Powder Metallurgical Processing For Graded Alloy Microstructures

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The understanding of microstructures and their effect upon alloy properties is a key part of metallurgical processing as developers seek materials for harsh applications such as those found in the oil & gas, chemical and aeroengine industries. Enhancement of alloy performance has been achieved for ranges of alloys, including steels and nickel superalloys, by addition of minor elements and thermomechanical processing, thereby manipulating the chemistries and microstructures to provide desired benefits. However, such additions and processing steps are generally performed on bulk alloys, often resulting in undesirable costs in finished components arising from the presence of expensive elemental additions in areas where they serve no purpose. This is particularly the case with additions of precious metals (platinum, palladium, ruthenium etc.). Such issues can be circumvented, for example, by deposition of surface coatings. However, thin surface coatings can be subject to degradation by in-use environmental conditions, exposing the underlying unprotected alloy and shortening component lifetime.In this project we will examine routes for generating asymmetric "graded" alloy microstructures to provide property enhancement at the surface of components, where they are needed, avoiding the cost of bulk alloying additions. Concentrating upon powder metallurgical processing to generate the graded microstructures, we will introduce precious metals into the surfaces of steels and nickel superalloys, examining the effect upon the microstructures, the interactions of the modified microstructures with the underlying base alloys, thermomechanical properties and corrosion resistance under environmental conditions relevant to the end-use applications of those alloys. The industrial partners, Johnson Matthey and Liberty Powder Metals, will work closely with the student to provide complementary manufacturing and characterization facilities, thereby allowing the successful student to gain experience of both base metal and precious metal-containing alloys.