Importance of Alloy Powder Properties in Laser Cladding Applications

Laser cladding is a surface strengthening technology that uses a high-energy laser beam to melt the coating material and the surface of the substrate to form a metallurgical bond. This technology is widely used in surface strengthening, damage repair and functional coating preparation. Its core advantage is that it can accurately control the heat input to achieve coating deposition with a low dilution rate (<10%).

Alloy Powders Products List

• High-Temperature Alloy Powders
• Stainless Steel Powders
• Precision Alloy Powders
• High-Entropy Alloy Powders
• Other Alloy Powders

The physical and chemical properties of the alloy powder directly determine the performance of the cladding layer. For example:

Hardness and wear resistance: Powder composition (such as carbide addition) can significantly improve hardness (up to 1200HV) and wear resistance (3 times higher than the substrate).

Corrosion resistance: Alloy design (such as nickel-based, cobalt-based) can optimize corrosion resistance.

Defect control: Improper powder morphology and particle size distribution can easily lead to pores and cracks, affecting density and bonding strength.

Key Characteristics of Laser Cladding Powder

Particle size and distribution: Typical range is about 20–200 μm. Micron-sized powder (such as 45-150 μm) is suitable for precision cladding. Too coarse powder can easily lead to unmelted particles, and too fine powder has poor fluidity.

Distribution effect: Uniform distribution (such as Gaussian distribution) can reduce porosity and improve density. Optimizing particle size distribution (such as 50-200 μm) can increase powder utilization by 42.6% and reduce operating costs.

Spherical powder: Good fluidity (angle of repose <25°), ensure stable transportation, reduce splashing, and is suitable for high-speed scanning (such as 300 mm/min).

Non-spherical powder: Block powder can enhance hardness in specific scenarios (such as in-situ synthesis of carbides), but the amount added needs to be controlled to avoid cracking.

Typical Powder Materials and Their Applications

Colmonoy series powders

Colmonoy-6: Nickel-based alloy powder, suitable for 316L stainless steel substrate. Experiments show that its cladding layer consists of hard Leydigite phase and interdendritic structure in γ-nickel matrix, and chromium-rich carbide/boride precipitates significantly improve hardness and wear resistance. After 42 hours of cladding, the surface roughness of the cladding layer is the lowest, the current density is significantly reduced, the passivation film is excellent in stability, and the corrosion resistance exceeds the substrate, which is especially suitable for the repair of harsh environments such as nuclear power equipment.

Colmonoy-52: It is also a nickel-based alloy, but the boron content is higher, forming more chromium carbide/chromium boride strengthening phases. It should be noted that it is different from Colmonoy-6: the particle size distribution is different, and it is more prone to cracking during welding, and the process needs to be optimized in a targeted manner when applied.

Stellite 6 powder

Basic characteristics: Cobalt-based alloy, high temperature hardness up to HRC 40–45. Experiments have shown that the hardness of H13 mold steel surface increased by 164% after cladding, and the high-temperature wear resistance is 6.1 times better than that of 316L substrate. The cladding layer phase is mainly γ-Co, (M=Co, Cr, Fe), and the hard phase contributes to high hardness (up to 736.2 HV).

Composite modification: Composite with Cr₃C₂ and WC can further enhance the performance. For example: Stellite6-60WC: The hardness of 60% WC composite coating is 3.5 times that of the substrate, and the improvement of high-temperature wear resistance is due to the synergistic effect of unmelted WC particles and hard phase.

Composite with Cr₃C₂: Cr₃C₂/Cr₇C₃ strengthening phase is formed on the H13 substrate, the microhardness reaches 1100 HV, and the wear resistance is significantly better than the substrate.

Key points of the process: Powder particle size should be controlled within 40–60 μm. Preheating the substrate to 120°C can reduce the risk of pores/cracks. The optimal parameters are laser power of 1.5 kW and scanning speed of 300 mm/min.

Scientific Principles of Powder Selection

(1) Thermal expansion coefficient matching

Importance: Reduce thermal stress between the substrate and the cladding layer to prevent cracking. For example, Stellite 6 and 42CrMo substrates have similar thermal expansion coefficients and are well bonded; Ni60 alloy is prone to cracking when clad on 316L stainless steel, and the process needs to be optimized to compensate for the difference in coefficients.

(2) Similar melting points

Mechanism of action: Ensure that the substrate and powder melt synchronously to form a metallurgical bond. The H13 matrix (melting point of about 1427°C) and Cr₃C₂-NiCr powder (melting point of about 1780°C) are effectively combined by adding 85% H13 powder to lower the overall melting point; Ni60 cladding requires precise control of laser power (1.5–2.0 kW) and scanning speed to match the melting point.

(3) Wettability optimization

Wettability determines the spread of the molten pool and the bonding strength. It can be improved in two ways:

Composition design: Adding NiCr improves the wettability of Cr₃C₂ in the H13 matrix and promotes the uniform distribution of the hard phase.

Process adjustment: Stellite 6 is preheated (120°C) and parameter optimized (powder feeding rate 18.8 g/min) to reduce pores caused by poor wetting.

Application Case Analysis

Case 1: Comparison of Colmonoy-6 and Stellite-6 cladding on 304 stainless steel

Trade-off between wear resistance and cost: Stellite-6 (cobalt-based alloy) shows significant advantages in H13 die steel cladding, and the coating hardness can reach 2-3 times that of the substrate. Its high wear resistance comes from the formation of γ-Co solid solution and (Cr, W)C hard phase. However, the scarcity of cobalt resources leads to high costs, while nickel-based alloys (such as Colmonoy-6) have lower costs, but their high-temperature wear resistance is weaker than that of cobalt-based alloys.

Process verification: When cladding Stellite-6 on H13 steel, the optimal process is 300 W laser power, 150 mm/min scanning speed, 30 g/min powder feeding rate, controllable dilution rate and 164% increase in hardness.

Case 2: Application of Stellite 6 and WC composite coating in H13 steel

Improved thermal fatigue resistance: The hardness of the Stellite-6 composite coating with WC (such as Stellite 6-60WC) on the 316L substrate reaches 736.2 HV (3.5 times that of the substrate), and the high-temperature wear resistance is improved by 6.1 times. WC particles and the γ-Co matrix form hard phases such as M₇C₃ and M₂₃C₆, which effectively resist thermal fatigue cracks.

Interface bonding optimization: The WC content needs to be controlled (30%-60%). Excessive amount can easily lead to pores and decreased corrosion resistance. The comprehensive performance is best when the WC addition is 30%, the coating has no cracks and good metallurgical bonding.

Case 3: Laser cladding WC reinforced coating on titanium alloy (Ti-6Al-4V) surface

Hardness jump mechanism: The average hardness of Ni60/WC composite cladding layer (35% WC) reaches 1141.6 HV₀.₅ at a scanning speed of 12 mm/s, which is 3.13 times that of the substrate.

Strengthening mechanisms include: in-situ generation of ceramics such as TiC and TiB₂; dispersion strengthening of unmelted WC particles.

Wear mechanism transformation: The substrate is mainly abrasive wear, while the composite coating shows slight adhesive wear, and the wear resistance is improved by 4.9 times. However, pure Stellite-6 is prone to cracking due to the difference in thermal expansion coefficient during cladding, and 80% Ti powder needs to be added to improve bonding, and the hardness is only increased by 80 HV.

Process Optimization and Future Trends

Parameter coordinated regulation

Laser power, scanning speed and powder feeding rate need to be adjusted according to powder particle size and fluidity. For example: when the particle size of Stellite-6 powder is 40-60 μm, the optimal power is 1100 W and the scanning speed is 8 mm/s; WC composite powder requires higher power (1.5 kW) to ensure the melting of WC particles; too high powder feeding rate (>18.8 g/min) is easy to cause unmelted particles, affecting density. Increasing the scanning speed can reduce the dilution rate, but too fast (>14 mm/s) will lead to a decrease in bonding strength.

Composite material development

Stellite 6/WC has become a research hotspot, but two major problems need to be solved: WC decomposition inhibition: adding Cr₃C₂ can refine WC particles (to 4-6 μm) and reduce high-temperature carbon loss; in-situ reaction generates new phases such as TiC and Co₄W₂C to improve interface bonding strength. High entropy alloy/WC (such as AlCoCrNiFe/WC) coatings have both high hardness and corrosion resistance.

Standardization and customization

Commercial alloy powders (such as nickel-based and cobalt-based) need to have uniform particle size distribution (recommended 40-100 μm) and component purity to avoid pores in the cladding layer. High temperature environments require self-lubricating phases (such as WS₂), and the friction coefficient is reduced by 30% at 200°C; titanium alloy cladding requires adjustment of the thermal expansion coefficient, such as adding Ti powder to reduce the risk of cracking.