The Effects of Composition and Microstructure on the Reaction Behavior of MCrAlY Alloys Under a Variety of Aggressive Environmental Conditions

Cast alloys with compositions similar to those of MCrAlY overlay coatings, which are commonly deposited on Ni-base superalloys in the hot section of gas turbine engines, were exposed to a variety of aggressive conditions. The materials studied include (in wt%): Ni-31Cr-11.25Al-0.65Y, Co-23Cr-13Al-0.65Y, Ni-20Co-18Cr-12.5Al-0.6Y-0.4Hf-0.25Si, Ni-10Co-18Cr-12.5Al-0.6Y-0.4Hf-0.25Si, and Ni-10Co-27.1Cr-12.5Al-0.6Y-0.4Hf-0.25Si . The microstructures of the Ni-base alloys contained FCC γ-Ni (or γ′-Ni3Al, depending on temperature and composition), primitive cubic β-NiAl , and a Ni-rich yttride. BCC α-Cr was also present in some cases. The CoCrAlY contained HCP α-Co, β-CoAl, and a Co-rich yttride. The experimental conditions were: Type I and Type II hot corrosion, cyclic oxidation, and intermittent hot corrosion. The effects of alloy composition and microstructure on the resistance to these modes of degradation were determined using scanning electron microscopy and kinetic data. All alloys showed good resistance to Type I hot corrosion. Conversely, Type II hot corrosion was catastrophic in most cases; however, the coarse-grained NiCrAlY alloy demonstrated reasonably good resistance to Type II attack. When the microstructure was refined via injection casting, however, this alloy showed substantial degradation under Type II conditions. This was attributed partially to differences in the morphology and distribution of the α-Cr phase. The Type II hot corrosion resistance of a NiCoCrAlY alloy was improved by lowering the cobalt content and increasing the chromium content such that a coarse distribution of α-Cr was present in the microstructure. All alloys formed protective Al2O3 scales during cyclic oxidation at 1100°C, with the exception of the NiCrAlY, which showed scale spallation after short exposures. The oxidation resistance of this alloy improved with decreasing temperature. This behavior was explained in part by a phase transformation which results in a volume contraction upon cooling and thus acompressive stress in the oxide. This transformation, as well as other aspects of the phase equilibria in this NiCrAlY system, was examined experimentally, and the results were compared with thermodynamic predictions. No difference in oxidation behavior was observed when cyclic oxidation of the MCrAlY alloys was preceded by a Type I hot corrosion exposure. Conversely, the cyclic oxidation resistance of uncoated René N5 was substantially reduced by such an initial exposure

Partner Interference with Health Care: Do We Want One More Piece of a Complex Puzzle?

As I sit down to write, scattered images of former patients fill my mind: a well-educated, elderly woman presenting to the hospital 2 days after having a large myocardial infarction; a young diabetic woman with erratic blood glucose control; one of my colleague’s “frequent flyers” coming in to see me on a Friday afternoon, panicked, asking for yet another early refill of her hydrocodone; a very ill, middle-aged woman whose doting husband kept immaculate notes on her many medical issues and 12 medications. Each of these women has her own, complex story. Each had a partner who negatively interfered with her medical care

Assessment of the Factors Affecting Protective Alumina Formation Under Hot Corrosion Conditions

In this study, the influence of microstructure, composition, and phase constitution on the Type I (900°C) and Type II (700°C) hot corrosion resistance of MCrAlY and β-NiAl base alloys was investigated. The Type II hot corrosion resistance of MCrAlY alloys is generally enhanced by microstructural refinement. This can be attributed to the more rapid establishment of a protective Al2O3-rich scale due to the higher density of short-circuit diffusion paths for Al (phase boundaries). However, it was shown that for a given bulk composition, the compositions of the individual phases is also extremely important. If one phase is lean in an element which is highly beneficial from a hot corrosion standpoint, e.g., Cr, Type II hot corrosion resistance is quite poor, regardless of the microstructural scale. In addition, coarse reactive-element-rich phases, which are commonly found in MCrAlY alloys, can be incorporated into the thermally grown Al2O3 scale and act as initiation sites for Type II attack. This stresses the importance of reactive element content and distribution in MCrAlY coatings. During Type I hot corrosion exposure of β-Ni-36Al (at. %) base alloys, the incubation stage is greatly extended by the addition of 5% Pt, Co, or Cr. In each case, the beneficial effects can be linked to an enhanced ability to rapidly form a protective Al2O3 scale, and to heal this scale when it sustains damage during exposure. With regard to Type II hot corrosion, individual additions of 5 at. % Pt or Cr are beneficial, largely for the same reason; however, additions of 5 at. % Co and co-additions of 5 at. % Pt + 5 at. % Cr result in a decrease in the duration of the incubation stage. Subsurface phase transformations that occur in the latter systems prevent the alloy from maintaining the growth of the Al2O3 scale. This mechanism is discussed in detail. Finally, the influence of alloy composition and exposure environment on the kinetics of the θ⇒α Al2O3 transformation in scales grown on β-NiAl alloys at 900°C was thoroughly investigated. The relative importance of the kinetics of this transformation during Type I hot corrosion exposure is discussed

Family presence during resuscitation in paediatric and neonatal cardiac arrest : A systematic review

Context: Parent/family presence at pediatric resuscitations has been slow to become consistent practice in hospital settings and has not been universally implemented. A systematic review of the literature on family presence during pediatric and neonatal resuscitation has not been previously conducted. Objective: To conduct a systematic review of the published evidence related to family presence during pediatric and neonatal resuscitation. Data sources: Six major bibliographic databases was undertaken with defined search terms and including literature up to June 14, 2020. Study selection: 3200 titles were retrieved in the initial search; 36 ultimately included for review. Data extraction: Data was double extracted independently by two reviewers and confirmed with the review team. All eligible studies were either survey or interview-based and as such we turned to narrative systematic review methodology. Results: The authors identified two key sets of findings: first, parents/family members want to be offered the option to be present for their child's resuscitation. Secondly, health care provider attitudes varied widely (ranging from 15% to >85%), however, support for family presence increased with previous experience and level of seniority. Limitations: English language only; lack of randomized control trials; quality of the publications. Conclusions: Parents wish to be offered the opportunity to be present but opinions and perspectives on the family presence vary greatly among health care providers. This topic urgently needs high quality, comparative research to measure the actual impact of family presence on patient, family and staff outcomes.Peer reviewe

How children eat may contribute to rising levels of obesity children's eating behaviours: An intergenerational study of family influences

The term ‘obesogenic environment’ is rapidly becoming part of common phraseology. However, the influence of the family and the home environment on children's eating behaviours is little understood. Research that explores the impact of this micro environment and intergenerational influences affecting children's eating behaviours is long overdue. A qualitative, grounded theory approach, incorporating focus groups and semi-structured interviews, was used to investigate the family environment and specifically, the food culture of different generations within families. What emerged was a substantive theory based on ‘ordering of eating’ that explains differences in eating behaviours within and between families. Whereas at one time family eating was highly ordered and structured, typified by the grandparent generation, nowadays family eating behaviours are more haphazard and less ordered, evidenced by the way the current generation of children eat. Most importantly, in families with an obese child eating is less ordered compared with those families with a normal weight child. Ordering of eating' is a unique concept to emerge. It shows that an understanding of the eating process is crucial to the development and improvement of interventions targeted at addressing childhood obesity within the family context