What was found
DFW - FLT 392 - ON TAKEOFF FROM DFW, EN ROUTE DFW-IAD, EXPERIENCED SEVERE VIBRATION FROM NR 2 ENGINE. VIBRATION WAS NOTICED IN THE CABIN AND COCKPIT. N2 ROLLED BACK TO ZERO. ACCOMPLISHED PRECAUTIONARY SHUTDOWN CHECKLIST. DECLARED AN EMERGENCY AND RETURNED DFW AND LANDED WITHOUT INCIDENT. REPLACED NR 2 ENGINE. SYSTEM GROUND CHECKED NORMAL OPERATION. DISASSEMBLY REVEALED DAMAGE TO THE 1ST STAGE HIGH PRESSURE TURBINE BLADES. VISUAL INSPECTION REVEALED MINIMAL SIGNS OF SULFIDATION IN ONE EACH THE LIGHTENING HOLES. FAILURE INDICATES THAT THE BLADE MATERIAL UNDERWENT CREEP AND STRESS RUPTURE. ONE EACH BLADE WAS EVALUATED FOR OVERTEMP SHOWING A METAL TEMP OF LESS THAN 2000 DEG F (LIMIT = 2000 DEG F, AT THE B