Process Heating and Postannealing Effects on Microstructure and Hardness of the Sputtered Ni-P-Al Coatings

Abstract EN

Ternary Ni-P-Al alloy coating was fabricated by magnetron sputtering technique with a Ni-P/Al composite target source.

The effects of thermal treatments, including deposition process heating and postannealing, on phase transformation phenomenon and related mechanical properties were investigated.

The as-deposited coatings produced under process temperature below 475°C showed an amorphous/nanocrystalline microstructure.

Significant crystallization of Ni matrix and precipitation of NixPy and NipAlq compounds were observed for the coatings manufactured under high sputtering temperatures above 500°C.

The amorphous Ni-P-Al coatings were postannealed from 500 to 600°C in vacuum environment for comparison.

The amorphous feature of the Ni-P-Al coating remained unchanged under a high annealing temperature of 550°C, showing a superior thermal stability as compared to those fabricated under high process temperatures.

Superior hardness was obtained for the post-annealed Ni-P-Al coatings due to volumetric constraint of crystallization and precipitation.

On the other hand, the overaging phenomenon and subsequent degradation in hardness were found for the Ni-P-Al coatings fabricated under high-temperature deposition processes.

The phase transformation mechanisms of the coatings through different thermal treatments were intensively discussed.