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.     

Effects of hafnium content on microstructures and properties of newly developed (Ti,Hf)(C,N) ceramics

In this study, novel (Ti,Hf)(C,N) ceramics with varying hafnium contents were fabricated via carbothermal reduction–nitridation and subsequent spark plasma sintering. The influence of Hf addition on the mechanical properties, wear properties, and corrosion resistance of the (Ti,Hf)(C,N) ceramics was systematically studied. The introduction of Hf promoted the sintering densification of the ceramics in the sintering process. The prepared (Ti,Hf)(C,N) ceramics exhibited excellent mechanical and wear properties owing to refinement and solution-strengthening mechanisms. The (Ti_0.9,Hf_0.1)(C_0.5,N_0.5) ceramic demonstrated higher Vickers hardness and fracture toughness, measuring 1997 HV5 and 4.28 MPa m^1/2, respectively, compared to the pure Ti(C_0.5,N_0.5) ceramic which exhibited values of 1635 HV5 and 3.94 MPa MPa m^1/2. The wear scar depth of the (Ti_0.9,Hf_0.1)(C_0.5,N_0.5) ceramic sample was 57.36% to that of the Ti(C_0.5,N_0.5) ceramic. Additionally, the addition of Hf improved the corrosion resistance of (Ti,Hf)(C,N) ceramics in a 0.5 M NaOH solution. The potential applications of (Ti,Hf)(C,N) ceramics include machining tools and wear-resistant parts.     

Effect of preparation conditions on mechanical,dielectric and microwave absorption properties of SiC fiber/mullite matrix composite

Silicon carbide fiber-reinforced mullite matrix (SiC_f/Mu) composites were fabricated via an infiltration and sintering method. Effects of sintering parameters on microstructure, mechanical, dielectric and microwave absorption properties of SiC_f/Mu composites have been investigated. The flexural strength is significantly improved with increasing sintering temperature, and the highest flexural strength of 213?MPa is obtained in vacuum at 1000?°C for 2?h. The performances of composites with different holding time are further studied at 1000?°C. The flexural strengths of composites sintered at 1000?°C for 2 and 4?h reach 213 and 219?MPa, respectively. The failure displacement of the composite sintered at 1000?°C for 4?h reaches 0.39?mm. The excellent microwave absorption properties are achieved for the composite sintered at 1000?°C for 2?h. The minimum reflection loss (RL) reaches ?38?dB with a thickness of 2.9?mm?at 12?GHz and the effective absorbing bandwidth (RL?≤??10?dB) with a thickness of 3.4?mm covers the whole X?band, which indicate that SiC_f/Mu composite is a good candidate for microwave absorbing materials. These results provide valuable solutions to obtaining structural-functional materials for microwave absorption applications in civil and military areas.     

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.     

Effect of composition on phase assemblage,microstructure, mechanical and optical properties of Mg-doped sialon

Mg-doped sialon (Mg_m/2Si_12−m−nAl_m+nO_nN_16−n) ceramics with different compositions of m = 2n = 0.6, 0.84, 1.0, 1.2, 1.6 were hot pressed at 1850 °C for 1 h. Phase assemblage, microstructure, mechanical and optical properties of these samples were investigated. All samples achieved/approached full densification. However, the densification of Mg-doped sialon ceramics with higher MgO/AlN content becomes more difficult. Additionally, the anisotropic growth of β-sialon grains was significantly inhibited. The unique characteristics of Mg-doped sialon ceramics intrinsically derive from the formation of Mg-containing AlN polytypoids, which consumed most of the high-temperature liquid. Furthermore, their high stability at high temperatures accounts for the difficulty in preparing single-phase Mg-α-sialon., The hardness of these samples gradually increases while indentation fracture toughness gradually decreases with increasing m = 2n value. Due to little residual glassy phase, high infrared transparency/translucency was more readily achieved in Mg-doped sialon. The m = 1.2 sample possesses the maximum transmittance of ∼50% at ∼2 μm.     

Effect of some rare-earth oxides on structure, devitrification and properties of diopside based glasses

Four diopside based glasses containing an equimolar concentration of different rare-earth oxides (La₂O₃, Nd₂O₃, Gd₂O₃ and Yb₂O₃) respectively, were obtained by melt-quenching technique. Structural and thermal behaviour of the glasses was investigated by density and molar volume, infrared spectroscopy (FTIR), dilatometry, and scanning electron microscopy (SEM). All the glasses exhibited amorphous phase separation. The crystallization behaviour of the glasses was investigated by using differential thermal analysis (DTA). Sintering, crystallization, microstructure, and properties of the glass-ceramics were investigated under non-isothermal heating conditions in the temperature range of 800–900 °C.     

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.     

Influence of brick pattern interface structure on mechanical properties of continuous carbon fiber reinforced lithium aluminosilicate glass-ceramics matrix composites

Continuous carbon fiber reinforced lithium aluminosilicate glass-ceramic matrix composites have been fabricated by sol-gel process and hot pressing technique. The results show that the Cf/β-eucryptite composites hot pressed at 1300 °C and Cf/β-spodumene composites hot pressed at 1400 °C form weak interface with brick pattern characteristics, leading to high mechanical performance. The maximum flexural strength and fracture toughness reach 571 ± 32 MPa and 9.8 ± 0.6 MPa m^1/2 for Cf/β-eucryptite composites and 640 ± 72 MPa and 19.9 ± 1.8 MPa m^1/2 for Cf/β-spodumene composites. On increasing the hot pressing temperature, the active chemical diffusion consumes brick pattern interface layer, which leads to the formation of strong bonding between carbon fiber and the matrix. As a result, the composites exhibit brittle fracture behavior and the mechanical properties decrease significantly.     

Mechanical and optical properties evaluation of rapid sintered dental zirconia

The purpose of this study was to compare the effects of conventional sintering (CS) and rapid sintering (RS) on the mechanical and optical properties of different generations of dental zirconia ceramics. Five commercial zirconia ceramics were used for the CS and RS processes. The microstructure, phase composition, biaxial strength, 3-point bending strength, and Vickers microhardness of the zirconia after different sintering processes were studied. Weibull analysis was also used to check the structural reliability of the zirconia. The translucency parameter (TP) and the color difference (ΔE) were determined from the L*, a*, and b* values. The surface morphology of each specimen was dense, with no obvious pores or microcracks. The grain size of the RS group was smaller than that of the CS group. Between the two sintering processes, the same characteristic peaks were detected in the X-ray diffraction (XRD) patterns. There was no statistically significant difference (p > 0.05) in the biaxial strength, 3-point bending strength, or Vickers microhardness in terms of the sintering process. After RS, the Weibull modulus of the materials ranged from 9.3 to 19.3. It seems that the RS process affected the TP and ΔE values to some degree and depended on the zirconia generation. The RS process had no impact on the mechanical properties and produced smaller grain sizes than the CS process. The effect of the RS process on the optical properties depended on the type of material used. These findings should assist the production of dental zirconia restorations through the RS process, which saves time and energy.     

Reproportioning of steel fibre reinforced concrete mixes and their impact resistance

In this experimental investigation, a practical rapid method of proportioning steel fibre reinforced concrete (SFRC) mixes is developed and validated. The basis for developing this is to use the reproportioning method, which has already been developed for proportioning normal density cement concrete mixes, for SFRC mixes. Based on the results of the trial mix, two SFRC mixes having 28 day target strength of 30 and 50 MPa are designed using this technique and examined regarding its validation. In addition, the impact resistance of these reproportioned Plain Concrete (PC) and SFRC is studied at 7 and 28 days. It is observed that the SFRC has developed significant impact resistance even for a small addition of steel fibres. Pulse velocity test is conducted at different ages to assess the quality of concrete. It is found that all concrete specimens could be classified under good quality.     

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.     

高岭土性能研究及其对炮泥性能的影响

对宝钢炮泥用过的两种不同产地的200目(≤0.074 mm)高岭土SZ和SX进行了化学分析、XRD物相分析、SEM显微结构观察和粒度分布测定,以了解两种高岭土的性能差异;并对添加15%(质量分数)的两种高岭土所制备的炮泥进行了马夏值和不同温度处理后常温耐压强度的测定,以研究选用不同高岭土的炮泥的性能差异。结果表明:与SZ高岭土相比,SX高岭土的纯度更高,粒度更细,含有叶蜡石相,且其片状晶层解理完整。因此,在同样条件下,含叶蜡石相的SX高岭土可以赋予炮泥更好的可塑性,并提高炮泥的烧结强度。     

Effect of SiO2 content on the microstructure,mechanical and dielectric properties of Si3N4 ceramics

This study investigated the effect of SiO₂ content in the Y₂O₃–Al₂O₃ additive system on the microstructure, mechanical and dielectric properties of silicon nitride (Si₃N₄) ceramics. The total sintering additive content was fixed at 8 wt% and the amount of SiO₂ was varied from 0 to 7 wt%. The crystalline phases of the samples were determined by X-ray diffraction analysis. Complete α-to-β transformation of the Si₃N₄ occurred during sintering of all of the samples, which indicated that the phase transformation was unaffected by the SiO₂ content. However, the microstructures showed that the aspect ratio of the β-Si₃N₄ grains decreased and the residual porosity increased with increasing SiO₂ content. Additionally, the flexural strength and the dielectric constant decreased with increasing SiO₂ content because of the residual porosity and the formation of the Si₂N₂O phase via a reaction of SiO₂ with Si₃N₄.     

Effect of MgF2 addition on sinterability and mechanical properties of fluorapatite ceramic composites fabricated by wollastonite and phosphate glass

In this paper, we successfully report the design and synthesis of fluorapatite ceramic composites using phosphate glass and wollastonite as raw materials via a simple sintering method. The effects of MgF₂ additives in phase composition, microstructure, densification, and mechanical properties are investigated at various temperatures from 600 °C to 900 °C, and characterized by SEM/EDS, XRD, FTIR, linear shrinkage and water absorption, flexural strength analysis. It shows that the densification and mechanical behavior of composites increase with both the sintering temperature and MgF₂ content. Especially, the sample SCPF-7 exhibits the highest densification and optimal mechanical properties at 900 °C. At these conditions, the water absorption of fluorapatite ceramic composite is less than 0.20%, and the flexural strength is over 70 MPa. For the microstructure analysis, the formation of fluorapatite with a rod-like microstructure is enhanced with the increase of MgF₂ content. The amelioration of these properties is due to the formation of a new phase which helps to the formation of compact microstructure. The findings in this work provide a feasible strategy for the preparation of fluorapatite ceramic composites from available phosphate glass and wollastonite at a lower temperature.     

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.     

Mechanical and optical properties of MgAl2O4 ceramics and ballistic efficiency of spinel based armour

This study was devoted to the understanding of the influence of MgAl₂O₄ ceramic properties on their ballistic performances. By modifying the processing parameters, ceramics with different microstructures were obtained. Among them, a transparent MgAl₂O₄ spinel with an in-line transmission between 77% and 83% in the visible range, an average grain size of 8.6 μm and good mechanical properties (11.3 GPa in Knoop hardness and 2.5 MPa√m in fracture toughness) was produced. A thorough characterisation of the ceramics was accomplished in order to establish a link between microstructure, mechanical properties and ballistic protective performances against an armour piercing projectile of calibre 7.62x51 mm. The ballistic evaluation demonstrated the advantage of using a spinel layer as the strike face to stop a threat, while reducing drastically the thickness and the areal density of the transparent multilayer, compared to a simple glass armour. MgAl₂O₄ spinel with fine grains presented a better combination of mechanical properties compared to coarser microstructures, hence a better potential to damage a projectile at the impact.     

Impact of enhanced interfacial strength on physical,mechanical and tribological properties of copper/reduced graphene oxide composites: Microstructural investigation

Copper/reduced graphene oxide (rGO) composites were prepared to improve the mechanical and tribological properties of copper without adversely affecting its physical properties in any significant manner. No hazardous chemicals were used for reduced graphene oxide production, which maintained the integrity of layers. For better dispersibility of rGO in the copper matrix, electroless deposition of copper was done on the activated and sensitized rGO surfaces. Different amounts of prepared Copper/rGO nanocomposites were then dispersed in bulk copper using ethanol and finally compacted using spark plasma sintering. The coefficient of friction of copper reinforced with 0.5 wt% of nanocomposite reduced by 77.5% compared to neat copper. The flexural strength of copper reinforced with 0.75 wt% of nanocomposite and modulus of 1 wt% of nanocomposite reinforced copper increased by 15.2% and 31.3%, respectively, with different strengthening mechanisms before and after yield point. The increase in hardness and strength of the material along with thin rGO films in the wear track accounted for the sharp decrease in the coefficient of friction for the composites. There was a minimal and gradual decrease in the physical properties (electrical and thermal conductivities) of the composites with an increase in the amount of reinforcement. The two-step composite fabrication process ensured better dispersion of rGO in the copper matrix, which resulted in even properties throughout the composite.     

Densification behavior and properties of hot-pressed ZrC ceramics with Zr and graphite additives

Densifications of hot-pressed ZrC ceramics with Zr and graphite additives were studied at 1800-2000 °C. ZrC with 8.94 wt% Zr additive (named ZC10) sintered at 1900-2000 °C achieved higher relative densities (>98.4%) than that of additive-free ZrC (<83%). The densification improvement was attributed to the formation of non-stoichiometric ZrC_0.9, whereas there had rapid grain growth with grain size about 50-100 μm in ZC10. By adding co-doped additive of Zr plus C and adjusting the molar ratio of Zr/C, ZrC with co-doped additives with Zr/C molar ratio at 1:2 (named ZC12), ZrC ceramics with both high relative density (98.4%) and fine microstructures (grain size about 5-10 μm) were obtained at 1900-2000 °C. Effect of formation of non-stoichiometric ZrC_1−x on densification of ZrC was discussed. The Vickers hardness and indentation toughness of ZC10 and ZC12 samples sintered at 1900 °C were 17.8 GPa and 3.0 MPa m^1/2, 16.2 GPa and 4.7 MPa m^1/2, respectively.     

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.     

Fabrication and properties of three-directional orthogonal aluminosilicate fiber fabric-reinforced mullite composite

In this study, a three-directional orthogonal aluminosilicate fiber fabric-reinforced mullite composite with excellent properties was prepared by the precursor impregnation and pyrolysis (PIP) method. The influence of the number of PIP cycles on the microstructure and mechanical properties of the composite was studied. The density and mechanical properties of the composite enhanced with increasing number of PIP cycles. After the 6th PIP cycle, the density of the composite increased by only 0.8%, and the flexural strength and fracture toughness of the composite reached 130.1 MPa and 4.91 MPa m^1/2, respectively. Moreover, the thermal shock resistance of the composite was investigated by the high-low temperature (from 1300 °C to room temperature) thermal treatment and water quenching method. The strength retention rate of the composite after 10 high-low temperature thermal cycles was 90.1%; the retention rate dropped to 79.5% after 15 thermal cycles. The composite with the critical thermal shock temperature difference 843.9 °C displayed excellent thermal shock resistance.