| 1. |
- Kronander, Håkan, et al.
(författare)
-
Analysis of ST/HR hysteresis improves long-term prognostic value of exercise ECG test.
- 2011
-
Ingår i: International Journal of Cardiology. - : Elsevier BV. - 0167-5273 .- 1874-1754. ; 148:1, s. 64-9
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: ST/HR hysteresis is one of the better diagnostic exercise ECG variables for coronary artery disease. This study evaluates the long-term prognostic value of ST/HR hysteresis in predicting acute myocardial infarction (AMI) and all-cause mortality in men and women. METHODS: The study population consisted of 8317 patients who had undergone routine exercise test on bicycle ergometer at one Swedish centre. Information on AMI and all-cause mortality was obtained from national Swedish registers covering a mean follow-up period of 9.5 years. RESULTS: The adjusted hazard ratio for AMI at a diagnostic cut point of ≤-20 µV for ST/HR hysteresis was 1.88 (95% CI, 1.62-2.17) in men and 2.31 (95% CI, 1.83-2.91) in women. For all-cause death the adjusted hazard ratio was 1.72 (95% CI, 1.52-1.96) in men and 1.90 (95% CI, 1.57-2.29) in women. The corresponding hazard ratios for ST-segment depression with horizontal or down-sloping ST-segment, ST-segment depression, ST/HR index, and ST/HR slope were lower. For comparison, the adjusted hazard ratio for AMI using maximal workload in percent of predicted was 2.02 (95% CI, 1.77-2.32) in men and 2.14 (95% CI, 1.71-2.67) in women. Area under the ROC curves for prediction of AMI was significantly larger using ST/HR hysteresis than using any of three other evaluated ECG indicators. CONCLUSIONS: ST/HR hysteresis appears to improve the prognostic ability of an exercise ECG test for AMI and all-cause mortality in a long-term perspective compared to conventional ST-segment and ST/HR indicators in both genders and clearly more markedly in women.
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| 2. |
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| 3. |
- Kronander, Håkan, et al.
(författare)
-
Diagnostic performance and partition values of exercise electrocardiographic variables in the detection of coronary artery disease - improved accuracy by using ST/HR hysteresis
- 2010
-
Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961 .- 1475-097X. ; 30:2, s. 98-106
-
Tidskriftsartikel (refereegranskat)abstract
- P>Exercise electrocardiography is widely used for initial identification of patients with coronary artery disease (CAD). This study compares the measurements of ST-segment changes during exercise and during early postexercise recovery in terms of diagnostic discrimination capacity and optimal partition values. Data from 1876 patients undergoing a routine bicycle exercise test were analysed. CAD was angiographically verified in 668 patients, and excluded by angiography (n = 119), myocardial scintigraphy (n = 250), and on clinical grounds (n = 839) in 1208 patients. Postexercise ST/HR hysteresis was calculated as normalized for heart rate (HR) ST/HR loop area during the first 3 min of recovery. ST/HR index was obtained by dividing the overall ST amplitude change during exercise by exercise-induced HR change, and ST/HR slope was calculated using linear regression analysis of ST/HR data pairs during exercise. ST-segment depression was measured during, and for 3 min after the exercise. Discriminating capacity of the methods was evaluated in terms of receiver operating characteristic areas and optimal partition values providing the combination of the best sensitivity and specificity were established. The best diagnostic discrimination was provided by ST/HR hysteresis at optimal partition value of -15 mu V, followed by postexercise ST amplitude measurements at gender-specific partition values of -10 to -90 mu V, ST/HR slope [partition value 2 center dot 4 mu V (beats/min)-1], ST/HR index [partition value 1 center dot 6 mu V (beats/min)-1], and ST-segment depression during exercise (partition value 70 mu V in men and 90 mu V in women). The results demonstrate that analysis of postexercise ST/HR hysteresis offers the most accurate and gender indifferent identification of patients with CAD.
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| 4. |
- Kronander, Håkan, et al.
(författare)
-
Exercise electrocardiography for diagnosis of coronary artery disease: impact of sampling rate on the diagnostic performance of ST/HR-loop based on data from early recovery phase
- 2007
-
Ingår i: Clinical Physiology and Functionel Imaging. - 1475-0961. ; 28:2, s. 96-100
-
Tidskriftsartikel (refereegranskat)abstract
- Quantitative analysis of electrocardiographic ST-segment/heart rate relationship (ST/HR loop) during early recovery phase of exercise stress test provides a sensitive tool for the detection of coronary artery disease (CAD). This study evaluates the effect of data sampling frequency on the diagnostic performance of ST/HR loop in 1876 patients undergoing a routine exercise test on a bicycle ergometer. CAD was verified angiographically in 668 patients and excluded by coronary angiography (n = 119), myocardial scintigraphy (n = 250) and on clinical grounds (n = 839) in 1208 patients. The normalized ST/HR loop area was calculated in all cases by integration of ST-segment amplitude difference from the end of exercise to the end of the first 3 min of recovery period over HR and dividing the integral by the HR difference over the integration period. The effect of different sampling rates (one, two and five samples per minute) on the CAD discrimination ability of ST/HR loop area was subsequently evaluated using receiver operating characteristic (ROC) curves. Reduction in ST/HR data sampling frequency from two to one sample per minute resulted in a significantly decreased diagnostic performance of the ST/HR loop whereas no differences in CAD discrimination capacity were observed between sampling frequencies of two and five samples per minute. The choice of ST/HR data sampling frequency may have a significant impact on the CAD diagnostic ability of the ST/HR loop. The use of sampling frequency below two samples per minute results in a significantly diminished diagnostic performance, a fact that should be taken into consideration when employing ST/HR diagnostic procedures.
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| 5. |
- Kronander, Håkan, et al.
(författare)
-
Improved capacity of exercise electrocardiography in the detection of coronary artery disease by focusing on diagnostic variables during the early recovery phase
- 2005
-
Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 0022-0736 .- 1532-8430. ; 38:2, s. 130-138
-
Tidskriftsartikel (refereegranskat)abstract
- The temporal distribution of the diagnostic information for the detection of coronary artery disease (CAD) provided by exercise-induced electrocardiographic (ECG) ST-segment amplitude changes in different ECG leads in men and women has not been fully investigated. To shed further light in this area, 1877 electrocardiograms selected from 8322 patients undergoing a routine exercise test on a bicycle ergometer were evaluated. ST-segment amplitude and the difference between heart rate-matched recovery and exercise ST-segment amplitudes (ST/HR difference) were measured. Coronary artery disease was verified angiographically in 669 patients and excluded in 1208 patients by angiography (n = 119), by myocardial scintigraphy (n = 250), or on clinical grounds (n = 839). The diagnostic performance of the 2 ECG methods used was assessed by constructing receiver operating characteristic curves for each sampling point every 12 seconds during 10 minutes of recovery as well as the last 4 minutes of exercise for the ST-segment amplitude. ST-segment amplitude performed better after exercise than during exercise and best within the first 2 minutes of recovery. Its diagnostic ability did not differ from the ST-amplitude hysteresis assessed by the difference between recovery ST-segment amplitude and exercise ST-segment amplitude at matched heart rate. Both methods performed better in men and the diagnostic information appeared mainly in leads I, -aVR, II, V-4, V-5, and V-6. The best discrimination of CAD is provided by analysis of ST-segment amplitude changes in 6 specific leads early during the recovery phase. This information should be targeted by exercise ECG diagnostic methods.
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| 6. |
- Söderqvist, Emil, et al.
(författare)
-
Design of a single segment conductance catheter for measurement of left ventricular volume
- 2001
-
Ingår i: Annual Reports of the Research Reactor Institute, Kyoto University. ; , s. 151-154
-
Konferensbidrag (refereegranskat)abstract
- The objective of this paper is to investigate how to best position the sensing electrodes on a single segment conductance catheter, and to calculate the expected performance. Using electrode potential data, obtained with the present five segment conductance catheter in pig experiments, we have interpolated the electrical field at any given point of time, and calculated what volume curve to expect with only two sensing electrodes. Comparison shows that the deviation between our calculated method and the present one is stable and small. Mean deviation with optimized electrode positions was 0.05% per sample, and the maximum deviation found for a single time sample was 2.57%. This indicates that it is possible to build a thin single segment catheter with as good performance as for the present five segment conductance catheter.
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| 7. |
- Adegoke, Olutayo, 1979-, et al.
(författare)
-
Influence of laser powder bed fusion process parameters on the microstructure and cracking susceptibility of nickel-based superalloy Alloy 247LC
- 2022
-
Ingår i: Results in Materials. - : Elsevier. - 2590-048X. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- Microstructures of material conditions of nickel-based superalloy Alloy 247LC fabricated using laser powder bed fusion (L-PBF) were investigated. Experiments designed in a prior study revealed the L-PBF process parameters for which the material conditions displayed a reduced susceptibility to cracking. Certain process parameters produced material conditions with an increased susceptibility to cracking. In this study, the material conditions were investigated in detail to reveal their microstructure and to determine the cause of cracking. The reason for the transition between a reduced to an increased susceptibility to cracking was examined. The results revealed solidification cracking occurred at high-angle grain boundaries. Solidification cracking may have been promoted at high-angle grain boundaries because of the undercooling contribution of the grain boundary energy. Furthermore, Si segregation was observed in the cracks. Thus, the presence of Si most likely promoted solidification cracking. It was observed that a high crack density, which occurred in the high energy density material condition, was associated with a large average grain size. The fact that certain combination of process parameters produced microstructures with a low susceptibility to cracking, indicates that reliable Alloy 247LC material may be printed using L-PBF by employing improved process parameters. © 2022
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| 8. |
- Adegoke, Olutayo, 1979-, et al.
(författare)
-
Influence of laser powder bed fusion process parameters on the microstructure of solution heat-treated nickel-based superalloy Alloy 247LC
- 2022
-
Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 183
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, Alloy 247LC samples were built with different laser powder bed fusion (L-PBF) process parameters. The samples were then subjected to solution heat treatment at 1260 °C for 2 h. The grain size of all the samples increased significantly after the heat treatment. The relationship between the process parameters and grain size of the samples was investigated by performing a design of experiment analysis. The results indicated that the laser power was the most significant process parameter that influenced the grain height and aspect ratio. The laser power also significantly influenced the grain width. The as-built and as-built + heat-treated samples with high, medium, and low energy densities were characterized using a field emission gun scanning electron microscope equipped with an electron backscatter diffraction detector. The micrographs revealed that the cells present in the as-built samples disappeared after the heat treatment. Isolated cases of twinning were observed in the grains of the as-built + heat-treated samples. The disappearance of cells, increase in the grain size, and appearance of twins suggested that recrystallization occurred in the alloy after the heat treatment. The occurrence of recrystallization was confirmed by analyzing the grain orientation spread of the alloy, which was lower and more predominantly <1° in the as-built + heat-treated conditions than in the as-built conditions. The microhardness of the as-built + heat-treated samples were high which was plausible because γ’ precipitates were observed in the samples. However, the L-PBF process parameters had a very low correlation with the microhardness of the as-built + heat-treated samples.
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| 9. |
- Adegoke, Olutayo, et al.
(författare)
-
Influence of laser powder bed fusion process parameters on voids, cracks, and microhardness of nickel-based superalloy alloy 247LC
- 2020
-
Ingår i: Materials. - 1996-1944. ; 13:17
-
Tidskriftsartikel (refereegranskat)abstract
- The manufacturing of parts from nickel-based superalloy Alloy 247LC by laser powder bed fusion (L-PBF) is challenging, primarily owing to the alloy’s susceptibility to cracks. Apart from the cracks, voids created during the L-PBF process should also be minimized to produce dense parts. In this study, samples of Alloy 247LC were manufactured by L-PBF, several of which could be produced with voids and crack density close to zero. A statistical design of experiments was used to evaluate the influence of the process parameters, namely laser power, scanning speed, and hatch distance (inherent to the volumetric energy density) on void formation, crack density, and microhardness of the samples. The window of process parameters, in which minimum voids and/or cracks were present, was predicted. It was shown that the void content increased steeply at a volumetric energy density threshold below 81 J/mm3. The crack density, on the other hand, increased steeply at a volumetric energy density threshold above 163 J/mm3. The microhardness displayed a relatively low value in three samples which displayed the lowest volumetric energy density and highest void content. It was also observed that two samples, which displayed the highest volumetric energy density and crack density, demonstrated a relatively high microhardness; which could be a vital evidence in future investigations to determine the fundamental mechanism of cracking. The laser power was concluded to be the strongest and statistically most significant process parameter that influenced void formation and microhardness. The interaction of laser power and hatch distance was the strongest and most significant factor that influenced the crack density. © 2020 by the authors.
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| 10. |
- Adegoke, Olutayo, et al.
(författare)
-
Laser beam powder bed fusion and post processing of alloy 247LC
- 2019
-
Ingår i: MS and T 2019 - Materials Science and Technology. - : Materials Science and Technology. - 9780873397704 ; , s. 27-34
-
Konferensbidrag (refereegranskat)abstract
- Alloy 247LC is sensitive to cracking during laser beam powder bed fusion (PBF-LB) manufacturing. Post processing is thus required to close cracks and achieve desired properties. In this study, samples of Alloy 247LC were manufactured by PBF-LB and subsequently post processed by hot isostatic pressing (HIP), HIP + solution and ageing heat treatments. The microstructure was characterized. Results showed cracks in the as-built condition. Cracks were not detected after HIP. Bright microconstituents were observed in the region between the cells, mainly, because of the partitioning of Hf and Ta into the intercellular region, where they presumably form carbides. What is assumed to be oxides were prominent in the microstructure. Thermodynamic calculations showed rapid formation of ?’ precipitates in the alloy, due to the high total concentration of Al and Ta and this was linked to the high hardness values in the as-built condition. © 2019 MS&T19®
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| 11. |
- Adegoke, Olutayo, et al.
(författare)
-
Review of laser powder bed fusion of gamma-prime-strengthened nickel-based superalloys
- 2020
-
Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 10:8
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.© 2020 by the authors. Licensee MDPI, Basel, Switzerland.
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| 12. |
- Adegoke, Olutayo, et al.
(författare)
-
Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy
- 2023
-
Ingår i: Micron. - 0968-4328 .- 1878-4291. ; 171
-
Tidskriftsartikel (refereegranskat)abstract
- Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC.
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| 13. |
- Arnbjörnsson, Einar, et al.
(författare)
-
Changes in hospital costs for an appendectomy : 1955, 1965, and 1975
- 1983
-
Ingår i: The American Journal of Surgery. - : Elsevier BV. - 0002-9610. ; 146:3, s. 342-345
-
Tidskriftsartikel (refereegranskat)abstract
- A reduction in the number of postoperative bed days for patients who underwent appendectomy led to a study of changes in hospital costs of appendectomies for the years 1955, and 1965, and 1975. No significant changes were found in the total hospital costs. However, the postoperative costs decreased by 36 percent from 1955 to 1975 due to a decrease in the mean duration of hospital stay. During the same period of time, the perioperative costs increased by 90 percent due to increased length of operation time correlated with an increasing proportion of inexperienced operating surgeons. At present, there seem to be few possible ways to increase the cost efficiency of treating appendicitis.
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| 14. |
- Aronsson, Håkan, 1961-, et al.
(författare)
-
Logistics Structures - drivers of environmental impact
- 2008. - 1
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Ingår i: Northern Lights in Logistics and Supply Chain Management. - Köpenhamn : Copenhagen Business School Press. - 9788763002189 ; , s. 183-198
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Northern Lights in Logistics & Supply Chain Management" portrays the past, present and future research of the subject in the Nordic countries. The NOFOMA conference - a network of Nordic researchers within the field of Logistics and Supply Chain Management - has been a focal point in the contribution to the continuous improvement and further development of Nordic research. The network has also opened up for interaction with fellow researchers from other countries. There are sixteen chapters in the book that in its own way colours the Nordic rainbow of research within Logistics and Supply Chain Management. The chapters are structured in four themes: 1) Origins and strategic aspects; 2) Research approaches in the Nordic countries; 3) Advancement of distribution strategies and; 4) Emerging application areas of logistics and SCM. The chapters provide an understanding and, perhaps more importantly, consciousness for scholars that are part of this research environment: Where are we now, what have we been influenced by, and in what area are we able to provide positive impact? The aim of the book is also to contribute to increased visibility to fellow international scholars within Logistics and Supply Chain Management.
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| 15. |
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| 16. |
- Brodin, Håkan, 1969-
(författare)
-
Aspects of fatigue life in thermal barrier coatings
- 2001
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBC) are applied on hot components in airborne and land-based gas turbines when higher turbine inlet temperature, meaning better thermal efficiency, is desired. The TBC is mainly applied to protect underlying material from high temperatures, but also serves as a protection from the aggressive corrosive environment.Plasma sprayed coatings are often duplex TBC's with an outer ceramic top coat (TC) made from partially stabilised zirconia - ZrO2 + 6-8% Y2O3. Below the top coat there is a metallic bond coat (BC). The BC is normally a MCrAlX coating (M=Ni, Co, Fe ... and X=Y, Hf, Si ... ). In gas turbine components exposed to elevated temperatures nickel-based superalloys are commonly adopted as load carrying components. In the investigations performed here a commercial wrought Ni-base alloy Haynes 230 has been used as substrate for the TBC. As BC a NiCoCrAlY serves as a reference material and in all cases 7% yttria PS zirconia has been used. Phase development and failure mechanisms in APS TBC during service-like conditions have been evaluated in the present study. This is done by combinations of thermal cycling and low cycle fatigue tests. The aim is to achieve better knowledge regarding how, when and why thermal ban'ier coatings fail. As a fmal outcome of the project a model capable of predicting fatigue life of a given component will help engineers and designers of land based gas turbines for power generation to better optimise TBC's.In the investigations it is seen that TBC life is strongly influenced by oxidation of the BC and interdiffusion between BC and the substrate. The bond coat is known to oxidise with time at high temperature. The initial oxide found during testing is alumina. With increased time at high temperature Al is depleted from the bond coat due to interdiffusion and oxidation. Oxides others than alumina start to form when the Al content is reduced below a critical limit. It is here believed that spinel appears when the Al content is lowered below 2w/o in the bond coat. Here it was shown that a faster growing oxide, rich in Ni, Cr and Co forms at the interface. Al depletion is also linked to BC phases. Initially the bond coat is a γ/ß-material possibly with very fine dispersed γ'. Simultaneously with Al-depletion the ß-phase is found to disappear. This occurs simultaneously with the formation of spinel. However, oxidation is not only a disadvantage. Low cycle fatigue tests reveal that oxide streaks within the bond coat will slow down crack growth due to crack deflection and crack branching. Therefore benefit of or damage from oxide growth on crack initiation and propagation is dependent on crack mode, spalling of the ceramic TC or growth of "classic" cracks perpendicular to the surface.From the observations conclusions are drawn regarding fatigue behaviour ofTBC systems. The basic idea is that all cracks leading to failure initiate in the thermally grown oxide (TGO). Following the initiation, they can, however, grow to form either delamination cracks leading to top coat spallation or cracks transverse to the surface leading to component failure.
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| 17. |
- Brodin, Håkan, et al.
(författare)
-
Behaviour of a Thermal Barrier Coating during High Temperature Oxidation
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- An air plasma sprayed thermal barrier coating was investigated in order to clarify links between heat treatment, oxidation and diffusion behaviour. In the study a thin Zirconia (PSZ) layer was used as top coat together with a NiCoCrAlY bond coat. The investigation was focused on differences for three geometries. Thermal barrier coatings on flat, concave and convex surfaces were studied. Isothermal oxidation was performed up to 1000 hrs at 1000°C in order to simulate true working conditions for the interface between ceramic top coat and metallic bond coat. The investigations show presence of Al-rich oxides for shorter times. When the coating system is heat-treated for 1000 hrs a change of oxide composition is obvious and beside Al the oxides contain Ni, Cr and Co. The oxides tend to grow with different rates depending on the macroscopic surface geometry. In the study convex surfaces reveal the highest oxide growth rates and concave the lowest growth rates. At 1000 hrs and 1000°C the difference between the fastest and the slowest growing oxide layer is 1 μm. Some interdiffusion is obvious. Between the superalloy substrate and the bond coat outward diffusion of Ni, W and Cr is present together with inward diffusion of Co and to some extent Al.
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| 18. |
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| 19. |
- Brodin, Håkan, et al.
(författare)
-
Bond Coat Influence on TBC Life
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the present study the influence of bond coat composition and coating process on thermal barrier coating (TBC) life has been evaluated. Six different coatings have been subjected to thermal cycling between 100 and 1100°C. After this the different systems have been characterised by light microscopy and SEM-EDS. Various commercial bond coats have been applied on one substrate material (Haynes alloy 230). The total fatigue life of the different TBC systems varies with 30% what is believed to be influenced by diffusion and oxidation phenomena in the bond coat. It is found that when the aluminium concentration is decreased phases other than alumina form at the top coat I bond coat interface. Oxides formed during later stages of the thermal cyclic test are rich in nickel, cobalt and chromium and the results can be interpreted as formation of nickel-, chromium- or spinel oxides. The reason for TBC failure is coupled to aluminium depletion, which here is believed to be due to inward diffusion and formation of thermally grown oxides (TGO) at the ceramic top coat (TC) metallic bond coat (BC) interface as well as growth of internal oxides in the bond coat.
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| 20. |
- Brodin, Håkan, 1969-, et al.
(författare)
-
Bond Coat Influence on TBC Life
- 2002
-
Ingår i: Turbin Forum, Advanced Coatings for High Temperatures,2002.
-
Konferensbidrag (refereegranskat)
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| 21. |
- Brodin, Håkan, et al.
(författare)
-
Bond coat influence on thermal fatigue behaviour of thermal barrier coatings
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the present study the influence of bond coat composition and coating process on thermal barrier coating (TBC) life has been evaluated. Six different coatings have been subjected to thermal cycling between 100 and 1100°C. After this the different systems have been characterised by light microscopy and SEM-EDS. Various commercial bond coats have been applied on one substrate material (Haynes alloy 230). The total fatigue life of the different TBC systems varies with 30% what is believed to be influenced by diffusion and oxidation phenomena in the bond coat. It is found that when the aluminium concentration is decreased phases other than alumina form at the top coat / bond coat interface. Oxides formed during later stages of the thermal cyclic test are rich in nickel, cobalt and chromium and the results can be interpreted as formation of nickel-, chromium- or spinel oxides. The reason for TBC failure is coupled to aluminium depletion, which here is believed to be due to inward diffusion and formation of thermally grown oxides (TGO) at the ceramic top coat (TC) metallic bond coat (BC) interface as well as growth of internal oxides in the bond coat.
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| 22. |
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| 23. |
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| 24. |
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| 25. |
- Brodin, Håkan, 1969-
(författare)
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Failure of thermal barrier coatings under thermal and mechanical fatigue loading : microstructural observations and modelling aspects
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industrial and air-borne gas turbine hot components suffer from creep, oxidation, corrosion and microstructural degradation if not shielded from the hot and aggressive combustion gases. Two major strategies commercially available are adopted; film cooling by pressurised air and application of protective coatings. Protective coatings form a slow-growing oxide that protects from oxidation and corrosion. By application of a thermal insulator, a thermal barrier coating, the material will be protected from high temperature through good insulation properties of the coating system.If thermal barrier coatings are to be used in situations where capabilities and possibilities for inspections are limited, better knowledge of the fatigue properties of the coatings is also needed. Therefore development of a reliable fatigue life model is needed. The present work aims at serving as a basis from which a general physically founded thermal barrier coating life model can be formulated. The effects of exposure to high temperatures and mechanical loads on thermal barrier coatings under service like conditions have been investigated in the present thesis. Emphasis is put on the coupling between materials science and solid mechanics approaches in order to establish a better knowledge concerning degradation mechanisms and fatigue life issues than what is common if only one discipline is explored.Investigations of material exposed to isothermal oxidation and thermal cyclic fatigue were performed on plasma-sprayed systems with NiCoCrAIY or NiCrAIY bond coats and yttria partially stabilised zirconia top coats. It has been shown that the thermally grown oxide that will form upon high temperature exposure influences the failure behaviour. If the oxide is composed mainly of alumina, the fatigue properties are good since the adhesion between the ceramic top coat and the metallic bond coat is good. This is also shown in a comparison between different plasma sprayed thermal barrier coating systems. If the oxide formed is based on alurnina and spinel is avoided the fatigue properties benefit from a relatively flat interface where out-of plane stresses are low in comparison to a rough interface between top- and bond coat. These findings indicate that the bonding in air-plasma sprayed systems is dependent on so called chemical bonding if the thermally grown oxide is not voluminous with high growth stresses.It is possible to establish a fatigue life model for thermal barrier coatings. This has been shown with a model based on a modified Paris law formulation. The formulation needs to be modified with regards to mode rnixity of growth. Results achieved in the present project show that it is possible to extract crack growth data for interfacial crack growth. However a combination of mechanical testing and finite element modelling is needed since the load situation in critical areas cannot be measured. Crack growth results are presented and crack growth data are compared to predictions with good agreement.
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| 26. |
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| 27. |
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| 28. |
- Brodin, Håkan, 1969-, et al.
(författare)
-
Fatigue life prediction of a plasma sprayed thermal barrier coating system
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings are commonly used in gas turbines for power generation. One major issue in TBC design is how to determine fatigue life in these material systems. The present paper aims at presenting a model for determination of TBC life based on the behavior of an air plasma sprayed coating system. This is done by analysis of fracture behavior and evaluation of data from thermal fatigue tests. The knowledge regarding fracture behavior in thermal fatigue tests is used as an input to the modelling work. For formulation of the fatigue life model, a Paris law approach has been used. FE calculations are used to obtain energy release rate and stress intensity factors, KI and KII, for a propagating delamination crack in the top/ bond coat interface. As a measure of failure, a delamination damage measure is used. A method for determination of delamination crack growth data is presented.
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| 29. |
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| 30. |
- Brodin, Håkan, et al.
(författare)
-
Fracture Mechanical Modelling of a Plasma Sprayed TBC System
- 2009
-
Ingår i: Advanced Ceramic Coatings and Interfaces IV. - Westerville, OH, United States : American Ceramic Society Inc.. - 9780470457535 ; , s. 113-124
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Konferensbidrag (refereegranskat)abstract
- A thermal barrier coating (TBC) system subjected to thermal cycling will develop a microcrack partem near the interface between the metallic bond coat and the ceramic top coat. These small cracks link up and form internal TBC delaminations during repeated heating / cooling. After a longer time period, the internal delamination cracks will form a larger spallation damage, where the TBC is detached from the underlying material. Since cracks are initiated in multiple sites of the thermal barrier coating, the damage is initially considered to be governed by local stress conditions. The purpose of the present work is to compare experimental data with predictions of a physically based fatigue life model. The present study has been performed on plasma-sprayed TBCs where the interface geometry has been varied. In the present work, calculation of fatigue life is done for a number of cases under thermal fatigue loading. Different interface geometries are compared in order to understand the influence of variations in the TC/BC interface roughness on oxidation behaviour and thermal fatigue life. Thermal fatigue tests indicate that an increased surface roughness is beneficial from a fatigue life point of view.
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Brodin, Håkan, et al.
(författare)
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Influence of high temperature exposure on thermal barrier coating behaviour
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- An air plasma sprayed thermal barrier coating was investigated in order to clarify links between heat treatment, oxidation and diffusion behaviour. In the study a thin Zirconia (PSZ) layer was used as top coat together with a NiCoCrAIY bond coat. The investigation was focused on differences for three geometries. Thermal barrier coatings on flat, concave and convex surfaces were studied. Isothermal oxidation was performed up to 1000 hrs at 1000°C in order to simulate true working conditions for the interface between ceramic top coat and metallic bond coat. The investigations show presence of Al-rich oxides for shorter times. When the coating system is heat-treated for 1000 hrs a change of oxide composition is obvious and beside AI the oxides contain Ni, Cr and Co. The oxides tend to grow with different rates depending on the macroscopic surface geometry. In the study concave surfaces reveal the highest oxide growth rates and convex the lowest growth rates. At 1000 hrs and 1 000°C the difference between the fastest and the slowest growing oxide layer is 1µm. Some interdiffusion is obvious. Between the superalloy substrate and the bond coat outward diffusion of Ni, W and Cr is present together with inward diffusion of Co and to some extent Al.
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| 35. |
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| 36. |
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| 37. |
- Brodin, Håkan, 1969-
(författare)
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Initiation and growth of delamination cracks in vacuum plasma sprayed thermal barrier coatings
- 2004
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Ingår i: Surface Engineering 2004: Proceedings of the 3rd International Surface Engineering Congress (ASM International). - 0871708191 - 9780871708199 ; , s. 284-290
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Konferensbidrag (refereegranskat)abstract
- Thermal barrier coatings are widely used in air-borne and land-based gas turbines. In these applications they serve as thermal insulators in hot components (burner cans/liners, turbine vanes and turbine blades). The present paper is aimed to describe the failure mechanism of a vacuum plasma sprayed thin thermal barrier coating system. Also the coating degradation mechanism (delamination followed by spallation) in terms of interfacial crack growth data is investigated and presented. In the present paper a 200 µm thick NiCrAlY bond coat was chosen together with a 350µm thick 7wt% yttria stabilised zirconia top coat. The coating system was exposed to thermal cyclic fatigue with a thermal cycle ranging from 100 °C to 1100 °C and a cycle time of 70 minutes. After thermal cyclic testing all specimen were subjected to standard sample preparation routines and inspected by optical microscopy and scanning electron microscopy. In order to describe interfacial crack growth an interface damage measure is used. For the present coating system under current thermal load conditions a mainly black interface fracture is discovered. The top coat exhibit microcrack formation after thermal fatigue, but these cracks do not contribute to the final fracture appearance. Crack growth rates are compared to local stress intensity levels at the top coat / bond coat interface. From crack length measurements are crack growth data da/dN = f(ΔKeff) calculated.
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| 38. |
- Brodin, Håkan, et al.
(författare)
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Mechanical Behaviour and Microstructure Correlation in a Selective Laser Melted Superalloy
- 2013
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Ingår i: ASME Turbo Expo 2013. - : American Society of Mechanical Engineers (ASME). - 9780791855195 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- Selective laser melting (SLM), or, as the industry standard denotes the process, laser sintering, is an additive manufacturing process where metal powder is melted by a laser source layer-wise, forming a solid, dense metallic component. With the SLM process, near net shape components can be manufactured directly from a CAD model. The model is sliced into thin (max 100μm thick) layers. Powder is spread onto a metallic build platform and the powder is fused by a laser as dictated by the CAD model. The laser energy is intense enough to permit full melting (welding) of the particles to form solid metal. The process is repeated layer by layer until the part is complete.A number of materials are available, including steel, aluminium, titanium and, in recent time, also superalloys. The material investigated in the current project is an alloy in agreement with the composition of Haynes International Hastelloy X, a solution strengthened superalloy typically used in large welded components exposed to high temperatures in oxidizing as well as reducing environments.Microstructurally, the material is different from both a hot-rolled, as well as a cast material due to the manufacturing process. Since the SLM process involves laser melting of powder particles in the size range of <50μm, the structure resembles of a weld structure, however on a smaller scale. Due to the layer-by-layer build strategy, the material will exhibit anisotropy. Different heat treatment approaches can be adopted in order to homogenize the material and to minimize the effect of anisotropy. A stress relieve heat treatment was adopted and compared to the findings of the as manufactured SLM material.The current project focuses on evaluating mechanical properties for a material manufactured by the SLM process and comparing to data for established manufacturing processes. For evaluation of the mechanical properties, low cycle fatigue testing and tensile testing has been performed. The microstructure and material deformation / cracking are evaluated by light optical microscopy and SEM, where electron backscatter diffraction is used. Due to the weld-like structure, the material will be transversely isotropic in the as-manufactured condition with one symmetry plane perpendicular to the build direction. Any direction perpendicular to the build direction tends to give increased strength compared to a direction parallel to the build direction if monotonic data are concerned. If fatigue properties are concerned, the anisotropy is also obvious. It is shown that the differences in behaviour can be coupled to microstructure.
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| 39. |
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| 40. |
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| 41. |
- Brodin, Håkan, 1946-
(författare)
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Regional variations in pharmaceutical consumption in Sweden
- 1987
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Secondary, non-sample data, mainly from official statistics from 259 municipalities in Sweden, are used to investigate systematic variations in the consumptian of pharmaceuticals on the county and municipality level.The theoretical framework is taken from health economics. The utilization of health care, and consequently the consumptian of pharmaceuticals, is determined simultaneausly by the demand for health care, derived from a demand for health, and the supply of health care. The model is exploratory, aiming at the identification of important factors for further study. In particular the importance of the economic budget restriction is examined.An analysis of variance shows that there is no reason to assume systematic differences in the consumptian of pharmaceuticals caused by actions on the county level. The existing variation more likely stems from differences in characteristics of the municipalities, thus reflecting intovariations on the county level.The impact of a number of explanatory variables on drug consumptian is measured by means of multiple regression analyses. The variables included are sick-leave, disability pension, unemployment, age, alcohol consumption, religiousness, occupational structure, commuting, physician density, rural population, presence of a hospital or a regional hospital and income.The regression results indicate that age structure, the number of doctars and commuting explain approximately one third of the variation. Detailed regression studies of the consumption of 19 pharmaceutical subgroups show a more diversified result, but the main pattern remains.Using predictians from the 19 subregressions, a case study is performed for Gotland, known as a divergent municipality with respect to drug consumption. Two pharmaceutical groups, cardiovasculars and analgesics, were identified as particularly divergent campared to the general consumptian behaviour of the municipalities of Sweden.An analysis using the LISREL technique is performed in order to study the relative importance of the latent, unmeasured variables 'morbidity', 'life style', 'availability' and 'economy', grouped from the measured variables. The analysis indicates that 'availability' is the most important factor underlying pharmaceutical consumptian and that 'econorny' is more important than 'morbidity' and 'life style'. The analysis also shows, that low income is associated with high consumption of drugs. Whether this relationship on the municipality leve! also holds on the individual levelis not known.
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| 42. |
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| 43. |
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| 44. |
- Brodin, Håkan, 1969-, et al.
(författare)
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The influence of oxidation on mechanical and fracture behaviour of an air plasma-sprayed NiCoCrAlY bondcoat
- 2004
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 187:1, s. 113-121
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Tidskriftsartikel (refereegranskat)abstract
- The influence of isothermal oxidation on room-temperature mechanical and fracture behaviour of an air plasma-sprayed Ni-23Co-17Cr12Al-0.5Y bondcoat was investigated by the miniaturised disc bending test (MDBT) technique. Disc specimens were extracted from the bondcoat region of both as-received and oxidised thermal barrier coating (1000 degreesC, 1000 h). Microstructure analysis revealed that the nonoxidised bondcoat consisted mainly of gamma-phase (Ni-structure) and beta-NiAl. After 500 h of oxidation no NiAl remained in the bondcoat, an effect due to internal as well as external oxidation of Al. The former resulted in the formation of an extensive oxide network and the latter in the formation of an oxide scale between the topcoat and the bondcoat. The crack propagation behaviour of the bondcoat, both in non-oxidised and oxidised condition can be characterised as intergranular with stable growth. The crack propagation resistance is substantial due to the lamellar gain (splat) orientation and the extensive intergranular oxide network, acting as crack deflection and crack branching mechanisms. As an effect of oxidation, crack propagation resistance of the bondcoat increases but the strain to crack initiation decreases.
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| 45. |
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| 46. |
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| 47. |
- Brodin, Karin, et al.
(författare)
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Kopplingen mellan affärsdokument och produktionsstyrning
- 1996
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Från att ha varit en råvarustyrd industri övergår nu sågverksindustrin alltmer till att producera direkt mot kundorder. Detta innebär fler produkter, kortare serier och produkter som är mer anpassade efter kundens krav och behov. En väl fungerande informationsöverföring behövs för att klara denna omställning. Informationen måste sållas, bearbetas och det måste finnas rutiner för att återföra erfarenheter i syfte att möjliggöra löpande processförbättringar. Med datorers hjälp finns stora möjligheter att rationalisera informationsflöden och hantera komplexa verksamheter. I denna studie beskrivs informationsflödet vid Iggesunds sågverk samt förslag till angelägna förbättringar.
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| 48. |
- Carlsson, Camilla, et al.
(författare)
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Initial experience with a thin single segment pressure and conductance catheter for measurement of left ventricular volume
- 2001
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Ingår i: Annual Reports of the Research Reactor Institute, Kyoto University. ; , s. 103-106
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Konferensbidrag (refereegranskat)abstract
- Aims: To evaluate a thin and soft multifunctionalcatheter for the simultaneous real time monitoring of leftventricular volume and pressure with special consideration toside elTects such as interference with normal cardiacelectrophysiology.Methods and results: In four pigs, pressure and volumewere simultaneously recorded by using the thin single segmentpressure and conductance catheter. Measurements were doneunder varied cardiac conditions: at baseline, during preloadreduction and afterload Increase. Volumes were calibrated withintracardiac ultrasound measurements. During preloadreduction the pressure and volume decreased as expected. Acautious afterload increase resulted in a corresponding pressureand volume increase, the maximum of the pressure curvechanged from early to late. Both SV and EDV increased. Thevery few arrhythmias were mainly caused by surgicalinterference.Conclusion: The present study demonstrates that our thinsingle segment conductance catheter for the simultaneousmeasurement of LV volume and pressure has a performancethat warrants further development with the goal to make themethod available for human use. In particular, the catheter didnot cause any arrhythmias.
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| 49. |
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| 50. |
- Deng, Dunyong, et al.
(författare)
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Microstructural Characterization of AS-Manufactured and Heat Treated Electron Beam Melted Inconel 718
- 2016
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Ingår i: Materials Science and Technology 2016 (MS&T16). - Warrendale, PA : Association for Iron and Steel Technology, AISTECH. - 9781510833142 ; , s. 105-112
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Konferensbidrag (refereegranskat)abstract
- As manufactured and heat treated electron beam melted Inconel 718 exhibit inhomogeneous grain morphologies, mainly equiaxed close to the surface and more elongated columnar grains in the bulk. Different processing settings i.e., contouring in the surface region and hatching in the bulk region are responsible for differences in grain morphologies and textures, which are characterized using the SEM techniques electron contrast channeling imagine (ECCI) and electron backscattering diffraction (EBSD). Niobium carbides prefer to nucleate at TiN and are found to be in the grain growth direction. Regarding processing conditions, defects, such as porosities and segregations are discussed, as well as differences in microstructure emphasizing on grain morphologies and precipitates with regards to heat treatment and hardness indentation.
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