Cavitation Erosion Characteristics and Properties of Nickel-Based Plasma Cladding Layers

Literature Overview

Published in the Journal of University of Science and Technology Beijing in 2008, this paper by Wang Guogang, Ma Guang, Fan Zishuan, Wang Yong, Yu Hongying, Meng Huimin, and Sun Dongbai from the Center for Corrosion and Protection at USTB investigates the cavitation erosion behavior of three nickel-based plasma cladding alloys: Ni46, Ni67, and Ni60/35WC. The study employs a rotating disc cavitation erosion test rig combined with SEM, XRD, microhardness, and weight loss analysis to characterize the erosion mechanisms and post-erosion microstructural evolution.

Core Technical Findings

Cavitation erosion is a significant degradation mechanism in hydraulic systems, pump impellers, propellers, and heat exchanger surfaces where liquid-vapor phase transitions occur. The study systematically compares the cavitation resistance of three commercial nickel-based overlay alloys against a 304 stainless steel benchmark.

Weight Loss Comparison

Alloy Type	Composition Characteristic	Relative Weight Loss vs. 304 SS
Ni46	High-nickel austenitic matrix	Greater than 304 SS
Ni67	Nickel-iron alloy with Cr	Greater than 304 SS
Ni60/35WC	Ni-Cr-Mo with 35% WC particles	Greater than 304 SS

All three nickel-based cladding layers exhibited greater cavitation weight loss than the 304 stainless steel reference, indicating that under the test conditions, the base stainless steel demonstrated superior cavitation resistance. This counterintuitive result warrants careful interpretation in engineering applications.

Erosion Mechanism Analysis

SEM observations revealed that all cladding layers contained inherent defects and porosity within the microstructure. Following cavitation exposure, these defects propagated in a crack-like manner, confirming that cavitation erosion involves a strong fatigue damage component. The process can be described as follows:

Cavitation bubble collapse generates localized high-pressure shock waves.
These shock waves initiate micro-cracks at pre-existing defects and pores.
Repeated cyclic loading causes crack propagation and material removal.
The fatigue-driven damage mechanism dominates over simple mechanical abrasion.

Microstructural Evolution Post-Erosion

Alloy	Post-Erosion Microstructural Change	XRD Findings
Ni60/35WC	Phase transformation induced	New phases detected at eroded surface
Ni67	Work hardening	Increased dislocation density
Ni46	Work softening	Decreased hardness at eroded zone

The XRD analysis revealed that cavitation erosion induced a phase transformation on the Ni60/35WC surface, likely involving decomposition or restructuring of the carbide phase under cyclic stress. Ni67 exhibited work hardening due to dislocation accumulation during cyclic plastic deformation, while Ni46 showed work softening, possibly due to dynamic recovery processes in its austenitic structure.

Engineering Practice Implications

The findings have direct relevance to the selection of overlay materials for cavitation-prone components in hydraulic machinery, marine engineering, and nuclear cooling systems. Key observations for practitioners include:

The presence of porosity and defects in plasma cladding layers significantly reduces cavitation resistance, emphasizing the need for quality-controlled cladding processes with minimal porosity.
The fatigue-dominated erosion mechanism suggests that surface integrity and defect-free microstructure are more critical than bulk hardness for cavitation resistance.
Ni46's work softening behavior under cyclic loading may limit its long-term performance in sustained cavitation environments despite its excellent corrosion resistance.
The phase transformation in Ni60/35WC indicates potential for microstructural instability under prolonged cavitation exposure.

Study Insights and Conclusions

This research provides valuable insight into the fundamental mechanisms governing cavitation erosion of nickel-based plasma claddings. The identification of fatigue as the dominant damage mechanism shifts the design focus from simple hardness maximization to microstructural integrity and defect minimization. The contrasting work hardening and work softening behaviors among the three alloys highlight the complexity of material response to cyclic loading and underscore the importance of alloy selection based on specific service conditions. Engineers should consider that superior corrosion resistance does not necessarily translate to superior cavitation resistance, and that process-induced defects in cladding layers can be the primary factor determining erosion life.