Since the birth of synthetic diamond in 1954, the application of diamond tools has become more and more extensive. Among them, the diamond saw blade in the stone processing industry is the largest field of diamond consumption, and its consumption accounts for about 90% of the total output of synthetic diamonds in China. According to statistics at home and abroad, about 70% of the world's industrial diamonds are currently used in the manufacture of stone processing tools, the majority of which are diamond circular saw blades.
In the use of diamond circular saw blades, the utilization rate of diamond is relatively low, because the diamond in the cutter head is not worn out, but is lost in a large amount in the form of shedding. The traditional diamond cutter head manufactures the diamond by the holding action of the carcass on the diamond. When the carcass is worn until the diamond is excessively exposed, the diamond will fall off by itself.
Increasing the bond strength between the carcass and the diamond is the most effective technical measure to avoid early diamond shedding. Unfortunately, diamond and carcass are difficult to connect. At present, the more effective technical measures are to plate the surface of diamond with titanium, nickel and Other metals in order to achieve effective combination of diamond and carcass.
Conventional carcass powders are composed of pure metals or simple alloys that either do not wet the diamond or have no wettability to the diamond at the sintering temperature. In the research, a conventional copper alloy is added with a metal such as chromium, titanium, vanadium, zirconium, nickel or manganese to form a prealloy, and the prealloyed powder contains an active element which is wetted by diamond, and is active during the sintering process of the diamond to the head. The element and the diamond interdiffuse to achieve a brazed connection between the carcass and the diamond.
On the one hand, the prealloyed powder can improve the wettability of the alloy to diamond, increase the edge height of the diamond, and improve the utilization rate of the diamond; on the other hand, the chemical composition of the powdered solder is more stable than that of the mechanically mixed powder, and overcomes the specific gravity of the mechanically mixed powder. Segregation, low-melting metal pre-melting and enrichment, easy oxidation and volatile, low melting point volatile metals are burned during sintering, which affect the performance of the carcass, ensuring the stability and consistency of the diamond cutter head.
1 skeleton and binder on the holding of diamond
The carcass of the synthetic diamond cutter head generally consists of two components: a skeleton component and a binder. Generally, a high melting point, high wear resistance, high strength metal is selected as the skeleton material, and a group of low melting point metals is selected as the binder.
In the selection of binders, because the commonly used low melting point metals (tin, zinc, etc.) have low strength, easy oxidation, and easy enrichment, their properties are not ideal. Silver, copper and other metals can overcome the above disadvantages, but higher melting points. Or the price limits their use.
In a mechanically mixed powder sintered carcass, the diamond present in the bit is joined to the carcass by mechanical wrapping and holding, and the connection of the diamond to the carcass is primarily a mechanical connection.
The sintered metal bond carcass has a certain density and a relatively high strength, hardness, toughness, and has a relatively strong mechanical setting effect on the diamond wrapped therein.
The bonding agent should have two basic functions: one is to connect the wear-resistant material into a mesh skeleton to hold the diamond; the other is to wear with the wear of the diamond, so that the diamond is normally edged. In addition, in addition to a certain hardness, toughness and wear resistance of the bonding agent, if the diamond has a certain wettability, the height of the diamond edge will be greatly improved, thereby improving the performance of the diamond tool.
The binder with good performance is able to form a sufficiently stable carcass under the conditions of diamond, carcass material, porosity, manufacturing and use conditions; the carcass can maintain synchronous wear or slightly ahead of the diamond when used. Wear and wear, let the diamond fully function and wear and fall off reasonably.
2 diffusion of active elements to diamond
Due to the softening and weakening of the carcass, the simple mechanical holding can not avoid the early shedding of diamond. It is always the goal of the diamond tool industry to seek the metallurgical bonding route between diamond and carcass material.
Plating the active element with a diamond surface is a viable technical solution. Active elements refer to strong carbide forming elements and transitional elements, which can react with diamond to form compounds, so that the surface of the diamond is covered with a metal that is easy to bond with the carcass metal. This layer of metal can be well matched with the tire. The body metals are brazed together.
Commonly used active elements are titanium (Ti), chromium (Cr), tungsten (W) and other elements; molybdenum (Mo), vanadium (V), zirconium (Zr), niobium (Nb), tantalum (Ta), etc. Carbonization occurs, but it is not used because of high price; other elements cobalt (Co), nickel (Ni), manganese (Mn), silicon (Si), aluminum (Al) can form carbides under certain conditions, The carbides formed are: Co2C, Ni3C, Mn3C, SiC, Al4C3, and the like.
At present, titanium plating and nickel plating are the most common in industrial applications.
Surface plating of active elements can partially solve the problem of metallurgical bonding, but it can not solve the problem of volatilization and enrichment of low melting point metals in the sintering of the carcass itself, the separation of high melting point metals, and the pre-alloyed powder binder in powder form according to the brazing principle. Solve this problem in two ways.
3 Pre-alloyed powder in the form of powdered solder
For different base binders, the added ingredients are also different. In the carcass composition, high melting point metals such as tungsten, tungsten carbide, etc. are often used to adjust the hardness and wear resistance of the carcass, and metals such as cobalt, nickel, manganese, titanium, chromium, which have good chemical wettability to diamond, are selected. Metals such as vanadium are used as bonding materials for diamonds, but the wetting temperature of diamond-impregnated metals is too high, which does not meet the process conditions of hot-press sintering of diamond tools. These metals are fused with copper to form low-melting copper-based alloys. It is the ideal technical route. Pre-alloyed powder technology is based on this principle.
According to the experimental results, the following conclusions are obtained: the wetting and diffusion connectivity of diamonds of Cr, Ti and V binary copper alloys are closely related to alloy content, diffusion atmosphere, diffusion time and operating temperature.
When the chromium content in the copper-chromium alloy is more than 0.01 at.%, the diamond is infiltrated. When the Cr content in the alloy is 0.5 at.%, the wetting angle is close to 450. When the Cr content in the Cu-Cr alloy is 0.1 at.%, the bond strength is the highest.
When the titanium content in the copper-titanium alloy is below 5 at.%, it has almost no effect on the diamond. Only when the Ti content is more than 5 at.%, the wetting angle is significantly decreased. When the Ti content is 10 at.%, the contact angle can be Reduce it to below 200.
When the V content in the copper-vanadium alloy reaches 0.01 at.%, the bond strength of the alloy to diamond peaks as high as 65 kg/mm2, and then the V content is increased, the bond strength is decreased, and when the V content is increased to 10 at.%, the bond is bonded. The strength drops to 15kg/mm2.
In summary, the concentration of Cr, Ti, and V elements in the copper alloy has a common influence on the bond strength, that is, at a certain concentration, the bond strength peaks.
4 Application characteristics of prealloyed powder
The use of a prealloyed powder as a binder for a diamond tool carcass has the following advantages.
The use of pre-alloyed powder as a binder for the diamond tool carcass makes it easy to adjust the carcass properties to make it more suitable for the object to be processed. At the same time, since the pre-alloy is pre-melted into an alloy and then made into a powder, each powder is used. Both contain various metal elements that make up the alloy, which is much more uniform than mechanically mixing multiple single metal powders.
The melting temperature of the prealloyed powder can be adjusted to the temperature required for sintering. In the process of sintering into a diamond cutter head, as long as the temperature rises to the melting temperature of the prealloyed powder, the powder of the entire bonding component is melted without being inconsistent. It is difficult to formulate a reasonable sintering temperature problem because the melting temperature difference of different components in the sintering agent is large.
The diamond tool made of pre-alloyed powder can improve the holding force of the carcass to the diamond, thereby increasing the height of the blade; the impact resistance of the diamond is increased due to the diffusion of the alloy to the diamond. The utilization rate of diamond has been improved from the above two aspects.
The pre-alloyed powder contains no volatile and easily oxidizable elemental elements, and the diamond tool made of pre-alloyed powder improves the compactness and uniformity of the carcass, thereby improving the wear state of the carcass.
The pre-alloyed powder of different properties can be selected according to the difference of the performance of the working object, which simplifies the carton compounding work.
The sintering temperature of the cutter head mainly depends on the melting point of the high melting point metal (copper, etc.) in the bonding metal. The melting temperature of the prealloyed powder is low, and the hot pressing temperature is low, which can avoid the thermal damage caused by the sintering high temperature to the diamond.
The pre-alloyed powder has a narrow melting range and can wet the diamond at a certain sintering temperature, and has a thixotropic flow behavior under pressure.
During the hot pressing process, the prealloyed powder reacts with the skeleton component to diffuse the brazed carcass, which is beneficial to enhance the mechanical properties of the carcass and does not form a low-melting brittle phase.
At the normal operating temperature of the diamond tool, the prealloyed powder does not remelt or deform, ensuring that the bonding layer can withstand the stress imparted to it by the hard particles (skeletal component and diamond) in the carcass without deformation or loosening.
5 Conclusion
(1) Add a small amount of strong carbide forming elements, such as Cr, Ti, W, Mo, etc., to the prealloyed powder. The diamond and the carcass can form carbides at the metal interface during the sintering process to achieve the diamond and the carcass. Diffusion connection.
(2) Under the action of pre-alloying, the mechanical properties of the matrix material of the carcass are improved, which is beneficial to the strengthening and improvement of the holding power of the carcass.
(3) Pre-alloyed powder can prevent premature loss and segregation of low melting point metal, which is beneficial to increase the elastic limit and yield strength of sintered products, increase the holding power of diamond, and reduce sintering temperature and holding time.
(4) Using powdered brazing filler metal as pre-alloyed powder to achieve diffusion of diamond Brazing joint is an effective way to improve the bonding force between diamond and carcass.
(Author: Zhengzhou Machinery Research Institute (Zhengzhou 450001) Zhongsu Juan, Long Weimin, Liu Wenming, Yang Jidong, Li Shengli)
In the use of diamond circular saw blades, the utilization rate of diamond is relatively low, because the diamond in the cutter head is not worn out, but is lost in a large amount in the form of shedding. The traditional diamond cutter head manufactures the diamond by the holding action of the carcass on the diamond. When the carcass is worn until the diamond is excessively exposed, the diamond will fall off by itself.
Increasing the bond strength between the carcass and the diamond is the most effective technical measure to avoid early diamond shedding. Unfortunately, diamond and carcass are difficult to connect. At present, the more effective technical measures are to plate the surface of diamond with titanium, nickel and Other metals in order to achieve effective combination of diamond and carcass.
Conventional carcass powders are composed of pure metals or simple alloys that either do not wet the diamond or have no wettability to the diamond at the sintering temperature. In the research, a conventional copper alloy is added with a metal such as chromium, titanium, vanadium, zirconium, nickel or manganese to form a prealloy, and the prealloyed powder contains an active element which is wetted by diamond, and is active during the sintering process of the diamond to the head. The element and the diamond interdiffuse to achieve a brazed connection between the carcass and the diamond.
On the one hand, the prealloyed powder can improve the wettability of the alloy to diamond, increase the edge height of the diamond, and improve the utilization rate of the diamond; on the other hand, the chemical composition of the powdered solder is more stable than that of the mechanically mixed powder, and overcomes the specific gravity of the mechanically mixed powder. Segregation, low-melting metal pre-melting and enrichment, easy oxidation and volatile, low melting point volatile metals are burned during sintering, which affect the performance of the carcass, ensuring the stability and consistency of the diamond cutter head.
1 skeleton and binder on the holding of diamond
The carcass of the synthetic diamond cutter head generally consists of two components: a skeleton component and a binder. Generally, a high melting point, high wear resistance, high strength metal is selected as the skeleton material, and a group of low melting point metals is selected as the binder.
In the selection of binders, because the commonly used low melting point metals (tin, zinc, etc.) have low strength, easy oxidation, and easy enrichment, their properties are not ideal. Silver, copper and other metals can overcome the above disadvantages, but higher melting points. Or the price limits their use.
In a mechanically mixed powder sintered carcass, the diamond present in the bit is joined to the carcass by mechanical wrapping and holding, and the connection of the diamond to the carcass is primarily a mechanical connection.
The sintered metal bond carcass has a certain density and a relatively high strength, hardness, toughness, and has a relatively strong mechanical setting effect on the diamond wrapped therein.
The bonding agent should have two basic functions: one is to connect the wear-resistant material into a mesh skeleton to hold the diamond; the other is to wear with the wear of the diamond, so that the diamond is normally edged. In addition, in addition to a certain hardness, toughness and wear resistance of the bonding agent, if the diamond has a certain wettability, the height of the diamond edge will be greatly improved, thereby improving the performance of the diamond tool.
The binder with good performance is able to form a sufficiently stable carcass under the conditions of diamond, carcass material, porosity, manufacturing and use conditions; the carcass can maintain synchronous wear or slightly ahead of the diamond when used. Wear and wear, let the diamond fully function and wear and fall off reasonably.
2 diffusion of active elements to diamond
Due to the softening and weakening of the carcass, the simple mechanical holding can not avoid the early shedding of diamond. It is always the goal of the diamond tool industry to seek the metallurgical bonding route between diamond and carcass material.
Plating the active element with a diamond surface is a viable technical solution. Active elements refer to strong carbide forming elements and transitional elements, which can react with diamond to form compounds, so that the surface of the diamond is covered with a metal that is easy to bond with the carcass metal. This layer of metal can be well matched with the tire. The body metals are brazed together.
Commonly used active elements are titanium (Ti), chromium (Cr), tungsten (W) and other elements; molybdenum (Mo), vanadium (V), zirconium (Zr), niobium (Nb), tantalum (Ta), etc. Carbonization occurs, but it is not used because of high price; other elements cobalt (Co), nickel (Ni), manganese (Mn), silicon (Si), aluminum (Al) can form carbides under certain conditions, The carbides formed are: Co2C, Ni3C, Mn3C, SiC, Al4C3, and the like.
At present, titanium plating and nickel plating are the most common in industrial applications.
Surface plating of active elements can partially solve the problem of metallurgical bonding, but it can not solve the problem of volatilization and enrichment of low melting point metals in the sintering of the carcass itself, the separation of high melting point metals, and the pre-alloyed powder binder in powder form according to the brazing principle. Solve this problem in two ways.
3 Pre-alloyed powder in the form of powdered solder
For different base binders, the added ingredients are also different. In the carcass composition, high melting point metals such as tungsten, tungsten carbide, etc. are often used to adjust the hardness and wear resistance of the carcass, and metals such as cobalt, nickel, manganese, titanium, chromium, which have good chemical wettability to diamond, are selected. Metals such as vanadium are used as bonding materials for diamonds, but the wetting temperature of diamond-impregnated metals is too high, which does not meet the process conditions of hot-press sintering of diamond tools. These metals are fused with copper to form low-melting copper-based alloys. It is the ideal technical route. Pre-alloyed powder technology is based on this principle.
According to the experimental results, the following conclusions are obtained: the wetting and diffusion connectivity of diamonds of Cr, Ti and V binary copper alloys are closely related to alloy content, diffusion atmosphere, diffusion time and operating temperature.
When the chromium content in the copper-chromium alloy is more than 0.01 at.%, the diamond is infiltrated. When the Cr content in the alloy is 0.5 at.%, the wetting angle is close to 450. When the Cr content in the Cu-Cr alloy is 0.1 at.%, the bond strength is the highest.
When the titanium content in the copper-titanium alloy is below 5 at.%, it has almost no effect on the diamond. Only when the Ti content is more than 5 at.%, the wetting angle is significantly decreased. When the Ti content is 10 at.%, the contact angle can be Reduce it to below 200.
When the V content in the copper-vanadium alloy reaches 0.01 at.%, the bond strength of the alloy to diamond peaks as high as 65 kg/mm2, and then the V content is increased, the bond strength is decreased, and when the V content is increased to 10 at.%, the bond is bonded. The strength drops to 15kg/mm2.
In summary, the concentration of Cr, Ti, and V elements in the copper alloy has a common influence on the bond strength, that is, at a certain concentration, the bond strength peaks.
4 Application characteristics of prealloyed powder
The use of a prealloyed powder as a binder for a diamond tool carcass has the following advantages.
The use of pre-alloyed powder as a binder for the diamond tool carcass makes it easy to adjust the carcass properties to make it more suitable for the object to be processed. At the same time, since the pre-alloy is pre-melted into an alloy and then made into a powder, each powder is used. Both contain various metal elements that make up the alloy, which is much more uniform than mechanically mixing multiple single metal powders.
The melting temperature of the prealloyed powder can be adjusted to the temperature required for sintering. In the process of sintering into a diamond cutter head, as long as the temperature rises to the melting temperature of the prealloyed powder, the powder of the entire bonding component is melted without being inconsistent. It is difficult to formulate a reasonable sintering temperature problem because the melting temperature difference of different components in the sintering agent is large.
The diamond tool made of pre-alloyed powder can improve the holding force of the carcass to the diamond, thereby increasing the height of the blade; the impact resistance of the diamond is increased due to the diffusion of the alloy to the diamond. The utilization rate of diamond has been improved from the above two aspects.
The pre-alloyed powder contains no volatile and easily oxidizable elemental elements, and the diamond tool made of pre-alloyed powder improves the compactness and uniformity of the carcass, thereby improving the wear state of the carcass.
The pre-alloyed powder of different properties can be selected according to the difference of the performance of the working object, which simplifies the carton compounding work.
The sintering temperature of the cutter head mainly depends on the melting point of the high melting point metal (copper, etc.) in the bonding metal. The melting temperature of the prealloyed powder is low, and the hot pressing temperature is low, which can avoid the thermal damage caused by the sintering high temperature to the diamond.
The pre-alloyed powder has a narrow melting range and can wet the diamond at a certain sintering temperature, and has a thixotropic flow behavior under pressure.
During the hot pressing process, the prealloyed powder reacts with the skeleton component to diffuse the brazed carcass, which is beneficial to enhance the mechanical properties of the carcass and does not form a low-melting brittle phase.
At the normal operating temperature of the diamond tool, the prealloyed powder does not remelt or deform, ensuring that the bonding layer can withstand the stress imparted to it by the hard particles (skeletal component and diamond) in the carcass without deformation or loosening.
5 Conclusion
(1) Add a small amount of strong carbide forming elements, such as Cr, Ti, W, Mo, etc., to the prealloyed powder. The diamond and the carcass can form carbides at the metal interface during the sintering process to achieve the diamond and the carcass. Diffusion connection.
(2) Under the action of pre-alloying, the mechanical properties of the matrix material of the carcass are improved, which is beneficial to the strengthening and improvement of the holding power of the carcass.
(3) Pre-alloyed powder can prevent premature loss and segregation of low melting point metal, which is beneficial to increase the elastic limit and yield strength of sintered products, increase the holding power of diamond, and reduce sintering temperature and holding time.
(4) Using powdered brazing filler metal as pre-alloyed powder to achieve diffusion of diamond Brazing joint is an effective way to improve the bonding force between diamond and carcass.
(Author: Zhengzhou Machinery Research Institute (Zhengzhou 450001) Zhongsu Juan, Long Weimin, Liu Wenming, Yang Jidong, Li Shengli)
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