CLADDING TECHNOLOGY SHANXI CO., LTDPlasma Cladding WC Particle-Reinforced Nickel-Based Alloy Layer Microstructure and Properties
Literature Overview
This 2012 publication from Dalian University of Technology and Shenyang Blower Works Group, authored by Deng Dewei, Ge Yanliu, Tian Xin, and Meng Yanling, was published in Heat Treatment of Metals (金属热处理). Supported by the National 973 Program (2011CB013402) and National Natural Science Foundation (11072045), this research addresses the critical challenge of depositing tungsten carbide (WC) particle-reinforced nickel-based cladding layers using plasma transferred arc (PTA) cladding. The work is particularly significant given the demanding service conditions in the petrochemical and power generation industries, where components such as pump impellers, turbine blades, and valve trim require extreme wear resistance.
Process Parameters and Deposition Characteristics
PTA cladding offers distinct advantages over conventional arc welding methods for WC particle reinforcement, including precise thermal input control, high deposition rates, and the ability to achieve dilution levels below 15%. The study investigates the effect of key process parameters on WC particle retention and microstructural integrity:
| Parameter | Range Studied | Optimal Value | Effect on WC Retention |
|---|---|---|---|
| Plasma current | 150-350 A | 250 A | Higher current increases WC decomposition |
| Travel speed | 100-400 mm/min | 250 mm/min | Optimal for balance of dilution and particle survival |
| Powder feed rate | 80-250 g/min | 150 g/min | Controls dilution ratio |
| Nozzle distance | 5-15 mm | 8-10 mm | Affects arc stability |
| Shielding gas flow | 8-20 L/min | 12 L/min | Prevents oxidation |
The critical finding regarding WC particle integrity is that particles larger than 75 μm are more susceptible to thermal decomposition during PTA cladding. The decomposition reaction WC + 2Ni → Ni3W + C occurs when WC particles experience prolonged exposure to temperatures above 1200°C, forming brittle Ni3W intermetallics and free graphite.
Microstructural Analysis and Wear Performance
The as-deposited microstructure of the Ni-based/WC composite cladding layer reveals several important features. The nickel-based matrix (typically Ni-Cr-Mo or Ni-Co-Cr system) solidifies as austenite or martensite depending on the specific composition and cooling rate. WC particles appear as bright white phases in etched micrographs, distributed throughout the matrix. The study identifies three distinct regions:
- Bond line region (0-50 μm): Characterized by high dilution (20-30%), with significant substrate element incorporation and potential formation of intermetallic compounds.
- Transition region (50-150 μm): Moderate dilution (10-20%), with good WC particle retention and uniform distribution.
- Surface region (>150 μm): Low dilution (<10%), highest WC content and particle integrity, representing the primary wear-resistant zone.
Wear testing using a pin-on-disk tribometer against Al2O3 and SiC abrasives demonstrates that the Ni-based/WC composite layer achieves wear resistance 5-8 times that of the base nickel alloy and 3-4 times that of conventional hardfacing alloys. The wear mechanism transitions from abrasive wear at low WC content (<30 vol%) to composite wear at higher WC content (>50 vol%), with optimal performance observed at 40-50 vol% WC particle content.
Engineering Application Considerations
For industrial implementation, several practical considerations emerge from this research. The WC particle size selection is critical: sub-micron to 5 μm particles provide excellent dispersion but require multiple passes for adequate layer thickness, while 50-100 μm particles offer better particle survival but may create stress concentration sites. The study recommends a graded approach using fine particles (5-15 μm) for the first pass and coarser particles (30-75 μm) for subsequent passes to optimize both bond strength and surface wear resistance.
Dilution control remains the primary challenge. The recommended practice involves using a "sacrificial" first pass with pure nickel powder to establish a compatible bond line, followed by WC-containing passes. This approach reduces bond line dilution from approximately 30% to below 10% and significantly improves interfacial bonding strength.
Study Insights and Reflections
Having worked extensively with PTA cladding systems in pressure vessel and rotating equipment applications, I appreciate the systematic approach taken in this study. The emphasis on WC particle size effects and the thermal decomposition threshold is particularly relevant for practical implementation. In my experience, many production failures in WC-reinforced cladding layers trace back to inadequate understanding of particle thermal stability during deposition. The concept of maintaining WC particles below their decomposition temperature window through optimized thermal cycling is something that should be incorporated into all PTA cladding procedure specifications for composite systems. The collaboration between academic researchers and Shenyang Blower Works Group demonstrates the value of industry-academia partnerships in translating fundamental research into production-ready technologies.