Microstructure and Properties of Submerged Arc Surfaced TiC Particle Reinforced Composite Coating

Literature Overview

This research by Liu Junhai and colleagues, spanning Beijing University of Science and Technology, Weihai Vocational College, and Weifang University, published in the Chinese Journal of Nonferrous Metals in 2011, investigates the in-situ synthesis of TiC particle-reinforced Fe-based composite coatings on Q235 steel using submerged arc surfacing technology. Funded by the Shandong Provincial Science and Technology Program (Project 2007GG30003003), the study utilizes TiFe powder, Cr powder, Ni powder, Fe powder, and colloidal graphite as raw materials to create a functionally graded composite coating with superior wear resistance.

Core Technical Analysis

In-Situ Synthesis Mechanism

The fundamental innovation in this study is the in-situ synthesis of TiC particles during the submerged arc surfacing process. When the alloy powder blend containing TiFe and carbon sources (colloidal graphite) is melted in the arc pool, titanium and carbon react to form TiC particles directly within the molten deposit. This in-situ approach offers advantages over ex-situ methods where pre-made TiC particles are added to the weld pool, as the resulting TiC particles have better interfacial bonding with the matrix and more uniform distribution. The submerged arc process, with its high heat input and relatively slow cooling rate, provides favorable conditions for the thermodynamic driving force of TiC formation while allowing sufficient time for particle nucleation and growth.

Microstructural Characterization

The coating microstructure consists of three primary phases: TiC particles, martensite, and austenite. The TiC particles are characterized by sizes below 2 micrometers with a dispersed distribution throughout the matrix. This fine particle size is critical because smaller reinforcing particles provide greater interfacial area for load transfer and better resistance to pull-out during abrasive wear. The martensitic matrix provides inherent hardness, while the retained austenite contributes to toughness and crack resistance. The combination of hard TiC particles in a tough martensitic-austenitic matrix creates an effective composite material with synergistic wear resistance.

Hardness and Wear Performance

The coating achieves an average microhardness of 601 HV0.2, approximately three times that of the Q235 carbon steel substrate. Under room-temperature dry sliding wear conditions, the coating exhibits wear mass loss approximately one-tenth that of the base metal, demonstrating exceptional wear resistance. The wear resistance improvement is attributed to the combined effect of hard TiC particles (which resist abrasive particle penetration and ploughing) and the hard martensitic matrix (which provides a tough substrate for the reinforcing particles).

Single-Layer vs. Dual-Layer Coating Comparison

The dual-layer configuration demonstrates improved performance because the second layer undergoes a different thermal cycle during deposition, with the first layer acting as a preheated substrate that reduces the cooling rate. This slower cooling promotes the formation of more austenite and allows for more complete TiC particle formation and growth. The increased TiC content in the dual-layer coating directly correlates with the improved wear resistance observed.

Engineering Practice Implications

In the context of pipe manufacturing and pipeline applications, this TiC-reinforced composite coating technology is applicable to several wear-critical components. Pipe fittings in slurry handling systems, such as elbows and tees in mining and mineral processing pipelines, are subjected to severe abrasive wear from solid-laden fluids. The application of TiC-reinforced composite coatings to the internal surfaces of these fittings can dramatically extend service life. Similarly, pump impellers, valve seats, and other components in slurry service benefit from this technology.

The submerged arc surfacing process used in this study is well-suited to industrial-scale application because it offers high deposition rates, good weld penetration, and the ability to build up substantial coating thicknesses in a single operation. For pipe repair applications, the process can be applied to worn pipe sections to restore dimensional accuracy while simultaneously providing enhanced wear resistance.

Study Insights and Reflections

The concept of in-situ synthesis of reinforcing particles during the welding process represents a paradigm shift in composite coating technology. Rather than relying on pre-made particles that may suffer from interfacial debonding, oxidation contamination, or poor distribution, in-situ synthesis produces particles with clean interfaces, controlled composition, and uniform distribution. This approach also eliminates the cost and handling challenges associated with purchasing and storing pre-made ceramic particles.

The dual-layer approach demonstrates an important principle in composite coating design: the thermal history of subsequent layers can be leveraged to optimize microstructure. By depositing multiple layers, engineers can create functionally graded coatings where the inner layer provides bonding compatibility with the substrate while the outer layer provides maximum wear resistance. This graded approach is particularly valuable for pipe components where the coating must withstand both mechanical wear and thermal cycling.

This research provides a practical pathway for applying advanced composite coating technology to industrial piping systems, with clear performance data and process parameters supporting industrial implementation.