Papers by Author: C.N. Jones

Abstract: Oxidation tests have been undertaken in air on two experimental fourth-generation Nibased superalloys containing, respectively, 3 and 5 wt.% Ru. A Ru-free, third generation alloy (CMSX-10K) was also included in the test programme which used temperatures covering the range 750-1100°C. Where possible, comparisons were also made with literature data on the secondgeneration CMSX-4 alloy and with IN738. After an initial period of transient oxidation, the subsequent parabolic rate constants for the 3%-Ru alloy were similar to those for CMSX-4 at all temperatures above 750°C. At 1000 and 1100°C these were consistent with the formation and growth of an α-alumina layer. At 950°C and lower, protective oxidation was obtained through the formation of an Al-rich spinel rather than alumina but, again, no deleterious influence of Ru additions could be found, at least in the temperature range of 800-950°C. Anomalous behaviour was found, however, at 750°C in that the Ru-bearing alloys oxidised non-protectively through the formation of sub-surface pits in which the γ΄ phase within the alloy was oxidised in situ.

Abstract: Effect of carbon and boron on the grain boundary strengthening of a second generation single crystal superalloy RR2072 was investigated. Single crystal and bicrystal specimen with three kinds of tilt type misorientation angle were grown by Bridgman technique. Creep and stress rupture tests were conducted at 950oC and 1050oC. Rupture life of single crystal of the alloy modified with carbon and boron was comparable to that of the RR2072 which is free from boron and carbon. TCP phase precipitation such as sigma was suppressed in the modified alloy during thermal exposure and creep deformation. Rupture life of the modified alloy bicrystal was superior to that of the RR2072 bicrystal. M23C6 carbide formation and suppression of γ′ band growth is thought to be the role of minor elements for the grain boundary strengthening of a nickel base single crystal superalloy RR2072.