Effect of milling type on the microstructural and mechanical properties of W-Ni-ZrC-Y2O3 composites

This study reports the effect of milling type on the microstructural, physical and mechanical properties of the W-Ni-ZrC-Y₂O₃ composites. Powder blends having the composition of W-1 wt% Ni-2 wt% ZrC-1 wt% Y₂O₃ were milled at room temperature for 12 h using a Spex™ 8000D Mixer/Mill or cryomilled in the presence of externally circulated liquid nitrogen for 10 min using a Spex™ 6870 Freezer/Mill or sequentially milled at room temperature and cryogenic condition. Then, powders were compacted in a hydraulic press under a uniaxial pressure of 400 MPa and green bodies were sintered at 1400 °C for 1 h under Ar/H₂ atmosphere. Phase and microstructural characterization of the milled powders and sintered samples were performed using X-ray diffractometer (XRD), TOPAS software, scanning electron microscope/energy dispersive spectrometer (SEM/EDS), X-ray fluorescence (XRF) spectrometer and particle size analyzer (PSA). Archimedes density and Vickers microhardness measurements, and sliding wear tests were also conducted on the sintered samples. The results showed that sequential milling enables the lowest average particle size (214.90 nm) and it is effective in inhibiting W grain coarsening during sintering. The cryomilled and sintered composite yielded a lower hardness value (5.80±0.23 GPa) and higher wear volume loss value (149.42 µm³) than that of the sintered sample after room temperature milling (6.66±0.39 GPa; 102.50 µm³). However, the sequentially milled and sintered sample had the highest relative density and microhardness values of 95.09% and 7.16±0.59 GPa and the lowest wear volume loss value of 66.0 µm³.     

Effect of Ge on microstructure and mechanical properties of Ti3SiC2/Al2O3 composites

Owing to the good physicochemical compatibility and complementary mechanical properties of Ti₃SiC₂ and Al₂O₃, Ti₃SiC₂/Al₂O₃ composites are considered as ideal structural materials. However, TiC and TiSi₂ typically coexist during the synthesis of Ti₃SiC₂/Al₂O₃ composites through an in-situ reaction, which adversely affects the mechanical properties of the resulting composites. In this study, Ti₃SiC₂/Al₂O₃ composites were prepared via in-situ hot pressing sintering at 1450 °C. Ge, which was used as a sintering aid, improved the purity and mechanical properties of the Ti₃SiC₂/Al₂O₃ composites. This is because Ge replaced some of the Si atoms to compensate the evaporation loss of Si to form Ti₃(Si_1-xGe_x)C₂, which showed a crystal structure similar to that of Ti₃SiC₂. Furthermore, the molten Ge accelerated the diffusion reaction of the raw materials, increasing the overall density of the Ti₃SiC₂/Al₂O₃ composites. The optimum Ge amount for improving the mechanical properties of the composites was found to be 0.3 mol. The flexural strength, fracture toughness, and microhardness of the composite with the optimum Ge amount were 640.2 MPa, 6.57 MPa m^1/2, and 16.21 GPa, respectively. The formation of Ti₃(Si_1-xGe_x)C₂ was confirmed by carrying out X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy analyses. A model crystal structure of Ti₃(Si_1-xGe_x)C₂ doped with 0.3 mol Ge was established by calculating the solid solubility of Ge.     

Preparation and mechanical properties of SiCw-Al2O3-YAG ceramic composite by hot oscillatory pressing

SiC_w-Al₂O₃-YAG ceramic composites were prepared by hot oscillatory pressing (HOP) and traditional hot pressing (HP). The results showed that compared with static pressure, the oscillatory pressure could effectively promote densi?cation and mechanical properties of the composites. The sample prepared by HOP exhibited higher hardness (15.72 ± 0.20 GPa) and fracture toughness (7.13 ± 0.19 MPa m^1/2). The current work suggests that HOP could be an effective technique for the preparation of whisker reinforced ceramic composites.     

Sintering,microstructure, and mechanical properties of vitrified bond diamond composite

The demand for high-performance grinding wheels is gradually increasing due to rapid industrial development. Vitrified bond diamond composite is a versatile material for grinding wheels used in the backside grinding step of Si wafer production. However, the properties of the vitrified bond diamond composite are controlled by the characteristics of the diamond particles, the vitrified bond, and pores and are very complicated. The main objective of this study was to investigate the effects of SiO₂–Na₂O–B₂O₃–Al₂O₃–Li₂O–K₂O–CaO–MgO–ZrO₂–TiO₂–Bi₂O₃ glass powder on the sintering, microstructure, and mechanical properties of the vitrified bond diamond composite. The elemental distributions of the composite were analyzed using electron probe micro-analysis (EPMA) to clarify the diffusion behaviors of various elements during sintering.The results showed that the relative density and transverse rupture strength of the composite sintered at 620 °C were 91.7% and 126 MPa, respectively. After sintering at 680 °C, the glass powder used in this study exhibited a superior forming ability without an additional pore foaming agent. The relative density and transverse rupture strength of the composite decreased to 48.2% and 49 MPa, respectively. Moreover, the low sintering temperature of this glass powder protected the diamond particles from graphitization during sintering, as determined by X-ray diffraction and Raman spectrum. Furthermore, the EPMA results indicate that Na diffused and segregated at the interface between the diamond particles and vitrified bond, contributing to the improved bonding. The diamond particles can remain effectively bonded by the vitrified bond even after fracture.     

Improvement of wetability,sinterability, mechanical and electrical properties of Al2O3-Ni nanocomposites prepared by mechanical alloying

The wetability improvement and particle size reduction of alumina/Ni composites through mechanical alloying were addressed. Their effect on the sinterability (at high temperature), mechanical and electrical properties were studied. Al₂O₃ matrix nanocomposites reinforced with different volume fractions of Ni up to 10 vol% were prepared by mechanical alloying. The milled powders were cold pressed and sintered at different firing temperatures up to 1600 °C. The morphology of powders and the microstructure of sintered bodies were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), respectively. Furthermore, relative density, apparent porosity, mechanical properties and electrical resistivity of the sintered composites were investigated. The results revealed that Al₂O₃ matrix was successfully coated with Ni thin film through mechanical alloying; the thickness of coat was increased with increasing the Ni content. Moreover, the increasing of both Ni content and sintering temperature up 1600 °C, led to a remarkable increase in the relative density and facture toughness of the sintered specimen. On the other hand, microhardness and elastic modulus were decreased with increasing of Ni content, while they increased significantly with the increase of sintering temperature. The electrical resistivity was decreased with increasing Ni content and sintering temperature.     

Pressureless sintering and mechanical properties of 3Y-TZP-reinforced LZAS glass-ceramic composites

LZAS glass-ceramic composites toughened by 5, 10, 15 and 20 vol% 3-mol%-Y₂O₃-tetragonal-ZrO₂-polycrystal (3Y-TZP) were prepared via pressureless sintering. Sinterability of composites was investigated in the temperature range of 520–720 °C using soaking time of 30 min. The sintered specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. The results revealed that during sintering 3Y-TZP particles agglomerated between the glass powders and were not dissolved by glass-matrix. Mechanical properties of the sintered samples such as bending strength, Vickers micro-hardness and fracture toughness were also investigated. Measurements showed that the relative density of the samples decreased with increasing 3Y-TZP content. The composite containing 15 vol% 3Y-TZP has a best mechanical properties and it would be the optimum composition. It can be confirmed that crack deflection and transformation toughening are the dominant mechanisms for improving mechanical properties of the composites.     

Effect of high SWNT content on the room temperature mechanical properties of fully dense 3YTZP/SWNT composites

This paper is devoted to correlate the microstructure and room temperature mechanical properties of single-wall carbon nanotube (SWNT) reinforced 3 mol% yttria stabilized tetragonal zirconia with high SWNT content (2.5, 5 and 10 vol%). Fully dense composites were prepared by using a combination of aqueous colloidal powder processing and Spark Plasma Sintering. SWNTs were located at the ceramic grain boundaries and they were not damaged during the sintering process. The weak interfacial bonding between SWNTs and ceramic grains together with the detachment of SWNTs within thick bundles have been pointed out as responsible for the decrease of hardness and fracture toughness of the composites in comparison with the monolithic 3YTZP ceramic.     

Influence of whisker-aspect-ratio on densification,microstructure and mechanical properties of Al2O3 whiskers-reinforced CeO2-stabilized ZrO2 composites

A novel composite of 12 mol% CeO₂-stablized tetragonal ZrO₂ reinforced with Al₂O₃ whiskers (designated as Ce-TZP/A_w) has been prepared and studied in this work. The objective of this investigation was to systematically study the influence of whisker-aspect-ratio on the densification behaviors, microstructure evolution, and mechanical properties of Ce-TZP/A_w composite. Results showed that the sintered density of composite increased and the grain growth tended to diminish with the decrease in whisker aspect radio. Both the fracture toughness and flexural strength reached maximum values of 475 ± 12 MPa and 11.4 ± 0.2 MPa m^1/2, respectively at a whisker aspect ratio of about 12. It was also observed that the fracture toughness, flexural strength and tetragonal to monoclinic ZrO₂ transformation of the dual-phase composite exhibited similar variation trend as a function of the whisker-aspect-ratio, which suggested that the stress-induced phase transformation should be the main toughening and strengthening mechanism in the Ce-TZP/A_w composite.     

Effects of mechanically alloying Al2O3 and Y2O3 additives on the liquid phase sintering behavior and properties of SiC

In order to improve the sintering of SiC, mixtures of Al₂O₃ and Y₂O₃ powders are commonly included as sintering additives. The aim of this work was to use mechanically alloyed Al₂O₃–Y₂O₃ mixtures as sintering additives to promote liquid phase sintering of SiC using spark plasma sintering. The results showed that milling reduced the particle size of the powders and led to the formation of complex oxide phases (YAP, YAM, and YAG) at low temperatures. As the ball milling time increased, the mass loss of specimens sintered with mechanically alloyed Al₂O₃–Y₂O₃ mixtures decreased, and accordingly the relative density increased. However, the hardness and flexural strength of sintered SiC specimens first increased and then decreased. Because the specimens prepared with oxides milled for a long time contained too much YAG/YAP and accordingly too much liquid at sintering temperature. This negatively affected the mechanical properties of the SiC specimens because of the increased volume of the complex oxide phases, which have inferior mechanical properties to SiC, in the sintered specimens. When the ball milling time was 6 h, the hardness (24.02 GPa) and flexural strength (655.61 MPa) of the SiC specimens reached maximum values.     

Effect of Y2O3-stabilized ZrO2 whiskers on the microstructure,mechanical and wear resistance properties of Al2O3 based ceramic composites

The aim of this study was to improve the mechanical properties of Al₂O₃ ceramics by the addition of Y₂O₃-stabilized ZrO₂ whiskers (designated as Al₂O₃/YSZ_W composite) through the flux method and hot-pressing technology. The effect of YSZ_W content on their microstructure, phase composition and transformability, mechanical properties, and wear resistance was systematically investigated. The Al₂O₃/YSZ_W composites containing 10 wt% YSZ_W exhibited the best mechanical performance, including the highest content of YSZ_W tetragonal phase and transformability as well as the largest values in their relative density (99.5%), hardness (1969 HV), fracture toughness (9.57 MPa m^1/2) and flexural strength (855 MPa). The strengthening and toughening of the Al₂O₃/YSZ_W composites were attributed to the YSZ_W tetragonal-monoclinic phase transformation as well as the whiskers reinforcing effect. Furthermore, the Al₂O₃/YSZ_W composites also showed the highest friction and wearing properties.     

Improved dielectric properties of Ba0.5Sr0.5TiO3–ZnAl2O4 composite ceramics using double sintering

Ba_0.5Sr_0.5TiO₃–ZnAl₂O₄ composite ceramics were prepared by double sintering and conventional sintering. The results show that the double sintering can effectively reduce the ion diffusion between Ba_0.5Sr_0.5TiO₃ and ZnAl₂O₄ phases. The double sintered samples exhibit higher density and more uniform grain size distribution than the conventional sintered samples. The dielectric permittivity of double sintered samples is lower than that of conventional sintered samples. Impedance spectrum analysis shows that the oxygen vacancy content and grain boundary resistance of the double sintered samples is lower than that of the conventional sintered samples, which indicates that the Q value of the double sintered samples is higher than that of the conventional sintered samples. The optimum dielectric tunability and Q value of double sintered 60 wt%Ba_0.5Sr_0.5TiO₃-40 wt%ZnAl₂O₄ sample are 23.4% at 30 kV/cm and 276 at 2.257 GHz, respectively. Therefore, double sintering is a strategy that can effectively adjust the dielectric tunability and Q value of BST-ZA composite ceramics.     

Microstructure and mechanical properties of plasma sprayed TiC/Ti5Si3/Ti3SiC2 composite coatings with Al additions

The mass production of MAX phase coatings such as Ti₃SiC₂ and Ti₃AlC₂ using the plasma spraying method is highly challenging due to its ultra-high temperature and short reaction time. In this study, agglomerate powders of 3Ti/SiC/C/xAl with various Al contents (x = 0–1.5) were prepared to form TiC/Ti₅Si₃/Ti₃SiC₂ composite coatings using the plasma spraying technique. The effect of the Al addition on the microstructures and mechanical performances of the as-sprayed coatings was investigated. The addition of Al decreased the TiC content of the coatings while increasing their Ti₃SiC₂ content significantly. The addition of even small amounts of Al improved the MAX phase fraction of the coatings from 8.95 wt% (x = 0) to 34.05 wt% (x = 0.2) and 41.60 wt% (x = 0.5). Excess Al did not affect the Ti₃SiC₂ content of the coatings. The composite coatings showed a lamellar structure with pores and microcracks. With the addition of Al, the microhardness of the coatings increased slightly, while the fracture toughness improved significantly. The composite coatings with Al showed better wear resistance than those without Al. The wear mechanism of the coatings was a combination of adhesive wear, abrasive wear, and oxidative wear.     

Effects of ZrC content and mechanical alloying on the microstructural and mechanical properties of hypoeutectic Al-7 wt.% Si composites prepared by spark plasma sintering

This paper reports on the preparation of ZrC particulate-reinforced Al-7 wt.% Si composites by using a consecutive method of mechanical alloying (MA) and spark plasma sintering (SPS). Al, Si (7 wt.%), and ZrC (0, 2, 5, and 10 wt.%) powders were blended and mechanically alloyed (MA'd) for 4 h in a high-energy vibratory ball mill. Subsequently, SPS (at 450 °C for 210 s) was carried out on non-MA'd and MA'd powders. Dissimilar to the inhomogeneous microstructure of the non-MA'd powders, the 4 h MA'd powders exhibited a homogeneous morphology with semi-equiaxed particles that revealed a lower average crystallite size and higher average lattice strain. Furthermore, microstructural, physical, and mechanical characterizations were performed on the spark plasma sintered (SPS'd) composites. The mechanical characterizations showed that MA'd/SPS'd Al-7 wt.% Si-5 wt.% ZrC composite displayed the highest hardness and strength values among all the fabricated composites. It exhibited a hardness of 1.52 ± 0.16 GPa, yield strength of 327.56 ± 7.16 MPa, and compressive strength of 406.42 ± 2.82 MPa. Besides, the MA'd/SPS'd Al-7 wt.% Si-10 wt.% ZrC composite exhibited the lowest wear rate of 0.0022 mm³/N.m, which was approximately 46% of that of the unreinforced composite (0.0048 mm³/N.m). It can be stated that the addition of ZrC and application of MA effectively improved the microstructural and mechanical properties of the composites.     

Al2O3-AlON复合材料的烧结性能和显微结构

研究了在保护气氛下1600℃烧成的Al2O3-AlON复合材料的烧结性能、物相组成和显微结构.结果表明在刚玉材料中加入AlON,烧结性能得到改善,物相组成主要为刚玉和尖晶石型构造的氧氮化铝,两者之间形成紧密结合结构,并有少量MgAlON微晶填充在大颗粒间的孔隙中,形成致密结构.     

Optimized mechanical properties and oxidation resistance of low carbon Al2O3-C refractories through Ti3AlC2 addition

The mechanical properties and oxidation resistance of the Al₂O₃-C refractories are of critical importance for iron and steel making processes. However, the evaporation of antioxidants related phases such as Al(g), Si(g), and SiO(g) would deteriorate these properties, especially during high-temperature treatment/application. Therefore, in the present work, a small amount of Ti₃AlC₂ compared with Al was introduced to overcome these problems. The phase compositions, microstructures, mechanical properties, and oxidation resistance of Ti₃AlC₂ containing refractories were investigated. The partial oxidation of Ti₃AlC₂ led to inherited lamellar structures such as Ti₃Al_1-xC₂, TiC, and granular Al₂TiO₅ phases. The controlled oxidation of Ti₃AlC₂ and its volume expansion contributed to the compact-structure, thereby limiting the escape of Si and SiO vapors at high temperatures. Consequently, the mechanical properties and oxidation resistance of Ti₃AlC₂ containing Al₂O₃-C refractories treated at 1600 ℃ were improved.     

Effects of nano-ZrO2 content on microstructure and mechanical properties of GNPs/nano-ZrO2 reinforced Al2O3/Ti(C,N) composite ceramics

Dense Al₂O₃/Ti(C,N) composite ceramics reinforced with GNPs/nano-ZrO₂ were fabricated by hot-press sintering. The effects of nano-ZrO₂ content on the microstructure and mechanical properties of the prepared Al₂O₃/Ti(C,N)/GNPs/ZrO₂ composites were investigated. Results showed that nano-ZrO₂ inclusions refined the matrix grains significantly and resulted in the formation of intra-granular structure. Excellent comprehensive mechanical properties were achieved via addition of combined GNPs and nano-ZrO₂. In particular, the fracture toughness of composites incorporating GNPs (0.4 wt%)/ZrO₂ (1 wt%) exceeded 11 MPa m^1/2, which was increased by more than 86 % compared with that of Al₂O₃/Ti(C,N) ceramic composites without GNPs/ZrO₂. The main toughening mechanisms have been identified as stress-induced phase transformation, crack bridging, deflection and pull-out of GNPs. The toughening effects originated from GNPs were enhanced with the introduction of nano-ZrO₂ because of not only the residual stress resulted from phase transformation but also the formation of intra-granular structure with uneven surface around GNPs.     

Effect of sintering conditions on optical and mechanical properties of MgAl2O4/Al2O3 laminated transparent composite fabricated by spark-plasma-sintering (SPS) processing

To realize a high hardness in transparent MgAl₂O₄, the MgAl₂O₄/Al₂O₃ laminated composite was fabricated by a one-step spark-plasma-sintering (SPS) method. By sintering at a temperature of 1225 °C for 10 min and at a heating rate of ≤ 10 °C/min under a pressure of 300 MPa, the MgAl₂O₄/Al₂O₃ laminated composites can attain a high hardness with maintaining the wide band transparency. The in-line and IR transmission were ～50 % at the visible wavelength of 500 nm and >77 % at the wavelength of 4 μm, respectively. The Vickers hardness measured on the surface of the Al₂O₃ layer perpendicular to the MgAl₂O₄/Al₂O₃ stacking exhibited 29 GPa, which is higher than those of the monolithic Al₂O₃ (26.6 GPa) and MgAl₂O₄ (17.2 GPa). The wide band transparency and mechanical properties can be realized by simultaneously attaining smaller grain sizes and higher densities of both the MgAl₂O₄ and Al₂O₃ phases in the laminated composite by optimizing the SPS conditions.     

Comparison of sintering behavior and reinforcing mechanisms between 3Y-TZP/Al2O3(w) and 12Ce-TZP/Al2O3(w) composites: Combined effects of lanthanide stabilizer and Al2O3 whisker length

The densification behavior, microstructural development, toughening and strengthening mechanisms of Al₂O₃ whisker-reinforced 3Y-TZP and 12Ce-TZP composites were systematically and comparatively investigated with varying whisker lengths. Compared with 3Y-TZP/A_w composites, the presence of a Ce-Al-Si-O amorphous phase, caused by the addition of Al₂O₃ whiskers, promoted the densification and grain growth of 12Ce-TZP/A_w composites. Crack deflection and bridging are proposed as the primary toughening mechanisms for 3Y-TZP/A_w composites, while the t-m martensitic transformation would dominate the toughening and strengthening processes of 12Ce-TZP/A_w composites. Changes in Al₂O₃ whisker length would vary the distributions of internal stress and amorphous phase within the ceria-stabilized ZrO₂ matrix, and hence affect the toughening and strengthening results. It indicates that effective toughening and strengthening of the Al₂O₃ whisker-reinforced TZP composites can be achieved by taking advantage of collaborative engineering control on the reinforcement morphology and the interface chemistry/structure.     

Microstructure of the directionally solidified ternary eutectic ceramic Al2O3/MgAl2O4/ZrO2

The directionally solidified Al₂O₃/MgAl₂O₄/ZrO₂ ternary eutectic ceramic was prepared via induction heating zone melting. Smooth Al₂O₃/MgAl₂O₄/ZrO₂ eutectic ceramic rods with diameters of 10 mm were successfully obtained. The results demonstrate that the eutectic rods consist of Al₂O₃, MgAl₂O₄ and ZrO₂ phases. In the eutectic microstructure, the MgAl₂O₄ and Al₂O₃ phases form the matrix, the ZrO₂ phase with a fibre or shuttle shape is embedded in the matrix, and a quasi-regular eutectic microstructure formed, presenting a typical in situ composite pattern. During the eutectic growth, the ZrO₂ phase grew on non-faceted phases ahead of the matrix growing on the faceted phase. The hardness and fracture toughness of the eutectic ceramics reached 12 GPa and 6.1 MPa·m ^1/2, respectively, i.e., two times and 1.7 times the values of the pre-sintered ceramic, respectively. In addition, the ZrO₂ phase in the matrix reinforced the matrix, acting as crystal whiskers to reinforce the sintered ceramic.     

Microstructure and mechanical properties of CaAl12O19 reinforced Al2O3-Cr2O3 composites

Al₂O₃-Cr₂O₃ refractories have excellent slag corrosion resistance and can adapt to the oxidation/reduction atmosphere in the smelting reduction ironmaking furnace. However, Al₂O₃-Cr₂O₃ refractories have poor mechanical properties and sintering properties. In order to improve the mechanical properties of Al₂O₃-Cr₂O₃ materials, the CaAl₁₂O₁₉ reinforced Al₂O₃-Cr₂O₃ composites were prepared by pressureless sintering process, and the influences of CaO content on the sintering properties, mechanical properties, and microstructure evolution of the composites were studied. The results show that a small amount of CaO can significantly improve the compactness of the composites, which is mainly due to the formed sheet-like CA6 fill the gap between the solid solutions, and reduces the porosity of the composites. In addition, the sheet-like CA6 makes the connection between solid solutions closer, and the intergranular fracture gradually transforms into a mixed mode of intergranular and transgranular fracture. The best mechanical propertie is observed at S4 with the CaO content of 2 wt.%. Compared with sample S0 without CaO, the hardness, compressive strength and flexural strength of the S4 were increased by 35.19 %, 49.69 %, and 68.34 %, respectively. The addition of excessive CaO will deteriorate the mechanical properties of the composites, because the formation of a large number of layered CA6 increases the porosity of the composites. Furthermore, a small amount of CaO addition can significantly improve the thermal shock resistance of the composites. After 10 and 20 thermal shock cycles, the strength loss rates of S4 are only 5.83 % and 8.74 %, respectively.