There are many types and brands of ceramic knives. According to their main components, they are roughly divided into two categories: alumina-based and silicon nitride-based. Around 1911 to 1913, Germany and the United Kingdom first adopted Al2O3-based ceramics as cutting tools. After several improvements and improvements, a number of excellent Al2O3-based ceramic tools have been developed. Most of the ceramic tools produced in the world are alumina-based ceramic tools.
Al2O3 ceramics are widely used in mechanical, electronic, chemical and other fields due to their high strength, high hardness, high wear resistance, oxidation resistance and thermal shock resistance. Pure Al2O3 ceramics have good high-temperature performance, but lack toughness, poor impact resistance, and are prone to slight chipping during cutting. By adding a toughening material to the Al2O3 matrix, this phenomenon can be significantly improved.
Overview of the development of alumina ceramic tools
(1) Pure Al2O3 ceramic cutter
This is the first generation of ceramic tools. The content of Al2O3 in the material accounts for more than 99%. It is made by adding a small amount of sintering aids (such as MgO, NiO, Cr2O3, TiO2, etc.) and sintering under pressure. Pure Al2O3 ceramics have low bending strength, poor impact resistance, and easy chipping of the cutting edge, but they have good high temperature performance. They are suitable for semi-finished cast iron and steel with small feed rates. Due to its low flexural strength, it is currently less commonly used.
(2) Al2O3-carbide ceramic tool
Adding certain carbides in Al2O3 can improve the strength and impact resistance of ceramics. Among them, TiC-added Al2O3 ceramics are most commonly used, and the proportion of TiC is 30% -60% (some are 5% -10%). Sintered by hot pressing. Suitable for high-speed rough and precision machining of hard-wearing materials such as wear-resistant cast iron, hardened steel and high-strength steel. Compared with pure Al2O3 ceramics, the bending strength of Al2O3-TiC ceramics is higher than that of pure Al2O3 ceramics at normal temperature or high temperature.
(3) Al2O3-carbide-cermet tools
This type of ceramic is made of Al2O3 by adding a small amount of bonding metals (Ni, Mo, Co, W, etc.) in addition to carbides, and sintering by hot pressing (also known as cermets). Due to the addition of metal, the bonding strength of Al2O3 and carbides is improved, and the performance is improved. It is suitable for processing hardened steel, alloy steel, manganese steel, cold hard cast iron, nickel-based and cobalt-based alloys, and non-metallic materials.
(4) Al2O3 ceramic tool with nitride added
The Al2O3-nitride combination ceramic tool with nitride added to Al2O3 has better thermal shock resistance. Its basic performance and processing range are comparable to Al2O3-carbide-cermet tools, and it is more suitable for intermittent cutting. The bending strength and hardness are lower than those of Al2O3-TiC-cermet tools, which need further research and improvement.
(5) Al2O3 ceramic tool with boride added
Ceramic tools made by adding TiB2 as a binder to Al2O3, because of its fine-grained Al2O3 and continuous TiB2 bonding phase, maintain the "three-dimensional continuity" of boride, so it has excellent resistance Impact and abrasion resistance.
(6) Toughened Al2O3 ceramic tool
Toughened Al2O3 ceramic refers to the addition of toughened or reinforced materials in the Al2O3 matrix. At present, the commonly used toughening methods are: ZrO2 phase transformation and toughening, whisker toughening, and second-phase particle toughening. ZrO2 phase change will accompany the volume change. It is an effective method of strengthening and toughening to improve the strength and toughness of ceramic materials through the phase change toughening mechanism. Whisker toughening is the use of whiskers to strengthen rods. Common whiskers include TiC whiskers and Si3N4 whiskers. The dispersion and toughening of the second-phase particles is to use the dispersed second-phase particles to hinder the dislocation slip and climbing, and to prevent cracks from expanding, thereby achieving toughening.
(7) Graphene toughened alumina-based ceramic tools
Some researchers believe that the range of toughening and strengthening of the above materials is limited, and new approaches and methods need to be considered. The composition and properties of typical alumina-based ceramic tool materials at home and abroad are listed in Table 1. It can be seen that despite the addition of different toughening particles, the fracture toughness of the material is still low and needs to be improved, and the bending strength is also much smaller than that of cemented carbide tool materials (2000-3500MPa).
Compared with the traditional toughening phase (micron-sized particles, whiskers) and other new toughening phases (nanoparticles, carbon nanotubes), graphene has a two-dimensional structure with a single atomic layer, high structural stability, and large size. Specific surface area and extremely high mechanical and thermal properties, adding it to ceramic tool materials can introduce crack bifurcation, crack deflection, graphene pull-out, bridging and other mechanisms, which is beneficial to the ceramic tool material's enhanced toughness .
Because graphene has a large specific surface area, a small amount of addition can obtain a good toughening effect. In recent years, due to the innovation of preparation methods and processes, graphene can be produced in large quantities, which reduces the production cost and facilitates the engineering application of graphene, thereby facilitating the development of graphene toughened ceramic tool materials.
Application range of alumina ceramic tools
Al2O3 ceramic tools are mainly used for processing various cast irons (gray cast iron, ductile cast iron, malleable cast iron, chilled cast iron, high alloy wear-resistant cast iron, etc.) and various steel materials (carbon structural steel, alloy structural steel, high strength steel, high manganese Steel, hardened steel, etc.); can also process copper alloys, graphite, engineering plastics and composite materials.
Due to the chemical affinity of aluminum, Al2O3 ceramic tools are not suitable for machining aluminum alloys and titanium alloys. Al2O3 ceramic hobs, reamers, forming lathes and other tools can not only be used for ordinary lathe processing, but also because of its stable and reliable cutting performance, it is especially suitable for CNC machine tools, machining centers and automatic line processing, especially for high precision, high Hardness and cutting of large workpieces have good results.