Porosity is expected to increase when the formation of brittle nitride phases is enhanced and particle velocity before impact is reduced. Since nitride formation mainly takes place during particle flight, by using nitrogen as the plasma gas and spraying in higher nitrogen pressure, thus improving reaction kinetics and decreasing particle velocity, the amount of nitrogen retained in the coating resulted higher as well as measured porosity values(Fig.1).
Fig. 1. Porosity values and percent wt. N in the as-sprayed coatings.
Calculated porosity values with Leica Qwin V2.2 image analysis, were, respectively,1-1.5% for coatings sprayed under 20 kPa and 2.6-3.7% for 90 kPa. The lowest values were found for Ar/H, plasma gas. Despite pore interconnection developed for higher spraying pressure values, the obtained increase in % wt. of nitrogen retained in the coating at 90 kPa, resulted in a significant reduction of weight loss after erosion tests, in accordance with higher measured microhardness values(Fig.2). This effect was more remarkable for the Ar/N2mixture as plasma gas.
Fig. 2. Weight loss after erosion tests vs. HV .
本文由桑尧热喷涂网收集整理。本站文章未经允许不得转载；如欲转载请注明出处，北京桑尧科技开发有限公司网址：http://www.sunspraying.com/
|
