Alumina Overview The alumina film has many excellent material properties, particularly high temperature stability, chemical stability and low thermal conductivity. Aluminum oxide film is now widely used as a wear resistant coating material on cemented carbide inserts. Despite these excellent properties, alumina films have not been widely used in other fields, mainly because the current industry standard is still based on the thermal chemical vapor deposition (CVD) process.
Although the CVD process has many advantages, there are also obvious disadvantages, namely the high temperature (1000°C) required for the process. Hauser has developed a new process that can deposit alumina by physical vapor deposition sputtering (PVDsputtering) at a standard temperature of 350°C to 600°C, which greatly expands its application range.
Since Hauzer announced a major breakthrough in the PVD coating of Al2O3 at EMO, the European machine tool trade show in 2005, Hauser has already started to cooperate with the world's major tool manufacturers and users of alumina die casting molds. The characteristics of the coating will be discussed below, and the results of this new coating obtained by deposition using a hybrid process combining arc and magnetron sputtering techniques will be presented.
Tool Wear In the machining process, the tool will experience several wear conditions. The tool itself must be able to withstand high temperatures, high pressures, wear and thermal shocks. The cutting edge temperature will exceed 1000°C during cutting. At this high temperature, the adhesive and other components of the tool degrade and cause harmful chemical reactions between the tool and the workpiece. The cutting process is always accompanied by the occurrence of wear, and the pressure between the tool and the workpiece when it comes into contact with the workpiece is greater than 140 bar (2000 PSI).
Thermal shock - the tool is hot and cold, which is common in milling. The blade heats during the cutting process and cools off the cutting surface. There are mechanical shocks when milling and cutting intermittent machining surfaces. There are sometimes mechanical shocks in turning, depending on the operating conditions and workpiece conditions. Sticking wear occurs when the workpiece and the tool are stuck together (bareties are generated).
Aluminum Oxide Coatings for CVD and PVD Nowadays, CVD alumina coated inserts are widely used in the industry, and the performance of CVD aluminum oxide coatings is widely recognized. Due to the high hardness (especially at high temperatures), high oxidation temperature (>1000°C), chemical inertness and low thermal conductivity of alumina, the performance of alumina coated tools is greatly improved. However, the CVD process usually needs to be performed at a high temperature of 800° C. to 1000° C., which limits the application of the CVD process to a cemented carbide substrate. Due to the brittleness of cemented carbide tools will result in reduced toughness. The PVD process has obvious advantages over the CVD process due to its low deposition temperature of 400°C to 600°C.
The main limiting factor in the manufacture of alumina coatings by the PVD process is the deposition of insulating layers on all surfaces inside the coating system during deposition, including the base and bottom pedestals, the target portions outside of the target eroded surfaces, and the inside walls of the vacuum chamber. This will lead to instability of the bias power supply and the cathode (arc) power supply due to the "poisoning" of the target and the disappearance of the anode. Two technologies that have succeeded in solving this problem are RF (radio frequency) sputtering and BP-DMS (two-pole pulse dual magnetron sputtering).
Alumina coating equipment PVD alumina systems should be able to deposit a lower limit of γ-alumina with a high deposition rate (short duty cycle) and have stable coating characteristics. The system should be able to operate at high temperatures and the technology itself is not costly. Single-cathode systems are preferred because they can upgrade existing equipment to aluminum oxide-coated equipment. Hauser's T-mode control system allows the target surface to be in a transitional state during the oxidative deposition process, requiring specialized cathode designs and unbalanced magnetization within a closed magnetic field. In order to get a better reaction gas introduction, a special control system is used. The system was verified on several production facilities in about two years.