The equilibrium dislocation distribution in the plastic zone at a crack tip has been calculated, where the influence of image force of dislocation was involved. The results were compared with that in which dislocation image force was omitted. A maximum value α_c was obtained for the applied stress level α, and thus a critical value α_c was correspondingly obtained for the size of plastic zone α, The dislocation image force makes the plastic zone become large while α<α_c, and the ligament yielding takes place if α>α_c. This qualitatively agrees with the experimental results of positron annihilation measurement published be fore.

Since carbon is a more intensive grain boundary active element and would replace the impurity at the grain boundary of steels, the grain boundary segregation of the impurity would be controlled by the carbon solubility in a-phase. The alloying elements, decreasing - the carbon solubility, would enhance the impurity segregation at the grain boundary. With this point of view, a new modified Guttmann's model is suggested from which the calculated results are in good agreement with the experimental data in carbon and Cr steels.

The coarse Widmanstatten structure in Ti-6A1-4V alloy casting can be refined effectively by means of the following heat treatment: quenching from β phase region and then cyclic heating in (α+β) region. The mechanical properties of this casting will also be improved by this treatment. The results show that queching from β phase region can remove the α grain boundaries and thus a whole martensite structure will be obtained. Consequently, the heredity of Widmanstatten structure was cut off. During the subsequent cyclic heating, the martensite decomposes and β phase precipitates on the dislocations and along the substructural boundaries of α′ Plates, so that they are separated into small segments. Accompanying with the increasing number of cycles or time of annealing, the α segments grow up and form acicular α with random orientation. Finally, fine basketwave structure emerges. The breaking of α plates can be well explained by dissolution-separation process caused by cyclic heating.

To investigate the structure of quenched and tempered large section die, the cooling rate simulating that of central part for 300×300mm section has been used during quenching. As a comparision, ordinary quenching process has also been carried out. TEM observation shows that the structure of the latter is mainly lath martensite, and that of the former is B_I -bainite, which possesses higher temper stability than those found in low carbon low alloy steels. Transforming of great quantity of retain austenite and creating of chain-like distributed M_3C are considered as the main reason of the embrittement for the large section dies.

The butterfly martensite formed in T12A, GCr18Mo, CrMn and 25Cr2Ni-4WA (carburized) steels have been examined using optical microscopy and TEM. It was found that the mid-rib of butterfly martensite is a thin plate martensite and the formation of butterfly martensite is not a continuous process, but rather a compound one consisting of some separated stages. In the initial stage, the crossed or kinked thin plate martensite forms, and then it grows toward cross-range into the butterfly martensite with or without tail.

High temperature microscope, scanning electron microscope and positron annihilation techniques have been used to study the influence of vacancy type crystalline defects on reverse martensite transformation and shape memory effect in a Cu-Al-Zn-Mn-Ni alloy. Experimental results indicate that by decreasing cooling medium temperature, the reverse transformation is shifted to higher temperatures and completed in a wider temperature range, and the maximum shape recovery ratio is correspondingly decreased. But decreasing cooling medium temperature further to below a certain point will then result in a lower reverse transformation temperature and a narrower temperature range of completion, and a higher maximum shape recovery ratio. Some anomaly is observed when the specimen is quenched into A_f-M_f range. The experimental results are well explained according to the average life time τ and Doppler broadening line-shape parameter S of positron annihilation as well as the analysis of microstructure.

Various types of carbide precipitation have been observed in steel 10 and 20SiMnMo during isothermal transformation. It seems that two interphase precipitation processes may occur. One of them takes place at the temperatures between pearlite and Bainite transformation, it may be associated with massive transformation and occurs mainly through a random transfer of atoms across γ/α interphase. Another involves bainite transformation, Ledge-propagation mechanism is the dominant feature of interphase precipitation. Both of them have been observed by means of TEM determination.

The hydrogen-induced embrittlement of rotor steel 34CrNi3Mo was studied by means of slow tensile test of specimens with various hydrogen contents. With the increase of hydrogen content in the steel and the retardation of strain rate, its plasticity drops sharply till almost wholly lost when hydrogen stexceeded 5mL/100g and strain rate was down to 3×10~(-5)s~(-1). The hydrogen content of steel to free flake or hydrogen-induced embrittlement is limited to 2 or 1.48mL/100g respectively. SEM observation shows that the flakes in slow tensile tested specimens revealed their elliptical freckles of sharp boundaries and the micromorphology is transgranular quasi-cleavage consisting of clear tearing ridges and tiny quasi-cleavage planes.

The stress intensity K_Ⅱ of a mode Ⅱ specimen was calculated using a finite element method via the J integral. The site direction and threshold value for crack initiation from the notch under cyclic mode Ⅱ loading in air, in water and under dynamic charging with hydrogen were investigated. The results showed that the mode Ⅱ fatigue crack in a high strength steel initiated at or close to the site of the maximum principal stress, rather than at the site of the maximum shear stress, and the subsequent crack growth was orientated approximately normal to the direction of the maximum principal stress. The site and direction of crack initiation in water and under dynamic charging with hydrogen were similar but different from that in air. The threshold values for crack initiation in air, in water and under dynamic charging were 28.8, 12.3 and 10.2 MPa·m~(1/2), respectively. The fracture surface of a corrosion fatigue crack in water and under dynamic charging consisted of intergranular facets at low △K_Ⅱ values but of quasi-cleavage at higher △K_Ⅱ values and were different than those in air.

In situ observations of the behavior of void formation and dislocations formed ahead of a crack in a spheroidized low carbon steel have been carried out during fracture tests with TEM. The results show that the fracture occurs through alternate processes of nucleation, growth and coalescence of voids during plastic deformation. Void coalescence generally associates with the necking of matrix metal between the voids. Most frequetly, the cracks are in a zigzag shape. The deformation on the two sides of a zigzag crack does not match microscopically with each other. Dislocations may emit from the crack tip when the crack is either propagating or blunting. The dislocation emission is the main cause of the crack blunting. The effect of dislocation distribution on the void formation has also been discussed.

The effect of microstructure on the room temperature fracture behaviour of a precipitation hardened austenitic steel has been investigated. Under the same aging conditions, the dimple or intergranular fracture is shown when the solution temperature is not higher than or above 1100℃ respectively. On this basis, the intracrystalline and intergranular fracture models were discussed separately.

The creep rupture behaviour of a wrought Ni-base superalloy GH37, bared or coated by a mixture of 10% NaCl and 90% Na_2SO_4 (by wt), has been studied from exposure to air at temperature range of 700-850℃ under stress range of 196-509.6MPa. The creep rupture life and ductility of the salt-coated specimens are reduced dramatically, whereas the ε_(min) is hardly influenced. The hot corrosion does Hot change the creep mechanism since the creep activation energy and stress exponent obtained of coated specimens are nearly similar to the bared ones in air. In the hot corrosion envirnonment of a higher temperature and lower stress, saying, 800℃ and 264 MPa, the finer the grain size, the more severe the reduction of creep rupture life is, while at lower temperature and higher stress, saying, 700℃ and 509.6MPa, the creep rupture life of the alloy with intermediate grain size is longest. It seems that the Shortening of creep rupture life of salted specimen is due to the decomposition of carbides, depletion of Cr and sulphation at grain boundaries which lead to an increase of creep crack nucleation and growth rate

The effect of single tensile overload on crack propagation near the threshold in an austenite stainless steel has been investigated. The threshold value increases with the increase of overload ratio P_o/P_(max) as it is larger than 1.4. But the threshold value will not be effected by this ratio while it is less than 1.4. It was supposed that the reduction of crack propagation and increase of the threshold value arise primaryly from crack tip closure,i.e. plasticity-induced and roughness-induced closure.

The first hydrogen absorption curves of TiMn_(1.5-x)Cr_x have been determined at 40℃ and an initial hydrogen pressure of 4.05MPa. Pressure-composition desorption isotherms for TiMn_(1.5-x)Cr_x-H system have also been determined at 19℃. The results show that hydrogen storage properties improve markedly while Mn was partially substituted by Cr: reducing the VIZ incubation period, enhancing the absorption rate, increasing the absorption capacity and slightly raising the desorption amount of hydrogen.

Zr promotes the formation of eutectic γ′, MC, Ni_5Zr and (Zr, Ti)_2 SC and stabilizes the microstructure of Ni-base superalloys at high temperatures as that Hf does.Furthermore, it enhances the mechanical properties of as-cast alloys at medium temperatures. But the efficiency of it is not as strong as Hf, because of its lower solubility in eutectic γ′. However, the solubility of Zr in Ni_5M is higher than that of Hf, it is helpful to the formation of Ni_5 M. This implies that one can not substitute Zr for Hf with same atomic fraction. Combination of Zr and Hf additive is beneficial to the mechanical properties of the alloys at medium temperatures.

The creep friction stress of γ' strengthened superalloys containing 5 and 10 wt-% Co has been measured by means of stress dip test on the creep machine modified by the authors. The results analized with either asymptote or McLean's method show that Co will linearly increase the friction stress value for Ni-base superalloys.

In view of interaction of hydrogen with point and line defects in initial stage of the plastic deformation, the influence of hydrogen charging on yielding behaviour of Armco-and Vacofer-Fe has been investigated. Various models on hydrogen embrittlement have been discussed. It is considered that the change of mechanical properties induced by hydrogen may be attributed to that hydrogen promotes the thermal activation, increases the movable ability of intestitial atoms and reduces the resistance of dislocation movement.The experimental show that these effects are directly related to the state and distribution of hydrogen atoms in the vicinity of the dislocation.

The dislocation velocity exponent and room temperature creeping of the alloy increase and the hardening exponent in tensile deformation decreases while suficient quantity of H was charged into the metastable β-phase Ti-15Mo alloy. It is considered that the hydrogen dissolved in the alloy reduces the atomic cohesion of the alloy, consequently, the resistance of movement of dislocations decreases, that causes the deformation occur easily.

The cooling rate results in the change of structural distortion of Y_1Ba_2Cu_3O_(9-x) phase, which depends upon the oxygen content in it. Y_1Ba_2Cu_3O_(9-x) phase reacts with O_2 in 600-400℃ during cooling, this causes the structural distortion related to superconductivity. Slow cooling in this temperature range benefits the absorption of O_2.

Resemble principle of electrical analog and the corresponding mathematical equations were described. Resistance paper was used as the simulator to investigate the variation of the gas flow field parameters in a blast furnace by means of observating the electric field. Some imformation for both the production process of ironmaking and design of the size of blast furnace may be provided by this method.

The crystallization kinetics studies during the recent years on the FeB and FeCoBSi Series of amorphous alloys as well as on the effect of alloying with various transition metals are summarized. The specimens were ribbons of 30—50 μm thickness and 1—2μm width prepared by the melt quenching technique. DSC and thermomagnetic measurements, and sometimes X-ray diffraction investigations were carried out. The main results are: (1) for the Fe_(100-x)B_x series, both the incipient crystallization temperature, T_(cr), and the corresponding activation energy, △E, exhibit a maximum value at x=16; (2) when the alloy composition was varied or an alloying transition element was added, both T_(cr) and △E increased with decreasing average number outer electrons per atom which was calculated by taking into account both the s, p and d electrons of the transition metal atoms. These and other less significant results are discussed in connection with various factors commonly regarded as effecting the stability of amorphous alloys.

The preparing processes of amorphous CoFeNiNbSiB soft magnetic thin films using r. f. sputtering have been investigated systematically. It was found that high quality soft magnetic films can be obtained at low pressure Ar(0.5 Pa), and the properties of films are less influenced by the bias. After annealing in a rotating field, the initial permeability of films is not less than 3000, at the field up to 10 MHz, and they show a good frequency response! The structural relaxation process of amorphous films during annealing has been studied by means of resistance monitoring method. Four successive relaxation stages have been observed at high temperature.

Oxidation and crystallization behaviours of three Ni-Zr amorphous alloys have been studied during isothermal annealing at the temperatures below their crystallization temperature by means of electrical resistance measurement, differential scanning calorimetery and X-ray diffraction. Selective oxidation of Zr has been found in these alloys. As a consequent, it increase the thermal stability of surface layer constructed by Ni_(37)Zr_(63) but decreases that constructed by Ni_(65)Zr_(35). The reason of this effect has also been discussed.

In order to assess the effect of stress triaxiality on the plasticity and ductility of the structural mild steel and the associated weld metals, the tensile tests on notched round bar specimens were performed. The results indicated that the strains to initiate failure for the boiler steel and weld metals were a strong function of stress states. Under the same triaxiality the failure initiation strain of J427 weld metal was the largest among these materials, and that of J422 weld metal was the smallest. Moreover, the material constant C values relating to the metallurgical characteristics were given for the experimental steel and weld metals.

The computer simulation was made of the rapid solidification in self-quenching with the moving Gaussian source model. Results are in agreement with those calculated analytically and coincide with experimental values when v= 4.25-97.5cm/s. The computation can be performed with a microcomputer.

Calculation of activities on the two-phase region boundaries in CaO-Al_2O_3-SiO_2 ternary system has been carried out. Relationships between the activities of components and the composition of intersection of tie-line and composition edges along two-phase boundaries have also been presented, upon which the activities may easily be read. This method can also be used in other ternary systems.

A Seemann-Bohlin X-ray diffraction attachment for thin film analysis has been developed and the" diffraction intensity of it has also been discussed. The results of calculation show that: (1) The diffraction intensity for solid surface or thin film analyzed by this attachment is 7—20 times as high as that by ordinary diffractometer. For example, to analyse a Au film of 7nm thickness using a 1 kW X-ray source, a fairly good diffraction pattern was obtained up to 2θ=120° with the scanning speed of 4° (2θ)/min. (2) It can also be used for determining of thick polycrystalline samples. In this case, its diffraction intensity is 3—20 times as high as that of ordinary diffractometer. These conclusions were confirmed by experimental results.

Oxygen concentration cells with β-Al_2O_3 solid electrolyte Pt

Internal friction and modulus (especially the changes of it at the temperatures below 500K) for Fe-Ni base metallic glass have been studied during structural relaxation using a Bordoni-type system. The results show that the structural relaxation may consist of two steps: the low temperature (below 500K)structural relaxation governed by TSRO and the high temperature (above 500K) one governed by both CSRO and TSRO. The activation energy of low temperature structural relaxation is about 17 kJ/mol.

The microstructure, especially M-A structure of the welds with 50—100kgf/mm~2 strength has been examined by optical and electron microscopy as well as selected area electron diffraction. It was observed that M-A structure practically consists of carbon-rich austenite or martensite or both of them. They appear particle or lath in morphology depending upon the contents of alloy elements. They distribute primarily at or near the grain boundaries and sometimes within the grains. The structure of weld metal varies from proeutectoid ferrite acicular ferrite and pearlite to granular bainite and finally to lath bainite and martensite, while the alloy content (also strength) increasing.