Abstract: A thermal barrier coating for metal articles subjected to rapid thermal cycling includes a metallic bond coat deposited on the metal article, at least one MCrAlY/ceramic layer deposited on the bond coat, and a ceramic top layer deposited on the MCrAlY/ceramic layer. The M in the MCrAlY material is Fe, Ni, Co, or a mixture of Ni and Co. The ceramic in the MCrAlY/ceramic layer is mullite or Al.sub.2 O.sub.3. The ceramic top layer includes a ceramic with a coefficient of thermal expansion less than about 5.4.times.10.sup.-6 .degree.C.sup.-1 and a thermal conductivity between about 1 J sec.sup.-1 m.sup.-1 .degree.C.sup.-1 and about 1.7 J sec.sup.-1 m.sup.-1 .degree.C.sup.-1.

Abstract: In a method of assembling a roller cone type rock bit, on a body having a tool joint adjacent one end and at least one leg portion adjacent the other end, the leg portion is provided with a longitudinally outer surface which is inclined longitudinally inwardly from its radially outer extremity to its radially inner extremity; on a base for a cone assembly, an end surface is provided configured to mate with the outer surface of the leg portion of the body; a roller cone is rotatably mounted on the base distal the end surface to form a cone assembly, and the end surface of the base is mated with the outer surface of the leg portion; the base is then welded to the leg portion along the juncture of the mating surfaces to mount the cone assembly on the leg portion.