Studies on electroless nickel boride coating on boron carbide particles

Abstract

Ni–B alloy deposits were successfully formed over alkali surface treated boron carbide by electroless technique and the effects of processing parameters such as reduction bath pH, temperature and post-heat treatment were investigated. Microstructural studies show remarkable changes in structural morphology from mesh-like structure to platelet type Ni–B coating. The main Ni–B phases observed were NiB, Ni₂B, Ni₃B and Ni₄B₃. An effective Ni–B alloy coating with better surface characteristics was formed at pH 8 under 75°C reaction bath temperature in the presence of bath stabiliser. The post-heat treatment of Ni–B coated particles under varying bath reaction temperatures at 400°C showed remarkable Ni–B phase transformation from metastable NiB and Ni₂B to stable crystalline Ni₃B phase. The NiB coated particle shows lower particle–matrix interfacial reaction, better wettability and enhanced dispersion in aluminium composites compared to uncoated particles.

Keywords:

• Nickel boride
• Electroless coating
• Boron carbide
• Amorphous coating
• Phase transformation
• Sodium borohydride

Acknowledgements

The authors are grateful to the Director and Members, NIIST, CSIR, Trivandrum for their support and help. We acknowledge the help rendered for SEM by Mr M. R. Chandran, XRD by Mr P. Gurusamy and Mr Subash for EDS from School of Nanoscience and Technology, NIT, Calicut. We are grateful to CSIR for fellowship.