Intermetallic in-situ Composites

Charles J. Larkin

Purdue University

Advising Professor: David Johnson

Introduction

High temperature structural materials are becoming of more interest since there is a higher demand for them. Intermetallic materials are of great interest since they can withstand higher temperatures than the superalloys that are currently used. They have high melting temperatures and good oxidation resistance but are very brittle and difficult to process. Ruthenium aluminide (RuAl) is different from other intermetallics since it has good room temperature toughness that has been reported from limited qualitative testing, but it is difficult to process. However, it is easier to process eutectic microstructures where two different solid phases form. One such alloy is RuAl-W, which forms a eutectic microstructure with 47weight percent W.

Objectives

  • To characterize the morphology of the eutectic W in the RuAl-W composite like material
  • Find a process to get an alignment of the W in the RuAl matrix
  • Find a process to get alignment of the RuAl dendrites
  • Find what RuAl deformation modes are

Experimental Approach

  • Create a RuAl-W alloy with 47 wt.% W to find the morphology of the W
  • Make a cigar shaped RuAl-W 47 wt.% W by arc zone melting at a rate of 20 mm/hr
  • Performed SEM analysis to check the microstructure of cigar
  • Make sample of RuAl-W 47 wt.% W in the tri-arc and cool by ramping power down from 200 amps to 70 amps over 2.5 minutes and then perform SEM analysis to check to see if W is aligned
  • Made like previous RuAl-W 15 wt.% W alloy and perform analysis in optical microscope to check for RuAl dendrite alignment

Findings

  • The W has rods form within the RuAl matrix and spheorodizes when heat treated
  • Arc zone melting of the cigar-shaped sample at a slow rate does not align the W rods in the RuAl-W alloy
  • Ramping the power down was not effective in aligning the W rods in the eutectic microstructure
  • Ramping the power produces alignment of RuAl dendrites


Fig. 1 Microstructure of the as-cast RuAl-47 wt.% W showing the morphology of the W taken in the SEM at 2000x.

Fig. 2 RuAl-15 wt.% W microstructure that DS the RuAl dendrites taken in an optical microscope at 20x.

Final Research Presentation