The deformation behaviours of Ni_3Al alloys with various chemicalcompositions and subjected to different heat treatments were in situ observed underSEM. Moreover, in situ observations of slip trace were supplemented by the directobservation of dislocation arrangements under TEM. In B-doped Ni_3Al alloys it isshown that close to the grain boundary there exists a thin slip transition region,within which slip lines are reoriented or other slip systems are operated to producea local strain accommodation and to relax the stress concentration at grain bound-aries. Boron seems to lower the stress for dislocation generation from the grainboundary or to ease the cross-slip close to the boundary,and also to increase the numberof dislocation sources. However, B-enhenced ductility is seriously affected by alloystoichiometry, the addition of a tertiary alloy element and heat treatment, etc.

The embedded atom type potentials and static relaxation method combin-ed with highest gradient computational technique have been used to simulate thegrain boundary atomic structures, grain boundary energies, grain boundary cohesiveenergies, the distribution of electron density and stress field in the grain boundaryregion, and other related problems of [100], [110] and [111] symmetric tilt grainboundaries in Ni_3Al with different grain boundary geometrical index and composi-tion.Their relations with the segragation of B, behaviours of the grain boundary,and especially the stoichiometrical effect of B induced ductility have also beenstudied and discussed.

The solid solubilities of 15 common alloying elements added to theLl_2-type intermetallic compound Ni_3Si at 900℃ have been estimated, and their sub-stitution modes have been deduced from the direction of solubility lobe of the com-pound. It is shown that the alloying behaviours in Ni_3Si are determined by bothsize and electronic factors, i. e., the substitution behaviour by electronic configura-tion and solubility by the both. An interaction parameter is presented to describequantitatively the influence of electronic configuration on substitution behaviour andthe solubility limit can be successfully explained together with atom radii.

An observation under TEM was carried out on the distinct images ofthe intragranular VC in the foils of an GH36 superalloy after normal heat treatmentand long-term aging. The size of VC was measured by means of the Moire pattern.The misfit between VC and austenite was also accurately calculated. The M_(23)C_6 en-voloped in VC shell was observed in the long-term aged specimens. The coherentrelation between the intragranular M_(23)C_6 twin and austenite as well as its coherentinterface were studied. The effects of the intragranular precipitation and of thegrain boundary phases in the superalloy on its stress rupture of life were alsodiscussed.

The formulas to calculate the electronic stopping power, S_c(E), forheavy ion implanting into metal have been developed by using the Wigner-Sietz ra-dius, equivaleni charge, Fermi velocity and Ziegler's values of hydrogen electronicstopping power. The results calculated are believed to be in agreement with thosemeasured experimentally in previous literature. The formulas to evaluate S_c(E) foralloy, boride containing or CsCl structure have been also derived. However, theseare favourable to only mono-or bi-borides, but not for borides with complex struc-ture such as Cr_5B_3 or W_2B_5. The coefficient of S_c(E) for alloy of CsCl structuredeviating from Bragg's S_c(E) is directly proportional to charge transfer in alloy.The larger the charge transferis, the stronger the metallic bond is. Hence, theS_c(E) created by metallic bond in alloy will be increased; there is a tendency forit to increase with increasing separation of two components in alloy on either sideof Cr group at same periods; and the tendency is larger when the two componentsare in different periods.

The stability of the thermoelastic martensite in a Cu-14.84wt-%Zn-7.75wt-%Al shape memory alloy with M_s=106℃ after direct quenching or steppedquenching has been investigated by using TEM, X-ray diffractometer and doubleelectric bridge instrument. The martensite aged for about 3h at room temperatureafter either direct quenching or stepped quenching (150℃, 2 min) is the structureof M18R. The martensite just directly quenched is not so stable, both its certaindiffraction peaks and specific electric resistivity change with aging at room tempera-ture; whereas it is stable after stepped quenching (150℃, 2min), and its diffractionpeaks and specific electric resistivity change no more with aging time at room temp-erature. The above mentioned results seem to be explained by the martensite re-ordering.

The hydriding and dehydriding properties, electronic structure, crysta-lline structure and micomorphology of Mg modificd by tetrahydrofuran, as well asthe stabllity of its hydride have been investigated. Experimental results show thatafter 20 cycles of hydriding and dehydriding, the modified Mg may absorb 3.5 wt-%hydrogen at 643 K under 3.5 MPa H_2, and evacuate 3.2 wt-% hydrogen at 642 Kunder vacuum. The tetrahydrofuran may cause the change of electron structure ofMg, but not change the crystalline structure. It was found a new hydride phasebesides MgH_2 in the hydrided products. The distortion in great extent may be result-ed by the hydriding transformation as the polycrystalline hydride formed in Mgand the slip band and twin widely spreaded in the crystals of Mg hydride.

The dynamic fracture toughness of a mild steel has been studied atdifferent loading rates and temperatures. The material exhibits a transition fromtough to brittle fracture with the changing of loading rate alone. Analysis of thefracture process by the theory of thermal activation suggests that the fracture activ-ation energy approximates the bond energy on the {100} plane of a unit cell. The tough-ness can be resolved into two parts, J_(Id)=J_a+J_t. where J_a is the athermal part, beingindependent on temperature and loading rate, while J_t=(K/K_0)~(1/″) exp (Q_f/nkT), whichcontrols the fracture process is temperature and loading rate dependent. the transi-tion of fracture mechanism caused by both temperature and loading rate is associatedwith the thermal movement of atoms.

The effect of ferrite content in ferrite-martensite dual-phase steel onthe initiation and propagation of fatigue crack and the plastic deformation at cracktip has been studied. In a range of ferrite content from 24.2 to 41.5%, the opti-mum seems to be 33.8%, of which the crack initiation will be prolonged, the thre-shold value increased, the propagation rate decreased and the closure stress intensityfactor increased. As the propagation force is described by effective stress intensityfactor, three steels with various ferrite contents will show the same propagationbehaviour on da/dN vs △K_(off) curve. It is shown that the closure effect increaseswith the decrease in △K at the fatigue crack tip. When △K equals to △K_(th), theclosure effect reaches a maximum value of 0.7 in a dual-phase steel with 33.8%ferrite.

The effect of grain boundaries on cyclic deformation and fatiguecrack growth in Al bicrystals under stress controlling in laboratory atmospherehas been studied. The effect of a grain boundary is found to be restricted in anarrow area, termed as grain boundary affecting zone (GBAZ), where the incom-patible plastic strain by the two sides of the interface under cyclic loads creats in-ternal stress which conversely promotes inhomogeneous slip in the area and grainboundary cracking. As an extended stage I crack initiated from a notch approachesthe grain boundary under a constant cyclic load, the crack branches, the crackfront splits into several pieces, meanwhile, the growth rate reduces to a minimumvalue at the centre of GBAZ. Such microstructure-sensitive growth of extendedstage I cracks is mainly attributed to the grain boundary-induced crack tip shielding.

The effect of Al content on the ductile-brittle transition temperatureof Al-Si coating and the effect of fracture behaviour of the Al-Si coating on thefatigue properties of Ni-base superalloys have been investigated to propose the the-oretical basis of search for an optimum of mechanical properties of the high tem-perature coating on Ni-base alloys.

The stabilization of the thermoelastic martensite in a rapidly solidi-fied Cu-Zn-Al alloy is believed to be an atomic configuration from ordering todisordering, and the transition of martensite structure from M18R to N9R (b/a=1/3~(1/2)). This is dependent upon the intrinsic decomposition tendency of the marten-site.

The microstructures of Ti-33wt-%Al-(1.6--4.5) wt-%Mn alloys arecomposed of γ+α_2 phases, but the valume of α_2 phase is a little. Mn alloying de-creases the α and c lattice axes of γ phase and the c/α value is more nearly to one,because the atomic radius of Mn is less than the atomic radius of Ti or Al. Mnalloying promotes the formation of twins in γ phase and increases the ability ofplastic deformation of TiAl alloys at room temperature.

The precipitation of (Ti, V) CN in the high carbon steel PD3 during soakingat austenitic area temperatures after deformation has been observed. The average size of (Ti,V) CN grains precipitated may be reduced as the increase of strain and the decrease of soakingtemperature, and vice versa. The growth of (Ti, V) CN grains at 920℃ is found to be con-trolled by the interboundary reaction between precipitated grains and matrix.

The influence of two different grain shapes and carbides in the HK40 alloy,the material for use of furnace tube, on the rate of creep crack growth has been investigated.The material of columnar grain is inferior resistance against creep crack growth to that ofequiaxial grain, when the load line is perpendicular to the columnar grain axis. The influenceof secondary carbides on the rate of creep crack propagation is dependent upon the grain shape.

Based upon the aspect of continuous damaging, the process of ore com-minution may be described as the growth and propagation of the microcraks in theore grains under external loading, and a theoretical expression has been developed onthe relationship between the grain size distribution and the total energy consumptionduring entire ore comminution process. The energy consumed totally may be consi-dered to consist of two portions: i.e., with fresh crack surfaces growth and withcrack propagation. The expression proposed seems to be an advance over previousconventional ones, especially that from the viewpoint of energy distribution.

By use of the two-component LDA and high speed camera, the watermodel of the flow field in matal bath under molten slag has been tested. On the basis ofexperimental results, the flow boundary conditions of liquid metal at the slag-metalinterface of a gas injecting bath were deduced. The flow field and the turbulent pa-ramaters of the metal bath covered with slag were solved by the vorticity-streamfundion method. Results reveal that the flow velocity, turbulent energy and circulat-ing rate of the melt under slag are lower than that of without slag cover. Anotherone "dead zone" of the lowest turbulent energy is formed in the top layer underthe cover of slag near the ladle linnng.

A separated flow model with stochastical trajectories has been develop-ed to describe the fluid flow in a bubble stirred ladle. The bubble dispersion, tur-bulent characteristics and gas liquid interactions can be predicted by this mathema-tic model. The bubble flow as a dispersed phase is treated in Lagrangian frame ofreference and the analysis of the turbulent flow for liquid phase is conducted inEulcrian field. The interactions between bubbles and liquid phase are considered asa bubble source term in the control equation for continuous phase. The Monte Carlosampling method is used to determine bubble trajectories. The homogeneous flowmodel is also taken into consideration so that it can be compared with the separatedflow model. Numerical predictions for a water model of a ladle show that thepredicting results for the separated flow model are satisfatory quantitative agreementwith experiment ones, but the predicting ones for homogeneous model are at variancewith experiment ones.

The solodification process of horizontal continuous cast gray iron barof 4.6 cm in diameter was simulated. The function for distribution of heat fluxon the internal surface of graphite sleeve, which is equal to that on the surface ofiron bar, was inversely derived by using numerical calculation from the tempera-ture distribution in the sleeve measured in real production. By using the distribu-tion of heat flux as a boundary condition on the surface of iron bar, numericalsimulation on solidification of iron bar taking longitudinal heat conduction intoaccount was made. The profile of solidification front obtained from numerical si-mulation was approximately similar to that in real production. In addition, thequantitative relationships of the thickness of solidified layer at the exit of crys-tallizer with the main technological parameters, including the temperature of liq-uid iron at entrance of crystallizer, the moving speed of the bar and the intensityof water cooling, were obtained by using numerical simulation.

The tertiary amine can be used to extract Fe(Ⅲ) very effectively inthe pH range resulting into partial hydrolysis of Fe~(3+) ions. The iron extractedinto the organic phase can be stripped rather easily with dilute H_2SO_4 or evenwith H_2O. Fe (Ⅲ) is extracted inio the tertiary amine sulfate solution in the formof [(R_3NH)_2Fe(OH)(SO_4)_2]_2 complex by adduct formation. Equation was derived torepresent the chemical reactions involved during extraction. From the infraredspectrum studies on the extraction species in waxy solid form separated from thesolution, sulfate group is a bideniate ligand to the iron atom. The extraction spe-cies has been considered to contain (FeOH)_2 unit based on the ultra violet spectra.The possible structure of the extraction species has been proposed.

Discussions were made of the principle, method and computerizedprogram for drawing the predominance diagrams of the bi-metal co-existed systemM_1-M_2-x-y in which the multimetallic compounds may be produced by interactionbetween compounds of both metals. The formation of zinc ferrite and its stableregion have been analyzed through drawing Zn-Fe-S-O system predomincance dia-gram. The availability of the diagram is given the direction to roast the zinc sul-fide ore as well.

By means of the Gibbs-Bogoliubov (GB) thermodynamical variationalcalculation, the thermodynamical properties of the liquid metals as supercooled sta-te, such as Al, Ga, Tl in the 3rd family of periodic table and transition metal Tiwere calculated using the hard-sphere (HS) system as reference. The values of meanatomic volume, Helmholtz free energy, internal energy and entropy as well asspecific heat at constant volume, isothermal bulk modulus, thermal expansion co-efficient and specific heat under constant pressure were determined. The glass tran-sition temperature, T_g, is easily obtained from c_p-T plot. The glass forming abili-ty for metal can be predicted with T_g/T_m, which is in agreement with the experi-mental results.

The texture change along the normal direction to rolling plane ofcross shear rolled commercial copper has been studied by means of the two-stepmethod for ODF calculation and computer simulation. The texture of cross shearrolling of copper is similar in primary components to that of conventional coldrolling, but the scattering degree and direction of the texture are different due to theresidual shear strain change in different position along the normal to rolling plane.It seems that no more effect of the shear strain upon the recrystallization texture.

The behaviour of TiAl intermetallic compound of Ll_0 type under com-pressive deformation at high temperature and its recrystallization microstructurehave been studied. The compressive proof stress of the polycrystalline TiAl wasfound to be a positive temperature dependence as same as the single crystal one.The correlation of the flow stress together with strain rate and deformation tem-perature is in good agreement with the expression: ε=Aσ_p~nexp(-Q/RT)Adjusting the deformation temperature and strain rate to a decrease in flow stressof alloy down to below its brittle fracture stress may improve successfully notonly the hot working of the TiAl-base alloy but also the fineness of the recry-stalline grains.

The microstraining prior to yield of several common metallic mate-rials has been studied. The resistances of metals to microstrain and to macroyieldare believed to be based on different deformation mechanisms and to be changedfrom different patterns. The influential factors upon the microstraining, such asheat treatment, predeformation, strain-aging and residual stress together withtheir mechanisms have been also discussed.

The amorphous alloys with wider stoichiometrical composition, Ti_(1-x)Pd_x (0.25 References | Related Articles | Metrics

The anionic species of the SiO_2-containing sodium aluminate solutions preparedby different methods have been investigated by Raman spectra and ultraviolet spectra. It wasfound that these solutions contain different Si-containing anions. The solution prepared byleaching industrial sinter of soda-lime sintering process contains polysilicate ions with Si-O-Siradicals.

The equilibrium products of Fe-Cu-Ce, Fe-P-Ce or Fe-Ti-Ce solution have beenidentified to be Ce_2O_2S, but not the intermetallic compounds of Ce against Cu, P or Ti.The equilibrium constant of Ce_2O_2S=2[Ce]+[O]+2[S] and the interaction coefficients betweensolutes in Fe-base solution have been determined as follows: K_(Ce_2O_2S)=2.57×10~(-15) e_(Ce)~(Cu)=-0.49; e_(Ce)~P=1.77; e_(Ce)~(Ti)=-3.62 e_(Cu)~(Ce)=-0.22; e_P~(Ce)=0.39; e_(Ti)~(Ce)=-1.23 ε_(Ce)~(Cu)=-128.0; ε_(Ce)~P=224.1; ε_(Ce)~(Ti)=-710.0The Ce decreases the activities of Cu and Ti in Fe-base solution and increases their solubilities,as well as increases the activity of P and decreases its solubility.

The surface morphology of the continuous SiC filament, prepared by radio frequen-cy heating CVD technique, has been observed and the tensile strength of the filament relatedto the technological parameters of preparation has also been investigated, The tensile strength isfound to be dependent directly upon the surface smoothness, grain size and uniformity. How-ever, the CVD temperature, the composition and flow rate of reactive gases, as well as thecleansing of W wire substrate, etc., are the very important factors. A protective layer coatedover the outer surface of SiC filament may effectively improve the smoothness, susceptibility tosurface damage and properties of the SiC filament.