Microstructure and Mechanical Properties of Cold Spray Deposited GRCoP-42

Author: Terrence Kuca, Department of Mechanical Engineering

Mentor: Dr. Prasoon Diwakar, Department of Mechanical Engineering

Mentor: Dr. Bharat Jasthi, Department of Materials and metallurgical Engineering

Additive manufacturing is excellent for building complex geometries such as those used in rocket engine cooling, while also keeping the overall structure and weight down as much as possible. A unique Cu-based alloy with high strength and high thermal conductivity, is being proposed for such geometries. However, because of these qualities, it is also challenging to design such geometries using conventional additive manufacturing processes. Cold spray additive manufacturing is a relatively new field that is potentially ideal for this application. Cold spray additive manufacturing uses kinetic energy rather than thermal energy to bond materials together. While promising, it is still a relatively new method that has been shown to have varying results depending on many different factors.

The main objective of this work is to develop a freeform fabrication of GRCop-42 (Cu-4 at.% Cr-2 at.% Nb) using a high-pressure cold spray process. GRCop-42 is a copper-based alloy with excellent elevated temperature strength, good creep resistance, long low-cycle fatigue (LCF), and higher oxidation resistance. It also has a lower thermal expansion than copper and many other low-alloy copper-based alloys. Cold spray is a solid-state process that avoids or minimizes problems related to liquid to solid phase transformations such as oxidation, hot tearing, alloying element segregation, and tensile residual stresses in the final part. The microstructure and mechanical properties of the cold sprayed GRCop-42 were evaluated and compared with other additive manufacturing methods. Preliminary analysis suggested that good depositions with minimal porosity can be achieved using the N2 carrier gas. Microstructural characterization was performed using optical and scanning electron microscopy. XRD analysis was performed to identify and quantify the presence of dispersoids present in the GRCop-42 powders and the results were compared with the cold sprayed coatings.