1. Introduction to PVD

PVD stands for Physical Vapor Deposition. It refers to a process conducted under vacuum conditions, employing low-voltage, high-current arc discharge technology. In this process, gas discharge causes the target material to evaporate, while both the evaporated species and the surrounding gas become ionized. Under the acceleration of an electric field, the evaporated material and its reaction products are deposited onto the workpiece.

2. Development of PVD Technology

PVD technology emerged in the late 1970s, and the thin films it produces exhibit high hardness, a low coefficient of friction, excellent wear resistance, and superior chemical stability. Its initial successful application in high-speed steel cutting tools drew significant attention from manufacturers worldwide. While developing high-performance, highly reliable coating equipment, researchers also conducted more in-depth studies on coating applications for cemented carbide and ceramic tools. Compared with CVD, PVD operates at lower temperatures—below 600°C—with no adverse effect on the flexural strength of tool materials; moreover, the compressive stress state within the coating is more favorable for depositing on precision, complex cemented‑carbide tools. PVD has minimal environmental impact, aligning with the principles of modern green manufacturing. Today, PVD coating technology is widely employed for surface treatment of cemented‑carbide end mills, drills, step drills, oil‑hole drills, reamers, taps, indexable milling inserts, special‑shaped tools, and brazed tools.

PVD technology not only enhances the adhesion between the coating and the tool substrate, but its coating compositions have also evolved from the first-generation TiN to include multi-component composite coatings such as TiC, TiCN, ZrN, CrN, MoS2, TiAlN, TiAlCN, TiN–AlN, CNx, DLC, and ta-C.

3. Main Methods

① The fundamental principle of vacuum evaporation coating is to evaporate metals, metal alloys, or compounds under vacuum conditions and then deposit them onto the substrate surface. Common evaporation methods include resistive heating, high-frequency induction heating, and bombardment of the coating material with high-energy electron beams, laser beams, or ion beams, which convert the material into the gas phase before deposition on the substrate. Historically, vacuum evaporation was the earliest technique employed in physical vapor deposition (PVD).

② The fundamental principle of sputter coating is that, under vacuum conditions filled with argon (Ar) gas, a glow discharge is initiated. In this process, argon atoms are ionized into argon ions (Ar+), which, under the influence of the electric field, are accelerated to bombard the cathode target material. The target material is then sputtered and deposited onto the surface of the workpiece. If direct-current glow discharge is employed, it is referred to as DC (Qc) sputtering; if radio-frequency (RF) glow discharge is used, it is called RF sputtering; and if magnetron (M) glow discharge is utilized, it is termed magnetron sputtering.

③ The fundamental principle of arc plasma coating is that, under vacuum conditions, an arc is initiated using an arc‑ignition needle, establishing an arc discharge between the vacuum chamber wall (anode) and the coating material (cathode). Multiple cathodic arc spots rapidly move across the cathode surface, continuously and swiftly vaporizing—sometimes even undergoing “transmutation”—the coating material, ionizing it into an arc plasma whose primary constituent is the coating material, and enabling its rapid deposition onto the substrate. Due to the presence of multiple arc spots, this process is also referred to as multi‑arc evaporation and ionization.

④ The fundamental principle of ion plating is that, under vacuum conditions, a plasma ionization technique is employed to partially ionize the coating material atoms into ions, while simultaneously generating numerous high-energy neutral atoms. A negative bias is applied to the substrate being coated; under the influence of this deep negative bias, the ions deposit onto the substrate surface, forming a thin film.

4. Process Steps of PVD

The fundamental principles of physical vapor deposition can be divided into three process steps:

① Vaporization of the coating material: Whether the coating material evaporates, sublimates, or is sputtered, it is accomplished via a vaporization source.

② Migration of atoms, molecules, or ions in the plating bath: Atoms, molecules, or ions supplied by the vaporization source undergo collisions, leading to a variety of reactions.

③ The atoms, molecules, or ions of the plating material deposit onto the substrate.

Physical vapor deposition is characterized by a simple process, environmental friendliness, zero pollution, low consumable usage, and the formation of uniform, dense films with strong adhesion to the substrate. This technology is widely employed in aerospace, electronics, optics, mechanical engineering, construction, light industry, metallurgy, and materials science, enabling the fabrication of thin films with properties such as wear resistance, corrosion resistance, decorative finishes, electrical conductivity, insulation, optical waveguiding, piezoelectricity, magnetism, lubrication, and superconductivity.

With the advancement of high technology and emerging industries, physical vapor deposition (PVD) has seen numerous innovative breakthroughs, including technologies that integrate multi-arc ion plating with magnetron sputtering, large rectangular long‑arc targets and sputtering targets, unbalanced magnetron sputtering targets, twin‑target technology, strip‑shaped foam‑based multi‑arc deposition for roll‑to‑roll coating, and strip‑type fiber‑fabric roll‑to‑roll coating, among others. The corresponding coating equipment is evolving toward fully computerized operation and scaling up to industrial‑scale production.