Composite Material Plasma Arc Surfacing for High Wear-Resistant Overlay Technology

Literature Overview

Published in Welding (1999, No. 2), this review article from the Harbin Institute of Welding provides a comprehensive overview of composite material plasma arc surfacing technology and its status both domestically (in China) and internationally. The authors, Zhao Kun and Cheng Zhiguo, discuss the principles, characteristics, and application progress of plasma arc surfacing of composite materials, emphasizing its potential for producing high wear-resistant overlay layers. The article serves as a state-of-the-art summary at the time of publication and outlines directions for future development.

Core Technical Points

Plasma Arc Surfacing Process Fundamentals

Plasma arc surfacing uses a transferred or non-transferred plasma arc as the heat source to melt a composite feed material (powder or wire) onto a base substrate. The plasma arc provides a concentrated, high-temperature heat source (10,000–30,000 K) that enables rapid melting and solidification of the overlay material.

Parameter	Typical Range	Effect on Overlay
Plasma arc current	100–500 A	Controls heat input and dilution
Arc voltage	18–40 V	Influences melt pool size and shape
Powder feed rate	100–500 g/min	Controls deposition rate
Travel speed	5–30 cm/min	Affects bead width and height
Shielding gas (Ar or He)	10–30 L/min	Prevents oxidation
Powder composition	Composite (matrix + reinforcement)	Determines final properties

Composite Material Design Principles

The key innovation in composite material plasma arc surfacing is the use of a powder mixture containing a ductile matrix material and hard reinforcing particles or fibers. Common combinations include:

Matrix: Nickel-based alloy, cobalt-based alloy, austenitic stainless steel, or cast iron
Reinforcement: WC, Cr₃C₂, TiC, SiC, B₄C, or carbide-nitride composites

The plasma arc melting process creates a metallurgical bond between the reinforcement particles and the matrix, producing a composite overlay with properties superior to either component alone. The rapid solidification rate (10–100 K/s) achieved in plasma arc surfacing promotes fine grain structures and can even produce amorphous or nanocrystalline phases in the matrix, further enhancing wear resistance.

Comparative Performance

Overlay Type	Hardness (HV)	Abrasive Wear Life	Impact Toughness	Cost
Conventional hardfacing (Ni-Cr)	400–500	Baseline	Moderate	Moderate
Plasma arc composite (Ni-WC)	800–1200	3–5× improvement	Moderate	Higher
Plasma arc composite (Co-Cr₃C₂)	900–1300	4–6× improvement	Good	Higher
Plasma arc composite (Fe-SiC)	700–1000	2–4× improvement	Good	Lower

Engineering Practice Integration

Plasma arc surfacing of composite materials has found extensive application in:

Mining and quarrying equipment: Crusher jaws, conveyor rollers, and bucket teeth
Power generation: Boiler tubes, turbine blades, and pump impellers
Oil and gas: Subsea pipelines, valve seats, and pump components
Aerospace: Turbine engine components requiring thermal barrier and wear-resistant coatings
Cement industry: Mill liners, chutes, and fan blades

The process is particularly advantageous for repair and remanufacturing applications, where damaged components can be restored to original or improved specifications without full replacement. The dilution ratio can be controlled by adjusting the powder feed rate and welding speed, allowing engineers to tailor the overlay composition to specific service requirements.

Quality Control Considerations

A systematic quality control approach following the PDCA (Plan-Do-Check-Act) cycle is essential:

Plan: Define the overlay specification including composition, thickness, hardness, and surface finish.
Do: Execute the surfacing process with calibrated equipment and qualified operators.
Check: Perform hardness testing, metallographic examination, and wear testing on witness coupons.
Act: Adjust process parameters based on test results and implement improvements.

Common defects in plasma arc composite surfacing include:

Porosity: Caused by trapped gas in the powder or insufficient shielding gas coverage.
Cracking: Due to high residual stress from rapid solidification or thermal mismatch between overlay and substrate.
Particle pull-out: Insufficient bonding between reinforcement particles and matrix.
Excessive dilution: Leading to a softer, less wear-resistant overlay layer.

Key Questions and Reflections

The 1999 review article reflects the state of the art at that time, and significant advances have been made since then, including the development of high-power plasma sources, automated powder delivery systems, and advanced in-situ monitoring techniques. However, several fundamental challenges remain:

Particle retention: Even with plasma arc surfacing, some degradation of hard carbide particles occurs during the melting process. Laser cladding and cold spray offer better particle retention but at higher cost.
Multi-layer uniformity: Achieving consistent composition and properties across multiple passes remains challenging, particularly for thick overlays.
Cost-effectiveness: The powder cost for composite materials can be prohibitive for large-area applications. Engineers must balance performance requirements against economic constraints.

Study Insights and Implications

This review article provides a valuable historical perspective on the development of composite material plasma arc surfacing technology. It underscores the versatility of the plasma arc process for producing functionally graded and composite overlay materials with tailored wear resistance. For contemporary engineers, the article serves as a reminder that the fundamental principles of composite design—combining a tough matrix with hard reinforcement—remain relevant, even as new processes and materials emerge. The continued development of plasma arc surfacing technology, particularly in terms of automation, in-situ monitoring, and advanced powder metallurgy, will ensure its relevance in the evolving landscape of surface engineering and component remanufacturing.