A diesel engine piston assembly comprises a piston body having a top wall with a combustion bowl formed in the top wall and having a combustion bowl edge, an outer ring belt formed with a plurality of ring grooves including a top ring groove with an upper wall of the top ring groove and a top land portion of the ring belt disposed between the top ring groove and the top wall, a pair of pin bosseswith aligned pin bores and a skirt; and a diamond dispersed chromium composite coating applied to at least the top wall, the combustion bowl edge, the top land portion and the upper wall of the top ring groove.