Grain boundary embrittlement by μ and σ phases was studied in 15Cr-25Ni and 15Cr-40Ni type iron-base superalloys. The embrittlement of iron-base superalloys can be sensitive to small amounts of μ and σ phases present at the grain boundaries, even when the weight fraction is between 0.01 and 1%. The degree of embrittlement was found to be directly proportional to the concentration coefficients of the μ and σ phases at the grain boundaries. The embrittlement effect results in intergranular fracture during impact testing. Fracture mechanisms caused by the μ and σ phases were quite different. This embrittlement effect was suppressed by reducing the grain size or by decreasing or removing the grain boundary embrittling μ and σ phases by controlling the chemical composition of the alloys.

The nucleation aria propagation of hydrogen induced cracking in various environments capable of supplying hydrogen such as H_2 gas, H_2S gas, distilled water, H_2S solution, 0.1N K_2Cr_2O_7 solution, acetone, alcohol and hydrogen introduced by charging have been traced by metallographic shadowing technique in four low-alloy steels with a wide range of tensile strength (900 to 1800 MPa). The variation of K_(ISCC)(Or K_(ⅠH)) with strength of the steels in these environments has also been investigated. It is shown that if K_Ⅰ of the crack tip exceeds K_(ISCC) (or K_(IH)), a hydrogen induced delayed plasticity will occur in all the environments experimented, followed by a nucleation and propagation of hydrogen induced cracking, i.e., with the entry of the hydrogen atoms, the size of the plastic zone and the plastic deformation in front of the crack tip are enlarged continuously with time. In ultrahigh strength steels, the hydrogen induced cracking is nucleated at the tip of the closure of the two paths of delayed plastic zones. These discontinuous cracks will grow and join one another with the progress of the delayed plasticity. In lower strength steels, the initial pre-crack propagates continuously along the path near to the border of the delayed plastic-elastic region with the enlargement of hydrogen induced delayed plastic zone. Thus, it is concluded that hydrogen induced delayed plasticity might be necessary and sufficient condition for hydrogen induced delayed cracking for Mode Ⅰ crack.In all the environments used, the K_(ISCC) (or K_(IH))is increased, and the da/dt decreased with the decrease of the strength of the steel. With identical strength level, anodic polarization in water or addition of the inhibitor (0.1N K_2Cr_2O_7) may bring about an increase in K_(ISCC) and a fall in da/dt, however, cathodic polarization in water affects inversely. Lower K_(ISCC) and higher da/dt are obtained for stress corrosion in saturated aqueous solution of H_2S or electrolytic charging during loading. It was also observed that another mechanism of hydrogen induced cracking, i.e. hydrogen pressure mechanism is operative during severe electrolytical charging without external stress.

Stress corrosion tests were conducted with a cantilever bend test machine. An aqueous solution of 3.5% NaCl was used as a corrodent. It was observed that the shape of the crack front is closely related to the surface deformation on the specimen surface perpendicular to the stress corrosion crack. This experiment shows that for ultra-high strength steels the change of the size of the deformation zone observed on the specimen surface can be hardly explained by the change of the size of the plastic zone at the tip of crack. Such an observation may be correlated with the stress state of the surface layer.

An investigation on the crystallographic orientation and elemental segregation of flakes (hairline cracks) has been carried out by means of etching method and electron optical techniques (SEM, TEM, EPMA and AES). The results obtained are as follow:(1) The microappearances of fracture surface of flakes are a mixed fracture mode of quasicleavages and intergranular tearing waves.(2) The direction of the crack propagation of flakes are mostly along {112} planes of ferrite. These planes are also quasicleavage facets. While the orientation of the dendritic surface of flakes are {111} planes.(3) There are positive segregations of P, Mn, Mo, Cr and Si on the fracture surface of flakes, among which the most one is phosphorus.

The effect of high temperature solution treatment on the structure and properties of a directionally solidified high strength nickel-base superalloy has been investigated. The size and amount of fine γ' particle in the ahoy increased with the increase of solution temperature. Creep rupture life τ_f was increased and secondary creep rate (?) decreased with the increase of the solution temperature. As the alloy was undergone 1210 to 1250℃ solution and 900℃, 16 h aging, a two-fold increase in creep rupture life was obtained at 760℃ under 66 kgf/mm~2 load, however, the secondary creep rate apparently decreased. The relationship between τ_f and (?) can be expressed as (?)~mτ_f =c, where m≈1, c≈8.0. It is thus regarded that the improvement of rupture life at intermediate temperature (760℃) is due primarily to a fall in secondary creep rate, and in turn to an extension in secondary stage of creep. The secondary creep rate is strongly dependent upon the size, a, and volume fraction, ν_f, of the fine γ' and (?)∞α/ν_f~(2/3).The dislocation substructure during secondary stage of creep has been examined by TEM. At a creep temperature of 760℃, there were a number of dense 3-dimensional dislocation networks in γ matrix, but only a few superlattice dislocation pairs appeared in γ'. When the temperature was increased to 980℃, the γ-γ' interface was found to be covered with 2-dimensional dislocation networks. A mechanism for secondary stage creep has been proposed according to the climbing model.

The effect of post-sintering heat treatment on the mechanical properties of a liquid phase sintered tungsten-base ahoy (95W-3.SNi-1.5Fe) has been investigated. Through heat treating in vacuum at 1200℃, the hydrogen content of the alloy was decreased by 70%, however, its strength was increased by 30%, and its ductility and fracture toughness were also improved. A SEM observation on the fracture surface of the alloy showed that interfacial failures occurred at the tungsten particle-matrix interface in specimens with higher hydrogen content. While in specimens with lower hydrogen content, the fracture mode were transfered from interfacial to interfacial plus partly cleavage failures in tungsten particles. It appears that the hydrogen brittleness is diminished, and the cohesion of the interfaces increased, as a result of decreasing the hydrogen content of the alloy. Ion microprobe analysis showed that in specimens with higher hydrogen content, hydrogen is concentrated at interfaces, which further accounts for the influence of hydrogen on the interracial failure of the alloy.

The steady state creep behaviour of the Ni-20Cr base alloys with various contents of W and Co has been investigated in the temperature range of 940 to 1040℃. Both W and Co may raise the activation energy for creep, Qo, obeyed the relationship:Q_c=Ae~(kx/lg~(?)) where x is the atomic fraction of W or Co additions; A is a constant for the alloy composition and k is equal to 7.0 and 0.55 for W and Co additions respectively. The steady state creep rate (?)_s of Ni-Cr-Co-W alloys was predicated to be:(?)_s=Cσ~m exp (-Q_e/RT) where m=6.45±0.10 or 5.3 depending on whether μ phase is present or not. It was also shown that the (?)_s varies with the stacking fault energy γ according to the correlation:(?)_s∞γ~(1.4)

The titanium loss during electroslag remelting superalloys A286 and V57 has been studied. It was shown that TiO_2 becomes the predominant oxidant causing the titanium loss of the superalloys when the concentration of TiO_2 in slag used is higher enough, and that the oxide of lower valence titanium which may be kept in eqilibrium with titanium in molten superalloy seems mainly to be Ti_3O_5. The controlling factor for the rate of titanium loss may be the speed of mass transfer of Ti~(4+) across metal/slag interface which increases with the increase of concentration of TiO_2 in the slag. Thus, the remedy for its titanium loss will be dependent upon reducing Ti~(3+) diffusion rate toward slag/atmosphere interface. Attempt has also been made on the correlation between TiO_2 concentration in the slag and the mass transfer coefficient of Ti~(4+) in CaF_2-Al_2O_3-TiO_2 slag system across either electrode/slag or metal pool/slag interfaces at 17004±10℃. The mass transfer coefficient of Ti~(4+) may be expressed as:k_(e/s)=6.59exp(-0.078TiO_2), 10~(-2)cm/sk_(p/s)=2.84exp(-0.079TiO_2), 10~(-2)cm/s The mass transfer coefficient of Ti~(3+) toward slag/atmosphere interface was measured, i.e. 2.2×10~(-1) cm/s at 1500℃.

The deformation and primary recrystallization texture in a MnS-AlN-inhibited 3%Si steel has been investigated by X-ray diffraction and etching pits technique. Differing from the convcntional grain oriented silicon steel, the hot rolling texture of the MnS-AlN-inhibitcd 3%Si steel consists mainly of {112}<110>, {111}<110>, {100}<110> and {111}<112> components. The cold roiling textures were found to be correlated with the hot rolling textures by inheritance as the cold reduction percentage is within the range of 80—87%, and changed toward thestable {100}<011> orientation when it is over 87%. Apparently, this latter case is unfavourable to the magnetic properties of the steel. The correlation between the transformations of hot rolling, cold rolling and primary rccrystallization textures has also been discussed.

The temperature dependence of the lattice constants of the compounds CeCo_5, Ce (Co_(0.8) Cu_(0.2))_5 and Ce (Co_(0.9) Fe_(0.1))_5 in the range from room temperature to 600℃ has been studied. CeCo_5 shows an invar-type thermal expansion anomalies in axis c below the Curie temperature. But the anomalies are considerably reduced on the partial substitution of the Co atoms by the Cu atoms. Studies of the neutrons diffraction have been carried out on the compounds Y (Co_(0.8) Cu_(0.2))5, and it has been found that the Cu atoms prefer to occupy the site 2c. There by the thermal expansion anomalies along axis c of the compounds RECo_5 is explained.

The crack-tip plastic zone in mixed-mode brittle fractured specimens of different K_Ⅱ/K_Ⅰ ratio of a high strength steel has been investigated under critical conditions. Both elastic approximate analysis and elastic-plastic finite element method were used to analyze the distribution of stress, strain and strain energy density in the vicinity of the crack-tip. It is shown that:(1) at the initial moment of crack growth, the (σ_θ)_(cr) and S_(cr) are notmaterial parameters, but increase with K_Ⅱ/K_Ⅰ;(2) for all specimens fractured under linear elastic condition, the crack tip plastic zone area of mode Ⅱ is larger than that of mode Ⅰ by two order of magnitude and the total plastic work absorbed before brittle fracture markedly increases with K_Ⅱ/K_Ⅰ;(3) the higher the K_Ⅱ/K_Ⅰ ratio is, the lower the σ_m/(?) in the vicinity of crack tip and initial growth directions;(4) under mode Ⅰ condition, the area of the plane stress plastic zone at specimen surface is larger than that of the plane strain plastic zone at the centre of the same specimen by a factor of 3. However, with the increase of K_Ⅱ component, their difference decreases. Therefore, the influence of thickness on mixed-mode brittle fracture toughness might be smaller than on mode Ⅰ.Besides, the increase of hydrostatic tension stress under plane stress condition is quite different from that under plane strain condition. Once the crack tip zone falls into plastic state, the increase rate of the hydrostatic tension stress in the plane stress crack tip zone will become gentle instantaneously, but scarcely any such change would be observed under plane strain condition. It seems that at the initial growth moment the hydrostatic tension stress in the plane stress plastic zone is much smaller than in the plane strain plastic zone.

An iron-nickel base superalloy (Fe-35Ni-15Cr-2.7Al-2.5Ti-2W-2Mo) was subjected to high temperature thermomechanical treatment (HTMT) at 900, 1000 and 1100℃. The mechanical properties were evaluated. Results indicate that substantial improvement in tensile and yield strength, ductility and notch toughness can be accomplished by HTMT. Under testing temperature of 650℃, the stressrupture life of 1100℃ thermomechanically treated superalloy is not lower even than that after conventional normal heat treatment. In particular, the influence of deformation temperature on the structure and the mechanical properties of the superalloy was studied by both optical and electron microscopy. It is clarified that the strengthening mechanism caused by HTMT under various temperatures may be grain refinement, cross slip, sawtoothed grain boundaries, precipitation along grain boundaries and dislocation substructure formation.

The distribution of atoms in lattice corresponding to different degree of order was calculated for Fe-Al alloy under given concentration. The atom co-ordination of the alloy may be resulted from analysis of the Mossbauer spectra obtained. The long-range order parameter of the alloy is then determined with comparison between the measured and calculated values. A brief discussion on these values has been also made.

The temperature dependence of electrical resistivity of PtW_(8.5) and PtW_(8.5) Re_5Ni_2 alloys as well as the effect of annealing temperature and cold deformation have been investigated by the measurement of thermo-electromotive force, by DTA and X-ray diffraction. Their resistivity increases after long-term annealing under elevated temperature or after slowly cooled down from high temperature, but decreases with cold deformation. It seems that their anomalous thermo-electro-resistivity may be resulted from the formation of K-state.

It is shown that the crystallization of the sputtered amorphous Sin-Co magnetic films is entirely different from that of the thicker plasma-sprayed ones given in literature. On heating the sputtered amorphous films, a β-Co transition metal phase forms first, no rare earth-transition intermetallic compound was observed till 750℃. This is believed to be related to the higher surface energy of thin films.