Oxidation and Microstructural Behaviors at 1200 °C of 32.5 wt.% Cr–Containing Co–Based Alloys Strengthened by HfC Carbides

Patrice Berthod

doi:10.3390/cryst12030361

Abstract

Two alloys based on cobalt, designed to be reinforced by HfC and containing chromium with content beyond 30 wt.%, were produced by casting. They were subjected to a 46 h–long isothermal exposure at 1200 °C in synthetic air with thermogravimetric monitoring of the oxidation progress. In the as–cast state, the two alloys contain high quantities of script–like shaped HfC carbides. Both of them demonstrated a much better behavior than previous similar alloys containing only 25 wt.% Cr. After 46 h at 1200 °C, the morphology of the carbides had almost not evolved. The control of the creep behavior at 1200 °C showed that these oxidation–resistant alloys are, additionally, as creep–resistant as the 25 wt.% Cr containing previous alloys.

Highlights

Aeronautic engines and power–production plants exploiting gas turbines are more and more demanding in terms of working temperatures level [1]
One can find polycrystalline cobalt–based experimental superalloys using hafnium, for improving the high temperature oxidation behavior [3] but for generating primary HfC expected to be efficient for a long time
This was successful since no chromium carbides appeared, neither after solidification and cooling nor during new exposures to high temperatures

Summary

Introduction

Aeronautic engines and power–production plants exploiting gas turbines are more and more demanding in terms of working temperatures level [1]. The higher the temperature of the gas mixtures produced in the combustion chambers, the higher the resulting energy efficiency. There is, a need for metallic materials able to be used at elevated temperatures, offering high refractoriness but with the density staying admissible. Good mechanical properties are demanded, together with the oxidation resistance staying acceptable. Numerous new metallurgical solutions are being explored to take over from nickel–based single–crystalline alloys, for working temperatures higher than 1100 ◦ C. One can find polycrystalline cobalt–based experimental superalloys using hafnium, for improving the high temperature oxidation behavior [3] but for generating primary HfC expected to be efficient for a long time

Methods

Results

Conclusion