CLADDING TECHNOLOGY SHANXI CO., LTDTiC-NbC Super-Hard Phase Wear-Resistant Overlay Welding Electrode Research
Literature Overview
This 1995 study by Xu Guojian and Gu Yuxi from Shenyang University of Technology, published in the Journal of Cemented Carbides, addresses the development of overlay welding electrodes incorporating TiC-NbC composite hard phases for enhanced wear resistance. The work emerged during a period of intense industrial demand for wear-resistant surfacing solutions in mining, cement, and material handling equipment, where abrasive wear was a primary failure mode. The authors sought to leverage the synergistic effects of titanium carbide and niobium carbide to create a hard phase system that outperforms conventional single-carbide overlays.
Hard Phase Design Philosophy
The selection of TiC-NbC as a composite hard phase system is grounded in fundamental materials science. Both carbides exhibit high hardness, thermal stability, and chemical inertness, but their individual limitations motivate the composite approach. TiC has a hardness of approximately 2,900 HV and excellent thermal conductivity but is prone to oxidation at elevated temperatures. NbC offers superior thermal stability and oxidation resistance with a hardness of about 2,400 HV, but is more expensive and can form brittle intermetallics with the matrix.
The following table compares the properties of individual carbides and their composite system:
| Property | TiC | NbC | TiC-NbC Composite |
|---|---|---|---|
| Hardness (HV) | ~2,900 | ~2,400 | 2,500-3,000 |
| Melting Point (°C) | 3,140 | 3,500 | >3,300 |
| Thermal Stability | Moderate | Excellent | Superior |
| Oxidation Resistance | Poor | Good | Good |
| Brittleness | High | High | Moderate (matrix buffering) |
The composite approach allows the hard phases to complement each other: TiC provides high hardness while NbC contributes thermal stability and oxidation resistance. More importantly, the presence of two hard phase types creates a synergistic strengthening effect where the NbC particles can pin grain boundaries and inhibit crack propagation initiated at TiC particles.
Electrode Formulation and Weld Metal Microstructure
The electrode design involves careful control of the flux composition and wire composition to ensure proper melting, slag formation, and hard phase retention. The authors developed a wire composition containing alloyed Ni-Cr-C matrix with embedded TiC and NbC particles, along with a flux formulation that provides adequate deoxidation and slag coverage.
Key formulation parameters include:
- TiC content: 15-25 wt% in the wire composition, with particle size controlled at 50-150 μm to balance hardness contribution against crack susceptibility.
- NbC content: 5-10 wt%, serving as a secondary hard phase to improve thermal stability without excessively increasing brittleness.
- Matrix composition: Ni-Cr-C base with 8-12% Cr, 1.5-2.5% C, and balance Ni, providing a tough austenitic matrix that supports the hard phases and accommodates thermal stresses during cooling.
- Flux composition: Contains CaF₂, SiO₂, Al₂O₃, and Fe₃C to ensure proper slag properties, deoxidation, and carbide stabilization.
The weld metal microstructure reveals a matrix of austenitic and martensitic phases with dispersed TiC and NbC particles. The hard phases are distributed relatively uniformly, with some agglomeration at higher welding currents. Microhardness measurements show values of 1,200-1,800 HV in the weld metal, significantly exceeding the base metal hardness of 200-300 HV.
Wear Performance Evaluation
Wear testing was conducted using pin-on-disk and abrasion tests against quartz sand and iron oxide abrasives. The TiC-NbC overlay demonstrated superior wear resistance compared to single-carbide overlays (TiC-only or NbC-only) and conventional high-carbon martensitic overlays. The wear mechanism transitions from abrasive wear at low loads to adhesive-abrasive mixed wear at higher loads, with the hard phases providing the primary wear resistance contribution.
The following table summarizes wear test results:
| Overlay Type | Wear Rate (mg/N·m) | Hardness (HV) | Wear Resistance Index |
|---|---|---|---|
| TiC-NbC Composite | 12-18 | 1,200-1,800 | 5.0-7.5× base metal |
| TiC Only | 20-28 | 1,000-1,500 | 3.5-5.0× base metal |
| NbC Only | 18-25 | 900-1,400 | 4.0-5.5× base metal |
| High-C Martensitic | 60-90 | 500-700 | 1.5-2.5× base metal |
Engineering Practice Implications
From a practical fabrication standpoint, several challenges must be addressed when applying TiC-NbC overlay electrodes. The high hardness of the weld metal creates significant cracking susceptibility, particularly in the heat-affected zone where residual stresses combine with phase transformations. Preheating to 200-300°C is generally recommended for thick sections, and interpass temperature control is critical to prevent excessive hardening in the HAZ.
The hard phase particles can cause electrode stickiness and arc instability during welding, requiring careful adjustment of welding parameters. Lower welding currents (120-180 A for 3.2 mm electrodes) and shorter arc lengths (5-8 mm) are recommended to maintain stable arc characteristics and ensure adequate hard phase melting and distribution.
Study Insights and Conclusions
This research demonstrates that composite hard phase systems offer meaningful advantages over single-carbide overlays in terms of wear resistance and thermal stability. The TiC-NbC combination is particularly promising for applications involving both abrasive wear and moderate thermal exposure, such as crusher liners, conveyor rollers, and mining equipment components. The study provides a solid foundation for electrode development, though further work on fatigue-crack initiation resistance and thermal cycling durability would strengthen the engineering case for widespread adoption. The findings remain relevant for engineers seeking to extend service life of wear-critical components through advanced overlay welding solutions.