Hybrid TIG Cladding Plus Laser Remelting for ZrAlNiCu Amorphous Coating

Literature Overview

This study by Guan Zhuosen et al. from Taiyuan University of Technology, published in Rare Metal Materials and Engineering (2015, Vol. 44, No. 7), addresses a well-recognized limitation in laser cladding of amorphous coatings: the difficulty of achieving both strong metallurgical bonding with the substrate and a high amorphous phase fraction simultaneously. Traditional laser cladding can produce rapid solidification rates conducive to amorphous formation, but often suffers from cracking, porosity, and incomplete bonding due to the high thermal gradient and short interaction time with the base material. The authors propose a two-step hybrid approach—TIG cladding followed by laser remelting—that leverages the strengths of each process independently.

Core Technical Approach

The hybrid method involves two distinct stages. In the first stage, Zr65Ni10Al7.5Cu17.5 alloy powder is deposited onto the substrate via TIG (Tungsten Inert Gas) arc cladding. The TIG process provides a relatively lower cooling rate compared to laser cladding, which promotes thorough melting and mixing of the powder with the substrate surface, resulting in excellent metallurgical bonding and uniform chemical composition. The slower solidification also minimizes the formation of cracks and pores that are common in single-pass laser cladding.

In the second stage, the TIG-deposited layer is subjected to laser remelting. The laser provides an extremely rapid cooling rate—often exceeding 10^3 K/s in the remelted zone—which suppresses nucleation and crystal growth, thereby promoting the formation of an amorphous phase. This step effectively overcomes the limitation of TIG cladding, which alone cannot achieve sufficient cooling rates for amorphous formation in Zr-based alloys.

Key Technical Parameters and Results

The microstructural analysis reveals that the hybrid coating consists of a mixture of crystalline and amorphous phases, with the amorphous fraction being notably higher than in a coating produced by conventional laser cladding under equivalent conditions. The energy dispersive spectroscopy (EDS) analysis confirms uniform elemental distribution throughout the coating thickness, indicating thorough mixing during the TIG stage.

Engineering Practice Insights

From a practical standpoint, this hybrid approach offers several advantages for industrial application. First, the TIG pre-cladding step acts as a "buffer layer" that ensures compatibility between the brittle amorphous overlay and the ductile substrate. This is particularly relevant when coating dissimilar substrates where thermal expansion mismatch could otherwise lead to delamination during service. Second, the two-step process allows independent optimization of each stage: TIG parameters (current, travel speed, shielding gas flow) can be tuned for bonding quality, while laser parameters (power, scanning speed, spot diameter) can be optimized for amorphous formation.

However, the process introduces additional complexity in terms of equipment requirements, cycle time, and cost. For mass production scenarios, the economic viability depends on the value-added performance gain of the amorphous coating relative to the incremental processing cost. The corrosion performance improvement—evidenced by a 0.07 V increase in corrosion potential and a tenfold reduction in corrosion current—is particularly significant for applications in aggressive chemical environments, such as petrochemical piping systems and marine engineering components.

Reflections and Implications

This work demonstrates a powerful philosophy in advanced surface engineering: combining complementary processes to overcome individual limitations. The TIG stage excels at bonding and defect minimization, while the laser stage excels at microstructure refinement and amorphous phase formation. This concept can be extended to other coating systems and even to other hybrid combinations such as plasma-sprayed pre-coating followed by laser remelting, or cold spray deposition followed by laser texturing. For engineers working on pipeline integrity and corrosion protection, the hybrid TIG-plus-laser approach opens new possibilities for tailoring surface microstructures to specific service demands, particularly where both mechanical durability and corrosion resistance are critical requirements.