Creep/Corrosion of Two Nickel Alloys in Combustion Gas
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1.
INTRODUCTION
INseveral high temperature applications metal components are exposed to the combined effects of mechanical and thermal stresses and corrosive environments. Such applications include gas turbines, fluidized beds, rocket engines, diesel engines, boilers, etc., which all are operated by the combustion of fuel oils. The interaction between corrosion and mechanical/thermal stresses has been somewhat neglected in the investigation of materials for such purposes. However, a knowledge of these interactions is necessary to establish the basis for a successful development of alloys of superior high temperature quality. This paper describes some preliminary results from a research program which recently was started at Central Institute for Industrial Research, Oslo, to analyze the problems concerning the combined effects of creep, thermal cycling, and corrosion at high temperatures in combustion gases. The entire program includes advanced gas turbine alloys as well as simpler materials like Nickel 201 and Inconel 600. In order to approach the problems gradually, the work was started by testing the two simpler materials, and the results obtained on these alloys are presented in two separate articles. The present paper deals with the interaction between creep and corrosion, and in Reference 1 the effect of thermal cycles on the creep properties in combustion gas is analyzed. II.
EXPERIMENTAL
A. Equipment The experimental equipment consisted of a creep furnace which was either connected to an oil combustion rig or to an argon gas supply for reference experiments. The rig conJ. K. SOLBERG, formerly with Central Institute for Industrial Research, Oslo, Norway, is now Senior Lecturer with the Norwegian Institute of Technology, Trondheim, Norway. H. THON is with Central Institute for Industrial Research, Oslo, Norway. Manuscript submitted November 17, 1981.
METALLURGICALTRANSACTIONS A
sisted of a burner, a combustion chamber, and a specimen chamber for pure corrosion tests. Combustion gas was circulated through the furnace via a gas tube which was heated to 200 ~ (above the dew point for sulfur acid). The oil which was used was a light fuel oil with impurity additions of 2.5 pct S, 50 ppm Na, and 50 ppm V. The oil was burned with an air excess of 10 pct, registrated by a Servomix O2-detector. The creep furnace had a constant temperature zone of 20 cm, along which the temperature was controlled within limits of -+2 ~ The loading system did not compensate for the reduction of specimen diameter, so only constant load tests were done. The instantaneous creep strain was registered via the movement of the lever arm.
B. Specimen Preparation Hot rolled bars (25 mm diameter) of the materials Nickel 201 and Inconel 600 were provided by Henry Wiggin & Co. Ltd., Hereford, England. The nominal composition of the alloys is given in Table I. To examine the effect of microstructure on creep and corrosion, the materials were given different heat treatments. The annealing was done in evacuated quartz ampullas ( - 10-s torr) whi
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