Zhuojin Pipe Fitting Co., LtdParameter Optimization for Tungsten Carbide Ni-Based Composite Coating by Plasma Transferred Arc Hardfacing
Literature Overview
The paper by Ying Wei, Xian-shun Wei, Bo Chen, Jian-yong Zuo, Tian-cai Ma, and Jun Shen, published in Transactions of Nonferrous Metals Society of China (Vol. 28, Issue 12, 2018, pp. 2511-2519), presents a systematic optimization of welding parameters for depositing tungsten carbide (WC) reinforced nickel-based composite coatings using plasma transferred arc (PTA) hardfacing. The study employs orthogonal experimental design to determine the optimal combination of welding current, powder feed rate, and welding speed that maximizes coating performance while minimizing tungsten carbide degradation. The research was supported by multiple national and provincial funding programs, reflecting its importance in the field of surface engineering for wear-resistant applications.
Core Technical Points
PTA hardfacing is a powder-based cladding process that uses a high-energy plasma arc to melt both the substrate and the powder feedstock, producing a dilution-free or low-dilution deposit with excellent metallurgical bonding. The process is particularly well-suited for depositing WC/Ni-based composite coatings because it provides precise control over heat input and powder melting, minimizing the degradation of tungsten carbide particles that occurs during conventional arc welding processes.
Orthogonal Experimental Design
The study employs a three-factor, three-level orthogonal array (L9) to systematically investigate the effects of welding parameters on coating quality:
| Factor | Level 1 | Level 2 | Level 3 |
|---|---|---|---|
| Welding current (A) | 80 | 100 | 120 |
| Powder feed rate (g/min) | 20 | 25 | 30 |
| Welding speed (mm/min) | 30 | 40 | 50 |
The response variables evaluated include: tungsten carbide degradation ratio, coating hardness, coating thickness, dilution ratio, and crack formation. The orthogonal design allows for the efficient identification of parameter interactions and optimal settings with a minimum number of experimental runs.
Optimal Parameter Determination
The analysis of the orthogonal experiments identified the following optimal welding parameters:
| Parameter | Optimal Value | Effect on Performance |
|---|---|---|
| Welding current | 100 A | Balances penetration with minimal WC degradation |
| Powder feed rate | 25 g/min | Ensures adequate deposition with stable arc |
| Welding speed | 40 mm/min | Optimizes heat input for complete melting without excessive thermal exposure |
At these optimal parameters, the produced WC/Ni-based composite coatings are crack-free and exhibit minimal tungsten carbide degradation. The dilution ratio is maintained at a low level (typically 10-15%), preserving the integrity of the WC particles and the nickel-based matrix.
Microstructural Analysis
The microstructure of the PTA-deposited WC/Ni-based composite coating at optimal parameters consists of:
- Nickel-based matrix: Solid solution of alloying elements (Cr, Mo, W) in nickel, providing toughness and corrosion resistance
- Intact WC particles: Retained from the feed powder, providing primary wear resistance
- Decomposed WC products: W2C, WC-Ni intermetallics formed by partial reaction of WC with the molten nickel
- γ-Ni solid solution: Matrix phase with dissolved alloying elements
The microhardness distribution across the coating shows a gradient from the surface to the interface:
| Location | Microhardness (HV) | Dominant Phase |
|---|---|---|
| Surface layer | 1200-1500 | Intact WC particles |
| Mid-layer | 900-1100 | WC particles + Ni matrix |
| Interface | 600-800 | Ni matrix with some WC remnants |
The high surface hardness is attributed to the presence of intact WC particles (hardness ~2500 HV) dispersed in the nickel matrix. The hardness gradient ensures a smooth transition to the substrate, reducing the risk of cracking at the interface due to thermal stress.
Parameter Interaction Effects
The study reveals important interactions between welding parameters:
- Current vs. speed: Higher current requires higher speed to maintain optimal heat input; otherwise, excessive heat causes WC degradation
- Feed rate vs. current: Higher feed rate requires higher current to ensure complete melting of the powder; insufficient current leads to unmelted powder particles
- Feed rate vs. speed: These two parameters must be balanced to maintain consistent deposition rate; mismatch leads to irregular coating thickness
The interaction between current and powder feed rate is particularly critical for WC preservation. Excessive current relative to feed rate increases the residence time of WC particles in the melt pool, promoting decomposition reactions. Conversely, insufficient current relative to feed rate results in incomplete melting and poor bonding.
Engineering Practice Integration
The optimized PTA parameters identified in this study have direct applications in several industrial sectors:
- Oil and gas industry: Hardfacing of drill collars, stabilizers, and bit components for enhanced wear resistance in drilling operations
- Mining equipment: Surface protection of crusher components, conveyor track shoes, and bucket liners for improved service life
- Power generation: Wear protection of turbine blades, valve seats, and pump impellers operating in abrasive environments
- Railway industry: Surface hardening of rail joints, wheel treads, and brake components for enhanced durability
- Aerospace: Repair and surface enhancement of engine components subject to erosion and thermal degradation
The PTA process offers several advantages over conventional arc hardfacing for WC/Ni-based coatings:
- Lower dilution ratio (10-15% vs. 25-40% for conventional processes)
- Reduced WC degradation (maintains particle integrity)
- Crack-free deposits (due to controlled heat input)
- Excellent surface finish (reduces post-processing requirements)
- Multi-layer capability (enables thick deposits without cracking)
Study Insights and Reflections
This paper exemplifies the systematic approach to process optimization that is essential for industrial surface engineering applications. The use of orthogonal experimental design demonstrates how statistical methods can efficiently identify optimal process parameters with minimal experimental effort. The finding that all three parameters (current, feed rate, and speed) significantly influence WC degradation underscores the complexity of PTA hardfacing and the necessity for careful parameter control. For engineers working in surface engineering and welding technology, this work provides both a practical reference for PTA parameter selection and a methodological framework for optimizing powder-based cladding processes. The emphasis on WC preservation through controlled heat input highlights the fundamental challenge of hardfacing processes: balancing the need for adequate melting and bonding with the requirement to preserve the integrity of hard particles or phases that provide wear resistance.