03/04/2023
一、Superhard material:
1. Type of superhard material:
Diamond
Cubic boron nitride
Polycrystalline mainly composed of diamond and cubic boron nitride
Composite sheets mainly composed of diamond and cubic boron nitride.
2. Why is diamond not suitable for processing iron-based metal materials:
Because diamond can chemically react with Fe-based metal materials at high grinding temperatures, the carbon in diamond reacts with these elements to form carbides, resulting in sticking to the knife, shortening the service life, and reducing the processing quality. Therefore, diamond is not suitable for processing. Steel, including ordinary steel and various tough alloy steels. Such materials are generally machined using CBN tools.
3. The main trends of superhard materials in the future:
Single crystal synthesis
Using different raw materials, different high temperature and high pressure synthesis equipment and different processes to synthesize different single crystal products
Single Crystal Sorting
Synthesized single crystal products are sorted according to particle shape, particle size, bulk density, impurity content, strength, toughness, heat resistance and other performance indicators, so as to be divided into different single crystal seeds.
Surface Plating
Sorted single crystals of different varieties are plated by electroless plating, electroplating, vacuum plating, etc.
Polycrystalline manufacturing
Using raw materials such as diamond single crystal powder or graphite powder and appropriate metal powder and non-metal powder, according to the appropriate formula, using the corresponding process method (high pressure and high temperature sintering method or direct growth method, to manufacture different shapes, specifications, properties and uses of polycrystalline)
Film growth
Using various v***r deposition growth methods under low pressure conditions to manufacture diamond films or diamond-like films with special properties and larger sizes.
4. Basic methods of synthetic diamond synthesis:
Dynamic high pressure method,
Static high pressure method,
Chemical v***r deposition (CVD) -- metastable growth
5. Static pressure catalyst method:
It refers to the method of synthesizing diamond under the condition of constant high pressure and high temperature and the participation of catalyst under the condition of diamond thermodynamic stability.
6. List the main excellent properties of diamond:
Maximum hardness,
Maximum thermal conductivity,
Minimum compressibility,
Widest light transmission band,
Corrosion resistance
7 Electronic structure and crystal structure of diamond structure:
Electronic structure: According to the hybridization theory, when the C atom reacts, it excites a 2s electron to the 2pz orbital. One s orbital and three p orbitals are mixed to form four new orbitals---sp3 equivalent hybrid orbitals, each sp3 hybrid orbital has 1/4 s composition and 3/4 p composition, and the shape is the same , the angles between the axes of symmetry of these four orbits are all 109.28.
Crystal structure: In a diamond crystal, each C atom forms four covalent bonds with four adjacent C atoms according to the equivalent sp3 hybrid orbital. All valence electrons participate in bonding, and there are no free electrons in the crystal.
Diamond crystal is a typical covalent bond crystal, which has the structural characteristics of covalent bond---directivity and saturation.
Therefore, diamond has extremely high hardness and melting point, and it does not conduct electricity.
8. Three-division diamond purification:
Metal removal, graphite removal, pyrophyllite removal
9. Electroless plating of superhard materials:
Electroless plating refers to a metal plating method in which the metal ions in the solvent are reduced to a metal state by means of a suitable reducing agent and deposited on the surface of the substrate.
10. Plating definition
It is an oxidation-reduction process under the action of electric current. The basic process of electroplating is to maintain a certain pH value, temperature and other conditions. Under the action of direct current, an oxidation reaction occurs at the anode, and metallic copper loses electrons and becomes copper ions into the solution; at the same time, a reduction reaction occurs at the cathode, and copper ions are obtained on the cathode. Electrons, reduced to metallic copper.
11. Definition of diamond powder:
According to the current national standard GB/T7991-1997, diamond powder with a particle size equal to or smaller than 54 μm is called diamond micropowder.
12. The main application of diamond powder:
⑴ Used directly or made into abrasive paste
⑵ As a raw material for the manufacture of large particle polycrystals
⑶ Coating micropowder on the surface of some workpieces to increase its wear resistance
⑷ Micropowder can sometimes be used to manufacture electroplated abrasives for grinding.
13. Three methods of diamond polycrystal and synthetic diamond polycrystal:
Polycrystalline diamond (PCD): refers to a class of superhard material products formed by agglomeration of many fine-grained (0.1-100μm) diamonds under high temperature and high pressure.
Synthetic diamond polycrystals are divided into 3 types according to the sintering mechanism:
Sintered type (S-type) (polycrystalline is a block-like agglomerate formed by sintering diamond fine powder as raw material with or without additives and under high temperature and high pressure conditions, and its structure is similar to that of Cabernet. , the grain arrangement is disordered, non-directional, and non-cleavage plane.)
Growth type (G-type) (polycrystalline is made of graphite as raw material, which is transformed into polycrystalline diamond under the conditions of catalyst participation and high temperature and high pressure. Because the synthesis process is accompanied by nucleation and growth processes, it is called growth type.)
Growth-sintering type (G-S) (polycrystalline is made of diamond and graphite as raw materials. Under the participation of catalyst and ultra-high temperature and high pressure conditions, graphite (including partially reversed graphite) is transformed into diamond, interacting with the original diamond. grow together, this combination of polycrystals is called growth-sintered polycrystals.)
14.Film growth method
In the growth process of abrasive grade diamond, since there is a thin (~100μm) metal film on the outside of the diamond crystal (the two sides of the metal are graphite and diamond respectively), the growth method of abrasive grade diamond is usually called For the film growth method (FGM).
15.Synthetic diamond requirements for reaction vessels:
(1) Good pressure transmission performance;
(2) Good sealing performance;
(3) Good insulation performance;
(4) Good heat insulation performance;
(5) Good thermal stability;
(6) Good chemical stability;
(7) Good machining performance
16. Six-sided top press
The Distribution Law of Pressure and Temperature in the Synthetic Rod of Diamond Synthesized by Domestic Six-sided Top Press
The temperature distribution law in the synthetic rod:
Along the axial direction, the temperature at both ends is lower than that in the middle; along the diameter direction, the peripheral temperature is lower than that of the inner part. The center of the synthetic rod has the highest temperature. There are temperature gradients both axially and radially. The value of the temperature gradient may reach 15 ~ 25 ℃ / mm.
The law of pressure distribution in the synthetic rod:
Along the axial direction, the pressure at both ends is high and the middle pressure is low; along the diameter direction, the peripheral pressure is high and the internal pressure is low. The center of the synthetic rod has the lowest pressure. Pressure gradients exist both axially and radially. The pressure gradient can reach 0.1-0.2MPa.
17. Crushing method
Most of the artificial diamond powder (more than 90%) is made of coarse-grained diamond produced by static pressure catalyst method, which is processed by ball milling, crushing and other processes. It is a micropowder production method commonly used at home and abroad, which can be called static pressure synthesis-ball milling pulverization method, or pulverization method for short.
二、 The application of superhard materials
1.Abrasives
Diamond abrasive tools are mainly used for grinding, polishing or cutting of the following materials: cemented carbide, ceramics and refractory materials, glass, graphite, gemstones, non-ferrous metal materials and non-metallic materials, etc.
CBN grinding tools are mainly used for grinding and polishing of various high-speed steels, bearing steels, cast irons, stainless steels, wear-resistant coatings, high-temperature alloys and other difficult-to-grind materials.
2.Tools (including thin-film coated tools).
Diamond tools are mainly used for turning, milling, boring, drilling and other processes of various non-metallic materials and non-ferrous metal materials, such as FRP, hard plastic, rubber, building materials, carbon fiber, ceramics, refractory materials, copper, aluminum-based composite materials and Alloy etc.
CBN cutting tools are mainly used for processing hardened steel, chilled cast iron, stainless steel, superalloy, wear-resistant coating and other materials.
3.Drilling tools.
It is used for exploration and mining in geology, petroleum, coal fields, engineering construction, etc.
4.Sawing tools.
Mainly used for cutting stone, building materials, ceramics, refractory materials, electric carbon products, semiconductors, gemstones, wood, etc.; also used for grooving and cutting of roads, airport runways, and building components.
5.Pulling tool.
Used for drawing wires and wires of the following metal materials, tungsten, molybdenum, copper, aluminum, stainless steel, galvanized steel, steel and alloys, etc.
6.Trimming tools.
Used for forming and dressing, shaping and sharpening of ordinary abrasive tools
7.Other tools.
Hand tools used for carbide molds, measuring tools and cutting tools, as well as glass knives, medical tools, anvils and indenters, etc.
