The Improvement of the Cavitation Resistance of Technical Surfaces Using High Power Laser Pulses

Rhoda Ayorkor Sai

Master's thesis

Abstract:

In this study, the effect of laser shock peening treatment on the cavitation erosion resistance of a stainless-steel type used in pump blades was characterized. The goal of the study was to compare and define the better process parameters of the treatment effective in improving the cavitation erosion resistance of the stainless-steel type. An experimental investigation was conducted using the vibratory apparatus with compliance to ASTM G32 standards. Specimens made of stainless steel 304 were treated using different laser pulse density, and beam size with a 50% overlap. Prior to the cavitation erosion test, the incubation time of the samples was estimated from previous tests of similar samples. Each sample was subjected to ultrasonic pressure pulses at different exposure times using a constant amplitude. mass loss was recorded for each The incubation period was used to characterize the materials impact resistance and the cavitation erosion resistance was achieved using mass loss tests and represented as the reciprocal of the cumulative volume loss rates. The mean depth of penetration was calculated from volume loss and affirmed using the cavitation erosion profile, measured with contact profilometer. The effect of exposure time on the mean depth was analyzed and found to stabilize after significant exposure time. The mean eroded depth was also compared to the compressive residual stress induced during the laser treatment and used quantitatively to describe the cavitation damage of SS304. The correlation between the cavitation erosion resistance and properties of the improved samples was perused. The variation of the cumulative volume loss with exposure time indicated improvement of the materials cavitation erosion resistance. The results of the study hawed that SS304 treated with higher power density depicted the highest erosion resistance whiles SS304 with lower power density showed the highest impact resistance during the incubation period. The summary of the results in the conclusion explains the outcome of the investigation.

Abstract:

In this study, the effect of laser shock peening treatment on the cavitation erosion resistance of a stainless-steel type used in pump blades was characterized. The goal of the study was to compare and define the better process parameters of the treatment effective in improving the cavitation erosion resistance of the stainless-steel type. An experimental investigation was conducted using the vibratory apparatus with compliance to ASTM G32 standards. Specimens made of stainless steel 304 were treated using different laser pulse density, and beam size with a 50% overlap. Prior to the cavitation erosion test, the incubation time of the samples was estimated from previous tests of similar samples. Each sample was subjected to ultrasonic pressure pulses at different exposure times using a constant amplitude. mass loss was recorded for each The incubation period was used to characterize the materials impact resistance and the cavitation erosion resistance was achieved using mass loss tests and represented as the reciprocal of the cumulative volume loss rates. The mean depth of penetration was calculated from volume loss and affirmed using the cavitation erosion profile, measured with contact profilometer. The effect of exposure time on the mean depth was analyzed and found to stabilize after significant exposure time. The mean eroded depth was also compared to the compressive residual stress induced during the laser treatment and used quantitatively to describe the cavitation damage of SS304. The correlation between the cavitation erosion resistance and properties of the improved samples was perused. The variation of the cumulative volume loss with exposure time indicated improvement of the materials cavitation erosion resistance. The results of the study hawed that SS304 treated with higher power density depicted the highest erosion resistance whiles SS304 with lower power density showed the highest impact resistance during the incubation period. The summary of the results in the conclusion explains the outcome of the investigation.

Keywords

cavitation, laser shock peening, residual stress, volume loss, cavitation resistance

Language used: English

Date on which the thesis was submitted / produced: 12. 6. 2020

Thesis defence

• Supervisor: Ing. Miloš Müller, Ph.D.

Technical University of Liberec

Faculty of Mechanical Engineering

Master programme / field:
Mechanical Engineering / Machines and Equipment Design