材料期刊网

Low Temperature Environmental Embrittlement in Ordered Intermetallics

N.S.Stoloff Department of Materials Engineering , Rensselaer Polytechnic Institute , Troy , New York , USAC.T.Liu Metals and Ceramics Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee , USA

材料科学技术（英文）

A comprehensive review of low temperature environmental embrittlement in intermetallics is pres- ented. Moisture and hydrogen are shown to severely embrittle many intermetallics, including iron, nickel and titanium aluminides. The roles of composition, microstructure and external test variables are emphasized. Several methods to reduce or avoid embrittlement are described.

关键词: environmental embrittlement , null , null

Progress in Joining Ceramics to Metals

钢铁研究学报(英文版)

关键词:

THE PARIS LAW IN METALS AND CERAMICS

Journal of Materials Science Letters

关键词: fatigue-crack-growth;partially-stabilized zirconia;cyclic fatigue;propagation;fracture

TEM investigations on layered ternary ceramics

材料科学技术（英文）

Layered ternary ceramics represent a new class of solids that combine the merits of both metals and ceramics. These unique. properties are strongly related to their layered crystal structures and microstructures. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM), selected area electron diffraction (SAED), convergent beam electron diffraction (CBED) represents a powerful method to link microstructures of materials to macroscopic properties, allowing layered ternary ceramics to be investigated in an unprecedented detail. Microstructural information obtained using TEM is useful in understanding the formation mechanism, layered stacking characteristics, and defect structures for layered ternary ceramics down to atomic-scale level; and thus provides insight into understanding the "Processing-Structure-Property" relationship of layered ternary ceramics. Transmission electron microscopic characterizations of layered ternary ceramics in Ti-Si-C, Ti-Al-C, Cr-Al-C, Zr-Al-C, Ta-Al-C and Ti-Al-N systems are reviewed.

关键词: layered ternary ceramics;MAX phase;TEM;STEM;interfacial structure;liquid reaction synthesis;transmission electron-microscope;high-temperature oxidation;ab-initio calculations;ti3sic2 thin-films;titanium-silicon carbide;si-c system;ti-al-c;mechanical-properties;crystal-structure

TEM investigations on layered ternary ceramics

Zhijun LIN , Meishuan LI , Yanchun ZHOU , null , null

材料科学技术（英文）

Layered ternary ceramics represent a new class of solids that combine the merits of both metals and ceramics. These unique properties are strongly related to their layered crystal structures and microstructures. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM), selected area electron diffraction (SAED), convergent beam electron diffraction (CBED) represents a powerful method to link microstructures of materials to macroscopic properties, allowing layered ternary ceramics to be investigated in an unprecedented detail. Microstructural information obtained using TEM is useful in understanding the formation mechanism, layered stacking characteristics, and defect structures for layered ternary ceramics down to atomic-scale level; and thus provides insight into understanding the ``Processing-Structure-Property" relationship of layered ternary ceramics. Transmission electron microscopic characterizations of layered ternary ceramics in Ti-Si-C, Ti-Al-C, Cr-Al-C, Zr-Al-C, Ta-Al-C and Ti-Al-N systems are reviewed.

关键词: Layered ternary ceramics , ternary , ceramics , MAX , phase , TEM , S

Fusion Equation of Metals

HONC Yongyan Zhejiang Institute of Technology , Hangzhou , China.

材料科学技术（英文）

An expression of initial slope of melting curve of pure metals was obtained as follows: (dT_m/dP)_o=T_(mo)/c, where c=1.09 (N_(at))~(5/3)z~(-1/3), the unit of c is GPa, N_(at) is the atomic concentra- tion (in 10~(28) m~(-3)), z is the valence, T_(mo) is the melting temperature (in k) of metal under one atmosphere. The calculated results for thirty-one metals agree well with experiments. It has also been proved that by using the free electron model of melting, the fusion equation of metals is Simon equation (T_m/T_(mo))q=1+(p/d). Two parameters q and d, which have to fit with experiments in Simon's empirical equation, now can be predicted theoretically, e.g. for Mg, giving q=1.56, d=7.88GPa, the calculated melting curve in a fairly wide pressure range (0～60GPa) is shown to be close to the experimental one.

关键词: melting curve of metals , null

Nanocrystal Model for Liquid Metals and Amorphous Metals

X.L. Tian C.W. Zhan J.X. Hou X.C. Chen J.J. Sun

材料科学技术（英文）

A nanocrystal model for liquid metals and amorphous metals has been developed. With the nanocrystal model, the broadening peak profiles (BPPs) of Cu, Al, Al₆₅Cu₂₀Fe₁₅ alloy, Cu₇₀Ni₃₀ alloy and Fe₅₀Si₅₀ alloy were gained by broadening the X-ray diffraction (XRD) peaks of a crystal lattice. By comparing the BPPs with the XRD intensity curves measured on the liquid metals, it is found that the BPPs are closely in agreement with the XRD intensity curves, respectively, except the Fe₅₀Si₅₀ alloy. Therefore, the nanocrystal model can be used to determine if the atomic cluster structure of the liquid metal is similar to the structure of its crystal lattice.

关键词: Liquid metal , Atomic Cluster , Structure , Crystal Lattice

Melting of metals: role of concentration and migration of vacancies at surfaces

Philosophical Magazine Letters

The mechanism of melting is investigated by considering the role of surfaces with regard to the concentration and migration of vacancies. For many metals, it is found that while the vacancy concentration in the bulk is similar to 0.37% at the equilibrium melting point (T-0), the vacancy concentration at the free surface is as high as 10%, i.e. similar to that in the bulk at the superheating limit. Melting is believed to be associated with a lattice instability induced at a critical vacancy concentration of similar to 10%, both at the surface and within the crystal lattice. The abrupt increase in vacancy concentration from 0.37 to 10% on melting at T-0 can be explained as a result of melting of the surface. The surface pre-melting behaviour of metals is quantitatively interpreted by considering the vacancy migration there.

关键词: kinetic stability limit;crystals;au(110);al(110);point;al

Twinnability Predication for fcc Metals

B.Q. Li

材料科学技术（英文）

Inherent twinnability of face-centered-cubic (fcc) metals was analyzed based on the direct competition between twinning partial dislocation nucleation and trailing partial dislocation nucleation, with which the twinnability of fcc metals can be simply expressed as function of the stacking-fault energy, the unstable stacking-fault energy, and the unstable twinning-fault energy of fcc metals. The predicted twinnability ranking matched well with former experimental results and provided a physical insight to understand twinnability from crystallographic orientation and fault energy parameters.

关键词: Deformation twinning

Twinnability Predication for fcc Metals

材料科学技术（英文）

Inherent twinnability of face-centered-cubic (fcc) metals was analyzed based on the direct competition between twinning partial dislocation nucleation and trailing partial dislocation nucleation, with which the twinnability of fcc metals can be simply expressed as function of the stacking-fault energy, the unstable stacking-fault energy, and the unstable twinning-fault energy of fcc metals. The predicted twinnability ranking matched well with former experimental results and provided a physical insight to understand twinnability from crystallographic orientation and fault energy parameters.

关键词: Deformation twinning;fcc metals;Twinnability;deformation twins;nanocrystalline aluminum;plastic-deformation;low;temperatures;single crystals;crack-tip;alloys;nucleation;copper