In order to reveal the formation mechanism of cubic carbide free layers （CCFL）, graded cemented carbides with CCFL in the surface zone were fabricated by a one-step sintering procedure in vacuum, and the analysis on...In order to reveal the formation mechanism of cubic carbide free layers （CCFL）, graded cemented carbides with CCFL in the surface zone were fabricated by a one-step sintering procedure in vacuum, and the analysis on microstructure and element distribution were performed by scanning electron microscopy （SEM） and electron probe micro-analyzer （EPMA）, respectively. A new physical model and ki- netic equation were established based on experimental results. Being different f^om previous models, this model suggests that nitrogen diffu- sion outward is only considered as an induction factor, and the diffusion of titanium through liquid phase plays a dominative role. The driving force of diffusion is expressed as the differential value between nitrogen partial pressure and nitrogen equilibrium pressure essentially. Simulation results by the kinetic equation are in good agreement with experimental values, and the effect of process parameters on the growth kinetics of CCFL can also be explained reasonably by the current model.展开更多
The effect of Si content on the microstructures and growth kinetics of intermetallic compounds(IMCs)formed during the initial interfacial reaction(<10 s)between solid steel and liquid aluminum was investigated by a...The effect of Si content on the microstructures and growth kinetics of intermetallic compounds(IMCs)formed during the initial interfacial reaction(<10 s)between solid steel and liquid aluminum was investigated by a thermophysical simulation method.The influence of Si addition on interfacial mechanical properties was revealed by a high-frequency induction brazing.The results showed that IMCs layers mainly consisted ofη-Fe_(2)Al_(5)andθ-Fe_(4)Al_(13).The addition of Si reduced the thickness of the IMCs layer.The growth of theηphase was governed by the diffusion process when adding 2 wt.%Si to the aluminum melt.When 5 wt.%or 8 wt.%Si was added to aluminum,the growth was governed by both the diffusion process and interfacial reaction,and ternary phaseτ1/τ9-(Al,Si)_(5)Fe_(3)was formed in theηphase.The apparent activation energies of theηphase decreased gradually with increasing Si content.The joint with pure aluminum metal had the highest tensile strength and impact energy.展开更多
This article reports the effects of phosphorus addition on the melting behavior, microstructure, and mechanical properties of Sn3.0Ag0.SCu solder. The melting behavior of the solder alloys was determined by differenti...This article reports the effects of phosphorus addition on the melting behavior, microstructure, and mechanical properties of Sn3.0Ag0.SCu solder. The melting behavior of the solder alloys was determined by differential scanning calorimetry. The interracial micro- structure and phase composition of solder/Cu joints were studied by scanning electron microscopy and energy dispersive spectrometry. Thermodynamics of Cu-P phase formation at the interface between Sn3.0Ag0.5Cu0.5P solder and the Cu substrate was characterized. The results indicate that P addition into Sn3.0Ag0.5Cu solder can change the microstructure and cause the appearance of rod-like CuaP phase which is distributed randomly in the solder bulk. The Sn3.0Ag0.5Cu0.5P joint shows a mixture of ductile and brittle fracture after shear test- ing. Meanwhile, the solidus temperature of Sn3.0Ag0.5Cu solder is slightly enhanced with P addition.展开更多
To investigate whether transcription of hepatitis B virus （HBV） gene occurs in human sperm, total RNA was extracted from sperm of patients with chronic HBV infection （test-I）, from donor sperm transfected with a p...To investigate whether transcription of hepatitis B virus （HBV） gene occurs in human sperm, total RNA was extracted from sperm of patients with chronic HBV infection （test-I）, from donor sperm transfected with a plasmid containing the full-length HBV genome （test-2）, and from nontransfected donor sperm （control）, used as the template for reverse transcription-polymerase chain reaction （RT-PCR）. Positive bands for HBV DNA were observed in the test groups but not in the control. Next, to identify the role of host genes in regulating viral gene transcription in sperm, total RNA was extracted from 2-cell embryos derived from hamster oocytes fertilized in vitro by HBV-transfected （test） or nontransfected （control） human sperm and successively subjected to SMART-PCR, suppression subtractive hybridization, T/A cloning, bacterial amplification, microarray hybridization, sequencing and the Basic Local Alignment Search Tool （BLAST） search to isolate differentially expressed genes. Twenty-nine sequences showing significant identity to five human gene families were identified, with chorionic somatomammotropin hormone 2 （CSH2）, eukaryotic translation initiation factor 4 gamma 2 （EIF4G2）, pterin-4 alpha-carbinolamine dehydratase 2 （PCBD2）, pregnancy-specific beta-l-glycoprotein 4 （PSG4） and titin （TTN） selected to represent target genes. Using real-time quantitative RT-PCR （qRT-PCR）, when CSH2 and PCBD2 （or EIF4G2, PSG4 and TTN） were silenced by RNA interference, transcriptional levels of HBV s and x genes significantly decreased （or increased） （P 〈 0.05）. Silencing of a control gene in sperm did not significantly change transcription of HBV s and x genes （P 〉 0.05）. This study provides the first experimental evidence that transcription of HBV genes occurs in human sperm and is regulated by host genes.展开更多
Based on Kolmgorov-Johnson-Mehl-Avrami analysis, a new bainite kinetics of high strength low alloy steel in fast cooling process was developed by utilizing different experimental methods. Upper bainite transformation ...Based on Kolmgorov-Johnson-Mehl-Avrami analysis, a new bainite kinetics of high strength low alloy steel in fast cooling process was developed by utilizing different experimental methods. Upper bainite transformation morphological evolutions at a cooling rate of 8.3 K/s were directly observed by laser scanning confocal microscopy. This qualitative analysis suggests that bainite packet is more suitable to give a one-dimensional growth model if it is considered as a transformation unit. The nucleation rate of bainite packets in fast cooling process is assumed to give an a priori item. One-dimensional growth model with constant growth rate which is assumed as a function of cooling rate is adopted as well. Thus, the devel- oped new bainite kinetics is simple in expression and contains an adjustable parameter and an empirical pa rameter. Experimental results show upper bainite and lower bainite transformations in fast cooling processes. Their referential phase volume fractions are calculated by the expanded lever rule on the first derivative dilatometer curves. For the similar transformation mechanisms, upper bainite and lower bainite are considered to give the same kinetics. With considering the Nakamura＇s equation, the bainite kinetics is fitted with experimental data. Results show that bainite volume fractions and bainite transformation rates can be expressed precisely bY the newly developed bainite kinetics.展开更多
基金financially supported by the National Key Technology Support Program (No.2007BAE05B02)
文摘In order to reveal the formation mechanism of cubic carbide free layers （CCFL）, graded cemented carbides with CCFL in the surface zone were fabricated by a one-step sintering procedure in vacuum, and the analysis on microstructure and element distribution were performed by scanning electron microscopy （SEM） and electron probe micro-analyzer （EPMA）, respectively. A new physical model and ki- netic equation were established based on experimental results. Being different f^om previous models, this model suggests that nitrogen diffu- sion outward is only considered as an induction factor, and the diffusion of titanium through liquid phase plays a dominative role. The driving force of diffusion is expressed as the differential value between nitrogen partial pressure and nitrogen equilibrium pressure essentially. Simulation results by the kinetic equation are in good agreement with experimental values, and the effect of process parameters on the growth kinetics of CCFL can also be explained reasonably by the current model.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(No.51875037)the Beijing Municipal Natural Science Foundation,China(No.3192021)the Fundamental Research Funds for the Central Universities,China(No.FRF-GF-18-004B).
文摘The effect of Si content on the microstructures and growth kinetics of intermetallic compounds(IMCs)formed during the initial interfacial reaction(<10 s)between solid steel and liquid aluminum was investigated by a thermophysical simulation method.The influence of Si addition on interfacial mechanical properties was revealed by a high-frequency induction brazing.The results showed that IMCs layers mainly consisted ofη-Fe_(2)Al_(5)andθ-Fe_(4)Al_(13).The addition of Si reduced the thickness of the IMCs layer.The growth of theηphase was governed by the diffusion process when adding 2 wt.%Si to the aluminum melt.When 5 wt.%or 8 wt.%Si was added to aluminum,the growth was governed by both the diffusion process and interfacial reaction,and ternary phaseτ1/τ9-(Al,Si)_(5)Fe_(3)was formed in theηphase.The apparent activation energies of theηphase decreased gradually with increasing Si content.The joint with pure aluminum metal had the highest tensile strength and impact energy.
文摘This article reports the effects of phosphorus addition on the melting behavior, microstructure, and mechanical properties of Sn3.0Ag0.SCu solder. The melting behavior of the solder alloys was determined by differential scanning calorimetry. The interracial micro- structure and phase composition of solder/Cu joints were studied by scanning electron microscopy and energy dispersive spectrometry. Thermodynamics of Cu-P phase formation at the interface between Sn3.0Ag0.5Cu0.5P solder and the Cu substrate was characterized. The results indicate that P addition into Sn3.0Ag0.5Cu solder can change the microstructure and cause the appearance of rod-like CuaP phase which is distributed randomly in the solder bulk. The Sn3.0Ag0.5Cu0.5P joint shows a mixture of ductile and brittle fracture after shear test- ing. Meanwhile, the solidus temperature of Sn3.0Ag0.5Cu solder is slightly enhanced with P addition.
基金This work was supported by the National Natural Science Foundation of China （No. 30972526） and by the Applied Basic Research Programs of Sichuan Province （No. 20141Y0110）. The authors thank Prof. Stanley Lin for his assistance in revising the final draft of the manuscript and editing for English grammar and syntax.
文摘To investigate whether transcription of hepatitis B virus （HBV） gene occurs in human sperm, total RNA was extracted from sperm of patients with chronic HBV infection （test-I）, from donor sperm transfected with a plasmid containing the full-length HBV genome （test-2）, and from nontransfected donor sperm （control）, used as the template for reverse transcription-polymerase chain reaction （RT-PCR）. Positive bands for HBV DNA were observed in the test groups but not in the control. Next, to identify the role of host genes in regulating viral gene transcription in sperm, total RNA was extracted from 2-cell embryos derived from hamster oocytes fertilized in vitro by HBV-transfected （test） or nontransfected （control） human sperm and successively subjected to SMART-PCR, suppression subtractive hybridization, T/A cloning, bacterial amplification, microarray hybridization, sequencing and the Basic Local Alignment Search Tool （BLAST） search to isolate differentially expressed genes. Twenty-nine sequences showing significant identity to five human gene families were identified, with chorionic somatomammotropin hormone 2 （CSH2）, eukaryotic translation initiation factor 4 gamma 2 （EIF4G2）, pterin-4 alpha-carbinolamine dehydratase 2 （PCBD2）, pregnancy-specific beta-l-glycoprotein 4 （PSG4） and titin （TTN） selected to represent target genes. Using real-time quantitative RT-PCR （qRT-PCR）, when CSH2 and PCBD2 （or EIF4G2, PSG4 and TTN） were silenced by RNA interference, transcriptional levels of HBV s and x genes significantly decreased （or increased） （P 〈 0.05）. Silencing of a control gene in sperm did not significantly change transcription of HBV s and x genes （P 〉 0.05）. This study provides the first experimental evidence that transcription of HBV genes occurs in human sperm and is regulated by host genes.
文摘Based on Kolmgorov-Johnson-Mehl-Avrami analysis, a new bainite kinetics of high strength low alloy steel in fast cooling process was developed by utilizing different experimental methods. Upper bainite transformation morphological evolutions at a cooling rate of 8.3 K/s were directly observed by laser scanning confocal microscopy. This qualitative analysis suggests that bainite packet is more suitable to give a one-dimensional growth model if it is considered as a transformation unit. The nucleation rate of bainite packets in fast cooling process is assumed to give an a priori item. One-dimensional growth model with constant growth rate which is assumed as a function of cooling rate is adopted as well. Thus, the devel- oped new bainite kinetics is simple in expression and contains an adjustable parameter and an empirical pa rameter. Experimental results show upper bainite and lower bainite transformations in fast cooling processes. Their referential phase volume fractions are calculated by the expanded lever rule on the first derivative dilatometer curves. For the similar transformation mechanisms, upper bainite and lower bainite are considered to give the same kinetics. With considering the Nakamura＇s equation, the bainite kinetics is fitted with experimental data. Results show that bainite volume fractions and bainite transformation rates can be expressed precisely bY the newly developed bainite kinetics.
