different schedules. Heat-treated samples at different temperatures (< 1273 K) exhibit a similar type of two-phase microstructure with columnar dendrites. However, compositional rearrangement takes place during long time exposure to develop polymorphically related phases. The alloy was observed to possess a high compressive yield strength and hardness, i.e., ~ 1047 MPa and 391 + or - 9 HV, respectively, at room temperature. Heat-treated samples at 600 degreesC and 900 degreesC (873 K and 1173 K) showed an increase in yield strength and ultimate strength with a significant increase in plasticity due to the increase in volume fraction of B2 phase and softening of the BCC matrix phase. The thermal stability and high strength of this alloy may open new avenues for high-temperature applications. Author Affiliation: (1) Department of Metallurgical Engineering, Indian Institute of Technology (BHU), 221005, Varanasi, India (a) vikas.rs.met13@itbhu.ac.in Article History: Registration Date: 02/12/2021 Received Date: 04/29/2020 Accepted Date: 02/07/2021 Online Date: 03/10/2021 Byline:
An as-cast ingot was used for rapid solidification and high energy ball milling in order to synthesize amorphous and/or nanocrystalline (Al4Cu9)94.5Cr5.5 gamma-brass alloy. Microstructure of the ...milled product has been characterized by X-ray diffraction, differential scanning calorimetry, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Rapid solidification by melt spinning produces nanocrystalline aggregate of size 40 nm and mechanical milling of the alloy up to 50 h yields a composite microstructure comprising of amorphous and nanocrystalline phases, with crystallite size in the range of 15-25 nm. No other metastable phases have been identified. Attempts have been made to understand the possibility of formation of amorphous phase through mechanical milling using semi-empirical model of Miedema.
Iron-rich and highly ordered 2D-hexagonal mesoporous ferrisilicates containing predominantly tetrahedrally coordinated Fe3+ in the silica network have been prepared using cetyltrimethylammonium ...bromide (CTAB) as the structure-directing agent (SDA) under mild alkaline hydrothermal conditions (initial pH = 8−8.5 in the synthesis gel). The optimum limit of iron loading for the ordered mesophase in the present study was 8.2 wt %; beyond this limit, disordered iron oxide/silica phase was observed in the same pH range. These mesoporous ferrisilicate samples were characterized using XRD, N2 sorption, EPR, SEM-EDX, TEM, FT-IR and UV−visible spectroscopies, and Mössbauer measurements. The average pore diameters were 2.2−2.8 nm, and the mesopore volumes were 0.39−0.5 cm3g-1. Moderately high Brønsted acidity was observed in the temperature-programmed desorption (TPD) pattern of ammonia over these mesoporous ferrisilicate materials. Wet chemical analysis, EPR, and Mössbauer spectroscopic data suggested that most of the iron species are tetrahedrally coordinated Fe3+ attached to the silica framework.
Ferritic stainless steel (FSS 430) has been deformed by equal-channel angular pressing (ECAP) at room temperature at an equivalent strain (
ε
vm
) of 1.2 by adopting the route B
c
. Microstructural ...developments were studied by optical microscopy, transmission electron microscopy, and microtexture by electron backscattered diffraction. Typical ultrafine-grains of less 0.2 µm could be identified. The XRD patterns confirm the presence of a BCC phase alone. An increase in peak broadening is attributed to the reduction of crystallite size and increase of lattice strain arising from deformation during ECAP. The grain refinement takes place through simple shear deformation by elongation of grains, splitting of grains into bands, the subdivision of bands into subgrains by dynamic recovery, and conversion of subgrains into grains by progressive lattice rotation (PLR). Weakly textured rolled ferritic stainless steel is strongly textured at an imposed equivalent strain of 0.6 with the development of ideal shear components of
D
2
θ
and
E
¯
θ
for bcc materials. On the second pass of ECAP texture is partially randomized and the intensity of components was decreased and new components of
D
1
θ
and
F
θ
are developed due to subdivision of grains into bands, bands into subgrains, and conversion of subgrains into grains of high angle of misorientation by PLR. The yield strength, tensile strength, and hardness are increased almost 1.5 times that of as-received coarse-grained material due to a high degree of grain refinement and an increase in defect density or strain. The yield strength of 687 MPa of as-received material was enhanced to 1093 MPa of ECAPed ferritic stainless steel. However, the material has lost its ductility significantly due to high defect density and a significant amount of non-equilibrium nature of grain boundaries.
The yttria was dispersed in 316L austenitic stainless steel powders processed by mechanical alloying (MA), and subsequently, the oxide dispersed strengthened (ODS) alloy powders were sintered by ...spark plasma sintering (SPS). Phase and microstructural evolutions were examined by x-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The 25 h milled sample with 2 wt.% yttria showed the formation of a single-phase FCC structure. The SPSed alloys showed the re-precipitation of yttria from the austenitic matrix. Relative density of more than 95% was achieved in SPSed samples containing 0.5, 1.5, and 2 wt.% yttria dispersion. The dispersion of yttria has shown a profound effect on the mechanical properties by restricting the grain growth kinetics in the sintered samples. The SPSed sample of 2 wt.% yttria has shown a high value of microhardness of ~ 6.9 GPa, which can be attributed to the dispersion of nano-yttria in the austenitic matrix. The impression creep results showed the primary and steady-state creep behavior for all alloy compositions. Differences in the creep behavior were observed due to the dispersion (0.5, 1.5, and 2 wt.%) of yttria, which affects the microstructure.
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