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Thin-walled structures, as common component specification for aerospace components, easily experience deformation and chatter issues during machining (e.g. milling) operations. With Additively Manufactured (AM) materials being increasingly applied in these areas, it is found that their microstructural anisotropy can lead to varied mechanical properties and machinability in different directions. However, former research on thin-walled parts mainly focused on bulk materials, while the machining performance of these thin-wall structures produced from AM processes remains unclear. In this view, this research aims to reveal the effect of microstructural anisotropy resulting from AM process on the machining (deformation and stability) of thin-walled parts by taking Ti6Al4V as an example. Three kinds of AM Ti6Al4V thin-walled parts were fabricated with different laser scanning strategies, in which the prior columnar β grains were found to grow along the building direction and led to a variation in mechanical properties. Owing to this, the deformation and machining stability varied in the AM thin-walled parts with different β phase crystallization orientations on the same milling directions, which could be attributed to the changes of cutting force and dynamic parameters (e.g., frequency, stiffness (determined by elastic modulus), damping ratio) in different orientations. This investigation could provide a reference for the selection of printing strategies and follow-up machining process of AM thin-walled parts when considering their microstructural anisotropy. [Display omitted] • Prior β phase was grown along the building direction in the additive manufactured Ti6Al4V part, resulting in differences in dynamic parameters. • The anisotropic machinability of the AM Ti6Al4V thin-walled part in force-induced deformation is revealed and studied. • The anisotropic machinability of the AM Ti6Al4V thin-walled part in machining stability is revealed and studied. [ABSTRACT FROM AUTHOR]

TiAlSiN multicomponent coating, owing to its high hardness and excellent high temperature resistance, was widely used in the cutting field of difficult-to-cut materials such as titanium alloys. For machining titanium alloys, high temperature is easy to gather on the tool chips and deteriorate the cutting tools. Moreover, high temperature will also promote the microstructure evolution and make the wear mechanism more complex. In this paper, TiAlSiN coatings were deposited on cemented carbides and annealed at 400 °C, 600 °C and 800 °C respectively for 60 min in air, followed by reciprocating friction tests against Ti6Al4V counterparts. AFM, SEM, EDS and XPS were applied to investigate the microstructure evolution and tribological behavior of TiAlSiN coating after high temperature annealing. The results demonstrated that the oxidation resistance of TiN phase in TiAlSiN coating was worse than Si 3 N 4 and AlN phases. These nitrides can be oxidized to TiO 2 , SiO x and AlO x under 600 °C, and the depth of oxide layer was increased with the rising annealing temperature, resulting in the coarsened microstructure. The wear mechanisms of as-deposited TiAlSiN coating were oxidation wear and adhesion wear. With the rising annealing temperature, abrasive wear was gradually enhanced. For the TiAlSiN coating annealed at 800 °C, abrasive wear became the dominant wear mechanism. [ABSTRACT FROM AUTHOR]

Complex-shaped ceramic tools were prepared by ultrasonic-assisted molding technology and microwave sintering. A uniaxial ultrasonic vibration compaction system was designed. The effects of ultrasonic vibration and molding pressures on mechanical properties and microstructures of A 2 O 3 and Al 2 O 3 /SiC complex-shaped milling cutters were investigated by simulations and experiments. The results indicated that the density was distributed unevenly within the green ceramic tool samples, especially poor in the tool edges. These drawbacks were well improved by ultrasonic-assisted molding technology and microwave sintering. Applying ultrasonic vibration during the compaction process of green ceramic tool samples could improve the densification, hardness and reduce the randomness of mechanical properties of the sintered ceramic tool materials, especially for the difficult-to-sinter composite ceramics (with poor density). For A 2 O 3 ceramic tool, fully dense microstructure was achieved, and for Al 2 O 3 /SiC ceramic tool, the cutting edges showed better density than that of the interior body, which was beneficial to improve the abrasion resistance of cutting tool. [ABSTRACT FROM AUTHOR]

Al 2 O 3 -based ceramic tool materials synergistically reinforced by SiC whiskers (SiC w) and SiC particles (SiC p) were prepared via spark plasma sintering (SPS) technique. The densification behavior, sintering kinetics and optimal ratios of SiC w and SiC p on Al 2 O 3 -based ceramic tool materials were investigated. Results indicated that densification mainly occurred from 1200 to 1450 °C. Grain boundary sliding or grain boundary diffusion was the primary cause of densification at 1200–1350 °C. Whereas, dislocation climbing was the main densification mechanism at 1400–1450 °C. W25P5 sintered at 1450 °C had a large relative density, small grain size and the best mechanical properties with the fracture toughness of 7.35 ± 0.19 MPa m1/2, Vickers hardness of 21.79 ± 0.21 GPa, and relative density of 98.86 ± 0.15 %. The synergistic toughening mechanisms included crack deflection, whisker bridging and whisker pull-out. [ABSTRACT FROM AUTHOR]

Fine-grained Al 2 O 3 /SiC composite ceramic tool materials were synthesized by two-step microwave sintering. The effects of first-step sintering temperature (T1), content and particle size of SiC on the microstructure and mechanical properties were studied. It was found that the sample with higher content of SiC was achieved with finer grains, and the incorporation of SiC particles could bridge, branch and deflect the cracks, thus improving the fracture toughness. Higher T1 was required for the densification of the samples with higher content of SiC (>5 wt%). The sample containing 3 wt% SiC particles with the mean particle size of 100 nm, which was sintered at 1600 °C (T1) and 1100 °C (T2) for 5 min had the fine microstructure and optimal properties. Its relative density, grain size, Vickers hardness and fracture toughness obtained were 98.37%, 0.78 ± 0.31 μm, 18.40 ± 0.24 GPa and 4.97 ± 0.30 MPa m1/2, respectively. Compared to the sample prepared by single-step microwave sintering, although near full densification can be achieved in both two methods, the grain size was reduced by 36% and the fracture toughness was improved by 28% in two-step microwave sintering. [ABSTRACT FROM AUTHOR]

Despite the well performance of SiAlON ceramic cutting tools in machining nickel-based superalloys, there is still the problem of rapid wear due to high cutting temperatures and high cutting forces. In this study, novel high x value Y-α/β-SiAlON ceramic cutting inserts were fabricated by microwave sintering. The microstructure and oxidation behavior were tailored by varying the designed α/(α + β) ratios to enhance the cutting performance. The oxidation behavior was studied by static oxidation tests at 1000–1400 °C in air, and the cutting performance was tested by milling Inconel 718 superalloys. The results indicated that increasing α/(α + β) ratio under high x value composition could promote the elongation of α-SiAlON grains thus improving the mechanical properties. However, this also increased the volume of intergranular phase (IGP), which gradually weakened the oxidation resistance. At temperature above 1200 °C, the oxidation of IGP was much faster than α' and β' phases. This resulted in the decline of surface hardness and grain boundary strength, which in turn affected the cutting performance. When controlling the designed α/(α + β) ratio to 50%, a balance was achieved between the microstructure and oxidation resistance that the tool life was promoted. • Novel high x value α/β-SiAlON ceramic cutting inserts were fabricated by microwave sintering. • Improvement of cutting performance was achieved via tailoring microstructure and oxidation behavior. • Oxidation mechanisms of α/β-SiAlON ceramics were further revealed. • Influence mechanisms of high temperature on cutting performance were discussed. [ABSTRACT FROM AUTHOR]

SiC whiskers (SiC w)-reinforced α/β-SiAlON ceramic tool materials were synthesized via spark plasma sintering (SPS). A comprehensive study was conducted on densification mechanism, phase composition, microstructure, mechanical properties, and wear resistance of the SiC w /α/β-SiAlON composites. The results indicated that SiC w constrained the densification process and impeded the growth of SiAlON grains, and the introduction of SiC w significantly enhanced mechanical properties of the α/β-SiAlON ceramic. The composite containing 28 wt% SiC w synthesized at 1700 °C showed well mechanical properties, with a density of 3.35 g/cm³, Vickers hardness of 19.38 ± 0.33 GPa, and fracture toughness of 7.35 ± 0.27 MPa m1/2.The principal toughening mechanisms of SiC w /α/β-SiAlON included crack deflection, branching, bridging, as well as transgranular fracture and whisker pullout. The addition of SiC w improved the wear resistance of α/β-SiAlON ceramic. Compared to those without whiskers, the wear volume and wear rate were decreased by 38.8 %. [ABSTRACT FROM AUTHOR]

Two kinds of α/β-SiAlON ceramic tools with different ratio of α-SiAlON to β-SiAlON (10α:90β, 40α:60β) were prepared via spark plasma sintering (SPS). The orthogonal and single-factor experiments were conducted to optimize the milling parameters of the tool. Also, the tool life, failure modes, and wear mechanisms of α/β-SiAlON ceramic tools were studied. The optimal milling parameters for the high-speed face-milling of Inconel 718 by SPS-sintered SiAlON ceramic tools were vc = 800 m/min, fz = 0.12 mm/z, and ap = 1.5 mm. Life of the tool containing high α-SiAlON content (40α:60β) was twice that of the tool with lower content of α-SiAlON (10α:90β), and 2.7 times that of commercially available SiAlON ceramic tool. The SPS-sintered SiAlON ceramic tools displayed better wear resistance than that of a commercially available tool even under recommended cutting parameters of the commercial tool (vc = 1000 m/min, fz = 0.08 mm/z, and ap = 1.5 mm). The failure modes of SPS-sintered tools were dominated by the flaking of rake face, chipping of cutting edge, and flank wear. The primary wear mechanisms were adhesive, diffusive, and abrasive wear. [ABSTRACT FROM AUTHOR]

α/β-SiAlON composite ceramics using powders mixed through different processes were prepared via spark plasma sintering. Effects of different powder mixing methods (ball-milling and ultrasonic vibration with mechanical stirring), ball-milling media (Al 2 O 3 and Si 3 N 4 balls), and mixing times (12 and 24 h) on the components and morphology of mixed powders, phase composition, microstructure, and mechanical properties of α/β-SiAlON ceramics were studied. Results indicate that additional oxides are mixed to powders when ball-milled with Al 2 O 3 balls, leading to an increase in the amount of amorphous glass and a decline in α/β ratio and mechanical properties. These effects were reduced when powders were ball-milled with Si 3 N 4 balls, and α-SiAlON content and fracture toughness increased significantly. Moreover, α/β-SiAlON ceramics that underwent ultrasonic vibration with mechanical stirring exhibited the highest hardness and oxidation resistance at high temperature, and their α/β ratio was close to expected value. [ABSTRACT FROM AUTHOR]

A fine-grained Al 2 O 3 -based ceramic tool reinforced with SiC particles (SiC p) and SiC whiskers (SiC w) was prepared by two-step microwave sintering (TSMS, 1650 °C/5 min, 1100 °C/5 min). Effects of the content of binder polyvinyl alcohol (PVA) and molding pressure on relative density, mechanical properties and microstructure of the ceramic tool were studied. As the PVA content and molding pressure were 1.5 wt% and 150 MPa, respectively, the best properties were obtained. Compared to other researches on microwave sintering, the PVA content was reduced by 50%, which effectively extended the service life of the thermal insulation device and was beneficial to the densification of the ceramic tools. When the SiC particles and whiskers were 3 wt% and 1 wt%, the relative density, Vickers hardness, fracture toughness and grain size were 99.8 ± 0.1%, 18.8 ± 0.3 GPa, 4.8 ± 0.3 MPa m1/2 and 1.3 ± 0.2 μm, respectively. Compared with the single-step microwave sintering (SSMS) (1650 °C/5 min), the grain size was reduced by 35% while the Vickers hardness and fracture toughness were increased by 9.3% and 29.7%, respectively. The fine grains resulted from two-step sintering, and the pinning and pull-out effects of SiC whiskers contributed to the improvement of fracture toughness. [ABSTRACT FROM AUTHOR]

The die‐pressed Al2O3‐based ceramic compacts for microwave sintering were prepared using uniaxial molding pressure. Effect of molding pressure on density distribution, microstructure, and mechanical properties of both green and sintered compacts were studied by simulation and experiments. The results suggested that the density distribution of green compact showed obvious stratification phenomenon as the pressure increased. High pressure could increase the density of green compact but led to large density variation. Cracks were formed within the sintered compact due to the severe stress concentration at high molding pressure. Better mechanical properties were obtained at the pressure of 200‐300°MPa. The optimal mechanical properties of Al2O3/Ti(C,N) ceramic tool were obtained at 1550°C with the soaking time of 10 minutes, which were as high as that of conventional sintering, but the sintering period was sharply shortened. [ABSTRACT FROM AUTHOR]

• A novel hybrid deep CNN has been proposed using Inception module and SR-block, named ISR-CNN. • All transition state data is discarded so that the data used to construct the dataset can be easily and correctly labelled. • The proposed method classifies chatter into slight and severe chatter based on small probability assumptions. • The cutting conditions in the test set are different from that in the training set while the cutting conditions in the validation set are the same as that in the training set. • The proposed method has higher chatter detection accuracy and generalisation capability. Unstable chatter seriously reduces the quality of machined workpiece and machining efficiency. In order to improve productivity, on-line chatter detection has attracted much interest in the past decades. Nevertheless, traditional methods are inevitably flawed due to the manually extracted features. Deep learning methods possess outstanding feature learning and classification capabilities, but the generalisation and accuracy are severely affected by the labelling and training of data. To address this, this paper proposed a novel hybrid deep convolutional neural network method combining an Inception module and a Squeeze-and-Excitation ResNet block (SR-block), namely ISR-CNN. The Inception module can automatically extract multi-scale features of cutting force signal to enrich the feature map. The SR-block can assign weights to different feature channels, thus suppressing useless feature maps and improving the model accuracy. Meanwhile, the introduction of SR-block also reduces the risk of gradient disappearance and speeds up the training of network. The generalisation and accuracy of the model is guaranteed by combining the two modules without training with transition state data. Milling tests were carried out on a wedge-shaped workpiece using different cutting parameters and tool overhang lengths to verify the accuracy and generalisability of the proposed method. The results showed that the proposed method outperforms other methods by achieving classification accuracy of on the validation and test sets 100% and 97.8%, respectively. In comparison to existing methods, the proposed method can correctly identify each machining state, including the transition states. Furthermore, the proposed method identifies the onset of chatter earlier than other methods, which is beneficial for chatter suppression. [ABSTRACT FROM AUTHOR]

The multi-cation doped α/β-SiAlON composite ceramics tool materials were prepared via spark plasma sintering. The effects of cation type (Yb, Sm, Yb/Sm), composition, and sintering temperature on densification behavior, phase formation, microstructural evolution, and mechanical properties of α/β-SiAlON were studied. Results showed that the addition of Sm 2 O 3 in Yb/Sm-SiAlON could decline the shrinkage temperature and accelerate the densification process due to the increased liquid phase volume and decreased viscosity. The Sm 2 O 3 played the role of both sintering additives and stabilizing cation of α-SiAlON, which could promote the formation of α-SiAlON and the elongation of β-SiAlON, thus acquired refined α grains and large aspect ratio of β grains. The SPS-sintered multi-cation doped Yb/Sm-SiAlON with 2 wt% additional Sm 2 O 3 possessed excellent comprehensive mechanical properties (3.40 g/cm3, 18.53 ± 0.18 GPa, and 6.13 ± 0.23 MPa m1/2). [ABSTRACT FROM AUTHOR]

A kind of Ti(C, N)‐based cermet tool material was prepared by microwave sintering. The influence of metal phases (Ni, Co, and Mo) on densification and mechanical properties was studied by orthogonal test. The results indicated that Co was more significant in improving relative density and fracture toughness than Ni, while Ni and Co had the similar effects on increasing the hardness of Ti(C, N)‐based cermet. Mo can improve fracture toughness but decrease hardness. Ti(C, N)‐based cermet with 6 wt% Ni, 6 wt% Co and 6 wt% Mo (TN6C6M6) had the optimal comprehensive mechanical performances, and its fracture toughness and hardness were better than that of Ti(C, N)‐based cermet prepared by conventional sintering. The increasing of sintering temperature promoted the uniformity of microstructure and significantly improved densification and hardness of the Ti(C, N)‐based cermet. The highest fracture toughness of TN6C6M6 (12.41 ± 0.33 MPa·m1/2) was achieved when sintered at 1600°C. For the microwave‐sintered Ti(C, N)‐based cermet, heat preservation period had little effect on densification. The relative density can reach up to 98.6% even though the heat preservation period was 0 minute. [ABSTRACT FROM AUTHOR]

Abstract Ti-DLC/α-C:H multilayer film was synthesized on cemented carbide by alternating Ti doped DLC and hydrogenated amorphous carbon through a combination of mid-frequency reactive magnetron sputtering and linear ion source technology. The microstructure, adhesion, toughness and wear behavior as well as the cutting performance were studied by the means of AFM, Raman, SEM, scratch test, ball-on-disk friction test and dry turning experiment. The results showed that the smooth and uniform surface morphology of Ti-DLC/α-C:H was the complementary results of each monolayer film, with decreasing sp3 content and rising sp2 graphite cluster compared with the monolayer α-C:H. The multilayer film displayed the adhesion of 110 N and toughness of 2980 N2, both of which were superior to each monolayer film. The friction coefficient of Ti-DLC/α-C:H was 0.075 with wear rate of 4.82 × 10−8 mm3/Nm decreasing by an order of magnitude compared with the monolayer α-C:H. The Ti-DLC/α-C:H coated YG8 cemented carbide cutting tool exhibited the longest service life of 25 min which was 1.4 times longer than the α-C:H coated and 1.7 times than the non-coated. The abrasive wear was the primary flank wear form of both non-coated and DLC coated tools with no distinct oxidative wear or diffusion wear. Highlights • The multilayer film was synthesized by alternating Ti-DLC and α-C:H. • The multilayer film was applied and studied in the GFRP turning process. • The service life of multilayer film coated tool was 1.4 times longer than the α-C:H coated. [ABSTRACT FROM AUTHOR]

Ti doped diamond-like carbon (Ti-DLC), as an advanced tool coating material, manifests good lubricating properties and strong wear resistance. By controlling the Ti concentration, the friction coefficient and wear rate of Ti-DLC against Ti 6 Al 4 V can be controlled at a lower level. Whereas in view of the high temperature easily aroused during Ti 6 Al 4 V machining process, the composition of Ti-DLC is generally greatly affected, causing changes in the carbon structure and the Ti concentration. In the current work, Ti-DLC deposited on YG8 substrate was heat-treated at different temperatures ranging from room temperature to 400 °C. The microstructure, mechanical properties, and Ti 6 Al 4 V wear resistance of Ti-DLC were investigated by Raman spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, nano-indentation tests, and ball-on-disk friction tests. It was found that the rearrangement of the carbon matrix occurred at 300 °C. At this elevated temperature, a large amount of hydrocarbon escaped causing a significant weight loss, and the particle size on the film surface increased due to oxidation. The atomic percentage of incorporated Ti varied from 2.43 at% at room temperature to 12.43 at% at 400 °C. Abrasive wear was observed when the temperature was below 300 °C, whereas adhesive-diffusive-oxidation wear occurred when the temperature exceeded 300 °C. • Temperature influenced wear properties of Ti-DLC against Ti 6 Al 4 V were investigated. • The atomic percentage of incorporated Ti ranged from 2.43 at.% to 12.43 at.%. • Abrasive wear was observed under 300 °C. • Adhesive-diffusive-oxidation wear occurred over 300 °C. [ABSTRACT FROM AUTHOR]