Yinghong Zhuang

Crystal lattice expansion of nanocrystalline materials

Nanocrystalline materials are characterized structurally by ultra-fine crystallites separated by grain boundaries. The structure of nanocrystallites shows significant differences in comparison to perfect crystals. A model is proposed to account for the effects of the defects in the grain boundaries of nanocrystalline materials on the crystal lattice, based on the fact that the grain boundaries of nanocrystalline materials contain a large number of vacancies and vacancy clusters. A 1/x3 law for the stress field caused by the vacancies and the vacancy clusters is considered, and the crystal lattice expansion of nanocrystalline materials is estimated. The theoretical results can interpret experimental observations well.

A thermodynamic explanation for the martensitic transformation of nanometer-sized γ-iron particles embedded in a copper matrix

The martensitic transformation of nanometer-sized particles precipitating in a copper matrix is analyzed from a thermodynamic viewpoint. It is shown that there exists a critical austenitic particle size below which the austenitic phase becomes more stable than the martensitic phase and the martensitic transformation cannot take place. Prolonged annealing, extraction of particle from the matrix, and plastic deformation would make the austenitic particle size exceed this critical value, and thus, cause the austenitic particles to transform to martensite. The theoretical results can interpret experimental observations well.

The 500°C isothermal section of the phase diagram of the ternary HoFeNb system

Abstract The 500°C isothermal section of the HoFeNb system was investigated by X-ray powder diffraction, differential thermal microanalysis and electron-probe microanalysis techniques. It consists of 10 single-phase regions, 18 two-phase regions and 9 three-phase regions. At 500°C, the maximum solubilities of Nb in Ho 2 Fe 17 and Ho in Fe 2 Nb and FeNb are about 2.0, 2.0 and 3.0 at.% respectively. In the FeNb binary system, the composition ranges of the phases β(Fe 2 Nb) and γ(FeNb) were determined as 32.0 to 41.0 at.% Nb and 48.0 to 53.0 at.% Nb respectively. The other compounds, including the tetragonal compound HoFe 11 Nb, have no observable homogeneity ranges.

Phase relationship of the La-Nd-Fe system at 770 K

Abstract Phase equilibria in the ternary La–Nd–Fe system have been established in the isothermal section of 770 K. The section consists of two single-phase regions, four two-phase regions and two three-phase regions. No ternary compounds were found in this section.

Possibility of the martensitic transformation triggered by thermal fluctuation

Motivated by the recent experimental results of martensitic transformation of nanometer-sized particles, we theoretically analyze the possibility of martensitic transformation triggered by thermal fluctuation in nanometer-sized particles and reconsider an earlier presented heterogeneous nucleation model. Our results show that homogeneous nucleation of martensite is possible in iron-based alloys.

The 773 K isothermal section of the phase diagram of ternary Ni–Ti–Y system

Abstract The 773 K isothermal section of the Ni–Ti–Y system was investigated by X-ray powder diffraction, differential thermal microanalysis and electron-probe microanalysis techniques. It consists of 15 single-phase regions, 28 two-phase regions and 13 three-phase regions. At 773 K, the maximum solubilities of Y in Ni and Ti in Ni 2 Y, Ni 3 Y and Ni 5 Y are about 5.0, 3.0, 2.0 and 5.0 at.%, respectively. In the Ni–Ti binary system, the composition ranges of the phase α-(Ni) was determined as 0–11.0 at.% Ti.

Phase equilibria in the Y-Ti-Si system at 773 K

Abstract Physico-chemical analysis techniques, including X-ray powder diffraction, scanning electron microscopy, optical microscopy and differential thermal analysis were employed in constructing the isothermal section of the Y – Ti – Si system at 773 K. The isothermal section consists of 12 single phase regions, 21 binary phase regions and 10 ternary phase regions. No ternary compound is found in the work. None of the phases in this system reveals a remarkable homogeneity range at 773 K.

The isothermal section of the phase diagram of the Dy–Mn–Ni ternary system at 803 K

The isothermal section of the phase diagram of the ternary system Dy–Mn–Ni system at 803 K was investigated by powder X-ray diffraction (XRD), differential thermal analysis (DTA), optical microanalysis and electron probe microanalysis techniques. It consists of 13 single-phase regions, 22 two-phase regions and 10 three-phase regions. At 803 K, the maximum solid solubilities of Mn in Ni, Dy2Ni17, DyNi5, Dy2Ni7, DyNi3, DyNi, Dy3Ni2 and Dy3Ni are about 31at.% Mn, 6 at.% Mn, 5.5 at.% Mn, 3 at.% Mn, 5 at% Mn, 5 at.% Mn, 3 at.% Mn and 1.5 at.% Mn, respectively. The maximum solid solubilities of Ni in Mn, DyMn12 and Dy6Mn23 are about 2.6 at.% Ni, 2 at.% Ni and 4 at.% Ni, respectively. DyMn2 and DyNi2 form a continous solid solution in this system. The binary compounds DyNi4 and Dy4Ni17 were not observed in this work. The existence of any ternary compound was not observed.

Isothermal section of Gd-Sm-Co ternary system at 773 K

Abstract The isothermal section of the phase diagram of the Gd-Sm-Co ternary system at 773 K was investigated by X-ray powder diffraction (XRD), differential thermal analysis (DTA)optical microscopy and scanning electron microscopy (SEM) techniques. The result shows that the isothermal section consists of 12 single-phase regions, 16 two-phase regions and 5 three-phase regions. Five pairs of corresponding compounds of Gd-Co and Sm-Co systems, i.e., Gd 2 Co 17 and Sm 2 Co 17 , Gd 2 Co 7 and Sm 2 Co 7 , GdCo 3 and SmCo 3 , GdCo 2 and SmCo 2 , Gd 3 Co and Sm 3 Co form continuous series of solid solutions. The maximum solid solubility of Sm in Gd 4 Co 3 and Gd 12 Co 7 were about 7.2 at.% and 47.8 at.% Sm, respectively. The maximum solid solubility of Gd in Sm 5 Co 19 and Sm 5 Co 2 were about 4.7 at.% and 7.6 at.% Gd, respectively. The binary compounds Sm 9 Co 4 , GdCo 5 and SmCo 5 were not observed at 773 K. No ternary compound was found.

Isothermal section of the Al-Tb-V ternary system at 773 K

Abstract The isothermal section of the phase diagram of the Al-Tb–V system at 773 K has been investigated by means of X-ray powder diffraction and scanning electron microscopy. The existence of 10 binary compounds and two ternary compounds, namely, Al3Tb, Al2Tb, AlTb, Al2Tb3, AlTb2, Al10V, Al45V7, Al23V4, Al3V, Al8V5, Al43V4Tb6 and Al20V2Tb were confirmed. The compounds AlV, AlV3 and Al4Tb were not observed, and no binary compound was found in the Tb–V binary system. The isothermal section consists of 15 single-phase regions, 30 binary-phase regions and 15 ternary-phase regions. The solubility of V in Al2Tb, AlTb and Al2Tb3 is about 2.4 at.%, 1.6 at.% and 1.2 at.%, respectively. The solubility of Al in V is about 40.0 at.%.