Small dimensional materials are widely used in micro/nano--systems, such as large scale integrated circuits and microelectromechanical systems (MEMS). Since the geometric and microstructural dimensions of the materials are ranged from microns to nanometers, the constraints of the dimensions on dislocation activities and the effects of surfaces and interfaces in the small dimensional materials result in fatigue behaviors different from that of the bulk materials. In this paper, fatigue testing methods, cyclic deformation, crack initiation and propagation behaviors of the small dimensional materials studied in recent years, such as thin films, are reviewed. The corresponding fatigue size effects and damage mechanisms are discussed. The prospective research directions of fatigue of small dimensional materials in the future are forecasted.

SEM--ECC technique was employed to observe and characterize the dislocation microstructures during the saturation stage of cyclic deformations in a copper single crystal. Some band--like or spot--like dark zones were found in the dislocation microstructures, which located either at the edge region of the deformed specimen or at the interface between the dislocation matrix and the PSB. To interpret the experiment results, the near surface dislocation microstructure were simulated and the internal stress distributions induced by those dislocations were calculated by using discrete dislocation dynamics method. The simulation results show that near the free surface region, the maximum internal stresses or stress concentration appear at the dark zones which correspond to the interfaces between the PSB and the dislocation matrix or the PSB--matrix--surface interfaces, meaning that fatigue cracks initiate preferentially at these dark zones. The simulated results can well explain the observated ones.

The creep indentation testing with cylindrical flat indenters has been simulated by the finite element method with special attention on the creep damage of the indented materials. For the equivalent-stress-controlled-damage materials, the user subroutine Creep has been programmed for Abaqus, which is used to analyze the one-phase half--infinite material and thin-film/substrate material systems. It is found that the creep indentation depth rate is influenced by the damage parameters of the indented materials as well as the size of the indenters and the ratio of the indenter size to thickness of the thin film. It is a possible, like that of the non--damage creep indentation experiments, to obtain the creep damage law of the indented materials from the creep damage indentation testing.

The AB2 type Laves phases with cubic MgCu2 and hexagonal MgZn2 structures are investigated by partial least square (PLS) method and some criteria for classification of the two structures of Laves phases are obtained. It is found that for nontransition-transition and transition-transition alloys the valence electron densities of component elements are significant in influencing their Laves phase structures, and for transition-lanthanide (actinides) alloys the valence electron density of the atom at B position is the most important factor influencing their Laves phase structures. Besides, the effects of both valence charge and atomic radius on Laves phase structures are in opposition to each other in transition-lanthanide (actinides) alloys.

Symmetrical push-pull fatigue tests were conducted on as--electrodeposited polycrystalline twin copper. Different dislocation configurations were formed in twins with different widths. When the twin width $W_{\rm t} >1~ \mu$m, loop patches and walls were found in twins, the same as that in single crystal; when 1um>W>200 nm, ladder--like structures formed in twin, which like persistent slip bands (PSBs); when 200 nm>W>20 nm, only some dislocation fragments were found; when W<20 nm, no stable crystal dislocation segments exist in the twin.

A low carbon martensite stainless steel 0Cr13Ni4Mo normalized at 1000℃ and tempered at 600℃, used in the guide stream assemblies of water turbine, was treated with shot peening. The depth distributions of microhardness, half-width value of X-ray diffraction profiles and yield strength in the shot-peening affected layer were measured. Correspondingly, the depth distributions of microstructure parameters, such as subgrain size, microstrain and dislocation density, in this layer were calculated. The experimental results indicate that the structure strengthening charactered by microhardness and yield strength is prominent. The subgrain size decreases, and the microstrain and dislocation density increase in the shot-peening affected layer. As a result, the microhardness and yield strength in this layer increase. The ratios of microhardness to proof stress, , are all about 3.37 in different depth of the affected layer. The relation of the half-width value, Hw, and microhardness, HV, in this layer is linear, which is composed of two beelines: if HV<2835MPa, Hw=2.07×10-3HV－3.47, and if HV>2835MPa, Hw=1.14×10-3HV－0.81. The relation of the proof stress, , and square root of dislocation density, , in this layer is also linear: =551+16.2×10-4 .

Doppler--broadening spectra of positron annihilation radiation of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ga have been measured by using 2--detector coincidence technique. The lower background of the spectrum allows to obtain the contribution of annihilations with core electrons. The experiments show that the background decreases with increasing the distance between the sample and the Ge detector. The magnitude of the peak of the ratio curve of Ni (ratio to Al) increases with decreasing the background of the spectrum. For Ti, V, Cr, Mn, Fe, Co, Ni and Cu, the heights of the peaks in the ratio curves rise with increasing the number of 3d--electrons.

The experiment of a coupling effect on propagation of unloaded indentation cracks in a PZT--5H ceramic shows that residual stress itself is too small to induce delayed propagation of the indentation crack in silicon oil. If applied constant electric field is larger than 0.2 kV/cm, the coupling of electric field, residual stress and silicon oil can cause delayed propagation of the crack after incubation time, but the crack will arrest after propagating for 10---30 um because of decrease of the stress intensity factor with increasing the crack length. The threshold electric field of delayed propagation of the crack in silicon oil is EDP=0.2 kV/cm. If the field is larger than the critical field of 5.25 kV/cm, coupling of the electric field and residual stress is enough to cause instant propagation of the crack and propagates continuously, then arrests if under the constant electric field. If the applied field is larger than 12.6 kV/cm, even if no residual stress, the electric field itself can make many cracks initiate, grow and connect in a smooth specimen, resulting in delayed failure. The threshold electric field of delayed failure of a smooth specimen in silicon oil is 12.6 kV/cm and the critical electric field for instant failure is EF=19.1 kV/cm.

XRD Rietveld analysis shows that LaxMg3-xNi9 (x=1.0---2.3) alloys consist of a main phase with hexagonal PuNi3-type structure and a few impurity phases (mainly LaNi5 and MgNi2, increasing x leads to an increase in both the lattice parameters and the unit cell volume of the main phase. The hydride of the alloys preserves the PuNi3 type structure, but shows a large unit cell volume expansion. The electrochemical measures indicate that the desorption plateau pressure Prm of the alloys decreases noticeably as x increases, while the maximum discharge capacity Cmax increases from 88.3 (x=1.0) to 397.5 (x=2.0), and then decreases to 230 mA.h/g (x=2.3). For the alloys with Cmax>348 mA.h/g (x=1.7-2.2), the high-rate dischargeability (HRD) of the electrodes at i=400-1200 mA/g decreases with increaseing x. The slower decrease of HRD is mainly attributed to the decrease of eletrocatalytic activity due to the charge--transfer reaction, and the more rapid decrease of HRD of the alloys with $x>$2.0 is related to the lower hydrogen diffusion rate in the bulk of alloy. The rate of capacity retention (S100) of the alloys after 100 charge/ discharge cycles is around 55.7%-62.9%, the rather fast cycling capacity degradation is mainly due to the corrosion of La and Mg and the large unit cell volume expansion in the hydride phase.

The as--cast microstructure of Mg-based alloys containing Ca and Si was investigated using optical microscopy, XRD, SEM/EDS and TEM. It was found that the alloy containing low Si consisted of Mg-rich matrix and CaMgSi phase, while the alloy containing higher Si consisted of Mg2Si besides the Mg-rich matrix and CaMgSi. The phase CaMgSi existed in three different morphologies, namely discrete large angular, dispersive dot-like, and needle-like, while the Mg2Si, also needle-like, existed in the “Chinese-script” colonies. The formation mechanism of the as-cast microstructure was discussed in details based on a proposed pseudo-ternary Mg-Mg2Si-CaMgSi phase diagram.

In Gasar process, the metal-gas binary system for non-compound forming, is solidified to fabricate regular porous materials through oriented growth. The characteristics of phase diagram of this kind of system and the principle for calculating the phase diagram were analyzed. The Cu--H binary phase diagram is calculated upon the above principle.

A new revised homogenous model is proposed to solve the problem about two phase flow in side blown reactor, in which the gas horizontal slip velocity is introduced in the gas conservation equation only in the injection zone, so as to make gas into bulk melt. The computed results show that the revised model can solve side blown problem reasonably and the computed gas distribution agrees very well with the experimental result.

Laser surface remelting experiments have been performed on Zn-2%Cu alloy with a 5 kW continous wave CO2 laser. With increasing scanning rate from 6 mm/s to 1207 mm/s, the microstructure transition from light band to lamellar structure, cell, and finally to absolute stability planar, has been clearly observed in the laser molten pool. The experiment results are in good agreement with the prediction of interface response function calculated with Lin's numerical model for cellular/dendritic growth and Jackson-Hunt model for eutectic growth.

Low cycle fatigue crack propagation tests were conducted on a circumferentially pre--cracked round bar of a stainless steel under various combinations of cyclic torsion and tension. The crack propagation rate was expressed as a power function of $J$ integral range for both single and mixed mode. For the same $J$--integral range, the mode I propagation rate is the highest and the mode III one is the lowest. The fatigue fracture surface is macroscopically flat under the conditions of excessive plasticity. Striations were observed on the fatigue fracture surface under mixed mode loading, and their spacing value is equal to the crack propagation rate value, the same as in mode I case.

Neutron irradiation--induced phosphorus intergranular segregation in the reactor pressure vessel steels is the one of main reasons resulting in brittle fracture of the nuclear reactor vessel. In this paper, a solute drag model was proposed to predict the phosphorus inter granular segregation in reactor pressure vessel steels and compared with the rate theory model. The predicted results show a good agreement with experimental data recently published for pressure vessel steels (C-Mn and MnMoNi steels).

Al-doped ZnO(ZAO) layers have been prepared by reactive DC magnetron sputtering from Zn:2.0%Al (mass fraction) alloy target on glass and silicon wafer substrates. The influences of the deposition parameters on the crystallization behavior as well as electrical and optical properties of ZAO films have been investigated. The crystallinity of the films was improved and the columnar crystalline growth became dominant as the substrate temperature increased. All the films show a compressive stress, which increased as the DC power increased, while it decreased as the substrate temperature was raised. Optical transmittance up to 80% in the visible range and electrical resistivity as low as were obtained under optimal deposition conditions.

A new model on the mixture law for predicting strength of metastable materials with martensite transformation has been proposed from modifying Olson model. In the new model, firstly, the power curves of austenite and martensite has replaced the straight line in Olson model; secondly, an interaction based on the interaction of austenite and martensite has been added.Results show that the values obtained by our model are better agreement with the experimental ones than other models.

The effect of the contents of ZrO2(3Y) and ZrO2(2Y) on the mechanical properties of the Al2O3/ZrO3(Y2O3) composites prepared by vacuum sintering has been studied. The change of m--ZrO2 and t-ZrO2 contents before and after fracture was detarmined by X-ray diffraction phase analysis, which is related to the toughening mechanism. When the content of ZrO2 is 15% (volume frection), the bending strength and fracture toughness of Al2O3/ZrO2(2Y) composite are 738 MPa and 6.7 MPa.m1/2, respectively, while those of the Al2O3/ZrO2(3Y) composite are 825 MPa and 7.8 MPa.m1/2, respectively. The difference in mechanical properties is due to the operation of different toughening mechanisms.

Initiation, growth and breakage of hydrogen blistering and hydrogen--induced delayed fracture under constant load in bulk metallic glass Zr41.2Ti13.8Ni10Cu12.5Be22.5 have been investigated. The results show that when charging current density i<20 mA/cm2, there are no hydrogen blisterings and microcracks on the surface of the specimens and the normalized threshold stress intensity factor is KIH/KIC=0.63. where KIC=62.2 MPa.m1/2. When i20 mA/cm2, hydrogen blisterings and microcracks appear in the specimen under no loading, while KIH}/ KIC decreases from 0.63 to 0.26. The critical pressure necessary for a stable blistering formation is pi3.6 GPa, and that for cleavage propagation of the blistering is pC3.9 GPa. The crack formed through blistering cracking will be arrested after propagating 20 to 30 um, and the arrested crack will propagate again because of entering of hydrogen atoms. At last, the blistering with cracking will be broken and leave local cleavage fracture surface with arrested lines on the surface of the sample without loading.

The pressure changes in the cavity of ADC12 and AZ91D die castings under the same processing technology have been measured. From liquid phase to solid phase, the pressure curves of ADC12 and AZ91D are divided into six sections and the characteristic parameters were defined based on the experimental results. The results show that the filling pressure and filling time as well as the trend of pressure change of these two alloys are almost the same. The pressure holding time and the effective holding time of the transferred pressure of ADC12 are much higher than those of AZ91D. For different measured points, the maximum transferred pressures of ADC12 are close to each other and those of AZ91D show a great difference. The difference of pressure curves between the two alloys is related to the solidification characteristic of the liquid metal and the mechanical properties of the alloys.

The elevated temperature fatigue strength and room temperature tensile properties and fatigue strength of cast Ti-47Al-2Cr-2Nb-0.15B(atomic fraction, %) alloy after thermal exposure were investigated. The microstructural change of the bulk alloy and the microstructure of surface layer after 650℃/100 h and 800℃/100 h exposures were analyzed by means of XRD and SEM. The room temperature tensile ductility and fatigue strength decreased slowly with increasing exposure temperature when it is below 650℃, and then rapidly decreased above this temperature. Dependence of fatigue strength for the unexposed alloy with test temperature exhibits the same trend. The surface layer formed after 650℃/100 h exposure is an oxygen-enriched layer, while that after 800℃/100 h exposure is an oxide layer consisting of TiO2 and Al2O3. Such a change in the nature of the surface layer corresponds to the onset of rapid drop in mechanical proerties and fatigue strength of the alloy with increasing exposure temperature.