Search

The presence of a gradient layer with an increased maximum microhardness and extended thickness is extremely attractive because it can enhance the service performances for surface-strengthened metallic materials. In this research, Cu-Al alloys with different Al contents and microstructures were processed by surface spinning strengthening (3S) and studies were conducted to examine the gradient microstructure and microhardness distributions of the 3S Cu-Al alloys. The experimental results show that each group of the 3S Cu-Al alloys having the same Al content has approximately the same maximum microhardness at the topmost surface layer and the maximum microhardness increases with an increase in the Al content. In addition, the thickness of the gradient layer in the 3S Cu-Al alloys increases with a decrease of yield strength and an increase in the work-hardening exponent, respectively. The relationship between the maximum microhardness and chemical composition which determines the Young's modulus and plastic deformation mode, and the relationship between the thickness of the gradient layer and the microstructure which governs the strength and work-hardening capacity, were both investigated. It is found that the maximum microhardness of the gradient layer depends mainly on the chemical composition; whereas the thickness of the gradient layer depends primarily on both the strength and work-hardening capacity which are closely related to the microstructure. By combining the compositional design and microstructure optimization of the materials, and improving the surface strengthening intensity, a gradient layer of the surface-strengthened materials with an enhanced maximum microhardness and an extended thickness may be achieved.

In this work, the tensile and bending yield strengths of 304 stainless steel and H62 brass are effectively enhanced by surface spinning strengthening (3S) that can introduce a strengthening layer with gradient microstructure on the samples. The results show that the two metals exhibit distinct grain refinement in the top layer as well as severe grain deformation in the subsurface layer with obvious gradient characteristics. For the tensile yield strength, it increases from 336 MPa to 372 MPa for 304 stainless steel, and 280 MPa–294 MPa for H62 brass, respectively. For the bending yield strength, it increases from 581 MPa to 667 MPa for 304 stainless steel, and 496 MPa–523 MPa for H62 brass, respectively. A two-phase (soft and hard phases) structure for the surface strengthened metals is proposed to analyze the enhancement of the tensile yield strength, and the enhancement of tensile yield strength is determined by the maximum microhardness and the thickness of the hardened layer. The enhancement of bending yield strength may be attributed to the maximum microhardness and the corresponding nano-scale grains in the topmost layer. Based on the results above, the tensile and bending yield strengths can be improved and optimized by constructing the gradient microstructure with different grain refinement and microhardness distributions.

Ostriches are the fastest bipeds in the world, but their tibias are very thin. How the thin tibia can withstand the huge momentum impacts of the heavy body during running? The present work revealed that the combination of hierarchical and gradient design strategies was the main reason for their high strength and fracture toughness. The microstructure of ostrich's tibias compact bone was self-assembled into the 6-level hierarchical structure from the hydroxyapatite (HAP) crystals, collagen fiber (sub-nano), mineralized collagen fiber (nano-), mineralized collagen fiber bundle (sub-micro), lamellae (micro-) and osteon (macro-scales). The most distinctive design in the ostrich compact bone was that the HAP crystals were embedded in collagen fibers as well as wrapped in the outer layer of mineral collagen fibers (MCFs) in the form of HAP nanocrystals, thus achieving a high degree of soft and hard combination from the nanoscale. The bending strength was gradient-structure dependent and up to 787.2 ± 40.5 MPa, 4 times that of a human's compact bone. The fracture toughness (K

Surface strengthening is an important method which can effectively improve the fatigue property of metallic materials. In order to improve the fatigue property, for the first time, a new developed surface spinning strengthening-II (3S-II) method and the traditional shot peening (SP) treatment were applied to modify the microstructure and fatigue performance in the surface layer of 50CrMnMoVNb spring steel. It is interesting to find that the fatigue lives of the samples treated by the 3S-II method show obvious polarization characteristics (either quite higher or slightly lower than those treated by SP method) at the high stress amplitude, which does not follow the traditional life distribution rules and cannot be evaluated by the S-N curve. Moreover, the fatigue lives of the samples with the fatigue crack initiated from the surface defects are extremely lower than those of the samples whose fatigue crack initiated from the subsurface. Therefore, a fatigue risk factor, "Rf", was proposed and developed based on the competition between the applied stress and the material property to evaluate the fatigue cracking risk of the surface strengthened 50CrMnMoVNb spring steel, especially the fatigue risk of the samples influenced by the mixed factors. The calculation results show that the position where Rf max appears is exactly the position of fatigue crack initiation. As a result, "Rf" can be used to quantitatively evaluate the fatigue risk of metallic material under the influence of a variety of factors, including surface strengthening, surface roughness and residual compressive stress and so on.

The surface strengthening behaviors of cold-rolled (CR) Cu, fully recrystallized (FR) Cu and partially recrystallized (PR) Cu with heterogeneous microstructures were investigated by using the surface spinning strengthening (3S) method. It was found that the heterogeneous microstructure significantly affects surface strengthening behaviors as the fine grains have good plastic deformation ability, the ultrafine grains can bear a high stress, and the whole hardened layer can be divided into grain refinement and deformation zones. The maximum microhardness is 173 HV across all Cu because all the grains were refined to the nano-scale with an average size of 40 nm in the topmost layer of the grain refinement zone. The fine grains in the deformation zone of the PR Cu deform plastically to generate a thick hardened layer. In addition, the surface strengthening behaviors and mechanisms are discussed in detail.

The gradient layer induced by surface mechanical strengthening attracts plenty of attention as it can effectively improve the service performance of metallic materials, but how to design a suitable gradient layer and evaluate gradient layer properties need to be investigated further. In this work, the 316 stainless steel and TC4 alloy processed by surface spinning strengthening (3S) were investigated, including the work-hardening capacity before the 3S treatment and gradient layer properties after the 3S treatment. Results show that 316 stainless steel has a higher work-hardening capacity compared to the TC4 alloy before the 3S treatment; the maximum microhardness increment ratio, thickness of gradient layer and surface strengthening energy are also higher, and surface strengthening exponent is lower in the 316 stainless steel compared to the TC4 alloy after the 3S treatment. In addition, the exponential relation between the maximum microhardness increment ratio and work-hardening exponent, the exponential relation between the thickness of gradient layer and work-hardening exponent, the power function relation between the surface strengthening exponent and work-hardening exponent, and the linear relation between the surface strengthening energy and surface strengthening exponent are studied, respectively. Based on the above results and analysis, the microhardness distributions of gradient layer were discussed based on the work-hardening capacity, and the effects of the work-hardening capacity of the as-received metallic materials on the gradient layer properties of the surface strengthened metallic materials were summarized.

Surface strengthening is an effective method to improve the service life of some important engineering components. In this study, four structural steels with different yield strength were treated by surface spinning strengthening (3S) technology, which created a hardened layer in the surface layer by applying the shear stress and compressive stress. As a result, the grains in the surface layers were refined to different dimensions with the increase of the depth to the surface, and the grains in the topmost surface layer were refined to nano-scale. The microhardness in the hardened layer increases dramatically due to the grain refinement and strain strengthening. Furthermore, an exponential-type microhardness model for the hardened layer was proposed to characterize the surface strengthening behaviors of the four structural steels with different yield strength. Especially, in the model, some parameters related to the nature of the hardened layer, including Hv M /Hv m (maximum microhardness increment ratio), λ (thickness of the hardened layer), R (surface strengthening exponent) and E (surface strengthening energy) were analyzed on the basis of the microstructure and microhardness evolution in the hardened layer. Results show that with the increase of the yield strength, Hv M /Hv m , λ and E/Hv m are decreasing, while R is increasing. The metal with a low yield strength is easy to obtain a thicker hardened layer and a better surface strengthening effect, i.e., higher surface strengthening energy and lower surface strengthening exponent.

A new designed surface strengthening method, surface spinning strengthening (3S), was applied to achieve gradient microstructure in the surface layer of a Cu–11 at.%Al alloy. According to the level of grain refinement, the gradient microstructure can be divided into four zones, including nanoscale grain zone, ultra-fine grain zone, fine grain zone and coarse grain zone from the surface to the matrix. Meanwhile, a plenty of grain boundaries and twin boundaries were introduced to inhibit the dislocation motion in the surface layer during the plastic deformation process. Consequently, the hardened layer with a microhardness gradient and high residual compressive stress was produced on the samples, and the yield strength of the Cu–11 at.%Al alloy was effectively improved after 3S processing due to the strengthening effect caused by the gradient microstructure.

Synchronous improvement of the strength and ductility for metallic materials is an everlasting object as the good service performance. In this study, the yield strength (σYS) and uniform elongation (eUE) of Cu-Al alloys with three Al contents, nine grain sizes induced by the controlled annealing treatment, and three gradient structures induced by surface spinning strengthening (3S) treatment were explored. Results show that the σYS and eUE may be enhanced synchronously by increasing Al content from 5Al, 8Al to 11Al, while the σYS decreases and eUE increases when increasing grain size from ultra-fined grain, fine grain to coarse grain, and the σYS increases obviously and eUE decreases slightly by constructing the gradient layer. The trade-off relation between strength and ductility is broken through by increasing Al content, however cannot be broken through by controlling grain size, and cannot be directly broken through by constructing gradient structure. In addition, the Cu-Al alloys with the high Al content, fine grain and gradient layers obtain the superior combination of strength and ductility, and the reason is that the solid-solution strengthening, boundary strengthening and work hardening are combined together. Inspired by these, the composition design, grain size regulation, and gradient structure construction may be considered as the three feasible approaches to enhance the strength and ductility of metallic materials.

Surface strengthened Cu samples with ultra-fine grain (UFG), fine grain (FG), and coarse grain (CG) matrixes were prepared by cold-rolling, controlled annealing, and then treated by surface spinning strengthening (3S) to reveal the effect of grain size on the feature of the hardened layer. The results indicate that the maximum microhardness of the hardened layer was slightly affected by grain size. The thickness of the hardened layer is significantly influenced by grain size. When decreasing the grain size of matrix from CG to UFG, the thickness of the hardened layer displays an increasing then deceasing trend, and approaches in the highest thickness at FG.

Hydrogen is very promising as engine fuel due to its excellent combustion and emission characteristics. In order to improve the emission of a spark-ignited gasoline engine car a set of hydrogen injection system was added to its gasoline engine and the engine can be fuelled with gasoline, hydrogen or both. An electronic control system was developed and applied to control the injection timings and duration of hydrogen and gasoline. The basic composition of the control system and the fuel injection control strategy of the hybrid hydrogen-gasoline engine were studied in this paper. Finally the tailpipe emission of the hybrid hydrogen-gasoline powered car was tested over the NEDC driving cycle, and compared with that of the original gasoline car. The experimental results showed that the emission of the hybrid hydrogen-gasoline powered car is improved and can meet China- IV emission standard. Keywords-hydrogen; gasoline; electronic control engine; NEDC; emission

Hf and Pt were deposited onto molybdenum grids by ion beam-assisted deposition (IBAD). Electron emission characteristics from these coated molybdenum grids contaminated by active electron emission substances (Ba, BaO) of the cathode were measured using the analogous diode method. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed on the surface of molybdenum grids coated with Hf and Pt films. When emission substances were deposited onto the grid surface, the reaction between BaO and Hf formed a BaHfO 3 compound that markedly reduced the accumulation of BaO and accordingly decreased grid emission. The decomposition of BaO on the surface of Pt under high temperature was believed to lead to the formation of Ba and its re-evaporation from the surface, reducing active electron emission substances with a consequent significant reduction in grid emission. According to the comparison of their grid emission suppression mechanisms, it could be concluded that grid emission suppression was mainly the reduction of active electron emission substances on the grid surface, in particular BaO. This could be a worthwhile approach for the development of new grid coating materials.

Hafnium and platinum were deposited onto molybdenum grids by ion-beam assisted deposition method. Electron-emission characteristics from molybdenum grids with Hf and Pt films, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using analogous diode method. The surfaces of grids were analyzed by X-ray diffraction. The results revealed that the reaction between BaO and Hf formed BaHfO 3 compound, which greatly reduced the accumulation of BaO on the surface and accordingly decreased grid emission. In contrast, Ba were formed by the decomposition of BaO on the surface of Pt film under high temperature and re-evaporated from its surface, which reduced the active electron-emission substances on the surface of the grid and effectively restrained grid emission. Their mechanisms for grid-emission suppression are discussed and a good method to develop new grid-coating materials is suggested.

Platinum thin films were prepared on Mo/Si(100) substrate by Argon ion beam assisted deposition. X-ray diffraction analysis showed that the crystal orientation in Pt film was influenced by the incidence angle of the Ar + beam. The films exhibited preferred (111) orientation without concurrent ion beam bombardment. The films, which were deposited with simultaneous bombardment by a 500 eV Ar + beam along normal direction, showed mixed (111) and (200) orientation. Tilting the Ar + beam off the normal direction of the film surface, the film exhibited highly preferred (111) orientation, even at the tilting angle of 45°. The results suggested that the surface free energy of (111) plane is much lower than that of other lattice planes and dominates during the film growing.

Hf was deposited onto the surface of molybdenum grids by ion beam assisted deposition (IBAD). The electron emission characteristics from molybdenum grids with and without Hf, which were contaminated by active electron emission substances (Ba, BaO) of the cathode, were measured using an analogous diode method. The results show that electron emission from the grid coated with Hf film was less than that from molybdenum grid without Hf. The mechanism for electron emission suppression of the grids coated with Hf film was discussed.

Hafnium (Hf) films with different preferred crystalline orientation have been prepared on Si(1 1 1) by ion beam assisted deposition (IBAD) at room temperature. The effects of the Ar + ion incidence angle and the ion/atom arrival ratio on the texture were investigated. Hf films deposited by vacuum electron-beam evaporation have polycrystalline orientations. Hf films deposited by sputtering method, with the deposition rate about 0.15 nm/s, have weak (1 1 0) orientations. Hf films have preferred (1 1 0) orientation when the growing films were bombarded by 500 eV Ar + ions with the incidence angle of 75° and current density of 90 μA/cm 2 with the ion/atom arrival ratio about 0.21. However, as the current density was beyond 120 μA/cm 2 with the ion/atom arrival ratio about 0.43, the Hf films exhibited mixed (0 0 2) and (1 0 0) orientations and which were independent of the ion incident angle. The preferred orientation of Hf films is determined by the competition between the surface energy and the strain energy.

SiC thin films were deposited on silicon substrates using an elemental silicon target, reactively sputtered in a DC sputtering system in which the substrate temperature was kept at 900°C during deposition. Auger electron spectroscopy was utilized for the study of composition and chemical status of the deposited films. The line shape of C KVV Auger peak shows a similarity with previously reported results of c-SiC. An Auger depth profile through the film was also obtained using argon sputtering to study the compositional distribution. In addition, the IRRS of our films feature a rather strong peak around 800 cm −1 . All these results indicate that SiC has been formed in the films deposited by reactive magnetron sputtering.

AlN thin films were prepared on Si(1 0 0) substrates by reactive ion beam coating (RIBC). The composition and morphology of these films have been analyzed through non-Rutherford backscattering (NBS), Auger electron spectroscopy (AES) and atomic force microscopy (AFM). It was found that the A1/N ratio and the surface morphology depend on the deposition conditions. We also concluded that those films which are nearly stoichiometric all have smooth surfaces. When beyond stoichiometry, the surplus A1 atoms will condense to form protruding tips.

Polycrystalline SiC films were deposited on Si(111) by reactive DC magnetron sputtering using a four inch elemental silicon target. Composition of the deposited films was studied by AES (auger electron spectroscopy) and RBS (Rutherford backscattering spectroscopy) which showed that stoichiometric SiC could be obtained. Both AES depth profile and RBS indicated the existence of a transition layer. XRD (X-ray diffraction) analysis revealed the formation of polycrystalline SiC films at a substrate temperature as low as 1123 K, and the absence of other peaks in XRD patterns except the SiC(111) peak implied that the films were (111) oriented. Furthermore, the films were found to consist of columnar nanometer sized crystallites by cross-section TEM (transmission electron microscopy) study.

Hydrogenated amorphous carbon (a-C:H) films were deposited on silicon substrates by single-source ion-beam-assisted deposition using a mixture of Ar+ and CH4+ ion beams at an ion energy of 400 eV and an ion-beam current of ≈50 mA. Infrared reflection spectroscopy, spectroscopic ellipsometry and ultraviolet–visible transmittance spectroscopy were used to characterize the structure and properties of the a-C:H films. In particular, the effect of ion bombardment on the structure and properties of the a-C:H films was investigated. It was found that changes in the optical properties and structural characteristics of the a-C:H films, i.e. graphitization, may be induced by ion bombardment. This effect will increase the absorption in a-C:H films and decrease the optical band gap.

(001) prefer-oriented and in-plane textured CeO 2 films have been deposited on polycrystalline Ni–Cr metallic substrates by ion beam assisted deposition (IBAD). The effects of the incident angle and energy of the assisted bombarding Ar + ions on the texture were investigated. CeO 2 films deposited on Ni–Cr substrates without ion beam assisted bombardment have a mixture of (111), (220) and (311) orientations. Under ions bombarding at 30°–60° incident angle to the substrate normal, CeO 2 films show (001) preferential orientation. At 55°, the strongest (001) preferential orientation was obtained and, furthermore, the films exhibit strong in-plane texture. The optimal biaxial texture of CeO2 films was obtained by depositing CeO 2 on biaxially textured yttria-stabilized zirconia (YSZ) films at ambient substrate temperature. The optimal energy of the assisted ions to produce biaxial texture was found to be 250–500 eV. The formation of the biaxial texture was found to be a gradual process involving ion beam selective resputtering. More than 100 nm in thickness is needed to develop the texture.

(0 0 1)-oriented and in-plane aligned yttria stabilized zirconia (YSZ) thin films have been synthesized on polycrystalline Ni–Cr alloy substrates by low energy ion beam assisted deposition (IBAD). The biaxial alignment of YSZ films on polycrystalline substrates was found to be mainly controlled by the incident angle and energy of the bombarding Ar + ions. Under incident angle of 55° and ion energy of 250–500 eV, optimal biaxial alignment of the film was obtained. The biaxial alignment of the YSZ needs about 1000 A thickness to develop. Monte Carlo method has been used to simulate the formation of YSZ biaxial alignment with Ar + bombarding zirconia crystals oriented with 〈0 0 1〉 parallel to normal of the film. Results of the simulation indicate that when the energy of the bombarding ions is below 50 eV, there is no obvious difference in the sputtering yields and the radiation damage of zirconia between different incident angles. However with the ion energy increasing, the variation increases rapidly. When the ion energy reaches 250 eV, the sputtering yields and the radiation damage of the (0 0 1)-oriented zirconia induced by Ar + bombardment along [1 1 1] direction (54.7° from [0 0 1]) of the zirconia are minimum as compared with those induced by Ar + bombardment along other directions. It could be concluded that YSZ grains with [0 0 1] orientation normal to the substrate are far less sputtered than other oriented grains under ion beam bombardment at 55° incident angle, which causes (0 0 1)-oriented YSZ grains to prevail over initial random oriented grains. So that the biaxial alignment is formed.

(001)-oriented and in-plane aligned yttria-stabilized zirconia (YSZ) films were synthesized on polycrystalline Ni Cr substrates by ion beam assisted deposition (IBAD). The YSZ biaxial alignment were found to be controlled by the assisted argon ion beam bombardment. The incident angle and energy of the assisted bombarding ion beam strongly influence the alignment. The optimal alignment was obtained with the assisted ion beam bombarding at 55° incident angle and 250–500 energy. The Monte Carlo method was used to simulate the alignment formation with argon ions bombarding the zirconia crystals. Results indicated that when the energy of the bombarding ions is less than 50 eV, there is no obvious difference in the sputtering yields and the radiation damage of zirconia between different incident angles. However with the ion energy increasing, the variation increases rapidly. When the ion energy reaches 250 eV, the sputtering yields and the radiation damage of zirconia induced by Ar+ bombarding along [111] direction (54.7° from the [001]) of the zirconia are much lower than those produced by Ar+ bombarding along other directions. It can be concluded that the (001)-oriented grains are resputtered less than other grains when the assisted ions bombarding at 55° incident angle, which causes YSZ grains with (001) orientation to prevail over initial random oriented grains and form the biaxial alignment.

Biaxially-textured yttria-stabilized zirconia (YSZ) films for use as buffer layers of YBCO superconducting films have been synthesized on NiCr metallic substrates by using ion-beam-assisted deposition (IBAD). Investigation of the growth mechanism of biaxially-textured YSZ films controlled by ion beam and the combined effect of substrate temperature and simultaneous ion bombardment on the structural property of YSZ films has been carried out in this paper.

Aluminum Nitride (AIN) is a promising material for a variety of technological applications because it has many exceptional properties, such as wide band gap (WBG) and negative electron affinity (NEA). AIN thin films were prepared by Reactive Ion Beam Coating. The properties of the AIN thin films may be a function of one of the preparation conditions: the beam energy. We used the non-Rutherford backscattering (non-RBS) and Auger Electron Spectroscopy (AES) results to analyze the composition of the AIN thin films. Atomic Force Microscopy (AFM) was applied to study the morphology of films. On the other hand, electron field emission properties were also studied to find the relationship between the compositional, morphological and electron field emission properties of the AIN thin films.

Pt was deposited onto molybdenum grids by the ion-beam-assisted deposition method. The electron emission characteristics of molybdenum grids, with and without Pt, contaminated by active electron emission substances (Ba, BaO) of the cathode were measured using analogous diode method. The x-ray diffraction, energy dispersive x-ray, and x-ray photoelectron spectroscopy analyses were preformed on the surface of the molybdenum grids coated with Pt. The electron emission current from the molybdenum grid coated with a Pt film is smaller than that without the Pt film, and the mechanism for electron emission suppression of the molybdenum grid coated with the Pt film was discussed.

A reactive ion beam etching system, which can be used for reactive ion beam milling and ion beam coating, has been developed. The effective ion beam diameter is 10 cm with nonunifonnity in beam density less than ± 5%. The etching target is cooled by a semiconductor refrigerator so that the temperature of samples can be kept below 100°C under working conditions. The ion beam energy, density and incident angle can be changed continuously from 200 to 1000 eV, 0 to 1.0 mA/cm2 and 0° to 90°, respectively. With the help of an improved Kaufman type ion source which is made of graphite and a unique ion beam current feedback system, the stability of the reactive ion beam current using CF4 gas is up to 0.4% per hour. For ion beam coating spherically dished grids are used, current densities of Ar+ up to 18 mA/cm2 at 1000 eV are achieved at a focal distance of 23 cm. Using CF4 gas, the etch ratio of SiO2 to Si is 9, and some other materials such as LiNbO3 and Bi12GeO20 can be etched with good results as well.

Y-Ba-Cu-O superconducting thin films have been fabricated by the reactive ion beam coating technique with good reproducibility. The influence of atom stoichiometry on the critical temperatures of the films is determined. Ba and Cu atoms diffusing into substrates were detected by auger electron spectroscopy and Rutherford backscattering. A thin silver film deposited on ZrO/sub 2/ substrate as a buffer layer can effectively retard the interface reaction. >