Recent studies by the authors are reviewed of the fine structure of both the materials interfaces and the interfacial reaction products in semiconductor superlattice, metal multilayer, ceramics and composite materials by means of selected area electron diffraction patterns and high-resolution electron microscopy. Analysis and discussion in details are presented concerning the orientation relationships, the characterization of steps, facets and roughness of interfaces, atomic bonding across interface, the degree of coherency, the structure of misfit dislocation and elastic strain relaxations at interface, the presence of defects at interface, the strure of interfacial reaction products, and the reaction kinetics and mechanism.

The precipitate phases of M42 matrix high speed steel, containing 4%Co, tempered in temperature range of 250 to 700℃ have been investigated. M_3C precipitate, mainly Fe_3C, occurs in the steel tempered at lower temperature, and lessens gradually over 400℃. Changing of diffracted streaks and fcc M_2C, mainly Mo_2C, are observed after tempered at 500 —560℃ and 580℃ respectively. When tempering temperature up to 700℃, all fcc M_2C transforms into hcp M_2C, and also VC, Cr_(23)C_6. The diffracted streaks are believed to be due to the segregation of alloying elements Mo and W together with C on {100}_α′,, and the change from mix-cluster to transition phase fcc M_2C, which results in secondary hardening of M42 matrix steel after tempering.

Based on study of the recoverable shape memory effect (SME) of shape memory alloys Ti_(50_Ni_(50), Ti_(50)Ni_(48)Cu_2 and Ti_(50)Ni_(45)Cu_5 by experiment, an empirical relationship between recoverable strain energy, U_r, and temperature, T, was derived as: U_r=U_0[1-exp(-mT_R~n)]where m-characteristic constant related to material, and n-shape-temperature sensitivity. This empirical expression will be correspondent with that of semiquantitative relationship between thermoelastic martensite transformation and temperature, associated with recoverable SME, if the Johnson-Mehl-Avrami's phenomenological method to a description of time dependence of phase transformation is adopted.

Effects of microstructure and hydrides contained on yield strength, σ_(ys), critical fracture strength, σ_F, and fracture toughness, K_(Ic), of TiAI alloy have been studied. Results show that σ_(ys) and σ_F increase slightly with size reduction of equiaxial grains of single phase γ. Yet σ_(ys), σ_F and K_(Ic) increase substantially if lamellar structure of bi-phase γ+α_2 occurred. Hydride may cause the increase of σ_(ys) and the decrease of K_(Ic). The suscepitibility for lamellar structure to hydrogen embrittlement may be lower than that for the equiaxial single phase γ. Resistance to cleavage-like crack initiation in TiAl alloy increases gradually with as steady-state propagation of crack. When plastic zone at crack tip and deformation developed up to critical value, the cleavage-like cracks initiate along slip band in plastic zone.

The fracture mechanism for A1-2.5Li-1.3Cu-0.9Mg-0.13Zr alloy is quite different from undergone various regimes of heat treatment. With the decrease of solution temperature and the increase of aging temperature, the intergranular delimination and necking fracture on the fracture surface increase and the shearing fracture decreases. Thus, the toughness of the alloy may be much improved.

20-40% austenite in austenitic-bainitic ductile nodular cast iron. During roiling contact fatiguing, only 5—10% of such austenite in surface layer may transform into stress-induced martensite in untransformed austenitic areas. The transformation seems to be slightly improved surface hardness and unaffected upon contact fatigue properties of the iron.

DETERMINATION OF ACTIVITIES OF S AND Fe IN MELTS OF MATTE CONVERTING PROCESS BY EMF METHOD

Phase equilibria at Fe-Mn side of isothermal section at 1000 and 1100℃ in Fe-Mn-Al system have been determined using the diffusion couple, technique and metallography. A three-phase, α+γ+β, region was found at 1000℃. The method of solid/gas diffusion couple used to determine equilibrium phase composition is believed to be feasible for the system containing volatile component.

In the light of estimation model for ternary excess properties, an approximate analytical procedure for ternary Gibbs-Duhem equation was proposed, and verification by previous ternary systems as Cd-Bi-Pb and Zn-In-Cd was also made.

Hot corrosion of Ni_3Al-0.2B in molten NaCl-(Na, K)_2SO_4 was studied by electrochemical methods and analytical techniques. The hot corrosion resistance of Ni_3Al-0.2B is quite bad, and the sulphidation-oxidation is responsible for corrosion damage. The addition of 6 at.-% Cr+0.5 at.-% Zr to Ni_3Al-0.2B may accelerate the hot corrosion.

Crystallization kinetics of Pd-Cu-Si glass was studied by DSC. Apparent activation energy was calculated according to Kissinger peak shift method and Arrhenius equation. The isothermal crystallization kinetics, ranged 0.15×0.85, was found to be in agreement with John-Mehl-Avrami equation with n=3.0. Nucleation and growth during isothermal crystallization of Pd-Cu-Si system were approached by introducing the concepts of local Avrami exponent and local activation energy.

Interfaces and surfaces of YBa_2Cu_3O_(7-x) (YBCO)-Ag have been studied by SEM-EDX and AES. No effect of Ag on 123 structure in X-ray diffraction pattern was observed for 0.4 mol Ag doped YBCO. AES analysis indicated that Ag segregated on surface of YBCO and resulted in decrease of YBCO-metal lead resistance. In addition, solution and segregation of Ag as elemental state were often appreared on interfaces and surfaces of high temperature annealed YBCO, whether elemental Ag or compound Ag_2O and AgNO_3 adopted as doping material.

Observations of microstructure of explosive compacts made of Al or Al-Li alloy powders by atomization with water, nitrogen or ultrasonic Ar gas were carried out under optical and scanning electron microscopes. The results indicate that super quality explosive compact can only be obtained by powders of which the thickness of the exide lager is less than 30 nm.

Observations of cross-sectional Ti/TiN film sample under TEM and of respective depth profiling by secondary ion mass spectroscopy showed that a periodic alternate multilayer structure, i.e., substrate/FeTi/Ti/Ti_2N/TiN/Ti_2N/Ti/Ti_2N/TIN…Ti/Ti_2N/TiN, where FeTi and Ti_2N being transition layer, was found during ion plating. SEM fractograph of indentation sample also showed that the hard coating deformed during indentation, an indentation dip and a pile-up of materials around appeared. With the increase of load applied, the deformation region extended beyond film/substrate boundary and into substrate, initiated interlayer cracking in film and formation of hole at film/substrate interface. It seems that the multilayered Ti/TiN film offered better toughness than single layer TiN film.

Investigation was made of the deposition rate, surface morphology and crystal preferred orientation of the dense TiC coating onto austenitic stainless steel in relation with CH_4/TiCl_4 mole ratio and temperature adopted in CVD processing. When the CH_4/TiCl_4 ratio is low or high, their preferred orientation may be (220) or (200), respectively, which is mainly dependent on the equilibrium concentration of active carbon in vapour phase.

In-situ formation fibrous polytype AIN composite ceramic material was prepared from AlN-Y_2O_3-SiO_2 system. In comparison with AlN ceramics, both bending strength and fracture toughness of the composite material are much bettered. Microstructural observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix. Y_2O_3 seems to act as a densifier for in-situ formation material and as medium for growth of fibrous polytype. SiO_2 is the growth promoter for fibrous polytype. The occurrence of fibrous polytype may increase the strength and toughness of AlN ceramic composite material.