An elastic-plastic axisymmetric increment finite element program based on f inite deformation theory has been applied to calculate the stress-strain curves of 12CrMo ferrite-martensite steel with different martensite contents The fraction and shape of martensite in the finite element meshes should be the same as those in actual materials. The calculated stress-strain curves are consistent with experimental ones. The flow stresses at low strain stage are directly proportional to the martensite content, but at high strain stage, the effect of martensite content dies down. The strength of the steel increases slightly with decreasing martensite size. When the martensite content is 50%, the strength of steel becomes higher than that of those with ferrite matrix. At uniform strain stage, the calculate stress-strain curves on Log-Log scales show two straight lines with slopes n_1 and n_2. The strain hardening exponent n_1 at the first strain hardening stage is sensitive to the character of matrix, while n_2 at the second stage is sensitive to that of particle phase.

By use of a computer program, the finite element method has been employed to calculated the effect of particle size, matrix and volume fraction of phases on the stress and strain distributions in 12CrMo ferrite-martensite steel. In particular, the distributions of hydrostatic stress and maximum shear stress in each phase are given. The microscopic fracture mechanism revealed by these stress distributions coincides with experimental observations.

Hot torsion tests were carried out on supersaturated solid solution of an aluminium alloy containing 0.7% Mg and 0.97%Si. The flow curves at 480/400/ 270℃ and a strain rate of 1.31s~(-1) were measured. The dynamic structure changes and their influences on the subsequent aging behavior of the alloy quenched immediately after hot deformation were investigated. It has been found that the aginghardening ability and the time to the peak hardness of the supersaturated solid solution quenched directly after hot deformation are related to the dynamic precipitation of Mg_2Si. Under the conditions of absence or presence of a small amount of the precipitates, the ability is about 15% higher and the time is an order of magnitude shorter for the sample quenched immediately after deformation than for that quenched conventionally. The microstructure of the sample hot deformed, directly quenched and aged is charactrized by existence of recovery substructure as well as much finer dispersive aging precipitates.

A convenient and reliable method for measuring the dynamic curves reflecting the effect of various heat-treatments upon the main properties of age-hardening alloys is described, that can be adopted to serve as a reference for determining the best technological parameters of heat-treatment. The method presented is very simple and effective and it has been guaranteed to meet the desired comprehensive requirements. In the study of strengthening phase, new phase-beryllide (Co_n_1>Cu_n_2· Si_n_3) Be_m in the alloy has been found. The composition of the strengthening phase of CuCo2Be alloy has also been analyzed.

The effect of an additive of 0.15 wt-% Ti in the Al-5.0Zn-1.8Mg alloy upon the precipitation, critical nucleation temperature, T'_c, and structural parameters has been investigated by means of hardness test as well as optical and TEM observations. The results showed that a trace additive of Ti may impel considerably the refinement of the grains of the alloy, but no more inhibition of its recrystallization and increase of T'_c.Ti may retard the growth of MPt, increase the density and the hardness of the alloy under lower temperature aging, namely, T_a T'_c. Furthermore, at any aging temperature between 120-200℃, the GBP and PFZ of the Ti-containing alloy are always finer and narrower than that of one free from Ti. It seems to be explained that influence of Ti addition on the precipitation and structural parameters would be caused by the participation of the Ti atom clusters in the nucleation of GP zone and the low concentration of excess vacancies in the Ti-containing alloy.

Curie temperature of Nd-Fe-B magnet was determined with a DSC set and thermal demagnetization curve (σ-T curve) was drawn with a magnetic balance High-temperature metallography was used for direct observation of the variation of domains with temperature. Melting process of Nd-rich phase and oxidation of the specimens were observed as well. The results show that the Curie temperature of Nd_2Fe_(14)B phase is 307.5±1℃ and the melting point of Nd-rich phase is approximately 600℃.The domain structure in Nd_2Fe_(14)B phase is that of strong uniaxial anisotropy. Instead of transverse closure domains, certain amount of cone-like reverse domians would appear on the surface when the domain spacing becomes wide enough. The magnetic contrast of domains decreases continuously with the increase of temperature, but neither local migration nor partial regulation of the domains can be found until Curie temperature. During cooling, renucleation of domains in the thermal-demagnetized specimens, which have to fit in with crystal orientation, still shows some randomness. Consequently, the domains in same grain look substantially identical before and after thermal demagnetization but with minor difference.

Stress corrosion cracking (SCC) of 7075 Al alloy in a 3.5% NaCl aqueous solution under compressive stress was studied using modified WOL notched specimen. The result showed that SCC could occur if an applied compressive displacement was larger than a critical value. Finite-element analysis indicated that there was a stress concentration and the stress components were negative at the notch tip under the compressive displacement. Since the unload displacements were equal but opposite to the loaded ones, no stress relaxation occurred throughout SCC. Thus, the SCC was induced by compressive stress. The threshold stress intensity nucleating SCC from the notch under the compressive applied stress was 27.6MPa·m~(1/2) but the corresponding value under tensile stress was 8.3MPa· m~(1/2). Besides, the incubation period for SCC under compressive stress was one order of magnitude longer than that under tensile stress in the same K_I The fracture surfaces of SCC under compressive stress were quite different from those under tensile stress. The latter was composed of intergranular but the former was quasi-cleavage characterized by parallel striation pattern.

The compositions and structures of the oxide films on three typical precise bearings have been investigated by means of Auger electron spectroscopic depth profile analysis as well as deconvolution and peak decomposition investigation of X-ray photoelectron spectroscopic depth profile. The results show that the bearing with best mechanical properties possesses the thinnest oxide film which is rich in C and poor in P, S impurities.

Microscopic deformation behavior in some dual-phase steels consisting of ferrite and martensite has been observed continuously by using a scanning electron microscope with tension stand, and the strain values of two phases have been measured with graphanalyse technique. The results show that the distribution of strain between two phase and that in each phase are so nonuniform as to cause a strain gradient in front of martensite islands. The ratio of strain in martensite to that in ferrite increases with the increase of martensite content and tempering temperature as well as the decrease of carbon content in marteniste. The yield strength of dual phase steel with ferrite matrix is controlled by the ferrite.

A study under EM cbservation was carried out on the effect of Mg or Zr on NbC, M_(23)C_6, M_4B_3 and other interstitial phases along grain boundary in a NiCrMoTiNb alloy, as well as the effect of Mg on MC, Mv6C and /or M_(23)C_6 phases along grain boundary in a NiCrWMoAlTi alloy. Their behaviours were also discussed.

Studies were made of the material performance of steel 35 under low cycle torsion as well as the relationship of the low cycle torsional fatigue life together with the torsional strain amplitude and fatigue energy under torsion strain. The feature of the fatigue failure of the steel under low cycle torsion was also discussed.

Such inheritance of fracture is a pseudo-inheritance of fracture if the quenching structure, overheated not too seriously, of the alloy structural steel 40CrNi underwent requenching from normal quenching temperature reheating up at medium rate. This coarse grain fracture, showing one of the priorly overheated coarse austenite grain, is, in reality, fine grain fracture along fine equiaxial austenite grain boundary formed on reheating at medium rate. So it is called the pseudo-inheritance of fracture. It seems to be not affected on the impact toughness. The origin of pseudo-inheritance of fracture has been discussed.

The adsorption of oxygen and initial stages of oxidation on clean In surface were studied using CLS and AES. It was observed that the oxygen was already absorbed on the surface at low oxygen exposure down to 10~(-2)LO_2. A monolayer oxide on In can be found at exposure of 10~2LO_2 and a continuous metal free thicker oxide layer at 10~3LO_2, then a fast adsorption stage is followed by a slower one after 10~3LO_2

A study was made of the effect of rare earth (RE) addition on the microstructure and fractograph of the controlled rolling low carbon MnMoNb ferrite steel. Further refinement of grains as well as the decrement and refinement of bainite and martensite, hence, a mixed structure of equiaxial and acicular ferrite in the steel may be achieved by RE addition. The ultrairdcrostructural RE inclusion, which is able to contribute RE-containing steel for refinement of grains in the process of controlled rolling, is observed on the fracture surface. Therefore, a satisfactory combination of mechanical properties, such as improved strength and impact toughness, may be approached for the steel containing RE addi(?)ion.

TONG Ting; WEI Shoukun; ZHANG Shengbi; HU Mingfu(Beijing University of Iron and Steel Technology)(Manuscript received 4 July, 1985; revised manuscript 10 April, 1986)

The migration of Ti between Ti-containing slag and molten iron was found to be controlled by the diffusion of Ti ions in slag under the experimental conditions. The apparent order of reaction was detected to be of quasi-zero, and the apparent activation energy to be 258kJ/mol. The effects of some factors such as content of Ti in slag, basicity and temperature on the rate of migration have been also discussed. It seems that the basicity of slag serves a dual influence: to increase the basicity in slag with higher TiO_2 content may restrain from the reduction of Ti, while with lower TiO_2 content may accelerate the Ti reduction. Two distinguished regions of the restraint and acceleration of the reduction of Ti by Si may be drawn by wt-% ratio [Si]/[Ti] on the basis of thermodynamical analysis.

The influence of La, Y, Ce and mischmetal on the mechanical behavior and solid-liquid coexisting zone of Al-Cu alloys during solidification has been investigated with equipment specially designed. An addition of rare earths will achieve to some extent lowering the quasi-solidus, widening the quasi-liquid region and narrowing the quasi-solid region. Rare earths enhance the strength around solidus and the rast of strength increase of the alloys remarkably. Moreover, they are able to decrease the temperature and increase the stress of hot cracking formation, as a result, decrease the tendency of hot cracking. The solubility of rare earths in α-Al is very low. The existing of them makes the size of dendrites fine and increases the interdendritic strength at the later stage of solidification

The leaching behaviour of Ag in NH_3-O_2 and NH_3-H_2O_2 aqueous solutions was investigated. The results show that the dissolution of Ag was restrained by forming of a silver suboxide film on the surface under low oxidant concentration and atmospheric pressure conditions (e.g., in NH_3-O_2-H_2O system); when the concentration of oxidant was high enough (e.g., in NH_3-H_2O_2-H_2O system), the leaching process was carried out without forming of the film and the rate of dissolution of Ag was controlled by a step of mass transfer. Based on experimental results, a reaction mechanism of oxidation leaching of Ag in ammoniacal solutions was discussed.

The electrochemically alloying on Ni surface with Ta and Nb was carried out In molten LiF-NaF-K_2TaF_7 or LiF-NaF-K_2NbF_7 at temperatures between 850 and 1050℃. In both cases only TaNi_3 and NbNi_3 stable phases are detected in the bulk of the layer. The intermetallic compounds of Ta-Ni binary system, including Ta_2Ni, TaNi, TaNi_2 and TaNi_3 have been identified and the Gibbs energy of formation of Ta-Ni compounds have been calculated. It is shown that the growth of the surface alloying layer follows a parabolic law versus the alloying time. The kinetic parameters of the intermetallic diffusion of Ta-Ni and Nb-Ni systems, including the dimensionless parameters which depends on the solid compositions at the boundary of the alloy layer and the intermetallic diffusion coefficients D have been estimated by combination of electrochemical measurements and diffusion equation. The following equations are confirmed: x~2=Kt and α=(K/D)~(1/2) where x is the thickness of the surface layer and K is the constant.

The TTT- curves and kinectic parameters of metallic glass Zr_(75.9)Ni_24.1) have been determined in both isothermal and non-isothermal (continuance scanning) crystallization processes. By means of peak analysis of DSC and the sequent data treatment with a computer program, the overall effective activation energy E= 224～194 kJ/mol and the reaction order n=3.38-3.77 have been obtained respectively. It is suggested that the process in discussion is characterized by eutectic growth with a decreasing nucleation rate. This is in agreement with the results of X-ray diffraction studies reported by Altounian et al. and present authors. A brief discussion about the isothermal and non-isothermal analysis used here and given.

The previous powder-particle boundary (PPB) problem has been studied in P/M superalloy FGH95. The results indicate that the PPB carbides begin to form on the powder surface during atomization and continuously precipitate during HIP-consolidation. As a result of complex composition of carbides the different types carbides interact probably. The amount of PPB precipitation increased significantly during post-HIP heat treatment. The formation of PPB carbides is related to the amount of residual oxygen in alloy.

The effect of previous powder-particle boundaries (PPB) on the quench crack has been studied. The serious quench crack is due to the PPB caroides and on their surfaces formation of rich-oxygen layer destroying continuity of alloy and promoting fracture along the previous particle boundaries. The slight quench crack is due to the precipitation in a coarse form at the grain boundaries of γ'-phase. The coarse predipitates are surrounded by Al, Ti depleted zones forming oxide layers which promote the fracture path along the grain boundaries of γ-phase. The major reasons of the formation of quench cracks are the contamination of oxygen and unsuitable quench cooling rate.

An XPS depth profile analysis was made of the passive films on one Al-Mg alloy and two Al-Cu alloys. It was clarified that in the K_2Cr_2O_7 treated passive films on these alloys, a certain amount of Cr_2O_3 is appeared besides the majority of A1_2O_3. Thus the long-time argument about the presence of Cr_2O_3 in now settled. It was also observed that in the passive films obtained by treatment with N_2-con-taining passivation agent, some A1N and metallic complexes are detected in addition to A1_2O_3. Futhermore, No Cu is signaled in the passive film on two Al-Cu alloys obtained by either K_2Cr_2O_7 or N_2-containing passivation agent, and Cu is shielded by the passive film. It is interesting that a definite Mg peak may be observed on these two passive films although Mg content in Al-Cu alloy is very low, but disappeared after sputtering 5 min.

To resolve the obvious discrepancy between the results of HDBP+TBP and HDEHP+ TBP systems, the extractive process U(VI) from aqueous sulphate media by HDBP+TBPO dissolved in benzene has been studied. The difference between two mechanisms lies in the fact that whether the constituent of the synergic extracted complex is UO_2A_2(HA)_2TBPO or UO_2A_2(HA)TBPO. The composition of the complex was found to be UO_2A_2(HA)_2TBPO by means of slope method and equimolar series method. This is considered reasonable by predicating with cone packing model. Thermodynamic parameters for the formation of UO_2A_2(HA)_2TBPO at 298K were evaluated. The entropy change associated with the synergistic reaction (3) is 20J/mol·K, contributed by releasing a water molecule in TBPO reaction, which is in harmony with the data of TOPO system. From this result, it is possible to conclude that the synergism process is associated with adduct formation but no replacement of HA molecules.

The S-lineshape measurements of Doppler-broadening of positron annihilation, which are strongly dependent on thermal cycling time, were performed for a Ti-51at.-%Ni alloy having two-way shape memory effect. As the S-parameter increased to about 80% of the maximum value, the property of the two-way shape memory effect in the alloy may be stabilized. Both microscopic and macroscopic measurements are identical. This result seems to be available not only for establishing an effective and convenient method to analyze the stability of two-way shape memory effect, but also for evaluating such microscopic positron annihilation spectroscopy as a measure of metallic material research.

The microstrueture and sintering behaviour of the hot pressed SiC influenced by A1_8B_4C_7 phase have been studied by SEM, X-ray diffraction analysis and optical microscopy. The A1_8B_4C_7, forming as liquid phase in the presence of additives B, C and Al at 1800-2100℃, may be coagulated at the grain boundaries among SiC particles. Because of an inferior wettability of the liquid phase A1_8B_4C_7 to SiC grains, the hot pressing may be significant to enhance its densification.