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.     

Effect of YAG content on creep resistance and mechanical properties of Al2O3-YAG composite

Comprehensive study on effect of YAG amount on densification, creep resistance and room-temperature mechanical properties of Al₂O₃-YAG composite pressureless sintered at 1600 °C was conducted. The main goal was to optimize the amount of YAG in order to fabricate a composite with improved creep resistance and sufficiently good room-temperature mechanical properties. The composite was made by mixing a commercially available Al₂O₃ powder with fine YAG powder obtained by glycine-nitrate combustion synthesis starting from aluminum nitrate and yttrium nitrate. Increased driving force for sintering of fine YAG powder allowed fabrication of dense Al₂O₃-YAG composite with up to 30 vol% YAG. The presence of YAG was found to be very effective in improving creep resistance of Al₂O₃-YAG composite. Large Y³⁺ ions blocked diffusion along Al₂O₃ grain boundaries, reduced diffusivity and therefore enhanced creep resistance of Al₂O₃-YAG composite which continuously increased as the YAG amount increased. Тhe presence of YAG was also found to improve mechanical properties such as hardness and elastic modulus. The improvement of these properties was ascribed to increased density of Al₂O₃-YAG composites owing to high sintering activity of YAG powder. While fracture strength of the composite can be as high as that of monolithic Al₂O₃, fracture toughness of composite decreased continuously as the YAG content increased. The decrease was ascribed to transgranular fracture of both YAG and Al₂O₃ grains in samples containing larger amounts of YAG. The proper balance between fracture toughness and creep resistance was found in composite containing 18 vol% YAG which had considerably improved creep resistance accompanied by a relatively small decrease in fracture toughness.     

Evaluation of mechanical properties of a dense SiC/SiCN composite produced via PIP process

The material behavior of Polymer Infiltration and Pyrolysis based SiC/SiCN composites is studied and the characteristic thermal and mechanical properties in on- (0/90 °) and off-axis (±45 °) direction are summarized. The tensile properties are determined at room temperature and 1300 °C. Based on the ratio of Young’s modulus and strength between on- and off-axis loading, a new approach for the classification of Weak Matrix Composites (WMC) and Weak Interface Composites (WIC) is proposed, which seems to be reasonable for various CMCs. Even without fibre coating mechanical behavior of SiC/SiCN is similar to that of WIC. In order to explain this, a microstructure model is developed and confirmed by analysis of fracture surface. The effect of temperature on the tensile properties is investigated through analysis of residual thermal stresses. Even though at 1300 °C the strength is slightly lower, the fracture strain increased significantly from RT to 1300 °C.     

Enhanced mechanical properties in Cf/LAS composite with yolk-shell structure interface

A new approach to improve the interfacial matching of carbon fiber-reinforced lithium-aluminum-silicon(C_f/LAS) composites is proposed, which is achieved by Ni nanoparticles catalyzing the formation of a tunable graphite layer on the surface of C_f. The interfacial structure between the composites can be effectively improved by tuning parameters such as Ni²⁺ content and sintering holding time, and ultimately, the mechanical properties of the composites can be improved. Interestingly, due to the introduction of Ni²⁺, a yolk-shell type graphite layer is formed between the C_f and LAS, and the bridging effect of the graphite layer improves interfacial bonding. The highest flexural strength (515 ± 30 MPa) and fracture toughness (14.7 ± 1.6 MPa·m^1/2) were obtained. Taking C_f/LAS as an example, the relationship between interfacial matching and mechanical properties of composites is systematically investigated and may provide a new idea for the improvement of mechanical properties of fiber-reinforced composites.     

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.     

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.     

Enhanced mechanical properties in ceramic multilayer composites through integrating crystallographic texture and second-phase toughening

Inherent brittleness and low mechanical reliability usually inhibit the application of ceramic materials in many structural applications. In this work, we demonstrate that integrating crystallographic texture and second-phase toughening strategies can effectively improve fracture resistance and mechanical reliability in alumina multilayer composites. Composites consisted of equiaxed (1-x)Al₂O₃-xZrO₂ and highly [0001]-textured Al₂O₃ layers were fabricated, and effects of ZrO₂ amount on fracture behavior and mechanical properties of the composites were studied. Increasing ZrO₂ amount x results in larger thermal expansion difference between equiaxed and textured layers. The composites with equiaxed layers containing 30 vol% ZrO₂ exhibit high apparent fracture toughness K_{apt, c} ~11.7 MPa·m^1/2 and work of fracture γ_WOF ~1540 J/m², which correspond respectively to about 260% and 410% enhancements relative to those without ZrO₂ addition. Moreover, adding ZrO₂ remarkably reduces sensitivity of failure stress to flaw size in the multilayer composites, and the failure stress substantially increases with increasing ZrO₂ content. The greatly enhanced mechanical performance achieved here can be mainly attributed to higher magnitude of compressive stresses, more crack bifurcations and longer crack deflection paths within the textured layers. This work can provide important guidelines for developing novel “bio-inspired” materials with improved fracture resistance and flaw tolerance behavior.     

The microstructural and mechanical properties of geopolymer composites containing glass microfibres

This paper presents the effects of microfibre contents on mechanical properties of fly ash-based geopolymer matrices containing glass microfibres at 0, 1, 2 and 3 mass%. The influence of glass microfibres on the fracture toughness, compressive strength, Young's modulus and hardness of geopolymer composites are reported, as are the microstructural properties investigated using scanning electron microscopy. Results show that the addition of 2 mass% glass microfibres was optimal, exhibiting the highest levels of fracture toughness, compressive strength, Young's modulus and hardness. The results of the microstructural analysis indicate that the glass microfibres act as a filler for voids within the matrix, making a dense geopolymer and improving the microstructure of the binder. This leads to favourable adhesion of the composites, and produces a geopolymer composite with good mechanical properties, comparable to pure geopolymer. The failure mechanisms in glass microfibre-reinforced geopolymer composites are discussed in terms of microstructure.     

Densification and mechanical properties of boron carbide prepared via spark plasma sintering with cubic boron nitride as an additive

Hexagonal boron nitride (h-BN) can reinforce boron carbide (B₄C) ceramics, but homogeneous dispersion of h-BN is difficult to achieve using conventional methods. Herein, B₄C/h-BN composites were manufactured via the transformation of cubic (c-) BN during spark plasma sintering at 1800 °C. The effects of the c-BN content on the microstructure, densification, and mechanical properties of B₄C/h-BN composites were evaluated. In situ synthesized h-BN platelets were homogeneously dispersed in the B₄C matrix and the growth of B₄C grains was effectively suppressed. Moreover, the c-BN to h-BN phase transformation improved the sinterability of B₄C. The sample with 5 vol.% c-BN exhibited excellent integrated mechanical properties (hardness of 30.5 GPa, bending strength of 470 MPa, and fracture toughness of 3.84 MPa⋅ m^1/2). Higher c-BN contents did not significantly affect the bending strength and fracture toughness but clearly decreased the hardness. The main toughening mechanisms were crack deflection, crack bridging, and pulling out of h-BN.     

Assessment of mechanical and micro-structural characterization of novel ambient cured cement-free composite concrete

To minimize the utilization of natural resources & consuming of huge energy and in order to control the global warming, industrial waste based geopolymer has attracted by the researchers. The manufacturing of GGBS-FA based Geopolymer Concrete (GFGPC) are essential due to its cost-effective reuse by recycling the industrial wastes. The impact of various quantities of Ground Granulated Blast-furnace Slag (GGBS), activator concentration, alkaline solution to solid ratios and liquid ratios of silicate to hydroxide of sodium on experimented mechanical strength and microstructural characterization are investigated. The novelty and research significance lie in adoption of ambient curing techniques, reduced time interval between Alkali Activator Solution (AAS) preparation and concrete casting from 24 h to 3–6. It was observed that with decrease of GGBS content from 70% to 30%, compressive strength at 28 days was reduced from 53 MPa to 36 MPa. A mix containing 40–50% GGBS, AAS to binder ratio of 0.45–0.55, 7 M(Molar) solution of Sodium Hydroxide (SH), ratio of sodium silicate (SS) to sodium hydroxide (SH) of 1.5–2.0 along with 3–6 h of time interval between AAS preparation and concrete casting were proposed as an optimum design mix with respect to compressive strength, workability and setting time. The empirical predictions of splitting-tensile strength and flexural strength of developed GFGPC were made based on the experimental laboratory results and made comparisons with respect to the equations of ACI 318, Eurocode 2, AS 3600 and IS 456 for OPC based conventional concrete (CC_OPC) and others existing literature for GPC. Additionally, XRF, XRD, FESEM and EDS were conducted to investigate the microstructural properties and the reaction mechanism of GFGPC.     

Mechanical properties of zirconia composite ceramics

Composite materials based on 8 wt% yttria partially stabilized zirconia, with additions of gadolinium zirconate, lanthanum lithium hexaaluminate, yttrium aluminum garnet and strontium zirconate were characterized. Samples were fabricated by hot-press sintering at 1550 °C. The effect of the secondary phase content on the mechanical properties of the composites was evaluated. Hardness, elastic modulus and fracture toughness of the fabricated composites were determined by means of depth-sensitive indentation testing. The fracture toughness of the samples as determined by the indentation method was found to increase with increasing YSZ content, reaching 3 MPa·m^0.5 for samples with 80 wt% YSZ. The fracture toughness appeared to be affected by thermal expansion coefficient mismatch, crack bridging and crack deflection.     

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.     

Influence of precursor characteristics on properties of porous calcium phosphate-titanium dioxide composite bioceramics

Highly porous (macroporosity 76–90%) bioceramics containing interconnected pores (>100 μm) with compressive strength between 0.54 and 0.32 MPa were prepared by polyurethane foam replica method. Effect of following variables, i.e., calcium phosphate/anatase ratio (30/70, 50/50, 70/30 wt%) in the ceramic slurry, anatase particle size (15 nm, 180 nm), Ca/P molar ratio of calcium phosphate (1.67 and 1.50 for hydroxyapatite and apatitic-tricalcium phosphate (ap-TCP), respectively), on the bioceramics properties was investigated. Bioceramics prepared using anatase and hydroxyapatite consisted of three high-temperature crystalline phases - β-tricalcium phosphate (β-TCP), rutile and CaTiO₃. In case of anatase and ap-TCP, two phases (β-TCP and rutile) were obtained. Interaction of anatase and hydroxyapatite during sintering caused formation of CaTiO₃ at β-TCP and rutile grain boundaries thus contributing to a denser grain packing. Combination of ap-TCP and nanosized anatase facilitated decrease of grain sizes. Correlation was found between compressive strength and calcium phosphate precursor in the ceramic slurry.     

Optimized preparation of alumina based fillers for tuning composite properties

Alumina based particles were prepared from aluminium chloride hydroxide as starting material by sol-gel technique. One series of particles was doped with ferrous oxide. Both series of particles were calcinated at three different temperatures: 700?°C, 800?°C and 900?°C. Poly(methyl methacrylate), PMMA, was used as a matrix and two different types of alumina based particles were added into the matrix to form the composites. All composites consisted of 3?wt% of alumina based particles. The aim of this study was to examine whether and how the temperature of particle calcination affects the microhardness and mechanical properties of the composite. The particles were characterized by the X-ray diffraction (XRD) and physical absorption methods. The morphology of the composites was examined using a field emission scanning electron microscope (FESEM). The microhardness of composites was measured using a traditional Vickers hardness (HV) method. The mechanical characteristics of obtained composites were determined using tensile test and impact testing.     

Preparation and mechanical properties of alumina composites reinforced with nickel-coated graphene

This paper discusses the influence of nickel–phosphorus coated graphene (Gn–Ni–P) and uncoated graphene (Gn) addition to an alumina matrix and its impact on the mechanical properties of obtained composites. The composites are prepared via powder processing and consolidated using the Spark Plasma Sintering (SPS) method. The effects of the addition of coated graphene and coating thickness on mechanical properties were evaluated. Physical properties such as relative density, hardness and fracture toughness were analyzed. Significant improvement of the fracture toughness (60%) for the composites with 2 vol% Gn–Ni–P compared to reference sample was observed. Moreover, 35% higher K_IC was noticed for Gn–Ni–P reinforced composites than for Al₂O₃–Gn.     

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.     

Structure and mechanical properties of in-situ synthesized α-Ti/TiO2/TiC hybrid composites through mechanical milling and spark plasma sintering

The main aim of this study was to apply high-energy longer mechanical milling and spark plasma sintering (SPS) techniques to produce in-situ α-Ti/TiO₂/TiC hybrid composites from commercially pure-Ti (CP–Ti, HCP structure) powders. The CP-Ti powders were subjected to different milling times (0, 20, 40, 60, 80, 100, and 120 h). The results showed that the powder samples milled for 120 h produced Ti, Ti₃O₅, TiO, TiO₂ phases, and dissolved C atoms from the process control agent (toluene) which were then converted to α-Ti, TiO₂, and TiC phases (formed in-situ composites) through spark plasma sintering. This was expected due to more reactivity in the 120 h sample as longer milling introduces severe and robust structural refinements. Structural evaluations with increasing milling time were carried out using XRD, HRSEM, and HRTEM. The synthesized powders were then consolidated by SPS at pressures of 50 MPa and 1323 K for 6 min. The micro-hardness results have shown that the hardness was started to increase from 1.40 GPa to 5.56 GPa with increasing milling time due to more dislocation and pinning effect produced by grain refinement and formed TiO₂/TiC intermetallic particles enhancing the strength of α-Ti matrix. The α-Ti/TiO₂/TiC in-situ hybrid composite bulk sample yielded an ultimate compressive strength of 1.594 GPa.     

Effect of Al2O3 particle size on the microstructure,phase transformation and mechanical properties of hot pressed Al2O3-CA6-ZrO2/Ni multi-phase composites

Al₂O₃-CA6-ZrO₂/Ni multi-phase composites were fabricated by vacuum hot pressing sintering at 1650 °C under the pressure of 30 MPa for 30 min. The microstructural evolution rule of the composites was investigated as a function of Al₂O₃ particle size. Upon increasing the Al₂O₃ particle size to 30 μm, the generated CA6 underwent a transformation from unfixed type to a plate-like pattern and to a combined CA6-Al₂O₃ matrix, whereas the fracture mode of m-ZrO₂ changed from an intergranular fracture to an intergranular and transgranular mixed type due to the improved interface binding energy. Additionally, satisfactory mechanical properties of the composites were achieved when the Al₂O₃ particle size was 30 μm. Under the synergistic effect of different strengthening and reinforcing phases, the inhomogeneous distribution caused by poor wettability between Al₂O₃ and Ni was effectively solved by the distributions of “intercrystalline type” and “intracrystalline type” for the Ni phase. The mechanisms of the microstructural evolution, phase transformation and improved mechanical properties are discussed in detail.     

ZrB_2－刚玉莫来石质复合材料显微结构及力学性能的研究

通过对不同刚玉－莫来石含量的ＺｒＢ２材料力学性能及显微结构的研究，探讨了刚玉莫来石对ＺｒＢ２强度和韧性的影响，同时也分析了强化和韧化机制。