WHILE TAXIING OFF THE RUNWAY AT DILLINGHAM, ALASKA, THE FLIGHT CREW HEARD A 'POP' AND 'GRINDING' SOUND. THE AIRPLANE WAS SUBSEQUENTLY FERRIED TO ANCHORAGE WITH THE NOSE GEAR PINNED IN THE DOWN POSITION. UPON TOUCHDOWN IN ANCHORAGE, THE NOSE GEAR SEPARATED FROM THE AIRPLANE. A METALLURGICAL EXAMINATION OF THE AFFECTED COMPONENTS, PRIMARILY THE NOSE LANDING GEAR INNER CYLINDER, SHOWED THAT THE INNER CYLINDER HAD SEPARATED CLOSE TO THE LOWER END NEAR THE AXLES FOR THE TIRES. VISUAL EXAMINATION OF THE FRACTURE SURFACE WITH THE AID OF A BENCH BINOCULAR MICROSCOPE REVEALED FEATURES TYPICAL OF AN OVERSTRESS SEPARATION INCLUDING CHEVRON MARKS OVER THE MAJORITY OF THE FRACTURE SURFACE AND THE PRESENCE OF A 45 DEGREE FRACTURE PLANE. DURING THE PREVIOUS 12 MONTH PERIOD THERE WERE NO 'HARD' LANDINGS ON RECORD FOR THE AIRPLANE.