The ultrafine WC-10Co cemented carbides were prepared by spark plasma sintering (SPS) using sub-micron WC/nano Co and sub-micron WC/micron Co with nanocrystalline structures as the raw powders in this paper. The SPS process, microstructure and properties of the sintered samples were investigated. The ultrafine cemented carbides with mean grain size of less than 200nm were prepared using the two kinds of raw powders. The sintered sample using sub-micron WC/micron Co powders as raw materials has a relative density of 98%, hardness of HRA94.5 and fracture toughness of 13.50MPa•m1/2, which indicate an very good combination of mechanical properties. While the sample sintered using the sub-micron WC/nano Co powders as raw materials has lower properties. The densification mechanisms of sintering the two kinds of WC/Co mixed powders were analyzed based on the special SPS mechanism.

Because of the important application of the austenitic stainless steel in the nuclear industry, formation enrgies of a single vacancy(V), a self-interstitial atom(SIA), an interstitial helium atom(HeI) and helium-vacancy(He-V) clusters in γ-Fe, which has the same faced-centered cubic (fcc) structure as the austenitic stainless steel, are calculated by molecule statics. The modified embedded atom method potential, Wilson-Johnson potential and Beck potential are employed to describe the interactions of Fe-Fe, Fe-He and He-He respectively. The calculation results show that the formation energy of slit <100> SIA in γ-Fe is lower than that of slit <110> in α-Fe, and the tetrahedral interstitial position in γ-Fe is the most stable site for HeI. When the number of helium atoms in cluster of HenV0, HenV1, HenV2, HenV3 is 2, 5, 9, 11 respectively, the clusters will self-trap by forming Frenkel pair. The He/V of self-trapped cluster is not a constant, it will gradually decrease with the number of vacancies increasing.

Regular porous metal with a radial pore distribution is produced by precipitation of supersaturated gas when the melt is bidirectionally solidified. A model was proposed to describe the ideal pore distribution of radial-type regular porous structure and rationality of the model was proved. This model can describe the effects of pore nucleation, pore coalition and pore interruption on structural characteristics and their quantitative relation can be deduced from the model. Probability of pore nucleation, pore coalition and pore interruption in the samples was also calculated.

Many lotus-type porous metals have been fabricated by unidirectional solidification in the pressurized hydrogen and/or other gases, such as Mg、Cu、Ni、Ag、Fe、Carbon Steel and Si etc. But the same process is not viable for Al. Researches on this problem both from theoretical and experimental aspects were made in this article. The conclusion is that the absolute quantity of hydrogen dissolved in Al melt is too small to form lotus-type porous structure.

ABSTRACT In this paper, the effect of ultrasonic field during horizontal continuous casting of ?0mm Al-1wt%Si alloy bonding wire on the solidification has been investigated and the phenomenon has been theoretically interpreted. Experimental results showed that when the ultrasonic power of 1000W was imposed, the surface quality was improved, the surface roughness decreased from 40祄 to 10祄; the solidification structure was refined, the average grain size reduced from 94.1祄 to 31.2祄 and the mechanical properties were enhanced, not only the tensile strength and elongation increased by 20.5% and 37.5% respectively, but the hardness value increased by 23.9%. Meanwhile, the uniformity of the distribution of Si in ?(Al) was improved and the boundary segregation was suppressed, the fine globular microstructure of Si could be effectively obtained.

AZ91 alloy has been successfully prepared by spray forming. The effect of the thermo-mechanical treatments on the microstructure and mechanical properties of the alloy was studied and the strengthening mechanism was analyzed. The results show that the spray-formed AZ91 alloy has, compared with the as-cast ingot, a finer microstructure with less intermetallic phase Mg17Al12 dispersed in the matrix, and, therefore, shows excellent workability. It can be hot-rolled with nearly 20% reduction for one pass. The spray-formed alloy exhibits outstanding mechanical properties after proper thermo-mechanical treatments.

The microstructure evolution of a medium carbon steel (0.48%C) during deformation of undercooled austenite at different deformation temperature and strain rate has been investigated by means of uniaxial hot compression simulation experiment. The predominant mechanism on the formation of ultrafine (冄+冡) microduplex structures has been studied in medium carbon steel The experimental results showed that the process of microstructure development can be divided into three stages: dynamic ferrite transformation, dynamic pearlite transformation and spheroidization of lamellae pearlite. And the effects of deformation temperature and strain rate on the process of dynamic transformation and spheroidization of pearlite were different. A large number of vacanies and high density dislocations introduced during large strain hot deformation provided short-circuiting paths for diffusion of carbon atoms, as a result the rate of cementite spheroidization was accelerated by four orders of magnitude through deformation of undercooled austenite as compared to a static annealing treatment. The redistribution of cementite particles in the ferrite matrix has been observerd, which can be interpreted in terms of dissolution-reprecipitation mechanism.

The hot deformation behavior of the heat resistant steel T122 was investigated with a compression test on Gleeble 3500 simulator at a temperature range of 900--1200 ℃ and strain rate range of 10 -2—10 1 s -1. A method was developed to determine the activation energy and material parameters in the hyperbolic sine constitutive equation. The activation energies determined are 570 kJ/mol and 548 kJ/mol for steel T122 in saturation stress and peak stress, respectively. The values of critical strain for dynamic recrystallization (DRX) initiation was determined from the strain-stress curves, a equation related to the Zener-Hollomon parameter was obtained.

ABSTRACT Sn3.8Ag0.7Cu alloys containing Ag3Sn intermetallic compound (IMC) with different morphology, size and distribution were prepared by controlling cooling rate in solidification and equal channel angle pressing process (ECAP) and, the relation between mechanical properties and IMC phase of the alloys was investigated. The tensile stress-strain curves of different microstructures were compared and the deformed microstructures were observed by SEM and TEM. While the large needle-like Ag3Sn was found to provide fiber-strengthening effect to the alloy, its brittle cracking promoted void nucleation, resulting in a deterioration of tensile elongation. The fine particles of Ag3Sn produced by ECAP enhanced dispersion strengthening by blocking the dislocation motion. The particles on the boundaries of fine equiaxed Sn grains inhibited the grain boundary sliding, leading to improve the tensile strength.

ABSTRACT After P-type rafted structure was obtained by compressive creep of a nickel base single crystal superalloy with [001] orientation, creep tests were performed to examine in more detail the relative creep behavior of rafted (pre-compression) and cuboidal (as-heat treated) γ’ microstructures. The experiments show that, at 800℃ and 600MPa, the alloy with the P-type structure has both much higher strain of primary creep and steady state creep rate, and rupture lives are shorter. TEM examination of the microstructures of the P-type structure indicates that, in addition to {111}<110>-slip system operated in γ matrix, the γ’ precipitates are cut by some superlattice dislocations and a few stacking fault. At low stress of 200MPa and temperature range from 980℃ to 1020℃, the glide-climb process along γ/γ’ interfaces is impeded most efficiently by P-type rafted structure, the alloy exhibits a lower minimum creep rate and longer rupture lives. It is deduced that the tensile creep strength of the alloy is improved by suitable pre-compression treatment.

The effects of hydrogen and flakes on impact toughness and fatigue properties of a wheel steel have been investigated. The results show that atomic hydrogen has no effect on impact toughness when the diffusible hydrogen concentration is low (C0≤0.7×10-6). The flakes decrease and fluctuate impact toughness. Atomic hydrogen has no effect on fatigue properties when the diffusible hydrogen concentration is low (C0≤0.7×10-6). But atomic hydrogen can promote the initiation of fatigue cracks and increase the fatigue crack growth rate when the hydrogen concentration is high enough (C0≥2.5×10-6). The flakes increase and undulate the fatigue crack growth rate.

For low carbon micro-alloyed steel, a process of nanocrystallization of steels through transformation mechanism was investigated. The austenite grain size was refined to 1~2m through heavy warmly deformation intigrating with repeatly heating and quenching; under common continous cooling conditions, the ferrite grain size transformed from1~2m ultrafine austenite will be near to or larger than the original austenite grian size, i.e.,d/d>1;but if the heavy deformation was applied below Ar3 during cooling, the uniform and equiaxed ferrites with grain size of 0.1~0.3冚m, close to nanosize, can be obtained. The results indicate that heavy warm deformation can make the carbides in original microstructrures distribute uniformly, and this accelerate the dissolving of the carbides and the formation of ultrafine austenite. The main mechanism of deformation induced ferrite transformation of ultrafine austenite is that the nucleation of ferrite along austenite boundarie is enhenced by the boundary slipping of austenite grains.

In this paper, the processing and corresponding mechanisms of the surface modification of 316L stainless steel by high current pulsed electron beam were studied in detail. The results showed that MnS inclusions in the 316LSS served as the nucleation sites for craters formed during the bombardment. The overheating of these inclusions or their interfaces and following eruptions are believed to be the reason for the crater formations. As a result, MnS inclusions in the surface layer decreased with the increasing number of pulses, leading to a selective surface purification of the material. On the other hand, the physical damages induced by the electron beam bombardment are repaired after repeated pulses, that is, the crater density decreases with the increasing number of bombardments, meanwhile the holes in the crater centers are removed gradually.

Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization procedures were used to investigate the pitting corrosion behaviors in the simulated body fluid of AISI 316L stainless steel treated by high current pulsed electron beam (HCPEB). The results showed that the corrosion resistance of 316L samples was significantly improved after HCPEB treatment, which was demonstrated by the increased polarization resistance (Rp) and decreased interface capacitance. The samples after 5 pulses are prone to pitting due to the existence of remnant MnS inclusions or holes in the crater centers. Comparatively, the sample after 20 pulses of HCPEB treatment shows the best corrosion resistance. Its corrosion current density has been decreased to 1/15 of the initial samples, which can be attributed to the selective surface purification effect and removal of physical damages with increasing number of pulses.

Atmospheric corrosion of pure copper under sheltered and unsheltered exposure condition during 1 year period in Shenyang atmosphere was studied. Atmospheric corrosion rate of pure copper, composition and protectiveness of corrosion product of pure copper was different under the different exposure conditions. Corrosion rate of pure copper exposed to unsheltered condition was higher than that exposed to shelter. Especially during rainy season, runoff by rain made the copper experience the longer wet time, and thus accelerated corrosion of pure copper evidently. The main corrosion product of copper under the different exposure conditions was Cu2O, there were still Cu4SO4(OH)6.H2O and (Cu4SO4(OH)6) under shelter. However, effects of runoff and dissolution by rain on corrosion products made a low formation process of Cu4SO4(OH)6.H2O, only Cu2O was identified after 6 months exposure under unsheltered exposure condition, Cu4SO4(OH)6.H2O was not found until 12 months exposure period. The thicker and compact corrosion product film had been formed under the unsheltered exposure, which could inhibit the cathodic reaction of copper corrosion effectively, and thus had the better protectiveness.

(Cu47Zr11Ti34Ni8)100-xMox (x = 0, 2 at.%) bulk metallic glasses (BMGs) were produced by copper mould casting. The amorphous feature of the samples was characterized by X-ray diffraction (XRD). The corrosion resistance and corrosion mechanism of the two BMGs in 1 mol/L H2SO4 solution open to air were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. It is found that the BMG with 2 at.% Mo exhibited a superior corrosion resistance over the base alloy, as indicated by a considerable increase in pitting potential (Eb) and significant decrease in passive potential (E0) and passive current density (ip) for the Mo-bearing BMG. EIS results revealed that the micro-addition of Mo increased the surface activity and promoted the generation of positive defects (i.e., oxygen vacancies), but suppressed the formation of negative defects at the interfaces between metal/passive film (M/F). As a result, the addition of Mo could speed up the formation of the passive film of Zr-, and Ti-oxides, and stabilize simultaneously the oxides film. Base on point defect model (PDM), a qualitatively kinetic model is established to explain tentatively the effect of micro-additionn of Mo on the improvement of the corrosion resistance of the Cu-based bulk metallic glasses.

The plastic deformation and effect of hydrogrn on deformation of electroless Ni-P amorphous coatings were studied through indentation test. The results showed that circular shear bands formed around the indent and the plastic zone size increased linearly with the square root of the applied load, hydrogen could enhance localized plastic deformation, deduced the yield strength.

The influence of pulsing current and isothermal annealing on the microstructure and micro-hardness of Fe73.5Cu1Nb3Si13.5B9 amorphous ribbons have been studied. It has been found that Fe73.5Cu1Nb3Si13.5B9 amorphous ribbons can significantly nanocrystallized by pulsing current treatment in a short processing time (within 30 s) at low processing temperature (100 K lower than glass transition temperature). At the early stage of pulsing current treatment, the micro-hardness increases by 10% from 8.2 to 9.0 GPa with respect to the initial ribbons, resulted by the structural relaxation. Then an abrupt increase by 50% from 8.2 to 12.4 GPa of the micro-hardness occur, as a result of the precipitation of abundant α-Fe nanocrystals with an average grain size of 8.5 nm. It indicates that pulsing current treatment is an effective way for the nanocrystallization of the studied amorphous alloy.

In-situ X-ray diffraction showed that Ti catalyst can reduce not only the dehydrogenation temperature of NaAlH4, but also that of Na3AlH6 from 250 ℃ to 160 ℃. The rehydrogenation of the decomposed NaAlH4 is reversible theoretically, but the intermediate hydride, Na3AlH6, is not fully converted into NaAlH4 because of the physical separation of NaH and Al formed in the decomposition, especially the formation of the large Al crystallites. These, therefore, result in a decrease in the hydrogen storage capacity as observed in the following cycling. Additional measurements have showed that those Al crystallites larger than 2.3 µm are no longer effective for rehydrogenatrion.

Nikel nanowires were prepared by direct current electrodeposition within the nanopores of anodic alumina membrane (AAM). The topography and texture of the nanowires were characterized by SEM, XRD, TEM. It is found that the nickel nanowires are the structure of single crystalline with a preferred orientation along the [111] direction. It is demonstrated that the nickel nanowires are dielectrical dissipation materials in the microwave electromagnetic experiment, the value of dielectrical dissipation is 0.55 at 9.5GHz. The nickel nanowires are considered as a candidate for microwave absorbing material.

The present work focus on the determination of the interfacial heat transfer coefficient (IHTC) between metal and die during the high pressure die casting (HPDC) process. Experiments were carried out on an aluminum alloy ADC12Z casting called “Step Shape Casting” because of its shape. The IHTC was successfully determined by solving one of the inverse heat problems using the nonlinear estimation method which was first used by J.V. Beck. The calculation results indicated that the IHTC between metal and die increased right after the liquid metal was brought into the cavity by the plunger and decreased as the solidification process of the liquid metal proceeded until the liquid metal solidified completely, when the IHTC intended to be stable. Casting thickness played an important role in affecting the IHTC between metal and die not only in its value but also in its change tendency. Besides different change tendencies of the metal solid fraction were found under the condition between casting with different thicknesses and the die.