Phase transformations in (111) Si after spherical indentation

Phase transformations in (111) Si after spherical indentation have been investigated by cross-sectional transmission electron microscopy. Even at an indentation load of 20 mN,a phase transformation zone including the high-pressure crystalline Si phases was observed within the residual imprints. The volume of the transformation zone, as well as that of the crystalline phases increased with the indentation load. Below the transformation zone, slip was found to occur on {311} planes rather than on {111}planes, usually observed on indentation of (100) Si. The distribution of defects was asymmetric, and for indentation loads up to 80 mN, their density was significantly lower than that reported for (100) Si. The experimental observations correlated well with modeling of the applied stress through ELASTICA

PANC Study (Pancreatitis: A National Cohort Study): national cohort study examining the first 30 days from presentation of acute pancreatitis in the UK

Abstract Background Acute pancreatitis is a common, yet complex, emergency surgical presentation. Multiple guidelines exist and management can vary significantly. The aim of this first UK, multicentre, prospective cohort study was to assess the variation in management of acute pancreatitis to guide resource planning and optimize treatment. Methods All patients aged greater than or equal to 18 years presenting with acute pancreatitis, as per the Atlanta criteria, from March to April 2021 were eligible for inclusion and followed up for 30 days. Anonymized data were uploaded to a secure electronic database in line with local governance approvals. Results A total of 113 hospitals contributed data on 2580 patients, with an equal sex distribution and a mean age of 57 years. The aetiology was gallstones in 50.6 per cent, with idiopathic the next most common (22.4 per cent). In addition to the 7.6 per cent with a diagnosis of chronic pancreatitis, 20.1 per cent of patients had a previous episode of acute pancreatitis. One in 20 patients were classed as having severe pancreatitis, as per the Atlanta criteria. The overall mortality rate was 2.3 per cent at 30 days, but rose to one in three in the severe group. Predictors of death included male sex, increased age, and frailty; previous acute pancreatitis and gallstones as aetiologies were protective. Smoking status and body mass index did not affect death. Conclusion Most patients presenting with acute pancreatitis have a mild, self-limiting disease. Rates of patients with idiopathic pancreatitis are high. Recurrent attacks of pancreatitis are common, but are likely to have reduced risk of death on subsequent admissions. </jats:sec

Berkovich indentation of diamondlike carbon coatings on silicon substrates

The deformation behavior of diamondlike carbon (DLC) coatings on silicon substrates induced by Berkovich indentation has been investigated. DLC coatings deposited by a plasma-assisted chemical vapor deposition technique were subjected to nanoindentation with a Berkovich indenter over a range of maximum loads from 100 to 300 mN. Distinct pop-ins were observed for loads greater than 150 mN. However, no pop-out was observed for the loads studied. The top surface of the indents showed annular cracks with associated fragmented material. The cross sections showed up to 20% localized reduction in thickness of the DLC coating beneath the indenter tip. Cracking, {111} slip, stacking faults, and localized phase transformations were observed in the silicon substrate. The discontinuities in the load-displacement curves at low loads are attributed to plastic deformation of the silicon substrate, whereas at higher loads they are attributed to plastic deformation as well as phase transformation

Correlation of nanoindentation-induced deformation microstructures in diamondlike carbon coatings on silicon substrates with simulation studies

The effect of the presence of diamondlike carbon coatings deposited on (100) Si substrateson the deformation mechanisms operating in the silicon substrate during contact loadinghave been investigated by both cross-sectional transmission electron microscopy andmodeling of the stresses generated beneath the indenter tip. The observed subsurfacemicrostructures were correlated to the Tresca shear stress and the hydrostatic stressgenerated in the silicon substrate beneath the indenter tip. The presence of the coatingaltered the stresses generated in the substrate, and changed the deformation mechanismfrom one of principally phase transformation in uncoated Si to predominantly dislocationmotion in the silicon substrate for the diamondlike C¿Si system. The magnitude anddistribution of the shear and hydrostatic stresses in the substrate were found to depend onboth the indentation load and the thickness of the coating. Furthermore, the observedwidth of deformation, parallel to the interface, which was found to increase with coatingthickness, was correlated to the wider distribution of the Tresca shear stress in thesubstrate brought about by the presence of the coating

Effect of microstructure and composition on hydrogen permeation in X70 pipeline steels

The influence of microstructure and composition on permeation of hydrogen in 1.2 and 0.5 wt.% Mn X70 pipeline steels after different processing was investigated using an electrochemical permeation technique. For 1.2 wt.% Mn (standard Mn) steel, the microstructure of normalised transfer bar was coarse equiaxed ferrite grains. This sample exhibited the highest diffusivity, followed by transfer bar, with a mixed ferriteebainitic ferrite microstructure; and hot rolled strip, with fine elongated ferrite grains. The 0.5 wt.% Mn (medium Mn) strip displayed lower diffusivity than the 1.2 wt.% Mn strip, due to hydrogen trapping by finer ferrite grains and a higher density of carbonitride precipitates. Moreover, the medium Mn strip exhibited a uniform microstructure and consequently similar diffusion coefficients for the edge and centreline regions, whereas the finer grains of the edge region of the standard Mn strip resulted in a lower diffusivity than the centreline region. Copyright © 2012, Hydrogen Energy Publications, LLC

Role of microstructure in susceptibility of X70 pipeline steel to hydrogen embrittlement

In order to investigate the susceptibility of steels to hydrogen embrittlement as a function of their microstructure X70 steel was chosen in different conditions: normalized transfer bar, as-received hot rolled strip and heat affected zone (HAZ). Notched and fatigue pre-cracked samples were subjected to electrochemical hydrogen charging to achieve 2 ppm hydrogen content. Three point bend tests were conducted on as-received and hydrogen charged samples. The results showed that HAZ samples are more susceptible to hydrogen embrittlement than the others. This was supported by fracture surface observations

Nanoindentation-induced deformation behaviour of tetrahedral amorphous carbon coating deposited by filtered cathodic vacuum arc

The nanoindentation-induced deformation behaviour of a ta-C (tetrahedral amorphous carbon) coating deposited on to a silicon substrate by a filtered vacuum cathodic vapour arc technique was investigated. The 0.17-μm-thick ta-C coating was subjected to nanoindentation with a spherical indenter and the residual indents were examined by cross-sectional transmission electron microscopy. The hard (~ 30 GPa) ta-C coatings exhibited very little localized plastic compression, unlike the softer amorphous carbon coatings deposited by plasma-assisted chemical vapour deposition. However, neither through-thickness cracks nor delamination was observed in the coating for the loads studied. Rather, the silicon substrate exhibited plastic deformation for indentation loads as low as 10 mN and at higher loads it showed evidence of both phase transformation and cracking. These microstructural features were correlated to the observed discontinuities in the load-displacement curves. Further, it was observed that even a very thin coating can modify the primary deformation mechanism from phase transformation in uncoated Si to predominantly plastic deformation in the underlying substrate

Effect of coating thickness on the deformation behaviour of diamond-like carbon silicon system

The effect of coating thickness on the deformation behaviour of diamond-like carbon (DLC) coatings on silicon substrates was investigated. Following nanoindentation of a 0.6 µm thick DLC coating, the subsurface microstructures were characterized and the data was compared to prior studies on a similar, but thicker coating. Indentation resulted in localized plastic compression in the coating without any through-thickness cracking. It was shown that the discontinuities in the load–displacement curves appeared at lower loads for the thinner coating. Accordingly, the silicon substrate exhibited cracking, plastic deformation and phase transformation at significantly lower loads than in the case of the thicker coating. Further, the widths, parallel to the interface, over which slip and the phase transformation zone are spread out in the substrate, was found to increase with the thickness of the coating. The mechanism responsible for the first pop-in was found to change from phase transformation in uncoated silicon to dislocation nucleation in the presence of the coating