Thermal barrier coating systems offer oxidation protection to alloy substrates under heat flux conditions. They consist of an yttria-stabilised zirconia top coat, of low thermal conductivity, bonded to the alloy substrate by an alumina-forming metallic layer. These systems develop considerable strain energy during cooling and are mechanically unstable. The failure by spallation of the top coat is a life-limiting event but its prediction has proved a difficult problem. The growth of the alumina layer on the bond coat surface has been implicated in the failure of the TBC system but complete understanding remains elusive. In this paper, finite-element computations are presented of the out-of-plane stresses that develop both isothermally and during cooling, as a result of oxide growth. A novel feature of the calculations is that oxide thickening and the associated volume expansion are modelled within the computation. It is shown that continuity strains can lead to the development of out-of-plane stresses at the base of the top coat at the oxidation temperature. These are associated with bond coat protuberances and their magnitude increases with surface roughness. The situation will be exacerbated if Al depletion is sufficient to trigger chemical failure and the formation of faster-growing Cr,Ni-rich oxides at bond coat protuberances. In this case, large (> 0.5 GPa) out-of-plane tensile stresses can develop within the top coat at the test temperature for realistic surface roughnesses.

1. Introduction 2. Aging, illness, and addiction 3. The exacerbation of personality: Woodrow Wilson 4. Leading while dying: Franklin Delano Roosevelt, 1943-45 5. Addicted to power: John F. Kennedy 6. Richard Nixon: bordering on sanity 7. 25th Amendment 8. Presidential care.

Picture quizPicture quizD LL Cochlin, K C Potter, H Evans, U Patel, D Svasti-Salee, C J Wilkins, P S Sidhu, E Simpson, C Allen, G Rottenberg, J Eaton and J RichenbergD LL Cochlin1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, K C Potter1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, H Evans1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, U Patel1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, D Svasti-Salee1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, C J Wilkins1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, P S Sidhu1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, E Simpson1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, C Allen1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, G Rottenberg1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author, J Eaton1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this author and J Richenberg1Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, 2Department of Radiology, St George's Hospital, London SW17 0QT, 3Department of Radiology, King's College Hospital, Denmark Hill, London SE5 9RS, 4Department of Radiology, University College London Hospitals, London, 5Department of Radiology, Guy's Hospital, St Thomas' Street, London SE1 9RT, 6Departments of Urology and 7Imaging, The Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UKSearch for more papers by this authorPublished Online:28 Jan 2014https://doi.org/10.1259/imaging/12170461SectionsPDF/EPUBFull Text ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail About Previous article Next article FiguresReferencesRelatedDetails Volume 17, Issue 2October 2005Pages: 91-viii © The British Institute of Radiology History Published onlineJanuary 28,2014 Metrics Download PDF

The zonal anatomy determines disease distribution. Cancer is principally a peripheral zone disease and benign prostatic hyperplasia affects the transition zone.Prostate diseases can affect urinary function in more ways than simple obstruction. Bladder frequency, hesitancy, urgency etc. can all result and the generic term lower urinary tract symptoms is used to describe this symptom complex.Prostate cancer is a common disease of variable morbidity. In most men it appears to be clinically silent.Prostate biopsy is the only reliable method for diagnosing prostate cancer. MRI is very useful for staging, but can only be reliably interpreted in those with biopsy proven cancer.Prostatitis is a difficult diagnosis to make, either clinically or on imaging.

Scale cracking and spallation behaviour under repeated thermal cycling has been studied for Haynes 214 and 20Cr25NNb for a spectrum of temperature ranges. Both alloys show an increase in the rate of mass gain after a small number of cycles in most cases. Continued cycling of Haynes 214 eventually results in spallation but this is not observed in the 20Cr25NiNb alloy. The increase in the rate of mass gain is consistent with predictions for FE models.

A common method of protecting superalloys from aggressive environments at high temperatures is by plasma spraying MCrAlY (M = Fe, Ni and/or Co) to form an overlay coating. Oxidation resistance is then conferred through the development of an alumina layer. However, the use of such coatings is limited at temperatures above about 1100 degrees C due to rapid failure of the protective oxide scales. In this study, the oxidation behaviour of air-plasma-sprayed NiCrAlY coatings has been investigated at 1200 degrees C in 1 atm air. A protective alumina layer develops during the early stages, but breakaway oxidation occurs after prolonged exposure. The results suggest that the critical temperature drop to initiate failure is inversely proportional to the scale thickness, and an analytical model is put forward to explain this behaviour. Local surface curvature of the coating can lead to delamination within the oxide during cooling and it is shown that the largest individual pore in a spall region is the critical flaw for oxide fracture.

Mechanical damage to thin, protective oxide layers arises principally in service from differential strains produced by temperature changes. For typical alumina- or chromia-forming alloys, in-plane tensile stresses are produced during cooling. Imposed strain rates can vary over many orders of magnitude and, since these are applied at high temperatures, the possibility exists that diffusional relaxation processes (generally termed 'creep') will reduce the development of high stresses within the oxide or at the oxide/metal interface and, thus, have a beneficial influence on the processes of scale failure. This aspect is considered in detail in this paper both by reviewing published data and by presenting new numerical results on the influence of metal creep strength on the growth characteristics of an interfacial crack. In general, it is shown that diffusional relaxation can be important but that its contribution will depend on the intrinsic creep properties of the phase concerned and also on the values of imposed strain rate and temperature.

The effect of oral vitamin C on chemotactic and random migration of neutrophils in 20 neonates (10 normal and 10 with suspected sepsis) was evaluated. Chemotaxis and random migration were studied between 24 and 48 hours of life, before and 24 hours after the administration of 400 mg (divided in four doses) of vitamin C. Chemotactic migration improved by 65% and random migration by 57% following vitamin C administration. The significant improvement in chemotaxis (P less than .01) and random migration may justify the inclusion of vitamin C as an adjunct to the therapy of neonatal sepsis.

The PMNs of five infants and children with homozygous alpha-1-antitrypsin deficiency (PiZZ phenotype) revealed defective chemotactic migration, and their PiZZ sera generated a higher quantity of chemotactic factor(s).