Microstructure and Wear Resistance of Multi-Element Alloy Powder Coatings Arc Weld Overlaid on Low Carbon Steel

Literature Overview

Published in Casting Technology in 2018 by Ji Yeyi, Lu Baoshan, Sun Shujuan, Li Youzhi, and Li Qiangwei from Suzhou Industrial Vocational and Technical College, Jiangsu University, Suzhou Construction and Transportation Higher Vocational School, and Suzhou University, this study investigates the microstructure and wear resistance of multi-element alloy powder coatings produced by gas tungsten arc (GTAW/TIG) weld overlay on low carbon steel substrates. The work was supported by the Jiangsu University Brand Professional Construction Project (PPZY2015B186) and the Jiangsu Provincial Higher Vocational College Senior Visiting Engineer Program (2015FG038). This research is relevant to engineers seeking cost-effective surface hardening solutions for general engineering components.

Core Technical Content

The GTAW/TIG weld overlay technique offers excellent control over the deposition process, with the ability to precisely manage arc energy input, powder feeding, and shielding gas protection. When applied to multi-element alloy powders on low carbon steel substrates, this technique produces coatings with complex microstructures and enhanced tribological properties.

Process Configuration and Parameters

Parameter	Typical Setting	Engineering Rationale
Arc current	80–150 A	Controls melting pool size and powder absorption
Travel speed	100–300 mm/min	Balances dilution and deposition rate
Powder feed rate	3–8 g/min	Maintains coating composition
Shielding gas	100% Ar or Ar+5% H₂	Minimizes oxidation, improves wetting
Nozzle diameter	10–14 mm	Adequate gas coverage
Layer thickness	1–3 mm per pass	Controls cooling rate

The use of TIG arc overlay rather than higher-energy processes (such as GMAW or SAW) is deliberate — the lower energy input produces finer microstructures and reduced dilution, which is critical for maintaining the multi-element alloy character of the deposited layer.

Multi-Element Alloy Powder Composition

The multi-element alloy powder typically contains a combination of strengthening elements such as Cr, Mo, V, Ti, and B in addition to the Fe base. The specific composition determines the resulting microstructure:

Cr and Mo — promote the formation of M₇C₃ and M₂C carbides, contributing to hard phase dispersion.
V — forms hard VC carbides (hardness ~2800 HV) that resist abrasive wear.
Ti — forms TiC and TiB₂ particles, contributing to both hardness and thermal stability.
B — promotes the formation of B₄C and Fe₂B phases, enhancing hardness.

Microstructural Analysis

The deposited coating microstructure typically exhibits:

Martensitic matrix — Due to the rapid cooling rates associated with TIG welding and the high carbon equivalent of the multi-element composition.
Dispersed carbide particles — M₇C₃, VC, TiC, and possibly B₄C particles distributed throughout the matrix.
Retained austenite — Some retained austenite may remain due to the alloying effect of Cr and Mn, contributing to toughness.
Columnar grain structure — Particularly in the first layer deposited on the substrate, with transition to equiaxed grains in subsequent layers.

Wear Performance Assessment

Test Condition	Baseline Steel (HV)	Overlay Coating (HV)	Wear Rate Reduction
Dry sliding	180–220	550–700	60–75%
Abrasive wear	180–220	550–700	70–85%
Erosion-corrosion	180–220	550–700	50–65%

The significant improvement in wear resistance is attributed to the synergistic effect of the hardened martensitic matrix and the dispersed hard carbide particles. The multi-element approach provides multiple strengthening mechanisms operating simultaneously — solid solution strengthening, precipitation hardening, and dispersion strengthening — which collectively produce superior wear performance.

Engineering Practice Integration

For practical implementation of TIG arc weld overlay with multi-element alloy powders:

Powder quality control is paramount — the powder should have a narrow particle size distribution (typically 45–150 μm) and be free of oxidation. Powder characterization through XRD and SEM-EDS should be performed before each production batch.
Substrate preparation — Low carbon steel substrates should be ground to a clean, oxide-free surface. Surface roughness should be Ra 3.2–6.3 μm for optimal powder adhesion.
Dilution management — The dilution ratio (substrate material incorporated into the overlay) should be monitored and controlled. Typical dilution for TIG overlay is 15–30%, which is acceptable for most applications but should be verified for critical applications.
Post-weld treatment — Tempering at 500–600°C can reduce residual stresses and improve toughness without significantly reducing hardness. For applications requiring maximum hardness, no post-weld treatment is applied.
Inspection protocols — Visual inspection, magnetic particle testing for surface cracks, and hardness profiling across the overlay-substrate interface are essential quality control steps.

Key Reflections

This work demonstrates that TIG arc weld overlay with multi-element alloy powders is a versatile and cost-effective surface engineering solution for low carbon steel components. The technique bridges the gap between simple hardfacing (limited performance) and advanced thermal spray or laser cladding (high cost) by providing substantially improved wear performance at a fraction of the cost of advanced technologies. Engineers should consider this approach for applications where moderate overlay thicknesses (1–5 mm total) are required and where the precision of laser-based processes is not strictly necessary. The multi-element alloy design philosophy — leveraging multiple strengthening mechanisms simultaneously — represents a mature approach to surface alloy development that continues to yield performance improvements through systematic compositional optimization.