Wear-resistant coatings have been widely used to improve the tribological properties of titanium-based parts, structures, and tools, such as engine blades, tanker trucks, heat exchangers, and ...drilling bits, in the aerospace industries, chemical industries, offshore engineering, and oil and gas engineering. In the view of the applications in the fabrication of wear-resistant coatings on titanium substrates, the laser deposition of ceramic reinforced titanium coatings is widely investigated. Reported investigations show that the (TiB + TiC) reinforced titanium matrix composite coatings with high ceramic content can significantly increase the hardness and wear resistance. However, due to the low compatibility between ceramics and titanium, a high ceramic content always leads to a relatively low bonding quality and the generation of cracks and defects. To fabricate the high ceramic content (TiB + TiC)–Ti coatings, this study investigates the feasibility of adding buffer layers for the first time. The phase compositions, microstructures, element compositions, and mechanical properties of the different layers have been analyzed by XRD, SEM, EDS, and instruments to measure hardness and wear resistance. The deposited gradient coatings are free of fabrication defects with good metallic adhesion with titanium substrates. In the center of the top coating layers, the extremely high-volume content of ceramic reinforcements (including the major component of TiB and TiC and the minor component of TiB2, B25C, and unreacted B4C) leads to high microhardness and excellent wear resistance. These results suggest that adding buffer layers is a feasible method to fabricate high-ceramic content coatings on titanium-based structures and tools.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Background: The research focused on the postoperative effect of using interbody fusion cage in lumbar posterior lamina decompression and interbody fusion with pedicle screw by comparing the ...postoperative effect of using 3D printing (Ti6Al4V) and PEEK material interbody fusion cage. Methods: Ninety-one patients with lumbar degenerative diseases from the Department of Spine Surgery of Tianjin Hospital were included in the study cohort. They were divided into 3D group (n = 39) and PEEK group (n = 52) according to the use of interbody fusion cage. The imaging data of the patients were collected and the postoperative data of the 2 groups were compared to evaluate patients’ health status and the recovery of lumbar structure and function after operation. Results: Combined with the degree of fusion, the clinical effect of 3D printing titanium alloy interbody fusion cage was comprehensively judged. At the last follow-up, the JOA score, ODI index, VAS, prolo function score, and SF-36 scale of the 2 groups showed that the clinical symptoms were better than those before operation ( P < .05). The height of intervertebral disc, the area of intervertebral foramen and the physiological curvature of lumbar vertebrae increased in varying degrees after operation ( P < .05). At the last follow-up, the vertebral cage fusion rates were as high as 89.13% and 90.91% in the 3D and PEEK groups, with collapse rates of 6.5% and 4.5%, respectively. There were 10 cases of cage displacement in 3D group and 7 cases of cage displacement in PEEK group. There was no significant difference between the 2 groups ( P > .05). Conclusions: In conclusion, 3D printed (Ti6Al4V) interbody fusion cage can obtain good clinical effect in the surgical treatment of lumbar degenerative diseases. Posterior lumbar lamina decompression, bilateral pedicle screw fixation combined with 3D printed cage interbody fusion is excellent in rebuilding the stability of lumbar vertebrae. 3D printed interbody fusion cage can be an ideal substitute material for intervertebral bone grafting. The stable fusion time of interbody fusion cage after lumbar fusion is mostly from 3 months to half a year after operation.
Laser directed energy deposition (DED) has been used for fabrication of Nickel-Titanium (NiTi) alloys. The raw material can be pre-alloyed NiTi powders or premixed Ni and Ti powders. Using premixed ...Ni and Ti powders to in-situ synthesize NiTi alloys shows more potential with advantages of cost-effectiveness and flexibility in tailoring the mechanical and phase transformation properties. However, a common problem for in-situ synthesis of NiTi lies in the difficulty in obtaining sufficiently dense parts due to the alloying effects, liquid capillary effects, and the difference in diffusivity between Ni and Ti. The porosity could be greatly affected by the powder morphology. For the first time, this paper reports the in-situ synthesis of high-quality pseudoelastic NiTi alloys using spherical powders in the laser DED process. The comparisons of the NiTi alloys in-situ synthesized using powders with different morphologies are made. The manufacturing defect formation mechanisms with different powder morphologies (spherical and irregular) are firstly discussed. It is found that the NiTi parts in-situ synthesized using spherical powders have comparable density with those fabricated using pre-alloyed powders. Moreover, Ni4Ti3 precipitates are only observed in the NiTi parts in-situ synthesized using spherical powders. The mechanical properties (pseudoelasticity, Young's modulus, and microhardness) are also affected by the powder morphology. The experimental results indicate that high-quality NiTi alloys can be in-situ synthesized with reduced manufacturing defects, the formation of Ni4Ti3 precipitates, and improved pseudoelasticity and microhardness.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nickel-Titanium (NiTi) alloys have the unique shape memory effect and pseudoelasticity, good damping capacity, good corrosion resistance, and excellent biomechanical compatibility. These properties ...make NiTi alloys attractive in industries like automobile, aerospace, medical device, etc. However, it’s difficult to fabricate and machine NiTi alloys due to their rapid work-hardening property and pseudoelasticity. Traditional manufacturing methods, such as casting and powder metallurgy, show disadvantages of high cost, time-consuming, and limitations in fabrication of parts with complex geometry. In order to reduce or solve these problems, laser additive manufacturing (LAM) methods have been applied for the fabrication of NiTi alloys. Among the LAM methods, laser directed energy deposition (DED) in-situ synthesis of NiTi alloys from the premixed Ni and Ti powders shows its unique advantages of cost-effectiveness and flexibility in altering NiTi alloys’ phase transformation and mechanical properties. However, heterogeneous microstructures and the formation of secondary phases are two crucial issues that impede the application of laser DED to in-situ synthesis NiTi alloys. Ultrasonic vibration has pronounced effects on liquid materials solidification processes, which could be utilized in homogenizing the microstructure and reducing the secondary phase of laser DED in-situ synthesized NiTi alloys. This paper, for the first time, reports in-situ synthesis of NiTi alloys by laser DED with ultrasonic vibration assistance. The effects of ultrasonic vibration on microstructure properties (microstructure homogeneity, internal defects, elemental composition, grain size, and phase constituents) and mechanical properties (pseudoelasticity, microhardness, and Young’s modulus) have been investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
CoCrFeNiTi high entropy alloy (HEA) has been extensively studied to serve as coating materials on complexly shaped parts of equipment used in industries such as oil, gas, and mining due to its high ...hardness, excellent wear resistance, and good high-temperature stability. Laser-directed energy deposition has potential to fabricated HEA caotings due to its advantages of excellent metallurgical bonding, high coating density, suppressed element segregation, and the capability of thick coating deposition. However, limited investigations have been conducted on the effects of input parameters (such as powder geometry and laser power) on the mechanical properties of laser DED fabricated CoCrFeNiTi high-entropy alloy coatings. In this study, CoCrFeNiTi HEA coatings have been fabricated on Ti substrates from spherical-shaped and irregular-shaped powders under different levels of laser power. The effects of powder geometry and laser power on molten pool thermal characteristics (including temperature, cooling rate, and solidification time), phase constitution, microstructure, and mechanical properties of hardness and wear resistance have been investigated. Under the same laser power, the utilization of irregular-shaped powders resulted in uniform microstructures and higher hardness. For the coatings fabricated from spherical-shaped powders, the increase of laser power could improve the microhardness and wear resistance. For the coatings fabricated from spherical-shaped powders, the increase of laser power could increase the microhardness. However, the wear resistance is increased and then decreased due to the increase in friction of coefficient.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The outlier data mining research is of great significance to ensure the reliable operation of data mining. However, the models adopted in the international marketing mining data research at present ...make use of only one of the time or spatial correlation mining. Taking the defects of the existing international marketing outlier data mining models and the spatial and temporal correlation of the error matrices into full consideration, a kind of international marketing outlier data mining model that relies on the subdivision market analysis algorithm (hereinafter referred to as SMAA for short) is put forward. In this model, the dimensionality reduction capacity of SMIA and the multi-scale modeling capacity of the subdivision transformation are fully leveraged to construct an international marketing outlier data mining model. In the analysis of the international marketing outlier data, it is mainly achieved through the SMAA. In addition, the sliding window mechanism is effectively used to achieve the online expansion of the international marketing outlier data mining model, and thus the international marketing outlier data mining model dependent on the online subdivision market analysis is obtained. Through the analysis of the international marketing outlier data mining and the simulation results thus obtained, it can be concluded that the international marketing outlier data mining model dependent on the subdivision market analysis has more prominent advantages compared with the BSA model and the detection performance is more superior.
The NiTi alloys have superior damping properties, which mainly originate from the stress-induced martensite phase transformations. The stress-induced martensite phase transformation can be improved ...by the intrinsic Ni4Ti3 precipitation in the NiTi alloys fabricated by laser-directed energy deposition (L-DED), making L-DED a promising method for fabrication of NiTi alloys. Reported investigations on L-DED of NiTi alloys focus on their microstructural features and phase transformation properties. There are no investigations on the damping properties of the NiTi alloys fabricated by L-DED. For the first time, NiTi alloys with excellent damping properties are in-situ synthesized by L-DED, in this paper. The processing parameters are optimized to fabricate NiTi alloys with relatively uniform distributions of small-sized Ni4Ti3 precipitates, which will benefit the damping properties. Dynamic mechanical analysis (DMA) tests were utilized to quantify the damping properties of the NiTi alloys in in two oscillation modes (loading mode and creeping mode) according to the different load conditions in industrial applications. Experimental results show that the damping ratios are in a range of 0.02–0.2, which is comparable or larger than the values of the NiTi alloys fabricated with more complex structures or fabricated using more complex methods. It can be concluded that L-DED can be a promising method to fabricate NiTi alloys without the need for additional post-processing methods. Besides, the correlations between the superior damping properties with the microstructures are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A novel refill friction stir riveting (RFSR) process is proposed for the first time.•Both solid-state bonding and mechanical interlocking are achieved in RFSR joints.•The size of mechanical ...interlock is predefined by the groove on the rivet shank.•The high-quality solid-state bonding is generated at the sheet faying surface.•The joint lap-shear and cross-tension forces are 9.09 kN and 6.82 kN respectively.
In this study, a novel refill friction stir riveting (RFSR) process was proposed to achieve hybrid solid-state bonding and mechanical interlocking of high-strength aluminium alloy AA7075-T6 sheets. The size of mechanical interlock is predefined by the depth of groove designed on the rivet shank, and realized through sheet material refilling. High-quality solid-state bonding is also generated at the sheet faying surface under the high pressure and strong friction stir from the rivet. The quality characteristics, microstructure, heat generation, microhardness distribution and mechanical properties were systematically investigated to uncover the joint formation mechanism and verify the effectiveness of the RFSR process. The results reveal that a mechanical interlock with 82% of the predefined value was successfully achieved by sheet material refilling into the groove on the rivet shank. An extra mechanical interlock, which was formed between the rivet shank and trapped bottom sheet, further enhanced the joint strength. Continuous solid-state bonding with a width of 0.39 mm was also generated between the two sheets. Strengthened by the multiple connection features, the peak lap-shear and cross-tension forces reached up to 9.09 ± 0.24 kN and 6.82 ± 0.11 kN respectively, and the corresponding failure modes were rivet shank fracture and pull-out of rivet shank from the bottom sheet.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This thesis is the first to explain the relationship between comparative advantage and heterogeneous firms' quality choices theoretically and empirically. It investigates how firms' quality varies ...across industries and firms' investment in quality. Chapter 2 examines how comparative advantage can affect firms' quality. It extends a Heckscher-Ohlin model with heterogeneous firms where they are allowed to choose the quality of the product they offer. The theoretical results show that when a trade happens, more productive firms choose to export while serving the domestic market, less productive firms serve the domestic market only and the least productive firms exit the market. Meanwhile, trade liberalisation leads to an increase in product quality for exporters and a decrease in product quality for non-exporters. Furthermore, the model also reveals that exporters in a comparative advantage industry improve their quality by more than those in a comparative disadvantage industry, and non-exporters in a comparative advantage industry lower their quality by more than those in a comparative disadvantage industry. One of the important stylised facts of the literature is that firms that offer higherquality products charge higher prices. However, the framework developed in Chapter 2, featuring increasing returns and monopolistic competition, presents the opposite result. I decided to improve it in Chapter 3 by introducing different intermediate inputs so that the framework reproduces this stylised fact. Simultaneously, it still concludes that exporters in a comparative advantage industry improve their quality more while non-exporters in a comparative advantage industry lower their quality by more. In addition, it also reveals a higher aggregate or average quality in a comparative advantage industry, which can potentially create additional welfare gains from trade. Chapter 4 provides the empirical evidence for one of the main predictions in the theoretical models. It uses detailed Chinese firm-transaction-level data and firmlevel production data and shows that Chinese exporters invest in product quality more in a comparative advantage industry than those in a comparative disadvantage industry conditional on productivity. It also suggests that China's comparative advantage stems from different factor endowments across countries, consistent with the theoretical models analysed in Chapter 2 and 3. In addition, it further explores the heterogeneity of this enhanced effect on export quality across the comparative advantage distribution and destinations and how it varies between firms with different export intensities and within firms for different varieties.
