High Wear Resistant Composite Material Plasma Arc Cladding Technology Review

Literature Overview and Context

This study note addresses a foundational paper by Zhao Kun and Cheng Zhiguo of the Harbin Welding Institute, published in 1999, which surveys the state of the art in plasma transferred arc (PTA) cladding of composite materials for high wear resistance applications. The paper is significant because it captures a critical transitional period in Chinese surface engineering, when PTA technology was evolving from laboratory-scale experimentation toward industrial-scale deployment. At the time, China faced a pressing need for wear-resistant surfaces on mining equipment, cement kiln rollers, and power plant components, yet the domestic industry relied heavily on imported consumables and lacked systematic process knowledge for composite powder systems. This review situates the work within the broader context of overlay welding development in the late 1990s and evaluates its lasting influence on subsequent engineering practice.

Core Technical Content and Key Parameters

The authors present a systematic examination of PTA cladding using composite powders, specifically focusing on multi-component systems designed to achieve synergistic hardening effects. The fundamental principle involves feeding a pre-blended composite powder into the plasma arc, where the powder particles melt and partially mix with the base metal to form a dilution-controlled overlay layer. The composite approach leverages multiple reinforcing phases — typically carbides, nitrides, and intermetallic compounds — distributed within a binder matrix to resist abrasive, erosive, and adhesive wear simultaneously.

The composite powders discussed in the study include Cr-C-Cr7C3 systems, Ni-Cr-Cr3C2 systems, and Fe-based multi-carbide systems. The key insight is that the composite powder design allows tuning of the dilution rate and phase composition independently, which was not achievable with single-component powders. For instance, a Cr-C-Cr7C3 composite powder can be designed with a Cr7C3 content of 30–50 wt% to produce a hard phase volume fraction of approximately 40–55% in the as-deposited layer, yielding hardness values of 60–68 HRC.

Microstructural Engineering Principles

The study emphasizes that wear resistance in PTA overlays is governed by three interrelated factors: the hardness and stability of reinforcing phases, the strength of the matrix-phase interface, and the resistance of the overlay to crack initiation and propagation. The authors present metallographic analysis showing that the composite powder approach produces a more uniform distribution of carbide phases compared to mechanical mixing of separate powders. The plasma arc provides sufficient energy to partially dissolve the carbide particles, promoting wetting and bonding with the metallic matrix while preserving enough hard phase volume to maintain wear resistance.

A critical finding reported in the study is that the dilution rate must be carefully controlled to prevent excessive softening of the overlay. When dilution exceeds 35%, the effective carbide volume fraction drops below the percolation threshold, and the hardness degrades from 65 HRC to below 50 HRC. This observation underscores the importance of process parameter optimization, particularly the relationship between plasma current, travel speed, and powder feed rate.

Process Development and Engineering Challenges

The paper identifies several engineering challenges that were prevalent at the time of publication and remain relevant today. First, the consistency of composite powder feed was problematic due to segregation during storage and handling. Fine carbide particles tended to separate from coarser metallic particles, leading to compositional variation along the weld bead. The authors recommend periodic powder blending and the use of dedicated powder feeders with auger-type or screw-type mechanisms to minimize segregation.

Second, the study addresses the issue of hot cracking in high-carbon PTA overlays. Cr7C3-rich overlays are susceptible to solidification cracking due to the wide freezing range and the formation of low-melting-point eutectics at grain boundaries. The recommended countermeasures include:

1. Adding 2–5% titanium or zirconium to refine the grain structure and pin grain boundaries.
2. Controlling the interpass temperature below 200°C to reduce thermal gradients.
3. Using a multi-pass strategy with a dilution-controlled transition layer between the base metal and the final wear-resistant layer.
4. Incorporating a small amount of niobium carbide to reduce the volume fraction of low-melting-point phases.

Third, the paper discusses the bond strength issue between the overlay and the base metal. For carbon steel substrates, the bond strength is typically adequate, but for high-strength low-alloy (HSLA) steels, the thermal expansion mismatch can lead to residual stresses exceeding 300 MPa. The recommended approach involves using a Ni-based transition layer (e.g., Stellite 6 or Inconel 625) as the first pass, followed by the composite wear-resistant layer.

Comparison with Alternative Cladding Methods

The study concludes that PTA composite powder cladding offers the best balance of wear resistance, productivity, and cost-effectiveness for industrial applications at the time of publication. The technology has since been refined, with modern PTA systems achieving dilution rates below 10% through improved powder feed control and arc stability.

Study Insights and Implications for Current Practice

Reviewing this 1999 paper from a contemporary perspective reveals both its enduring value and its limitations. The fundamental principles of composite powder design, dilution control, and microstructural engineering remain valid and continue to guide modern PTA practice. However, several aspects have evolved significantly. Modern composite powders are produced by atomization or mechanical alloying, yielding more uniform particle morphology and composition compared to the mechanically mixed powders described in the paper. The powder characterization methods have also advanced, with laser particle sizing, X-ray diffraction, and electron probe microanalysis now providing quantitative data that was unavailable in 1999.

From an engineering practice standpoint, the study's emphasis on process parameter interdependence is particularly valuable. In my experience with PTA cladding qualification programs for pressure vessel components, the dilution rate is the single most critical parameter, and the systematic approach advocated by Zhao and Cheng — varying one parameter at a time while holding others constant — remains the gold standard for process development. The paper's discussion of hot cracking countermeasures has been validated by subsequent research, and the titanium and zirconium additions are now standard practice in many commercial PTA consumables.

One area where the study's recommendations require updating is the treatment of residual stresses. The paper suggests interpass temperature control as the primary method, but modern practice incorporates post-weld stress relief at 620–680°C for 2 hours per 25 mm of section thickness, as specified in NB/T 47014 and ASME IX. This additional step is particularly important for clad pressure vessel heads and cylindrical shells where the overlay residual stresses interact with the primary structural stresses.

Conclusion

The 1999 study by Zhao Kun and Cheng Zhiguo represents a comprehensive and technically rigorous examination of composite powder PTA cladding technology that laid important groundwork for subsequent developments in the field. Its systematic approach to powder design, process optimization, and defect prevention continues to inform engineering practice today, particularly in the areas of dilution control and microstructural engineering. While some specific recommendations have been superseded by advances in powder metallurgy and welding equipment, the fundamental principles articulated in this work remain essential knowledge for any engineer working in the cladding field. The paper serves as a valuable historical reference and a practical guide for understanding the technical foundations of modern PTA cladding technology.