Abstract
Results of basic research and experiments on chromium diffusion coating of nickel superalloys were reported in the previous papers for the purpose of obtaining high corrosion resistance of gas turbine blades.
In this paper, there are discussed inner diffusion behavior indispensable to evaluation of surface concentration of chromium and thickness of surface layer at the time of designing turbine blades which will be exposed to high temperature atmosphere for long hours.
The results obtained were as follows:
(1) Interdiffusion coefficient of chromium and base metal of nickel superalloys extremely depended on chromium concentration; its value was lower with the increase of the chromium concentration.
(2) The dependence of the diffusion coefficient on temperature conformed to an Arrhenius type equation within the error of 5% at maximum.
(3) There were no great differences among the diffusion coefficients of several kinds of alloy materials. However, the base metal of higher nickel content gave higher value of coefficient. The materials were arranged in decreasing order of coefficient as follows:
Ni>Inco X>Inco 700>U -500 (at higher than 1000°C)
Ni>U -500>Inco X>Inco 700 (at lower than 1000°C)
(4) When gas turbine blades with chromium diffusion coating were used in high temperature (900°C) gas, the surface layer was gradually corroded, and the surface concentration of chromium decreased to 45% after the use of 20, 000hrs.
