Diffusion of Chromium in Alpha Cobalt-Chromium Solid Solutions

Diffusion of chromium in cobalt-chromium solid solutions was investigated in the range 0 to 40 atomic percent at temperatures of 1360 degrees, 1300 degrees, 1150 degrees, and 10000 degrees c. The diffusion coefficients were found to be relatively constant within the composition range covered by each specimen. The activation heat of diffusion was determined to be 63,000 calories per mole. This value agrees closely with the value of 63,400 calories per mole calculated by means of the Dushman-Langmuir equation

Engine Operating Conditions that Cause Thermal-Fatigue Cracks in Turbojet-Engine Buckets

Five engine tests were conducted to definitely establish the failure mechanism of leading-edge cracking and to determine which conditions of engine operation cause the failures. Five groups of S-616 and M-252 buckets from master lots were run consecutively in the same J47-25 engine. The tests included a steady-state run at full-power conditions, rapid cycling between idle and rated speed, and three different start-stop tests. The first start-stop test consisted of cycles of start and stop with 5 minutes of idle speed before each stop; the second included cycles of start and stop but with 15 minutes of rated speed before each stop; the third consisted of cycles of gradual starts and normal stops with 5 minutes at idle speed before each stop. The test results demonstrated that the primary cause of leading-edge cracking was thermal fatigue produced by repeated engine starts. The leading edge of the bucket experiences plastic flow in compression during starts and consequently is subjected to a tensile stress when the remainder of the bucket becomes heated and expands. Crack initiation was accelerated when rated-speed operation was added to each normal start-stop cycle. This acceleration of crack formation was attributed to localized creep damage and perhaps to embrittlement resulting from overaging. It was demonstrated that leading-edge cracking can be prevented simply by starting the engine gradually

NACA Technical Reports

Diffusion of chromium in cobalt-chromium solid solutions was investigated in the range 0 to 40 atomic percent at temperatures of 1360 degrees, 1300 degrees, 1150 degrees, and 10000 degrees c. The diffusion coefficients were found to be relatively constant within the composition range covered by each specimen. The activation heat of diffusion was determined to be 63,000 calories per mole. This value agrees closely with the value of 63,400 calories per mole calculated by means of the Dushman-Langmuir equation

NACA Technical Notes

Report presenting testing of heat-treated cast HS-21 turbine blades to determine the effect on the service life by running the blades to failure in a J33-9 turbojet engine. The heat treatment effects were found to depend on the initial structure of the cast blades. Results regarding engine operation, metallurgical studies of as-cast and heat-treated blades, and metallurgical studies of failed blades are provided

NACA Research Memorandums

Report presenting an investigation to determine the suitability of alloy 73J as a turbojet turbine-blade alloy and the effect of grain size on engine operating life. Blades made of alloy 73J were run in a full-scale J33-9 turbojet engine under cyclic conditions. Results regarding the macroexamination of blades, engine life, engine life against stress-rupture life, blade failures, blade elongation, metallographic results, and blade dimensions and the possible effects of overdimensions are provided