Experimental Study on Cutting Performance of Plasma Cladded Nickel-Based Alloys

Literature Overview and Research Background

This 2017 paper published in "Tool Engineering" by Hou Qingkun, Li Man, and Pei Jiangtao from Dalian University of Technology investigates the cutting performance of nickel-based alloys deposited through plasma transferred arc (PTA) cladding. The research addresses a critical challenge in the manufacturing of components with PTA-cladded surfaces, where the cladding layer must withstand not only corrosion and wear but also subsequent machining operations such as turning, milling, and drilling. The cutting performance of the cladding material directly affects the manufacturing cost, dimensional accuracy, and surface finish quality of the final component.

The study is particularly relevant in the context of turbine blade manufacturing, where PTA cladding is extensively used to deposit Ni-based superalloys such as IN718, IN625, and IN738 onto nickel-based or titanium-based substrates. The cladding layer often requires precision machining to achieve the final aerodynamic profile, and understanding the cutting behavior of these materials is essential for optimizing the machining parameters and tool selection.

Core Technical Analysis

PTA Cladding Process Parameters

Plasma transferred arc cladding offers several advantages over conventional arc welding cladding methods, including lower dilution rates (typically 5–15%), excellent cladding layer homogeneity, and precise control of the cladding layer composition. The study examines PTA cladding of Ni-based alloys using both self-shielded and gas-shielded consumable electrodes.

Parameter	Typical Value	Influence on Cutting Performance
Plasma arc current	150–300 A	Higher current increases dilution and grain size
Plasma gas flow rate	2–5 L/min	Affects arc stability and cladding uniformity
Shielding gas flow rate	15–25 L/min	Prevents oxidation of cladding surface
Powder feed rate	100–300 g/min	Must be synchronized with travel speed
Travel speed	200–600 mm/min	Affects heat input and microstructure
Powder type	Ni-22Cr-12Mo or Ni-15Cr-7Mo	Determines hardness and cutting characteristics

Microstructural Characterization

The microstructure of PTA-cladded Ni-based alloys is characterized by a columnar dendritic structure with grain orientation aligned with the heat flow direction. The grain size is typically in the range of 50–200 μm, which is coarser than the powder metallurgy route but finer than the cast state. The presence of carbide precipitates, particularly MC and M₂₃C₆ type carbides, significantly influences the cutting performance by acting as abrasive particles that accelerate tool wear.

The study reveals that the microstructure of the PTA cladding layer is highly sensitive to the process parameters. Higher powder feed rates relative to travel speeds result in thinner individual cladding layers with finer grain structures, which generally improve cutting performance by reducing the grain size effect on tool wear. Conversely, lower powder feed rates produce thicker cladding layers with coarser grains and larger carbide precipitates, leading to accelerated tool wear during machining.

Cutting Performance Evaluation

The cutting performance is evaluated through orthogonal cutting tests, measuring cutting forces, cutting temperature, tool wear, and surface roughness of the machined surface. The results show that PTA-cladded Ni-based alloys exhibit significantly higher cutting forces compared to conventional cast Ni-based superalloys, primarily due to the higher density of carbide precipitates and the work hardening rate of the cladding material.

Cutting Condition	Cutting Force (N)	Tool Wear (VB, mm)	Surface Roughness (Ra, μm)
Conventional carbide tool, v_c = 80 m/min	320–380	0.45–0.65	2.5–3.5
Ceramic tool (Si₃N₄), v_c = 120 m/min	280–340	0.25–0.40	1.5–2.5
CBN tool, v_c = 150 m/min	250–300	0.15–0.25	1.0–1.8
CBN tool with MQL, v_c = 180 m/min	230–280	0.10–0.20	0.8–1.5

The cutting temperature measurements indicate that the peak temperature at the tool-chip interface can exceed 800 °C during high-speed cutting, which is sufficient to cause significant diffusion wear and chemical reactions between the tool material and the workpiece. The use of minimum quantity lubrication (MQL) with appropriate cutting fluids can reduce the cutting temperature by 100–150 °C and extend tool life by 30–50%.

Process Optimization and Engineering Implications

The study identifies several strategies for improving the cutting performance of PTA-cladded Ni-based alloys:

Cladding process optimization: Adjusting the PTA parameters to produce a cladding layer with finer grain size and more uniform carbide distribution can improve machinability. This involves optimizing the powder feed rate, travel speed, and arc current to achieve a balance between cladding thickness and microstructural quality.
Tool selection: CBN (cubic boron nitride) tools are recommended for high-speed dry cutting of PTA-cladded Ni-based alloys, offering tool life 2–3 times longer than conventional carbide tools. For lower-speed machining operations, coated carbide tools with TiAlN or AlCrN coatings provide acceptable performance at lower cost.
Cutting parameter optimization: The study recommends cutting speeds in the range of 100–180 m/min for CBN tools, with feed rates of 0.05–0.15 mm/rev and depths of cut of 0.5–2.0 mm. These parameters provide an optimal balance between productivity and tool life.
Workpiece preparation: Pre-machining the PTA cladding layer with a rough turning operation using a carbide tool to remove the surface oxide layer and any porosity defects can improve the quality of the subsequent finish machining operation.

Key Questions and Reflections

An important consideration that arises from this study is the variability of cutting performance across different regions of a PTA-cladded component. The cladding layer near the substrate interface typically exhibits higher dilution and a different microstructure compared to the top surface layers, which can lead to non-uniform cutting performance during machining. Engineers must account for this variability when setting machining parameters, potentially using adaptive control strategies that adjust the cutting parameters based on real-time force monitoring.

Another critical issue is the effect of multiple PTA cladding passes on the cutting performance. The topmost cladding layer, which is the last to be deposited, typically has the finest microstructure and the best cutting performance. However, if the component requires machining from the substrate side, the interface region with higher dilution and coarser microstructure will be encountered first, potentially leading to premature tool failure. This highlights the importance of considering the machining sequence in the overall manufacturing process planning.

Study Insights and Conclusions

This experimental study provides valuable insights into the cutting performance of PTA-cladded Ni-based alloys, bridging the gap between cladding process development and subsequent machining operations. The key finding is that the cutting performance of the cladding layer is strongly influenced by the PTA process parameters through their effect on the microstructure, particularly the grain size and carbide distribution. Engineers involved in the manufacturing of PTA-cladded components should adopt an integrated approach that considers both the cladding and machining requirements during process development, rather than treating them as independent operations. The study also underscores the importance of CBN tool technology for high-productivity machining of Ni-based alloy cladding layers, and the potential of MQL technology for sustainable manufacturing practices. Future research should focus on developing predictive models for the cutting performance of PTA-cladded materials based on process parameters, enabling real-time optimization of both cladding and machining operations.