Microstructure and mechanical properties of hydroxyapatite obtained by gel-casting process

In the present work, well-shaped HAp green bodies were obtained by the gel-casting process with 50 vol.% slurry. After drying, the microstructure and pore distribution of the green body were investigated. The density, compressive strength and flexural strength of the green body were 1.621 g/cm³, 32.6 ± 3.2 MPa and 13.8 ± 1.0 MPa, respectively. After pressureless sintering at the range of 1100–1300 °C for 2 h, the relative density of the final product ranges from 71.8 to 97.1% th. The maximum value of flexural strength, elastic modulus, hardness and fracture toughness were 84.6 ± 12.6 MPa, 138 ± 7 GPa, 4.45 ± 0.18 GPa and 0.95 ± 0.13 MPa m^1/2, respectively. SEM images show a compact and uniform microstructure; the average grain size was found by using the linear intercept method. XRD and FTIR determined the phase and the radical preserved after sintering.     

Microstructure and mechanical properties of ZTA composites fabricated by oscillatory pressure sintering

The influence of sintering temperature on the microstructure and mechanical properties of Al₂O₃?20 wt% ZrO₂ composites fabricated by oscillatory pressure sintering (OPS) was investigated by means of X-ray diffraction, scanning electron microscopy, three-point bending test and Vickers indentation. Results were compared to specimens obtained by conventional hot pressing (HP) under a similar sintering schedule. The optimum oscillatory pressure sintering temperature was found to be 1600 °C; almost fully dense materials (99.94% of theoretical density) with homogeneous microstructure could be achieved. The highest flexural strength, fracture toughness and hardness of such composites reached 1145 MPa, 5.74 MPa m^1/2 and 19.08 GPa when sintered at 1600 °C, respectively. Furthermore, the oscillatory pressure sintering temperature could be decreased by more than 50 °C as compared with the HP method, OPS favouring enhanced grain boundary sliding, plastic deformation and diffusion in the sintering process.     

Microstructure and mechanical properties of three-dimensional oxide/oxide composite fabricated by a slurry infiltration and sintering process

Oxide/oxide composites reinforced by two-dimensional fiber fabrics are important structural materials at high temperatures but exhibit low delamination resistance. This study developed a simple slurry infiltration and sintering (SIS) process to fabricate three-dimensional oxide/oxide composites. The results showed that a homogeneous microstructure in three directions was obtained. This composite possessed a weak matrix, which had a porous structure and low elastic modulus. Typical mechanical properties of the composite were not lower than those of two-dimensional oxide/oxide composites since the flexural strength and fracture toughness were 332.4 MPa and 11.6 MPa·m^1/2, respectively. Particularly, the composite had a good interlaminar shear strength of 25.4 MPa and a superior transthickness tensile strength of 5.6 MPa. X-ray computed tomography showed that fiber yarns in the through-thickness direction effectively impeded crack propagation and enhanced delamination resistance. Therefore, the reported SIS process is a very promising method for manufacturing three-dimensional oxide/oxide composites.     

Microstructure and mechanical properties of a Pt-Rh alloy produced by powder metallurgy and subjected to plastic working

The paper presents the results of investigations of the Pt-Rh8 wires produced by powder metallurgy. The powder was consolidated by isostatic pressing followed by sintering. Examinations of the microstructure and the microhardness of the wires thus obtained showed that this treatment yields solid wires characterized by fine-grained microstructure and low porosity. The wires have better mechanical properties than those produced by plastic treatment of moulded alloys.     

O＇－Sialon－ZrO_2复合材料的显微结构与力学性能的研究

研究了Ｏ＇－Ｓｉａｌｏｎ－ＺｒＯ２复合材料的显微结构与力学性能的关系。结果表明，Ｏ＇－Ｓｉａｌｏｎ形成连续网络编织状结构。ＺｒＯ２加入量较少时充当填充结构骨架的作用；ＺｒＯ２加入量增多时（至４０％），会有更多的ＺｒＯ２形成聚集体。随着ＺｒＯ２引入量的增加，材料的常温抗折强度提高，但高温抗折强度下降。Ｏ＇－Ｓｉａｌｏｎ的编织状结构可能阻碍晶界滑移。这种复合材料的高温抗折强度在１４００℃为１１２～１７３ＭＰａ。     

Microstructure and mechanical properties of TiB2-reinforced 7075 aluminum matrix composites fabricated by laser melting deposition

In this study, we adopt laser-melting deposition (LMD) technology to fabricate TiB₂/7075 aluminum matrix composites (AMCs), and we investigate in detail the effect of the TiB₂ content on the microstructure, nano-hardness, compressive properties, and wear performance. We prepare experimental samples by using a laser power of 800?W and a velocity of 0.01?m/s, and the results are evaluated. It was observed that the reinforcement particles dispersed irregularly throughout the Al matrix as the TiB₂ contents increased. The grain size of the fine-grain zone decreased appreciably by 31.9% from 8.41?µm (LMD sample without TiB₂ reinforcement) to 5.73?µm. Furthermore, the AMCs with 4?wt% reinforcement exhibited impressive mechanical properties, i.e., nanohardness of 1.939 Gpa, compressive strength of 734.8?MPa, and a wear rate of 1.889?×?10^?4 mm³/Nm. The wear resistance improved and the wear mechanism changed from adhesive wear to debris wear with the addition of TiB₂ reinforcement.     

Microstructure and mechanical properties of Cf/ZrC composites fabricated by reactive melt infiltration at relatively low temperature

Carbon fiber-reinforced zirconium carbide matrix composites (C_f/ZrC) were prepared by vacuum infiltrating porous carbon/carbon preforms with molten Zr₂Cu alloy at 1200 °C. X-ray diffraction, scanning electron microcopy and transmission electron microscopy analysis were used to characterize the composition and microstructure of the final composites. It was found that the matrix of the composites were composed of the Cu–Zr–C amorphous phase dispersed with either single- or polycrystalline ZrC. Based on the microstructural analysis, the formation mechanism of the matrix was proposed to be a solution-precipitation and grain coalescence process. The influence of the heat treatment at 1800 °C was also investigated. Results indicated that at very high temperature the volatilization of residual metal somewhat deteriorated the flexural strength and the elastic modulus, but the fracture toughness of the composites was improved due to the sintering of ZrC grains.     

Microstructure,mechanical and tribological properties of TaCN composite films by reactive magnetron sputtering

In this paper, a series of TaCN composite films with different carbon content were deposited by the magnetron sputtering system and the microstructure, mechanical and tribological properties were investigated. The results showed that the deposited TaCN films exhibited a three-phase of face-centered cubic (fcc) Ta(C,N), hexagonal closed-packed (hcp) Ta(C,N) and amorphous CNx. With the increase of carbon content, the hardness of the TaCN films first increased and then decreased, after reaching a maximum of 33.1 GPa; the adhesion strength increased gradually; the coefficient of friction decreased monotonically and the wear property initially improved and then weakened at room temperature. The coefficient of friction of the TaCN film at 28.21 at.% carbon decreased first, then increased and then decreased again and its high-temperature wear rate first decreased slightly and then increased, as the temperature increased from room temperature (RT) to 600 °C. The TaCN film at 28.21 at.% carbon exhibited excellent an elevated-temperature tribological properties.     

Microstructure and mechanical properties of hot-pressed carbon nanotubes compacted by spark plasma sintering

Bulk carbon nanotube samples were prepared by spark plasma sintering. The as-prepared bulk carbon nanotube material exhibited brittle fracture similar to that of common ceramics. Its fracture toughness was around 4.2 MPa m^1/2 while flexural strength was 50 MPa due to the weak bonding between carbon nanotubes. Obvious carbon nanotube bridging was found during the development of the crack induced by an indenter, which provides a possibility of carbon nanotube tough material.     

Microstructure and mechanical properties of Mo0.9Cr0.1AlB solid solution

In this study, Mo_0.9Cr_0.1AlB solid solution ceramic bulks were prepared from the element powder mixtures using hot pressing sintering method. Compared with MoAlB ceramics, the grains of as-prepared Mo_0.9Cr_0.1AlB were refined obviously. The lattice constants of Mo_0.9Cr_0.1AlB were confirmed to be a = 3.205 Å, b = 13.999 Å and c = 3.098 Å. The density of Mo_0.9Cr_0.1AlB was lower than that of MoAlB due to the incorporation of Cr element. In addition, the effect of doping Cr element on the comprehensive mechanical properties was studied as well. The hardness and compressive strength were improved significantly. In comparison with MoAlB ceramic, the improvement of mechanical properties could be attributed to solid solution strengthening and grain refinement.     

Recent advances in bionanocomposites: Preparation,properties, and applications

The authors report recent advances in the research and development of bionanocomposites based on four types of nanofillers, namely organically modified layered silicate (OMLS), cellulose nanofibers (CNs), carbon nanotubes (CNTs), and halloysite nanotubes (HNTs). These composite materials have received significant attention from academia and industries due to their unique advantages such as excellent biodegradability, availability, cost effectiveness, and eco-friendliness. The preparation and properties of bionanocomposites have been reviewed in detail together with their current and potential applications in the fields of electronics and sensors, tissue engineering, drug delivery, gene therapy, and cosmetics, as well as packaging.     

Microstructure and mechanical properties of boron carbide/graphene nanoplatelets composites fabricated by hot pressing

In this study, boron carbide (B₄C)-graphene nanoplatelets (GNPs) composites, with enhanced strength and toughness, were fabricated by hot pressing at 1950 °C under a pressure of 30 MPa for 1 h. Microstructure analysis revealed that the GNPs are homogenously dispersed within the B₄C matrix. Raman spectroscopy and electron microscopy showed the orientation of the GNPs in the composites. The effects of the amount of GNPs on the microstructure and mechanical properties of the composites were also investigated. The optimal mechanical properties were achieved using 1 wt% GNPs. The relative density, Vickers hardness, flexure strength, and fracture toughness of the B₄C-GNPs composite ceramic were found to be 99.12%, 32.8 GPa, 508 MPa, and 4.66 MPa m^1/2, respectively. The main toughening mechanisms included crack deflection in three dimensions, GNPs pull-out, and crack bridging. The curled and semi-wrapped GNPs encapsulated individual B₄C grains to resist GNPs pull-out and to deflect propagating cracks.     

Microstructure and mechanical properties of Si3N4f/Si3N4 composites with different coatings

The Si₃N₄ coating and Si₃N₄ coating with Si₃N₄ whiskers as reinforcement (Si₃N_4w-Si₃N₄) were prepared by chemical vapor deposition (CVD) on two-dimensional silicon nitride fiber reinforced silicon nitride ceramic matrix composites (2D Si₃N_4f/Si₃N₄ composites). The effects of process parameters of as-prepared coating including the preparation temperature and volume fraction of Si₃N_4w on the microstructure and mechanical properties of the composites were investigated. Compared with Si₃N₄ coating, Si₃N_4w-Si₃N₄ coating shows more significant effect on the strength and toughness of the composites, and both strengthening and toughening mechanism were analyzed.     

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.     

Microstructures and mechanical properties of B4C-TiB2-SiC composites fabricated by ball milling and hot pressing

B₄C-TiB₂-SiC composites were fabricated via hot pressing using ball milled B₄C, TiB₂, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84?GPa, 858?MPa and 8.21?MPa?m^1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B₄C-TiB₂-SiC composite.     

Microstructure and mechanical properties of in-situ grown mullite toughened 3Y-TZP zirconia ceramics fabricated by gelcasting

In-situ grown mullite toughened zirconia ceramics (mullite-zirconia ceramics) with excellent mechanical properties for potential applications in dental materials were fabricated by gelcasting combined with pressureless sintering. The effect of sintering temperature on the microstructure and mechanical properties of mullite-zirconia ceramics was investigated. The results indicated that the columnar mullite produced by reaction was evenly distributed in the zirconia matrix and the content and size of that increased with the increase of sintering temperature. Mullite-zirconia ceramics sintered at 1500 °C had the optimum content and size of the columnar mullite phase, generating the excellent mechanical properties (the bend strength of 890.4 MPa, the fracture toughness of 10.2 MPa.m^1/2, the Vickers hardness of 13.2 GPa and the highest densification). On the other hand, zirconia particles were evenly distributed inside the columnar mullite, which improved the mechanical properties of columnar mullite because of pinning effect. All of this clearly confirmed that zirconia grains strengthened columnar mullite, and thus the columnar mullite was more effective in enhancing the zirconia-based ceramics. Simultaneously, the residual alumina after reaction was distributed evenly in the form of particle, which improved the mechanical properties of the sample because of pinning effect. Overall, the synergistic effect of zirconia phase transformation toughening with mullite and alumina secondary toughening improved the mechanical properties of zirconia ceramics.     

Microstructure control and mechanical properties of porous silicon nitride ceramics

Porous silicon nitride ceramics with a fibrous interlocking microstructure were synthesized by carbothermal nitridation of silicon dioxide. The influences of different starting powders on microstructure and mechanical properties of the samples were studied. The results showed that the microstructure and mechanical properties of porous silicon nitride ceramics depended mostly on the size of starting powders. The formation of single-phase β-Si₃N₄ and the microstructure of the samples were demonstrated by XRD and SEM, respectively. The resultant porous Si₃N₄ ceramics with a porosity of 71% showed a relative higher flexural strength of 24 MPa.     

Effect of sintering on the microstructure and mechanical properties of alloy titanium-wollastonite composite fabricated by powder injection moulding process

Composite biomaterials are in high demand in the medical field of today. The combination of bioactive wollastonite (WA) glass ceramic with the biocompatibility of alloy titanium (Ti6Al4V) could be a good candidate for implant applications. The rheological properties of Ti6Al4V/WA feedstock show a pseudoplastic behaviour with low activation energy. The feedstock was successfully injected as a green part with no defects. The green part was solvent debound for 6?h in heptane and thermal debound in an argon environment for 1?h. The brown part was successfully sintered at 1300?°C for 3?h with 5?°C/min heating and cooling rates. The average sintered density was 4.12?g/cm³; which is 97.5% from the theoretical density. The highest Young's modulus obtained was 18.10?GPa; which is in the range of human bone strength. EDX analysis shows that by increasing sintering temperature, the level of oxygen decreased. Cell viability test shown an absorbance increased with days increasing indicated that the cellular were proliferated on the composite Ti6Al4V/WA composite which also proved that the composite was non-toxic. This indicates that the Ti6Al4V/WA composite is suitable for bone implant applications.     

Microstructure and properties evolution of silicon-based ceramic cores fabricated by 3D printing with stair-stepping effect control

A ceramic core is the key component in the manufacture of the hollow turbine blades of aeroengines. Compared with the traditional injection molding method, 3D printing is more suitable for manufacturing ceramic cores with a complex geometry at high precision. However, the stair-stepping effect is inevitable in the 3D printing process and affects the surface roughness and strength of the ceramic core. In this study, to explore the influence of nano-silica content on the microstructure and properties of the ceramic core, silicon-based ceramic cores were fabricated with the addition of nano-silica powder by digital light processing and subsequent sintering at 1200 °C. The results showed that the apparent porosity and pore size of the ceramic core gradually decreased as both the nano-silica powder content and bulk density increased. Meanwhile, the printing interlayer spacing was significantly reduced, resulting in a low surface roughness, high flexural strength, and creep-resistance. To simulate the entire casting process of a superalloy blade, the thermal deformation behavior of the ceramic core was observed by heating and cooling cycles performed in a thermal dilatometer at 1540 °C. The total linear shrinkage decreased as the nano-silica powder content increased, which was mainly due to the phase transformation of cristobalite and the densification of the ceramic core sintered at 1200 °C. The low surface roughness and linear shrinkage as well as high flexural strength of the ceramic core can contribute to the excellent quality of cast superalloy blades.