Improved thermal barrier coatings
Power generation using gas turbines relies on the combustion of fuel and subsequent use of the very hot gases to power a turbine. Currently, gas turbines are one of the most widely used technologies for power generation, mostly using natural gas seen as having major benefits compared to coal combustion. Future plans include exploiting hydrogen or syngas (a mixture of hydrogen, carbon monoxide and carbon dioxide). TBCs protect components from the high operating temperatures and also significantly enhance the efficiency of electricity generation by minimising heat loss. A large European consortium launched the project THEBARCODE (Development of multifunctional thermal barrier coatings and modelling tools for high temperature power generation with improved efficiency) to develop improved, cost-effective TBCs. The team investigated both wet and dry topcoat formulations as well as bond coats to be used directly below the topcoat. THEBARCODE researchers successfully prepared a number of unconventional materials with eco-friendly synthesis techniques and a corrosion-resistant nanopowder formulation for the bond coat. Surface modification of market-ready thermal spraying powder was investigated as a simple and cost-effective route to surfaces with graded functionality. Low-cost application methods were employed, including thermal spray and plasma spray technologies, and pulsed vapour deposition. The team employed micro-indentation testing for measuring the hardness of topcoats on a microscopic scale. They also performed a three-point bending flexural test to determine the elasticity in bending between the top- and bond coats. The research team investigated the mechanical properties, effect of annealing procedure, thermal cycling and thermal shock behaviour of the developed TBCs. This work led to the selection of five promising coat formulations to be deposited on real parts of the engine. New models were developed for crack growth analysis that allow TBC failure and lifetime prediction. Furthermore, the team investigated different methods of obtaining strain energy release rate as a function of thermal cycles. Scientists have delivered a holistic TBC technology complete with new materials and cost-effective processing that will significantly improve the efficiency of gas turbine power generation. This is an important transition technology as the world moves to relieve dependence on fossil fuels. Enhancing its efficiency will increase its impact.
Thermal barrier coatings, gas turbines, power generation, THEBARCODE, bond coats