Experimental Investigation of Air-Cooled Turbine Blades in Turbojet Engine 13: Endurance Evaluation of Several Protective Coatings Applied to Turbine Blades of Nonstrategic Steels Page: 15 of 41
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NACA RM E53E18
PROCEDURE section of this report. The blades were then nickel-coated,
and in this manner the Nicrobraz formed an undercoat for the nickel
along the leading edge.
Blades 17 and 18 failed in fatigue at the blade root after 11.4
and 23.7 hours of operation, respectively. The coatings were in good
condition at the inspections prior to the time of the fatigue failures.
Blade 19 was damaged beyond repair by fragments from a failed blade
after 25.6 hours of operation. The coating on this blade, had shown evi-
dence of slight flaking in the midchord region near the tip, but the
coating on the rest-of the blade was in good condition prior to the time
the blade was damaged. Blades 16 and 20 wee operated successfully for
101.2 and ..100 hours, respectively. The coating on blade 16 was in good
condition except for scaling of the nickel on the rear third of the suc-
tion surface. No corrosion of the blade metal was apparent in this area.
At the end of 100 hours of operation on blade 20 the coating was in
excellent condition except for a small area on the pressure surface near
the trailing edge where the coating had begun to flake off (fig. 6). No
corrosion of the parent metal was observed. In the leading-edge region
near the tip on the suction surface of blade 20 there appeared to be
several small areas where the nickel had flaked away. This damage was
caused by foreign particles passing through ,the engine which struck the-
blade in the leading-edge region where there was a Nicrobraz undercoat,
and, although the nickel chipped away, the Nicrobraz protected the parent
metal. The adherence of the nickel to the Nicrobraz appeared to elim-
inate flaking of the nickel and enabled it to protect the blade. The
underlying Nicrobraz, while capable of providing protection, was not
called upon to do so except where the nickelwas chipped away by foreign
particles striking the blade.
During the investigation of the five nickel-coated blades having
Nicrobraz undercoat at the leading edges, none of the tests were termi-
nated because of coating failure. Adherence of the nickel over the
entire blade appeared to be better in this group of blades than in those
previously employed. Blades 16 through 20 had shells of Timken 17-22A(S)
steel; while the previous group, with the exception of blades 7 and 8,
had shells of SAE 4130 steel (see table II). Based solely on observa-
tion of these blades, it appears that the adherence of nickel, when
applied in the manner previously described, is greater to Timken 17-22A(S)
steel than to SAE 4130 steel.
Nicrobraz Coatings
Blades 21, 22, and 23. - Because of the success obtained in using
Nicrobraz as an undercoat for nickel, it was believed that a completely
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Bartoo, Edward R. & Clure, John L. Experimental Investigation of Air-Cooled Turbine Blades in Turbojet Engine 13: Endurance Evaluation of Several Protective Coatings Applied to Turbine Blades of Nonstrategic Steels, report, July 16, 1953; (https://digital.library.unt.edu/ark:/67531/metadc64866/m1/15/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.