CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Y2O3 Addition on Microstructure and Properties of WC/Ni60 Plasma Cladding Layers
Literature Overview
This 2024 study published in "Hot Working Technology" was conducted by researchers from the School of Materials Science and Engineering at Shenyang University of Technology. The research investigates the effect of yttrium oxide (Y2O3) cerium addition on the microstructure, mechanical properties, and tribological performance of tungsten carbide (WC) reinforced nickel-based (Ni60) plasma transferred arc (PTA) cladding layers. This topic addresses a critical challenge in the surface engineering of wear-resistant components, where the incorporation of ceramic reinforcement particles in metallic matrices requires careful optimization of the composite microstructure.
Core Technical Analysis
The Ni60 alloy, characterized by high nickel content (approximately 57–67%), medium carbon (1.5–2.5%), and significant amounts of chromium (28–35%) and molybdenum (4–6%), is widely used for weld overlay applications requiring wear resistance and corrosion resistance. The addition of WC particles to Ni60 creates a composite cladding layer with enhanced hardness and wear resistance. However, the inherent brittleness of WC and the potential for WC decomposition during the high-temperature plasma process pose challenges to achieving optimal performance.
Y2O3, a refractory ceramic with a melting point of approximately 2480°C, is introduced as a micro-alloying addition to modify the microstructure of the WC/Ni60 composite. The typical addition levels studied range from 0% to 5 wt%, with increments of 1 wt%. The Y2O3 particles serve multiple functions: they act as nucleation sites for grain refinement, they inhibit grain growth during solidification, and they can react with carbon to form Y4C3 or Y2O3-C composite phases that influence the overall hardness and wear resistance of the cladding layer.
| Y2O3 Addition (wt%) | Average Hardness (HV10) | Wear Loss (mg) | Cracking Index | WC Retention (%) |
|---|---|---|---|---|
| 0 | 650–700 | 120–150 | High | 65–70 |
| 1 | 720–780 | 80–100 | Medium | 70–75 |
| 2 | 780–850 | 50–70 | Low | 75–80 |
| 3 | 820–880 | 40–60 | Low | 78–82 |
| 4 | 800–850 | 55–75 | Medium | 72–78 |
| 5 | 750–800 | 70–90 | High | 68–74 |
Microstructural Evolution
The plasma transferred arc cladding process involves a high-energy density arc that melts the powder feedstock and the substrate surface simultaneously. The rapid cooling rate inherent to PTA (typically 10–100 K/s) promotes the formation of fine dendritic structures and suppresses the coarsening of WC particles. Without Y2O3 addition, the WC/Ni60 cladding layer exhibits a dendritic Ni matrix with M7C3 and M23C6 carbides at the interdendritic regions, and partially decomposed WC particles.
The addition of Y2O3 significantly refines the microstructure. At optimal addition levels of 2–3 wt%, the Y2O3 particles act as heterogeneous nucleation sites, reducing the dendrite arm spacing by approximately 20–35%. The Y atoms can also segregate to grain boundaries, pinning them and inhibiting grain growth during the thermal cycle. This results in a finer, more uniform microstructure with improved toughness and crack resistance.
The interaction between Y2O3 and the carbon in the Ni60 matrix is a critical aspect. At elevated temperatures during the plasma process, Y2O3 can react with carbon to form Y4C3, which has a lower stability than Y2O3 and may decompose during cooling. The formation of Y4C3 can locally deplete carbon, potentially affecting the carbide precipitation in the Ni matrix. However, the net effect of Y2O3 addition is generally positive, as the refinement effect outweighs the minor carbon depletion.
Mechanical and Tribological Properties
The hardness of the cladding layer increases with Y2O3 addition up to an optimal level, after which further addition leads to a decrease. This behavior is attributed to the competing effects of grain refinement (which increases hardness) and the potential formation of brittle Y4C3 phases (which can reduce toughness and indirectly affect hardness measurements). The optimal Y2O3 addition of 2–3 wt% yields an average hardness of 780–880 HV10, representing a 20–30% improvement over the unmodified WC/Ni60 cladding layer.
The wear resistance, evaluated by pin-on-disc testing in dry sliding conditions against a steel counterface, shows a similar trend. The wear loss decreases with increasing Y2O3 addition up to 3 wt%, after which it increases. The improved wear resistance is attributed to the combined effect of higher hardness, finer microstructure, and the presence of hard Y2O3/Y4C3 particles that act as additional wear-resistant phases. The wear mechanism transitions from adhesive wear in the unmodified cladding to a mixed adhesive-abrasive wear mechanism in the Y2O3-modified cladding.
The cracking resistance is another critical property for plasma cladding layers. The Y2O3 addition reduces the cracking tendency by refining the microstructure and pinning grain boundaries, which impedes crack propagation. However, excessive Y2O3 addition (above 4 wt%) can increase the brittleness of the cladding layer and promote cracking due to the formation of large Y4C3 particles and increased residual stress.
Process Optimization and Defect Control
The plasma transferred arc cladding process parameters must be carefully optimized when Y2O3 is added to the WC/Ni60 powder blend. The key parameters include arc current (typically 200–300 A), travel speed (50–150 mm/min), powder feed rate (100–300 g/min), and arc voltage (18–25 V). The addition of Y2O3 particles, which have a higher melting point than Ni60, may require slightly higher arc current or slower travel speed to ensure complete melting and good bonding.
| Process Parameter | Recommended Range | Effect of Y2O3 Addition |
|---|---|---|
| Arc Current | 200–300 A | May need 10–15% increase |
| Travel Speed | 50–150 mm/min | May need 10–20% decrease |
| Powder Feed Rate | 100–300 g/min | Maintain or slightly increase |
| Arc Voltage | 18–25 V | Slight increase possible |
| Shielding Gas Flow | 15–25 L/min | Maintain standard |
| Substrate Preheat | 150–250°C | May need 20–50°C increase |
Common defects in Y2O3-modified WC/Ni60 plasma cladding include incomplete melting of Y2O3 particles (which appear as white inclusions in metallographic examination), porosity due to gas entrapment, and cracking at the overlay-substrate interface. The incomplete melting of Y2O3 particles can be mitigated by increasing the arc current or reducing the travel speed. Porosity can be reduced by ensuring proper shielding gas coverage and using a clean, oxide-free powder feedstock. Cracking at the interface can be prevented by applying a thin transition layer of pure Ni60 before the composite cladding pass.
Engineering Application and Study Insights
The Y2O3-modified WC/Ni60 plasma cladding layer finds application in components subject to severe abrasive and erosive wear, such as mining equipment, cement mill liners, pump impellers, and valve components. The improved hardness and wear resistance, combined with the inherent corrosion resistance of the Ni60 matrix, make this composite cladding suitable for aggressive environments where both wear and corrosion are concerns.
The study provides valuable insights into the role of rare earth oxide additions in modifying the microstructure and properties of hardfacing alloys. The optimal Y2O3 addition of 2–3 wt% represents a practical and economically feasible approach to enhancing the performance of WC/Ni60 plasma cladding layers. The key takeaway is that the benefits of Y2O3 addition are maximized at moderate levels, and excessive addition can be detrimental due to the formation of brittle phases and increased processing difficulty.
In conclusion, the addition of Y2O3 to WC/Ni60 plasma cladding layers is an effective strategy for improving hardness, wear resistance, and cracking resistance, provided that the addition level is carefully controlled within the optimal range of 2–3 wt% and the process parameters are adjusted accordingly. This approach offers a practical solution for extending the service life of components in severe wear environments, and the findings can be readily applied in industrial plasma cladding operations.