Polycrystalline diamond compacts（PDC）, which are composed of diamond and WC/Co substrate, and synthesized at high pressure and high temperature（HPHT）, are widely applied as the tooth of drilling bit. However, the ...Polycrystalline diamond compacts（PDC）, which are composed of diamond and WC/Co substrate, and synthesized at high pressure and high temperature（HPHT）, are widely applied as the tooth of drilling bit. However, the thermal stability of PDC will be reduced when diamond transforms into graphite due to cobalt in PDC acting as a catalyst during the drilling work. In this study, a new three-layer structured PDC with enhanced thermal stability has been successfully synthesized at pressures of 5.5–7.0 GPa and temperatures of 1650–1750？C. In this structure, the diamond-Si C composite acts as the working layer,and the diamond-Si C-Co composite and WC/Co cements are as the intermediate layer and substrate,respectively. It is found that the initial oxidizing temperature of the three-layered PDC is enhanced up to820？C, which is significantly higher than that（～780？C） of the conventional PDC counterpart.展开更多
Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the invest...Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the investigated powder Distaloy AE were determined as functions of relative density through typical mechanical property tests of powder. The model was implemented as a user subroutine USDFLD. Single sided compaction of a d20 ram^5 mm disk green compact of Distaloy AE was simulated, and the residual stress of the disk after ejection was predicted with FEA. The FEA results of the compaction process and the residual stress of the disk show good agreement with compaction experiments and X-ray diffraction measurements, which validates the model and its parameters. The results indicate that the compressive residual stresses exist mainly in a thin layer on the side surface, but the residual stresses are very small on the top and bottom surfaces.展开更多
Porous sintered Ti-Ag compacts with different Ag content were fabricated by powder metallurgy. The associated hydrothermal treatment and the effect on the apatite formation were studied. The results suggested that TiO...Porous sintered Ti-Ag compacts with different Ag content were fabricated by powder metallurgy. The associated hydrothermal treatment and the effect on the apatite formation were studied. The results suggested that TiO was generated under the condition of low vacuum （1 ×10^-2 Pa） during the process of burning out the spacer-holding particles. After hydrothermal treatment, a sub-microscale porous layer was formed at the pore wall surface of the samples. The apatite-inducing ability of hydrothermal treated porous sintered Ti-Ag compacts with different Ag content was evaluated in modified simulated body fluid （SBF）. And the results proved that there is a clear correlation between the apatite-inducing ability and Ag content. The higher Ag content in porous leads to the decrease of Na＋ ions and basic hydroxyl （OH）b amount, resulting in the decline of apatite-inducing ability in the first stage. However, their apatite-inducing ability was not significantly different from that of Ti after two weeks SBF immersing. Hence, the ionic activity should restore with the processing of SBF soaking, as the saturation of Ag effect.展开更多
Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure ...Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM). The TRS on the surface of polycrystalline diamond(PCD) table was obtained,which can be used to calculate the radial thermal residual stress(RTRS) at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.展开更多
为生产高性能的电机铁芯,软磁复合材料(Soft Magnetic Composite,SMC)通常以高纯高压缩性铁粉为原料,如果能用较低纯度铁粉取代高纯铁粉,将使生产成本大大降低。本文以3种不同纯度铁粉为原材料,通过在不同工艺条件下压坯密度及表面显微...为生产高性能的电机铁芯,软磁复合材料(Soft Magnetic Composite,SMC)通常以高纯高压缩性铁粉为原料,如果能用较低纯度铁粉取代高纯铁粉,将使生产成本大大降低。本文以3种不同纯度铁粉为原材料,通过在不同工艺条件下压坯密度及表面显微硬度的变化,来表征铁粉纯度对压坯密实程度及加工硬化程度的影响。结果表明:铁粉纯度、杂质元素种类及含量、铁粉颗粒形貌均影响粉末压坯密度。较低纯度铁粉的压坯在500℃氮气中退火30 min,硬度迅速降低30%;而相同条件下高纯铁粉的压坯表面硬度基本不变。当热处理温度达到再结晶温度时,再结晶过程可使硬度降低近50%。展开更多
Aluminium-alumina compacts with varying wt% of alumina were compacted in the pressure range of 115 - 290 MPa. Compacts prepared at 290 MPa pressure, were sintered in an argon atmosphere at 573, 673, 773 and 873 K for ...Aluminium-alumina compacts with varying wt% of alumina were compacted in the pressure range of 115 - 290 MPa. Compacts prepared at 290 MPa pressure, were sintered in an argon atmosphere at 573, 673, 773 and 873 K for 1 hour. The green density, % porosity, % spring back and hardness of the green compacts were determined. Scanning Electron Microscopy was carried out to observe the morphology of pores and alumina particles in green and sintered compacts. The present study indicates that, densification of the compact increases with increasing compacting pressure and decreases with increasing alumina content. Maximum density achieved is 93% for pure aluminium compacts and decreases to 85% for Al-20 wt% alumina compacts. Grain growth of aluminium particles is noticed in the compacts after sintering at 773 and 873 K. Dispersion of fine alumina particle in the aluminium matrix occurs predominantly in the compact when sintered at 773 K which results in increase in hardness value.展开更多
To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM...To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM process. A comparison between the requirements of flowability and moldability and the compacts shape retention has been made in this work. There is often a contradiction between the requirements of flowability and the compacts shape retention. Many works have been done to attain good molding conditions. However, they fail to take into account the effect of some factors that satisfies good molding conditions on the compacts shape retention during debinding. This paper studies the effect of the powder-binder mixture characteristics and the molding conditions on the flowability and moldability and the shape retention of PIM compacts during debinding process so as to attain the benefits of each.展开更多
Numerical simulation of hot-press sintering of nano-sized ceramic powders was introduced by the commercial finite element code MSC.MARC. The powder plastic model and the thermo-mechanical coupled quadrilateral element...Numerical simulation of hot-press sintering of nano-sized ceramic powders was introduced by the commercial finite element code MSC.MARC. The powder plastic model and the thermo-mechanical coupled quadrilateral element were developed and adopted in the simulation. The mechanical and thermal properties of the nano-sized alumina based powders were determined.In addition, the experimental research and numerical simulation of the sintering process of different initial densities were carried out. The stress state in sintering of green compacts with different initial densities was analyzed by the densification theory.The reason for the density fluctuations of as-sintered ceramic bulks was found out.展开更多
基金financial supports from the National Natural Science Foundation of China (No. 41572357)
文摘Polycrystalline diamond compacts（PDC）, which are composed of diamond and WC/Co substrate, and synthesized at high pressure and high temperature（HPHT）, are widely applied as the tooth of drilling bit. However, the thermal stability of PDC will be reduced when diamond transforms into graphite due to cobalt in PDC acting as a catalyst during the drilling work. In this study, a new three-layer structured PDC with enhanced thermal stability has been successfully synthesized at pressures of 5.5–7.0 GPa and temperatures of 1650–1750？C. In this structure, the diamond-Si C composite acts as the working layer,and the diamond-Si C-Co composite and WC/Co cements are as the intermediate layer and substrate,respectively. It is found that the initial oxidizing temperature of the three-layered PDC is enhanced up to820？C, which is significantly higher than that（～780？C） of the conventional PDC counterpart.
基金Project(2009ZX04004-031-04) supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China
文摘Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the investigated powder Distaloy AE were determined as functions of relative density through typical mechanical property tests of powder. The model was implemented as a user subroutine USDFLD. Single sided compaction of a d20 ram^5 mm disk green compact of Distaloy AE was simulated, and the residual stress of the disk after ejection was predicted with FEA. The FEA results of the compaction process and the residual stress of the disk show good agreement with compaction experiments and X-ray diffraction measurements, which validates the model and its parameters. The results indicate that the compressive residual stresses exist mainly in a thin layer on the side surface, but the residual stresses are very small on the top and bottom surfaces.
基金supported by the National Basic Research Program of China("973 Program",Nos.2012CB619102 and 2012CB619100)National Science Fund for Distinguished Young Scholars(Grant No.51225101)+1 种基金the Fundamental Research Funds for the Central Universities(Nos.HEUCFZ1017 and HEUCFR1020)the Natural Science Foundation of Heilongjiang Province,China(No.ZD201012)
文摘Porous sintered Ti-Ag compacts with different Ag content were fabricated by powder metallurgy. The associated hydrothermal treatment and the effect on the apatite formation were studied. The results suggested that TiO was generated under the condition of low vacuum （1 ×10^-2 Pa） during the process of burning out the spacer-holding particles. After hydrothermal treatment, a sub-microscale porous layer was formed at the pore wall surface of the samples. The apatite-inducing ability of hydrothermal treated porous sintered Ti-Ag compacts with different Ag content was evaluated in modified simulated body fluid （SBF）. And the results proved that there is a clear correlation between the apatite-inducing ability and Ag content. The higher Ag content in porous leads to the decrease of Na＋ ions and basic hydroxyl （OH）b amount, resulting in the decline of apatite-inducing ability in the first stage. However, their apatite-inducing ability was not significantly different from that of Ti after two weeks SBF immersing. Hence, the ionic activity should restore with the processing of SBF soaking, as the saturation of Ag effect.
基金supported by the Natural Science of Hunan(06JJ4062)
文摘Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM). The TRS on the surface of polycrystalline diamond(PCD) table was obtained,which can be used to calculate the radial thermal residual stress(RTRS) at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.
文摘为生产高性能的电机铁芯,软磁复合材料(Soft Magnetic Composite,SMC)通常以高纯高压缩性铁粉为原料,如果能用较低纯度铁粉取代高纯铁粉,将使生产成本大大降低。本文以3种不同纯度铁粉为原材料,通过在不同工艺条件下压坯密度及表面显微硬度的变化,来表征铁粉纯度对压坯密实程度及加工硬化程度的影响。结果表明:铁粉纯度、杂质元素种类及含量、铁粉颗粒形貌均影响粉末压坯密度。较低纯度铁粉的压坯在500℃氮气中退火30 min,硬度迅速降低30%;而相同条件下高纯铁粉的压坯表面硬度基本不变。当热处理温度达到再结晶温度时,再结晶过程可使硬度降低近50%。
文摘Aluminium-alumina compacts with varying wt% of alumina were compacted in the pressure range of 115 - 290 MPa. Compacts prepared at 290 MPa pressure, were sintered in an argon atmosphere at 573, 673, 773 and 873 K for 1 hour. The green density, % porosity, % spring back and hardness of the green compacts were determined. Scanning Electron Microscopy was carried out to observe the morphology of pores and alumina particles in green and sintered compacts. The present study indicates that, densification of the compact increases with increasing compacting pressure and decreases with increasing alumina content. Maximum density achieved is 93% for pure aluminium compacts and decreases to 85% for Al-20 wt% alumina compacts. Grain growth of aluminium particles is noticed in the compacts after sintering at 773 and 873 K. Dispersion of fine alumina particle in the aluminium matrix occurs predominantly in the compact when sintered at 773 K which results in increase in hardness value.
基金This work was supported by the National Natural Science Foundation of Chira(project No.50044012)the Natural Science Foundation of Hunan Provience(project No.99JJYY20048).
文摘To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM process. A comparison between the requirements of flowability and moldability and the compacts shape retention has been made in this work. There is often a contradiction between the requirements of flowability and the compacts shape retention. Many works have been done to attain good molding conditions. However, they fail to take into account the effect of some factors that satisfies good molding conditions on the compacts shape retention during debinding. This paper studies the effect of the powder-binder mixture characteristics and the molding conditions on the flowability and moldability and the shape retention of PIM compacts during debinding process so as to attain the benefits of each.
基金This work was supported by the National Natural Science Foundation of China (Grant No.50375037).
文摘Numerical simulation of hot-press sintering of nano-sized ceramic powders was introduced by the commercial finite element code MSC.MARC. The powder plastic model and the thermo-mechanical coupled quadrilateral element were developed and adopted in the simulation. The mechanical and thermal properties of the nano-sized alumina based powders were determined.In addition, the experimental research and numerical simulation of the sintering process of different initial densities were carried out. The stress state in sintering of green compacts with different initial densities was analyzed by the densification theory.The reason for the density fluctuations of as-sintered ceramic bulks was found out.
