Copper solder vacuum brazing diamond
Vacuum brazing diamond description:
Current monolayer diamond grinding tool used in the industrial USES electroplating products, mostly due to a combination of coating and metal substrate and abrasive interface does not exist solid metallurgy chemical combination, abrasive just mechanical embedding framed in coating metal, thus holding force is not big, in the high efficiency grinding load heavy homework, abrasive easily for grinding grain fall off or peeling off and cause the overall failure of coating and to increase the holding force will have to increase the coating thickness, the result of abrasive dust exposed height and the space of reduced, grinding wheel easily blocked. Abroad since the early 1990 s, the research use high temperature brazing instead of developing a new generation of electroplating monolayer diamond tool, its starting point is to use in diamond, when high temperature brazing filler metals with parent metal interface on the possibility of interactions, such as dissolution, diffusion, chemical combination, fundamentally improve (solder alloy) and substrate bond, bond strength between the three. The high-temperature brazing process can achieve the combination of diamond, bond (brazing alloy material) and chemical metallurgy on the metal matrix interface, which has high bonding strength and the exposed height of abrasive particles can be up to 70%-80%. Therefore, the brazing wheel is sharp, has large chip space, is not easy to clog, and the abrasive is more fully utilized. Under the same conditions as electroplated grinding wheel, the grinding force, power consumption and grinding temperature are lower. As the single layer high-temperature brazed diamond emery wheel has obvious technical advantages, it will become the replacement product of traditional electroplating emery wheel in the future industrial production practice, and it has the important significance of energy saving and environmental protection, and will produce huge social and economic benefits.
Diamond has very high interfacial energy with general metals and alloys, which cannot be soaked by general low melting point alloys. It was found that Al, Fe and Co can infiltrate diamond in liquid state, but they have serious erosion on diamond at the temperature of infiltration. Strong carbide such as Ti, Cr, W, Mo active element can infiltrate the diamond, but its melting temperature as high as 1600 ℃, the temperature of diamond will seriously graphitization. Therefore, it is an urgent problem to search for alloy materials with low melting point as solder, and to consider adding some active elements to improve the infiltration and affinity of diamond, so as to achieve the purpose of being able to bond diamond and meet the requirement of good mechanical properties of matrix. In this paper, copper alloy solder was used to discuss how to select low melting point solder, the specific brazing effect was discussed, and the microstructure of bonding surface was analyzed by means of modern physical and chemical analysis, so as to verify the combination of solder and diamond.
2 test conditions and process
The base material is 45 steel and the alloy is Cu2Sn2Ti. Two series A and B are used in the mixing ratio of solder. Then, five points were used to change the proportion of titanium based on A and B alloys from 5% to 15%. The diamond in brazing has no coating film and the particle size is 45/50 mesh. The steel matrix and diamond surface were treated before brazing. Soldering test in vacuum condition, brazing temperature 30 ℃ higher than the melting point, heat preservation after a certain period of time, along with the furnace cooling to room temperature.
Test and analysis methods: SEM and energy spectrum were performed on Japanese electron JSM25610LV tungsten filament electron microscopy; Strength test was carried out on the microcomputer controlled electronic universal testing machine (wdw-e100) of jinan gold group co., LTD. The solder smelting is conducted in a vacuum non-consumable electric arc furnace.
3. Brazing results and analysis
2.1 interface analysis between diamond and Cu2Sn2Ti alloys
Figure 2 shows the SEM and BSE morphology of the bonding of Cu2Sn2Ti alloy with diamond after vacuum brazing. It can be seen from figure 1 that the edge of diamond is covered by a lot of white crescent alloy. Obviously, Cu2Sn2Ti alloy shows good infiltration to diamond abrasive particles, which indicates that the wetting reaction between diamond abrasive and molten solder occurs. It can be seen from the figure that the height of diamond exposure is relatively ideal. If the solder layer reaches a certain thickness, the whole diamond abrasive will be wrapped up by the solder due to the effect of capillary action. However, it is impossible to determine whether there is a chemical metallurgical reaction between diamond and Cu2Sn2Ti alloy based on morphology. In addition, the crystal shape of diamond abrasive grains remained intact after brazing. No crack with heating damage.
Figure 1. SEM and BSE images of Cu2Sn2Ti welding
Table 1 shows the results of the energy spectrum analysis of the alloy composition on the surface of diamond. The Ti element concentration in the metal on the surface of the diamond was significantly higher than that of the solder, indicating that the Ti element in the solder was diffused from the solder to the diamond surface under the effect of brazing temperature, and combined with the element in the diamond to form carbide.
Table 1 diamond surface composition distribution of Cu2Sn2Ti alloy (wt%)
In order to further prove the existence of carbide, X-ray diffraction analysis was applied to diamond abrasive particles after brazing, and the existence form of new compounds at the welding interface between diamond and filler was determined. Figure 2 shows the X-ray diffraction results at the brazing interface. The compounds of Ti include TiC, SnTi2C, TiCu and Cu2SnTi, and the formation of metallurgical connection between filler and diamond is mainly caused by the formation of new compounds TiC and SnTi2C, which are formed by the combination of Ti in filler and C of diamond. It is the formation of TiC and SnTi2C that reduces the interfacial tension between diamond and solder and relatively improves the wettability of solder.
Figure 2 X-ray diffraction analysis results
Function of solder and steel matrix
In order to understand the microstructure of the solder and the combination of the solder and steel matrix in the process of brazing diamond, the energy spectrum scanning analysis of the brazed diamond sample is shown in FIG. 3. At the interface of the two, Ti elements are enriched, while the concentration gradients of Cu and Sn at the interface show a slow transition trend. In the process of brazing filler metals with the steel substrate in the brazing temperature mutual diffusion between components, forming a solid phase diffusion zone, when the composition of solid phase diffusion zone close to the eutectic composition liquid would appear, then solder melted together with the steel substrate on the interface, in the subsequent cooling process, the solder and the steel substrate raw crystallization, formation of solid solution and its compounds, so as to realize the high strength of solder and the steel substrate.
FIG. 3 solder and steel matrix wire scan after brazing
2.3 brazing process
Pressure shear strength experiment: under the condition of vacuum, in the process of brazing temperature 10 ℃ / min, heat preservation time to 20 min, and then with furnace cooling. After brazing, it was tested in the way shown in figure 4, and the falling speed of the pressure head was 1mm/min. The strength test results are shown in table 2.
Table 2 relation of filler strength
FIG. 4 strength test method
The strength of the solder alloy increased with the increase of titanium content increase, in the process of test, the fracture occurred in the chip in the solder joint surface, part of the fracture distribution in the solder surface after a layer of small diamond, here in diamond for polycrystalline diamond fine powder, that is to say, the fracture occurred in in polycrystalline diamond fine powder and filling material, in the actual production and use process, solder strength may be greater than the current test results.
Cu-sn-ti alloy is an ideal binder, and the liquid phase alloy is completely wetted to diamond at high temperature. Sufficient cementation force for diamond; Furthermore, Ti can react with C to form TiC, and the alloy forms metallurgical bond with diamond.
(1) alloy solder brazing with Ti containing strong carbide forming element is adopted to weld single layer of diamond. The solder has good penetration property to diamond, and the carbide forming element is offset on the surface of diamond, which enables the metallurgical bonding between diamond and solder and matrix, and improves the matrix's control on diamond.
(2) after brazing, copper base solder can be combined with steel matrix to achieve high strength.
(3) the B5 best soldering process is 880 ℃ ~ 900 ℃, 10 min ~ 15 min can meet the process requirements.