The core of achieving high-adhesion coatings in magnetron ion coating machines lies in the synergistic effect of magnetic and electric fields to efficiently ionize target atoms and precisely bombard the substrate surface. This, combined with process optimization and equipment design, creates a dual physical and chemical anchoring effect. The technological path can be analyzed from six dimensions: magnetic field design, bias control, target and gas synergy, process parameter optimization, equipment structural innovation, and post-processing.
Magnetic field design is crucial for improving ionization rate and ion beam density. Traditional magnetron sputtering uses a balanced magnetic field, confining electrons near the target surface. While this increases ionization rate, it limits plasma density. Closed-field unbalanced magnetron sputtering ion plating technology, through the alternating arrangement of multiple target magnetrons, forms a closed loop of magnetic field lines, effectively preventing electron escape and increasing plasma density several times that of traditional methods. For example, in an unbalanced magnetron sputtering device with a four-target closed magnetic field arrangement, the magnetic field lines can extend from one magnetron to another, forming an "electron trap." This creates a dense plasma region on the target surface, significantly increasing the ionization rate of target atoms and providing a high-energy ion source for high-adhesion coatings.
Bias control is the core method for regulating ion energy and bombardment direction. During the coating process, after applying a negative bias to the substrate surface, positive ions in the plasma are accelerated towards the substrate under the influence of the electric field, bombarding the surface with high energy. This bombardment has a dual effect: on the one hand, the high-energy ions transfer kinetic energy to the substrate, causing lattice distortion of the substrate surface atoms and forming defect sites, providing embedding anchors for the coating atoms; on the other hand, ion bombardment can remove contaminants such as oxide layers and oil stains from the substrate surface, exposing a clean, active surface and enhancing the chemical bonding between the coating and the substrate. For example, in the deposition of hard coatings, the introduction of a negative bias can increase the bonding strength between the coating and the substrate several times, significantly improving the coating's wear resistance and peel resistance.
The synergistic effect of the target material and reactive gases is fundamental to the preparation of composite coatings. Magnetron sputtering machines can fabricate targets from almost any material, including metals, alloys, and ceramics. During reactive magnetron sputtering, reactive gases such as nitrogen, oxygen, or hydrocarbons react with target atoms to form a compound film. For example, using pure titanium as the target and introducing nitrogen gas can produce a dense TiN coating with a hardness exceeding HV2000 and strong adhesion to the substrate. This composite coating achieves a balance between high adhesion and high performance through both chemical bonding and physical anchoring.
Optimizing process parameters is crucial for balancing deposition rate and adhesion. If the deposition rate is too fast, the deposited atoms are not fully diffused before being covered by subsequent atoms, easily forming a loose structure and reducing adhesion; conversely, a deposition rate that is too slow leads to low production efficiency. By adjusting parameters such as target-substrate distance, working gas pressure, and power supply, the energy of the deposited atoms and the flux reaching the substrate can be controlled. For example, reducing the target-substrate distance can decrease collision losses during atomic flight, improving deposition efficiency; while appropriately reducing the working gas pressure can extend the mean free path of atoms, allowing more high-energy atoms to reach the substrate surface and enhancing adhesion.
Structural innovation in magnetron ion coating machines is a guarantee for improving coating uniformity and stability. Closed-field unbalanced magnetron sputtering ion plating equipment employs a multi-target synergistic sputtering design, enabling large-area uniform coating. For example, when coating large workpieces, adjusting the magnetron arrangement and magnetic field distribution can ensure uniform plasma coverage of the workpiece surface, avoiding localized excessive thickness or thinness. Furthermore, the equipped molecular pump or cryogenic pump effectively solves the problem of oil backflow, maintains the cleanliness of the vacuum environment, and reduces the impact of impurities on adhesion.
Post-treatment processes are supplementary means to further strengthen adhesion. After coating, annealing can eliminate residual stress between the film and the substrate, regularize the crystal lattice arrangement, and improve the stability of the film. For example, annealing the deposited TiN coating can further improve its bonding strength and toughness, making it more suitable for high-load conditions.
