Characterization and consolidation of a high temperature aluminum transition metal powder alloy

A gas atomized powder Al-TM alloy containing approximately 12 weight percent total iron, chromium, plus titanium alloy addition was consolidated by direct extrusion and friction stir extrusion, with promising thermal stability and elevated temperature properties. Previous work focused on production of this alloy with an icosahedral phase, studying melt spun ribbons along with limited work on extruding to a bulk form due to difficulties in maintaining the icosahedral phase at hot extrusion conditions. In this study, two powders,20 µm and 150 µm average particle size, were characterized for phases present in the as received condition, and phase stability with thermal exposure. The icosahedral phase was not present in the 150 µm powder, however the as-received microstructure remained stable following high temperature anneals. The initial powder of average size 150µm was consolidated at 350, 425, 450, and 550°C at reduction ratios of 10:1, 16:1, and 25:1. Two friction stir extrusions were provided for this study from consolidated powders screened below 100µm, and powder screened between 100-400 µm. Differential scanning calorimetry and X-ray diffraction confirmed that the icosahedral phase was not present in the alloy consolidated by direct extrusion from the 150 micron powder or friction stir extrusions from 100-400 µm powder, as expected based on the starting powder size. Despite the absence of the icosahedral phase, the alloy displayed both microstructure stability and retention of hardness following annealing at temperatures up to 550°C for times up to 100 hours. Hot hardness testing of the alloy determined an increase of 100°C in the deformation transition temperature relative to a representative high temperature aluminum wrought alloy (Al 2618-T61), which is associated with the transition to deformation with dislocation climb. Room temperature tensile testing demonstrated only minor variations between extrusion conditions indicating minor influence of extrusion temperature or reduction ratio on mechanical properties. All extrusion conditions were also found to produce nominally fully consolidated bars. At elevated temperatures up to 550°C, the ultimate tensile strength of the Al-TM alloy approaches that of rapidly solidified and extruded 8009. Finally, hot compression testing determined the activation energy for high temperature (i.e., above the transition to dislocation climb) deformation to be 293 kJ/molK, and the strain rate sensitivity increased significantly with deformation temperature. A fine microstructure was retained in the alloy following annealing studies and compression testing demonstrating the viability of extrusion as a feedstock for forging at high temperatures of 0.8 the homologous temperature without concern of severe microstructure coarsening during heating. Additionally, the samples of Al-TM consolidated by friction stir extrusion demonstrated a similar retention of hardness following 100 hours at 550°C. EBSD of the FSE demonstrated a very fine grain size in the as extruded material. This work demonstrates the ability to consolidate an Al-TM alloy over a range of extrusion conditions allowing for process flexibility while maintaining mechanical properties with good thermal stability.

Name thesis:degree_name

Master of Science (M.S.)

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Metallurgical and Materials Engineering

Grantor dc:publisher

Colorado School of Mines. Arthur Lakes Library

Year dc:date.issued

2022

Author dc:creator

• Shirley, Stuart

Advisor dc:contributor.advisor

• Clarke, Kester

Committee members dc:contributor.committeemember

• Clarke, Amy
• Klemm-Toole, Jonah

• bulk materials
• deformation processing
• high temperature aluminum

Statement dc:rights

• Copyright of the original work is retained by the author.

Language dc:language.iso

eng, English

Identifier

T 9337

OAI identifier oai:identifier

oai:repository.mines.edu:11124/15420