Performance Study of Nickel-Based Alloy Powder Plasma Arc Surfacing Layer

Literature Overview

This 2006 study by Bao Junfeng and Wei Wei from the Beijing Research Institute of Mining Technology, published in Nonferrous Metals (Metallurgy), examines the performance characteristics of nickel-based alloy powder deposited via plasma arc surfacing. The research is particularly relevant to mining applications where severe abrasive and corrosive conditions demand high-performance surfacing solutions. The choice of nickel-based alloys reflects the well-established superiority of Ni-Cr-Mo and Ni-Cr-Si-B alloy systems in combined wear-corrosion environments, which are common in mineral processing operations.

Core Technical Content

Nickel-Based Alloy Systems for Surfacing

The study focuses on the plasma arc surfacing of nickel-based alloy powders, which typically fall into several categories:

Microstructural Characteristics

The plasma arc surfacing process produces distinctive microstructural features in nickel-based alloys:

• Dendritic matrix of austenitic or ferritic nickel solid solution
• Eutectic carbides distributed along dendrite boundaries
• Fine grain structure resulting from rapid solidification rates (10²-10³ K/s)
• Columnar grains aligned in the direction of heat flow from the substrate

The rapid solidification characteristic of PTA surfacing is a significant advantage over conventional welding processes, as it produces finer microstructures with smaller inter-dendritic spacing, which directly contributes to enhanced hardness and wear resistance.

Performance Evaluation Results

Key performance indicators examined in this study typically include:

• Microhardness: HRC 55-65 for Ni-Cr-Mo systems, HRC 45-55 for Ni-Cr-Si-B systems
• Wear resistance: 2-5 times that of the substrate material under dry sliding conditions
• Corrosion resistance: significant improvement in acid, alkali, and neutral salt solutions compared to carbon steel substrates
• Bond strength: typically exceeding 300 MPa when proper preheating and dilution control are maintained
• Dilution rate: critical parameter, ideally controlled below 10% for optimal performance retention

Process Analysis and Quality Considerations

Critical Process Parameters

The PTA process for nickel-based alloys requires careful parameter control:

1. Preheating: 200-300°C for carbon steel substrates to minimize thermal cracking and reduce dilution
2. Interpass temperature: maintained between 150-250°C to prevent excessive heat input
3. Powder moisture control: powders must be dried at 150-200°C for 2-4 hours prior to use to prevent porosity
4. Shielding gas purity: minimum 99.99% argon to prevent oxide inclusions
5. Layer thickness: typically 0.5-1.5 mm per pass, with multiple passes for thicker deposits

Common Defects and Countermeasures

Engineering Practice Applications

The mining industry context of this research is particularly instructive. In mineral processing operations, components such as:

• Pump casings and impellers exposed to abrasive slurries
• Ball mill liners and grinding media
• Slurry pipelines subject to erosion-corrosion
• Hydrocyclone components experiencing high-velocity particle impact

The nickel-based PTA surfacing provides a cost-effective solution that extends component life by factors of 3-10 compared to unprotected carbon steel, while also improving corrosion resistance in the aggressive chemical environments typical of ore processing circuits.

Key Reflections

This study underscores an important principle in surfacing technology: the selection of the overlay alloy system must be matched to the specific service environment, not simply to the highest available hardness. Nickel-based alloys offer a unique combination of hardness, corrosion resistance, and thermal stability that makes them ideal for combined wear-corrosion environments. The PTA process provides the rapid solidification advantage needed to fully realize the potential of these alloy systems. The emphasis on dilution control is particularly noteworthy, as excessive dilution can dramatically reduce the performance benefits of expensive nickel-based alloys, making process optimization a critical economic factor in surfacing operations.