Study on Cavitation and Cavitation Erosion of Surfaced Stainless Steel

Literature Overview

Published in Large Electric Machinery Technology (1989, No. 2, pp. 52-55) by Lü Xiaoli and Wei Jianjun from Zhengzhou Mechanical Research Institute, this paper investigates the cavitation resistance and cavitation erosion behavior of three austenitic stainless steel surfacing alloys used in hydraulic turbine runner protection. The study employed both a rotating disk cavitation test rig and a rotating sand abrasion test apparatus, providing dual-mode evaluation of surface degradation mechanisms under combined cavitation and solid particle erosion conditions.

Materials and Test Configuration

Three surfacing alloys were evaluated:

The rotating disk cavitation test simulates the high-velocity water flow conditions encountered on turbine runner surfaces, where local pressure drops below vapor pressure cause bubble formation and subsequent violent collapse. The rotating sand abrasion apparatus introduces solid particles (simulating sediment-laden water) into the cavitation environment, creating synergistic erosion mechanisms.

Key Findings on Material Properties and Degradation

The study established clear correlations between material properties and cavitation resistance:

• Hardness: Higher hardness generally improves cavitation resistance by increasing resistance to micro-plastic deformation during bubble collapse. However, extremely high hardness without adequate toughness leads to brittle fracture and rapid material loss.
• Impact toughness: Materials with higher impact toughness exhibit better resistance to the shock loading associated with cavitation bubble collapse. The dynamic loading from cavitation is essentially a high-frequency impact phenomenon.
• Cavitation damage morphology: The paper documents characteristic damage patterns including micro-pitting, micro-cracking, and material removal in plate-like fragments.

The 18-8 type material demonstrated the best overall cavitation resistance due to its balanced combination of moderate hardness and excellent ductility. The Mo-containing variants showed improved resistance under cavitation-abrasion combined conditions, suggesting that molybdenum contributes to the formation of harder carbide precipitates that resist both cavitation and abrasion.

Engineering Practice Integration

For hydraulic turbine applications, the selection of surfacing material must consider the operating environment:

The synergistic effect of cavitation and abrasion is particularly important for turbines operating in rivers with high sediment content. In such environments, cavitation damage exposes fresh material that is then rapidly removed by abrasion, accelerating degradation far beyond what either mechanism alone would cause.

Study Insights

This research from 1989 remains remarkably relevant to modern hydraulic turbine maintenance practices. The fundamental understanding that cavitation resistance requires a balance between hardness and toughness—rather than maximizing either property independently—is a principle that continues to guide material selection for hydroelectric applications. For engineers involved in turbine runner refurbishment programs, the findings support the use of multi-layer surfacing strategies where a tough underlayer provides fatigue resistance and a harder overlay provides surface protection. The rotating disk test methodology described here has been standardized in various national and international test procedures and remains a standard qualification method for cavitation-resistant coatings.