Rezumat
Reliable connection between titanium alloys and stainless steel has long been a critical technical challenge in high-end equipment manufacturing. This article systematically reviews the challenges faced in titanium/steel dissimilar metal welding, including issues with brittle phases, thermal stress, and process compatibility. It highlights the core advantages of laser cladding technology in transition layer preparation, interface regulation, and performance enhancement. The article also summarizes cutting-edge research in Vanadium (V) transition layers, multifunctional antibacterial hydrophobic coatings, and high-entropy alloy-enhanced coatings. Laser cladding has become the core technology for overcoming the titanium-steel connection bottleneck and achieving high-performance, long-lifetime, multifunctional integrated coatings, providing a new-generation solution for fields such as aerospace, shipbuilding, nuclear power, and marine engineering.

1. Introducere

Titanium alloys and stainless steel are widely used in industries such as aerospace, shipbuilding, nuclear power equipment, and high-end machinery due to their high strength, corrosion resistance, and lightweight advantages. However, the significant differences in their physical and chemical properties make direct welding difficult, often resulting in the formation of brittle intermetallic compounds and high residual stress, leading to cracking and substandard joint performance. In recent years, laser cladding technology has emerged as the core solution to address the connection of dissimilar materials and the preparation of high-performance protective coatings, thanks to its high precision, strong metallurgical bonding, low dilution rate, and strong controllability. This article focuses on the challenges in titanium/steel connection, transition layer technology, multifunctional coatings, and high-entropy alloy reinforcement, emphasizing the breakthroughs and application value of laser cladding.

2. Core Challenges in Titanium-Steel Welding

There are two major bottlenecks in titanium and stainless steel welding:

1. Formation of brittle intermetallic compounds: During welding, reactions between Ti and Fe, Cr, Ni, C result in the formation of hard and brittle phases such as TiFe, TiFe₂, TiCr₂, NiTi, and TiC, leading to very low plasticity and making the joints prone to brittle fracture.
2. Mismatch in thermal expansion coefficients and high residual stress: The significant difference in the thermal properties of these materials generates large internal stresses during the cooling process, which can easily cause cold cracks and deformation.

Traditional methods such as brazing, diffusion bonding, and friction welding are complex and inefficient. Electron beam welding requires a vacuum environment, while conventional laser welding struggles to suppress the formation of brittle phases, making them unsuitable for the reliable long-term operation of high-end equipment.

3. Transition Layer Technology: The Key Path to Solve Titanium-Steel Welding

To prevent direct contact between Ti and Fe, researchers commonly use Cu, Ni, Nb, Zr, and other materials as intermediate transition layers. Among them, Vanadium (V) transition layers exhibit the best overall performance:

• Vanadium’s excellent solubility in both titanium and steel effectively prevents the formation of brittle phases.
• Teng Yi et al. (2023) și Zhang Yan (2019) have confirmed that the use of Vanadium as an interlayer significantly improves joint strength and stability.

However, traditional methods for preparing transition layers often suffer from weak bonding and difficult thickness control. Laser cladding has emerged as the best solution for preparing high-quality Vanadium transition layers.

4. Laser Cladding: The Core Technology for Titanium-Steel Connection and High-Performance Coatings

Laser cladding uses high-energy lasers as a heat source to rapidly melt and solidify a metallurgically bonded, low-dilution, dense coating or transition layer. It is currently the most suitable advanced surface technology for high-end industrial applications.

Core Advantages of Laser Cladding:

1. Rata de diluție scăzută: Precise control over elemental diffusion can strictly suppress the mutual diffusion of Ti and Fe, preventing the formation of brittle intermetallic compounds from the source.
2. Lipire metalurgică puternică: The layer achieves atomic-level bonding with the substrate, significantly enhancing joint reliability and lifespan.
3. Precise and controllable forming: Laser cladding allows flexible control over the thickness, morphology, and composition of transition layers, making it adaptable to complex structures.
4. Zonă mică afectată de căldură: Minimal deformation and low stress, making it ideal for joining lightweight alloys like titanium and aluminum with high-strength steels.
5. Multifunctional integration: Simultaneously achieves high-strength bonding, wear resistance, corrosion resistance, antibacterial properties, hydrophobicity, and high-temperature resistance.
6. Stable process and high automation: Suitable for mass production, meeting the standards of high-end manufacturing in aerospace, nuclear power, and shipbuilding.

5. Frontier Progress in Multifunctional Coatings Based on Laser Cladding

1. Vanadium Transition Layer Laser Cladding
   Laser cladding can prepare homogeneous, dense Vanadium transition layers that effectively control the formation of σ-phase, improving both the strength and toughness of titanium/steel joints.
2. Antibacterial Superhydrophobic Laser Cladding Coatings
   For marine engineering, medical, and food machinery needs, laser cladding can create superhydrophobic coatings with silver ion release for synergistic antibacterial action:
   1. Superhydrophobic interfaces reduce bacterial adhesion.
   1. Silver ions provide long-lasting antibacterial effects.
   1. Laser cladding ensures mechanical wear resistance and corrosion resistance.
3. High-Entropy Alloy (HEA) Laser Cladding Coatings
   High-entropy alloys offer extremely high hardness, excellent wear resistance, and corrosion resistance. By using ultra-high-speed laser cladding (EHLC), coatings with finer microstructures, lower stress, and more stable performance can be achieved, significantly extending the service life of components in extreme environments.

6. Research Gaps and Future Trends

Currently, most coatings focus on a single function. Future developments will focus on:

• Placare cu laser + transition layer + multifunctional coatings integration.
• Rare-earth dual-phase particle synergy for reinforcing high-entropy alloy coatings.
• Coupling of superhydrophobic, antibacterial, wear-resistant, and corrosion-resistant properties.
• High-speed laser cladding (EHLC) for efficient mass production applications.

7. Concluzie

The reliable connection between titanium alloys and stainless steel is a key technology in high-end equipment manufacturing. Laser cladding, with its low dilution rate, strong metallurgical bonding, precise controllability, and multifunctional integration, has become the most effective solution to address issues of brittleness, stress, and performance deficiencies in titanium/steel welding. From the precise preparation of Vanadium transition layers to multifunctional antibacterial hydrophobic coatings and high-entropy alloy reinforcement, laser cladding is driving the evolution of connection technologies from “traditional welding” to “high-performance surface engineering,” supporting the future development of lightweight, long-life, and high-reliability industrial applications.