What was found
(CAN) DURING APPROACH BRAKE RT FAULT EICAS MESSAGE DISPLAYED AND AFTER LANDING EMERGENCY BRAKE FAULT MESSAGE ALSO DISPLAYED ON EICAS. DURING CREW POST FLIGHT WALK AROUND, FOUND NR 4 BRAKE ASSY DISINTEGRATED AND HYDRAULIC FLUID LEAKING. DISPATCH WAS ADVISED TO CONTACT ATC DUE TO DEBRIS POSSIBLY LEFT IN THE RUNWAY. MAINTENANCE ADVISED THAT NR 4 MAIN WHEEL REQUIRES REPLACEMENT WHICH WE HAVE IN DCA. NR 4 MAIN BRAKE ASSEMBLY REPLACED ALONG WITH NR 4 MAIN WHEEL AND AIRCRAFT RETURNED TO SERVICE. NO OTHER DAMAGE NOTED.