CLADDING TECHNOLOGY SHANXI CO., LTDPlasma Cladding of Co106F Powder on Valve Surfaces with Different Substrate Materials
Literature Overview
Published in 2023 in Physical Testing and Chemical Analysis (Physical Methods) by Wang Xuepeng, He Tao, Liu Haibo, Dai Wanxiang, Li Zhenhua, and Deng Dewei, this study investigates the plasma transferred arc (PTA) cladding of Co106F cobalt-based alloy powder on valve surfaces made from different substrate materials. Co106F is a widely used cobalt-chromium-tungsten alloy powder known for its exceptional wear resistance, corrosion resistance, and high-temperature performance, making it an ideal overlay material for critical valve components in oil and gas, chemical processing, and power generation applications. The study was supported by the High-End Control Valve Industry Technology Collaborative Innovation Center Fund and the Liaoning Major Equipment Manufacturing Collaborative Innovation Center Fund, underscoring its industrial relevance.
Core Technical Content
The study examined the PTA cladding of Co106F powder on three different substrate materials: 304 stainless steel, 316 stainless steel, and 17-4PH precipitation-hardened stainless steel. These substrates represent a range of compositions and mechanical properties commonly encountered in valve manufacturing. The PTA process was selected because of its low dilution rate, high deposition rate, and ability to produce dense, crack-free overlay layers with excellent metallurgical bonding to the substrate.
The Co106F powder composition is characterized by approximately 63% cobalt, 28% chromium, 6% tungsten, and 3% molybdenum, with trace amounts of carbon and other elements. The as-deposited microstructure consists of an FCC cobalt matrix with dispersed carbide particles of Cr7C3 and WC, which provide the wear resistance. The authors characterized the microstructure, hardness, and corrosion resistance of the cladding layers on each substrate material and investigated the influence of substrate composition on the overlay properties.
Comparative Results Across Substrate Materials
| Substrate | Dilution Rate | Overlay Hardness (HV) | Corrosion Potential (mV) | Interface Integrity |
|---|---|---|---|---|
| 304 SS | 12–18% | 650–720 | -650 to -720 | Good bonding, no cracks |
| 316 SS | 10–15% | 680–750 | -680 to -750 | Excellent bonding |
| 17-4PH SS | 15–22% | 600–680 | -620 to -700 | Good bonding, slight dilution |
Interpretation of Technical Points
The study revealed that the substrate composition has a measurable but manageable effect on the properties of the Co106F overlay layer. The dilution rate was highest for the 17-4PH substrate, which contains higher levels of copper, nickel, and chromium than the austenitic stainless steels. This increased dilution resulted in a slightly lower overlay hardness, as the dilution elements alter the carbide formation and matrix composition. However, even with the highest dilution rate, the overlay hardness remained well above 600 HV, which is adequate for most valve seat and trim applications.
A key finding was the influence of substrate composition on the corrosion potential of the overlay. The Co106F overlay on 316 stainless steel exhibited the most negative corrosion potential, indicating the best corrosion resistance. This is attributed to the molybdenum content of the 316 substrate, which partitions into the dilution zone and enhances the pitting resistance of the overlay. The 304 substrate, lacking molybdenum, produced an overlay with slightly less negative corrosion potential, which is still acceptable for most service conditions but may be marginal in chloride-containing environments.
The interface integrity between the Co106F overlay and each substrate was evaluated through metallographic examination and microhardness profiling across the interface. All three substrates exhibited good metallurgical bonding without cracks, porosity, or lack of fusion. The microhardness transition from the substrate to the overlay was gradual, indicating a well-mixed interface zone that provides a smooth transition in mechanical properties. This gradual transition is important for preventing stress concentrations at the interface during thermal cycling or pressure fluctuations in service.
PTA Process Parameters
| Parameter | Value | Purpose |
|---|---|---|
| Arc current | 200–280 A | Adequate melting of powder and substrate |
| Travel speed | 60–120 mm/min | Control dilution and deposition rate |
| Powder feed rate | 80–150 g/min | Maintain powder-to-arc ratio |
| Shielding gas | Argon | Prevent oxidation of cobalt alloy |
| Gas flow rate | 15–25 L/min | Adequate protection of molten pool |
| Layer thickness | 0.5–1.0 mm per pass | Control dilution and residual stress |
Integration with Engineering Practice
The findings of this study have direct implications for the selection of PTA cladding procedures for valve manufacturing. The results indicate that Co106F can be successfully applied to a wide range of stainless steel substrates, providing flexibility in material selection for valve components. Engineers designing PTA procedures for valve seats, plugs, and trim should consider the substrate composition when specifying process parameters to achieve the desired overlay properties.
From a quality control perspective, the study emphasizes the importance of verifying the dilution rate through chemical analysis of the overlay layer. The dilution rate can be calculated from the composition of the as-deposited overlay compared to the pure Co106F powder composition, and this value should be within the acceptable range specified in the applicable standard or specification. ASTM B414 and related standards provide guidance on the acceptable dilution range for cobalt-based overlay alloys.
The PTA process parameters recommended in this study are consistent with current industry practice for cobalt-based cladding. The relatively low dilution rate achievable with PTA (typically 5–20% compared to 20–40% for submerged arc welding) makes it the preferred method for critical valve applications where the overlay composition must closely match the specification. The use of argon as a shielding gas is standard practice, and the powder feed rate and travel speed should be optimized for each specific application to achieve the desired layer thickness and surface quality.
Study Insights and Implications
This study contributes valuable data on the compatibility of Co106F with different stainless steel substrates, which is essential information for engineers selecting materials and processes for valve cladding. The systematic comparison across substrate types provides a practical framework for process selection that can be adapted to other cobalt-based overlay alloys and substrate combinations.
The research also underscores the importance of substrate selection in cladding technology. While the Co106F overlay performs well on all three substrates, the optimal combination depends on the specific service requirements. For applications requiring the highest corrosion resistance, the 316 stainless steel substrate with Co106F overlay provides the best performance. For applications requiring high mechanical strength, the 17-4PH substrate offers a good balance between substrate strength and overlay performance.
The collaborative research model demonstrated in this study, combining industrial expertise with academic research capability, exemplifies the effective partnership between industry and academia that drives technological advancement in manufacturing. The funding from industry collaborative innovation centers reflects the growing recognition of the importance of applied research in supporting China's transition to high-end manufacturing.