Best armor to protect parts: "Normal hard coating" of hard coatings

In the field of machinery manufacturing and processing, a large number of work parts will be in contact, collision, vibration and other complex conditions of service, so it is easy to occur various forms of damage and failure. However, with the rapid development of modern science and technology, there are reliable ways to improve the surface performance of all kinds of materials and components, that is, to apply a hard coating on their surface, not only can effectively improve the performance of work parts, but also improve work efficiency and extend service life.
of hardness coatings
hard coatings are those with a certain thickness (generally micron scale) and micro-hardness above 20GPa

. Hard coatings with high hardness, low friction coefficient, good high temperature and corrosion resistance, in machining, mold manufacturing, geological drilling, textile industry and aerospace and other fields play an increasingly important role. Depending on the micro-hardness, the hard coating can be divided into two types: one is a normal hard coating with a micro-hardness between 20 and 40GPa, and the other is an ultra-hard coating with a micro-hardness of more than 40GPa, which is summarized first today.
common hard coating
ordinary hard coating materials are mostly transition family metals and non-metallic compounds, intermetallic compounds and so on. These compounds are usually bonded by a mixture of metal bonds, co-price bonds, ion bonds or ion bonds and metal bonds due to their high hardness, excellent heat resistance, antioxidant resistance, corrosion resistance and good insulation properties. At present, the common common hard coating mainly includes nitride, boron, oxide and carbide coating.
(1) nitride coating
metallic nitride is generally characterized by high melting point and hardness, thermal stability, corrosion resistance and excellent antioxidant properties. Nitride from transition metals such as titanium, chromium, vanadium, andare commonly used as reinforced coatings on tool surfaces. The most common and widely studied and widely used coatings are titanium and chromium nitride.
TiN coating has the advantages of high hardness, good toughness, good chemical stability and gorgeous color, has been successfully applied in the tool industry, has been known as "a revolution in tools." In addition to being a functional coating, the coating can also be used as a decorative coating, and the CrN coating has a lower coefficient of friction, better resistance to high temperatures and corrosion, and a high sputtering yield, which is conducive to large-scale industrial production. In addition, the internal stress of the CrN coating is low, the thickness of the coating on different substrings can be up to 40 m, while the thickness of the TiN coating can only be about 10 m.
TiN coating
(2) carbide coating
carbide is a class of melting point and very high hardness, thermal stability and mechanical stability of the material, it can be almost resistant to corrosion of various chemical reagents at room temperature, some carbide also has similar electrical and magnetic properties to its parent metal. Carbides coatings are widely used in mechanical cutting, mineral extraction, wear and high temperature components. Carbides coating materials are mainly IV. family carbides (e.g. TiC, ZrC, HfC), V carbides (e.g. VC, NbC, TaC) and VI carbides (e.g. Cr3C2, MoC, WC). TiC, Cr3C2 and WC coatings are the most widely used of the various carbides coatings mentioned above.Similar to TiN,
TiC coatings are highly hard and wear resistant and can be used as wear-resistant coatings for cutting tools, drill bits and various molds, but are more brittle, often adding nitrogen to the coating preparation process to form Ti (C, N) coatings to improve toughness, and chromium carbide (Cr3C2) has the strongest antioxidant properties. Still maintaining a fairly high hardness at high temperatures, significant oxidation only begins at 1100 to 1400 degrees C in the air, making it an excellent corrosion-resistant coating, and WC is considered an ideal alternative to electroplating hard chrome coatings for applications such as friction, wear and erosion, as compared to TiC and Cr3C2.
Ti (C, N) coating
(3) oxide coating
Common oxide coating materials are Mainly Al2O3, ZrO2, Cr2O3, TiO2, etc., they have high hardness, good chemical stability and thermal stability, etc., is the ideal hard protective coating. ZrO2 is widely used as a thermal barrier coating for heat protection of high temperature alloys, and Al2O3 and Cr2O3 are very hard and dense, mainly used as wear and anti-high temperature oxidation corrosion coatings.
Al2O3 insoluble in water, slightly soluble in strong acid and strong alkali solution, is the most used metal oxide coating material in industry, often used as a wear-resistant coating on carbide cutting blades and mechanical components working at high temperatures; Hardness, also has excellent chemical stability, high temperature resistance and low coefficient of friction, is usually used as a barrier layer for microelectronic devices and wear device protection layer, TiO2 hardness is low, but it has a very low pore rate, not easy to chemical reaction, good toughness, easy to process, after grinding surface roughness is very low, resistant to most acid, salt and other solvent corrosion, is important corrosion resistance, wear-resistant coating materials.
(4) Boron coating
transition group metal borates are usually gap phase compounds, boron and boron can form a variety of complex co-price bonds, while boron atoms and metal atoms can form ion bonds, its hardness and carbonate hardness is equivalent to or even higher, and more inert, chemical properties are more stable. Among them, ZrB2, TiB2 and other binary borates due to excellent performance is considered to be the most promising widely used borates, has been widely used as wear-resistant corrosion-resistant coatings, neutron absorption coatings and self-melting alloys in the reinforced carbide phase and ultra-high temperature coatings.
summary
Although some distance from the ultra-hard coating in terms of performance, ordinary hard coating with good performance, low cost is still widely used in many fields. However, with the rapid development of modern science and technology and industry, mechanical and structural parts in some areas need to work in more demanding conditions than ever before, so the performance of materials and surface protective coatings is higher requirements, the next article will be more hard "ultra-hard coating" finishing summary.
source:
, Gao Jie, He Zhiyong, etc. Advances in the study of common hard coatings and ultra-hard coatings, mechanical engineering materials, 2016, 40 (5): 1-15