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A Novel Approach for Durability Evaluation of Metal Protective Coatings in Dynamic Interplay with the Liquid Alloy

Pałka Paweł, Boczkal Grzegorz, Hotloś Agnieszka, Mrówka-Nowotnik Grażyna

Archives of Foundry Engineering

2023

Vol. 23, iss. 4

40--48

The article describes a new test method to quickly evaluate the durability of a protective coating to dynamic contact with liquid metal. The essence of the method is the movement of a drop of liquid metal inside a rotating ring, covered from the inside with the protective coating under test. The parameters determined in the test are analogous to the classic pin-on-disk tribological test. The method was tested for the system: liquid alloy 2017A vs. AlTiN coating on a copper substrate. The test temperature was 750°C, and exposure times ranged from 30 to 90 minutes. Sliding path equivalent for the metal droplet/coating system ranged from 31.6 to 95 m. The study, which included visual evaluation of the surface of the samples, followed by phase and microstructural analysis, showed the high efficiency of the method for assessing the lifetime of protective coatings on contact with liquid metal. The investigated issue was also analyzed from the model side taking into account changes in the diffusion coefficient at the contact of liquid metal with the substrate, occurring with the progressive degradation of the protective coating.

Testing of a sag of a dosimetry system rotating with a gantry using the interplay effect between detector motion and MLC motion

Morawska-Kaczyńska M., Dąbrowski R., Drozdyk I., Kukołowicz P.

Polish Journal of Medical Physics and Engineering

2017

Vol. 23, Iss. 2

21--28

Purpose: An interplay between detector motion and MLC motion is a source of measurement error, when dose for dynamic arc is measured using a dosimetry system moving relative to the beam central axis during its rotation with a gantry. The purpose of this study is to develop and to evaluate a method of quantitative testing of a sag/flex of such dosimetry systems. Methods: The method is based on evaluation of relative differences between signals measured for two single arc beams, where a narrow slit field is sliding during gantry movement in opposite directions. The component of a measurement error related to the interplay effect was first assessed based on theoretical computer simulations and then on measurements for four dosimetry systems. The sag pattern of EPID and 2D array was extracted from the measurement results. Results: The simulations showed a 4 mm difference in field width and 3.3% difference in relative signals at beam axis between test beams where the slit field swept over 19 cm in opposite directions ( sinusoidal sag pattern with amplitude of 1 mm was assumed). The signal differences exceeding 4% and 5% were measured for EPID and 2D array, respectively. Conclusions: Even relatively small detector sag (less than 1 mm) can produce significant measurement error; therefore, the detector sag test should be an obligatory component of a validation of rotating dosimetry systems used for QA of dynamic arcs.