An experimental apparatus, which has a convection generator and anaid-heater, is developed for the study of the effect of stable laminar liquid flow on thedirectional solidification process by the use of transparent alloy SCN-2wt-% Ace. The flowis perpendicular to primary arms. By,in-situ observation and photographing at different spe-cific moments, it has been found that such a flow can cause a great change in primaryspacings of constrained columnar crystals: for cells, the spacings become smaller; but fordendrites, they become larger. The former is mainly due to the tilted growth of upstreamsidebranches, while the latter is mainly due to the coupling effect of liquid flow with solutal fieldaround dendrite tips. The faster the liquid flows, the further smaller the cells space and thefurther larger the dendrites space.

The cyclic behaviours of two prestrained materials with different slip modeshave been compared. From the analysis of hysterisis loops, it is suggested that the decreasein back stress dominates the cyclic process of Cu-Zn alloy with planar slip mode, while thedecrease in frictional stress is the main factor affecting the behaviour of Cu with wavy slipmode.The relation between the dislocation configuration and internal stress has been also dis-cussed. By means of the relation just mentioned, the variations of dislocation configurationbefore and after fatigue of the two materials, the differences in their softening mechanismand mechanical behaviour could be interpreted.

The phasse transformation temperature of α→α+γ and the volume fractions ofprimary γ-phase and lamellar zone after solution treatment at different temperatures were de-termined for Ti_(50)Al_(48)M_2(M=Ti, V, Cr, Mn, Zr, Ga, Cu and Nb) alloys. The thickness of γand α_2 lamellae in lamellar zone of some Ti_(50)Al_(48)M_2 alloys and the concentration of Al, Cr,Mn, Nb in α and γ_p phases were measured statistically. These results seem to be available toselect reasonably the third alloying element and heat treatment regime of TiAl base alloy.

Effect of Y, containing 0.1 or 0.5 wt-%, on precipitation and tensile proper-ties of Al-Li-Cu-Mg-Zr alloy has been studied. An addition of Y may refine the grain size,promote the β′-phase precipitation, improve S′-phase distribution, and restrain the growthof δ′-phase. Tensile tests at room temperature indicate that 0.1 wt-% Y addition may in-crease the ductility but no more strength. However, 0.5 wt-%Y contained alloy exhibits high-er strength without reducing ductility.

Equilibrium equation of point defects in Ll_2 type intermetallic compoundswas established to calculate the relations of the concentration of antisite defects and vacanciesand bulk composition in Ni_3Al. The examination of temperature effects on the point defectscleared up the misunderstanding of the properties of the "constitutional point defects" inNi_3Al.

Microstructural studies have been made on the Mg-0.54Zr, Mg-5.68Zn andMg-5.65Zn-0.50Zr alloys in the as-cast and homogenenized states. The lenticular plates of{012} twins were found in the three alloys. After homogenization, the ZrH_2 phase formed inthe Mg-0.54Zr alloy. The Mg_7Zn_8 phase of cubic structure with α=1.417 nm distributes atthe grain boundaries of Mg-5.68Zn alloy. After homogenization, the Mg_7Zn_8 phase dissolvesand the MgZn_2 phase occurs. The as-cast Mg-5.65Zn-0.50Zr alloy consists ofMgZn_2 phase and Zn-Zr compounds. After homogenization, the dispersed acicularMgZn_2 phase may precipitate.

The creep crack propagation in superalloy Rene80 of two differentmicrostructures, i.e., equiaxed grain structure by conventional casting and columnar grain bydirectional solidification, was investigated under static load at 1123 K. The creep crackgrowth rate, dα/dt, seems to be correlated with the stress intensity factor, K. The creep crackgrowth rate in the directionally solidified alloy is lower than that in the conventional castalloy, owing to the elimination of transverse grain boundaries. The effect of microstructure oncreep crack propagation has also been discussed.

Nature of prior pacticle boundary precipitation of P/M superalloy Rene 95and its effects on mechanical properties, fracture morphology and micro-fracture characteris-tics are discussed. The precipitates of densely distributed prior particle boundary mayembrittle the bonding boundaries among particles, reduce the plasticity and fracture alongtheir globular surfaces. An improvement on interfacial bonding strength, plasticity at hightemperature, as well as stress rupture life of the alloy may be made by broadening theinterstices between precipitated particles. Thus, the fracture mode is changed fromintergranular to transgranular.

An improvement on the flow and mixing conditions in bottom blown ladlesmay be made by either shifting the nozzle from centre to off-centre or changing from one totwo nozzles. Thus, the shorter time for homogeneous mixing in ladle seems to be available.

Resistance to surface corrosion on brass may be obviously improved bypassivating treatment with mixed solution of BTA and PVA. A sequent apitaxial growth ofPVA film on the Cu(I)BTA film was observed by ellipsometry and X-ray photoelectronspectroscopy. The effect of passivating treatment with the BTA-PVA mixed solution seemsto be similar to that with first-BTA last-PVA. The chemical conversion film on brasss is thusrevealed as tri-layer structure, i.e., Cu_2O/Cu(I)BTA/PVA.

The micro-processes on tensile deformation and fracture of graphite-matrix in-terface in cast iron with ferrite matrix under SEM have been observed in situ. It was revealed thatthe graphite in cast iron would be not regarded as a cavity and not formed yet notch stress con-centration. A new explanation on the effect of graphite on strength of cast iron was suggested.

The secondary reinforcement, carbon whiskers, may grow on the surface ofparent reinforcement, carbon fibres, by chemical vapour growth from acetylene using Fe saltsolution as catalyzer. The optimal growing temperature is about 1000℃, and while the con-centration of catalytic solution is appropriate, the carbon whiskers may deposite uniformlyand link each other on the parent carbon fibre surface. If the temperature or concentration istoo high, the coarse cluster of carbon may deposite on the fibre surface. The mechanism ofcarbon whisker growth is believed that the carbon atoms in vapour phase dissolve first in theFe salt drops over fibres, then the solid carbon grains precipitate on the film surface.

Na_2SO_4 deposits accelerate significantly the corrosion rates of 3 intermetallicsFe_3Al, Ni_3Al and Ti_3Al in the simulated combustion gases at 600℃. The corrosion product ismixture of oxides and sulphides of both the base metal and Al. Corrosion resistance of Fe_3Aland Ti_3Al is superior to that of Ni_3Al owing to the formation of an inner layer rich inAl_2O_3 for Fe_3Al and of an intermediate layer composed of TiO_2 and NbO_2 for Ti_3Al modi-fied by Nb. While, Ni_3Al forms an inner layer which is so abundant in Ni sulphide as to facili-tate the migration of Ni outward. The addition of NaCl to Na_2SO_4 has no significant influ-ence on the corrosion behaviour of the three intermetallics.

Hydrogen attack on 304 austenitic stainless steel in the service for 2×10~4 h at450℃ under 5 MPa was detected to result from the occurrence of Cr_(23)C_6. The methane bub-bles were formed preferentially along grain boundaries and twin boundaries, and some ofthem in grains. Experimental results and thermodynamical analysis indicated that the Cr-de-pleted region around bubbles is not necessary condition in growth stage of bubbles.

BN films, synthesized by ion beam assisted deposition, were analysed by RBS,AES, IR spectra and TEM. Formation of c-BN phase was shown not only by IR spectra atabsorption peak of 1100 cm~(-1), but also by electron diffraction pattern. The results of AESdemonstrate an effect of N~+ implantation near the film surface. The deposited films consist ofthree layers, i.e., ion implantation layer, film layer and mixed intermediate layer, according tothe difference of concentration. The micro-Knoop hardess of the film is 25-35 GPa.

Effect of increasing content of Ti on the crystalline to amorphous transition inalloy films of stainless steel 321 plus Ti synthesized by high rate magnetron sputtering deposi-tion is reported. X-ray diffraction analysis revealed that the microstructure of film issequently changed from α-Fe, α-Fe+x-phase, microcrystalline-amorphous into amorphouswith increasing content of Ti from 0-3, 3-10, 10-18 to 18-30wt-% respectively.

The room temperature stability and crystallization of amorphousNd_xFe_(1-x) thin films with x=0.06-0.90, prepared by flash evaporation at 77 K, were investi-gated by X-ray diffraction and TEM. The amorhous Nd_xFe_(1-x) films are stable at room tem-perature when 0. 19 References | Related Articles | Metrics

The scattered distribution of the lattice parameters in the Seemann-Bohlinmethod for stress measurement was discussed. A linear relation can be achieved by modifica-tion with the theory deduced from Kroner model. However, the Seemann-Bohlin methodcannot achieve good accuracy in comparison with the Bragg-Brentano method, particularlyfor low stress value.