Roughness measurement as an alternative method in evaluation of cavitation resistance of steel

Abstract

The purpose of this study was to investigate possible application of roughness measurement in the evaluation of resistance of steel under conditions of cavitation effect, where these materials are commonly used. Different classes of steel were selected for testing. Cavitation testing was performed by using the ultrasonic vibratory cavitation test set up (stationary specimen method). Mass loss and surface degradation of investigated samples were monitored during the exposure to cavitation erosion. Mass loss was measured by an analytical balance. The morphology of the damaged surfaces with the change of the test period was analyzed using scanning electron microscopy (SEM). The surface roughness tester was used to monitor changes of surface roughness during the test and for obtaining the line profile of surface samples after cavitation tests. Cross-sections of samples were made after testing and optical microscopy was used to obtain complete information about the roughness change and compare the images with the lines of the profile obtained by the measurement of roughness. It can be concluded that the behaviour of steel under conditions of cavitation can be estimated by measuring the change in surface roughness. Conclusions adopted based on roughness changes are consistent with those based on measurements of mass loss and morphology of surface damage during cavitation testing time.

U ovom radu ispitivana je mogućnost procene kavitacione otpornosti čelika sa aspekta promene hrapavosti površine izložene dejstvu kavitacije. Za ispitivanje su odabrani čelici koji pripadaju različitim klasama. U laboratorijskim uslovima je primenjena ultrazvučna vibraciona metoda (sa stacionarnim uzorkom). Za praćenje promene morfologije površine sa promenom vremena ispitivanja primenjena je skenirajuća elektronska mikroskopija (SEM) i optička mikroskopija. Promena hrapavosti površina uzoraka odabranih materijala registrovana je merenjem parametra Ra koji je definisan kao prosečna hrapavost. Pokazano je da se kavitaciona otpornost može proceniti merenjem promene hrapavosti površina sa istom sigurnošću kao i konvencionalnim postupkom (merenjem gubitaka mase u toku ispitivanja).