Advances in test and measurement of the interface adhesion and bond strengths in coating-substrate systems, emphasising blister and bulk techniques

In this paper, recent advances in the minimum-destructive testing of the adhesion of coating-substrate systems are reviewed, focusing on key techniques such as micro- and nano-scale levels of indentation, scratching, laser-induced wave shock, as well as the blister and buckle approach. Along with adhesion failure tests, the latest and most extensive applications of the adhesion test methods in nano-, micro- and bulk-coating technology and the associated techniques to determine the minimum damage defects left on the coatings are discussed and their use reviewed

Synthesis and characterization of titanium carbon nitride films by High Power Impulse Magnetron Sputtering

The aim of this study is to investigate the potentiality of an HiPIMS reactive process with two gases, evaluating the process control and the properties of the deposited coatings compared to DCMagnetron Sputtering. TiCN(H) nano-composite films have been deposited in a CFUBMS apparatus and HiPIMS generator. Coatings have been characterized from compositional, microstructural as well as mechanical and tribological point of viewope

High temperature ceramic composites

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.Includes bibliographical references (leaves 111-120).by Leonid C. Lev.Ph.D

Mechanical and thermal stability of hard nitride coatings

Cotutela Universitat Politècnica de Catalunya i Linköping UniversityTesi per compendi de publicacionsHard coating 's thermal stability is essential due to the high temperature environment of high-speed cutting applications, while the induced phase and microstructure evolution affects the mechanical properties. In this thesis, the mechanical stability of arc-evaporated hard nitride coatings annealed at high temperature is analyzed and connected to the phase evolution. In addition to hardness, fracture toughness is evaluated by surface and cross-sectional investigations by scanning/transmission electron microscopy of damage events by mechanical tests. The crack resistance of Ti1-xAixN with a range of Al content (x = 0.23-0.82) is studied by contact fatigue tests, where the difference in the microstructure plays a major role. Superior mechanical properties are found in annealed Ti0.63AI0.37N at 900 oC due to the spinodal decomposition. The mechanical and high-temperature properties of hard coatings can be enhanced by alloying or multi-layering. Quaternary Ti-Al-X-N (X = Cr, Nb and V) alloys are studied, and superior toughness is found in TiAI(Nb )N in both the as-deposited and annealed (1100 oC) states. The h-AIN formation in TixAI0.37Cr1-0.37-xN (x = 0.03 and 0.16) is analyzed by in-situ x-ray scattering during annealing. The kinetic energy for h-AIN formation is found to be dependent on the microstructure evolution during annealing, which varies with coating composition. High Al content h-ZrAIN/c-TiN and h-ZrAIN/c-ZrN multilayers are investigated through scratch tests followed by focused ion-beam analysis of the crack propagation. A c-Ti(Zr)N phase forms in h-ZrAIN/c-TiN multilayers at high temperatures and that contributes to enhanced hardness and fracture toughness by keeping the semi-coherency at the sub-interfaces. Finally, an in-situ analysis of coatings by x-ray scattering during a turning process is carried out. lt demonstrates the possibility of observation of stress evolution and thermal expansion of the coatings or the work piece material during machining. This experiment provides real-time information on the coating behavior during cutting.La estabilidad térmica del recubrimiento es esencial debido a que estos recubrimientos durante su aplicación son utilizados a elevada temperatura y a alta velocidad. Durante dicho proceso, la evolución microestructural afecta a las propiedades mecánicas. En dicha tesis, la estabilidad mecánica de los recubimientos duros base nitruro producidos mediante arco y recocidos a elevada temperatura son analizados y se correlacionado con su transformación de fase. La dureza, la resistencia a la fractura son evaluados mediante la observación tanto superficial como transversal mediante microscopia electrónica de barrido. La resistencia a la propagación de grieta de Ti1−xAlxN con un contenido en Al que fluctúa entre 0.23-0.82 se estudia mediante ensayos de fatiga por contacto, donde la diferencia microstructural juega un papel importante. Las mejores propiedades mecánicas se encentran en las muestras con un 0.63 de Ti donde se ha realizado un proceso de recocido a 900o C debido a la descomposición espinoidal. Las características mecánicas y de alta temperatura de recubrimientos duros pueden ser mejoradas si tenemos un recubrimiento multicapa. Aleaciones cuaternarias de Ti-Al-X-N (X = Cr, Nb y V) son estudiada, y una mejor tenacidad de fractura se encuentra para la muestra TiAl(Nb)N sin tratamiento de recocido como recocida a 1000ºC. La formación del AlN con una estructura hexagonal en la muestra TixAl0.37Cr1−0.37−xN (x = 0.03 y 0.16) son analizadas mediante ensayos in-situ de difracción de rayos X durante el proceso de recocido. Cabe mencionar que la energía cinética para la formación de la AlN con una estructura hexagonal depende del proceso de recocido, la cual hace variar la composición química del recubrimiento. Multicapas de h (hexagonal)-ZrAlN/c (cúbica)-TiN con un elevado contenido de Al son estudiadas mediante ensayos de rayado y la generación de daño es observado mediante la técnica del haz de iones focalizados. Las formas de la fase de c-Ti(Zr)N en las multicapas de (h)-ZrAlN/c-TiN formadas a elevadas temperaturas contribuyen a mejorar la dureza y la tenacidad de fractura manteniendo la semicoherencia en las intercaras entre cada capa. Finalmente, se realiza un análisis in-situ de los diferentes recubrimientos me diante dispersión de rayos X durante un proceso de torneado. En este caso, se demuestra la posibilidad de observar la evolución de las tensiones residuales y de la expansión térmica durante el proceso de conformado. Dicho experimentos proporciona información en tiempo real sobre el comportamiento del recubrimiento en condiciones de servicio.Hårda skikts högtemperaturstabilitet är viktig på grund av den höga temperaturskikten utsätts för under skärande bearbetning, och den utveckling av faser och mikrostruktur som då sker påverkar skiktets mekaniska egenskaper. I den här avhandlingen har den mekaniska stabiliteten hos arcförångade, hårda metallnitridskikt som värmebehandlats vid höga temperaturer studerats. Förutom hårdhet har även skiktens seghet utvärderats genom yt- och tvärsnittsstudier av den sprickbildning som uppstår vid mekanisk provning med hjälp av svep- och transmissionselektronmikroskopi. Segheten hos Ti1−xAlxN skikt med varierande Al-halt (x = 0.23-0.82) studerades genom utmattningsprovning och resultaten visar att förändringar i mikrostrukturen spelar en stor roll. Ti0.63Al0.37N skikten hade överlägsna mekaniska egenskaper; på grund av en fördelaktig kornstorlek i de obehandlade skikten och efter värmebehandling som ett resultat av det spinodala sönderfall som skett. De mekaniska egenskaperna och högtemperaturegenskaperna hos hårda skikt kan förbättras genom legering eller genom multilagring. I den här avhandlingen har kvarternära Ti-Al-X-N (X = Cr, Nb eller V) skikt studerats och TiAl(Nb)N skikten hade en överlägsen seghet i både obehandlat och värmebehandlat (1100oC) tillstånd. Bildandet av h-AlN i TixAl0.37Cr1−0.37−xN (x = 0.03 and 0.16) skikt studerades genom in situ röntgenspridning under värmebehandling. Den energi som krävs för att bilda h-AlN beror av mikrostrukturutvecklingen under värmebehandling vilken i sin tur beror av skiktens kemiska sammansättning. h-ZrAlN/c-TiN och h-ZrAlN/c-ZrN multilager med hög Al-halt undersöktes genom reptester följda av tvärsnittsstudier av sprickbildningen genom en analys med en fokuserad jonstråle (FIB). En c-Ti(Zr)N fas bildas vid höga temperaturer i h-ZrAlN/c-TiN multilagren och det bidrar till förhöjd hårdhet och förbättrad seghet på grund av en bibehållen koherens mellan lagren. Slutligen har in situ röntgenspridningsstudier av ytskikt utförts vid svarvning. Studien visar på möjligheten att observera spänning och värmeutvidgning av skikten eller arbetsmaterialet under bearbetning. Experimenten ger information om skiktens beteende under bearbetning i realtid.Postprint (published version

The effect of sintering and CMAS on the stability of plasma-sprayed zirconia thermal barrier coatings

State of the art thermal barrier coatings (TBCs) for gas turbine applications comprise (7 wt.%) yttria partially stabilized zirconia (7YSZ). 7YSZ offers a range of attractive functional properties – low thermal conductivity, high thermal expansion coefficient and high in-plane strain tolerance. However, as turbine entry temperatures are raised, the performance of 7YSZ coatings will be increasingly affected by sintering and environmental contamination, by calcia-magnesia-alumina-silica (CMAS) deposits. The effect of sintering-induced stiffening on the driving force for spallation of plasma-sprayed (PS) TBCs was investigated. Spallation lifetimes of TBC specimens sprayed onto alumina substrates were measured. A simple fracture mechanics approach was employed in order to deduce a value for the strain energy release rate. The critical strain energy release rate was found to be constant, and if this value had been known beforehand, then the rationale presented here could be used for prediction of coating lifetime. The effect of vermiculite (VM) and volcanic ash (VA) contamination on the sintering-induced spallation lifetime of PS TBCs was also investigated. The presence of both VM and VA was found to accelerate the rise in their Young’s modulus with sintering. Spallation results show that coating lifetime may be significantly reduced, even at relative low addition levels, due to the loss of strain tolerance caused by the penetration of glassy deposits. This result gives a clear insight into the role CMAS plays in destabilizing TBCs. Finally, the adhesion characteristics of ingested volcanic ash were studied using a small jet engine. The effects of engine speed and particle size were investigated. Deposition on turbine surfaces was assessed using a borescope. Deposition mainly occurred on the nozzle guide vane and blade platform. A numerical model was used to predict particle acceleration and heating in flight. It was observed that larger particles are more likely to adhere because they have greater inertia, and thus are more likely to impact surfaces. The temperature of the larger particles at the end of its flight was predicted to be below its softening point. However, since the component surface temperatures are expected to be hotter, adhesion of such particles is probable, by softening/melting straight after impact.I gratefully acknowledge the provision of funding by the Schools Competition Act Settlement Trust (SCAST), Sulzer Metco Inc., the Royal Aeronautical Society, Cambridge Philosophical and the Worshipful Company of Armourers and Brasiers to support this work

Correlating Microstructural Development And Failure Mechanisms To Photo Stimulated Luminescence Spectroscopy And Electrochemical Impedance Spectroscopy In Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are widely used for thermal protection of hot section components in turbines for propulsion and power generation. Applications of TBCs based on a clearer understanding of failure mechanisms can help increase the performance and life-cycle cost of advanced gas turbine engines. Development and refinement of robust nondestructive evaluation techniques can also enhance the reliability, availability and maintainability of hot section components in gas turbines engines. In this work, degradation of TBCs was non-destructively examined by photostimulated luminescence spectroscopy (PSLS) and electrochemical impedance spectroscopy (EIS) as a function of furnace thermal cycling carried out in air with 10-minute heat-up, 0.67, 9.6 and 49.6 - hour dwell duration at 1121°C (2050°F), and 10-minute forced-air quench. TBCs examined in this study consisted of either electron beam physical vapor deposited and air plasma sprayed yttria-stabilized zirconia (YSZ) on a variety of bond coat / superalloy substrates including bond coats of NiCoCrAlY and (Ni,Pt)Al, and superalloys of CMSX-4, Rene‟N5, Haynes 230 and MAR-M-509. Detailed microstructural characterization by scanning electron microscopy and energy dispersive spectroscopy was carried out to document the degradation and failure characteristics of TBC failure, and correlate results of PSLS and EIS. Mechanisms of microstructural damage initiation and progression varied as a function of TBC architecture and thermal cycling dwell time, and included undulation of the interface between the thermally grown oxide (TGO) and bond coats, internal oxidation of the bond coats, and formation of Ni/Co-rich TGO. These microstructural observations were correlated to the evolution in compressive residual stress in the TGO scale determined by PSLS shift. Correlations iv include stress-relief and corresponding luminescence shift towards stress-free luminescence (i.e. = 14402 cm-1 and = 14432 cm-1 ) associated with subcritical cracking of the TGO scale and stress-relaxation associated with gradual shift in the luminescence towards stress-free luminescence (i.e. = 14402 cm-1 and =14432 cm-1 ) is related to the undulation of TGO/bondcoat interface (e.g., rumpling and ratcheting). Microstructural changes in TBCs such as YSZ sintering, TGO growth, and subcritical damages within the YSZ and TGO scale were also correlated to the changes in electrochemical resistance and capacitance of the YSZ and TGO, respectively. With thermal exposure the YSZ/TGO resistance and capacitance increased and decreased as result of sintering and TGO growth. With progressive thermal cycling damages in the TGO was related to the TGO capacitance showing a continuous increase and at failure TGO capacitance abruptly increased with the exposure of bondcoat. Further correlations among the microstructural development, PSLS and EIS are documented and discussed, particularly as a function of dwell time used during furnace thermal cycling test, with due respect for changes in failure characteristics and mechanisms for various types of TBC

CORRELATION OF SHORT-TERM TO LONG-TERM OXIDATION TESTING FOR ALUMINA FORMING ALLOYS AND COATINGS

Engineering long cyclic oxidation life of high temperature materials requires success on two fronts. First a slow growing protective oxide scale must form during the elevated temperature exposure. To satisfy this aspect, alumina-forming alloys and coatings are widely accepted as leading materials for use in this environment and are the focus of this discussion. The second aspect is the formation of an adherent oxide that resists spallation during thermal cycling. The driving force for spallation is the stored elastic strain energy that develops from stresses in the oxide scale. Once this stored elastic strain energy exceeds the oxide-substrate interfacial toughness, cracking and subsequent spallation occurs followed by rapid oxidation of the substrate. With advances in alloy and coating development resulting in higher operating temperatures and increased service lives, researchers are faced with excessive laboratory time and cost required to perform a long-term cyclic oxidation test.The challenge is to predict long-term oxidation behavior from short-term experiments. Since the rate limiting step to high temperature oxidation is a thermally activated process, previous investigations were performed at increased exposure temperatures for rapid degradation of the alloys and coatings to rank material performance. Others have mechanically induced oxide spallation to give insight on the adherence of oxide scales prior to spontaneous failure. In this investigation, short-term testing is employed to gain insight on long-term performance and to determine inputs into a cyclic oxidation model for life-time prediction. This model operates in an iterative process where one iteration is a thermal cycle. The amount of oxide formed during the high temperature segment is calculated followed by the amount that is lost due to scale spallation during cooling. Retained oxide at the end of this cycle is used as the starting point for the following iteration. The two inputs into this model are the oxide scale growth and spallation behavior. Scale growth behavior corresponds to the isothermal growth kinetics that are experimentally determined by thermogravimetric analysis. Oxide scale spallation behavior is quantified by two short-term experiments of a novel acoustic emission experiment during a 24 hour exposure and the stress measurement of the scale after an exposure to the temperature of interest. Results from these short-term tests and modeled cyclic oxidation are compared to life-times from long-term cyclic oxidation tests