Microstructure and Wear Resistance of Dissimilar Material Surfacing Layers on Low Carbon Steel

Literature Overview

The paper by Liu Zhengjun, Song Xingkui, and Tang Xingtao from Shenyang University of Technology, published in Transactions of the China Welding Institution in 2011 (Volume 32, Issue 4, pages 99-102), investigates the microstructure and wear resistance of aluminum bronze alloy surfacing layers deposited on low carbon steel using reverse-polarity weak plasma arc surfacing. The work is classified under TG455 and addresses the important engineering challenge of achieving low-dilution dissimilar material surfacing with controlled microstructure.

Core Technical Content

The study employs reverse-polarity weak plasma arc surfacing (PAW) to deposit aluminum bronze alloy powder onto low carbon steel substrates. The reverse polarity configuration (electrode positive, workpiece negative) is selected to minimize dilution, while the weak plasma arc provides concentrated heat input with limited heat penetration into the substrate.

Microstructure Characterization Results

The surfacing layer achieves metallurgical bonding with the low carbon steel substrate, confirming proper wetting and fusion during the surfacing process. The dilution rate is reported to be low, which is critical for maintaining the desired aluminum bronze alloy composition and properties in the surfacing layer.

Wear Mechanism Analysis

The study identifies that the wear resistance of the surfacing layer is significantly enhanced when the microstructure contains a dense α phase or when the α phase precipitates along grain boundaries in a network distribution. The wear mechanism involves the interaction between the surfacing layer and the 45 steel counterface, and the wear resistance is governed by the combined effects of microstructure, hardness, and counterface material properties.

Process Parameter Analysis

The reverse-polarity weak plasma arc surfacing process offers several advantages for dissimilar material surfacing:

1. Low dilution: The reverse polarity configuration directs the majority of the arc energy to the powder feed rather than the substrate, minimizing substrate dilution and preserving the alloy composition of the surfacing layer.
2. Controlled heat input: The weak plasma arc provides concentrated, controllable heat input, enabling precise control of the melt pool geometry and solidification conditions.
3. Powder utilization efficiency: Plasma arc surfacing typically achieves high powder utilization rates (80-95%), making it economically attractive for expensive alloy powders such as aluminum bronze.
4. Surface quality: The plasma arc process produces smooth, dense surfacing layers with minimal surface defects, which is important for functional applications requiring surface integrity.

Engineering Practice Integration

For engineers considering aluminum bronze surfacing on steel substrates, several practical considerations emerge from this study:

1. Dilution control: The low dilution achieved with reverse-polarity weak plasma arc surfacing is essential for maintaining the wear-resistant properties of the aluminum bronze alloy. If dilution is excessive, the surfacing layer composition shifts toward the steel substrate, reducing the beneficial effects of the aluminum bronze alloy.
2. Microstructure optimization: The dense α phase or network α phase distribution is identified as the key microstructural feature for enhanced wear resistance. Process parameters such as arc current, travel speed, and powder feed rate must be optimized to achieve this target microstructure.
3. Counterface material selection: The wear resistance is not solely determined by the surfacing layer properties but also by the counterface material characteristics. In practical applications, the tribological pair must be considered as a system rather than evaluating the surfacing layer in isolation.
4. Application suitability: Aluminum bronze surfacing is particularly suitable for applications involving abrasive wear, cavitation erosion, and corrosion-wear synergy, such as pump impellers, marine propellers, and valve components.

Key Questions and Reflections

The study raises an important question about the stability of the α phase network distribution under thermal cycling conditions. In service applications involving temperature fluctuations, the network α phase may undergo coarsening, dissolution, or transformation, potentially degrading the wear resistance over time. Thermal cycling tests would be valuable to assess the long-term stability of the optimized microstructure.

Another reflection concerns the scalability of plasma arc surfacing for large component applications. While plasma arc surfacing offers excellent dilution control and surface quality, the deposition rate is typically lower than that of conventional arc surfacing processes such as GMAW or SMAW. For large components requiring extensive surfacing coverage, the process efficiency and cost-effectiveness must be carefully evaluated against alternative surfacing methods.

Study Insights and Implications

This paper provides valuable insights into the microstructure-property relationships of aluminum bronze surfacing layers on low carbon steel substrates. The identification of dense α phase and network α phase distribution as key microstructural features for enhanced wear resistance offers a clear target for process optimization. The reverse-polarity weak plasma arc surfacing process demonstrates excellent capability for low-dilution dissimilar material surfacing, making it a preferred choice for applications requiring precise alloy composition control. For surfacing engineers working with aluminum bronze overlays, this study emphasizes the importance of systematic microstructure characterization and the need to consider the tribological pair as a system when evaluating wear performance. The findings contribute to the broader understanding of how process parameters influence microstructure and, ultimately, the functional performance of dissimilar material surfacing layers in demanding engineering applications.