Investigations of crystal habit, micro-topographic imaging, micro-composition and micro-structural analysis of HPHT synthetic diamonds from the Fe-C(H) system indicate that most of them have an oc-tahedral habit. The ...Investigations of crystal habit, micro-topographic imaging, micro-composition and micro-structural analysis of HPHT synthetic diamonds from the Fe-C(H) system indicate that most of them have an oc-tahedral habit. The crystals grow mainly layer-to-layer from center to periphery. HPHT synthetic dia-mond is smaller in size than natural diamond because it only goes through nucleation and growth in the early stage. In the middle and late stages, due to the coalescence of diamond grains related to dif-ferences of surface energy, the growth of HPHT synthetic diamond is limited. The active energy (E) of transforming single nitrogen into a nitrogen-pair is lowered and the time of transforming single nitro-gen into a nitrogen-pair is shortened because of the existence of hydrogen. Therefore, aggregate ni-trogen (A-centers) may exist in synthetic diamond from HPHT and explosive detonation processes. It needs further discussion on a worldwide view that the time of natural diamond formation extracted from nitrogen aggregation is some hundred million years. Consideration of the way in which surface energy influences the growth of diamond can help to understand some of the remaining issues (e.g. growth mechanism, etc.) in the HPHT synthetic process and effectively explain the formation of natural diamond in terms of HPHT thermodynamic theory. Especially, it is important to pay more attention to the influence of hydrogen on surface energy in that hydrogen may be a "bridge" for explaining the formation of HPHT synthetic and natural diamond.展开更多
A growth-type polycrystalline diamond compact （PDC） was synthesized under high temperature and high pressure （HPHT）. The infiltration technique was used with an Fe55Ni29Co16 （KOV） alloy as the sintering solvent....A growth-type polycrystalline diamond compact （PDC） was synthesized under high temperature and high pressure （HPHT）. The infiltration technique was used with an Fe55Ni29Co16 （KOV） alloy as the sintering solvent. The morphology and weight ra- tio of the PDC were investigated through scanning electron microscopy （SEM） and electron dispersion spectroscopy （EDS）. Note that the KOV alloy evenly infiltrated throughout the polycrystalline diamond （PCD） layer and WC-Co substrate in a short sintering time due to its low viscosity and high soakage capability. A transition layer confirmed the presence of the M^C phase near the interface of the PDC, which can make the diamond layer and WC-Co substrate combine as a complex material. X-ray diffraction （XRD） performed on the PCD layer confirmed the presence of cubic diamond, WC, cubic CoCx, the high tempera- ture cubic phase of c^-Co, the alloy phase of FeNix, and no graphite phase. Besides, a surface residual stress of the PCD layer, measured with reasonable accuracy using micro-Raman spectroscopy, is found to be a homogeneous compressive stress with an average value of 0.16 GPa, much lower than that of the powders-mixing method.展开更多
High quality grown polycrystalline diamond compact (PDC) with low residual stress was prepared using the infiltration method with nickel based alloys as the solvent under high temperature and high pressure (HPHT). Sca...High quality grown polycrystalline diamond compact (PDC) with low residual stress was prepared using the infiltration method with nickel based alloys as the solvent under high temperature and high pressure (HPHT). Scanning electron microscopy (SEM) was used to observe the micro morphology of the diamond layer and the diamond/WC substrate interface. It was found that dense and interlaced microstructure with diamond-diamond (D-D) direct bonding formed in the diamond layer of PDC. Micro-Raman spectroscopy was used to measure the Raman shift of diamonds in the polycrystalline diamond (PCD) layer and the residual stress was calculated based on the Raman shift of diamonds. Experimental results show that the residual stress of PCD layer is compressive stress, and the range of the residual stress is from 0.075 to 0.250 GPa in the whole PCD layer, much lower than that of other reports (up to 1.400 GPa). Moreover, the distribution of the residual stress from the diamond surface layer to the inner cross-section is homogeneous.展开更多
The growth of coarse grains of diamond was observed with graphite as carbon source and Fe80Ni20 alloy powder as catalyst at HPHT in a China-type SPD 6×1670T cubic high-pressure apparatus with highly exact control...The growth of coarse grains of diamond was observed with graphite as carbon source and Fe80Ni20 alloy powder as catalyst at HPHT in a China-type SPD 6×1670T cubic high-pressure apparatus with highly exact control system. To synthesize coarse grains of diamond crystal with high quality,ad-vanced indirect heat assembly,powder catalyst technology and catalyst with optimal granularity were used. Especially the nucleation of diamond and the growth rate were strictly controlled by the opti-mized synthesis craft. At last,diamond crystals (about 0.85 mm) in the perfect hex-octahedron shape were successfully synthesized at ～5.4 GPa and ～1360℃ in 60 min. The characteristic of crystal growth with powder catalyst technology under HPHT was discussed. The results and techniques might be useful for production of coarse grains of diamond.展开更多
基金the National Natural Science Foundation of China (Grant No. 40502007)
文摘Investigations of crystal habit, micro-topographic imaging, micro-composition and micro-structural analysis of HPHT synthetic diamonds from the Fe-C(H) system indicate that most of them have an oc-tahedral habit. The crystals grow mainly layer-to-layer from center to periphery. HPHT synthetic dia-mond is smaller in size than natural diamond because it only goes through nucleation and growth in the early stage. In the middle and late stages, due to the coalescence of diamond grains related to dif-ferences of surface energy, the growth of HPHT synthetic diamond is limited. The active energy (E) of transforming single nitrogen into a nitrogen-pair is lowered and the time of transforming single nitro-gen into a nitrogen-pair is shortened because of the existence of hydrogen. Therefore, aggregate ni-trogen (A-centers) may exist in synthetic diamond from HPHT and explosive detonation processes. It needs further discussion on a worldwide view that the time of natural diamond formation extracted from nitrogen aggregation is some hundred million years. Consideration of the way in which surface energy influences the growth of diamond can help to understand some of the remaining issues (e.g. growth mechanism, etc.) in the HPHT synthetic process and effectively explain the formation of natural diamond in terms of HPHT thermodynamic theory. Especially, it is important to pay more attention to the influence of hydrogen on surface energy in that hydrogen may be a "bridge" for explaining the formation of HPHT synthetic and natural diamond.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50801030 and 50731006)the Open Project of State Key Laboratory of Superhard Materials of Jilin University (Grant No.201201)
文摘A growth-type polycrystalline diamond compact （PDC） was synthesized under high temperature and high pressure （HPHT）. The infiltration technique was used with an Fe55Ni29Co16 （KOV） alloy as the sintering solvent. The morphology and weight ra- tio of the PDC were investigated through scanning electron microscopy （SEM） and electron dispersion spectroscopy （EDS）. Note that the KOV alloy evenly infiltrated throughout the polycrystalline diamond （PCD） layer and WC-Co substrate in a short sintering time due to its low viscosity and high soakage capability. A transition layer confirmed the presence of the M^C phase near the interface of the PDC, which can make the diamond layer and WC-Co substrate combine as a complex material. X-ray diffraction （XRD） performed on the PCD layer confirmed the presence of cubic diamond, WC, cubic CoCx, the high tempera- ture cubic phase of c^-Co, the alloy phase of FeNix, and no graphite phase. Besides, a surface residual stress of the PCD layer, measured with reasonable accuracy using micro-Raman spectroscopy, is found to be a homogeneous compressive stress with an average value of 0.16 GPa, much lower than that of the powders-mixing method.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50572032 and 50731006)
文摘High quality grown polycrystalline diamond compact (PDC) with low residual stress was prepared using the infiltration method with nickel based alloys as the solvent under high temperature and high pressure (HPHT). Scanning electron microscopy (SEM) was used to observe the micro morphology of the diamond layer and the diamond/WC substrate interface. It was found that dense and interlaced microstructure with diamond-diamond (D-D) direct bonding formed in the diamond layer of PDC. Micro-Raman spectroscopy was used to measure the Raman shift of diamonds in the polycrystalline diamond (PCD) layer and the residual stress was calculated based on the Raman shift of diamonds. Experimental results show that the residual stress of PCD layer is compressive stress, and the range of the residual stress is from 0.075 to 0.250 GPa in the whole PCD layer, much lower than that of other reports (up to 1.400 GPa). Moreover, the distribution of the residual stress from the diamond surface layer to the inner cross-section is homogeneous.
基金Supported by the National Natural Science Foundation of China (Grant No.50572032)
文摘The growth of coarse grains of diamond was observed with graphite as carbon source and Fe80Ni20 alloy powder as catalyst at HPHT in a China-type SPD 6×1670T cubic high-pressure apparatus with highly exact control system. To synthesize coarse grains of diamond crystal with high quality,ad-vanced indirect heat assembly,powder catalyst technology and catalyst with optimal granularity were used. Especially the nucleation of diamond and the growth rate were strictly controlled by the opti-mized synthesis craft. At last,diamond crystals (about 0.85 mm) in the perfect hex-octahedron shape were successfully synthesized at ～5.4 GPa and ～1360℃ in 60 min. The characteristic of crystal growth with powder catalyst technology under HPHT was discussed. The results and techniques might be useful for production of coarse grains of diamond.
