Effect of Blade Geometry on γ′ Lattice Parameter and Primary Orientation of SX Cored Turbine Blades (I)

Abstract

The γ′ lattice parameter aγ′ and the α angle defining the primary crystal orientation of the single-crystalline cored turbine blades made of CMSX-4 superalloy were measured in the areas located near the selector situated asymmetrically, considering the top view of the blade. The distributions of the aγ′ and the α angle were determined along the lines parallel to the vertical blade axis Z using X-ray diffraction methods. The relations between changes in the aγ′(Z) and α(Z) were analyzed on the Z levels where the shape of the blade’s cross-section changes. For the first time, the local increase in aγ′(Z) was found near the root–airfoil connection level and near certain other root levels, which is related to the change in blade section shapes on such levels. The local extremes in α(Z), representing the dendrite bend, were observed at these levels. The increase in the aγ′(Z) with the local bending of dendrites was discussed concerning the local redistribution of alloying elements and local residual stresses of the γ-dendrites. For the first time, a method of analyzing the local bending of the dendrites was proposed by studying the behavior of the α(Z). The presented results concern the first stage of the research covering areas relatively close to the selector, considering the top view of the blades. The second stage will include the analysis of the areas of the blade localized at a longer distance from the selector.

Effect of Blade Geometry on γ′ Lattice Parameter and Primary Orientation of SX Cored Turbine Blades (II)

“…Figure 2 shows the graphs of the a γ′ (Z n ), α(Z n ), and β(Z n ) relationship obtained for the measuring line n. The value of a γ′ for the Z n ranged between 1 mm and 5.5 mm and varied about 3.5805 Å in the range of 0.001 Å, which corresponds to the fluctuations of a γ′ in an undisturbed dendritic structure [ 5 , 33 ]. However, for Z n equal to 6 mm, a γ′ decreases, and then, near Z n equal to 7 mm corresponding to the RA level, it increases by 0.002 Å, reaching the value of 3.5810 Å.…”

“…The areas of the blade root over which the airfoil is not located and areas in which the airfoil is a continuation of the root, as well as the areas similar to the latter but located near the walls of the cooling bore, were examined. The current paper describes the continuation of the studies presented in [ 5 ] in which the research results on regions of the L-section located close to the selector and its continuer extension were presented.…”

“…The [001]-type crystal direction is parallel to the γ-dendrite growth direction in the crystallization of blades by the Bridgman method. Stochastic misorientation of the neighboring dendrites, and thus the areas of the blades, and also the misorientation created due to the complex shape of the blade [ 5 ] can allow the formation of low-angle boundaries (LABs) [ 6 , 7 , 8 ] that reduce the strength parameters of the blade. The crystal orientation of SX blades significantly influences thermal fatigue strength [ 9 ], and its local changes may also affect the corrosion resistance of SX Ni-base superalloys [ 10 ].…”

“…In the first part of the studies reported in [ 5 ], the distribution of the α angle and the a γ′ lattice parameter along the measuring lines traced parallel to the main axis Z 0 of the blade on the surface of the L-section ( Figure 1 a,b) that passed through the selector’s continuer extension (CE) region was examined. The measuring lines were located relatively close to the CE region ( Figure 1 b).…”

“…As presented in [ 5 ], clear changes in the relations of α and a γ′ as the functions of coordinates of the measuring line axes traced parallel to Z 0 on the surface of the L-section were found on certain levels, i.e., for certain Z. These changes were related to chamfer of the root surface and the root–airfoil connection; in other words, they occurred at the CH and RA levels ( Figure 1 a).…”