金刚石与磨料磨具工程

Sintering super-strong micro-grained polycrystallinediamond compacts under ultrahigh pressure

LIU Jin, HE Duanwei

2018, 38(6): 1-6. doi: 10.13394/j.cnki.jgszz.2018.6.0001

Abstract(152)

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Abstract:
Using micro-grained diamond powder as starting material, centimeter-sized super-strong micro-grained polycrystalline diamond (MPD) compacts have been prepared under about 15 GPa with a lab-designed two-stage 6-8 type multi-anvil large volume high pressure apparatus. The polycrystalline bulk is composed of micron diamond particles with nano-substructure induced by work hardening under high pressure. The Vickers hardness of the MPD bulk can reach the top limit of the single crystal diamond (about 120 GPa). The fracture toughness of MPD sample is as high as 18.7 MPa·m^1/2, which is similar to that of high performance tungsten carbide material.

Preparing and characterizing ultrafine diamond coated with titanium dioxide

ZHAO Yucheng, LI Yapeng, YAN Ning, WANG Mingzhi, ZOU Qin, MIAO Weipeng

2018, 38(6): 7-12. doi: 10.13394/j.cnki.jgszz.2018.6.0002

Abstract(180)

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Abstract:
Using polyvinylpyrrolidone (PVP) as a coupling agent, tetrabutyl orthotitanate (TBOT) as the precursor of titanium dioxide, and ammonia as catalyst, the ultrafine diamond coated with titanium dioxide (UFD@TiO₂) with core-shell structure was prepared by Stöber method. The influences of the pH value of the solution and the additions of ammonia and deionized water on the formation of UFD@TiO₂ were studied. The phase composition, microphotograph and oxidation resistance of UFD@TiO₂ were characterized by XRD, SEM and DSC-TG. The flexural strength of specimens of UFD-vitrified bond and UFD@TiO₂-vitrified bond was tested by three point bending method. The fracture micro-morphologies of vitrified bond specimens were observed by SEM. Results showed that when the pH value was approximately 8 and the volume fractions of ammonia and deionized water were both 0.8%, TiO₂ was heterogeneously nucleated on the surface of diamond with TBOT hydrolysis, evenly forming a dense layer of TiO₂ film. The initial oxidation temperature of UFD@TiO₂ was 650℃, which was 67℃ higher than that of the UFD. The flexural strength of UFD@TiO₂-vitrified bond specimen was 20.9% higher than that of UFD-vitrified bond specimens.

New composite grinding wheel for rail grinding and experiments

ZHANG Yiquan, XIAO Bing, YAN Xinlin, LIU Sixing, WU Hengheng, XIAO Haozhong, DOU Liyun

2018, 38(6): 13-18. doi: 10.13394/j.cnki.jgszz.2018.6.0003

Abstract(172)

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Abstract:
A new composite grinding wheel for rail grinding was developed by brazing technology and traditional hot pressing technology. The composite grinding wheel contained not only the components of traditional resin grinding wheel but also metal bonded diamond inserts.The new type of grinding wheel was used in the rail grinding test machine to compare with the traditional resin grinding wheel for workpiece grinding.The changes of grinding temperature and surface roughness after workpiece grinding were analyzed, and the grinding debris after rail grinding was analyzed by SEM and EDS.The results show that compared with the pure resin grinding wheel, the peak grinding temperature of the workpiece ground with the new composite grinding wheel decreases by about 10%, and the more inserts in the grinding wheel, the larger the proportion of the decrease.The surface roughness of the workpiece decreases by more than 9% and increases with the increase of inserts in the grinding wheel. At the same time, the proportion of spherical debris is lower, and the atomic mass fraction of O element in the spherical debris is smaller.

Improving strength and toughness of vitrified bond by adding nano-rare earth oxides

TAN Qiuhong, ZHAO Yucheng, WANG Mingzhi, ZOU Qin

2018, 38(6): 19-24. doi: 10.13394/j.cnki.jgszz.2018.6.0004

Abstract(259)

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Abstract:
To improve the strength and toughness of vitrified bond in CBN grinding wheel, composite bonds are prepared by adding different fractions of nano-sized CeO₂, Sm₂O₃, Y₂O₃, La₂O₃ or Er₂O₃ as additives. X-ray diffractor (XRD) and scanning electron microscope (SEM) are used to analyze their phases and micro structures, and three-point bending test and single-edge notched beam test to indicate their mechanical properties. Results show that the flexural strengths of samples with 2vol% Ce₂O or Er₂O₃ are 187 MPa and 194 MPa, respectively, which are 13.3% and 17.6% higher than 165 MPa of basic bond, while the other oxides could not improve the strength. On the other hand, all the five oxides could improve the fracture toughness and Er₂O₃ does the best by 2.7 MPa·m^1/2 at 2.5vol%, i.e. 108.2% higher than 1.3 MPa·m^1/2 of the basic bond. The composite bond with 2vol% nano-Er₂O₃ and CBN grains (concentration 200%) are used to prepare test samples, which possess good bonding between bond and grain and flexural strength of 102 MPa.

Preparing low-temperature vitrified bond composite sintered body withnano-diamond by polyacrylamide-gel method

YIN Xiang, LI Yapeng, LIU Wei, LIU Yibo, ZHAO Yucheng, WANG Mingzhi

2018, 38(6): 25-30. doi: 10.13394/j.cnki.jgszz.2018.6.0005

Abstract(230)

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Abstract:
Low-temperature vitrified bond composite sintered body with nano-diamonds (ND) are prepared by polyacrylamind-gel method. The samples with different diamond contents are made to test the uniformity of ND@SiO₂ dispersed in the vitrified bond. Then the micro structure, phase composition, bending strength and porosity of sintered body are analyzed and compared. Results show that when the diamond concentration increases from 25% to 100%, the ND@SiO₂ are uniformly dispersed and there is no obvious agglomeration in the gel. The sintering temperature of ND@SiO₂-vitrified bond ranges from 670 to 720℃, then bending strength of which is 66.4 to 87.6 MPa with the porosity of 10.2% to 22.4%.

Influence of Cu mass fraction on properties of Fe-Ni-Mn based binder

TAO Hongliang, ZHOU Haojun, WEN Ping, LI Guangfeng

2018, 38(6): 31-34. doi: 10.13394/j.cnki.jgszz.2018.6.0006

Abstract(149)

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Abstract:
Fe-Ni-Mn based binder was prepared by powder metallurgy. The effects of different mass fraction of copper on the properties of Fe-Ni-Mn based binder were studied by electronic universal testing machine and impact testing machine. Results show that under the conditions of sintering temperature 850 to 880℃, pure-Co binder reaches its maximum forming density, which is 8.75 g/cm³ and that under the same condition, the impact strengths of different brand Co binders are at their tops, namely 18.92 kJ/m² and 17.32 kJ/m². It is also found that when Cu content is 15wt% to 20wt%, the Fe-Ni-Mn based binder has better mechanical property with maximum bending strength of 1 202.19 MPa, 75% of that of pure-Co binder, and maximum impact strength of 9.73 kJ/m², 65.7% of that of pure-Co binder. In addition, increase of Cu content will promote a high-strength alloy to form inside the Fe-Ni-Mn based binder, thus quickly increasing the toughness of the matrix.

Study on ultra-fine iron and copper powder used in diamond core drill bits

ZHANG Xuhong, WANG Chengjun, HU Weili, LI Zhonglin

2018, 38(6): 35-38. doi: 10.13394/j.cnki.jgszz.2018.6.0007

Abstract(170)

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Abstract:
In the Fe-Cu and Fe-Cu-Ni matrices, the influence mechanism of adding ultrafine powders (Fe and Cu) on their sintering hardness, stress-strain curve and sintering interface morphology was investigated, and its effect on the performance of diamond core drill bits was studied. Results show that the hardness of the two sintered body can be increased by 6.25% and 12.20% respectively when ultrafine metal powders are applied to Fe-Cu, Fe-Cu-Ni matrix. The service life of the two bits is increased by 21.6% and 82.5% respectively, and the cutting speed of the two bits is slowed by 4.5% and 16.2% respectively. The wear surfaces on the top edges of the bits are fine and smooth, and the friction coefficients between bits and drilling material are. However, the Fe-Cu-Ni matrix prepared by adding ultrafine metal powders has strong wear resistance, which results in significant height decrease of exposed diamonds at the cutting edges.

Effect of single size diamond on drilling performance of the Fe-Cu-based bit

PAN Xiaoyi, XIE Delong, LIN Feng, XIAO Leyin, CHEN Chao

2018, 38(6): 39-43. doi: 10.13394/j.cnki.jgszz.2018.6.0008

Abstract(204)

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The effects of diamond particle size and concentration on drilling performance and mechanical properties of Fe-Cu matrix bits were studied by using diamonds of the same concentration but different particle size, or the same particle size but different concentration in Fe-Cu matrix formula. Results show that the diamond bit with particle size of 40/45 and concentration of 50% has the best drilling performance by using granite at Fe-Cu formula, which is bit wear ratio of 9000 and drilling efficiency of 1.1 mm/s.

Effect of alumina hollow spheres on bits drilling into hard and compact rock

YE Hongyu, YANG Zhan, TAN Songcheng, XIE Tao, ZHANG Jianwei

2018, 38(6): 44-47. doi: 10.13394/j.cnki.jgszz.2018.6.0009

Abstract(147)

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Abstract:
Based on the rock breaking principle, the performance of bits which are used to drill into hard and compact rock is analyzed and studied. The composition and performance of prealloyed powder matrix and the hot pressing process parameters are designed. On this basis, it is proposed to use alumina hollow spheres to weaken the matrix. Tests are implemented by using alumina hollow spheres with 0.3 mm, 0.6 mm and 0.9 mm particle size and 12%, 15% and 18% volume fraction. It is found that the wear resistance of matrices is decreased by 9% to 31%, respectively. In conclusion, the decrease of matrix wear resistance could be decreased by 31.25% when the particle size of alumina hollow spheres is 0.3 mm and its volume fraction is 18%.

Experiment on grinding performance of high-density aramid honeycombs

WANG Yidan, KANG Renke, BAI Dujuan, MA Yixin, DONG Zhigang, SHI Yaohui

2018, 38(6): 48-53. doi: 10.13394/j.cnki.jgszz.2018.6.0010

Abstract(172)

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High-density aramid paper honeycomb consists of high toughness aramid fibers and a high-content of brittle resin, and it is commonly used in the aerospace industry as weight-reducing composite material. High-density honeycomb is difficult to process after molding. In order to meet the processing requirements of material after forming, according to the composition and structural characteristics of the material, we carried out grinding process experiments on high density honeycombs with diamond grinding wheels, and summarized that there are three typical processing features of high density honeycombs after the grinding process, namely the double-layer honeycomb paper widening topography, the unseparated chip topography and the fiber pull-out morphology. The influences of grinding speed, feed speed and cutting depth on surface morphology were studied by single factor test method. The results show that different process parameters have different effects on the morphology of high density honeycomb. When the grinding speed is increased from 5.2 m/s to 20.9 m/s, the three characteristic morphologies are improved. When the feed speed is increased from 50 mm/min to 350 mm/min, the number of fibers pull-out increase, and when the cutting depth is increased from 0.1 mm to 0.9 mm, the width of the unseparated chips become large.

Influence of slurry on lapping SiC workpiece by using fixed abrasives

JIN Zhenhong, ZHU Yongwei, MO Honglei, WANG Zikun

2018, 38(6): 54-60. doi: 10.13394/j.cnki.jgszz.2018.6.0011

Abstract(158)

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Abstract:
For efficient and stable machining the SiC workpiece, slurries containing SiC particles are used to assist precision lapping SiC with hydrophilic fixed abrasive pad. Experiments are conducted to compare the difference of slurry-assisted lapping and traditional lapping, as well as the influence of the size and concentration of SiC particles in the slurry on the material removal rate and surface of SiC workpiece after precision lapping. The swelling rate and wear rate of pad matrix are tested and calculated, thus exploring the mechanism of SiC slurry. The results show that when adding SiC sized 3-5 μm with mass fraction 3% in to the slurry, the average material removal rate of precision lapping is 1.424 6 μm/min with surface roughness of workpiece 84.6 nm, while the rate and roughness of traditional lapping are 0.040 0 μm/min and 61.4 nm, respectively. In conclusion, adding SiC particles could enhance the self-dressing of the pad. As the size and concentration of SiC particles increase, the self-dressing effect is enhanced, resulting in higher material removal rate but slightly poorer surface quality.

Polishing performance of annular magnetorheological finishing head

WANG Zhongxi, ZHU Yongwei, ZHANG Long

2018, 38(6): 61-68. doi: 10.13394/j.cnki.jgszz.2018.6.0012

Abstract(197)

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The processing efficiency of the hemispherical shell resonator (HSR) is the main factor affecting the application of the hemispherical resonator gyroscope (HRG). Based on the annular magnetorheological finishing method, a simplified planar toroidal polishing head was adopted to estimate its machining performance. The effect of several factors on polishing performance was explored through single factor test and orthogonal test, namely magnetic field intensity, polishing head rotation speed, gap between workpiece and polishing head, and abrasive size. Results show that when polishing fused quartz glass at strong magnetic field intensity, polishing head rotation speed of 350 r/min, gap of 0.6 mm, and diamond size of 0.5 to 1.0 μm, the material removal rate reaches 191.2 nm/min and the average surface roughness R_a is 3.31 nm, thus exhibiting excellent processing properties.

Chemical-mechanically polishing large areafree-standing CVD diamond films

ZHANG Pingwei, TONG Tingting, CAI Yunhong

2018, 38(6): 69-72. doi: Code:10.13394/j.cnki.jgszz.2018.6.0013

Abstract(195)

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Chemical mechanical polishing is used to polish large area free-standing CVD diamond films with diameters of 66 mm. The influence of polishing plates (iron plate, asphalt plate and soft cushion) and oxidizing agents (K₂S₂O₈ and K₂FeO₄) on polishing results are investigated. Profilometer (tip radius 5 μm), optical microscope and Raman spectroscopy are used to evaluate the polishing effects of the CVD diamond films. Results show that the material removal rate of iron plate is the highest, while the surface polished by soft cushion is the most uniform with roughness of 2 nm. It is also found that the most effective oxidizing agent is K₂FeO₄. In conclusion, the optimum polishing conditions are soft cushion and K₂FeO₄.

Simulation and verification of burr sectional area during single-grit abrasive reaming

HUANG Jianzhong, YANG Changyong, GAO Shaowu, XU Jiuhua

2018, 38(6): 73-79. doi: 10.13394/j.cnki.jgszz.2018.6.0014

Abstract(115)

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A single-grit micro-cutting model is established and the burr formation process during abrasive reaming is analyzed. Side burr sectional area is taken as the evaluation index of burr size. The influences of cutting depth, cutting width and cutting edge inclination angle on burr formation are studied. The accuracy of the model is verified by experiments. The results show that plastic deformation is the important factor affecting burr formation. With larger plastic deformation, the burr sectional area is larger. Side burr sectional area increases with the raise of cutting depth and cutting width. With the change of cutting edge inclination angle from negative to positive, the amount of plastic deformation increases and the direction of material flow changes, and then the burr size grows.

Surface residual stress measurement of silicon carbidebased on fast surface detection method

YAN Shuai, LIN Bin, CHEN Jingyue

2018, 38(6): 80-85. doi: 10.13394/j.cnki.jgszz.2018.6.0015

Abstract(168)

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Abstract:
One-dimensional X-ray diffraction method is usually used to measure the residual stress on the surface of ceramics after processing. There are some problems in the measurement process, such as tedious, inefficient and high cost. Therefore, a new fast two-dimensional X-ray diffraction residual stress measurement method is used to measure the residual stress on the surface of silicon carbide ceramics. In the experiment, the residual stress on the initial surface and polished surface of three different brands of silicon carbide workpieces are measured. The results show that the new method can obtain the diffraction information of 500 points in a single measurement, which is especially suitable for the stress measurement of ceramic materials. It is also found that for the residual compressive stress of the machined surface, polishing can eliminate up to 80% of the residual stress, but can not change the residual stress distribution of the workpiece.

Development of special generator for ultrasonic assisted grinding

ZHENG Weishuai, KANG Renke, LIU Jinting, ZHAO Fan, DONG Zhigang

2018, 38(6): 86-91. doi: 10.13394/j.cnki.jgszz.2018.6.0016

Abstract(149)

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Ultrasonic assisted grinding has special requirements on its generator, such as stable and high frequency output and rapid response to real-time tracing. To solve the problems of low working frequency, low output power and slow tracing speed of traditional generator, a new type of generator for ultrasonic system is designed using STM32 controller and DDS (direct digital synthesize) technology. An automatic frequency-tracing method based on fuzzy PID (proportion, integral, differential) controller is proposed, which works fast and accurate. The electrical performance test on the generator and the verification test on ultrasonic assisting grinding system are carried out. It can be concluded that the developed special generator runs well in the ultrasonic assisted grinding of hard-to-machine materials.

2018 Vol. 38, No. 6

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