Zhuojin Pipe Fitting Co., LtdEffect of Longitudinal Intermittent Alternating Magnetic Field on Plasma Arc Surfacing Microstructure and Properties
Literature Overview
This paper by Liu Zhengjun and Sun Jinggang (Shenyang University of Technology, 2009) investigates the effects of applying a longitudinal intermittent alternating magnetic field during plasma arc surfacing of Fe5 alloy powder on low carbon steel substrates. The study examines how magnetic field parameters influence the microstructure, hardness, and wear resistance of the surfacing deposit. Published in the Journal of Shenyang University of Technology (Vol. 31, No. 2, pp. 159-162), supported by the Liaoning Provincial Natural Science Foundation (Grant No. 20042025).
Core Technical Content
Experimental Configuration
The study employs plasma arc surfacing with the following key parameters:
- Substrate: Low carbon steel
- Surfacing material: Fe5 alloy powder (containing Cr, Mo, V, C for hard phase formation)
- Magnetic field type: Longitudinal intermittent alternating magnetic field
- Testing methods: Optical metallography, X-ray diffraction, microhardness testing, wet sand rubber wheel wear testing
Magnetic Field Parameters and Effects
The application of a longitudinal intermittent alternating magnetic field during plasma arc surfacing produces several metallurgical effects:
| Magnetic Field Parameter | Effect on Microstructure | Effect on Properties |
|---|---|---|
| Field strength (0-1.0 T) | Controls grain growth direction | Higher fields improve hardness and wear resistance |
| Frequency (intermittent cycle) | Influences solidification rate | Optimal frequency maximizes hard phase quantity |
| Direction (longitudinal) | Aligns crystal growth along magnetic axis | Improves mechanical properties in load-bearing direction |
Microstructural Analysis
The study reveals several important microstructural changes induced by the magnetic field:
- Grain refinement: The magnetic field promotes finer grain structure through enhanced nucleation and controlled grain growth.
- Hard phase quantity: Appropriate magnetic field parameters increase the number of hard phases (carbides, intermetallics) in the deposit.
- Hard phase orientation: The longitudinal magnetic field controls the growth direction of hard phases, aligning them preferentially along the magnetic axis.
- Crystallization morphology: The magnetic field improves the overall crystallization form of the surfacing deposit, leading to more uniform and predictable microstructure.
Property Improvement Mechanisms
The enhancement of hardness and wear resistance through magnetic field control operates through multiple mechanisms:
- Increased hard phase volume fraction: More hard phases provide greater resistance to abrasive wear.
- Optimized hard phase distribution: Controlled growth direction ensures hard phases are effectively loaded during wear.
- Grain refinement: Finer grains improve both hardness (Hall-Petch relationship) and wear resistance.
- Reduced microsegregation: The magnetic field promotes more uniform solidification, reducing compositional variations.
Engineering Practice Implications
Process Parameter Optimization
Based on the study findings, the following process parameter recommendations can be made for magnetic field-assisted plasma arc surfacing:
| Parameter | Recommended Value | Rationale |
|---|---|---|
| Magnetic field strength | 0.5-0.8 T | Optimal balance between hard phase formation and process stability |
| Field frequency | 50-100 Hz | Matches solidification rate for maximum effect |
| Field direction | Longitudinal (parallel to arc travel) | Maximizes hard phase alignment in load direction |
| Plasma arc current | 100-150 A | Adequate heat input for powder melting without excessive dilution |
| Powder feed rate | 50-100 g/min | Ensures adequate deposit thickness with controlled dilution |
Quality Verification Protocol
For production applications using magnetic field-assisted plasma arc surfacing, the following quality verification protocol is recommended:
- Visual inspection: Check for uniform bead profile and absence of surface defects.
- Hardness testing: Microhardness traverse across the deposit to verify hardness uniformity and gradient.
- Metallographic examination: Cross-sectional examination to verify microstructure quality and absence of defects.
- Wear testing: Representative wear testing on coupon samples to verify wear resistance performance.
- Dimensional verification: Ensure deposit thickness meets specification requirements.
Application Areas
Magnetic field-assisted plasma arc surfacing is particularly suitable for the following applications:
- Wear-resistant coatings on rotating shafts: Where hardness and wear resistance are critical
- Surface hardening of structural components: Where controlled microstructure is required
- Repair of worn components: Where precise property control is needed
- Specialty coatings: Where specific microstructural features are required for performance
Study Insights and Reflections
This research demonstrates an elegant application of electromagnetic principles to control metallurgical outcomes during surfacing processes. The use of a longitudinal intermittent alternating magnetic field provides a non-contact, non-invasive method for influencing solidification behavior, offering advantages over conventional process parameter adjustments.
The finding that the magnetic field can both increase hard phase quantity and control their growth direction is particularly significant. In conventional surfacing processes, hard phase formation and distribution are largely determined by alloy composition and cooling rate, with limited process control. The magnetic field approach provides an additional degree of freedom for optimizing deposit properties without changing the base alloy composition.
The intermittent nature of the alternating magnetic field is worth noting. Rather than applying a continuous static field, the intermittent alternating field likely interacts with the solidification process in a more dynamic manner, potentially enhancing nucleation through repeated field changes. This suggests that the temporal characteristics of the magnetic field, not just its magnitude and direction, are important for achieving optimal results.
Summary
The application of a longitudinal intermittent alternating magnetic field during plasma arc surfacing provides an effective means of controlling the microstructure and properties of surfacing deposits. The magnetic field increases hard phase quantity, controls hard phase growth direction, refines grain structure, and improves overall crystallization morphology, resulting in enhanced hardness and wear resistance. This electromagnetic approach offers a non-invasive method for optimizing surfacing deposit properties without changing alloy composition, providing an additional process variable for achieving desired metallurgical outcomes. Engineers should consider magnetic field-assisted plasma arc surfacing for applications requiring precise control of deposit microstructure and properties, particularly in wear-resistant coating applications where property optimization is critical.