Xinsheng Huang

Metastable BCC and FCC alloy bulk bodies in Fe-Cu system prepared by mechanical alloying and shock compression

Abstract Bulk bodies of metastable body-centered-cubic (BCC) and face-centered-cubic (FCC) alloys of solid solutions in the iron (Fe)–copper (Cu) system were prepared by mechanical alloying (MA) and shock compression. The X-ray diffraction pattern of the BCC structure was obtained for the MA-treated powder in the Fe–Cu system with a Cu content of less than about 30 mol%, and those of FCC structure were obtained for the MA-treated powders in Fe–Cu systems with a Cu content of larger than about 30 mol%. The lattice parameters of both the BCC and FCC structures of the MA-treated powders were larger than those of pure Fe and pure Cu, respectively. No large crack could be observed in shock-consolidated bulk bodies, and the cross sections of the bulk bodies showed a metallic gloss. The X-ray diffraction patterns of both types of shock-consolidated bulk bodies formed in a specific low pressure range did not change significantly from those of the MA-treated powders, which indicated that the metastable phases were successfully consolidated by shock compression. Above a driving shock pressure of 13.0 GPa in brass capsule, the recovered specimens of the BCC structure in the Fe–Cu system (Fe:Cu=80:20 in mol%) began to decompose to Fe and Cu, while the recovered specimens of the FCC structure in the Fe–Cu system (Fe:Cu=50:50 in mol%) did not decompose up to a driving shock pressure of 14.9 GPa. It was confirmed by Electron Probe Micro Analysis (EPMA) that Fe and Cu dispersed well at the submicron level in the shock-consolidated bulk bodies. The Vickers hardnesses of the bulk bodies were much higher than those of pure Fe and Cu polycrystals.

Non-equilibrium W-Cu system alloy powder and bulk body prepared by mechanical alloying and shock compression

Abstracts are not published in this journal

Formation of atomic-scale graded structure in Se-Te semiconductor under strong gravitational field

A large linearly graded structure on atomic scale up to 88 at. %/mm with oriented grown crystals was formed in selenium-tellurium (Se-Te) semiconductor using a strong gravitational field of one million G level at 260 °C. The lattice constants and the binding energies of Se and Te 3d electrons continuously changed along the direction of gravity accordingly, which indicated the formation of the graded band gap structure. The grown crystals showed the crystalline orientation with the c axis of hexagonal structure roughly perpendicular to the direction of gravity. It was found that the diffusion coefficient of sedimentation was larger than that of normal diffusion by more than 100 times, which suggested a different diffusion mechanism from the normal vacancy mechanism.

Metastable alloy bulk bodies in the Fe–W system prepared by mechanical alloying and shock compression

Abstract Bulk bodies of metastable alloys including supersaturated solid solutions and amorphous phases in the iron (Fe)–tungsten (W) system were prepared by mechanical alloying (MA) and shock compression. The X-ray diffraction patterns of the W solid solutions were obtained for the MA-treated powders in the Fe x W 100− x system with Fe content of x ≤30 mol%, and that of Fe solid solution was obtained with an Fe content of x =90 mol%. For the mixed powders with Fe content of 40≤ x ≤70 mol%, the peaks of Fe completely disappeared, and the amorphous halo-like patterns were observed around the (110) peak of W solid solution. For the mixed powder with an Fe content of 80 mol%, an X-ray diffraction pattern of a two-phase mixture of Fe and W solid solutions was obtained. For the MA-treated powders, the lattice parameters of W solid solutions were smaller than that of pure W, and those of Fe solid solutions were larger than that of pure Fe. No large crack could be observed in shock-consolidated bulk bodies, and the cross sections of the bulk bodies showed a metallic gloss. The X-ray diffraction patterns of shock-consolidated bulk bodies formed in a specific low pressure range did not change significantly from those of the MA-treated powders, which indicated that the metastable phases were successfully consolidated by shock compression without decomposition or recrystallization. Above a driving shock pressure of 40.1 GPa in capsule for the 30:70 mol% Fe–W system and that of 30.5 GPa for the 50:50 mol% Fe–W system, the X-ray diffraction patterns of the recovered bulk bodies showed the appearance of the peaks of Fe 7 W 6 intermetallic compound and the peaks of Fe. The recovered specimens of the metastable solid solution phases in the 80:20 mol% Fe–W system did not recrystallize or decompose up to a driving shock pressure of 39.5 GPa. It was confirmed by the Electron Probe Micro Analysis (EPMA) that Fe and W dispersed well at the submicron level in the shock-consolidated bulk bodies. The Vickers hardnesses of the bulk bodies were much higher than those of pure Fe and pure W polycrystals.

Nonequilibrium alloy powders and bulk alloys in W–Ag system prepared by mechanical alloying and shock compression

Abstract W x Ag 100− x alloy powders and bulk alloys consisting of metastable solid solution and nanocrystals were prepared by mechanical alloying (MA) and shock compression. The MA-treated (21 h) powder for x =90 showed the X-ray diffraction (XRD) pattern of a single phase of b.c.c. structure, and those for x ≤80 showed the XRD patterns of two-phase mixtures of b.c.c. and f.c.c. structures. The lattice parameters of the b.c.c. structure phases increased with milling time and approached saturation values at about 15 h. The shock-consolidated bulk alloys for x =70 and 80 consisted of two-layer structures of a thick undecomposed layer and a thin decomposed one. The Vickers hardnesses of the undecomposed areas were much higher than those of the decomposed areas in the shock-consolidated bulk alloys.

Sedimentation of isotope atoms in monatomic liquid Se

A strong gravitational field resulted in the sedimentation of isotope atoms in monatomic liquid. The concentration ratio Se82∕Se76 increased by greater than 3.5% in specimen ultracentrifuged at (0.7–0.9)×106G and at 300°C. The recovered sample had a feather-shaped crystalline morphology. The concentration gradient was nearly twice that of the steady state analytical result (ideal gas system), indicating a nonideal system diffusion. The present result is evidence of sedimentation of substitutional atoms in condensed matter via self-diffusion and suggestes its possible application to isotope separation, crystalline control, and matter dynamics in massive star.

Gravity-induced diffusion of isotope atoms in monoatomic solid Se

A strong gravitational field resulted in the gravity-induced diffusion (sedimentation) of isotope atoms in monoatomic solid Se. The layer crystalline morphology consisting of three zones of the fine-grained crystals, the long crystals and feather-shaped crystals grown parallel to gravity direction appeared in the specimen ultracentrifuged at (0.8–1)×106 G and at 190 °C. Change in the concentration ratio 82Se/76Se of >0.8% was observed in the grown crystalline region. These results show an evidence for the sedimentation of substitutional atoms in solids via self-diffusion, and suggest the possibility of application to the control of impurity and crystalline states as well as to isotope separation.

Preparation of Fe-W system metastable alloy bulk body by mechanical alloying and shock compression

Abstract Iron (Fe)–tungsten (W) system (50:50 in mol%) metastable alloy powder including solid solution and the bulk body were prepared by mechanical alloying (MA) and shock compression, respectively. The MA-treated Fe–W powder and the shock consolidated bulk body showed by X-ray diffraction an almost single phase of body-centered cubic (BCC) structure. The lattice parameter of BCC structure of the MA-treated powder for 21 h was smaller than that of pure tungsten. It was confirmed that Fe and W dispersed well within submicron level in the bulk body by the electron probe micro analysis (EPMA).

Effects of decomposition on the magnetic property of shock-consolidated Sm2Fe17Nx bulk magnets

It had been found that fully dense Sm2Fe17Nx bulk bodies can be prepared by shock compression in a certain low pressure region, using the magnetically aligned powder pellets and without binder. In this study, the correlations between the shock condition, the crystal chemical state and magnetic property of the shock-consolidated bulk bodies were investigated by means of X-ray diffraction (XRD) analysis, chemical analysis and magnetic measurement. It was found that the maximum energy products decreased a great deal when the driving shock pressure (using a copper standard capsule) exceeded about 15–16 GPa. In these driving pressures, the coercivity simultaneously decreased with an appearance of Fe due to decomposition, while the decrease in remanent magnetization was almost constant. If we chose the suitable shock conditions, the decrease rate of maximum energy product from the starting material could be suppressed to less than 20–30%.

Preparation of fine-grained bulk materials in the Fe–Co system by shock compression

Fine-grained bulk alloys with no crack in the 70:30 mol% Fe–Co system were prepared by means of shock compression of water-atomized powder and mechanical alloying (MA) treated ones. The grain size of the water-atomized bulk body was smaller (≤50μ m) than that of the molten bulk body (about 100μ m). The grain size decreased greatly with the MA treatment time, and ones for 21 h were estimated to be about 15 nm from the x-ray diffraction patterns. The coercivity value of the water-atomized bulk body was much larger than that of the molten bulk body. The coercivity value of the MA-treated bulk body increased with the MA treatment time, and then decreased, despite the very small grain size, probably due to the effect of ferromagnetic exchange interaction.