The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Bruce A Pint - One of the best experts on this subject based on the ideXlab platform.
-
Effect of boron on the oxidation behavior of NiCrAlYHfTi in H2O and CO2 environments
Surface & Coatings Technology, 2014Co-Authors: Kinga A. Unocic, Donovan N. Leonard, Bruce A PintAbstract:Abstract Cast NiCrAl alloys, co-doped with Y, Hf, Ti, and/or B, were evaluated at 1100 °C and 1150 °C in dry air, wet air (10 or 50% H 2 O), and CO 2 –10% H 2 O, in order to study the effect of boron additions on alumina Scale growth and Adhesion. After 200, 1-h cycles at 1100 °C, all of the alloys with Y and Hf showed good Scale Adhesion. By increasing the test temperature to 1150 °C, the addition of ~ 0.3 at.% (0.07 wt.%) B was shown to improve alumina Scale Adhesion during 1-h cycles in air with 10% H 2 O. Analytical transmission electron microscopy showed no effect of B on the alumina Scale microstructure and only minor effects on the depth of internal oxidation at 1100 °C. Combined Ti and B additions did not produce an additional benefit and Cr–B precipitates were detected in both B-doped alloys. Exposures in O 2 -buffered CO 2 –H 2 O did not result in any detrimental effect at 1100 °C.
-
Oxidation behavior of co-doped NiCrAl alloys in dry and wet air
Surface & Coatings Technology, 2013Co-Authors: Kinga A. Unocic, Bruce A PintAbstract:Abstract Cast NiCrAl alloys with additions of Y, La, Hf and Ti were evaluated at 1100 °C in wet (10 and 50% H 2 O) and dry air (0% H 2 O) in order to optimize such dopants for superalloy bond coatings. The results suggest that the typical Y addition in most coatings could be replaced by La. Also, Scale Adhesion in cyclic testing was improved with the co-addition of Hf with La or Y. Ti was added to investigate its incorporation in coatings on superalloys containing significant Ti additions. Particularly with co-doped alloys, the addition of Ti had little effect on Scale Adhesion but did reduce the depth of internal oxidation. Water vapor increased spallation, especially for the least adherent alloys, such as Y,Ti-doped NiCrAl. For the co-doped compositions with Hf, water vapor had a limited effect on Scale Adhesion and on the alumina growth rate in isothermal exposures. In addition to specimen mass change, the extent of internal oxidation and the depletion of β phase in the substrate were evaluated. Analytical transmission electron microscopy showed that Y, La and Hf co-segregated to the alumina Scale grain boundaries and formed dopant-rich oxide precipitates in the Scale.
-
Cyclic oxidation behavior of HVOF bond coatings deposited on La- and Y-doped superalloys
Surface & Coatings Technology, 2011Co-Authors: Bruce A Pint, Michael A Bestor, James A HaynesAbstract:Abstract One suggested strategy for improving the performance of thermal barrier coating (TBC) systems used to protect hot section components in gas turbines is the addition of low levels of dopants to the Ni-base superalloy substrate. To quantify the benefit of these dopants, the oxidation behavior of three commercial superalloys with different Y and La contents was evaluated with and without a NiCoCrAlYHfSi bond coating deposited by high velocity oxygen fuel (HVOF) spraying. Cyclic oxidation experiments were conducted in dry O 2 at 1050°, 1100° and 1150 °C. At the highest temperature, the bare superalloy without La showed more attack due to its lower Al content but no difference in oxidation rate or Scale Adhesion was noted at lower temperatures. With a bond coating, the alumina Scale was non-uniform in thickness and spalled at each temperature. Among the three coated superalloys, no clear difference in oxide growth rate or Scale Adhesion was observed. Evaluations with a YSZ top coat and a bond coating without Hf are needed to better determine the effect of superalloy dopants on high temperature oxidation performance.
-
optimizing Scale Adhesion on single crystal superalloys
Materials Science Forum, 2001Co-Authors: James L. Smialek, Bruce A PintAbstract:To improve Scale Adhesion, single crystal superalloys have been desulfurized to levels below 1 ppmw by hydrogen annealing. A transition to fully adherent behavior has been shown to occur at a sulfur level of about 0.2 ppmw, as demonstrated for PWA 1480, PWA 1484, and Rene N5 single crystal superalloys in 1100°-1150°C cyclic oxidation tests up to 2000 h. Small additions of yttrium (15 ppmw) also have been effective in producing Adhesion for sulfur contents of about 5 ppmw. Thus the critical Y/S ratio required for Adhesion was on the order of 3-to-1 by weight (1-to-1 atomic), in agreement with values estimated from solubility products for yttrium sulfides. While hydrogen annealing greatly improved an undoped alloy, yielding ≤0.01 ppmw S, it also produced benefits for Y-doped alloys without measurably reducing the sulfur content.
-
Effects of Platinum Additions and Sulfur Impurities on the Microstructure and Scale Adhesion Behavior of Single-Phase CVD Aluminide Bond Coatings
1999Co-Authors: Kevin M. Cooley, Bruce A Pint, James A Haynes, Ian G. Wright, Y. ZhangAbstract:The Adhesion of alumina Scales to aluminide bond coats is a life-limiting factor for some advanced thermal barrier coating systems. This study investigated the effects of aluminide bond coat sulfur and platinum contents on alumina Scale Adhesion and coating microstructural evolution during isothermal and cyclic oxidation testing at 1150 C. Low-sulfur NiAl and NiPtAl bond coats were fabricated by chemical vapor deposition (CVD). Lowering the sulfur contents of CVD NiAl bond coatings significantly improved Scale Adhesion, but localized Scale spallation eventually initiated along coating grain boundaries. Further improvements in Scale Adhesion were obtained with Pt additions. The observed influences of Pt additions included: (1) mitigation of the detrimental effects of high sulfur levels, (2) drastic reductions in void growth along the Scale-metal interface, (3) alteration of the oxide-metal interface morphology, and (4) elimination of Ta-rich oxides in the Al{sub 2}O{sub 3} Scales during thermal cycling. The results of this study also suggested that the microstructure (especially the grain size) of CVD aluminide bond coatings plays a significant role in Scale Adhesion.
Bumkyoo Choi - One of the best experts on this subject based on the ideXlab platform.
-
measurement and analysis of micro Scale Adhesion for efficient transfer printing
Journal of Applied Physics, 2011Co-Authors: Jungyul Park, Bumkyoo ChoiAbstract:The Adhesion-based transfer printing process allows the devices to be fabricated through low temperature process, which is important for realizing flexible electronics with high mobility. Therefore, comprehensive understanding about Adhesion between the solid object and the surface of elastomeric stamp (generally, polydimethylsiloxane is used) and the optimal strategy to control Adhesion can support the effective and high yield transfer. In this paper, a novel adhesive force measurement system is developed to measure dynamic adhesive forces from the surface on the flexible stamp. The thermodynamic work of Adhesion at the moment of debonding of a tip of sensor from the flexible stamp is modeled and used for developing the Adhesion control strategy. The measurement results show that the work of Adhesion is strongly dependent on the peel-off velocity of tip, while the indentation force has only minor effects on it. The effect of Young’s modulus of elastomeric stamp is also investigated using the model of wor...
-
Measurement and analysis of micro-Scale Adhesion for efficient transfer printing
Journal of Applied Physics, 2011Co-Authors: Min Sock Kim, Jungyul Park, Bumkyoo ChoiAbstract:The Adhesion-based transfer printing process allows the devices to be fabricated through low temperature process, which is important for realizing flexible electronics with high mobility. Therefore, comprehensive understanding about Adhesion between the solid object and the surface of elastomeric stamp (generally, polydimethylsiloxane is used) and the optimal strategy to control Adhesion can support the effective and high yield transfer. In this paper, a novel adhesive force measurement system is developed to measure dynamic adhesive forces from the surface on the flexible stamp. The thermodynamic work of Adhesion at the moment of debonding of a tip of sensor from the flexible stamp is modeled and used for developing the Adhesion control strategy. The measurement results show that the work of Adhesion is strongly dependent on the peel-off velocity of tip, while the indentation force has only minor effects on it. The effect of Young's modulus of elastomeric stamp is also investigated using the model of work of Adhesion based on the relation between the adhesive force and peel-off velocity. The elastomeric stamp with low Young's modulus is preferred for efficient transfer printing. (C) 2011 American Institute of Physics. [doi:10.1063/1.3611033]
James L. Smialek - One of the best experts on this subject based on the ideXlab platform.
-
Unusual Oxidative Limitations for Al-MAX Phases
2017Co-Authors: James L. SmialekAbstract:Alumina-forming MAX phases are well-known for their excellent oxidation resistance, rivaling many metallic NiAl, NiCrAl, and FeCrAl counterparts and with upper temperature capability possible to approximately1400C. However a number of limitations have been emerging that need to be acknowledged to permit robust performance in demanding applications. Ti2AlC and Ti3AlC2 possess excellent Scale Adhesion, cyclic oxidation/moisture/volatility resistance, and TBC compatibility. However they are very sensitive to Al content and flux in order to maintain an exclusive Al2O3 Scale without runaway oxidation of ubiquitous TiO2 transient Scales. Accelerated oxidation has been shown to occur for Al-depleted, damaged, or roughened surfaces at temperatures less than 1200C. Conversely, Cr2AlC is less sensitive to transients, but exhibits volatile losses at 1200C or above if common Cr7C3 impurity phases are present. Poor Scale Adhesion is exhibited after oxidation at 1150C or above, where spallation occurs at the Cr7C3 (depletion zone) interface. Delayed spallation is significant and suggests a moisture-induced phenomenon similar to non-adherent metallic systems. Re-oxidation of this surface does not reproduce the initial pure Al2O3 behavior, but initiates a less-protective Scale. Cr2AlC has also been shown to have good long term bonding with superalloys at 800C, but exhibits significant Beta-NiAl + Cr7C3 diffusion zones at 1100C and above. This may set limits on Cr2AlC as a high temperature TBC bond coat on Ni-based superalloys, while improving corrosion resistance in lower temperature applications.
-
Moisture-Induced Spallation and Interfacial Hydrogen Embrittlement of Alumina Scales
2013Co-Authors: James L. SmialekAbstract:While interfacial sulfuris the primary chemical factor affecting Al2O3 Scale Adhesion, moisture-induced delayed spallation appears as a secondary, but impressive, mechanistic detail. Similarities with bulk metallic phenomena suggest that hydrogen embrittlement from ambient humidity, resulting from the reaction Alalloy+3(H2O)air=Al(OH)− 3+3H+ may be the operative mechanism. This proposal was tested on pre-oxidized Rene N5 by standard cathodic hydrogen charging in 1N H2SO4, as monitored by weight change, induced current, and microstructure. Cathodic polarization at −2.0 V abruptly stripped mature Al2O3 Scales at the oxide-metal interface. Anodic polarization at +2.0V, however, produced alloy dissolution. Finally, with no applied voltage, the acid electrolyte produced neither Scale spallation nor alloy dissolution. Thus, hydrogen charging was detrimental to alumina Scale Adhesion. Moisture-induced interfacial hydrogen embrittlement is concluded to be the cause of delayed Scale spallation and desktop thermal barrier coating failures.
-
Moisture-induced delayed spallation and interfacial hydrogen embrittlement of alumina Scales
JOM, 2006Co-Authors: James L. SmialekAbstract:While interfacial sulfuris the primary chemical factor affecting Al_2O_3 Scale Adhesion, moisture-induced delayed spallation appears as a secondary, but impressive, mechanistic detail. Similarities with bulk metallic phenomena suggest that hydrogen embrittlement from ambient humidity, resulting from the reaction Al_alloy+3(H_2O)_air=Al(OH)^− _3+3H^+ may be the operative mechanism. This proposal was tested on pre-oxidized René N5 by standard cathodic hydrogen charging in 1N H_2SO_4, as monitored by weight change, induced current, and microstructure. Cathodic polarization at −2.0 V abruptly stripped mature Al_2O_3 Scales at the oxide-metal interface. Anodic polarization at +2.0V, however, produced alloy dissolution. Finally, with no applied voltage, the acid electrolyte produced neither Scale spallation nor alloy dissolution. Thus, hydrogen charging was detrimental to alumina Scale Adhesion. Moisture-induced interfacial hydrogen embrittlement is concluded to be the cause of delayed Scale spallation and desktop thermal barrier coating failures.
-
26th Annual Conference on Composites, Advanced Ceramics, Materials, and Structures: B: Ceramic Engineering and Science Proceedings, Volume 23, Issue 4 - Scale Adhesion, sulfur content, and TBC failure on single crystal superalloys
Ceramic Engineering and Science Proceedings, 2002Co-Authors: James L. SmialekAbstract:The Scale Adhesion of single crystal superalloys was studied as a function of sulfur content. Cyclic oxidation tests of as-received PWA 1480 (6 ppmw S) at 1100°C resulted in severe Scale spallation and produced weight losses of >30 mg/cm after 500 1-h cycles. However, samples des Ifurized by hydrogen annealing ( 2000 h by geometric modifications that avert standard edge delamination and buckling failure modes.
-
optimizing Scale Adhesion on single crystal superalloys
Materials Science Forum, 2001Co-Authors: James L. Smialek, Bruce A PintAbstract:To improve Scale Adhesion, single crystal superalloys have been desulfurized to levels below 1 ppmw by hydrogen annealing. A transition to fully adherent behavior has been shown to occur at a sulfur level of about 0.2 ppmw, as demonstrated for PWA 1480, PWA 1484, and Rene N5 single crystal superalloys in 1100°-1150°C cyclic oxidation tests up to 2000 h. Small additions of yttrium (15 ppmw) also have been effective in producing Adhesion for sulfur contents of about 5 ppmw. Thus the critical Y/S ratio required for Adhesion was on the order of 3-to-1 by weight (1-to-1 atomic), in agreement with values estimated from solubility products for yttrium sulfides. While hydrogen annealing greatly improved an undoped alloy, yielding ≤0.01 ppmw S, it also produced benefits for Y-doped alloys without measurably reducing the sulfur content.
Somrerk Chandra-ambhorn - One of the best experts on this subject based on the ideXlab platform.
-
CHAPTER 6 Development of SOFC Interconnect Stainless Steels
Solid State Phenomena, 2020Co-Authors: Sébastien Chevalier, Somrerk Chandra-ambhorn, Lionel Combemale, I. Popa, Walairat Chandra-ambhorn, Piyorose Promdirek, Patthranit WongpromratAbstract:The chapter introduces components and working principle of solid oxide fuel cells (SOFCs). It is followed by the explanation on the choices of materials focussing on ferritic stainless steels. The review is further made on the required properties of these steels, i.e. low oxidation rate, low chromium species volatilisation rate, high electrical conductivity and good Scale Adhesion. For the oxidation aspect, the behaviour of stainless steel interconnect in cathode, anode (hydrogen and biogas), and dual atmospheres are described. Surface modification by pre-oxidation and coatings to improve the oxide electrical conductivity and to reduce chromium species volatilisation is finally reviewed.
-
On the hot-rolled recycled carbon steels: their oxide formation, pickling ability and Scale Adhesion
Anti-corrosion Methods and Materials, 2019Co-Authors: Somrerk Chandra-ambhorn, Thanasak Nilsonthi, Jennarong Tungtrongpairoj, Anuwat Jutilarptavorn, Tanongsak SomphakdeeAbstract:Purpose The purpose of this study is to investigate the formation, pickling ability and Adhesion of thermal oxide Scales on the hot-rolled recycled steels produced from the medium and thin slabs. Because the Scale on the steel produced from the medium slab was relatively thick of about 11 µm, it contained cracks after hot-rolling. Thus during pickling, the Scale was uniformly attacked with the simultaneous dissolution of the inner Scale because of the penetration of acid through cracks. However, the Scale on the steel produced from the thin slab was thinner of about 6 µm and thus, nearly crack-free. The pickling solution thus attacked the Scale surface uniformly. At longer pickling periods, pits were also nucleated and propagated. Concurrently, the tensile testing machine with a CCD camera has been applied to observe Scale Adhesion. Design/methodology/approach The formation, pickling ability and Adhesion of thermal oxide Scales on the hot-rolled recycled steels produced from the recycled slab, e.g. medium slab and thin slab, were investigated. The morphology and phase identification were examined by using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Furthermore, the Adhesion behaviour of oxide Scale was investigated by immersion test and tensile test with a CCD camera. Findings For the Scale formation, it was found that the hematite and magnetite were formed on the hot-rolled recycled steels produced from the medium and thin slabs. For the immersion test, it was found that the Scale on hot-rolled recycled steels produced from the medium slab was more difficult to be pickled as represented by the longer time for the complete pickling. This was consistent with the result of tensile test; the steel produced from the medium slab had better Scale Adhesion as represented by the higher strain initiating the first spallation of Scale. Originality/value The effects of slab types and its alloying element were investigated to understand the Scale Adhesion behaviour. The empirical pickling mechanisms and the mechanical Adhesion energy were proposed. It led to the understanding in the control of alloying element in the hot-rolled steel.
-
High temperature oxidation behaviour of Fe–15.7 wt.% Cr–8.5 wt.% Mn in oxygen without and with water vapour at 700 ºC
Corrosion Science, 2019Co-Authors: Somrerk Chandra-ambhorn, P. Saranyachot, Thammaporn ThublaorAbstract:Abstract Fe–15.7 wt.% Cr–8.5 wt.% Mn was oxidised in O2 and O2–9 vol.% H2O at 700 °C. Oxide Scales in both atmospheres consisted of M2O3 and M3O4 where M could be Mn, Cr and Fe. The graphical representation of the water vapour effect on the concentrations and dominant regimes of defects in the Brouwer diagram was proposed. The enhanced oxidation rate due to water vapour was found possibly as a result of the increased metal vacancy concentration and its dominant regime and the inwards diffusion of hydroxyl ions supported by the Scale Adhesion results.
-
High Temperature Oxidation of Micro-alloyed Steel and Its Scale Adhesion
Oxidation of Metals, 2017Co-Authors: Komsan Ngamkham, Somrerk Chandra-ambhornAbstract:The present work investigated the high temperature oxidation behaviour of the micro-alloyed steel and the Adhesion of thermal oxide Scale to its steel substrate. Oxidation testing was conducted at 815 °C in oxygen without and with 17.9% v/v water vapour. The oxidation kinetics in the two atmospheres were parabolic with similar rate constants, i.e. 1.13 × 10^−9 and 1.17 × 10^−9 g^2 cm^−4 s^−1 for the sample oxidised in oxygen without and with water vapour, respectively. The XRD peaks for wustite, magnetite, Ti-doped magnetite and titanium carbide were detected for the sample oxidised in oxygen. For the sample oxidised in the humidified atmosphere, Ti-doped magnetite was dominantly observed, additionally with titanium carbide. A tensile testing machine equipped with an optical lens was used to monitor Scale failure during straining. For the sample oxidised for 1 min, the strain initiating the first spallation of the steel oxidised in the humidified oxygen was 1.74 ± 0.14%. This strain was higher than the strain initiating the first spallation of the steel oxidised in oxygen which was 1.00 ± 0.04%, indicating the improved Adhesion of Scale formed in the atmosphere containing water vapour. Mechanisms of water vapour effect on Scale Adhesion are discussed.
-
Development of the Scale Adhesion Assessment Using a Tensile Testing Machine Equipped with a CCD Camera
Oxidation of Metals, 2017Co-Authors: Thanasak Nilsonthi, Wannapha Issaard, Somrerk Chandra-ambhornAbstract:The objective of this work was to develop a Scale Adhesion assessment method by using a tensile testing machine equipped with a CCD camera to instantaneously observe the Scale failure during a given exposure. The sample studied was carbon steel oxidised at 900 °C in synthetic air for 2 min, giving the Scale thickness of 3.45 μm. The strain initiating the first spallation was determined to semi-quantitatively assess the Scale Adhesion, which was 3.71 ± 0.86% in the present study. The Galerie–Dupeux model based on U.R. Evans’ criterion was used to quantify the Adhesion energy, which was 345 ± 39 J m^−2 at the strain initiating the first spallation. However, during the tensile loading the Scale spalled with the increased strain and at each strain there existed a particular value of the Adhesion energy. To take into account the statistical nature of the Scale spallation at different strains with different spallation ratios, the present work proposed the quantification of the average Adhesion energy by weighting the Adhesion energy at each strain by the increase in the spallation ratio taking place at that strain. Owing to the developed testing method that could record the spallation ratio as a function of the strain, the weighted average Adhesion energy at strains up to 10% was quantified giving the value of 530 ± 9 J m^−2. This energy represented the Scale Adhesion characteristics not only at the strain that Scale firstly spalled but in a wider range of the imposed strains.
Nima Rahbar - One of the best experts on this subject based on the ideXlab platform.
-
nano Scale Adhesion in multilayered drug eluting stents
Journal of The Mechanical Behavior of Biomedical Materials, 2013Co-Authors: Sina Youssefian, Nima RahbarAbstract:Using stainless steel 316L for drug-eluting stents needs specific surface finishing due to corrosion phenomena that take place on the metal surface upon prolonged contact with human tissue. Poly (o-chloro-p-xylylene) (Parylene C) is one of the inert and biocompatible materials that are used for 316L coating with g-methacryloxypropyltrimethoxysilane as an Adhesion promoter. In this study, a combination of atomic force microscopy experiments and contact theories have been used to quantify the work of Adhesion between parylene C/316L and silane added parylene C/316L. An atomistic simulation has been used, first, to investigate and compare the Adhesion at the room temperature with the experiments and then, to investigate the effect of aqueous environment with higher temperature, inside the body, on the Adhesion between layers in the structure of drug eluting stent. The simulation results of simplified model for 316L are in good agreement with the experimental results and suggest that the week affiliation between this polymer and 316L is mainly due to Van der Waals interactions. The effect of temperature on the Adhesion is found to be regressive and as the water molecules permeate the polymer the Adhesion decreases. They also imply
-
Nano- and Micro-Scale Adhesion in Drug-eluting Stents
MRS Proceedings, 2009Co-Authors: Juan Meng, Nima Rahbar, Hannah Li, George Papandreou, Cynthia A. Maryanoff, Winston O. SoboyejoAbstract:AbstractThis paper presents a combined experimental and theoretical/computational study of Adhesion and interfacial fracture between multilayers in a CYPHER® model drug eluting stents (DES). Atomic Force Microscopy (AFM) is used to obtain pull-off forces between coated AFM tips and substrates that simulate the bimaterial surfaces in the DES. Adhesion theories and fracture mechanics concepts are then applied to obtain estimates of the fracture toughness over a range of mode mixities between pure mode I and pure mode II. The trends in the estimates are shown to be in good agreement with experimental measurements of interfacial fracture toughness obtained from Brazil disk specimens over the same range of mode mixities.
