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Scanning strategy is a critical parameter for selective laser melting (SLM) processing of metals, alloys as well as metal-ceramic composites, while related research has rarely been reported yet, especially for additive manufacturing of WC–Co cemented carbides. In this study, three scanning strategies, i.e., stripe, checkerboard, and spiral scanning, were used for additive manufacturing of WC-32Co cemented carbides. Checkerboard scanning leads to the highest relative density of 96%. Stripe scanning results in the largest average WC grain size followed by checkerboard and spiral scanning. SLM-processed carbides demonstrate agglomeration of WC grains mixed with isolated Co pools and pores. The WC grain growth mechanisms of SLM-processed cemented carbides include mosaic agglomeration growth and incomplete and uneven step growth regardless of scanning strategies.

WC–Co cemented carbides, well-known as the conventional tooling materials, have not been successfully produced by one step additive manufacturing processes such as selective laser melting (SLM) yet. The microstructure evolution as well as WC grain growth behavior has rarely been investigated in detail during SLM process. In this study, the WC–Co cemented carbides with different Co contents (12–32 wt%) were prepared by optimized SLM processes for comparative investigation of densification behavior, microstructure characterization and mechanical property. The increase in Co content in feedstock carbide granules can improve the densification behavior during SLM process. The SLM processed WC-12Co shows larger average WC grain size and higher percentage of coarser WC grains as compared with both WC-20Co and WC-32Co. The microstructure characterization, combined with finite element simulation, shows the WC grain growth mechanisms include agglomeration and dissolution-deposition of WC during SLM process and agglomeration of WC is an important mechanism especially for WC–Co cemented carbides with Co content as low as 12 wt%. The comparison between horizontal (perpendicular to the SLM laser beam) and vertical (parallel to the SLM laser beam) cross sections of carbides shows that SLM process introduces a certain degree of microstructure and mechanical behavior anisotropy for WC-12Co, WC-20Co, and WC-32Co.

In this study, the chemical precipitation coating (CP) process was creatively integrated with DLP-stereolithography based 3D printing for refining and homogenizing the microstructure of 3D printed Al2O3ceramic. Based on this novel approach, Al2O3powder was coated with a homogeneous layer of amorphous Y2O3, with the coated Al2O3powder found to make the microstructure of 3D printed Al2O3ceramic more uniform and refined, as compared with the conventional mechanical mixing (MM) of Al2O3and Y2O3powders. The grain size of Al2O3in Sample CP is 64.44% and 51.43% lower than those in the monolithic Al2O3ceramic and Sample MM, respectively. Sample CP has the highest flexural strength of 455.37±32.17 MPa, which is 14.85% and 25.45% higher than those of Samples MM and AL, respectively; also Sample CP has the highest Weibull modulus of 16.88 among the three kinds of samples. Moreover, the fine grained Sample CP has a close thermal conductivity to the coarse grained Sample MM because of the changes in morphology of Y3Al5O12phase from semi-connected (Sample MM) to isolated (Sample CP). Finally, specially designed fin-type Al2O3ceramic heat sinks were successfully fabricated via the novel integrated process, which has been proven to be an effective method for fabricating complex-shaped Al2O3ceramic components with enhanced flexural strength and reliability.

In this study, a ball-milling method was successfully used to coat yttrium nitrate on the surface of aluminum nitride (AlN) powder and the effects of yttrium nitrate content on the AlN powder particle size, viscosity and curing behavior of the AlN suspension, and performance and microstructure of the sintered AlN bodies were investigated. The results indicated that the AlN powder surface coating significantly reduced the viscosity of the suspension and enhanced the cure depth while increasing the powder particle size, which in turn reduced the stability of the suspension. By studying the performance of sintered bodies, it was found that as the yttrium nitrate content increased, the AlN thermal conductivity and flexural strength initially increased and then decreased. Microstructural analysis results revealed that the second phase in samples with 9.23 and 14.49 wt% yttrium nitrate exhibited an island-like distribution, whereas in samples with 19.18 wt% yttrium nitrate, the second phase exhibited a continuous distribution. Finally, the heat-dissipation performance of AlN components with different structures was also studied, and testing was conducted on the driving chip of a 3D printing device. The results indicated that complex-structured AlN ceramic components exhibited an excellent heat-dissipation performance.

Additive manufacturing (AM) has become a versatile and diverse technology that has a significant impact on manufacturing processes. Therefore, ceramic materials have been developed rapidly for use in AM processes. Vat photopolymerization (VPP) is an AM method that enables the production of dense ceramic components with increased dimensional accuracy. In particular, it facilitates the fabrication of small and intricately shaped parts. This review summarizes the research advancements in ceramics prepared via VPP. Special attention is paid to the current status of relevant areas, such as slurry preparation and process optimization, as well as the forming mechanisms, debinding, sintering, performance characterization, and use of VPP-based ceramics. Moreover, earlier studies performed by our research group on numerous VPP-based ceramic aspects are considered. In addition, a concise overview of the differences in forming principles, mechanical performance, advantages, and disadvantages between VPP-based ceramics and conventional colloidal-forming ceramics is presented. Finally, the challenges and prospects of VPP-based ceramics are discussed.

The digital light processing (DLP)-based vat photopolymerization enables the fabrication of intricate silicon nitride (Si3N4) components. However, challenges still persist in producing low-defect and high-performance ceramic parts at lower volume fractions. In this study, a new block copolymer was employed for the modification of Si3N4powders. The rheological behavior, dispersant mechanism, curing properties, printing performance of green body, mechanical properties and Weibull modulus of the sintered sample were systematically investigated. The results indicated that the modifier characterized by the long molecular chains and C=C double bonds adhered successfully to the surface of Si3N4particles through hydrogen bonding, and the viscosity reduction effect of this modifier was ten times lower than that of the reported KH560 modifier. Besides, the synergistic dispersion effect achieved via the combination of the long chain modifier with a small molecular dispersant, facilitates the preparation of a 60 vol.% (80.74wt.%) Si3N4slurry. Subsequently, the tightly bonded interlayer of the green body and the complex Si3N4sintered components with different volume fractions, high consistency and superb mechanical performance (the strength of 865.87 ± 54.35MPa and the Weibull modulus of 18.49) were fabricated. These findings highlight the promising potential of the proposed modification approach for advancing the fabrication of high volume fraction and high-performance Si3N4components.

Nitrous oxide (N2O) contributes up to 8% of global greenhouse gas emissions, with approximately 70% from terrestrial sources; over one-third of this terrestrial emission has been linked to increased agricultural fertilizer use. Much of the nitrogen in fertilizers is converted to N2O by microbial processes in soil. However, the potential mechanism of biofertilizers and the role of microbial communities in mitigating soil N2O emissions are not fully understood. Here, we used a greenhouse-based pot experiment with tea plantation soil to investigate the effect of Trichoderma viridebiofertilizer on N2O emission. The addition of biofertilizer reduced N2O emissions from fertilized soil by 67.6%. Quantitative PCR (qPCR) analysis of key functional genes involved in N2O generation and reduction (amoA, nirK, nirS, and nosZ) showed an increased abundance of nirSand nosZ genes linked to the pronounced reduction in N2O emissions. High-throughput sequencing of nosZ showed enhanced relative abundance of nosZ-harboring denitrifiers in the T. viridebiofertilizer treatments, thus linking greater N2O reduction capacity to the reduced emissions. Our findings showed that biofertilizers can affect the microbial nitrogen transformation process and reduce N2O emissions from agroecosystems.

Treating activated sludge with free nitrous acid (FNA) to selectively eliminate nitrite-oxidizing bacteria (NOB) and retain ammonium-oxidizing bacteria (AOB) is increasingly regarded as a promising technology for achieving partial nitrification. This study provided a comprehensive assessment of this technology based on optimal FNA treatment conditions, functional microbial community response, and resistibility of established partial nitrification to high dissolved oxygen (DO) concentration and low temperature. An FNA concentration of 1.2 mg HNO2-N per L and an exposure time of 18 hours were found to be the most effective conditions to simultaneously inactivate NOB completely and maintain an AOB activity of 56.76%. Under these conditions, no damaging side effects on the functional microbial community were observed except for the NOB groups being substantially reduced. The results of inoculating two 10 L SBRs with FNA-treated sludge and operating them under different DO concentrations and temperatures showed that stable partial nitrification could be maintained at a DO concentration as high as 3.0 mg L−1and temperature as low as 5 °C. However, vigorous multiplication of NOB, especially Nitrobacter, caused destruction of the partial nitrification after long-term operation under a DO concentration of 5.0 mg L−1. Although stable partial nitrification was not destroyed by low temperature, the ammonia oxidation rate was impaired.

High refractive index and ultraviolet (UV) absorption of AlN powders make it challenging to use the digital light processing (DLP)-based vat photopolymerization (VPP) technology for fabricating AlN ceramic components with fine precision. In this work, powder coating strategy (PCS) was creatively integrated with DLP-based VPP to optimize the curing behavior and rheological of AlN ceramic suspensions and homogenize the microstructure of sintered AlN ceramics. This novel approach is in favor of the improvement of the rheological and curing characteristics of AlN suspensions. The viscosity of the PCS ceramic suspension at the shear rate of 100 s−1was 57.0% lower than that of the BM suspension. The cure depths and broadening depth at the exposure energy of 120 mJ/cm2for PCS ceramic suspension (with a 45 vol% solid loading) were 41.6% and 25.8% higher than those of the BM ceramic suspension, respectively, illustrating that the PCS is beneficial to enhance the 3D printing speed and accuracy of AlN ceramics. Moreover, the microstructure uniformity of the 3D-printed AlN ceramic can be improved by the novel approach as compared with the conventional ball-milled (BM) method. The thermal conductivity (144.11 W·m−1·K−1) and bending strength (400.07 ± 13.49 MPa) of Sample PCS were 7.44% and 9.72% higher than those of Sample BM, respectively, which was owing to the change in the second phase distribution from semi-connected (Sample BM) to isolated (Sample PCS) location. Finally, the integrated process successfully produced a fin-type AlN ceramic heat sink, demonstrating its effectiveness in manufacturing complex-shaped AlN ceramic components with exceptional thermal conductivity and mechanical properties.

Ceramic components with complex geometry are difficult to fabricate. Layer-based additive manufacturing processes such as ceramic-suspension-based stereolithography (SL) provide a direct way of fabricating ceramic components from computer-aided design (CAD) models. In such an SL process, fine ceramic powders are mixed with liquid photocurable resin into ceramic suspension. The suspension-based slurry is then used in the SL process to fabricate green parts with desired shapes. A sintering process is further required to convert the green parts into dense ceramic components. In this paper, several key challenges of the ceramic-suspension-based SL process are discussed including the recoating and curing ceramic suspension with high solid loading. A novel Mask-Image-Projection-based Stereolithography(MIP-SL) process by integrating ceramic tape-casting and bottom-up projection methods is presented for fabricating dense ceramic components from CAD models. Various approaches to increase the solid loading in green parts are discussed including suspension preparation, image projection, layer recoating and separation. A prototype system based on the presented ceramics fabrication process has been developed. Test cases of different types of ceramics are presented to demonstrate the effectiveness of the presented fabrication method. The post-processing of green parts to convert them into dense ceramic components is also discussed with some sintering results presented.

Improved heat dissipation performance, by way of thermal management, is critical in many engineering applications. In this study, three types of silane coupling agents were used to modify aluminum nitride (AlN) powder for vat photopolymerization. The effect of silane coupling agents on the rheology, stability, and curing behavior were systematically studied. The results showed that, compared with two other types of silane coupling agents, one silane agent (KH570) had a larger positive effect on the rheology and stability of the AlN suspension, and the absorbance of the AlN powder increased after surface modification. In addition, the effects of different solid loadings on the curing behavior and CC double-bond conversion rate were systematically investigated. It was found that a higher solid loading resulted in a lower curing depth, cure width, and CC double-bond conversion rate. For the sintered AlN components with increased solid loading, the shrinkage decreased while both the flexural strength and thermal conductivity increased. In addition, the shrinkage in the Z-direction was higher than that in the X- and Y-directions. Scanning electron microscopy analysis showed that the mean grain size decreased with increasing solid loading. Furthermore, a heat dissipation performance evaluation system was designed to illustrate the heat transmission capacity of AlN ceramics. Simulation and experimental results showed that AIN ceramic parts with complex shapes achieved better heat-dissipation performance than those with simple shapes.