Microstructure and Properties of TiC-VC Wear-Resistant Particle Overlay A Technical Study Note

Literature Overview and Research Significance

This study investigates the microstructure evolution, mechanical properties, and wear performance of overlay layers containing TiC-VC composite carbide particles produced by plasma arc cladding and other welding-based surface modification techniques. The incorporation of titanium carbide and vanadium carbide particles into the overlay matrix represents a strategy to achieve superior abrasion resistance through the combined effects of hard particle strengthening and matrix toughening. TiC and VC are both refractory transition metal carbides with extremely high hardness values (TiC: 2600-2800 HV; VC: 2000-2400 HV), making them ideal reinforcing phases for wear-resistant overlay applications. The study is particularly relevant to applications in mining, cement, and power generation industries where components are subjected to severe abrasive wear.

Core Technical Content

The study systematically examines the effect of TiC-VC particle content, particle size distribution, and base matrix composition on the overlay microstructure and wear performance. The base matrix compositions investigated include austenitic stainless steel (Fe-18Cr-8Ni), martensitic steel (Fe-1.2C-5Cr), and nickel-based alloy (Fe-30Ni-15Cr-5Mo). The TiC-VC particle content ranges from 5 to 40 percent by weight, with particle size distributions of 10-50 micrometers, 20-80 micrometers, and 40-100 micrometers.

A key finding is that the optimal TiC-VC particle content for maximizing wear resistance while maintaining acceptable toughness is in the range of 15 to 25 percent by weight. Below 15 percent, the volume fraction of hard particles is insufficient to provide significant improvement in abrasion resistance. Above 25 percent, the excessive particle content leads to reduced matrix continuity, increased porosity, and decreased fracture toughness. The study reports that overlay layers with 20 percent TiC-VC content and particle size of 20-80 micrometers exhibit a dry sand wear rate reduction of 70 to 85 percent compared to the unmodified base material.

Microstructural Evolution

The microstructure of the TiC-VC overlay layer is characterized by a complex interaction between the added carbide particles and the solidification behavior of the weld metal. During plasma arc cladding, the TiC and VC particles partially dissolve in the molten pool, with the degree of dissolution depending on the particle size, cladding temperature, and residence time in the melt. Smaller particles (10-50 micrometers) exhibit higher dissolution rates, with 30 to 50 percent of the original particles dissolving during cladding. Larger particles (40-100 micrometers) retain more of their original morphology, with dissolution rates of 10 to 25 percent.

The dissolved Ti and V atoms participate in the formation of new carbides during solidification and subsequent cooling. In austenitic stainless steel matrices, the primary carbides formed are TiC and VC, with some (Ti, V)C mixed carbides. In martensitic steel matrices, additional Fe3C and (Fe, Cr)7C3 carbides form alongside the Ti and V carbides. In nickel-based alloy matrices, the carbide formation is more limited due to the lower carbon activity, resulting in a higher proportion of retained TiC and VC particles.

The following table summarizes the microstructural characteristics of overlay layers with different TiC-VC contents:

Wear Mechanism Analysis

The study employs scanning electron microscopy and energy-dispersive spectroscopy to analyze wear surfaces after dry sand abrasion testing in accordance with ASTM G65. The dominant wear mechanisms identified are micro-ploughing, micro-cutting, and adhesive transfer. In overlay layers with low TiC-VC content (5-10 percent), the wear surface shows evidence of matrix plastic deformation with embedded carbide particles, indicating a micro-ploughing mechanism. As the TiC-VC content increases to 20-25 percent, the wear surface shows evidence of matrix cutting between carbide particles, indicating a transition to a micro-cutting mechanism. The carbide particles act as barriers to matrix deformation, forcing the abrasive particles to plough through the softer matrix between the hard particles.

At TiC-VC contents above 30 percent, the wear mechanism shifts to a combination of micro-cutting and particle pull-out, where the reduced matrix continuity leads to debonding of carbide particles from the matrix. This is accompanied by increased porosity and reduced fracture toughness, which can lead to catastrophic failure under impact loading. The study therefore recommends a TiC-VC content of 15 to 25 percent as the optimal range for balancing wear resistance and toughness.

Process Parameters and Their Effects

The study examines the effect of plasma arc cladding parameters on the overlay microstructure and properties. The following table presents the parameter windows investigated and their effects:

The study finds that a plasma current of 280 A, arc voltage of 38 V, travel speed of 320 mm/min, and powder feed rate of 350 g/min produces overlay layers with the best combination of hardness (920-960 HV), low porosity (<2 percent), and acceptable impact toughness (6-8 J). These parameters provide a heat input of approximately 5-7 kJ/mm, which is sufficient to achieve good fusion with the base metal while limiting excessive carbide dissolution and dilution.

Engineering Practice Considerations

From an engineering practice perspective, this study provides important guidance for the selection and application of TiC-VC particle overlays in industrial wear-resistant applications. The study demonstrates that the particle size distribution is a critical factor that must be carefully controlled during powder preparation. A bimodal particle size distribution, combining fine particles (10-30 micrometers) with coarse particles (50-100 micrometers), can improve the packing density of the powder and reduce porosity in the overlay layer. The study recommends a 70:30 ratio of fine to coarse particles for optimal results.

The study also highlights the importance of substrate preparation and preheating. For steel substrates with carbon equivalent above 0.4 percent, a preheat temperature of 200 to 300 degrees Celsius is recommended to minimize the risk of cold cracking. The substrate surface should be machined to a roughness of Ra 12.5 micrometers or better to ensure good powder adhesion during cladding. For multi-pass cladding, the interpass temperature should be maintained between 150 and 250 degrees Celsius to avoid excessive grain growth while ensuring adequate fusion between passes.

Study Insights and Reflections

This study makes a significant contribution to the understanding of TiC-VC particle reinforcement in weld overlay layers. The systematic investigation of particle content, particle size, matrix composition, and process parameters provides a comprehensive framework for optimizing TiC-VC overlay systems. The key insight is that the optimal TiC-VC content is not simply the highest achievable value but rather a balanced value that maximizes wear resistance while maintaining adequate toughness and processability. The study's emphasis on the interplay between particle dissolution, new carbide formation, and matrix microstructure provides valuable guidance for process development and qualification. The practical parameter windows and substrate preparation recommendations make this study directly applicable to production environments, enabling engineers to implement TiC-VC overlay solutions with confidence in their performance and reliability.