The Berkovich indentation loading curves of the initially only extraterrestrial available polymorphs of SiO2 are physically analyzed by applying the now well established FN-h3/2 plots for conical/pyramidal indentation...The Berkovich indentation loading curves of the initially only extraterrestrial available polymorphs of SiO2 are physically analyzed by applying the now well established FN-h3/2 plots for conical/pyramidal indentations, in view of determining the phase-transition onset forces, indentation energies, and transition energies. Two phase-transitions of synthesized Stishovite yielding 2 polymorphs (one of them is Seifertite) with these properties are characterized. A third post-Stishovite polymorph is safely projected for higher load indentation. Both of them are now available at room temperature on earth for further investigation and the projected third of them is waiting. The published “pop-ins” had to be removed by self-evident repair of the force-depth curve. The meaning of published “pop-ins” is elucidated, apparently for the first time. The reasons for them and their avoidance are manifold. They are not materials’ properties but mechanical artefacts. Published pop-ins are not at all connected to phase-transitions, despite theoretical considerations claiming elastic-plastic conversion at the start of “pop-ins”. Spherical indentation analyses before them are obsolete. Final support is inter alia that one of the two new MgO twinning transitions is within a published “pop-in excursion”. The putting of a pop-in arrow at smooth loading curve without discontinuities is criticized, as the transfer between chemically different phases is neither phase transition nor “pop-in”. The polymorph’s onset forces, their energies and their endo- or exo-thermic phase-transition energies are reported. The development of the Stishovite, post-Stishovite and MgO polymorphs is mechanochemical analyzed. High pressure polymorph energetic properties are important for the earth’s sub mantel investigations and for public safety of technical materials such as MgO for constructions, or covered superalloys for e.g. airplanes, turbines, etc. Breakage and catastrophic cracks are more easily initiated at polymorph interfaces, the onset and transition energies must be above the highest possible mechanical and thermal stress for their being safe.展开更多
Nanoindentation is an attractive characterization technique,as it not only measures the local properties of a material but also facilitates understanding of deformation mechanisms at submicron scales.However,because o...Nanoindentation is an attractive characterization technique,as it not only measures the local properties of a material but also facilitates understanding of deformation mechanisms at submicron scales.However,because of the complex stress-strain field and the small scale of the deformation under the nanoindenter,the results can be easily influenced by artifacts induced during sample preparation.In this work,a systematic study was conducted to better understand the influence of sample preparation methods on the nanoindentation results of ductile metals.All experiments were conducted on a steel(Fe-22Mn-0.65C,wt%)with twinning-induced plasticity(TWIP),which was selected for its large grain size and sensitivity to different surface preparation methods.By grouping the results obtained from each nanoindent,chemical polishing was found to be the best sample preparation method with respect to the resulting mechanical properties of the material.In contrast,the presence of a deformation layer left by mechanical polishing and surface damage induced by focused ion beam(FIB)scanning were confirmed by the dislocation-nucleation-induced pop-in events of nanoindentation.展开更多
Fe40Ni40P14B6 bulk metallic glass rods have been prepared by water quenching the fluxed alloy. The deformation behavior was investigated by nanoindentation tests and compressing tests. The average hardness and elastic...Fe40Ni40P14B6 bulk metallic glass rods have been prepared by water quenching the fluxed alloy. The deformation behavior was investigated by nanoindentation tests and compressing tests. The average hardness and elastic modulus of the as-prepared Fe40Ni40P14B6 BMG (bulk metallic glass) measured by nanoindentation tests are 8.347 and 176.61 GPa respectively. The displace- ment-load curve shows “pop-in” characteristics which correspond to the loading rate bursts. Many shear bands around the indent were observed. The as-prepared Fe-based BMG exhibits a compressive plastic strain of 5.21%, which is much larger than that of other Fe-based glassy alloys and most of other BMGs.展开更多
The haloarchaea Haloferax mediterranei and Haloarcula hispanica are both polyhydroxyalkanoate producers in the domain Archaea, and they are becoming increasingly attractive for research and biotechnology due to their ...The haloarchaea Haloferax mediterranei and Haloarcula hispanica are both polyhydroxyalkanoate producers in the domain Archaea, and they are becoming increasingly attractive for research and biotechnology due to their unique genetic and metabolic features. To accelerate their genome-level genetic and metabolic analyses, we have developed specific and highly efficient gene knockout systems for these two haloarchaea. These gene knockout systems consist of a suicide plasmid vector with the pyrF gene as the selection marker and a uracil auxotrophic haloarchaeon （apyrF） as the host. For in-frame deletion of a target gene, the suicide plasmid carrying the flanking region of the target gene was transferred into the corresponding apyrF host. After positive selection of the single-crossover integration recombinants （pop-in） on AS-168SY medium without uracil and counterselection of the double-crossover pyrF-excised recombinants （pop-out） with 5-fluoroorotic acid （5-FOA）, the target gene knockout mutants were confirmed by PCR and Southern blot analysis. We have demonstrated the effectiveness of these systems by knocking out the crtB gene which encodes a phytoene synthase in these haloarchaea. In conclusion, these well-developed knockout systems would greatly accelerate the functional genomic research of these halophilic archaea.展开更多
Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic(FCC)lattice,can significantly affect the dislocation behaviors on deformation.Recently,interstitial doping has b...Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic(FCC)lattice,can significantly affect the dislocation behaviors on deformation.Recently,interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent,often termed high-entropy alloys(HEAs)or medium-entropy alloys(MEAs).However,the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear.Therefore,in the present work,an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading.The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field,regardless of the interstitial concentration.Moreover,the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration,which definitely suggests the participation of interstitial atoms in the nucleation process.Besides,it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration.Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations.Furthermore,the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion,which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens.The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys,which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.展开更多
文摘The Berkovich indentation loading curves of the initially only extraterrestrial available polymorphs of SiO2 are physically analyzed by applying the now well established FN-h3/2 plots for conical/pyramidal indentations, in view of determining the phase-transition onset forces, indentation energies, and transition energies. Two phase-transitions of synthesized Stishovite yielding 2 polymorphs (one of them is Seifertite) with these properties are characterized. A third post-Stishovite polymorph is safely projected for higher load indentation. Both of them are now available at room temperature on earth for further investigation and the projected third of them is waiting. The published “pop-ins” had to be removed by self-evident repair of the force-depth curve. The meaning of published “pop-ins” is elucidated, apparently for the first time. The reasons for them and their avoidance are manifold. They are not materials’ properties but mechanical artefacts. Published pop-ins are not at all connected to phase-transitions, despite theoretical considerations claiming elastic-plastic conversion at the start of “pop-ins”. Spherical indentation analyses before them are obsolete. Final support is inter alia that one of the two new MgO twinning transitions is within a published “pop-in excursion”. The putting of a pop-in arrow at smooth loading curve without discontinuities is criticized, as the transfer between chemically different phases is neither phase transition nor “pop-in”. The polymorph’s onset forces, their energies and their endo- or exo-thermic phase-transition energies are reported. The development of the Stishovite, post-Stishovite and MgO polymorphs is mechanochemical analyzed. High pressure polymorph energetic properties are important for the earth’s sub mantel investigations and for public safety of technical materials such as MgO for constructions, or covered superalloys for e.g. airplanes, turbines, etc. Breakage and catastrophic cracks are more easily initiated at polymorph interfaces, the onset and transition energies must be above the highest possible mechanical and thermal stress for their being safe.
文摘Nanoindentation is an attractive characterization technique,as it not only measures the local properties of a material but also facilitates understanding of deformation mechanisms at submicron scales.However,because of the complex stress-strain field and the small scale of the deformation under the nanoindenter,the results can be easily influenced by artifacts induced during sample preparation.In this work,a systematic study was conducted to better understand the influence of sample preparation methods on the nanoindentation results of ductile metals.All experiments were conducted on a steel(Fe-22Mn-0.65C,wt%)with twinning-induced plasticity(TWIP),which was selected for its large grain size and sensitivity to different surface preparation methods.By grouping the results obtained from each nanoindent,chemical polishing was found to be the best sample preparation method with respect to the resulting mechanical properties of the material.In contrast,the presence of a deformation layer left by mechanical polishing and surface damage induced by focused ion beam(FIB)scanning were confirmed by the dislocation-nucleation-induced pop-in events of nanoindentation.
文摘Fe40Ni40P14B6 bulk metallic glass rods have been prepared by water quenching the fluxed alloy. The deformation behavior was investigated by nanoindentation tests and compressing tests. The average hardness and elastic modulus of the as-prepared Fe40Ni40P14B6 BMG (bulk metallic glass) measured by nanoindentation tests are 8.347 and 176.61 GPa respectively. The displace- ment-load curve shows “pop-in” characteristics which correspond to the loading rate bursts. Many shear bands around the indent were observed. The as-prepared Fe-based BMG exhibits a compressive plastic strain of 5.21%, which is much larger than that of other Fe-based glassy alloys and most of other BMGs.
基金supported by the National Natural Science Foundation of China(51971167,52031011,12004294)the Ministry of Science and Technology(2017YFA0700703 for Gan B)the National Youth Talents Program(Ding J)。
基金supported by the National Natural Science Foundation of China(Nos.30830004,30925001)the National 863 Program of China(No.2009AA09Z401)the Chinese Academy of Sciences(No.KSCX2-EW-G-2)
文摘The haloarchaea Haloferax mediterranei and Haloarcula hispanica are both polyhydroxyalkanoate producers in the domain Archaea, and they are becoming increasingly attractive for research and biotechnology due to their unique genetic and metabolic features. To accelerate their genome-level genetic and metabolic analyses, we have developed specific and highly efficient gene knockout systems for these two haloarchaea. These gene knockout systems consist of a suicide plasmid vector with the pyrF gene as the selection marker and a uracil auxotrophic haloarchaeon （apyrF） as the host. For in-frame deletion of a target gene, the suicide plasmid carrying the flanking region of the target gene was transferred into the corresponding apyrF host. After positive selection of the single-crossover integration recombinants （pop-in） on AS-168SY medium without uracil and counterselection of the double-crossover pyrF-excised recombinants （pop-out） with 5-fluoroorotic acid （5-FOA）, the target gene knockout mutants were confirmed by PCR and Southern blot analysis. We have demonstrated the effectiveness of these systems by knocking out the crtB gene which encodes a phytoene synthase in these haloarchaea. In conclusion, these well-developed knockout systems would greatly accelerate the functional genomic research of these halophilic archaea.
基金financially supported by the Natural Science Foundation of Hunan province(nos.2021JJ40736,2019JJ60062 and 2020JJ6090)。
文摘Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic(FCC)lattice,can significantly affect the dislocation behaviors on deformation.Recently,interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent,often termed high-entropy alloys(HEAs)or medium-entropy alloys(MEAs).However,the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear.Therefore,in the present work,an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading.The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field,regardless of the interstitial concentration.Moreover,the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration,which definitely suggests the participation of interstitial atoms in the nucleation process.Besides,it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration.Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations.Furthermore,the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion,which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens.The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys,which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.
