Investigation on the Microstructure of ECAP-Processed Iron-Aluminium Alloys.

Bernd-Arno Behrens,Kai Brunotte,Tom Petersen,Roman Relge

doi:10.3390/ma14010219

Abstract

The present work deals with adjusting a fine-grained microstructure in iron-rich iron-aluminium alloys using the ECAP-process (Equal Channel Angular Pressing). Due to the limited formability of Fe-Al alloys with increased aluminium content, high forming temperatures and low forming speeds are required. Therefore, tool temperatures above 1100 °C are permanently needed to prevent cooling of the work pieces, which makes the design of the ECAP-process challenging. For the investigation, the Fe-Al work pieces were heated to the respective hot forming temperature in a chamber furnace and then formed in the ECAP tool at a constant punch speed of 5 mm/s. Besides the chemical composition (Fe9Al, Fe28Al and Fe38Al (at.%—Al)), the influences of a subsequent heat treatment and the holding time on the microstructure development were investigated. For this purpose, the average grain size of the microstructure was measured using the AGI (Average Grain Intercept) method and correlated with the aforementioned parameters. The results show that no significant grain refinement could be achieved with the parameters used, which is largely due to the high forming temperature significantly promoting grain growth. The holding times in the examined area do not have any influence on the grain refinement.

Highlights

Iron-aluminium alloys have been researched and developed for many years
Due to the very low ductility at room temperature caused by hydrogen embrittlement in a humid environment and the rapid drop in strength at temperatures above 600 ◦ C, iron-aluminium alloys have long been neglected in structural applications [5]
Incremental hot forming was used for reshaping at different temperatures, Fe9Al at 1250 ◦ C, Fe28Al at 1150 ◦ C, and Fe38Al at 1100 ◦ C, with a punch speed of 30 mm/s; these forming parameters were determined by Huskic [16]

Summary

Introduction

The particular interest lies in the many advantages of these alloys, which make them very versatile. Because of their corrosion resistance in an oxygen- and sulphur-containing environment, their high melting point, and their high strength at low density (up to 25% weight reduction with Fe38Al (at.%—Al) compared to steel), they are used, for example, as high temperature materials in the aerospace industry [1]. Due to the very low ductility at room temperature caused by hydrogen embrittlement in a humid environment (elongation at break well below 5%) and the rapid drop in strength at temperatures above 600 ◦ C, iron-aluminium alloys have long been neglected in structural applications [5]

Methods

Results

Discussion

Conclusion