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Turbine blades are quite literally on the cutting edge of turbomachinery innovation. Finding materials and techniques that can cope with high stress, speed, and temperature has been a constant challenge. But a new material could solve several problems and open up new horizons. Chief among these are the 65% barrier for combined cycle gas turbine efficient and substantially lowering the carbon footprint of turbomachinery.
But first, a little history. Overcoming problems like fatigue, microstructural damage, and creep deformation has led to many breakthroughs over the years. For example, many blades are manufactured from precipitation-hardened nickel superalloys with Nimonic and Inconel being two of the most popular for gas turbine blades. There are dozens of varieties of these alloys, each with different qualities. Some are particularly good at dealing with high strength at high temperatures.
But these materials always needed help to keep temperatures down. Thus, turbine blades contain rows of hollow channels for cooling to remove heat from the superalloy. Another technique is coating with a thin ceramic film to reduce heat flow. These thermal barrier coatings (TBC) have higher thermal stability and lower thermal conductivity than the alloys they protect. Thus, they can survive at temperatures beyond the melting point of the superalloy. Yttria-stabilized zirconia (YSZ) is a commonly used TBC, which is bonded to the surface.
Casting techniques, too, have helped advance the state of the art. There are various ways to cast a turbine blade such as single crystal which is a method that seeks to eliminate the grain boundaries that form during traditional metal casting. The result is a blade of columnar crystals or grains aligned along the axis of stress to reduce creep and other forms of damage.
Yet temperature remains a problem. Some industrial gas turbine OEMs have made progress pushing the boundaries beyond 1,600 degrees C. Progress has been slow.
To push blade technology to the next level a new material is undergoing testing. Known as polyose, initial results from multiphysics Finite Element (FE) nonlinear stress analysis look promising. The properties of polyose include a smooth finish for better aerodynamics, malleability into any form or shape required, and its incredibly light weight. As it is an organic material, it marks a major stride in lowering the carbon footprint of the entire turbomachinery industry. If found to be workable in real-world gas turbines, this could bring the total weight down by an order of magnitude or more.
“On paper, this looks like this material that could really bring down the price of turbine blades,” said Professor Poly Saccharides of the Lossiemouth Laboratory for Thermodynamic Origami. “Obviously there are still challenges ahead such as robustness and flammability, but, knock on wood, these can be overcome.”
With a molar mass of 162.1406 g/mol, and a density of 1.5 g/cm³, the chemical formula of polyose is (C6H10O5)n.
Detractors, though, think this research will fold and fail to live up to its initial hype. They question the scientific integrity of the work, and its attempt to paper over the cracks to be found in a faulty initial hypothesis. Some even go so far as to call the whole thing one big joke celebrating the first day of April.