Via embedded atom type potential, molecular dynamics simulation has been performed to study the influence of single edge dislocation on both thermally and stress induced martensitic transformations in a stoichiometric NiAl B2 alloy. If no external force is applied to the system, the strain field of single edge dislocation can not nucleate martensites. Edge dislocation can be inherited during the growth processes of thermally induced martensite, and can also migrate toward the surface with the help of the transformation. When a tensile force is applied, stress induced martensite with 3R structure can initially nucleate near the dislocation core. Butterfly martensite appeared first during the growth process, and then another martensitic variant nucleated in the middle of the dislocation.Edge dislocation can reduce the activation energy for stress induced martensitic nucleation, and it also plays a role of plastic accommodation in the transformation processes.

Using the TEM weak beam technigue,the APB energies on the (111) and (100) planes of Ni74.5Pd2A123.5 alloy with L12 structure were determined to be(144±20) mJ / m2 and (102±11) mJ/m2 respectively.The relation of ordering energies on the ductility of the alloy was also discussed in this paper.

Based on the statistical distribution function of the dislocation link length derived by the author,an expression of dislocation link length distribution parameters for zero plastic volume change has been obtained as following where w=l2c/2λand or it can be expressed by the relation between mobile dislocation density and inmobile dislocation density as follows The in situ creep test results of Al-1%Mg alloy in electron microscope confirmed the theoretical prediction.

In unidirectional solidification of Al-4.5Cu alloy,history-dependent selection of the primary dendritic spacing is systematically investigated by the experimental method of step-variation in growth rate. A single crystal is formed in the sample before each experimental run, so that the influence of crystal boundary on the primary spacing is avoided. It is found that the primary dendritic spacing is remarkably history-dependent in the metallic alloy as in the transparent model alloy. The average primary spacing is dependent not only on the current growth conditions as described in the previous models, but also on the way those conditions were achieved remarkably. There exists a wide allowable range of primary spacing for given growth conditions. The lower limit obtained experimentally is compared with that calculated theoretically with the Hunt-Lu model, which shows excellent fit between them.

The Evolutional manners and dimensional rules of γmatrix and γ'precipitates in the [001], [110] and [111] oriented specimens of nickel-base single crystal superalloy CMSX-4 during the tensile creep at 1253 K and 350 MPa were studied.The effects of the change in characteristic dimensions of γand γ' phases on the strain and strain rate were compared for the differently oriented single crystal specimens.It was found that the effect of change in mean width of γchannels along the direction of directional coarsening of γ' precipitates(the lamella spacings between adjacent rafted γ'precipitates)on the strain and strain rate is remarkable. Based on the evolutional rule of γchannels and the plastic deformation mechanisms, the anisotropic creep behaviour in the tested specimens was synthetically analyzed.

Mechanical alloying of the Al57.1C42.9 powder mixture has been performed in a high-energy ball mill.The structural evolution has been characterized by X-ray diffraction, transmission electron microscopy and infrared spectrometry. Carbide Al4C3 intermediate product is firstly formed. The reaction is controlled by interdiffusion of elements. Further milling leads to transformation of Al4C3 to amorphous phase.Destabilization of Al4C3 is assumed to arise from the fact that defects and chemical disordering raise the free energy of crystal beyond that of the amorphous phase.

Adiabatic shear band was observed in surface white-etching layer in impact wear test.The band possesses very fine crystalline grains,and is harder than white-etching layer.The adiabatic shear bnad in white-etching layer is liable to fracture or cracking in impact wear.It's supposed that dynamic recrystallization occures in the band in white-etching layer whereas dynamic recovery takes place in the white-etching layer.

Ni/Cr multilayer film was prepared by the way of Ne+ ion beam mixing. The distribution of elements and phase structure in Ni/Cr multilayer film were investigated using Auger electron spectroscopy sputtering depth profiles and X-ray diffraction analysis. The microhardness and tribological properties of multilayer film were measured. The results showed that Ni/Cr ion beam mixing multilayer film had high microhardness and anti-wear property compared with that of Ni/Cr multilayer film without ion beam bombardment. The high anti-wear property of ion beam mixing Ni/Cr multilayer film was attributed to the change of microstructure of the multilayer film and the dispersed chromium carbide microcrystals moved to the interfaces of multilayer film.

Thermal activation volume V, activation enthalpy △H, activation free enthalpy △G and activation entropy △S of tensile deformation of a gamma titanium aluminide have been measured in a temperature range from low temperature(285 K) to 1273 K. The γ-TiAl has a chemical composition of Ti-47Al-2Mn-2Nb-0.8TiB2 and a microstructure of near lamellar, and the measurement was conducted at yield points. From the values and their temperature dependence of the measured activation parameters, as well as the temperature dependence of yield stress,the dislocation mechanisms of tensile deformation of the alloy have been speculated.It is found that there exist three temperature regions,which correspond to different possible thermal activation mechanisms of dislocation motion. In low temperature region(285-398K), the mechanism is mainly characterized by the overcoming of Peierls-Nabarro resistence. In intermediate temperature region(523-873K), the mechanism is a weak thermally activated process as the plastic flow is neither sensitive to temperature nor to the strain rate.In high temperature region(≥973 K), the rate controlling machanism is dislocation climbing.In addition,it is found that,activation entropy △S, whose variation with temperature is similar to that of activation volume V, also reflects the thermal activation mechanism of dislocation movement in some degree.

The mechanical properties,fracture behaviours and micro-mechanism of damage have been studied for three spheroidized steels.It is shown that voids formation and growth due to carbonide particles are the main reason for the failure of these materials during plastic deformation. Experimental results show that the void volume fractions of these materials increase as strain increases,and the void volume fraction increases more rapidly for material with more carbonide particles than that with fewer carbonide particles.Theoretical analyses show that the influence of void damage on mechanical behaviours can be considered as strain softening. Based on this consideration,the analytical expressions of equivalent strain hardening exponent and fracture strain for plastic damaged materials with second-phase particles were derived, the results calculated with these expressions are in good agreement with the experimental results.

Driving forces for diamond and graphite growth in CH4/H2 mixtures are calculated in consideration of activated effect of super-equilibrium atom hydrogen on graphite under 4.8 kPa pressure. The driving force for diamond growth is positive with simultaneous negative driving force for graphite in the suitable ranges of temperature and mole fraction of CH4. The result indicates that the chemical potential of carbon in the vapor phase is higher than that in diamond and lower than that in graphite simultaneously. So diamond is deposited without graphite co-deposition, and the preexisting graphite will be etched during diamond deposition process.

The technology of industrial nickel foils production is researched in the present paper.The results show that the process is stable,the equipment structure is reasonable, the nickel foils produced have uniform thickness,high purity and good mechanical and apparent performance.

The microstructural variations of the bonded zones in an explosive welded Al/Ti/Steel plate system were studied by using electron microscopy techniques.The direct transmission electron microscope(TEM) observation found the transition zones in the bonded zone, and there are obvious interfaces between the transition zones and between transition zone and base metal.In the Al/Ti bonded zone, the transition zone is an Al+Ti mixture.In the Ti/Steel bonded zone,the transition zone is composed of the FeTi intermetallic layer and an amorphous layer.The morphology and size of the transition zones depend upon the diffussion of alloy elements and cooling rate during explosive welding.

Electromagnetic braking on flow field of molten steel in the thin-slab continuous casting mold is analyzed by mathematical modeling and experiment.Magnetic flux density and velocity of liquid Sn in the physical model are measured, and the low-Reynolds'number k-ε turbulence model is used to solve the eddy viscosity in the momentum equations. The results show that flow field in the mold can be effectively changed by electromagnetic field. With the increasing of magnetic flux density,the let stream intensity of molten steel from nozzle discharged is gradually reduced until its moved direction is changed, at the same time, the velocity rates of whole field is decreased. When the level magnetic field is used, the induced current of liquid metal in the mold is large eddy distribution in the whole flow zone.

A Mathematical model to describe three-dimensional turbulent flow in continuous casting tundishes has been developed by choosing two different types of turbulent model as k-εand LES(Large eddy simulation).Numerical calculations have been performed to study the characteristics of flow in the tundish without/with now control,and the reasonability of the turbulent models has been discussed.The results show that the proper flow control is in favor of inclusions floating in the tundish;basically, the phenomena of flow in the tundish can be described by using traditional k-εmodel, however,the phenomena which could not be well calculated by k-εmodel can be described by using LES.

Ni, Al, Ti, and C powders mixed at a composition of Ni37Al37Ti37C13 were milled in a high-energy ball mill.Upon milling for 107 min,an abrupt reaction occurred, resulting in in situ formation of NiAl and TiC compounds.The formation mechanism is suggested to be two separated combustion reactions, i.e. Ni+Al→NiAl and Ti+C→TiC. The combustion reaction conducted incompletely and small amount of elemental powders still existed. Prolonged milling led to gradual formation of NiAl and TiC as well as the refinement of grain sizes. The final saturated grain size for TiC is 2.5 times as large as that for NiAl, though TiC has a much higher melting point compared with NiAl, this is attributed to a different deformation mechanism.

The high temperature creep and cyclic creep behaviours of SiCw/6061Al and SiCp/2024Al composites were studied at 298℃. It was found that SiCw/6061Al composite showed better creep resistance but lower creep threshold stress as compared to SiCp/2024Al composite.Both composites showed cyclic creep retardation(CCR)in the tested stress region, while the CCR for SiCp/2024Al composite was more pronounced. For the SiCw/6061Alcomposite,the minimum cyclic creep rate decreased first and then increased with increasing the unloading amount, while for the SiCp/2024Al,the minimum cyclic creep rate decreased monotonically with increasing unloading amount.