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During Soviet and subsequent Russian era, the jet engine technology development regarding turbine section, has been concentrated on directionally solidified turbine blade production. They have in house perfected the directionally solidified crystals to their own needs by attaining equiaxed crystals (these are crystals that have mostly axes of equal lengths.) .
By perfecting air cooling channel geometry and ceramic coatings they have managed to keep the boundary grain defects to a minimum and achieved acceptable high performance from these blades.
Directionally solidified blades are in essence layers of crystals. But due to their layered construction, under extreme heat and centrifugal forces the layers move unevenly away from each other, giving boundary grain imperfections and causing the Crystal lattices to deteriorate. Hence shorter lifecycles on engines especially if they are pushed hard too often.
Russians, according to western sources, have dabbled in Single Crystal blade manufacturing in some of their AL31 series engines. But did not get too far. AL41/AL51 series engines, according to unofficial sources may contain single crystals. But the fact remains that the Russian engines predominantly are produced with directionally solidified turbine blades.
It is also a known fact that the Russian jet engines’ combustion chambers are designed as shorter than western ones. Although this may give certain advantages, it also increases the chance of throwing out unspent fuel hence a smoke when pushed hard. (This however is less prominent in later engines). When you have a school of thought and design set on a specific way to produce your engine, it is not always feasible and workable to add new tech that works in the West. Hence may be their struggle with single crystals?
@Nilgiri may shed more light on this issue.
By perfecting air cooling channel geometry and ceramic coatings they have managed to keep the boundary grain defects to a minimum and achieved acceptable high performance from these blades.
Directionally solidified blades are in essence layers of crystals. But due to their layered construction, under extreme heat and centrifugal forces the layers move unevenly away from each other, giving boundary grain imperfections and causing the Crystal lattices to deteriorate. Hence shorter lifecycles on engines especially if they are pushed hard too often.
Russians, according to western sources, have dabbled in Single Crystal blade manufacturing in some of their AL31 series engines. But did not get too far. AL41/AL51 series engines, according to unofficial sources may contain single crystals. But the fact remains that the Russian engines predominantly are produced with directionally solidified turbine blades.
It is also a known fact that the Russian jet engines’ combustion chambers are designed as shorter than western ones. Although this may give certain advantages, it also increases the chance of throwing out unspent fuel hence a smoke when pushed hard. (This however is less prominent in later engines). When you have a school of thought and design set on a specific way to produce your engine, it is not always feasible and workable to add new tech that works in the West. Hence may be their struggle with single crystals?
@Nilgiri may shed more light on this issue.
