Abstract
The plastic deformation behavior of single crystals of two transition-metal diborides, ZrB
2
and TiB
2
with the AlB
2
structure has been investigated at room temperature as a function of ...crystal orientation and specimen size by micropillar compression tests. Although plastic flow is not observed at all for their bulk single crystals at room temperature, plastic flow is successfully observed at room temperature by the operation of slip on {1
$${\bar{1}}$$
1
¯
00}<11
$${\bar{2}}$$
2
¯
3> in ZrB
2
and by the operation of slip on {1
$${\bar{1}}$$
1
¯
00} and {1
$${\bar{1}}$$
1
¯
00}<11
$${\bar{2}}$$
2
¯
0> in TiB
2
. Critical resolve shear stress values at room temperature are very high, exceeding 1 GPa for all observed slip systems; 3.01 GPa for {1
$${\bar{1}}$$
1
¯
00}<11
$${\bar{2}}$$
2
¯
3> slip in ZrB
2
and 1.72 GPa and 5.17 GPa, respectively for {1
$${\bar{1}}$$
1
¯
00} and {1
$${\bar{1}}$$
1
¯
00}<11
$${\bar{2}}$$
2
¯
0> slip in TiB
2
. The identified operative slip systems and their CRSS values are discussed in comparison with those identified in the corresponding bulk single crystals at high temperatures and those inferred from micro-hardness anisotropy in the early studies.
Graphite crucibles are used for melting uranium and its alloys in VIM furnace. Various coating materials namely Al2O3, ZrO2, MgO etc. are applied on the inner surface of the crucibles using paint ...brush or thermal spray technique to mitigate U-C interaction. These leads to significant amount of carbon pick-up in uranium. In this study, the attempts are made to develop multilayer coatings comprising of SiC/Y2O3 and Mo/Y2O3 on graphite to study the feasibility of minimizing U-C interaction. The parameters are optimized to prepare SiC coating of about 70μm thickness using CVD technique on graphite coupons and subsequently Y2O3 coating of about 250μm thickness using plasma spray technique. Molybdenum and Y2O3 layers were deposited using plasma spray technique with 70μm and 250μm thickness, respectively. Interaction studies of the coated graphite with molten uranium at 1450°C for 20 min revealed that Y2O3 coating with SiC interlayer provides physical barrier for uranium-graphite interaction, however, this led to the physical separation of coating layer. Y2O3 coating with Mo interlayer provided superior barrier effect showing no degradation and the coatings remained intact after interaction tests. Therefore, the Mo/Y2O3 coating was found to be a promising solution for minimizing carbon pick-up during uranium/uranium alloy melting.
•Pack-siliconizing of Mo–Si–B alloy improves its oxidation resistance at 750, 900 and 1400°C.•A marginal weight change of the coated alloy is detected in isothermal and cyclic oxidation ...tests.•Kinetics of growth of protective SiO2 scale is much faster at 1400°C.•Self-healing SiO2 is developed at the cracks formed in MoSi2 layer during cyclic oxidation tests.
Oxidation behaviour of MoSi2 coated Mo–9Si–8B–0.75Y (at.%) alloy has been investigated at three critical temperatures including 750, 900 and 1400°C in static air. Thermogravimetric analysis (TGA) data indicates a remarkable improvement in the oxidation resistance of the silicide coated alloy in both isothermal and cyclic oxidation tests. The cross-sectional scanning electron microscopy and energy dispersive spectroscopic analysis reveal the occurrence of internal oxidation particularly at the crack fronts formed in the outer MoSi2 layer during thermal cycling. The dominant oxidation mechanisms at 750–900°C and 1400°C are identified. Development of MoB inner layer further improves the oxidation resistance of the silicide coated alloy.
Iron aluminide-based oxidation-resistant and permeation barrier coatings were formed on P91 steel using pack cementation and post-coating annealing treatment. Fe
2
Al
5
layers of variable thicknesses ...were formed at the coating temperatures in the range of 600–700 °C. The as-coated alloy annealed at 625–750 °C for different duration revealed the formation of multilayered coating structure that consisted of FeAl
2
, FeAl and Fe(Al) phases of varying thicknesses. Knoop hardness of Fe
2
Al
5
phases was found to be 700 HK. High-resolution nanoindentation mappings were carried out for heat-treated specimen to establish structure–property interlink at the micron length scale. Hardness and modulus maps were generated using large numbers of arrays of nanoindentations at intervals of 2 µm. Scratch tests performed at varying loads revealed superior scratch resistance of FeAl as compared to Fe
2
Al
5
phase. Oxidation studies under pure O
2
environment of as-coated alloy in the temperature range of 700–1000 °C for 8 h revealed the parabolic growth of alumina scale.
In the present work, a novel refractory multi-principal element alloy (Mo98W2)85Nb10(TiHf)5 was developed through comprehensive material testing, including high-temperature exposure and oxidation ...resistance assessments. It was found that after pack siliconizing, the samples could withstand high temperatures up to 1300 °C with a marginal weight change of 0.255 mg/cm2 during four hours holding time. The overall activation energy for the coating process was found to be 123 kJ/mol, which is a consequence of the decreased atomic mobility of silicon and other atoms to overcome sluggish diffusion phenomena. Minor addition of hafnium created a peg effect in the outer silica scale, which improved its oxidation resistance covering coating cracks. The findings of this research provide valuable insights into the potential applications of such alloys with silicide coatings in high-temperature environments, such as aerospace, energy, and high-temperature manufacturing processes.
Display omitted
Myositis is one of the uncommon adverse events following COVID‐19 vaccination, and its mechanism is still unclear. A strong clinical suspicion and further evaluation are important not only for early ...diagnosis and management but also for better understanding of the unprecedented effects of this novel vaccine. We present a case of myositis following the first dose of the ChAdOx1 nCoV‐19 Corona Virus Vaccine, evidenced by serology and MRI.
COVID‐19 vaccine‐associated myositis. Coronal short tau inversion recovery magnetic resonance (STIR MR) images of left arm (A and B) showing edema in the deltoid muscle with adjacent perifascial fluid.
Two alloys of compositions Mo-26Nb-19Si and Mo-26Nb-19Si-0.5Y (at.%) were prepared by non-consumable arc melting. The alloys characterized using BSE, EDS and EBSD techniques confirmed the formation ...of two phase (Mo, Nb)SS-(Mo, Nb)5Si3 microstructures. Y-rich (Y2O3) particles were mainly found to be present at the inter-phase boundaries creating different phase morphologies in Mo-26Nb-19Si-0.5Y alloy. Both the phases showed a preferred orientation indicating a directional growth during solidification. Oxidation tests conducted in air at 1000 and 1300 °C showed a porous oxide scale formation on the alloy surface and loss of material due to evaporation of MoO3. The detailed SEM-EDS analysis of the oxide scale formed on these alloys in argon environment at 1000 °C, indicated the presence of Nb2O5 particles in the silica (SiO2) matrix.
•Two phase (Mo, Nb)SS – (Mo, Nb)5Si3 microstructure was established in Nb added Mo-Nb-Si alloy.•Minor Y alloying led to morphological changes in two phase microstructure.•Solidification texture was identified in as cast microstructure.•Oxidation tests revealed formation of mixed oxide SiO2-Nb2O5 layer on the alloy surface.•Oxidation behaviour showed a dependence on the grain morphologies in the microstructure.
High-temperature oxidation behaviour of Mo-40Ti-30Si (at.%) alloy was investigated in the temperature regime of 900-1300
C in air. Isothermal weight change data recorded up to 100 h of exposure ...revealed parabolic weight gain kinetics at all the tested temperatures. The protective oxide scale composed with SiO
(silica) and TiO
(titania) forming a duplex oxide microstructure consisting of TiO
particles embedded in the continuous SiO
matrix. The oxide scale showed parabolic growth kinetics, and the activation energies for the scale growth were found to be 72.2 kJ/mol in 900-1200
C and 324.9 kJ/mol in 1200-1300
C. The kinetics of the protective scale growth on the alloy surface was mainly controlled by the growth of the silica film and the inward diffusion of oxygen through the duplex oxide layer.
Chest CT can provide a simple quantitative assessment of the extent of the parenchymal opacities in COVID-19 patients. In this study, we postulate that CT findings can be used to ascertain the ...overall disease burden and predict the clinical outcome.
In this prospective study undertaken from March 28, 2020, until May 20, 2020, 142 patients with CT features suggestive of viral pneumonia, and positive RT-PCR for COVID-19 were enrolled. A dedicated spiral CT scanner was used for all COVID-19 suspects. CT features were reported as typical, indeterminate, or atypical for COVID-19 pneumonia. A CT involvement score (CT-IS) was given to each scan and assigned mild, moderate, or severe category depending on the score range. The patients were followed up for at least 15 days.
Ground glass opacity was present in 100% of the patients. There was a significant association between CT-IS and the final outcome of the patients. A statistically significant increasing trend of mortality and requirement of critical medical attention was observed with the rising value of CT-IS in COVID-19.
The severe CT-IS score group has a high mortality. The CT-IS score could be valuable in predicting clinical outcome and could also be useful in triage of patients needing hospital admission. In situations where healthcare resources are limited, and patient load high, a more careful approach for patients with higher CT-IS scores could be indispensable.
CT-IS is a simple quantitative method for assessing the disease burden of COVID-19 cases. It can be invaluable in places with limited resources and high patient load to segregate patients requiring critical medical attention.
Development of a suitable iron aluminide coating layer on 9Cr-Mo (P91 grade) steel at or below 750 °C finds importance for improving its oxidation and corrosion behaviour while retaining the tempered ...ferritic-martensitic microstructure. A theoretical model to predict the kinetics has been developed for correlating growth of the aluminide coating on P91 steel substrate with process parameters of pack aluminizing. Experiments were conducted by varying the pack Al (2–10 wt%) and activator NH4Cl (2–8 wt%) content, temperature (600–700 °C), and time (2-16 h). The coating formation results obtained from the experiments authenticated the validity of the proposed model. The coating mainly consisted of single Fe2Al5 phase. The activation energy for Fe2Al5 formation during pack aluminizing was calculated to be 95 ± 7 kJ mol−1. Interdiffusion studies between Fe2Al5/steel in 550–750 °C with varying times of 8–40 h revealed the formations of FeAl2, FeAl, and Fe(Al) layers of different thicknesses. The diffusional growth of the most desired FeAl aluminide found to follow the parabolic kinetics and the activation energy for the growth of FeAl was calculated to be 237.5 kJ mol−1. Scanning electron microscopic and electron back scattered diffraction analysis revealed the formation of columnar grains in B2-FeAl layer.
PDF
