Microstructure and Properties of TiC Particle-Reinforced Composite Coating by Submerged Arc Cladding

Literature Overview

This study by Liu Junhai, Huang Jihua, Liu Junbo, and Song Guixiang from the University of Science and Technology Beijing, Weihai Vocational College, and Weifang University, published in 2011 in the journal The Chinese Journal of Nonferrous Metals under the Shandong Provincial Science and Technology Project (2007GG30003003), investigates the microstructure and properties of TiC particle-reinforced composite coatings produced by submerged arc cladding (SAC). The incorporation of TiC particles into the overlay layer represents a particle-reinforced metal matrix composite (MMMC) approach that combines the toughness of a metallic matrix with the exceptional hardness and wear resistance of TiC.

Core Technical Content

Titanium carbide (TiC) is one of the hardest and most thermally stable carbides, with a hardness of approximately 2800 HV and a melting point of 3140°C. When incorporated into a metallic matrix, TiC particles provide significant wear resistance enhancement while maintaining the toughness of the matrix. The submerged arc cladding process is well-suited for producing TiC-reinforced composite coatings due to its high deposition rate, deep penetration, and ability to incorporate refractory particles into the molten pool.

Microstructure Characteristics

The microstructure of TiC-reinforced composite coatings produced by SAC is characterized by a metallic matrix with dispersed TiC particles. The matrix is typically composed of martensite and retained austenite, with the TiC particles serving as nucleation sites for grain refinement.

TiC Content	Matrix Microstructure	TiC Distribution	TiC Morphology	Hardness (HV)
5–10 wt% TiC	High-carbon martensite	Uniformly dispersed	Angular, 5–20 μm	900–1100
10–20 wt% TiC	Martensite + retained austenite	Semi-continuous network	Angular, 10–30 μm	1100–1300
20–30 wt% TiC	Martensite + carbide network	Continuous network	Angular, 15–40 μm	1200–1400
>30 wt% TiC	Ferrite + carbide	Interconnected network	Coarse, 20–50 μm	1100–1300 (reduced toughness)

The distribution and morphology of TiC particles are influenced by several factors, including the initial particle size, the melting behavior during welding, and the solidification conditions. TiC particles with a melting point of 3140°C are generally refractory to the welding process, meaning they remain largely unmelted and are incorporated into the solidifying matrix as discrete particles.

Mechanical Properties

The mechanical properties of TiC-reinforced composite coatings are characterized by:

High hardness: Achieved through the combined effect of the hard TiC particles and the hardening of the metallic matrix. Hardness values of 1100–1400 HV are typical for optimized compositions.
Good toughness: The metallic matrix provides adequate toughness to accommodate impact loading, making these coatings suitable for impact-abrasive wear conditions.
Excellent wear resistance: The combination of hard TiC particles and a tough matrix provides superior resistance to abrasive wear, particularly in conditions involving hard, angular abrasive particles.
Thermal stability: TiC retains its hardness at elevated temperatures, making these coatings suitable for applications involving thermal cycling or high-temperature wear.

Particle Reinforcement Mechanisms

The wear resistance enhancement provided by TiC particles is attributed to several reinforcement mechanisms:

Load-bearing mechanism: The hard TiC particles bear a significant portion of the applied load, reducing the stress on the metallic matrix and delaying wear initiation.
Ploughing resistance: The hard TiC particles resist ploughing by abrasive particles, reducing material removal from the coating surface.
Crack deflection: The TiC particles act as obstacles to crack propagation, deflecting cracks and increasing the energy required for crack growth.
Grain refinement: The TiC particles serve as nucleation sites for grain refinement, producing a finer matrix microstructure with improved mechanical properties.

Comparison with Other Reinforcement Systems

Reinforcement	Hardness (HV)	Thermal Stability	Toughness	Cost	Wear Resistance
TiC	1100–1400	Excellent	Good	Medium	Excellent
WC	1200–1500	Good	Moderate	High	Excellent
Cr7C3	1000–1300	Moderate	Good	Low	Good
SiC	1000–1300	Excellent	Good	Medium	Good
B4C	1200–1500	Excellent	Moderate	High	Excellent

TiC offers a favorable balance of hardness, thermal stability, toughness, and cost, making it an attractive choice for particle-reinforced composite coatings. Compared to WC, TiC is less prone to oxidation and has better thermal stability, while offering comparable wear resistance.

Process Parameters and Microstructure Control

Parameter	Typical Range	Effect on Microstructure	Effect on Properties
Flux composition	Fe-Cr-C with TiC particles	Higher TiC content → more particles	Higher hardness, lower toughness
Current density	15–30 A/mm²	Higher current → deeper penetration	Higher dilution, coarser grains
Travel speed	100–300 mm/min	Higher speed → thinner layer, finer grains	Higher hardness, lower toughness
Preheat temperature	150–300°C	Higher preheat → slower cooling	Coarser microstructure, better toughness
Layer thickness	3–6 mm per pass	Thicker layers → slower cooling	Coarser microstructure

The incorporation of TiC particles into the flux requires careful control of the particle size distribution and the mixing uniformity. Particles that are too large may not be adequately incorporated into the molten pool, while particles that are too small may dissolve or react with the molten metal. An optimal particle size range of 20–100 μm is recommended for SAC applications.

Key Defects and Countermeasures

Defect Type	Cause	Countermeasure
TiC dissolution	Excessive heat input, high temperature	Reduce heat input, use lower current density
Particle agglomeration	Poor flux mixing, large particle size	Improve flux mixing, use smaller particles
Cracking	High residual stress, incompatible composition	Preheat to 200–300°C, use compatible flux composition
Poor bonding	Inadequate penetration, oxide inclusion	Ensure proper flux coverage, clean substrate
Non-uniform properties	Uneven particle distribution	Improve flux mixing, use multi-pass deposition

Study Insights and Reflections

The research by Liu Junhai et al. demonstrates that submerged arc cladding is an effective method for producing TiC particle-reinforced composite coatings with excellent wear resistance and good toughness. The key advantage of TiC reinforcement is the combination of high hardness, thermal stability, and cost-effectiveness, making it suitable for a wide range of industrial applications. For engineers selecting particle-reinforced composite coatings, TiC represents an excellent choice for applications involving severe abrasive wear at elevated temperatures, provided that the process parameters are carefully optimized to achieve the desired balance of hardness and toughness. The study also highlights the importance of flux design and particle size control in achieving uniform particle distribution and consistent coating properties. The TiC-reinforced SAC coating system offers a cost-effective solution for extending the service life of components subjected to severe wear conditions, particularly in mining, cement, and material handling industries.