CLADDING TECHNOLOGY SHANXI CO., LTDOptimization of Plasma Transferred Arc Cladding Composition and Wear Resistance Performance
Literature Overview
This paper, published in 2006 in the journal of Mechanical Engineering Materials, was authored by Lu Jianbo, Yao Shun, Lou Songnian, Du Zeyu, and Li Shaoqing from the Welding Engineering Research Institute of Shanghai Jiao Tong University and the School of Materials Science and Engineering at Tianjin University. The work addresses a fundamental challenge in PTA cladding technology: how to systematically optimize the chemical composition of overlay coatings to achieve superior wear resistance while maintaining metallurgical integrity at the dilution interface. The study is situated in a period when PTA cladding was transitioning from experimental research to broader industrial application in China, making composition optimization a critical knowledge gap.
Core Technical Approach and Composition Design
The authors adopted a systematic approach to composition optimization, varying the concentrations of key alloying elements including chromium, cobalt, tungsten, molybdenum, and carbon within the PTA powder formulation. The experimental matrix was designed to evaluate the interaction effects between hard phase formation and matrix properties. The dilution ratio between the base material and the overlay layer was identified as a primary variable influencing the final composition of the deposited layer.
Key Alloying Element Roles
| Element | Role in Wear Resistance | Typical Range Studied | Mechanism |
|---|---|---|---|
| Cr (Chromium) | Forms Cr7C3, Cr23C6 carbides; enhances oxidation resistance | 15-40 wt% | Carbide precipitation hardening |
| Co (Cobalt) | Stabilizes austenite; improves high-temperature strength | 10-30 wt% | Solid solution strengthening |
| W (Tungsten) | Forms WC, W2C hard phases; refines microstructure | 5-20 wt% | Precipitation hardening |
| Mo (Molybdenum) | Enhances solid solution strengthening; improves creep resistance | 5-15 wt% | Solid solution + carbide formation |
| C (Carbon) | Primary carbide former; controls hardness level | 3-6 wt% | Carbide precipitation |
The study demonstrated that the hard phase content and morphology are directly governed by the carbon activity and the availability of carbide-forming elements. When the carbon content exceeds the solubility limit in the austenitic matrix, excess carbon combines with chromium, tungsten, and molybdenum to form primary and secondary carbides. The morphology of these carbides—whether they appear as coarse primary particles or fine secondary precipitates—has a decisive influence on the wear resistance and fracture toughness of the overlay layer.
Microstructural Analysis and Dilution Effects
Metallographic examination revealed that the dilution zone at the interface between the base steel and the overlay layer exhibits a distinct gradient in composition and microstructure. The authors observed that excessive dilution leads to a reduction in hard phase volume fraction, thereby degrading wear resistance. Conversely, insufficient dilution can result in cracking due to high residual stresses and poor wetting.
The optimal dilution ratio was found to fall within a narrow window, typically between 15% and 25% base metal dilution for the compositions studied. This finding aligns with the general principle that PTA cladding processes must balance metallurgical bonding with compositional integrity of the functional overlay layer. The authors recommended multi-pass welding strategies with controlled interpass temperature to achieve the target dilution while minimizing thermal cracking susceptibility.
Wear Testing Methodology and Results
Abrasive wear tests were conducted using a pin-on-disk apparatus with SiC abrasive paper and alumina ceramic balls as counterfaces. The results showed that compositions with higher chromium and tungsten content exhibited superior wear resistance, attributed to the increased volume fraction of hard carbide phases. However, the relationship was not purely linear—excessive hard phase content led to a deterioration in toughness, resulting in microcracking and spalling under cyclic loading.
The optimal composition achieved a hardness of approximately 700-800 HV in the overlay layer, with a specific wear rate reduction of over 60% compared to the base material. The wear mechanism transitioned from adhesive wear in the base material to abrasive wear with ploughing and cutting in the optimized overlay, indicating effective hard phase dispersion.
Engineering Practice Implications
This study provides valuable guidance for engineers selecting PTA powder compositions for wear-critical components such as pump impellers, valve seats, and hydraulic cylinder liners. The key takeaway is that composition optimization must be viewed holistically—hardness alone is insufficient as a design criterion, and the balance between wear resistance and fracture toughness must be carefully managed through controlled dilution and appropriate powder formulation.
Study Insights and Reflections
After reviewing this literature, I reflect that the systematic approach to composition optimization presented here remains highly relevant to modern cladding practice. The emphasis on dilution control is particularly noteworthy, as many field failures in PTA cladding applications trace back to inadequate control of the dilution ratio during production welding. The study also highlights the importance of understanding the wear mechanism transition—designing a coating that is merely hard but lacks toughness will inevitably fail in service under impact or cyclic loading conditions. This insight directly informs the selection of welding parameters such as current density, travel speed, and powder feed rate in industrial PTA operations.