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Laser directed energy deposition (LDED) is widely utilized due to its high precision, fast processing speed, small heat affected zone, strong machinability, environmental protection, energy saving, and high reliability. 316L stainless steel is one of the most extensively studied materials employed in the LDED process. The process parameters of LDED are known to affect the thermal history process, which subsequently influences the microstructure and mechanical properties of the final product. Therefore, the effects of different interlayer residence times (interlayer cooling after each deposition of four layers to enhance production efficiency) on the microstructure and mechanical properties of LDED 316L stainless steel are discussed in this paper. The experimental results indicate that with the extension of the interlayer residence time (IDT), the morphology of the molten pool becomes increasingly stable, the surface quality of the component improves, and the grains are refined. When the IDT is set to 360 s, it is observed that the ultimate tensile strength of the sample is 34% higher compared to when the IDT is 0 s, the elongation is increased by 47%, and the hardness is enhanced by 13%. These findings underscore the importance of optimizing the laser interlayer residence time to improve the overall performance of 316L stainless steel parts.

In this paper, based on the extended dielectric theory, Euler beams theory and von Karman’s geometric nonlinearity, a nonlinear FGM piezoelectric microbeam model is established with flexoelectric effect. The governing equations, initial conditions and boundary conditions are obtained by applying Hamilton’s principle and then solved by combining the differential quadrature method (DQM) and iteration method. The innovation of this paper is to construct a nonlinear forced vibration model of piezoelectric microbeams. The coupling response between the inverse flexoelectric effect and the inverse piezoelectric effect is investigated. Various effects are examined, including the functional gradient index m and transverse distributed load q affecting the distribution of electric potential. Results indicated that the functional gradient index m, beam thickness h, and span-length ratio L/h have a significant impact on the dimensionless deflection of the FGM microbeam. The influence of the flexoelectric effect on dimensionless deflection increases with the decrease of scale. In addition, transverse load q and the functional gradient index m also have a significant impact on the distribution of electric potential. This paper will provide useful theoretical guidance for the design of micro-sensors and micro-actuators.

The cladding layer of high entropy alloy (HEA), specifically AlCoCrFeNiMo, was fabricated using both continuous wave (CW) and pulse wave (PW) laser techniques, with pulse frequencies set at 0.5 Hz, 5 Hz, 50 Hz, 500 Hz, and 5000 Hz. The microstructure of the cladding layer was analyzed using X-ray diffraction, ultra-depth-of-field metallographic microscopy, and scanning electron microscopy. The wear resistance, corrosion resistance, and combined corrosion-wear resistance of the cladding layer were assessed using friction and wear tests, electrochemical corrosion tests, and corrosion-wear experiments. Additionally, the impact of pulse frequency on the microstructure and properties of HEA cladding layers was examined and compared with CW cladding layers. The research results indicate the presence of body-centered cubic (BCC), σ, and B2 phases in all cladding layers. Compared to the CW cladding layer, the PW cladding layer exhibits smaller grain sizes and a reduced proportion of the σ phase. With an increase in pulse frequency, there is a gradual increase in the proportion of the σ phase and a corresponding evolution in the grain sizes within the HEA cladding structure. Notably, at a specific pulse frequency of 50 Hz, the grain size reaches its minimum. PW cladding exhibited superior wear resistance, corrosion resistance, and corrosion-wear resistance compared to CW cladding, primarily due to the finer grain size observed in the former. The optimal performance of the cladding layer can be achieved when the pulse frequency was set at 50 Hz. The refinement of grain size, combined with an appropriate presence of the σ phase, synergistically contributes to enhancing cutting resistance during friction processes. This collaborative effect further hinders plastic deformation, consequently improving the wear resistance of HEA cladding. Furthermore, the grain refinement in PW cladding promotes the development of surface oxide films, which play a crucial role in reducing galvanic corrosion of alloying elements and minimizing oxygen atom diffusion rates during corrosion processes. Consequently, both corrosion resistance and corrosion wear resistance of PW cladding are significantly enhanced.

Laser melting deposition–produced Ti6Al4V additive manufacturingparts tend to manifest as coarse columnar grains. This paper optimises the laser pulse frequency to manage the microstructuralcharacteristics of Ti6Al4V parts and enhance their tensile properties and corrosion resistance. A fiber laser processing equipment with a laser power of 1200 W and a spot diameter of 2.0 mm was employed for all experiments, which provides pulsed lasers at 4, 40, 400, and 4000 Hz at a scanning speed of 8 mm/s and a duty cycle of 95 % for comparative research.The findings demonstrated that increasing the pulse frequency improved the deposition efficiency.An appropriate pulse frequency could promote the refinement and columnar-to-equiaxed transition (CET) of primary β grains.At 400 Hz, the Ti6Al4V-deposited parts yielded refined equiaxed grains.The average grain size in the middle of the sample was about 206.8 μm,and the microstructure mainly comprised fine α-laths in a lamellar structure, which yielded the best overall performance of the parts, with the ultimate tensile strength and elongation reaching 1083 MPa and 4.09 %, respectively.Therefore, improvingthe structural properties of partsby regulating the deposition process, which is conducive to the online regulation of the forming quality of laser deposition parts, is an effective and feasible approach.

A CoCrFeNi high-entropy alloy (HEA) coating, enhanced with Al and Mo, was fabricated on Q235 steel using laser cladding technology. The synergistic enhancement effect of Al and Mo on the coatings was studied. The findings revealed that the CoCrFeNi coating mainly comprised the single-phase FCC. In contrast, the BCC and σ phases were observed when Al and Mo were individually doped. The simultaneous doping of both these elements resulted in a coating consisting of the BCC and σ phases. Mo addition led to grain refinement and increased the kernel average misorientation value; similarly, Al addition further enhanced these effects. The separate additions of Al and Mo significantly refined the microhardness and wear resistance of the coating. When both elements were added simultaneously, the microhardness and wear resistance of the coating were further enhanced, demonstrating the synergistic effects of Al and Mo on these characteristics. Moreover, the individual doping of Al and Mo decreased the Kp value and the oxide layer's thickness. Meanwhile, their combined addition reduced the Kp value by approximately 82.5 % and 89.8 %, respectively. During the initial oxidation stage, rapid oxidation of Al occurred, thereby decreasing the oxidation rate. In contrast, Mo facilitated the formation of Al2O3.

Coarse β-columnar grains are often present in Ti–6Al–4V laser-additive-manufactured samples, resulting in anisotropic and inferior fatigue performance under dynamic loading. Fine-equiaxed grains (FEGs) with a mean grain size of approximately 139 μm were successfully obtained by a novel deposition strategy through coordinated regulation of direct energy deposition technological parameters. Microstructures were transformed from α′ martensite to α'' martensite. As a result, the comprehensive performance was significantly improved. Without the use of an argon atmosphere glovebox and post heat treatment, the tensile strength and elongation in the horizontal direction of the FEGs were 1091 MPa and 4.09%, respectively. The corrosion resistance was 11.71-fold higher than that of the coarse columnar grains (CCGs). Improving the microstructure and performance by optimizing pulsed laser parameters is simple, effective, and conducive to online regulation of the quality of laser additive samples.

In this work, a high-frequency pulsed laser-welding process was successfully implemented to fabricate a Ti–6Al–4V alloy butt joint. The microstructure of each zone of the welded joint was systematically characterized by carrying out scanning electron microscopy and electron backscatter diffraction measurements. In addition, the corrosion resistance of the welded joint was tested using traditional electrochemical and local electrochemical methods, while the main factors affecting corrosion resistance and the mechanism of the galvanic corrosion were also thoroughly investigated. From the acquired results, it was demonstrated that the α′ martensitic phases constituted the microstructure in the fusion zone (FZ), where the grain size, grain orientation, and misorientation distribution of the different zones varied, and the α′ martensitic and bulk α covered the heat-affected zone (HAZ). The corrosion resistance in the HAZ was slightly better than that in the base material, and both were worse than that of the FZ, which was related to the phase type. In addition, the corrosion current density values of FZupper were about 1/4.6 and 1/2.6 those of FZmiddle and FZdown, respectively, which was attributed to differences in the grain size and grain orientation. The FZ was protected as a cathode during galvanic corrosion, which is of great importance for ensuring the service life of the component during practical applications.

In-situ V carbides reinforced Fe-based plasma arc cladding layers were prepared in the condition of air-cooled and water-cooled substrate, the microstructure, grain size and properties were comparatively studied. Results showed that microstructures of the two cladding layers were lath martensite. When the substrate was water-cooled, the residence times above 1495 °C decreased 46.3%, and the average cooling rates above 870°Cincreased 53.3%. The average grain size of the layers’ matrix and carbides was clearly refined from 3.12 to 1.39 μm and from 0.37 to 0.09 μm, respectively. Moreover, the depth of heat-affected zone reduced by 14.3%, and the dilution rate reduced by 16.90%. The comprehensive performances of the water-cooled cladding layer were obviously improved. The microhardness increased from 258 to 1040 HV0.2, the corrosion resistance increased 2.10 times and was about 13.75 times that of the low-carbon steel substrate.

This paper investigates the influence of the concentration and particle size of h-BN nanoparticles in a nanofluid on the surface integrity of 304 austenitic stainless steel during turning, focusing on the cutting force, friction coefficient, cutting temperature, surface roughness, surface residual stress, work hardening capacity, and 3D surface topography. The results show that, compared to dry cutting, the addition of 3 wt.% h-BN nanofluid can reduce the friction coefficient on the rake face by 38.9%, lower the cutting temperature by 43.5%, decrease the surface roughness by 53.8%, decrease the surface residual stress by 61.6%, and reduce the work hardening degree by 27.5%. Two-dimensional profiles and the 3D surface topography display a more balanced peak–valley distribution. Furthermore, by studying the effect of different h-BN particle sizes in nanofluids on the surface integrity of the machined workpiece, it was found that nanoscale particles have a greater tendency to penetrate the tool–chip interface than submicron particles. Moreover, the h-BN particles in the nanofluid play a “rolling effect” and “microsphere” effect, and the sesame oil will also form a lubricating oil film in the knife-chip contact area, thereby reducing the friction coefficient, reducing the cutting force, and improving the machining surface quality.

To address the tracking control problem of the periodic motion fast tool servo system (FTS), we propose a control method that combines adaptive sliding mode control with closed-loop iterative learning control. Adaptive sliding mode control enhances the system’s robustness to external non-repetitive disturbances, and exponential gain iterative learning control compensates for the influence of periodic disturbances such as cutting force. The experimental results show that the proposed iterative learning controller based on adaptive sliding mode control can effectively eliminate the influence of various interference factors, achieve accurate tracking of the FTS system’s motion trajectory within a limited number of iterations, and ensure the stability of the system, which has the advantages of a fast convergence speed, high tracking accuracy, and strong robustness.

Dimple-textured surfaces of square arrays with different geometrical parameters (area density, diameter and depth) were prepared on the surface of GCr15 steel. The friction and wear experiments were carried out under the lubrication of Suspension of graphene and liquid crystal 4-n-pentyl-4'-cyano biphenyl (5CB). By controlling the area density, diameter and depth of the dimples, the lubrication performance of laser surface texturing under the condition of starved lubrication was analyzed, and the reducing friction and wear resistance mechanism of laser surface texture was preliminarily discussed. The lubrication performance of the dimple-textured surface is best when the depth of the dimple is 10 μm, the area density is 8%, and the diameter is 100 μm. The friction coefficient at this textured parameter is 0.031, which is a 32.6% decrease compared to the untextured surface (0.046). The reduction friction mechanism of the textured surface is mainly to improve load-bearing capacity, store lubricant, reduce contact area and secondary lubrication. Meanwhile, XPS analysis shows that during the friction, the graphene/5CB suspension has a tribochemical reaction in the textured surface, and a chemical reaction film is formed on the steel surface. The research results can provide theoretical guidance for the optimization of texture geometric parameters under different application conditions.

Molecular dynamics simulations allow to investigate the microscopic evolution of a structure, and can also point the way to tool material design. In this paper, the effect of adding CaF2 and CaF2@SiO2 on the Si3N4/TiC system is studied using molecular dynamics simulations. The results show that the system with the addition of CaF2@SiO2 to the model has a higher hardness than the system with the addition of CaF2. In order to obtain the optimum parameters for self-lubricating ceramic tools, the effect of adding different amounts of CaF2@SiO2 on the Si3N4/TiC system was investigated. The Si3N4/TiC/CaF2@SiO2 system achieved optimum mechanical properties when four CaF2@SiO2 were included in the model. By analyzing the effect of the sintering temperature on the system, it was deduced that the hardness achieved a maximum value of 15.89 GPa and the modulus of elasticity reached 132.53 GPa when the sintering temperature was at 2073 K. Based on this sintering parameter, the Si3N4/TiC/CaF2@SiO2 composite ceramic tool material was experimentally prepared with the mechanical properties of 15.66 GPa hardness and 128.08 GPa modulus of elasticity. The experimental results were consistent with the simulation results.

Cutting force in lathe work is closely related to tool wear and affects the turning quality. Direct measurement of the cutting force by measuring the strain of the tool holder is challenging because the tool holder design aims to be highly rigid in order to undertake large cutting forces. Accordingly, the most popular dynamometer designs modify the standard tool holder by decreasing the structural rigidity of the holder, which reduces the machining precision and is not widely accepted. In order to solve the issue of the low stiffness of the dynamometer reducing the machining precision, in this paper, the ultra-low strain on the tool holder was successfully detected by the highly sensitive semiconductor strain gauges (SCSG) adjacent to the blade cutting insert. However, the cutting process would generate much heat, which increases the force measuring area temperature of the tool holder by about 30 °C. As a result, the readout drifted significantly with the temperature changes due to the high temperature coefficient of SCSG. To solve this problem, the temperature on the tool holder was monitored and a BP neural network was proposed to compensate for temperature drift errors. Our methods improved the sensitivity (1.14 × 10−2 mV/N) and the average relative error of the BP neural network prediction (≤1.48%) while maintaining the original stiffness of the tool holder. The smart tool holder developed possesses high natural frequency (≥6 kHz), it is very suitable for dynamic cutting-force measurement. The cutting experiment data in the lathe work show comparable performance with the traditional dynamometers and the resolution of the smart tool holder is 2 N (0.25% of total range).

We studied the effects of peak temperature and cooling rate in the secondary welding thermal cycles on the martensite/austenite (M/A) constituents’ characteristics (including fraction, average size and distribution), corrosion resistance and hydrogen permeation behaviors in the inter-critically reheated coarse-grained heat-affected zone (ICCGHAZ) of X80 pipeline steel. We observed that the M/A constituents’ characteristics mainly depend on the secondary peak temperature and cooling rates, while the microstructure style and prior austenite grain size are dependent on the first peak temperature. In addition, the variations in the M/A constituents’ characteristics result in different corrosion resistance and hydrogen permeation behaviors by changing the micro-galvanic effect and the number of hydrogen trapping sites. The high fraction and coarse grain size of M/A constituents are against the corrosion resistance and hydrogen permeation in ICCGHAZs, and their functional relationships are established. Moreover, the effects of the fraction of M/A constituents on the corrosion resistance and hydrogen permeation behaviors are much greater than those of the average size.

Mechanical properties and microstructure of graphene platelets reinforced Si3N4 composites have been investigated and compared to monolithic Si3N4. The microstructure shows that graphene platelets are parallel to each other and perpendicular to the hot pressing direction. Fracture toughness and flexural strength of composite with 1 wt.% graphene measured on polished surface perpendicular to hot pressing direction are 8.7 MPa·m1/2 and 892 MPa, respectively, which are increased about 14.5% and 20.2% compared with that parallel to hot pressing direction. The anisotropy of microstructure and mechanical properties of composites can be explained by the intrinsic anisotropy of graphene as well as the crack deflection energy release rate and the weak boundary bonding between graphene and Si3N4 caused by the thermal expansion mismatch.

In order to develop a new ceramic tool material with self-repairing capability, Al2O3/TiC/TiB2 ceramic tool material was prepared by vacuum hot-pressure sintering method. The toughening and strengthening mechanism of TiB2 on Al2O3/TiC substrate was analyzed. The results show that the ceramic tool material has good comprehensive mechanical properties when the TiB2 content is 10 vol.%. Its flexural strength was 701.32 MPa, hardness was 18.3 GPa, and fracture toughness was 6.2 MPa·m1/2, which were improved by 11.6%, 2.2% and 16.1% respectively, compared with the Al2O3/TiC tool material. Fracture surfaces of the Al2O3/TiC/TiB2 ceramic tool material were characterized by SEM, EDS and XRD. The results showed that the fracture mode was a mixture of transgranular fracture and intergranular fracture. The growth of Al2O3 and TiC grains can be effectively inhibited by adding appropriate amount of TiB2, and the internal grains of the material can be refined. The TiB2 has a uniform distribution in the matrix and acts as a diffusion toughening agent. The cutting performance of Al2O3/TiC/10 vol.%TiB2 tool material was further investigated. Experiments conducted on tools made of Al2O3/TiC and Al2O3/TiC/TiB2 materials showed that the main forms of wear for both tools were abrasive wear and bonded wear. The friction coefficient of Al2O3/TiC/TiB2 tools was reduced by 10.77% compared to Al2O3/TiC tools.

By optimising the particle size of cladding alloy powders, in situ micron and submicron (Ti-V)C reinforced Fe-based laser cladding layers were prepared and the dry sliding friction properties were comparatively studied. Results showed that there were same phases of α-Fe, γ, TiC, and TiVC2 in the two cladding layers. The average grain size of the Fe-based matrix was 3.46 μm and 3.37 μm, the microhardness was 731 HV0.2 and 736 HV0.2, and the area ratio of carbides was 11.14% and 11.02%, respectively. The dry sliding wear resistance of the cladding layer reinforced by 1.95 μm carbides was 2.76 times higher than that of the 0.49 μm carbides. The failure mechanism of the cladding layer with the micron carbides was mainly caused by plastic deformation of the cladding layer matrix, whereas that of the submicron carbides involved both the plastic deformation of the cladding layer matrix and the abrasion that was caused by the peeled carbides.

The Al2O3/Ti(C,N) ceramic material added micron ZrO2 whisker and nano coated CaF2@Al(OH)3 powder was fabricated. The micron ZrO2 whisker was for the toughening and reinforcing phase and the nano coated CaF2@Al(OH)3 powder was the lubricant. For obtaining a ceramic material with optimal comprehensive mechanical properties and friction properties, the influences of different compositions of the ZrO2 whisker and nano coated CaF2@Al(OH)3 powder on the microstructure and mechanical properties were analyzed, respectively. The result demonstrated that as the addition of the ZrO2 whisker was 6 vol% and the addition of the nano coated CaF2@Al(OH)3 powder was 10 vol%, the optimal self-lubricating ceramic material had optimal mechanical properties. The hardness of the ceramic material was 16.72 GPa, the flexural strength was 520 MPa and the fracture toughness reached 7.16 MPa·m1/2. The formation of the intragranular structure, whisker toughening and the phase transition of ZrO2 were the main mechanisms.