Surface and Subsurface Analysis of Stainless Steel and Titanium Alloys Exposed to Ultrasonic Pulsating Water Jet.

Jakub Poloprudský,Alice Chlupová,Sergej Hloch,Tomáš Kruml,Ivo Šulák

doi:10.3390/ma14185212

Abstract

This article deals with the effect of periodically acting liquid droplets on the polished surfaces of AISI 316L stainless steel and Ti6Al4V titanium alloy. These materials were exposed to a pulsating water jet produced using an ultrasonic sonotrode with an oscillation frequency of 21 kHz placed in a pressure chamber. The only variable in the experiments was the time for which the materials were exposed to water droplets, i.e., the number of impingements; the other parameters were kept constant. We chose a low number of impingements to study the incubation stages of the deformation caused by the pulsating water jet. The surfaces of the specimens were studied using (1) confocal microscopy for characterizing the surface profile induced by the water jet, (2) scanning electron microscopy for detailed surface observation, and (3) transmission electron microscopy for detecting the changes in the near-surface microstructure. The surface described by the height of the primary profile of the surface increased with the number of impingements, and was substantially more intense in the austenitic steel than in the Ti alloy. Irregular surface depressions, slip lines, and short cracks were observed in the Ti alloy, whereas pronounced straight slip bands formed in the austenitic steel. The dislocation density near the surface was measured quantitatively, reaching high values of the order of 1014 m−2 in the austenitic steel and even higher values (up to 3 × 1015 m−2) in the Ti alloy. The origins of the mentioned surface features differed in the two materials: an intense dislocation slip on parallel slip planes for the Ti alloy and mechanical twinning combined with dislocation slip for the austenitic steel.

Highlights

Water jet technology has been extensively used for cutting, drilling, and cleaning [1].Water jet peening, a nonthermal method for surface strengthening, is considered a relatively new advance compared with other applications of water jet technology [2,3]
The advantages of pulsating water jets (PWJs) can be grouped into three main areas: first, they are more efficient compared with continuous water jets under the same hydraulic conditions [9]; second, the pressure acts upon the impacted area in a periodic manner, which can be used for surface reinforcement, such as the peening method [10,11]; and third, A PWJ acting without added solid particles can be used in the treatment of structural parts for medical applications [12,13,14,15]
We focused on the observation and comparison of the incubation stage of a PWJ applied to Ti6Al4V

Summary

Introduction

Water jet technology has been extensively used for cutting, drilling, and cleaning [1].Water jet peening, a nonthermal method for surface strengthening, is considered a relatively new advance compared with other applications of water jet technology [2,3]. The first is the addition of solid particles, which are erodents, into the water jet [4]; the accelerated abrasives wear the material [5]. The advantages of pulsating water jets (PWJs) can be grouped into three main areas: first, they are more efficient compared with continuous water jets under the same hydraulic conditions [9]; second, the pressure acts upon the impacted area in a periodic manner, which can be used for surface reinforcement, such as the peening method [10,11]; and third, A PWJ acting without added solid (abrasive) particles can be used in the treatment of structural parts for medical applications [12,13,14,15]

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Conclusion