Automated Plasma Surfacing Technology for Engine Cylinder Block Thrust Surface Remanufacturing

Literature Overview

Published in China Surface Engineering (2009, Vol. 22, No. 6, pp. 72-76), this study by Xiang Yonghua and colleagues from the Key Laboratory of Equipment Remanufacturing Technology, Academy of Armored Force Engineering, presents an automated powder plasma arc surfacing (PAS) system for the remanufacturing of engine cylinder block thrust surfaces. The research is supported by multiple national funding sources including the National Natural Science Foundation (50735006, 50675223), the National 973 Program (2007CB607601), and the National Defense Science and Technology Key Laboratory Fund.

The work represents a practical application of surface engineering technology in the remanufacturing sector, addressing the economic and environmental imperatives of extending the service life of high-value engine components.

Core Technical Findings

Process System and Parameters

The automated PAS system uses Ni15 alloy powder as the surfacing material. The system was validated through thrust surface remanufacturing trials on engine cylinder blocks. Key process parameters and their effects on coating quality were systematically evaluated.

Microstructural Analysis

Metallographic and energy dispersive spectroscopy (EDS) analysis reveals that the coating is free of metallurgical defects such as porosity and cracking. The bottom region of the coating exhibits an austenitic matrix formed by Cr dissolved in a Ni-Fe solid solution, with dispersed carbide hard phases and eutectic structures.

The planar crystal growth zone near the fusion line shows distinct carbon enrichment (solubilization) phenomena, resulting in elevated hardness of approximately 200 HV in this region. The remainder of the coating maintains hardness comparable to the substrate at approximately 130 HV.

Process Quality Assessment

Defect Analysis

The absence of porosity and cracking in the coating is a significant quality achievement, particularly for an automated system. This indicates that the process parameters were well-optimized to achieve:

1. Adequate shielding gas coverage to prevent atmospheric contamination
2. Appropriate thermal input to avoid excessive cooling rates that could induce cracking
3. Controlled powder feeding to prevent incomplete melting or excessive dilution
4. Proper joint preparation to ensure adequate fusion without excessive substrate melting

Dilution and Carbon Enrichment

The carbon enrichment in the fusion zone (planar crystal region) is a direct consequence of substrate dilution. During plasma arc surfacing, the molten pool incorporates substrate material, and in the case of carbon steel substrates, carbon dissolution from the base metal into the nickel-rich coating creates a hardened transition zone. This carbon enrichment zone at 200 HV provides a beneficial hardness gradient that can enhance the coating's resistance to fretting and micro-slip wear at the interface.

Economic and Engineering Analysis

Cost-Benefit Assessment

The material cost of less than 20 CNY per remanufactured thrust surface represents exceptional cost-effectiveness. When compared to the cost of replacing the entire cylinder block or machining and resizing the thrust surface, the PAS remanufacturing approach offers substantial savings while restoring or exceeding original specifications.

Remanufacturing Process Flow

1. Surface preparation: machining to remove damaged material and provide adequate fusion depth
2. Substrate preheating: controlled temperature to reduce thermal shock and residual stress
3. Automated PAS deposition: multi-pass deposition to achieve required thickness
4. Post-deposition inspection: visual, dimensional, and hardness verification
5. Final machining: precision finishing to dimensional tolerances

Engineering Practice Implications

The automated PAS system demonstrated in this study is particularly suited for high-volume remanufacturing operations where consistency and repeatability are essential. The key advantages include:

• Consistent coating quality through automated parameter control
• Low material consumption and high cost-effectiveness
• Defect-free coatings suitable for critical engine components
• Compatibility with existing remanufacturing infrastructure

For engineers managing remanufacturing operations, the Ni15 alloy selection represents a proven solution for thrust surfaces where moderate wear resistance and good bonding strength are required. The process is also well-suited for other cylinder block applications such as camshaft journals and crankshaft thrust bearings.

Key Questions and Reflections

The study focuses primarily on the coating microstructure and hardness but does not provide extensive wear testing data. For thrust surfaces subjected to high contact pressures and sliding velocities, quantitative wear rate measurements would strengthen the case for this technology.

Additionally, the long-term performance under thermal cycling and combined loading conditions typical of engine service should be evaluated. The carbon-enriched fusion zone, while beneficial for hardness, may be susceptible to temper embrittlement under prolonged thermal exposure.

Summary and Conclusions

This study demonstrates that automated plasma arc surfacing with Ni15 alloy powder is a technically sound and economically viable solution for engine cylinder block thrust surface remanufacturing. The defect-free coatings, low material consumption (40 g per surface), and minimal cost (<20 CNY per surface) make this approach highly attractive for industrial remanufacturing operations. The carbon-enriched fusion zone providing elevated hardness (200 HV) offers a beneficial interface characteristic. Engineers in the remanufacturing sector should consider this technology as a reliable option for restoring wear-damaged engine components while maintaining dimensional accuracy and surface integrity.