The distribution of Nb among γ, γ' and carbide phases is found to be about 5: 3: 1 in the Ni-Cr-Ti type wrought superalloy of various Nb contents. With the increasing content of Nb, the stress-exponent, n, decreases and the apparent creep activation energy, Q_(app), increases and fulfils the expression: Q_(app)=B e~(kx/lge) The grain size of the alloy and the stacking fault energy of γ matrix may be decreased by the Nb added. The steady-state creep rate, ε, obeys the following relationship: s∝L~bγ_(SFE)~α The volume fraction, the particle radius and the long range order of the γ'-phase may be also increased by the Nb added. If the effective stress(σ-σ_b) was introduced to describe the stress relationship of the steady-state creep rate, the typicalcreep equation may be: S=A_1L~bγ_(SFE)~α(σ-σ_b)~n 0exp(-(Q_(app)/RT)where σ_b is the average tensile stress opposing dislocation motion in creep. An observation on the thin foil specimens under TEM shows that the perfect dislocation α/2[10] cutting γ'-phase in glide plane (111) is resolved into two partial dislocations α/6-[11] and α/6[2]. The spacings of superlattice dislocation pairs examined are about 100—165  which fit in nearly with the measured particle size of γ'-phase.

Studies were made of the cryogenic properties, structural stability and magnetism transition of a fcc γ-Fe-Mn-Al alloy containing 25.6% Mn,4.1%Al, 0.16%C and 0.27%Si, of which the strength, ductility and austenitic stability are satisfactory at temperature range of 300 to 4 K. Its physical properties were determined as follows: lower magnetic susceptibility about 34.6×10~(-4) to 22×10~(-4) from 300 to 4 K; higher electric resistivity up to 105μΩ·cm and lower cold contraction than conventional Fe-Cr-Ni austenitic steels. A peak value is presented on the plot of temperature T dependence of magnetic susceptibility x at 320 K. The sign change of dx/dT shows the paramagnetism-antiferromagnetism transition at which an anomaly of several physical properties such as elastic modulus, heat expansion, etc. is accompanied. Furthermore, by an addition of Al to Fe-Mn alloy, its Néel temperature may be markedly lowered. The magnetic susceptibility may be increasing to a greater value at Néel temperature. In comparison with AISI 300 Cr-Ni austenitic stainless steels, the γ-Fe-Mn-Al alloy is characterized by both stable austenite and quite low magnetic susceptibility within temperature range down from 20 to 4 K. It seems to be a potential constructional material for superconducting magnet applications.

The overheating behaviour of several experimental Cr-Ni-Mo steels has been investigated whereby the appearance of the ductile intergranular facets on the fracture surface may be considered as a criterion of overheating. Different overheating phenomena were resulted from that the particles of certain second phase dissolved in the solid solution at high austenization temperature and then reprecipitated along the prior austenite grain boundaries during cooling. It was observed in the Cr-Ni-Mo steels that the intergranular ductile fracture is caused by the reprecipitation of MnS particles in the steel with ordinary S content, and the overheating is also performed by the repreeipitation of AlN or VC particles along the prior austenite grain boundaries in one containing low S. Thus, a proposal seems to be made that the mechanism of overheating of Cr-Ni-Mo steels is related to the solution and reprecipitation of MnS, AlN or VC particles along the prior austenite grain boundaries. The RE additions may act as an inhibitor for the overheating of certain Cr-Ni-Mo steels. If the RE/S ratio reached a critical value, namely about 4, not only the MnS inclusion is completely converted into sulphide and oxysulphide of RE, but also the prior austenite grain is remarkedly refined and their toughness is improved. While the ratio was much greater than 4, the excess RE may be interacted with atoms of C or N.

An electron microscope study was made of the effect of B, especially as M_3B_2, on a NiFeCrWMoTiAl alloy using the fractograph of extraction carbon replica. The B additive may decrease and dissipate the, brittle flakes of Ti_4C_2S_2 which ordinarily embrittle the alloy without any B along the grain boundaries. The M_3B_2 was observed in the shape of flakes or dendritic flakes and of blocks in the alloys containing 0.025—0.050 and 0.075—0.100% B respectively. During heating under temperature below 1200℃, the M_3B_2 grains precipitate and the flaky M_3B_2 transforms into grains as well.

An investigation was conducted to examine the tensile property of 47121 β-Ti alloy in relation to the morphology of α-phase and to the fracture behaviour by means of TEM, SEM and X-ray diffraction as well as tension test. The results showed that with the increasing of volume fraction of the dispersive α-phase particles, transformed from ω-phase in situ during its aging at low temperature, the coherent stress field between particles overlapped each other and the stronger internal stress field formed in the specimen. Under the action of loading the macroscopic brittle fracture followed but on the microscopic fracture mechanism it fractured really into dimples. Therefore, the local internal stress peaks may be considered as the nuclei to form the fine dimples. The α-phase of Widmans(?)tt structure has much effect on the work-hardening. Cutting through the α-phase particles by dislocation seems to be the main strengthening mechanism in this condition, but the particles of deformation-twinned α-phase obstruct the cutting by dislocation. The non-precipitated zone formed nearby the both sides of grain boundaries together with the colony of further grown feather-like α-phase might weaken the grain boundary zone and lead it to form an alike intergranular fracture on the broken specimen.

Fatigue-crack initiation and growth was investigated by testing an ultra-high strength steel and Al alloy using a notch specimen under cyclic compressive load. Results showed that the fatigue-crack initiation and growth is started from the notch tip and its threshold value △σ_(th) or △K_(th)(ρ) is about 4 times the magnitude of that under tensile load. The crack growth could propagate at a decreasing rate and stop eventually until such length as 0.2—0.5 mm. The threshold value △K_(th)(ρ) under cyclic compressive load would be identical with that under cyclic tensile load and the fatigue-crack could continue to propagate if the minimum cyclic compressive load is near zero. The dα/dN under compression-zero fatigue, however, is 10 to 100 times smaller than that under tensile fatigue.

EFFECT OF Mn UPON THE ACTIVITY COEFFICIENT OF Nb IN IRON MELT CONTAINING Nb AND Mn

The activity of La_2O_3 in liquid slags of various composition of La_2O_3-Al_2O_3-CaF_2 ternary system has been determined by equilibrating the slag with liquid Sn in a graphite crucible under one atmosphere of CO at 1600℃ in Mo-wire furnace. The iso-activity diagram and the liquid boundary for La_2O_3 at 1600℃ were ascertained. It was resulted that the activity of La_2O_3 increases with the increase of CaF_2 concentration or with the decrease of Al_2O_3 concentration when the La_2O_3 concentration remained constant; and with the increase of La_2O_3 concentration when the concentration of OaF_2 and Al_2O_3 remained constant.

A study was made of the corrosive effect of hot salt mixed by Na_2SO_4 and NaCl on the creep rupture life of a Ni-base superalloy. It was shown that for such superaUoy the rupture life is shortened, the rupture elongation is reduced and the creep rupture curve is shifted toward the left when its specimens coated with a mixture of 75% Na_2SO_4 and 25% NaCl layer and heated under testing temperatures of 750 and 800℃. No marked influence upon their creep rupture lifes of specimens seems to be resulted either with 90% Na_2SO_4+10% NaCl under 750℃ or with 95% Na_2SO_4+5% NaCl under 800℃. The susceptibility of the superalloy to hot salt corrosion is increased by treatment of electrolytic polishing. Observations under metalloscope, SEM and EMPA revealed that the effect of the hot salt corrosion on the creep rupture life of the superalloy is substantially due to destroying of the protective oxide film on its surface, and then caused by oxidization along the grain boundaries under stress applied. Hence, the harmfulness of this corrosion effect may be concerned with the surface condition, salt composition and stress applied at elevated temperatures.

The defects in the heavily Te-doped GaAs crystals were observed under optical microscope using A/B etchant. It showed that the distance from the dislocation line to metallographic etched surface may be qualitatively ascertained on the basis of the etched figure on the specimen surface. Thus, to make an approach to concept of "stereo-etching" was tried and its principle was also discussed. After observation on the helicoidal dislocation and boat pit by means of "stereo-etching", it was confirmed that a boat pit is in correspondence with either one pitch of helicoidal dislocation or an individual dislocation loop.

A one-dimensional mathematic model was developed for describing a moving bed reactor in which theiron oxide pellets are reduced to metallic iron with hydrogen and/or CO in a counter-current flow arrangement. The model uses the "three-interface shrinking core model" as the expression of single-pellet reaction kinetics. The model consists of the reaction rate equations of iron oxides and the heat and mass balance equations for both of the gas and the solid streams. The model shows the longitudinal distribution of the process variables such as degree of pellets reduction, and composition, pressure as well as temperature of the gas stream. For the purpose of investigating the reduction process of pellets in a moving bed and checking the correctness of the model, a bench-scale moving bed reactor was established. The experiments were carried out until the steady state was reached. The calculating results based on the model show reasonable agreement with the experimental measuements. The model cart be used for describing an industrial shaft furnace, and shows a difference characteristic between the reduction process of iron ore in a shaft furnace and the reduction process of iron ore under fixed conditions in laboratory.

Precise control of chemical composition and uniform distribution of alloying elements are the requirements to obtain final products in high quality, Up to now, the problem of how to effectively control the changes in chemical composition and the redistribution of alloying elements during the remelting process is still not well resolved. The general problems introduced into the modelling of ESR chemical reac tions by virtue of the various reactions stoichiomctries are discussed. In particular it is described the difficulties in using simplified reaction schemes such as the Mn/FeO/Fe/MnO exchange as the basis for modelling systems in which as many as eight separate reactions may require simultaneous equilibrium solutions. Based upon the penetration and film theories, a scheme of describing such systems is developed. The new model, theoretically, may be applied to any ESR system, i. e. to the ESR process of any steels and alloys, and the changes in composition of both metal and slag phases may be more precisely predicted. The theoretical model has been solved. The parameters for the model are discussed and determined.

The applicability of the new model developed in Part Ⅰ of this work for the chemical reactions and mass transfer processes during the ESR is considered to the laboratory experiments of A. C. ESR of SAE 1020. The remelting experiments were carried out on the U. B. C. 250 kVA ESR furnace of It capacity using water cooled moulds of 200 mm nominal diameter, with an electrode diameter of 76 mm, and used two kinds of slag system: CaF_2+30wt-% Al_2O_3(under Ar) and 50 wt-% CaF+2+30wt-% Al_2O_3+20 wt-% CaO(in air). After the remelting process reached a steady state the system was made to undergo discontinuous oxidation-reduction reactions by point additions of either FeO or Ca powder. The model is used to predict the ingot and slag compostion. The results show that the model is in good agreement with those of practical ESR processes under the experimental conditions.

The influence of HIP (hot isopressing) on the rupture, tensile and LCF properties of three wrought Ni-base superalloys has been investigated. The mieroporosity of these alloys may be substantially eliminated by the HIP technique: 100—120 MPa for 3h at 1150℃. After HIP, these superalloys of dense and homogeneous structure were produced as compared with conventionally casting process. Their rupture properties under different temperatures and stresses, tensile properties under different temperatures and LCF lives under different stresses may be remarkably improved for the notched and/or unnotehed specimens, as well the scattering bands of rupture and tensile properties may be evidently narrowed down.

To extend the Collins' model of two-dimensional system into binary substitutional system, its Gibbs' function and free energy may be evaluated and then the equation for determination of binary phase equilibrium curve may be obtained. Certain common phase diagrams were investigated, as well as a concrete calculation was made of the "cigar" phase diagram. The obtained results are quite analogous to the behaviour of the three-dimensional ones.

The effects of the environmental conditions, such as temperature (—78—100℃), 100℃ aging, vibration, collision, shock and acceleration, on the DC and AC magnetic properties of five types of zero-magnetostrictive Co-base amorphous alloys have been stadied. These five alloys are chosen from that of low loss at high frequency, high initial permeability, square loop, high excursion range of induction and constant permeability respectively. All results were compared with five similar crystalline permalloys. The possible causes of various effects on magnetic properties were analyzed. Their suitability for various uses has also been dicussed.

The 350℃ isothermal annealing kinetic behaviour and the temperature dependence of the magnetization-and strain-induced magnetic anisotropy constants, K_(um) and K_(us), of the metallic glass Fe_(78)Si_(10)B_(12) have been studied. The K_(um) of positive value varies with annealing time t_a as a linear function of lg t_a and with temperature T in proportion to M_s~(4.6)(T). However, the K_(us) of negative value varies reversibly in a relaxation manner when tension is applied to or removed from the annealed samples and with temperature T in proportion to M_s~(7.5)(T). The behaviour has been qualitatively interpreted using a distortion-directional ordering model.

The specific conductances of molten LiF-KCI or LiF-KBr system was determined. Discussion of the results obtained from the computer simulation on the reciprocal salt pair systems according to Monte Carlo's method has been made.