Abstract
The purpose of this study was to investigate possible application of roughness measurement in evaluation of resistance of steels in conditions of cavitation effect where these materials are usually applied. Steels which belong to different classes 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 steels under conditions of cavitation can be estimated by measuring the change in surface roughness. Conclusions adopted on the basis of roughness changes are consistent with that based on measurements of mass loss and morphology of surface damage during cavitation testing time.
Highlights
Zaključci o ponašanju odabranih čelika dobijeni na osnovu merenja promene hrapavosti bili su u skladu sa zaključcima dobijenim merenjem gubitaka mase i mikroskopskom analizom morfologije površina oštećenih dejstvom kavitacije
The cross section of samples after 240 min of cavitation tests characterized by the mean roughness, Ra, a) Ra = 1.55 μm, b) Ra = 1.05 μm
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
Summary
Rast i imploziju (urušavanje) mehura u tečnosti delovanjem ultrazvuka. Kompresija nastalih mehura tokom kavitacije je brža od prenosa toplote i zato kompresija gasa generiše toplotu pri čemu dolazi do lokalno visokih porasta temperature u tečnosti. Primenom ultrazvučne vibracione metode u toku ispitivanja meri se gubitak mase uzorka u određenim vremenskim intervalima a kavitaciona otpornost se definiše preko inkubacionog perioda i brzine kavitacione erozije. Kod direktne kavitacione metode uzorak je preko navoja postavljan na vrhu koncentratora mehaničkih vibracija. U slučaju indirektne kavitacione metode ili metode sa stacionarnim uzorkom, uzorak je postavljen u vodenom kupatilu ispod koncentratora mehaničkih vibracija na određenoj udaljenosti [10,11,12,13,14]. Prednost metode sa stacionarnim uzorkom je što uzorak u toku ispitivanja nije izložen mehaničkim naprezanjima kao i u mogućnosti ispitivanja uzoraka od krtih materijala kod kojih se ne može narezivati navoj. Zaključci o ponašanju odabranih čelika dobijeni na osnovu merenja promene hrapavosti bili su u skladu sa zaključcima dobijenim merenjem gubitaka mase i mikroskopskom analizom morfologije površina oštećenih dejstvom kavitacije
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