2002 Volume 42 Issue 9 Pages 1018-1025
There is a clear trend of lowering Cr and increasing Re content in the evolution from the 1st-to the 2nd-and to the 3rd-generation Ni-based single crystal (SC) superalloys. Following this trend, two groups of superalloys were made with the aid of the d-electrons concept. One is the A-group which is characterized by the lower Cr and the higher Re contents in the alloys than in the 3rd-generation SC alloys. A homogeneous microstructure was obtained in these A-group superalloys containing 0, 1 and 2 mass% Cr, while their Re and Co contents were set at about 8.5 mass% and 13.5 mass% respectively. The other is the B-group which is characterized by the lower Re content than the A-group. Three alloys in the B-group containing 2.5, 4.2 and 12.1 mass% Cr were studied for the comparison with the A-group. According to a hot corrosion test, weight gain occurred in a Cr-free alloy instead of observing weight loss in Cr containing alloys. Hot corrosion resistance of 2 mass% Cr alloy was quite good as long as the alloy contains about 8.5 mass% Re. The oxidation resistance was improved remarkably in 1 mass% Cr alloy than in the Cr-free alloy. It was found that the addition of at least 2 mass% Cr into superalloys is necessary in order to keep good surface stability at high temperatures. Also, it was seen that Re is a harmful element for oxidation resistance.