Research Status and Progress of Plasma Arc Powder Cladding Materials

Literature Overview and Core Thesis

This comprehensive review examines the current state of research and development in plasma arc transferred (PTA) powder cladding materials, encompassing material development, process optimization, microstructure-property relationships, and industrial applications. The review covers the period from the early 1990s to the present, highlighting the evolution from simple hardfacing alloys to sophisticated multi-component systems with tailored properties. The document serves as a reference guide for engineers selecting appropriate cladding materials for specific service conditions.

Classification of PTA Cladding Materials

Material System Classification

Recent Material Development Trends

The review identifies several key trends in PTA cladding material development:

1. High-entropy alloy (HEA) powders: Multi-principal element alloys with equal or near-equal atomic percentages of five or more elements are being developed for PTA applications. These materials exhibit unique combinations of hardness, toughness, and corrosion resistance due to the high-entropy effect, severe lattice distortion, and sluggish diffusion.
2. Nanocomposite cladding materials: Powder systems containing pre-dispersed nano-particles (TiC, TiN, SiC, Al₂O₃, WC) are being developed to achieve fine, uniformly distributed hard phases without requiring post-weld heat treatment.
3. Functionally graded materials (FGM): Multi-layer cladding systems with gradually varying compositions from substrate to surface are designed to minimize thermal stresses and optimize the property gradient.
4. Recycled and sustainable powders: Economic and environmental pressures are driving the development of cladding powders from recycled materials, including recycled stainless steel, nickel, and cobalt scrap.

Process-Structure-Property Relationships

Effect of Process Parameters on Microstructure

Key Thermodynamic and Kinetic Considerations

The review emphasizes the importance of thermodynamic modeling in predicting cladding layer composition and phase formation. The dilution ratio, defined as the ratio of substrate material to deposited material in the cladding layer, is a critical parameter that directly affects the final composition and properties. Typical dilution ratios for single-pass PTA cladding range from 15% to 40%, depending on the heat input and substrate thermal properties.

The Schatzer equation and its modifications are used to predict the dilution ratio based on process parameters:

• Dilution ratio increases with increasing arc power and decreasing travel speed
• Dilution ratio decreases with increasing powder feed rate
• Dilution ratio is lower for substrates with lower thermal conductivity
• Multi-pass cladding typically achieves lower dilution in subsequent passes due to the thermal mass of previously deposited layers

Industrial Applications and Case Studies

Power Generation Industry

In the power generation sector, PTA cladding is extensively used for:

• Steam turbine blade repair and overlay (Ni-Co-Cr-W systems for hot gas path components)
• Boiler tube protection at burner exit and furnace walls (stainless steel and nickel-based overlays)
• Condenser tube sheet cladding (nickel-aluminum bronze or nickel-based alloys)
• Coal mill classifier blades and liners (Fe-B-Si and Co-Cr-W systems)

A notable case study involves the cladding of a 600 MW supercritical boiler furnace wall where the original carbon steel tubes experienced severe slagging and corrosion at the burner exit. PTA cladding with a 310 cast stainless steel powder (Cr: 25%, Ni: 20%) extended the tube life from 6 months to over 24 months. The cladding was applied with a minimum thickness of 1.5 mm, using a two-pass technique with a dilution ratio controlled below 20%.

Mining and Mineral Processing

In mining applications, PTA cladding materials must withstand extreme abrasive conditions involving hard, angular mineral particles. The review highlights several successful applications:

• Crusher hammers and jaws: Co-Cr-W (Stellite-type) and Fe-C-B-V systems extend life by 3–5 times compared to unclad carbon steel
• Excavator bucket teeth: Ni-Cr-B systems provide excellent resistance to sliding abrasion against hard rock
• Slurry pump impellers: Ni-Cr-Mo-Si systems resist both abrasion and corrosion in acidic slurries
• Ball mill liners: High-chromium white iron and Fe-B-Si systems reduce liner replacement frequency by 40–60%

Oil and Gas Industry

In the oil and gas sector, PTA cladding addresses:

• Hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSSC) resistance in sour service
• Erosion-corrosion in high-velocity multiphase flow lines
• High-temperature oxidation in refinery furnace tubes
• Chloride stress corrosion cracking resistance in desalination plants

The NACE MR0175/ISO 15156 standard requirements for sour service materials have driven the development of specific PTA cladding compositions that meet the hardness limits (≤250 HV for carbon steel) and HIC/SSC test requirements.

Quality Control and Inspection

Non-Destructive Testing Requirements

Mechanical Property Verification

Post-cladding verification typically includes:

• Hardness testing (Vickers HV0.3 or HV1) across the cladding cross-section
• Bond strength testing (peel test or bend test per ASTM A263/A264 or ISO 14273)
• Metallographic examination of the cladding-substrate interface
• Chemical analysis of the cladding layer composition (to verify dilution ratio)
• Impact testing for ductility assessment (where applicable)

Study Insights and Implications

The PTA cladding material landscape is evolving rapidly, driven by the need for more efficient, sustainable, and high-performance solutions. The integration of computational thermodynamic modeling (CALPHAD) with experimental validation is accelerating material development and reducing the trial-and-error approach that historically dominated cladding material selection. The emergence of high-entropy alloy and nanocomposite powders represents a paradigm shift, offering property combinations previously unattainable with conventional alloy systems. However, the commercial adoption of these advanced materials is limited by powder cost, supply chain maturity, and lack of established qualification databases. Engineers must carefully balance performance requirements against cost constraints, recognizing that the most advanced material is not always the most appropriate solution for a given application. The future of PTA cladding lies in the intelligent integration of material science, process engineering, and digital manufacturing technologies to deliver optimized, cost-effective surface engineering solutions.