The solid-liquid interface morphology and solute segregation behaviour of 8090 Al-Li alloy during unidirectional solidification were studied by the liquid metal quenching method under varied processing conditions. When solidification rate, R<0.13 or>0.75 mm/min (temperature gradient, GL=130℃/cm), the structure revealed of planar or dendritic interface respectively. With the increase of R, the interface morphology becomes cellular from planar gradually within a narrow range. And the greater the R is, the finer the dendrite will be. Segregation of element Cu and impurity elements Fe and Si quite severe. The interface morphology markedly influences on solute segregation. During solidification at coarse dendrite interface. Their segregation ratios are rather great and solidified structure is coarse.

Cryogenic strength, ductility and toughness of 8090 Al-Li alloy were found to be superior to those at ambient temperature, and up to optima at about 20 K. Different aging regimes may influence on its cryogenic yield strength and elongation.

Because Nb accelerates the uniform distribution of MC phase and the grain refinement, as well as, increases the amount and stability of γ'-phase, the tensile strength, ductility, stress rupture life and fatigue limit of an Fe-30Ni-13Cr-1.2W-1.5Mo-2.5Ti-0.4Al superalloy at 650℃ may be improved with increase of Nb content up to 1.22wt-%. The precipitation of small Laves phase dispersed along grain boundaries may be favourable to combined properties of the superalloy containing 1.22 wt-% Nb. And it will be worsened only that the precipitation of Laves phase is too more and Nb content is overmuch.

Polycrystalline Ni was implanted with 50 keV B~+ to a dose of 3×10~(17) ions/cm~2 at room temperature. The specimens with and without B~+ implantation were tested in micro-hardness and load or unload tensile fatigue under stress-controlled condition. The surface layer structure was observed with IMA, SEM and TEM before and after implantation and/or fatigue. The B~+ implanted surface region consists of amorphous Ni-B phase, Ni_3B and Ni_4B_3 second phases, and damage structure. The corresponding measurements indicate that both surface micro-hardness and endurance limit of the specimens have increased after implantation. Compared with unimplanted specimens under the same fatigue condition, all implanted specimens show the smallest overall fatigue damage. The cyclic loading at room temperature can lead to migration of implanted B~+ out of surface layer and recrysatallization of amorphous Ni-B phase. Possible strengthening mechanisms for these experimental results were discussed.

Mechanical alloying was employed to produce super-saturated solution of Fe_(1-x)Cu_x, which is virtually immiscible under an equilibrium condition at ambient temperature. XRD results show that the solutions formed in the concentration ranges of x≤0.15 and x≥0.40 are of bcc structure of α-Fe and fcc structure of Cu, respectively. For the region in between (0.15 References | Related Articles | Metrics

Residual stress concentration at a notch depends on both notch geometry and yield strength of the material. It varies through the depth, and its magnitude may be higher than the theoretical one. Compressive residual stress concentration at the notch of shot-peened specimen of soft material is easy to be relaxed, with the surface damage during shot-peening results in a minor contribution to the fatigue limit. Compressive residual stress increases the crack closure effect at the notch and may lead to a non-propagating crack.

In situ high temperature metalloscopic observation was made of deformation and fracture for superalloy GH169 under combined action of fatigue and creep. The mode of deformation is revealed as slipping, twinning and grain boundary sliding. The mode of failure is dependent upon microstructure. The intergranular cracks arise from W-type voids produced by strees concentration at triple point which would not be relaxed by interior deformation of grains and local deformed region along grain boundaries, and its propagation mechanism is nucleation, growth and linkage of cavities at grain boundaries. Tranagranular cracks result from deformation damage of grain, and its propagation mechanism is shear rupture along slip plane.

Small bar specimens of steel 16Mn with 4 blind-holes were fatigued under constant amplit■de loading on rotating bending fatigue machine. Short crack propagation emanating from ■e blind-holes was obtained. Based on the experimental results, an expression of average opagation rate of short cracks was proposed. Statistical behaviour of short crack propagatien was also discussed and evoluation of surface sizes of short cracks with fatigue cycle number was given.

The features of Cu_6Sn_s, growing slowly at lower temperature and growing rapidly up over 350℃, and of Cu_3Sn, growing at higher temperature, have been detailedly observed under SEM. The increase of Pb content seems to inhibit sequentially the growth of Cu_6Sn_5 in Sn-Pb alloy.

The formation and aggravation of hydrogen damage in Fe-3wt-%Si alloy during cathodic charging were studied by means of Lange transmission X-ray topography. Results showed that hydrogen damage did not form in the specimens charged in 0.5 mol/L H_2SO_4 solution without poison, and occurred with addtion of 250 mg / L As_2O_3 even at very low current density. As charging at a certain current density, the size of the damage may enlarge up to a limit yet no more by prolonged time. The damage size increases with increase of charging current density, but not so apparent at higher current density. An external tensile stress could promote obviously the formation of hydrogen damage. It seems that for charging in H_2SO_4 solution containing poison, the drop of hydrogen permeation curve against time prolongation is due to the formation of hydrogen damage.

Size distribution and precipitation of VC particles in the ferritic nodular cast iron have been examined by techniques of ultrasonic screening, small angle X-ray scattering and chemical dissolution.The VC particles are sized over a wide range. The superfine ones, dispersed in the ferrite matrix, are the large majority. A saturated dispersion with ultrafine VC particles may be approached as the increasing of V content in the iron. This seems to play an important role in the precipitation strengthening for ferritic noldular cast iron.

Si segregation was observed in the vacancy condensation pits, formed by supersaturated vacancies below the oxidation layer of Al—0.35 wt-%Si alloy, by optical microscopy, X-ray photoeletron spectroscopy and microhardness test. This phenomenon could only be explained by diffusion of vacancy-Si complex inducing non-equilibrium segregation.

Observations were carried out of the structure of sulphuric, oxalic or phosphoric films on AI after treatment of reanodizing and electrolytic depositing lubricant in (NH_4)_2MoS_4 solution, as well as of the deposited products by means of EMPA, TEM and energy spectroscopic analysis. The deposited products are compounds of S and Mo other than single MoS_2, and most of them deposited near the surface layer of the film. Some regular long pores without barrier layer occurred in the film, but the regular fine channels without relation to the structural element parameters of original anodized film were found in the thickened barrier layer of phosphoric film. Sulphur may be remained as molybdenum sulphide in the film during heating under Ar protective environment.

Stability of nanocryatalline Ni-P ribbon was investigated by DSC and internal friction technique. The nanocrystalline Ni-P ribbon seems to be unstable within range of 518 to 887 K owing to obvious exothermal phenomenon, decrement of internal friction values and grain coarsening.

Fe/Pd compositionally modulated films (CMF) were prepared by vapour deposition from two sources onto glass substrate under vacuum. The modulation and crystal structures of the film were examined by X-ray diffaction. The magnetic properties were determined by vibrating sample magnetometer. The Pd layer in the Fe/Pd CMF is of fcc structure, and the Fe layer structure transits from bcc into amorphous state with decreasing thickness of Fe layer. The dependence of specific saturation magnetization on thickness of Fe layer has also been discussed.

Diffusion bonding of superplastic LC4 AI alloy, with prior surface treatment of organic solution protecting coating Sfter electropolishing and stainless steel wool brushing, was performed by Gleeble test machine under conditions ranged 490—530℃, 1.0 —3.0 MPa, 30—180 min and vacuum of 1.0×10~-3 Pa. The joints were examined to have similar strength and microstructure to the base metal. Discussion was made on the effect of superplastic treatment on bonding. The micromechanism for diffusion bonding of superplastic metal was suggested as the migration of original bond interfaces caused by atomic diffusion and grain growth. Experimental results for the alloy as quench-aged state were presented to compare with the superplastic one.

The in situ forming TiB_2 reinforced AI composite was favourably prepared by reaction-sintering of pure AI, Ti and B powders under vacuum. It is of microsize and free from lattice defect practiclly. A superior room temperature strength and modulus, as well as good elevated temperature properties were obtained as comparison with that of pure Al.

The cantilever bending test, particularly monitored by an acoustic emission technique, was adopted to measure the tensile and interfacial adhesive strengths of the HCD ion-plated fine TiN film on pure Ti substrate. The behaviours of film damaging were found due to: for TiN facing upward, an exceeded internal tensile stress over its tensile strength, and for TiN facing downward, an exceeded shearing stress along film/substrate interface over its adhesive strength. The measured tensile and adhesive strengths are 603 and 242 MPa respectively.