چکیده

Laser cladding has emerged as a leading surface engineering technology due to its high energy density (>10^4 W/cm^2), low dilution rate (<5%), and rapid solidification characteristics (cooling rates up to 10^6 °C/s). This paper comprehensively reviews six major material systems – metal-based alloys, ceramics, composites, high-entropy alloys, amorphous alloys, and functionally graded materials – with particular emphasis on their microstructure-property relationships. The technical challenges including crack susceptibility (observed in 23% of reported cases) and residual stress control are critically analyzed. Future development directions incorporating machine learning-assisted material design and hybrid process innovations are proposed, highlighting the transition from empirical approaches to quantitative material-structure-performance paradigms.

۱. مقدمه

Modern industries including aerospace, marine engineering, and power generation increasingly demand components capable of withstanding extreme operational conditions involving high temperatures (>800°C), corrosive environments, and severe mechanical wear. Traditional surface modification techniques such as electroplating and thermal spraying often fail to meet these stringent requirements due to inherent limitations in coating adhesion strength and service lifetime.

Laser cladding, as an additive surface modification technology, offers unique advantages through its metallurgical bonding mechanism. The process utilizes a focused laser beam to create a molten pool on the substrate surface while simultaneously delivering clad material in powder or wire form. This results in coatings with exceptional properties including:

• Ultra-fine microstructures due to rapid solidification
• Minimal heat-affected zone (typically 50-200 μm)
• Tailorable chemical composition across the coating thickness

2. Fundamental Characteristics

2.1 Process Principles

The laser cladding process involves three concurrent phenomena:

1. Laser-material interaction (absorption coefficients ranging 30-80%)
2. Molten pool dynamics (Marangoni convection velocities ~0.5 m/s)
3. Rapid solidification (dendrite growth velocities up to 10 m/s)

2.2 Comparative Advantages

3. Material Systems

3.1 Metallic Alloys

3.1.1 Nickel-Based Systems

Ni-Cr-B-Si alloys dominate high-temperature applications due to their:

• Excellent hot corrosion resistance (oxidation rates <0.1 mg/cm²·h at 900°C)
• Balanced hardness (550-750 HV) and toughness (KIC ~40 MPa·m½)
• Self-fluxing characteristics from boron/silicon additions

Recent advances include the development of γ’-Ni3Al strengthened variants with service temperatures exceeding 1000°C.

3.1.2 Cobalt-Based Systems

Co-Cr-W alloys exhibit outstanding:

• Wear resistance (specific wear rates <10^-6 mm³/N·m)
• High-temperature stability (up to 1100°C)
• Biocompatibility for medical implants

The formation of hard Laves phases (Co3Mo2Si) through molybdenum additions can increase hardness beyond 900 HV.

3.2 Ceramic Materials

3.2.1 Carbide Systems

Tungsten carbide composites demonstrate:

• Extreme hardness (up to 2200 HV in WC-Co systems)
• Excellent abrasion resistance (wear coefficients <0.2)
• Thermal stability up to 1300°C

Critical challenges include:

• Decarburization during processing (up to 30% WC→W2C conversion)
• Interfacial reactions with metallic matrices

3.3 High-Entropy Alloys

The novel alloy design concept (minimum 5 principal elements) enables:

• Unique cocktail effects for property enhancement
• Lattice distortion strengthening
• Sluggish diffusion kinetics

Notable systems include:

• FCC-type CoCrFeNiMn (ductility >50%)
• BCC-type AlCoCrFeNi (strength >1.5 GPa)

4. Technological Challenges

4.1 Defect Formation

• Cracking susceptibility index: CI = Δα·ΔT·E (Δα: CTE mismatch)
• Porosity control requires powder sphericity >85% and size distribution 45-150 μm

4.2 Residual Stress Management

Strategies include:

• Preheating (200-400°C reduces stress by 30-50%)
• Post-process heat treatment
• Compositional grading

5. Future Perspectives

5.1 Intelligent Processing

• Machine learning models for parameter optimization (prediction accuracy >85%)
• Real-time monitoring using optical emission spectroscopy

5.2 Advanced Materials

• Nanostructured composite coatings
• Self-lubricating systems with solid lubricant inclusions
• Self-healing coatings incorporating microencapsulated healing agents

5.3 Hybrid Processes

• Laser-arc hybrid cladding for improved deposition rates
• Ultrasonic-assisted laser cladding for microstructure refinement

6. Conclusions

This review establishes that laser cladding material systems are evolving toward:

1. Multi-component alloy designs with tunable properties
2. Hybrid material architectures combining metallic and ceramic phases
3. Intelligent processing incorporating Industry 4.0 technologies

The development of comprehensive material databases and standardized evaluation protocols will be critical for widespread industrial adoption. Future research should prioritize the fundamental understanding of microstructure evolution under ultra-rapid solidification conditions to enable predictive material design.