Fine tungsten precipitates in the matrix phase and their influence on the mechanical properties of a tungsten heavy alloy

ABSTRACT

Post-sintering cyclic heat treatment of W–Ni–Co alloys results in the formation of an intermetallic phase which subsequently dissociates into fine tungsten precipitates in the matrix. The volume fraction of such precipitates in the matrix phase increases with the number of heat treatment cycles. In an effort to understand the influence of increasing fraction of precipitates on the mechanical properties of 92W–5Ni–3Co alloy, this study has been carried out with an increasing number (2, 4, 6 and 8) of heat treatment cycles. In addition, to understand and avoid the re-formation of the brittle intermetallic phase upon cooling, the cooling rate has also been varied by incorporating oil and water quenching in the processing. This study assumes significant importance considering the fact that W–Ni–Co alloys with fine precipitates in the matrix phase reportedly exhibit an excellent combination of tensile and impact properties in undeformed condition. With scope for further improvement in the properties by means of thermomechanical treatments, any refinement in the heat treatment parameters of these alloys will enhance the potential of this alloy system that is already being widely used in critical applications such as kinetic energy penetrators.

KEYWORDS:

• Cyclic heat treatment
• intermetallic phase
• tungsten precipitates
• cooling rate
• quenching medium

Acknowledgements

The authors would like to thank Defence Research and Development Organization (DRDO) for sponsoring the activity through a research project. The authors are thankful to the Director, Defence Metallurgical Research Laboratory (DMRL) for his encouragement and guidance. We also thank all the technical staff of DMRL for their valuable contributions.

Disclosure statement

No potential conflict of interest was reported by the author(s).