Effect of feedstock injection methods on oxidation behavior and microstructure of plasma sprayed W/Cu composites

Free-standing tungsten/copper composite plates that may be used as heat sink material for electronic packaging were produced by the air plasma spray process. Two kinds of spray torch were used to investigate the oxidation, microstructure, composition recovery, and coefficient of thermal expansion (CTE) with respect to internal feedstock injection (IFI) and external feedstock injection (EFI). Very little copper oxidation from the IFI was detected by XRD analysis. Most pores were found in the vicinity of tungsten-rich grains. More tungsten in the deposits was lost in the use of the EFI than with IFI. Thermal expansion coefficient of plasma sprayed composite (72W/28Cu vol.%) was approximately 5.2×10−6/K. The experimental results indicated that the IFI shows higher energy efficiency for the tungsten recovery than the EFI. Some detailed observations of microstructures are also discussed.