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To explore the evolution mechanism of multistage machining processes and torsional fatigue behaviour based on strain energy for the first time and provide process optimization of axis parts of low-alloy medium-carbon steel for service performance, four multistage machining processes were applied to the 45CrNiMoVA steel, including the rough turning process (RT), RT + the finish turning process (FRT), FRT+ the grinding process (GFRT) and RT+ the finish turning process on dry cutting condition (FRT0). The result showed that the FRT process’s average low-cycle torsional fatigue life increased by 50% when it evolved from the RT process. The lower surface roughness of Ra 1.3 μm caused the total strain energy to increase by 163.8 Pa mm/mm instead of the unchanged strain energy density, and the crack feature evolved from some specific bulges to flat shear plane characteristics. When the GFRT process evolved from the FRT process, its average fatigue life increased by 1.45 times, compared with the RT process. Plastic strain amplitude decreased by 21%, and the strain energy density decreased by 4% due to more considerable compressive residual stress (-249 MPa). Plastic deformation layer depth had a consistent tendency with surface roughness. In this paper, surface integrity evolutions on cyclic characteristics and fatigue behaviour have also been explained. A fatigue life prediction model based on the energy method for machined surface integrity is proposed.

Laser Shock Peening (LSP) is a well-established surface treatment commonly used to improve mechanical properties of material's surfaces. To further understand the relationship between tensile property and fatigue life improvement of high strength low alloy steel in the LSP process, LSP treatment of 32CrNi high strength low alloy steel was carried out by YAG laser with pulse energy of 15 J, and tensile property was tested by electronic universal material testing machine. Surface morphology, residual stress and tensile fracture of the specimens before and after LSP were observed by white light interferometer (WLI), X-ray measuring apparatus and scanning electron microscope (SEM). Result shows that LSP did not change tensile strength of 32CrNi steel but cause yield characteristic transform from obvious yield point to no yield phenomenon which is the only factor benefiting fatigue life, indicating that the increment of fatigue life was probably related to the disappearance of yield phenomenon. Formation mechanisms of tensile fractures and yield phenomenon induced by LSP at room temperature were also discussed and completely revealed. Deeper compressive residual stress and flat grains contributed to the transition of yield characteristic and lower elongation rate of 32CrNi steel subjected to LSP.

Bimetallic catalysts possess unique physical and chemical properties that distinct from the individual, which offer the opportunity to ameliorate the hydrogen storage properties of MgH2. Herein, a Ni3Fe catalyst homogeneously loaded on the surface of reduced graphene oxide (Ni3Fe/rGO) was prepared based on layered double hydroxide (LDH) precursor. The novel Ni3Fe/rGO nano-catalyst was subsequently doped into MgH2 to improve its hydrogen storage performance. The MgH2-5 wt.% Ni3Fe/rGO composite requires only 100 s to reach 6 wt% hydrogen capacity at 100 °C, while for MgH2 doped with 5 wt% Ni3Fe, Ni/rGO and Fe/rGO all require more than 500 s to uptake 3 wt% hydrogen under the same condition. The onset dehydrogenation temperature of the MgH2-5 wt.% Ni3Fe/rGO composite is about 185 °C, much lower than that of the MgH2 doped with 5 wt% Ni3Fe (205 °C), Ni/rGO (210 °C) and Fe/rGO (250 °C), and it can release H2 completely even in 1000 s at 275 °C. Besides, the MgH2-5 wt% Ni3Fe/rGO displays the lowest dehydrogenation apparent activation energy of 59.3 kJ/mol calculated by Kissinger equation. The synergetic effect attributing to rGO, in-situ formed active species of Mg2Ni and Fe is in charge of the excellent catalytic effect on hydrogen storage behavior of MgH2. Meanwhile, this study supplies innovative insights to design high efficiency catalysts based on the LDH precursor.

Chatter is one of the challenging topics in the field of metal cutting. The dynamic characteristics of five-axis milling system are complex and variable. Especially in high-speed milling process, the influence of the tool-workpiece interactions and speed effect on milling stability is more obvious. It is necessary to investigate the influence of various interaction effects on milling stability. In this paper, the dynamical model of spindle system was established, and then the model was applied to investigate the influence of gyroscopic effect and centrifugal force on the dynamical characteristics of the tool tip. In order to solve the chatter problem of five-axis flank milling, the extended dynamical model of five-axis flank milling which considers the tool-workpiece interactions and speed effect was established. Based on the established milling dynamical model, the influence mechanism of the spindle system-tool-workpiece interaction effects on five-axis flank milling stability was investigated. The stability lobe diagrams of five-axis flank milling which contains the tool-workpiece interactions and speed effect can be obtained. Experimental results show that the proposed five-axis flank milling dynamical model can predict the milling state more reliable than the traditional ones. The research results are of great significance in preventing five-axis flank milling chatter.

Carbon-fiber reinforced silicon carbide matrix (C/SiC) composites are typical difficult-to-cut materials due to high hardness and brittleness. Aiming at the problem of the serious tool wear in conventional milling (CM) C/SiC composite process, ultrasonic vibration–assisted milling (UVAM) and conventional milling tests with a diamond-coated milling cutter were conducted. Theoretical and experimental research on the cutting force during the ultrasonic vibration milling process of C/SiC composites is carried out. Based on the kinematics analysis of tool path during ultrasonic vibration milling process, the cutting force model of ultrasonic vibration milling is established, and the influence mechanism of ultrasonic vibration on the cutting force is revealed. Based on the analysis of the evolution law of tool wear profile and wear curve during the traditional milling and ultrasonic vibration milling of C/SiC, the tool wear forms and mechanism of diamond-coated milling cutters in two processing modes and the influence mechanism of ultrasonic vibration on tool wear are revealed. It is found that the main wear mechanism of the diamond-coated milling cutter is abrasive wear, and the main wear form is the coating peeling. Compared with the traditional milling, the tool wear can be reduced by the ultrasonic vibration milling in machining process. In the range of test parameters, the tool wear decreases first and then increases with the increase of ultrasonic amplitude.

In five-axis ball-end machining, stability of the milling process is not only determined by the combination of depth of cut and the spindle speed, but also determined by the lead and tilt angles of the milling tool (i.e., the tool orientations). As the degree of freedom increases, five-axis machining machines have more complex dynamic characteristics. Therefore, the influence of the tool-workpiece interactions on the machining performance is more obvious. In this paper, a new five-axis ball-end milling dynamical model which considers the multiple interactions between the tool and workpiece is established for the first time. Based on the established dynamical model, the effects of regenerative effect, structural mode coupling and process damping on the dynamic characteristics of five-axis milling are investigated. In addition, the effects of lead angle and tilt angle on the stability prediction of five-axis milling are investigated. The experimental results show that the proposed five-axis milling dynamical model is more reliable than the traditional one in predicting the stability of five-axis milling.

As an unfavorable factor of machining process, chatter threatens the machined quality of workpiece, which determines the assembly and fatigue performance of the workpiece. During the interaction between machine tool and thin-walled workpiece, the process damping effect, multiple modes response and dynamic changes caused by the material removal of the in-process workpiece (IPW) will make the machining process more complicated and introduce great difficulties to dynamic modeling and performance prediction. In this paper, we considered the process damping determined by the indentation volume between flank face of milling tool and machined surface, and used multi-mode model to describe this behavior. In order to establish the assembled material removal model of the IPW dynamics with multiple modes, the structure dynamic modification (SDM) and finite element method (FEM) were combined together. The updated third-order full discretization method was applied to solve the dynamic equation in modal space. Then, the three-dimensional stability lobe diagrams (SLDs) with and without material removal along the tool path were obtained respectively by enveloping multiple modes of the IPW and milling tool together. Finally, the cutting tests were carried out. The experiments showed that the assembled model could predict the dynamics of IPW accurately, and the proposed stability analysis model was relatively close to experimental results. Besides, the modes of thin-walled workpiece with weak rigidity do not always play a dominant role in the process of machining. Although the material removal rate is limited by considering the multiple modes of the system, the processing quality can be ensured.

A reduced graphene oxide-supported NiCu nanocatalyst (NiCu/rGO) was prepared via the reduction of self-assembled layered double hydroxide (LDH) and graphene oxide (GO) composite precursor. The effect of NiCu/rGO on the hydrogen sorption kinetics of MgH2 was investigated systematically. TEM observations reveal that the ultrafine NiCu (6 nm) particles highly disperse on the rGO surface. Hydrogen storage measurements reveal that MgH2-5 wt.% NiCu/rGO has superior hydrogen sorption kinetics over as-milled MgH2 and MgH2-5 wt.% NiCu without rGO. MgH2-5 wt.% NiCu/rGO absorbs 5.0 wt% hydrogen within 100 s at 200 °C, while MgH2-5 wt.% NiCu only absorbs 2.0 wt% hydrogen and as-milled MgH2 hardly absorbs hydrogen under the same conditions. Moreover, MgH2-5 wt.% NiCu/rGO starts to desorb hydrogen at 185 °C, which is 115 °C lower than that of as-milled MgH2, and desorbs 5.8 wt% hydrogen within 1200 s at 300 °C. The apparent activation energy for hydrogen desorption of MgH2-5 wt.% NiCu/rGO is 71.7 kJ/mol H2, significantly lower than 107.3 kJ/mol H2 for MgH2-5 wt.% NiCu. The enhanced hydrogen sorption kinetics of MgH2-5 wt.% NiCu/rGO mainly attributes to the synergistic effect between rGO and NiCu nanoparticles. This research extends the knowledge of designing efficient catalyst via layered double hydroxides precursor in the hydrogen storage materials.

Metal-containing catalysts have been successfully applied in the Mg-based hydrogen storage materials. Here, a layered Ni/Al2O3 obtained by calcination of NiAl-layered double hydroxide (NiAl-LDH) is firstly reported for enhancing hydrogen sorption kinetics of MgH2. The hybrid catalyst of Ni/Al2O3 with high stability shows better catalytic performance than the corresponding complex oxides: the onset dehydrogenation temperature of MgH2-Ni/Al2O3 (190 °C) is much lower than that of MgH2-NiO/Al2O3 (240 °C) and the as-milled MgH2 (298 °C), and the MgH2-5 wt.% Ni/Al2O3 desorbs about 5.6 wt.% hydrogen within 3500 s at 275 °C, while only 4.6 wt.% hydrogen is released for MgH2-5 wt.% NiO/Al2O3 and the undoped MgH2 can hardly dehydrogenate at the same conditions. The catalytic mechanism of Ni/Al2O3 was investigated in detail by combining the experiment and density functional theory (DFT) calculations. The enhanced hydrogen desorption kinetics is mainly due to the destabilizing effect of MgH2 caused by Ni/Al2O3 acting as electron acceptors to capture the electrons in the Mg−H bond, resulting in a weakening of the bond strength. This study might be of interest for designing high-efficiency metal-metal oxide hybrid catalysts applied in the field of hydrogen storage.

In this work, Magnesium nanoparticles with Pd decoration, ranging from 40 to 70 nm, were successfully coprecipitated from tetrahydrofuran (THF) solution, assigned as the Mg–Pd nanocomposite. The Mg–Pd nanocomposite exhibits superior hydrogen storage properties. For the hydrogenated Mg–Pd nanocomposite at 150°C, the onset dehydrogenation temperature is significantly reduced to 216.8°C, with a lower apparent activation energy for dehydrogenation of 93.8 kJ/mol H2. High-content γ-MgH2 formed during the hydrogenation process, along with PH0.706, contributes to the enhancing of desorption kinetics. The Mg–Pd nanocomposite can take up 3.0 wt% hydrogen in 2 h at a temperature as low as 50°C. During lower hydrogenation temperatures, Pd can dissociate hydrogen and create a hydrogen diffusion pathway for the Mg nanoparticles, leading to the decrease of the hydrogenation apparent activation energy (44.3 kJ/mol H2). In addition, the Mg–Pd alloy formed during the hydrogenation/dehydrogenation process can play an active role in the reversible metal hydride transformation, destabilizing the MgH2.

Cross-shaped chisel edge thinning is an effective method to improve the drilling performance of non-coaxial helical flank micro-drill. In order to study the effect of the cross-shaped chisel edge on drilling performance, the mathematical model of cross-shaped chisel edge is proposed. The rake angle, lip inclination angle, uncut chip thickness, and uncut chip width are calculated by MATLAB software. Finite element models of four kinds of micro-drills with a different thinned chisel edge are established using DEFORM-3D software, and micro-drilling simulations on 304 austenitic stainless steel are carried out. The simulation results show that with a decrease in chisel edge length, the drilling force, tool temperature, tool wear, and curl degree of the chip are clearly reduced. However, for micro-drill without chisel edge, the torque and tool temperature are larger than other micro-drills, and string chips are generated during the drilling process. Furthermore, the non-coaxial helical flank micro-drill with an optimal cross-shaped chisel edge is manufactured by a six-axis CNC grinding machine, and the measurement results indicate that the geometrical parameters meet the designed values. At last, the micro-drill with an optimal cross-shaped chisel edge has a satisfactory drilling performance by the micro-drilling experiment.

The stability of micro-milling has an important influence on the machined surface, and choosing proper machining parameters can effectively avoid machining process instability and dynamic error. The frequency response function (FRF) of micro-milling tool point varies with tool overhang lengths, and it affects stability lobe diagram (SLD) of the machining system. During the micro-milling process, the cutting thickness was divided into the shearing zone and the plowing zone. In the shearing zone, the cutting thickness was calculated with considering cycloidal tool path and dynamic cutting thickness. After the micro-milling force model was established, the receptance coupling substructure analysis (RCSA) and experimental modal analysis (EMA) were used to obtain the FRFs at the micro-milling tool point. The 2 three-dimensional diagrams, SLD and surface location error (SLE), were developed comprehensively by means of frequency domain method, and the flank micro-milling experiments were carried out. The validity of the three-dimensional SLD containing tool overhang length and the prediction model of SLE was verified by the experimental results, and surface topography was characterized to show the actual machining state. The experimental results show that, compared with SLE, the change of tool overhang length had more significant influence on SLD, and the chatter remarks were not very obvious on the bottom of the workpiece no matter whether the machining process was stable or not. In unstable region, chatter caused by cutting tool left marks on the machined surface. Under the condition of stable milling, a machined surface with smaller SLE and better topography was obtained. The 2 three-dimensional diagrams can provide good references for the selection of optimal tool overhang length and machining parameters comprehensively.

Chatter is a kind of self-excited vibrations which is related to regenerative effect, mode coupling effect, and process damping, etc. To predict milling chatter more accurately, a suitable dynamical model of milling process which can reflect the practical chatter mechanism should be obtained firstly. In this paper, a new milling dynamical model which simultaneously considers the regenerative effect, mode coupling effect, and process damping is established. Based on the new dynamical model and the updated full-discretization method (FDM), the coupling influences of regenerative effect, mode coupling effect, and process damping on the accurate of the stability lobe diagrams (SLDs) for up-milling and down-milling operations are investigated. A series of numerical simulation and experiments are carried out to verify the accuracy of the proposed milling dynamical model. The experiment results show that the mode coupling effect and process damping have great influences on the prediction of milling stability. The SLD which obtained by the new milling dynamical equation (considering the regenerative effect, mode coupling, and process damping) is more accurate than that which obtained by only considering the regenerative effect.

In this work, we report a novel core–shell-like structure of uniform coating PMMA-MWCNTs composite film on the surface of the Mg3MnNi2 alloy particles prepared by hydriding combustion synthesis. The structures and electrochemical performances of Mg3MnNi2 alloy with different PMMA-MWCNTs coating content have been studied in detail. Results show that the PMMA-MWCNTs composite film has no effect on the phase composition of Mg3MnNi2 alloy and the composite film has been successfully coated on the surface of Mg3MnNi2 alloy with a thickness of about 30 nm. In addition, MWCNTs are dispersed in the PMMA layer successfully, improving the electrochemical catalytic activity and working as a conductive path and a hydrogen diffusion channel as well. It is found that the coating of proper amount of PMMA-MWCNTs film can enhance obviously the cycling stability of the alloy electrode. The Mg3MnNi2-75% PMMA-MWCNTs sample exhibits the best overall electrochemical properties, with the best cycling stability, the optimal high-rate dischargeability, the maximum exchange current density and the minimum charge-transfer resistance (Rct).

Micro mills are widely applied in the micro manufacturing and mainly fabricated using the grinding method. Cutting edges have significant influences on the performance of micro mills such as the micro mill life and machining quality. In this paper, the cutting edge damage mechanisms in the grinding of cemented carbides micro mills are investigated. The micro end mills grinding experiments are carried out and the cutting edge maximum edge damage width and surface roughness of the end teeth flank are measured. The results show that the micro fractures and micro cracks are generated in the cutting edge following micro pits in the grinding surface. The grain size and composition of cemented carbides have significant impacts on the damage of the cutting edge. The maximum edge damage width increases with the increase of Co binder content and WC grain sizes. However, a better flank quality with less micro pits is obtained as the reduction of Co binder content and grain size of WC.

This paper presented the influence of machined surface texture on fretting cracks behaviors of Titanium alloy Ti–6Al–4V under radial loading in conformal contact. The contacted holes of specimen were machined with combined helical and flank milling before fretting fatigue tests, and a special fretting fatigue test apparatus was proposed to focus on conformal contact fretting fatigue (CCFF) test under radial loading. The test results showed that all the specimens failed at the contact area where characterizes an inner obtuse angle between the material flow direction (or cutting direction) and the direction of the tangential component of the contact force. The area with higher surface skewness and kurtosis values was also prone to nucleate fretting fatigue crack. These results suggested that the corresponding machining conditions in hole-making and surface strengthen processes should be adjusted to guide the production of surface texture properties, in terms of obtaining desirable lower skewness and kurtosis features to relieve nucleation of fretting cracks. Additionally, the debris in conformal contact tended to aggregate towards the partial slip zone (PSZ) due to the conformal geometry and form a compacted layer in the gross slip zone (GSZ) subjected to radial loading. These characteristics exacerbated and alleviated fretting damage in the PSZ and GSZ, respectively. In this research, a set of suitable milling parameters for the hole flank milling process in terms of prolonging fretting fatigue life were also defined.

Mg3GeNi2 hydrogen storage electrode alloy was synthesized successfully via mechanical milling followed by sintering, and its electrochemical performance as the negative electrode material in a nickel-metal hydride (Ni-MH) battery was studied for the first time. Then, different amounts of nano-nickel were added to the selected alloy with the pre-milling duration of 60 h to further improve the electrochemical performance. XRD results indicate that partial substitution of Mg by Ge in Mg2Ni can form a stable new phase of Mg3GeNi2 with excellent cycle stability. Nano-Ni addition can increase dramatically the discharge capacity and electrochemical kinetics of the alloy, which is attributed to the good electrocatalytic capability of the nano-Ni. The Mg3GeNi2-5 wt.% nano-Ni sample shows the optimum overall properties with the best electrochemical kinetics and the highest discharge capacity.

The surface location error (SLE) is used to evaluate the machining error caused by forced vibration at the contact zone during the stable machining. When the workpiece was machined continuously, the convergent SLE would change with the dynamic response of the workpiece as well. In this paper, we first established the conservative stability lobe diagram (SLD) caused by regenerative effect, and excluded the instability induced by cumulative effect with continuous radial immersion. An assumption was made that multiple immersion-by-immersion was equivalent to one immersion with the same material removal, and then the in-process workpiece (IPW) dynamics was obtained by means of structural dynamic modification. Finally, we used the improved third-order full discretization method to obtain the predicted cumulative surface location error (CSLE) with considering the dynamics of milling tool and workpiece simultaneously. Based on the stable machining parameters, the cutting tests and measurement were performed. The experimental results showed that the proposed model could effectively predict the distribution of CSLE. Under the same spindle speed, the CSLE at different cutter locations were not the same and the difference was obvious, which indicated that the dynamics from the workpiece played an important role in the formation of CSLE during the continuous machining process and should be included in the predicted model.

In the face milling of large low-rigidity aluminium alloy parts, the heat generated is one of the most important issues and leads to thermal expansion of the workpiece and the serious reduction of dimensional and geometrical precision. In this paper, a new heat transfer analytical model for face milling was established based on the heat source method, in which the cutting edge of the machine tool was considered as a finite-length rotating line heat source. Then, a transient numerical simulation was also conducted to predict the temperature field on the machined surface in single-tooth and multi-tooth milling by using the finite-element method (FEM). Finally, experiments involving the measurement of the aluminium alloy milling temperature were performed using a semi-artificial thermocouple, in which the hot end of the thermocouple was embedded into the machined surface to obtain the instantaneous face milling temperature. Those experimental results exhibited good agreement with the results from the theoretical analytical model and numerical simulation.

An investigation is carried out to analyze and quantify the wear mechanisms of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire. The EUAG is a new grinding method proposed by the present authors in which an elliptical ultrasonic vibration is imposed on the workpiece by using an elliptical ultrasonic vibrator. In this paper, a series of grinding experiments under the presence/absence of ultrasonic vibration assistance are performed. The grinding forces and work-surface roughness are measured, and the wheel surface is examined too. The experimental results indicate that during grinding, the steady process region performed in EUAG is longer than that in Conventional Grinding (CG) by 20%, meaning that the grinding wheel has a longer sharp cutting period in EUAG. It is validated that the main wear mechanisms in EUAG is micro-fracture and cleavage of abrasive grains, which has a positive effect on the better grinding performance, such as lower grinding forces, force ratio Fn/Ft, wheel loading, and smoother work-surface. This study demonstrates that the improved grinding performance of diamond wheel can be realized by using EUAG method.

Mg–Ni–C composite hydrogen storage materials were prepared by first ball milling the powder mixtures of carbon aerogel and nano-Ni, and then mixed with magnesium powder followed by hydriding combustion synthesis (HCS). The HCS product was further treated by mechanical milling for 10 h. The effect of Ni/C ratio on the structures and hydrogen absorption/desorption properties of the materials were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and pressure–composition–temperature (PCT) measurements. It is found that 90Mg–6Ni–4C system shows the best hydriding/dehydriding properties, which absorbs hydrogen at a saturated capacity of 5.23 wt.% within 68 s at 373 K and desorbs 3.74 wt.% hydrogen within 1800 s at 523 K. Moreover, the dehydriding onset temperature of the system is 430 K, which is 45 K lower than that of 90Mg–10Ni system or 95 K lower than that of 90Mg–10C system. The improved hydriding/dehydriding properties are related greatly to the Ni/C ratio and the structures of the composite systems.

Micro turn-milling is a new prospective technology for the precision machining of micro/meso scale rotationally symmetrical workpieces. Micro orthogonal turn-milling experiments were carried out on aluminum alloy 2A12 with high speed steel end mill in miniature turn-milling machine tool. The characteristic of surface profile were investigated using numerical characteristic parameters and mathematical statistics functions such as amplitude density function(ADF) and power spectral density (PSD). The relationship between surface roughness and cutting conditions such as machining strategy and cutting regime was established in orthogonal test and auto regression analysis. The results show that the characteristic of surface profile of up turn-milling is better than that of down turn-milling in general, the surface spatial frequency component within both of the machining strategy are deteriorated to some extent because of the irregular contact between end mill and workpiece caused by the elasticity deformation in micro turn-milling process. The surface roughness of micro turn-milling is close to micro turning and the influence of machining regime on the surface roughness is not very significant. From this perspective, the process parameters of micro turn-milling can be selected in a wide range. (4 pages)

30CrNi3MoV high-strength steel is a difficult-to-cut material which is extensive used in vehicle and aircraft. The possibility of high efficiency dry milling with cemented carbide added with TaC, NbC and Si3N4 composite ceramic is discussed based on the analysis of the material mechanical properties. The result of cutting tool wear and life shows that, the cutting tool life of 49 min and 55 min respectively is obtained within the cutting speed range of 118 to 186 m/min. The indices in the cutting tool life expressions of ceramic is bigger than that of cemented carbide, which shows that the composite ceramic is more suitable for the face milling of 30CrNi3MoV high-strength steel in the high speed range. The main wear form is the long irregular wear land in flank face, crater in the middle of the chamfer, as well as sector peeling in rake face and triangular breakage in the corner due to the high cutting temperature and the periodical mechanical shock. (4 pages)