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Abstract Lightweight thin-walled parts are widely used in the aviation and aerospace industries, and with the further increase in the complexity of their features, the traditional manufacturing process can no longer fully meet the high requirements of industrial component manufacturing. In this work, thin-walled parts are processed by Laser based powder bed fusion of metals (PBF-LB/M), and the effects of process parameters on residual stress, hardness, mechanical properties and microstructure of thin-walled parts are systematically investigated. The simulation results show that the maximum equivalent residual stresses are distributed in the combination of the solid and the substrate, and the minimum equivalent residual stresses are mainly distributed in the top two ends and the middle part of the solid, and the stress distribution is symmetrical. In addition, the maximum equivalent residual stress increases with the increase of laser power, and decreases with the increase of scanning spacing or scanning speed. The experimental results show that with the increase of laser energy density, the tensile strength and yield strength of thin-walled parts show a tendency of increasing first and then decreasing. Finally, high-quality thin-walled parts were successfully fabricated by the optimized process parameters, and their tensile and yield strengths were increased by 6.1% and 15.9%, respectively.

In this work, the resistance spot welding (RSW) process was performed to join aluminum alloy and low-alloy carbon steel plates. The macro characteristics including nugget diameters and indentation rates, microstructure and tensile-shear strength of RSW joints were investigated. The results showed that the nugget of the RSW joints comprises a ‘bowl’ shape nugget on the aluminum side and an elliptical shape nugget on the steel side. Also, the intermetallic compound (IMC) layers containing Fe4Al13 and Fe2Al5 were formed around the aluminum/steel interface with the steel side having a tongue-shape and the aluminum side having a needle-shape. According to metallurgical evaluation and temperature distribution of RSW joints analyzed by the finite element method, the nugget on the aluminum side contained the dendritic grains and equiaxed dendritic grains. The nugget on the steel side consisted of a large amount of bainite and a small amount of coarse lath martensite. The nugget diameters and the indentations rates of RSW joints increased when increasing either welding current or welding time, and decreased when increasing the electrode pressure. The maximum values of nugget diameter and indentation rate of RSW joints were 9.076 mm and 4.144% when using the welding current of 16 kA, welding time of 450 ms and electrode force of 3 kN. In tensile-shear tests, the RSW joints showed a shear-off fracture mode. When increasing the welding current, welding time or electrode force, the tensile-shear strength of RSW joints increased first, and then reached a maximum, and finally decreased. The welding current of 16 kA, the welding time of 300 ms, and the electrode pressure of 3 kN were considered as the optimal welding parameters in the present study which resulted in the maximum tensile-shear strength of 2.24 kN. In addition, the IMC layers of the RSW joints exhibited a uniform and continuous appearance with a thickness of approximately 1.9 μm, and the IMC layer in the central area was thicker than that in the edge area.

The high-temperature mechanical properties and tribological behavior of the Al0.5CoCrFeNb0.5Ni high-entropy alloy (HEA) were investigated. The results show that Al0.5CoCrFeNb0.5Ni HEA consists of FCC, BCC and (Cr–Co–Fe)2Nb-type Laves phases. The hardness is about 572 HV at room temperature and decreases slightly at high temperatures, still maintaining a high value (>350 HV) at 900 °C. The yield strength is nearly 2000 MPa at room temperature and tends to decrease with rising temperature (800–1200 °C). The observation of the microstructure after the hot compression tests and the evaluation of the true stress-strain curves illustrate that the softening mechanism is primarily dynamic recrystallization, which occurs mainly in the FCC and BCC phases. The degree of wear increases and then decreases from 200 °C to 800 °C. The best wear resistance was observed at 800 °C, showing the maximum friction coefficient and the minimum wear rate, which was attributed to the increased oxidation that formed oxide layers mainly consisting of Cr2O3 to protect the wear surfaces. The wear mechanism of alloys is affected by temperature. Below 400 °C the wear is mainly abrasive and adhesive wear, at temperatures above 600 °C, the wear transitions from abrasive to oxidative wear, and at 800 °C the wear changes to oxidative wear.

The current study innovatively proposed to prepare TiC nanoparticles reinforced high-Cr hot work die steels through an aluminum master alloy. The influences of TiC nanoparticles on the microstructure and wear resistance of high-Cr hot work die steels were thoroughly investigated. It was found that the addition of nanoparticles refined the pro-eutectoid ferrite in the as-cast condition, and the granular pearlite in the isothermal spheroidized condition, respectively. After receiving the quenching and tempering heat treatment, the size of lath martensite, retained austenite and nanosized precipitates were reduced. The TiC nanoparticles were used as heterogeneous cores to improve the nucleation rates of austenite and ferrite during phase transformation. The finer grains with more grain boundaries and nanoparticles refined the size of tempered microstructure of high-Cr hot work die steels. In ball-on-plate reciprocating sliding wear tests, it was found that the presence of TiC nanoparticles enhanced the wear resistance of high-Cr hot work die steels under various test conditions. The nanoparticles increased the strength of the substrate and inhibited the formation of cracks. More grain boundaries and nanoparticles hindered the migration of dislocations, which resulted in less plastic deformation. Also, the nanoparticles could partially withstand the external load during the relative motion. The results obtained in this research provide applicable values for optimizing the strength-ductility and tribological performance of hot work die steels.

Due to the emergence of root rot (RR), it can cause harm to the health of Zanthoxylum bungeanum (Z. bungeanum) plants. However, the reason for this is not clear, and further research is needed. We selected healthy and RR-affected 6-year-old Z. bungeanum trees (infected for 1 year), collected their rhizosphere and bulk soils, and analyzed soil microbial communities, enzyme activities, and physicochemical properties. When the plants were diseased, soil water content (SWC), available potassium (AK), organic matter (OM) contents, β-1,4-glucosidase (β-G) activity, and fungal Shannon index significantly decreased, while bacterial Shannon index significantly increased in the rhizosphere soil. Soil total nitrogen (TN), SWC, AK, OM contents, and β-G and N-acetyl-glucosamine (NAG) activity significantly reduced, while fungal Simpson index significantly increased in the bulk soil. There were significant differences in the bacterial communities of bulk and rhizosphere soil. However, there were no obvious differences in the fungal communities. Pearson's correlation analysis showed that changes in soil microbial communities were significantly correlated with changes in the contents of TN, AK, OM, and SWC, as well as the activities of β-G and NAG. In summary, changes in soil AK, OM, SWC, and TN resulted in changes in microbial community composition, as well as changes in β-G and NAG activities, and these alterations may lead to RR in Z. bungeanum.

The present study investigated the microstructure and wear properties of annealed carbon steels with the addition of TiC–TiB2 ceramic nanoparticles. It was found that the presence of 0.02 wt% nanoparticles could decrease the amount of widmanstatten structure, promote the formation of finer pearlite from 33.0% to 46.3% and refine the grains from 67.0 μm to 47.5 μm. In ball-on-plate reciprocating sliding wear tests, the wear volume loss was reduced up to 27.2% while the test load of 50 N and sliding velocity of 60 mm/s were utilized. After examining the wear tracks, it was observed that the spalls, grooves, smearing, delamination, oxidative areas and wear debris were found within the worn areas. The ceramic nanoparticles increased the hardness of substrates, inhibited dislocations and plastic deformation, retarded the cracks on surfaces and sub-surfaces, and withstand the load which enhanced the anti-wear performance of annealed carbon steels. This research could provide a new method to improve the wear performance of carbon steel components.

The present research utilized the resistance spot welding process on stainless steel and low carbon steel. The diameters of joint and nugget, microstructure and shearing strength of joints were examined. When increasing the welding current, welding time or clamping force, the diameters of welding joints and nuggets became larger due to the higher heat input and normal load. The shearing strength of joints increased and then decreased with increasing welding current or welding time and decreased with increasing clamping force. For the metallurgical evaluation, it was found that there were five regions around the joint, which consisted of the nugget (austenite and martensite with dendritic structures), coarse heat-affected zone (martensite and pro-eutectoid ferrite), fine heat-affected zone (ferrite and pearlite), base material (ferrite and pearlite) for low carbon steel, and base material (austenite) for stainless steel. In orthogonal tests, it was found that the welding current had the most significant influences on shearing strength, and then welding time and clamping force. Finally, an artificial neural network was established to predict the shearing strength of joints under various welding conditions. The results showed that the shearing strengths predicted by the artificial neural network had good correlation with experimental values. A shearing strength higher than 10000 N could be achieved when welding current was higher than 12.5 kA and welding time was longer than 85 ms. The artificial neural network model has applicable values for predicting the shearing strengths of joints between dissimilar steel plates.

High-performance aircraft engines require superior aviation oils to enhance their lubricating performance and prolong service life. Addition of nano-sized ceramic particles has been considered as a useful way to improve the tribological performance of base fluids. Up to now, few previous studies focused on the tribological properties of ZrO _2 nanoparticles in aviation oil. The current study dispersed ZrO _2 nanoparticles into PAO _20 aviation base oil as lubricant additives. A dual-step method comprised of physical blending and ultrasonic dispersing was applied in the preparation of ZrO _2 nanofluids. Oleic acid was utilized as surfactant to enhance the stability of ZrO _2 nanofluids. Ball-on-plate reciprocating sliding wear tests were conducted to obtain the coefficient of friction and wear volumes. It was found that the PAO _20 base oil produced the highest coefficient of friction of 0.278 and wear volumes of 2.305 × 10 ^−2 mm ^3 . 5 wt% ZrO _2 nanofluids with 5 wt% oleic acid showed the best lubricating performance. The coefficient of friction was reduced by 31.29%, and wear volume was reduced by 42.95%. In the examination of wear tracks, a physically embedded tribo-layer of ZrO _2 nanoparticles and an oleic acid tribo-film with low shearing resistance were formed, which lowered the friction, and protected the mating surfaces against abrasive and adhesive wear. The results obtained in this study have applicable values in the development of high-performance aviation lubricants.

The present research investigated the effects of welding current and welding time on the shearing strength of resistance spot-welded joints of low carbon steel and stainless steel plates. The macro characteristics, microstructure and micro-hardness of welded joints were also examined. It was found that the welded joints produced with a welding current of 10 kA and welding time of 80 ms showed the highest shearing strength. The diameter of welded joints and nuggets increased with increasing welding current and welding time. For evaluation of the microstructure, different regions including the nugget, coarse heat-affected zone, fine heat-affected zone and base materials were observed within the welded joints. Also, the nugget and coarse heat-affected zone showed higher hardness than the fine heat-affected zone and base materials due to the presence of martensite. The findings obtained in this research are applicable in the development of resistance spot welding processes for joining dissimilar steel plates.

The generative adversarial network (GAN) has recently emerged as a promising generative model. Its application in the image field has been extensive, but there has been little research concerning point clouds.The combination of a GAN and a graph convolutional network has been the state-of-the-art method for generating point clouds. However, there is a significant gap between the generated point cloud and the point cloud used for training. In order to improve the quality of the generated point cloud, this study proposed multi-scale gradient point GAN (MSG-Point-GAN). The training of the GAN is a dynamic game process, and we expected the generation and discrimination capabilities to be symmetric, so that the network training would be more stable. Based on the concept of progressive growth, this method used the network structure of a multi-scale gradient GAN (MSG-GAN) to stabilize the training process. The discriminator of this method used part of the PointNet structure to resolve the problem of the disorder and rotation of the point cloud. The discriminator could effectively determine the authenticity of the generated point cloud. This study also analyzed the optimization process of the objective function of the MSG-Point-GAN. The experimental results showed that the training process of the MSG-Point-GAN was stable, and the point cloud quality was superior to other methods in subjective vision. From the perspective of performance metrics, the gap between the point cloud generated by the proposed method and the real point cloud was significantly smaller than that generated by other methods. Based on the practical analysis, the point cloud generated by the proposed method for training the point-cloud classification network was improved by about 0.2%, as compared to the original network. The proposed method provided a stable training framework for point cloud generation. It can effectively promote the development of point-cloud-generation technology.

The current research focused on the tribological properties of flake-like WS2 particles dispersed into PAO4 base oil with oleic acid as surfactant. Various concentrations of 0.2 mass%, 1 mass% and 3 mass% were applied in the preparation of WS2-OA lubricant. The wear tests were carried out using a ball-on-plate reciprocating sliding test configuration. It was found that the highest COF of 0.578 was obtained using PAO4 base oil with significant fluctuations. The COF could be reduced to approximately 0.34 and stabilized after adding the OA. When introducing the WS2 articles, the COF was around 0.158 under 0.2 mass%, 0.143 under 1 mass% and 0.145 under 3 mass%, and became almost constant after 4 min. In addition, the highest wear rate in width of 61.5 µm/m and in depth of 2.2 µm/m was found using PAO4 base oil. The wear rate can be reduced to 51.6 µm/m in width (16.1%) and 0.9 µm/m (59.1%) in depth under 3 mass% OA. While using the WS2 particles, the wear rate in width could be further reduced to 45.2 µm/m using 1 mass% but with slightly higher wear rate in depth than that of OA. Based on the analysis in SEM and EDX, the abrasive grooves became less after introducing the OA, some dark spots composed of carbon acted as tribo-films on the worn area. While using WS2 particles, it could be found that WS2 flakes were adhered on the surfaces to reduce the friction and wear.

Austempered ductile iron has been considered as a substitution to replace conventional steel castings, steel forgings and even aluminum in many applications. Its excellent mechanical properties are mainly attributed to its unique ausferritic structure containing acicular ferrite and carbon saturated austenite. Some ADI components such as camshaft and engine valve commonly experience surface contact and relative motion under external load and pressure. Outstanding wear resistance of ADI is required to ensure the satisfactory working performance and service life of these key components. In order to meet the advanced requirements of mechanical properties and wear behavior of ADI, a dual-step austempering process and additional surface hardening treatments are suggested to be utilized. In this review, conventional single-step austempering process and corresponding ausferritic structure are introduced. Second, the positive effects of a novel dual-step austempering process on microstructure and mechanical properties of ADI are provided. Next, wear behavior of single-step and dual-step ADIs and wear mechanisms are discussed. Then, studies regarding the applications of surface hardening treatments on wear resistance of ADI are reviewed. Finally, a summary and expectations are discussed. The information presented in this paper would be beneficial to future studies and applications for any grade of ADI.

The present research studied the combined effects of quench-tempering and laser surface hardening treatments on wear behavior of gray cast iron, and compared results with conventional austempered gray cast iron. Four tempering temperatures of 316 °C (600 °F), 399 °C (750 °F), 482 °C (900 °F) or 552 °C (1025 °F) with a constant holding time of 60 min and four austempering temperatures of 232 °C (450 °F), 288 °C (550 °F), 343 °C (650 °F) or 399 °C (750 °F) with a constant holding time of 120 min were utilized in the heat treatment design. The wear tests were carried out on a universal mechanical tribometer with a reciprocating ball-on-plate sliding configuration. Also, the microstructure, micro-hardness profiles and worn tracks were examined. Through this work, it was found that three zones existed under the laser hardened surface. Zone 1 was the laser hardened zone containing ledeburite with hardness of approximately 68HRC. Zone 2 was the heat affected zone containing the martensite with hardness of approximately 66HRC. Zone 3 was the substrate with hardness ranging from 42.1 to 24.8HRC. In the sliding wear tests, the quench-tempering treatment only resulted in higher wear resistance of gray cast iron when compared with untreated specimens, but lower wear resistance than that of austempered gray cast iron under similar macro-hardness. The wear performance of the quench-tempered gray cast iron was enhanced after receiving the laser surface hardening treatment. Finally, the laser hardened and quench-tempered gray cast iron with tempering temperature of 552 °C showed similar mass loss due to wear as austempered gray cast iron with an austempering temperature of 232 °C. By observing the worn surfaces, the laser hardened regions could effectively inhibit the formation and propagation of cracks developed within the substrate regions. In addition, the substrate with low hardness in laser hardened and quench-tempered gray cast iron may provide enhanced ductility and toughness for gray cast iron engineering components. The results obtained in this research have significant value in selecting the optimum heat treatment process for laser hardened gray cast iron components.

The present study mainly investigated the phase transformation and wear performance of laser hardened austempered gray cast iron specimens. Ball-on-Plate reciprocating sliding wear tests with PAO4 base oil were carried out on untreated, quench-tempered, austempered, laser hardened austempered gray cast iron specimens. Micro hardness profiles and worn surfaces were analyzed for specific wear mechanisms. It was found that four different zones were formed beneath the laser hardened surface including laser hardened zone (Ledeburite, ≈67HRC), upper heat affected zone (Martensite, ≈69HRC), lower heat affected zone (Tempered Ausferrite, ≈36HRC) and substrate (Ausferrite, ≈39HRC). In the sliding wear tests, the laser hardened austempered gray cast iron specimens showed higher wear resistance than others, which could be associated with the benefits of ausferritic structure with high fracture toughness and laser hardened regions with high hardness. By observing the worn surface, grooves and micro-sized material removal occurred within the substrate. The surface of the substrate ploughed by the asperities of the ball and hard wear debris stopped on the edge of the laser hardened regions since ledeburite and martensite had high hardness and abrasive wear resistance. However, some micro-cracks and spalls were developed within the laser hardened zone. The results obtained from this study could be used as reference in future research and applications of laser hardened austempered gray cast iron. Keywords: Gray cast iron, Austempering, Laser hardening, Sliding wear resistance

Austempered ductile iron (ADI) is a type of graphite cast iron produced by an isothermal heat treatment process. It is an alternative to traditional steel castings and forgings and even aluminum due to the exceptional mechanical properties such as high strength, good toughness and excellent machinability. In the matrix, the unique ausferritic structure consists of graphite nodules uniformly surrounded by acicular ferrite and carbon saturated austenite. In the automotive industry, ADI has been commonly applied in the manufacturing of camshafts, crankshafts, gears and engine valves. These components are frequently subjected to surface contact with relative motion and external load. Therefore, it is necessary to understand the wear behavior of ADI in order to solve the tribological issues in existing ADI applications and utilize ADI into future designs appropriately. This paper was aimed at reviewing the fabrication processes of single-step and dual-step ADIs. The corresponding microstructure and mechanical properties were also briefly discussed. The studies on wear performance of ADI and potential mechanisms have been systemically reviewed. Keywords: Austempered ductile iron, Single-step austempering, Dual-step austempering, Stress-induced transformation, Wear resistance

The objective of this research was to investigate the bainitic formation in austempered SAE 52100 steel. The original microstructure of SAE 52100 steel consisted of spheroidized pearlite. In the formation of bainite, SAE 52100 steel samples were austenitized at a temperature of 849 °C for 20 min, and then quickly quenched to the isothermal temperatures between 232 °C and 427 °C for various holding times from 20 s to 120 min. The hardness and microstructure of austempered SAE 52100 samples were analyzed using a Rockwell C hardness tester and metallurgical optical microscope. In addition, the bainitic formation in SAE 52100 steel was characterized using the theory of kinetic phase transformation. The activation energies of lower bainite and upper bainite microstructure were found to be 4.72 × 104 J/mol and 6.07 × 104 J/mol with frequency factors of 23.03 (1/s) and 273.65 (1/s), respectively. Keywords: SAE 52100 steel, Austempering, Bainite, Rockwell hardness, Transformation kinetics

Inhibitory effects (IEs) of flavonoids from Rosa roxburghii and R. sterilis fruits against α-glucosidase were investigated. Crude extract of R. roxburghii fruits (RrCE) and R. sterilis fruits (RsCE) were extracted with ethanol. The n-butanol extraction of aqueous RrCE dispersion (RrCE-B) showed the greatest inhibition of α-glucosidase. The most abundant three components in RrCE-B were kaempferol hexose, rutin, and catechin (Cat). The predominant active compounds were characterized as flavonoids by UV–vis spectra. Combination analysis suggested that RrCE was a favorable choice to combine with acarbose (Aca). After simulated gastric digestion, IEs of flavonoids decreased greatly, especially when sodium nitrite was supplemented in the simulated gastric fluid (SGF). The UV–vis spectra indicated that flavonoids were basically stable in the SGF without sodium nitrite, but were oxidized by the HNO2, a natural component in the gastric fluid. The results of this study will help food scientists design special foods for diabetic patients.

At present, the LiDAR ground filtering technology is very mature. There are fewer applications in 3D-object detection due to the limitations of filtering accuracy and efficiency. If the ground can be removed quickly and accurately, the 3D-object detection algorithm can detect objects more accurately and quickly. In order to meet the application requirements of 3D-object detection, inspired by Universal-RANSAC, we analyze the detailed steps of RANSAC and propose a precise and efficient RANSAC-based ground filtering method. The principle of GroupSAC is analyzed, and the sampled points are grouped by attributes to make it easier to sample the correct point. Based on this principle, we devise a method for limiting sampled points that is applicable to point clouds. We describe preemptive RANSAC in detail. Its breadth-first strategy is adopted to obtain the optimal plane without complex iterations. We use the International Society for Photogrammetry and Remote Sensing (ISPRS) datasets and the KITTI dataset for testing. Experiments show that our method has higher filtering accuracy and efficiency compared with the currently widely used methods. We explore the application of ground filtering methods in 3D-object detection, and the experimental results show that our method can improve the object detection accuracy without affecting the efficiency.

Austempered ductile iron (ADI) is produced by an isothermal heat treatment. Tempering is an effective method to increase the toughness and decrease the hardness of ADI. In the present research, the transformation of ADI was investigated after applying various tempering temperatures. The hardness of ADI samples with and without tempering was measured and the microstructure of ADI samples was analyzed by using metallographic optical microscopy. It was found that the ausferrite decomposed into dispersive cementite particles above a tempering temperature of 538 °C. Thus, the tempering process for ADI must be carefully selected so that the excellent properties of ADI are not degraded. Keywords: ADI, Tempering process, Hardness measurement, Phase transformation, Microstructure

The current research studied the effects of laser surface hardening treatment on the phase transformation and wear properties of gray cast irons heat treated by austempering or quench-tempering, respectively. Three austempering temperatures of 232 °C, 288 °C, and 343 °C with a constant holding duration of 120 min and three tempering temperatures of 316 °C, 399 °C, and 482 °C with a constant holding duration of 60 min were utilized to prepare austempered and quench-tempered gray cast iron specimens with equivalent macro-hardness values. A ball-on-flat reciprocating wear test configuration was used to investigate the wear resistance of austempered and quench-tempered gray cast iron specimens before and after applying laser surface-hardening treatment. The phase transformation, hardness, mass loss, and worn surfaces were evaluated. There were four zones in the matrix of the laser-hardened austempered gray cast iron. Zone 1 contained ledeburite without the presence of graphite flakes. Zone 2 contained martensite and had a high hardness, which was greater than 67 HRC. Zone 4 was the substrate containing the acicular ferrite and carbon-saturated austenite with a hardness of 41–27 HRC. In Zone 3, the substrate was tempered by the low thermal radiation. For the laser-hardened quench-tempered gray cast iron specimens, three zones were observed beneath the laser-hardened surface. Zone 1 also contained ledeburite, and Zone 2 was full martensite. Zone 3 was the substrate containing the tempered martensite. The tempered martensite became coarse with increasing tempering temperature due to the decomposition of the as-quenched martensite and precipitation of cementite particles. In the wear tests, the gray cast iron specimens without heat treatment had the highest wear loss. The wear performance was improved by applying quench-tempering heat treatment and further enhanced by applying austempering heat treatment. Austempered gray cast iron specimens had lower mass loss than the quench-tempered gray cast iron specimens, which was attributed to the high fracture toughness of acicular ferrite and stable austenite. After utilizing the laser surface hardening treatment, both austempered and quench-tempered gray cast iron specimens had decreased wear loss due to the high surface protection provided by the ledeburitic and martensitic structures with high hardness. In the worn surfaces, it was found that cracks were the dominant wear mechanism. The results of this work have significant value in the future applications of gray cast iron engineering components and provide valuable references for future studies on laser-hardened gray cast iron.

Research was carried out to develop a mathematical model based on the cutting tool surface profile geometry to predict surface roughness in face milling. Previous models were derived using either the simple assumption of a perfectly round tool nose or statistical analysis based on a large number of experiments. In this research, three milling cases were defined based on the magnitude of the feed rate using a triangular insert with a round corner. In case 1, the machine marks only consisted of a series of arcs. In case 2, the machine marks included a series of an arc and one straight line. In case 3, the machine marks consisted of a series of an arc and two straight lines. Three different equations for surface roughness prediction were obtained based on each of the three cases. Experiments were done to validate the models, and the results showed that the mathematical models had good correlation with experimental results.