Thermal Barrier Coating - Essay Example

Thermal Barrier Coating Thermal barrier coating performs a crucial function in insulating components like a gas turbine and parts of the airplane that are operating at high temperatures. Typical examples are combustor cans, turbine blades, nozzle guide vanes and ducting. Thermal barrier coating have made it possible to increase the operating temperature of a turbine. They are characterized by their very low thermal conductivity, with their coating having high-temperature gradients when the system is exposed to the flow of heat. The commonly used thermal barrier coating material is the yttria-stabilized zirconia (YSZ) that has resistance to thermal fatigue and thermal shock up to over 1150oC. YSZ is deposited by spraying plasma and a physical beam of electrons vapor deposition processes (Chen and Dong 380). The material can be deposited by HVOF of the spraying applications like blade tip prevention wear, where the resistant properties to wear of the material are also used. In common practice to pre-coat or aluminize the substance material with say MCrAIY bond-coat. The bond coat is essential to accommodate the residual stresses, which might otherwise develop in the insulating system. This residual stress is caused by the initial metallic substance, and the ceramic material has different coefficients thermal expansion. Thermal barrier coatings are an advanced system of elements that when applied to metallic surfaces they form a heat management mechanism. They have the capability of shielding the inner surfaces from greater heat loads due to their thermally insulating properties. The coating gives the allowance of operation at high temperatures and limits the exposure to the thermal covered surface. The coating extends the life of the covered surface by the reduction of the heat fatigue and reduction of oxidation (Chen and Dong 382). Together with the active film cooling, the thermal barrier coating allows the working fluid temperatures to be higher than the temperature of the metal’s melting of the aerofoil in the turbine. The thermal barrier coating has four layers; metal bond coat, the metal substrate, ceramic topcoat, and the thermally grown oxide. The ceramic part has yttria stabilized that is used due to its low conductivity and remains stable at the optimum operating temperature typically seen in applications. Recent developments in the seeking for an alternative for YSZ there was establishment of ceramic topcoat, where different novel ceramics has superior workability at high temperatures of above 1200 0C, where has in ferior fracture toughness as compared to the YSZ. The ceramic layer forms the largest thermal gradient that keeps the lower layers at relatively low temperatures than the surface. Thermal barrier coating may fail through different degradation modes that entail the mechanical rumbling of the surface bond during the cyclic thermal exposure, mostly the aircraft coating on the engines, hot corrosions, accelerated oxidation and molten deposit degradation (He et al. 100). There are cases of oxidation of the thermal barrier coating that makes the life of the metal be shorter, and the metal drastically suffers thermal fatigue. The thermal barrier coating can be locally modified at the interface between the thermal grown oxide and the bond coat to act as the thermographic phosphor that allows the measurement of the remote temperature. Aspects of Thermal Barrier Coating Due to the promise of the enhanced engine efficiency and the life of the component, the thermal barrier coating may get extensive applications in days to come in the diesel engines or the industrial gas turbine that is burning at less quality fuel and under highly corrosive environment. Thermal barrier coating are envisioned for military use or sea engines that are supposed to survive low-quality fuel under corrosive environments at the emergency time of war. Thus, to understand well and make good predictions where necessary the effects of sweltering corrosion are quite crucial. Many present day engine thermal barrier coating are of Y2O3 that is stabilized type. This material has been over many years developed and current is believed to have given the thermal barrier coating its performance mostly in aviation gas turbines (He et al. 103). Modes of corrosion by molten deposits The molten deposits react with the thermal barrier coating and affects its the critical phase, and the phases of the ZrO2 becomes complicated and especially in presence salt phases that are commixed. Less evidence is found in the literature that shows the effects of salt that is in a molten state in driving various zirconia transformations. The hot corrosion of the thermal barrier coatings in molten deposits can be categorized into four different modes. These modes include; attack by mineralization, chemical reaction, physical damage, and the corrosion of the bond coating, resulting from the molten phases that penetrate into the thermal barrier coating intergranular voids. The chemical reaction attack is characterized by the availability of the identifiable reaction product and results from the capability to postulate a particular reaction. The laws of thermodynamics and stoichiometry apply and the conditions reaction to take place chemically should be predictable (Song, Fang and Wang 295). The attack by mineralization is a kind of phase of reaction that involves the non-reactive liquid that will move a non-equilibrium or the stressed phase towards the level of stability. This mechanism is usually undefined; however, it may include limited precipitation or dissolution. Mineralization has been greatly used in obtaining phase stability in systems of silica and particular systems of zirconia. NaVO3 has been used to mineralize CeO2 in most of the cases that have been observed. Sometimes the thermal barrier coating undergoes failure. In last years of recent past primary gas industrial turbines, manufacturers developed new engines to the market that have significant high efficiencies mostly when combined with hot steam turbine. The inlet gas temperatures of the engines are over 1300 degree Celsius, and at those temperatures which are very high, single crystal alloy and high power directionally solidified alloys or HP-blading is required together with extra protection of the materials forming the base of the thermal barrier coating. The front stage blades in the airplane are covered by the thermal barrier coating that reduce metal temperatures at the time of take-off and enhances TMF resistance of blades. To have full advantage of TBC potentiality, right reproductivity of the surface deposition and significant degree of reliability process are required to make sure that appropriate mechanical and physical properties of the ceramic coating (Song, Fang and Wang 297). Much effort has been used to develop and enhance thermal barrier coating applied to a beam of electrons assisted physical vapor deposition techniques that are preferred in producing TBC systems in the aerofoils. The study have been focusing on understanding the mechanisms of failure of systems operating under different conditions and directed towards enhancement of deposition technique together with design methods and methodologies of life predictions. Thermal barrier coatings in low heat truck diesel engine The coming generation of truck engines that use diesel will be operating at high temperatures than the ones that are presently used. The water cooled engines will be replaced, and the mean and peak cylinder pressures will be increased. The in-cylinder insulation will assist in keeping the heat energy in the gas exhaust to be recovered by turbo compounding and turbocharging. This engine that will be also referred to as the little heat rejection engine will be more efficient, robust and reliable (Chen and Dong 378). The underway goal is to improve the existing engine by 30% from the levels that were initially started in 1982. When the high heat diesel engines will be developed there will be a lot of advantages associated with them. There will be high efficiency and reliability of the engines. The development will enhance quality, optimization control, and advanced coating system. Works Cited Chen, Zhaoyun, and Zichao Dong. Isothermal Oxidation Behavior Of A Thermal Barrier Coating Prepared Using EB-PVD. Surf. Interface Anal. 47.3 (2014): 377-383. Web. He, Bo et al. Thermal Failure of Thermal Barrier Coating with Thermal Sprayed Bond Coating on Titanium Alloy. Journal of Coatings Technology and Research 5.1 (2008): 99-106. Web. Song, Yan, Qin Zhi Fang, and T.J. Wang. Experimental Investigation of Residual Thermal Stress in Thermal Barrier Coating (TBC). KEM 462-463 (2011): 295-300. Web. Read More