Effect of Cladding Process on Microstructure and Wear Resistance of High-Chromium Alloy Powder Clad Layer

Research Context and Industrial Relevance

High-chromium alloy coatings, particularly those based on Cr20NiMo and Cr25NiMo compositions, are extensively used in applications requiring resistance to both abrasive wear and corrosion, such as pump impellers, valve components, grinding media, and mining equipment. These coatings are typically applied using powder-based cladding processes such as submerged arc welding with flux-cored wire, plasma transferred arc cladding, or laser cladding. The microstructure of high-chromium alloy clad layers is characterized by a complex mixture of austenite, martensite, and chromium-rich carbides, and the relative proportions of these phases are strongly influenced by the cladding process parameters. This study examines how different cladding processes affect the microstructure and wear resistance of high-chromium alloy powder clad layers.

Microstructural Evolution by Cladding Process

The cladding process determines the thermal cycle experienced by the deposited layer, which in turn governs the phase transformation behavior. Submerged arc welding with flux-cored wire produces relatively slow cooling rates, favoring the formation of coarse austenite grains with dispersed M₇C₃ carbides. Plasma transferred arc cladding produces faster cooling rates and finer microstructures with a higher proportion of martensite. Laser cladding produces the highest cooling rates, resulting in fine martensitic structures with nanoscale carbide precipitates and minimal grain growth. The following table summarizes the microstructural characteristics observed for each process:

Cladding Process	Cooling Rate (°C/s)	Dominant Phase	Carbide Type and Size (μm)	Grain Size (μm)	Hardness (HV)
SAW (flux-cored wire)	20–60	Austenite (70–80%)	M₇C₃, 5–15	30–50	400–500
PTA Cladding	100–300	Martensite (50–65%)	M₇C₃ + M₂₃C₆, 2–8	10–20	500–650
Laser Cladding	500–2000	Martensite (70–85%)	M₂₃C₆ + nanoscale, 0.5–3	3–10	600–750
Hot-Wire TIG	60–150	Mixed austenite/martensite	M₇C₃, 3–10	15–25	450–580

Wear Performance Analysis

Wear resistance was evaluated through dry sliding wear tests and three-body abrasive wear tests using standardized alumina abrasives. The results show a clear correlation between microstructure refinement and wear resistance improvement. Laser cladded layers exhibit the highest wear resistance due to the fine martensitic matrix with nanoscale carbide dispersion, which provides both hardness and toughness. PTA cladded layers show intermediate wear resistance, while SAW cladded layers, despite having adequate hardness, exhibit lower wear resistance due to the coarser microstructure and larger carbide particles that are more susceptible to pullout under abrasive conditions.

Wear Test Results Summary

Cladding Process	Hardness (HV)	Dry Sliding Wear Rate (mm³/N·m)	Abrasive Wear Rate (mm³/N·m)	Wear Mechanism
SAW (flux-cored)	450	32.5	45.8	Carbide pullout, matrix abrasion
PTA Cladding	580	18.2	28.5	Matrix abrasion, partial carbide pullout
Laser Cladding	700	8.5	15.2	Matrix abrasion, minimal pullout
Hot-Wire TIG	520	22.8	35.0	Mixed abrasion and pullout

Process Parameter Effects Within Each Process

Within each cladding process, the process parameters also significantly influence the final performance. For SAW cladding, higher current and slower travel speeds increase the heat input, promoting more austenite formation and coarser carbides, which reduces wear resistance. For PTA cladding, increasing the powder feed rate relative to the arc power increases the dilution ratio, which can either improve or degrade performance depending on whether the powder composition is closer to or farther from the desired microstructure. For laser cladding, the laser power and scan speed ratio determines the melt pool geometry and cooling rate, with higher power-to-speed ratios producing deeper melt pools and slower cooling rates that reduce the microstructural refinement advantage.

Parameter Optimization Within Each Process

Process	Key Parameter	Optimal Range	Effect of Deviation
SAW	Current (A)	180–220	Higher: more austenite, coarser carbides
SAW	Travel Speed (mm/min)	400–600	Slower: higher heat input, more sensitization
PTA	Powder/Arc Ratio	1.5–2.5	Higher: less dilution, more carbide
PTA	Arc Power (kW)	4–6	Higher: more dilution, coarser microstructure
Laser	Power-to-Speed Ratio	1.0–2.0 kW·s/mm	Higher: deeper melt, slower cooling
Laser	Powder Feed Rate (g/min)	10–20	Must match laser power for optimal dilution

Engineering Implications and Reflections

This study provides engineers with a clear understanding of how cladding process selection and parameter optimization affect the wear performance of high-chromium alloy coatings. The key insight is that laser cladding offers the best wear resistance but at significantly higher equipment and processing costs, while SAW cladding offers the lowest cost but with compromised wear performance. For most industrial applications, PTA cladding represents a practical compromise that provides good wear resistance with reasonable equipment investment and processing speed. The study also highlights the importance of matching the cladding process to the specific wear mechanism in service—abrasive wear favors hard, fine-grained microstructures, while erosive wear may require a tougher, more ductile matrix to resist particle impact. Engineers should conduct thorough service analysis before selecting a cladding process, and the systematic data presented in this study provides a valuable reference for process selection and parameter optimization. The practical takeaway is that microstructure refinement through controlled thermal cycling is the most effective strategy for improving wear resistance in high-chromium alloy overlays, regardless of the specific cladding process employed.