Zhuojin Pipe Fitting Co., LtdKey Technology Progress and Applications in Hardfacing and Thermal Spray Fields
Literature Overview
This comprehensive review by Huang Zhiquan, Li Changjiu, He Dingyong, Chen Qian, Zhao Junjun, Gao Zhanqi, and Wang Chongyang, published in China Surface Engineering (2026, Vol. 39, No. 1), provides a state-of-the-art assessment of hardfacing and thermal spray technologies over the past decade. Authored by researchers from the Zhengzhou Mechanical Research Institute, Xi'an Jiaotong University, Beijing University of Technology, the Chinese Society of Mechanical Engineering, and Zhejiang Baton Welding Technology Research Institute, this paper serves as a definitive reference for understanding current capabilities and future directions in surface engineering.
Core Technical Framework
The paper organizes surface engineering technologies into two major categories—hardfacing and thermal spray—and examines each from the perspectives of materials, processes, equipment, and applications.
Hardfacing Technology Development
Arc Hardfacing
Arc hardfacing remains the workhorse technology for industrial surface protection. The paper highlights several recent advances:
| Technology | Key Feature | Typical Deposition Rate | Dilution Control | Application |
|---|---|---|---|---|
| Manual Arc Hardfacing (SMAW) | Flexibility, portability | 1-3 kg/h | High (20-40%) | Repair, small areas |
| Gas Metal Arc (GMAW) | High deposition rate | 5-15 kg/h | Moderate (10-25%) | Large area overlay |
| Submerged Arc (SAW) | Very high productivity | 10-30 kg/h | Moderate (15-30%) | Heavy wear parts |
| Plasma Arc (PAW) | Low dilution, precision | 3-10 kg/h | Low (5-15%) | Critical components |
| Flux-Cored Arc (FCAW) | High deposition, flux protection | 8-20 kg/h | Moderate (10-20%) | Thick overlay layers |
High-Energy Beam Hardfacing
The paper identifies laser cladding and electron beam cladding as transformative technologies for high-performance overlay applications:
- Laser cladding achieves dilution rates as low as 2-5%, enabling the use of high-alloy and ceramic-reinforced materials that would be impossible with conventional arc welding. Recent advances include multi-laser head systems for large-area coverage and high-power fiber lasers (up to 10 kW) for increased productivity.
- Electron beam cladding operates in vacuum or controlled atmosphere, producing extremely low porosity overlays with excellent metallurgical bonding. This technology is particularly valuable for aerospace applications where overlay integrity is critical.
- Magnetic arc cladding uses electromagnetic forces to levitate and shape the molten pool, achieving dilution rates below 5% while maintaining high deposition rates of 10-20 kg/h.
Special Hardfacing Technologies
The review also covers emerging hardfacing approaches including:
- Wire explosion welding for thick composite overlay layers
- Cold spray hardfacing combining thermal spray with plastic deformation for cold bonding
- Friction stir processing for in-situ surface modification
- Hybrid processes combining multiple energy sources for synergistic effects
Thermal Spray Technology Development
Cold Spray
Cold spray has emerged as one of the most important developments in thermal spray technology over the past decade. The process deposits material through high-velocity particle impact without melting, preserving the original material properties and avoiding thermal distortion of the substrate.
| Parameter | Typical Range | Effect on Coating |
|---|---|---|
| Particle velocity | 400-1200 m/s | Higher velocity improves bonding |
| Substrate temperature | 20-300°C | Moderate heating aids bonding |
| Gas temperature | 200-800°C | Affects particle heating and deformation |
| Coating density | >95% | Comparable to solid material |
| Residual stress | Compressive | Beneficial for fatigue life |
Plasma Spray PVD
Plasma spray physical vapor deposition (PSPVD) represents a novel hybrid technique that combines the high deposition rate of thermal spray with the fine microstructure of PVD coatings. This technology is particularly promising for thermal barrier coatings on turbine blades, where traditional PVD has limited thickness capability and thermal spray has limited microstructure refinement.
Suspension Plasma Spray
Suspension plasma spray (SPS) enables the deposition of oxide coatings with particle sizes below 1 μm, overcoming the fundamental limitation of conventional thermal spray with ceramic materials. This technology has found applications in:
- Thermal barrier coatings with improved spallation resistance
- Biocompatible coatings for medical implants
- Catalytic coatings with high surface area
- Transparent conductive coatings for photovoltaics
Explosive Spray
Explosive spray, particularly HVOF (High Velocity Oxy-Fuel) variants, continues to advance with newer fuel mixtures and process parameters:
| Fuel Type | Particle Velocity | Coating Density | Application |
|---|---|---|---|
| Propane/Oxygen | 500-700 m/s | 95-98% | General wear protection |
| Acetylene/Oxygen | 600-800 m/s | 96-99% | High-performance overlays |
| Methane/Oxygen | 700-900 m/s | 97-99% | Critical aerospace components |
| Hydrogen/Oxygen | 800-1000 m/s | 98-99.5% | Ultra-high performance applications |
Application Overview
The paper surveys applications across multiple industries:
- Mining and quarrying: Wear-resistant coatings on crusher components, conveyor rollers, and excavator buckets using carbide-reinforced overlays
- Power generation: Thermal barrier coatings on turbine blades, corrosion-resistant overlays on boiler tubes, and erosion-resistant coatings on fan blades
- Oil and gas: Corrosion-resistant coatings on wellhead components, downhole tools, and subsea pipelines
- Aerospace: Thermal barrier coatings, ablation-resistant coatings, and high-temperature structural coatings
- Automotive: Wear-resistant coatings on engine components, brake rotors, and transmission parts
- Chemical processing: Corrosion-resistant linings for reactors, heat exchangers, and piping systems
Future Development Directions
The paper identifies several key development directions for both hardfacing and thermal spray technologies:
Hardfacing Future Directions
- High-end equipment overlay materials: Development of new superalloys, high-entropy alloys, and ceramic-metal composites for extreme environment applications
- Composite hardfacing technology: Multi-layer and multi-material overlay designs that combine different functional properties in a single component
- Automation and intelligence: Robotic hardfacing systems with real-time monitoring and adaptive process control
- Flexibility: Multi-process systems capable of switching between different overlay techniques based on component geometry and requirements
Thermal Spray Future Directions
- New materials and processes: Development of nanocomposite feedstock materials and novel spray techniques for improved coating properties
- Coating densification: Reducing porosity in thermal spray coatings through advanced process parameters and post-treatment techniques
- In-situ monitoring: Real-time characterization of coating properties during deposition using optical, acoustic, and thermal sensors
- Sustainable manufacturing: Reducing energy consumption and material waste through process optimization
Integration with Engineering Practice
From a practical engineering perspective, this review highlights several critical considerations for technology selection:
- Cost-benefit analysis: High-performance technologies like laser cladding and cold spray offer superior coating properties but require significant capital investment. The decision to adopt new technologies should be based on total cost of ownership including maintenance savings and extended service life.
- Process compatibility: The selected surface engineering technology must be compatible with the substrate material, component geometry, and production volume. For example, laser cladding is ideal for high-value, complex-shaped components but impractical for high-volume, simple geometries.
- Quality assurance: Establishing robust quality control procedures is essential for surface engineering applications, particularly in safety-critical industries. This includes process parameter documentation, coating characterization protocols, and performance verification testing.
- Operator training and skill: Advanced surface engineering technologies require skilled operators and engineers. Investment in training and knowledge transfer is essential for successful technology implementation.
Study Insights and Implications
This comprehensive review serves as an excellent reference for engineers seeking to understand the current landscape of surface engineering technologies. The key takeaway is that the field is rapidly evolving, with new materials, processes, and equipment continuously expanding the capabilities available for surface protection and modification. The convergence of hardfacing and thermal spray technologies into a unified surface engineering discipline reflects the increasing demand for multifunctional surface solutions that address multiple degradation mechanisms simultaneously. Engineers should remain informed about these developments and consider how emerging technologies might be applied to solve current challenges in their specific applications. The emphasis on automation, intelligence, and flexibility in the future directions section suggests that the next generation of surface engineering systems will be more capable, more consistent, and more accessible to a broader range of industries and applications.