1 Introduction
The failure of the workpiece is usually caused by the surface damage of the workpiece. Improving the surface and near-surface morphology, chemical composition, microstructure and properties of materials is an effective and economical means to improve the quality of workpieces, prolong their service life and avoid failure. Surface engineering is a systematic engineering to improve the surface morphology, chemical composition, microstructure and properties of materials through surface modification, surface coating or composite treatment of various surface technologies after pretreatment, so as to obtain the required surface properties.
Surface engineering is a science that takes "surface" and "interface" as the research core, and applies various surface engineering and composite surface engineering technologies to improve the properties of materials on the basis of related discipline theories and according to the failure mechanism of material surfaces. Its contents include the basic theory of surface engineering, surface technology and composite surface technology, surface processing technology, surface detection and control technology and surface design, among which surface technology and composite surface technology are the technical basis and core of surface engineering.
Surface technology and composite surface technology integrate electronics, vacuum, plasma, physics, chemistry, metallurgy, materials and other technologies, and regard the surface and matrix of materials as a unified whole to improve the performance of materials or obtain new materials. Commonly used surface technology can be divided into surface modification technology, surface coating technology and composite surface technology.
2 surface modification technology
Surface modification technology does not change the macro-geometric size of the original surface, but only changes the physical and chemical properties of the surface. There are two ways of surface modification technology: one is to change the chemical composition of the workpiece surface, including chemical heat treatment and ion implantation; The other is not to change the chemical composition of the workpiece surface, but to change the surface microstructure, including surface deformation strengthening, surface phase transformation strengthening and so on.
2. 1 chemical heat treatment
Chemical heat treatment is to keep the workpiece in an active medium at a certain temperature, so that one or more elements can penetrate into its surface, thus improving the chemical composition, microstructure and properties of the surface. Chemical heat treatment can improve the surface strength, hardness, wear resistance and other properties of the workpiece, while still maintaining its good strength and toughness in the center, so that the product has higher comprehensive mechanical properties; Chemical heat treatment can also obviously improve the physical and chemical properties of the workpiece surface.
Commonly used chemical heat treatments include carburizing, nitriding, sulphurizing, boronizing, siliconizing, aluminizing, chromizing, zincifying, vanadizing, carbonitriding, sulphocarbonizing and other multi-element carburizing. According to the medium used in chemical heat treatment, it can be divided into solid infiltration, liquid infiltration, gas infiltration, salt bath infiltration, vacuum infiltration and plasma chemical heat treatment. Carburizing, nitriding, carbonitriding, etc. It can improve the surface hardness, wear resistance and fatigue strength of the workpiece, while processes such as sulphurizing, sulphurizing, nitrogen oxidation and nitrogen oxidation can significantly improve the antifriction, wear resistance and seizure resistance of the workpiece.
There are many kinds and technological methods of chemical heat treatment. With the improvement of surface properties of workpieces, the original alloying system and treatment methods can not fully meet the requirements of service conditions under different working conditions, and the application of multi-element co-infiltration and composite treatment is more and more extensive. The emergence of various new technical means has provided new energy for chemical heat treatment. Plasma chemical heat treatment, laser surface alloying and electron beam surface alloying have been applied in industry.
2.2 ion implantation
The principle of ion implantation is to ionize the atoms of an element into ions, which are accelerated under the action of high-voltage electric field and then incident on the solid surface at high speed. The incident ions have a series of physical and chemical interactions with atoms or molecules in the material, gradually losing energy and finally staying in the material, causing changes in the surface composition and structure of the material, optimizing the surface properties of the material or obtaining some new excellent properties.
Ion implantation significantly improves the surface hardness, wear resistance, fatigue strength, corrosion resistance, oxidation resistance and other physical and chemical properties of the workpiece, and is applied to tools, molds, precision wear-resistant parts, corrosion-resistant parts, medicine and microelectronics.
2.3 Surface deformation strengthening
The principle of surface deformation strengthening is to use mechanical methods to produce strong plastic deformation on the surface of materials, produce a certain thickness of cold work hardening layer on the surface, and produce residual compressive stress to improve the fatigue resistance and corrosion resistance of the surface. The methods of surface deformation include shot peening, rolling, extrusion, ultrasonic impact and so on.
2.4 Surface Phase Transformation Strengthening
Surface transformation strengthening is a heat treatment process that changes the microstructure and properties of materials without changing the chemical composition of the surface layer. The process principle is that the surface of the workpiece is rapidly heated to above the critical point of phase transformation by electromagnetic induction, flame, laser and electron beam, so that the surface material is transformed into fine austenite structure, while the core material is still below the critical point of phase transformation, maintaining the original structure; Then the surface layer is quenched by rapid cooling at the center or outside of the workpiece to obtain fine martensite structure, which improves the surface hardness and wear resistance of the workpiece, while the center of the workpiece still maintains the original characteristics of good strength and toughness.
Surface transformation hardening includes induction heating surface hardening, flame heating surface hardening, electron beam surface hardening, laser surface transformation hardening and high energy density beam surface hardening. It is often used for surface strengthening of gears, shaft workpieces, cylinder liners and pistons.
3 surface coating technology
Surface coating technology is a process of growing a new substance with obvious interface with the substrate, including electroplating, electroless plating, thermal spraying, physical vapor deposition, chemical vapor deposition, conversion coating technology and so on.
3. 1 Electroplating and Electroless Plating
3. 1. 1 electroplating
Electroplating is a technique of depositing metal or alloy on the surface of the substrate by electrochemical method, which can make the metal ions uniformly dissolved in the solution get electrons on the contact surface of the solution/substrate to be reduced to metal atoms and deposited on the surface of the substrate, thus forming a metal or alloy coating.
Electroplating layer includes single metal layer, alloy layer, composite layer, etc. Practical coatings are usually composed of various single metal coatings or coatings with different properties that cooperate with each other to form composite coatings with excellent comprehensive properties. Electroplating layer is mainly used to improve the corrosion resistance, decoration and wear resistance of workpieces.
3. 1.2 Brush plating
Brush plating technology adopts a special DC power supply, the anode of which is connected to the brush plating pen and the cathode is connected to the workpiece; Brush plating pens usually use high-purity fine graphite blocks as anode materials, and the graphite blocks are wrapped with cotton and wear-resistant polyester-cotton sleeves. During brush plating, the brush immersed in the plating solution moves on the surface of the workpiece at a certain speed under appropriate pressure. In those parts where the brush plating pen contacts the workpiece, the metal ions in the plating solution diffuse to the surface of the workpiece under the action of electric field force, and are reduced to metal atoms, which are deposited on the surface of the workpiece to form a coating.
Brush plating does not need plating solution, and has the advantages of small volume, light weight, easy field use and high deposition rate. Widely used in repairing worn workpieces, repairing out-of-tolerance products, strengthening the surface of workpieces, improving the corrosion resistance of workpieces, reducing the friction coefficient of workpieces, decorating and other fields.
3. 1.3 Electroless plating
Electroless plating is a process of reducing and depositing metal ions on the surface of workpiece with reducing agent in solution. Commonly used electroless plating processes include electroless nickel plating, electroless copper plating and composite electroless plating. Electroless plating can obtain a uniform coating with good compactness, good corrosion resistance and high hardness on the surface of complex workpieces, which can significantly improve the physical and chemical properties of workpieces such as wear resistance, corrosion resistance and decoration, and is widely used in petrochemical industry, electronics, automobiles, machinery and other fields.
3.2 Thermal spraying
Thermal spraying technology is to use a certain heat source to heat the sprayed material to a molten or semi-molten state, and spray and deposit it on the pretreated substrate surface at a certain speed to form a coating, so as to achieve the purpose of giving the substrate surface special functions. The formation process of thermal spraying coating generally goes through four stages: the heating and melting stage of sprayed materials, the atomization stage, the flight stage and the collision deposition stage. According to the different heat sources used, thermal spraying is mainly divided into flame spraying, arc spraying, plasma spraying and laser spraying.
Flame spraying is to use the heat generated by the mixed combustion of fuel gas or liquid and combustion-supporting gas in a certain proportion to heat and melt the sprayed material, and then spray it on the surface of the workpiece at a certain speed to form a coating. The initial spraying material can be powder, rod, core wire or wire. It includes metal wire flame spraying, ceramic rod flame spraying, powder flame spraying, high-speed flame spraying and powder flame spray welding.
Arc spraying uses two metal wires of spraying material as consumable electrodes. When two metal wires are short-circuited to ignite the arc, the electrode material is melted by the high temperature of the arc and sprayed on the surface of the workpiece to form a coating, and the subsequent metal wires are continuously fed into the supplementary melting part to maintain the stable combustion of the arc.
Plasma spraying is a thermal spraying process in which spraying powder is sent into a plasma flame and heated to melt or semi-melt, and then sprayed on the surface of the workpiece at a certain speed to form a coating. It has the advantages of high flame temperature, good controllability and fast flying speed of molten particles. The materials that can be used for plasma spraying include all the materials that can be made into powder at present. Plasma spraying includes atmospheric plasma spraying, controlled atmospheric plasma spraying, low pressure plasma spraying and plasma spray welding.
By choosing different coating materials and process methods, thermal spraying can prepare coatings with antifriction, wear resistance, corrosion resistance, high temperature oxidation resistance, thermal barrier function, catalytic function, biocompatibility and far infrared radiation. Thermal spraying is widely used in machinery, transportation, petrochemical industry, aerospace, metallurgy, energy, national defense and other fields to improve the surface properties of workpieces and repair worn and corroded workpieces.
3.3 Physical Vapor Deposition
Physical vapor deposition (PVD) is a process of controllably transferring atoms from source materials to the surface of substrates by using some physical processes, such as thermal evaporation or sputtering of materials. The main characteristics of physical vapor deposition are as follows: ① solid or molten substances need to be used as source substances in the deposition process; (2) the source substance enters the gas phase through physical process; ③ Need a relatively low air pressure environment. Common physical vapor deposition processes can be divided into vacuum evaporation, sputtering and ion plating.
3.3. 1 vacuum evaporation
Vacuum evaporation is to use a certain heat source to heat the source material under vacuum condition, so that it can be gasified to form steam with a certain vapor pressure, and the steam particle flow is directly directed at the substrate and crystallized on the surface of the substrate to form a thin film. The physical process of vacuum evaporation includes: all kinds of energy are converted into heat energy to vaporize the source material, vapor particles are transported to the surface of the substrate, gaseous particles condense and nucleate on the surface of the substrate, grow into solid films, and the atoms that make up the films are rearranged or chemically bonded.
The heating methods of vacuum evaporation process of source materials include resistance heating, electron beam heating, induction heating, arc heating and laser heating. Pure metal films, alloy films and compound films can be prepared by vacuum evaporation, which has the advantages of high deposition rate, high vacuum degree and good film quality. However, there are also some problems, such as low density and poor bonding strength with the substrate.
Vacuum evaporation is widely used. Evaporating aluminum film on the surface of packaging materials is its biggest application field. In addition, it also occupies a certain position in the fields of preparing optical films, decorative films and conductive films.
sputtering
Sputtering technology is to bombard the sputtered target electrode with charged ions accelerated by electric field. When the ion energy is appropriate, the incident ions will be sputtered out during the collision with the atoms on the target surface. Sputtering atoms with certain kinetic energy shoot at the substrate in a certain direction, forming a thin film on the surface of the substrate.
The main sputtering methods include DC sputtering, RF sputtering, magnetron sputtering, ion beam sputtering, reactive sputtering and so on. These methods can be combined with different bias application methods, or several methods can be combined, such as RF sputtering, magnetron sputtering and reactive sputtering, to form reactive RF measurement and control sputtering.
DC sputtering
DC sputtering of diode uses sputtered material as cathode and applies thousands of volts to the substrate as anode. After the system is pumped to a high vacuum, inert gas with appropriate pressure is filled, and a large number of gas atoms are ionized under the high pressure between the positive and negative electrodes; In the process of ionization, Ar atoms are ionized into Ar+ and electrons. Ar+ with positive charge is accelerated by high voltage electric field and flies to the target as cathode at high speed. In the process of collision with the target, a large number of target atoms get quite high energy and get rid of the constraints of the target, and the high-energy target atoms fly to the surface of the substrate to form a thin film.
The diode DC sputtering device is simple and suitable for sputtering metal targets and semiconductor targets, but it can't be sputtered in high vacuum because of high discharge voltage, high substrate temperature, low cathode target current, low sputtering rate and easy damage. In order to avoid the disadvantages of diode DC sputtering, a heating filament cathode is introduced into the diode sputtering device, and thermionic emission is used to enhance the ionization of sputtering gas, thus reducing the pressure and sputtering voltage of sputtering gas and increasing the discharge current, which can be controlled independently.
3.3.2.2 RF sputtering
DC sputtering deposition of thin films requires that the target has good conductivity, and it is not suitable for preparing thin films with non-metallic targets with poor conductivity. If alternating current is applied between two electrodes, when the frequency of alternating current exceeds 50kHz, electrons oscillating between the two electrodes can obtain enough energy from the high-frequency electric field to ionize gas molecules, so that sputtering can be carried out at an air pressure one order of magnitude lower than that required by bipolar sputtering. In addition, the high-frequency electric field can be coupled into the deposition chamber through other impedance forms, thus getting rid of the limitation that the electrode is a conductor. RF sputtering can sputter not only metal targets, but also dielectric targets. Most RF sputtering methods are 13.56MHz.
3.3.2.3 magnetron sputtering
In order to improve the sputtering rate of diode sputtering and reduce the adverse effect of secondary electrons on the substrate, an annular closed magnetic field is established on the cathode target surface of diode sputtering, and the magnetic field component parallel to the target surface and the electric field perpendicular to the target surface form an electron trap for trapping secondary electrons. Secondary electrons generated from the target surface are accelerated in the cathode potential drop region to gain energy and become high-energy electrons. When they fall into the electron trap of the orthogonal electromagnetic field, they can't be directly absorbed by the anode, but do cyclotron motion in the orthogonal electromagnetic field, which greatly increases the travel of secondary electrons before reaching the anode, increases the collision probability with sputtering gas, and improves the sputtering current and sputtering rate. In addition, the anode of magnetron sputtering device is near the cathode, and the substrate is not on the anode, which significantly inhibits the bombardment of secondary electrons on the substrate.
The commonly used forms of magnetron sputtering target are planar magnetron sputtering target, cylindrical magnetron sputtering target and S gun magnetron sputtering target. The initial magnetron sputtering is to seal the magnetic field near the target surface, and the plasma density near the workpiece is very low, so the intervention effect on thin film deposition is not obvious. In order to improve the film quality by bombarding the substrate with high-density ion current with appropriate energy, an unbalanced magnetron sputtering device was developed, which is characterized by increasing stray magnetic field to expand the plasma range to the substrate and interfering the deposition process of the film through ion bombardment, thus improving the film performance.
3.3.2.4 reactive sputtering
Sputtering can be realized by using this compound as the target, but in some cases, the compound will decompose during sputtering, resulting in the chemical composition of the deposited film being very different from that of the target. One way to solve this problem is to limit the decomposition process of compounds by adjusting the gas composition and pressure in the sputtering chamber. In addition, a proper amount of active gas can be doped into the sputtering gas, and chemical reaction occurs at the same time of sputtering and deposition to generate specific compounds, thus completing the process from sputtering to reaction to deposition. This sputtering process is called reactive sputtering.
The thin film prepared by reactive sputtering has high purity, good controllability of components, low deposition temperature and few restrictions on the substrate, which is suitable for large-area uniform coating and industrial production. However, when preparing high resistivity dielectric films, if the pressure of reaction gas is too high, it will lead to target poisoning, arc discharge and anode disappearance, which will make the sputtering process unstable and the film quality decline. In order to avoid these adverse effects, it is necessary to change the power supply mode and the gas supply mode of the reaction gas. Optional power supply modes include automatic arc extinguishing power supply, asymmetric pulse sputtering power supply and intermediate frequency AC power supply. The supply methods of reaction gas include grid-grid partition gas supply, pulse gas intake and so on.
3.3.2.5 medium frequency magnetron sputtering
Medium frequency magnetron sputtering usually adopts double target structure, and AC power supply is connected to the two targets. In the negative half cycle, the first target is bombarded by positive ions and the other target is used as an anode. When in the positive half cycle, the first target becomes the anode, at this time, the electrons in the plasma are accelerated to reach the target surface, neutralizing the positive charges accumulated in the insulating part of the target surface, while the other target is sputtered as the cathode. When the frequency of alternating current reaches a certain value, the two targets are anode and cathode, which can eliminate arc and anode disappearance and ensure the stability of sputtering process. Common power supply methods include symmetrical power supply, sine wave and 40kHz AC power supply with self-matching network.
The unbalanced magnetic field is used in the intermediate frequency magnetron sputtering target, which enhances the interference of plasma on the film deposition process. Optimizing the supply mode of reactive gas can further improve the stability of sputtering process, which is an ideal method to prepare various high-performance films with poor conductivity. Many functional films have been developed, including diamond-like carbon (DLC) films.
DLC film is an amorphous carbon film with a spatial network structure containing sp2 and sp3 bonds. It has many diamond-like properties, low deposition temperature, smooth surface and mature technology. It is superior to diamond film in many application fields. At present, it is widely used in tools, molds, precision wear-resistant parts, speakers, optical disks, optical antireflection and protective films, field emission flat panel display devices, solar cells, medicine and other fields.
Application of 3.3.2.6 Sputtering Coating
Sputtering coating can prepare pure metal films, alloy films and compound films, which are widely used in machinery, electronics industry, solar energy utilization, optics, decoration, chemical industry, military, biomedicine and other fields.
Ion plating
Ion plating is a new coating technology based on vacuum evaporation and sputtering technology. Ion plating is a process of partially ionizing gas or evaporated substance by gas discharge under vacuum, and depositing evaporated substance or its reactant on the surface of the substrate under the ion bombardment of working gas ions or evaporated substance. The activity of plasma reduces the synthesis temperature of the compound, and ion bombardment can improve the density, microstructure and bonding strength of the film with the substrate.
Ion plating can be divided into DC bipolar ion plating, triode ion plating, multi-cathode ion plating, radio frequency ion plating, hollow cathode ion plating, hot wire arc ion plating, vacuum cathode ion plating and magnetron sputtering ion plating.
DC bipolar ion plating
DC bipolar ion plating applies a DC voltage between the evaporation source and the workpiece, and the workpiece is a negative electrode; The working gas and evaporated substance are ionized by glow discharge between the two electrodes, and the formed ions are accelerated by the cathode potential drop zone near the substrate, which bombards the substrate surface at high speed and interferes with the deposition of thin films.
3.3.3.2 three-pole and multi-cathode ion plating
The ionization rate of DC bipolar ion plating is low, so it is difficult to excite and maintain glow discharge. In order to overcome these shortcomings, an electron emitter and an electron collector are added between the evaporation source and the substrate to introduce a large number of electrons emitted by the high-temperature filament into the plasma region, which increases the collision probability with evaporation particles and improves the ionization rate. This ion plating process is called triode ion plating. Sometimes, in order to further improve the ionization rate, multiple electron emitters are introduced into DC bipolar ion plating equipment, which is called multi-cathode ion plating.
3.3.3.3 RF ion plating
Radio-frequency ion plating is an ion plating process in which a high-frequency induction coil is arranged between the substrate and the evaporation source to enhance the ionization of working gas and evaporated substances, so as to independently control evaporation, ionization and acceleration. This method has high ionization rate, can be deposited under high vacuum, and is easy for reactive ion plating.
3.3.3.4 hollow cathode ion plating
Tantalum (or tungsten) tube with high melting point is used as cathode and crucible is used as anode. After the equipment is pumped to high vacuum, argon is introduced into the vacuum chamber from the tantalum tube, and the arc ignition power supply is turned on to ignite the gas, resulting in cathode glow discharge. Due to the hollow cathode effect, the current density in the hollow tantalum tube is very high. A large amount of Ar+ bombards the wall of tantalum tube to raise its temperature to above 2000 K. The tantalum tube emits a large amount of hot electrons to transform glow discharge into arc discharge, and the high-density electron bombardment makes the substances in the crucible evaporate. In the process of moving to the crucible, electrons constantly collide with argon and evaporated substances to ionize them. When a certain negative bias is applied to the substrate, a large number of ions will bombard the surface of the substrate during the film deposition process. Hollow cathode ion plating has high ionization rate and good winding performance, and can be used for metal films, alloy films and compound films.
3.3.3.5 Hot Wire Arc Ion Plating
The hot cathode ion gun chamber is installed at the top of the hot wire arc ion plating equipment. The hot cathode is made of refractory metal wire, which is electrified and heated to high temperature to release a large number of hot electrons, which collide with argon gas in the hot cathode ion gun chamber to produce arc discharge and produce high-density plasma. The auxiliary anode or crucible which is positively charged relative to the hot cathode is arranged at the lower part of the ion gun chamber and the coating chamber of the hot cathode. Electrons from the plasma in the ion gun chamber are introduced into the coating chamber to form a stable, high-density low-energy electron beam in the deposition space, which acts as an evaporation source and an ionization source. Hot wire arc ion plating is characterized by multi-purpose in one arc. Hot cathode ion gun is not only the evaporation source, but also the ionization source of evaporated substances, the heating source of substrate and the bombardment purification source. It has high metal ionization rate, high plasma density and good film quality, and is suitable for depositing films such as TiN, TiCN, TiAlN, diamond-like carbon (DLC) and diamond. TiN film is the most mature protective film system at present, which has good hardness, toughness and chemical stability, and is widely used in building materials, decorative materials, tool materials, acoustic materials and other fields. The properties of TiN thin films can be further improved by alloying and multilayers.
3.3.3.6 vacuum cathode arc ion plating
Vacuum cathode arc ion plating uses cathode arc to directly evaporate and highly ionize the plated material (the ionization rate of metal particles reaches 75% ~ 95%). Under the bias of the workpiece, highly ionized particles are deposited on the surface of the workpiece with high energy, forming a solid film. Reactive ion plating can be performed by introducing a reactive gas into a deposition atmosphere to produce a compound film.
Vacuum cathode arc deposition technology can prepare various metal films, alloy films, compound films, multilayer films and composite films. It is especially suitable for the protective film of tools, molds and wear-resistant parts. In addition, it is also suitable for preparing high-grade corrosion-resistant decorative coatings, which has been widely used in national defense, machinery, chemical industry, light industry, textiles, daily hardware and other fields.
3.3.3.7 magnetron sputtering ion plating
Magnetron sputtering ion plating is a coating technology which combines magnetron sputtering and ion plating. Different from ordinary magnetron sputtering ion plating, negative bias is applied to the substrate to modulate the ion energy reaching the surface of the substrate, which not only realizes the stable sputtering of the magnetron target, but also realizes the interference of high-energy target ions in the film deposition process.
Magnetron sputtering ion plating can prepare metal films, alloy films and compound films, which are widely used in hard films, corrosion-resistant films, decorative films, optical films, microelectronic films, medical films and other fields.
3.4 chemical vapor deposition
Chemical vapor deposition (CVD) is a process that uses gaseous precursor reactants to generate solid thin films through the chemical reaction of atoms and molecules on solid surfaces. It decomposes some components in the mixed gas, and forms a metal, alloy or compound film on the substrate surface through the interaction between the mixed gas and the substrate surface.
From the point of view of reaction kinetics, in order to realize the deposition reaction, there must be some activation energy during the interaction between the initial mixed gas and the solid surface and the deposition reaction. According to different activation methods, chemical vapor deposition can be divided into thermochemical vapor deposition, plasma-assisted chemical vapor deposition (PACVD), laser-assisted chemical vapor deposition (LCVD), metal-organic chemical vapor deposition (MOCVD) and so on.
Thermochemical vapor deposition (CVD) is a kind of thin film formed by the interaction between mixed gas and surface at a certain temperature. The equipment is simple, the repeatability is good, and the film-substrate bonding strength is high. However, the deposition temperature is high and the choice of substrate is limited. It is mainly used to prepare hard films on cemented carbide or ceramic tools.
PACVD relies on the energy of plasma to activate the chemical reaction of gas on solid surface, which has been widely used in electronic industry, and more and more applications have been made in depositing protective films on the surfaces of tools, molds and wear-resistant parts.
LCVD is a chemical vapor deposition process induced and promoted by laser, and its deposition process is the interaction between laser and reactive gas or substrate surface, which has important applications in the preparation of solar cells, integrated circuits, special functional films, optical films, hard films and superhard films.
Replacing the precursor of inorganic chemical vapor reaction with organometallic compounds can significantly reduce the temperature of chemical vapor reaction. MOCVD can deposit all kinds of inorganic materials at low temperature, which is widely used in microwave and photoelectric devices, advanced lasers and so on.
3.5 Conversion coating technology
Aluminum alloy material is put into electrolyte as anode, and a conversion film can be formed on its surface by electrolysis, which improves the surface hardness and corrosion resistance. After hard anodizing treatment, the aluminum alloy surface can form a film with a thickness of 30 ~ 50 μm and a hardness of about Hv500, which has excellent corrosion resistance, insulation, chemical stability and adsorption. Anodizing treatment is suitable for cylinder liner, piston, gear, impeller, guide rail, bearing and die engineering parts. In addition, it is a good coating for basement membrane.
4 composite surface technology
Single-sided technology often has some limitations in practical application and cannot meet the higher performance requirements required by service conditions. Therefore, it is necessary to combine various surface treatment technologies, develop strengths and avoid weaknesses, and significantly improve the surface performance of the workpiece. This method is called composite surface technology. For example, in order to improve the bonding strength between the vapor deposition film and the substrate, the substrate is usually subjected to chemical heat treatment before depositing the film to obtain a thick high-hardness transition layer. The combination of thermal spraying and laser remelting reduces the internal stress of the coating and improves the compactness and bonding strength between the coating and the substrate. Ion beam assisted deposition is developed by combining ion implantation with evaporation or sputtering technology, which significantly improves the properties of thin films.
5 conclusion
As an effective and economical means to improve the performance of workpieces, surface technology has been rapidly developed and widely used. At present, a variety of advanced surface technologies and materials have been developed, which have made important contributions to the development of the national economy. However, with the deterioration of service conditions of workpieces, traditional surface technologies and surface materials can no longer meet the increasingly demanding requirements put forward by industry, which requires the continuous development of new surface technologies and surface materials; From the aspects of material design, surface processing equipment and technology, use conditions and so on. Taking the substrate, surface and environment as a system, combined with various surface technologies, the surface properties of the workpiece are further improved.
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