Effect of graphite flake on the mechanical properties of hot pressed ZrB2-SiC ceramics

A ZrB₂ ceramic containing 20 vol.% SiC and 10 vol.% graphite flake (ZrB₂-SiC-G) was fabricated by hot pressing. It was shown that the fracture toughness was improved due to the introduction of graphite flake, whereas the flexure strength and hardness decreased slightly. The fracture toughness of ZrB₂-SiC-G composite was 6.1 ± 0.3 MPa·m^1/2, which was much higher than that of monolithic ZrB₂, ZrB₂-SiC composite and similar ZrB₂-SiC-C composite. The toughening mechanisms are crack deflection and branching as well as stress relaxation near the crack tip. The results here pointed to a potential method for improving fracture toughness of ZrB₂-based ceramics.     

Microstructure and mechanical properties of hot rolled TiNbSn alloys

Titanium alloys with lower elastic modulus and free from toxic elements such as Al and V have been studied for biomedical matters. Ti–Nb–Sn alloys showed up as presenting great potential for the aforementioned purpose. The current study got Ti–35Nb-XSn alloys (x = 2.5; 5.0; 7.5) by applying the following techniques: arc melting, homogenizing and cooling in furnace, homogenizing and water quenched, hot rolling and water quenched. According to each step of the study, the microstructures were featured by means of optical microscopy, by applying a scanning electron microscopy (SEM) analysis as well as X-ray diffraction. The mechanical properties were gotten by means of: Vickers microhardness, tensile and ultrasonic tests. Their ratio between tensile strength and elastic modulus as well as the ductility were compared to other biomedical alloys already available in the literature. The mechanical behavior of the Ti–Nb alloys directly depends on the Sn rates that constitutes the phases as well as on the thermomechanical background to which the alloy was submitted to. The hot rolled Ti–35Nb–2.5Sn alloy showed high ratio between strength and elastic modulus as well as high ductility, just as high as those of some cold rolled Ti alloys.     

Microstructure and mechanical properties of low-pressure injection-moulded reaction-bonded alumina ceramics

Reaction-bonded alumina was fabricated using standard powder preparation methods and the low-pressure injection moulding (LPIM) forming technique, followed by reaction sintering. The feasibility of LPIM was investigated in terms of the compounding ability of a highly agglomerated mechanically alloyed powder in a non-polar organic vehicle, and the microstructural homogeneity and resulting reliability of sintered LPIM parts. The green density of LPIM parts after debinding, roughly corresponding to the solids loading in the LPIM feedstock, was in the range of fractional density achieved by dry pressing, although the powder packing and aluminium particle deformation during forming were not the same. LPIM forming and debinding induced microstructural inhomogeneities (i.e. larger voids due to trapped air and density fluctuations) which were reflected in a slightly lower Weibull modulus, while the average strength did not differ significantly from the values obtained with dry pressed samples. The microstructure and mechanical properties of sintered parts were also related to the purity of the starting powders. The presence of impurities in the starting aluminium powder resulted in a somewhat coarser microstructure, characterized by a broader Al2O3 grain-size distribution, as well as in the presence of a thin glassy phase on the grain boundaries and in partial destabilization of dispersed tetragonal (Y2O3-stabilized) ZrO2 particles. In spite of a less favourable microstructure, the room-temperature strength and Weibull modulus were still comparable to those obtained from high-purity starting powder. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructure and mechanical properties of hot pressed ZrB2-SiCp-ZrO2 composites

The present paper investigated the microstructure and mechanical properties of ZrB₂-10 vol.%SiC_p-10 vol.%ZrO₂ composites hot pressed at three temperatures. Phase transformability from t-ZrO₂ to m-ZrO₂ during fracture was analyzed through calculating the volume fractions of m-ZrO₂ and t-ZrO₂ on polished and fracture surfaces. The densification temperature was found to have a significant effect on the microstructure, phase transformation and the properties of the composites. When the composite was hot pressed at 1950 °C, the average grain size was 9.5 µm, and the fracture toughness was 4.5 MPa·m^1/2. Comparatively, when the composite was hot pressed at 1750 °C, the average grain size was 3.4 µm, and the fracture toughness increased by ~ 50% to 6.8 MPa·m^1/2.     

Microstructure and mechanical properties of a hot pressing-dynamic partition treated steel

The microstructure and mechanical property of improved press-hardened steel with hot pressing combined dynamic partitioning (HP-DP) treatment are presented. Microstructure of the steel subjected to HP-DP treatment is featured by multi-martensite phases and the retained austenite (RA) phase with carbon content gradient. Compared with conventional hot-pressed samples, the HP-DP samples show better tensile property especially ductility. The effect of HP-DP parameters on the evolution of RA and mechanical property is then discussed. Finally, hot pressing of a double U-shaped part using both 22MnB5 steel sheet and the developed HP-DP steel sheet was carried out with exact control of part temperature at the end of hot pressing followed by air cooling.     

Microstructure and mechanical properties of cordierite ceramics toughened by monoclinic ZrO2

The effects of m-ZrO₂ addition on the mechanical behaviour of the cordierite ceramics were studied. Below 10 vol % of m-ZrO₂ content, zircon (ZrSiO₄) was formed as a second phase at the expense of all m-ZrO₂ due to the reaction between ZrO₂ and silica in the cordierite. The sintered density was improved with ZrO₂ addition through glass phase formation along grain boundaries, and maximum sinterability was obtained at 4.6 vol % m-ZrO₂. When sintered at 1300 °C for 4 h, the flexural strength at 4.6 vol % ZrO₂ was 190 MPa, compared with 55 MPa for the pure cordierite. Fracture toughness was gradually enhanced from 1.75 MPa m^1/2 to 2.4 MPa m^1/2 with m-ZrO₂ addition up to 10 vol %, which could be explained partly by thermal expansion mismatch between cordierite and the second-phase ZrSiO₄ and partly by crack deflection at the cordierite-ZrSiO₄ interfaces.     

Microstructure and mechanical properties of reaction-formed joints in reaction-bonded silicon carbide ceramics

A reaction-bonded silicon carbide (RB-SiC) ceramic material (Carborundum's Cerastar RB-SiC) has been joined using a reaction f rming approach. Microstructure and mechanical properties of three types of reaction-formed joints (350 m, 50–55 m, and 20–25 m thick) have been evaluated. Thick (350 m) joints consist mainly of silicon with a small amount of silicon carbide. The flexural strength of thick joints is about 44±2 MPa, and fracture always occurs at the joints. The microscopic examination of fracture surfaces of specimens with thick joints tested at room temperature revealed the failure mode to be typically brittle. Thin joints (<50–55 m) consist of silicon carbide and silicon phases. The room and high temperature flexural strengths of thin (<50–55 m) reaction-formed joints have been found to be at least equal to that of the bulk Cerastar RB-SiC materials because the flexure bars fracture away from the joint regions. In this case, the fracture origins appear to be inhomogeneities inside the parent material. This was always found to be the case for thin joints tested at temperatures up to 1350°C in air. This observation suggests that the strength of Cerastar RB-SiC material containing a thin joint is not limited by the joint strength but by the strength of the bulk (parent) materials.     

注射成型羟基磷灰石/聚酰胺6多孔支架的微观结构和力学性能

采用注射成型法制备了羟基磷灰石/聚酰胺6(HA/PA6)多孔支架,用SEM、XRD、DSC等手段表征了支架的组成结构和形貌,检测了其力学性能.研究表明,调节羟基磷灰石(HA)含量、偶氮二甲酰胺(AC)用量和预塑量能有效控制支架的力学性能、孔径大小和孔隙率.HA/PA6支架的孔径在100～500μm左右,孔隙率达到甚至超...     

Processing and properties of nanoporous hydroxyapatite ceramics

Method for fabrication and properties of nanoporous hydroxyapatite (HA) ceramic were described in the present work. The nanoporous hydroxyapatite was derived from nano hydroxyapatite powder and polyvinyl alcohol (as a pore former). The HA nanopowder was obtained from vibro-milling for 4 h. The nanoporous ceramics were sintered at 1200 °C. Properties of the nanoporous ceramics were investigated using various methods. Average porosity of the final product was found to be 64.6 ± 1.4%. Open and interconnected pores were obtained with an average pore size less than 100 nm, confirming the nanoporous structure of this ceramic. A high bending strength of 14.7 ± 3.2 MPa for the nanoporous ceramic, shows significant promise as a potential bone repairing material.     

Characterization of hot pressed Al2O3-platelet reinforced hydroxyapatite composites

Hydroxyapatite reinforced with monocrystalline Al₂O₃ platelets was densified by hot pressing. The effect of volume fraction and size of platelets on the microstructure, strength and toughness was investigated. It was demonstrated that no phase degradation occured during thermal treatments. A better homogeneity of composite mixtures was achieved when large platelets had been used. In return, the incorporation of small platelets appeared more favourable to increase the mechanical characteristics although limiting effect induced by microstructural defects. The flexural strength can reach 140 MPa with an associated fracture toughness of 2.5 MPa % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaOaaaeaaca% qGTbaaleqaaaaa!36F8!\[\sqrt {\text{m}} \] compared to 137 MPa and 1.2 MPa % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaOaaaeaaca% qGTbaaleqaaaaa!36F8!\[\sqrt {\text{m}} \] for dense monolithic HAP. The observation of crack propagation allowed us to point out the mechanisms responsible of this toughening. Crack deflection on disk faces should be considered as the initiating phenomenon leading to platelet debonding, crack bridging or branching. Crack deflection and branching may also result in the formation of unbroken ligaments of material which bridge the crack.     

Effects of rolling and hot pressing on mechanical properties of boron carbide-based ceramics

A study of hot pressed B₄C-based laminates, after rolling and without rolling, has been performed to elucidate the existence of fracture resistance/crack length anisotropy induced by this processing technique. While the crack lengths/fracture resistance was affected significantly by the presence of the residual stresses in B₄C/B₄C–ZrB₂ laminates, no differences in Vickers crack lengths were observed in B₄C/B₄C laminates prepared by rolling and hot pressing, as compared to the crack lengths seen in pure B₄C ceramics prepared by hot pressing without rolling. X-ray diffraction analysis confirmed that no texture has been formed during the rolling and hot pressing of B₄C ceramics.     

Microstructure and mechanical properties of spray-deposited ultra-high carbon steel after hot rolling

The tensile mechanical properties of as-cast ingot metal (IM), spray-formed (SF), and as-hot-rolled (HR) ultra-high carbon steels (UHCS) containing silicon were investigated in this paper. The relationship between microstructure and tensile properties was described for these steels. The carbide networks, the pearlitic interlamellar spacing, the size of carbide particles, and the volume ratio between lamellar and spheroidized structure are all microstructure factors influencing the tensile properties in UHCS.     

The comparison of powder characteristics and physicochemical,mechanical and biological properties between nanostructure ceramics of hydroxyapatite and fluoridated hydroxyapatite

In this study, several fluorine-substituted hydroxyapatite ceramics with the general chemical formula Ca₅(PO₄)₃(OH)_1 ? xF_x (0 ≤ x ≤ 1), where x = 0.0 (hydroxyapatite; HA), x = 0.68 (fluorhydroxyapatite; FHA) and x = 0.97 (fluorapatite; FA) were prepared. The powders were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infra-red (FTIR), X-ray diffraction (XRD), F-selective electrode, atomic absorption spectroscopy (AAS) and EDTA titration analyses. The powders were uniaxially pressed and were formed as a disc shape. Subsequently, sinterability and thermal stability of synthesized powders were compared together. Also the effect simultaneously of fluoride content and temperature were examined on the lattice parameters and crystallites size of the obtained powders. Mechanical properties including hardness, elastic modulus and fracture toughness were measured using indentation. The in vitro dissolution studies of the samples were carried out at osteoclastic resorption conditions. Finally, the biocompatibility and cytotoxicity of the samples were carried out using osteoblast-like cells and L929 cell line, respectively. The obtained results showed that the thermal stability substantially is increased with increase incorporated fluoride into HA structure. Also it was found that the fluoride reduced the lattice parameters and crystallites size of HA. Finally, the in vitro dissolution studies results suggest that the fluoride substitutions in HA offer the ability to prepare HAs with different degrees of solubility.     

Fracture behaviour of chemical vapour deposited and hot isostatically pressed zinc sulphide ceramics

Fracture behaviour of zinc sulphide ceramics prepared by chemical vapour deposition (CVD) followed by hot isostatic pressing (CVD + HIP) was investigated in terms of flexural strength (σ_f), plane-strain fracture toughness (K_Ic), even conditional fracture toughness (K_IQ), R-curve behaviour (variation of total fracture energy release rate, J_c with crack extension, δ/δ_c) and fracture mode. The corresponding Knoop Hardness number (KHN) and its correlations to flexural strength (σ_f) are also evaluated and reported. The present study showed that the zinc sulphide (ZnS) ceramics processed by CVD exhibited higher fracture resistance compared to ZnS processed by CVD + HIP condition. This observation is principally attributed to higher grain size associated with post-CVD HIPing process. In both conditions, the ZnS materials exhibited conditional fracture toughness (K_IQ) that decreased moderately with increased crack length due to the change in fracture mode form grossly tensile to predominant shear. A constantly rising R-curve behaviour was indicated in both the materials with significant increase in total fracture energy release rate (J_c with the normalised displacement (δ/δ_c), a parameter representing crack extension.     

Microstructure,mechanical and degradation properties of equal channel angular pressed pure magnesium for biomedical application

Abstract

Magnesium is a biocompatible and biodegradable metal, which has attracted much interest in biomedical engineering. Pure magnesium shows the low strength and plasticity at ambient temperature. Microstructure, mechanical properties and degradation properties of the equal channel angular pressed pure magnesium have been investigated for biomedical application in detail by optical microscopes, mechanical properties testing and corrosion testing. The results have revealed that the processing temperature and routes are important factors that affect the properties of pure Mg by equal channel angular pressing. The two-step equal channel angular pressing processing (one pass at 360°C and three passes at 200°C) has been successfully applied to control the microstructure, mechanical and degradation properties of the pure Mg. Optical microscopy observation has indicated that the grain size of the as cast pure magnesium has been significantly decreased after equal channel angular extrusion, which has mainly contributed to the high tensile strength and good elongation. Equal channel angular pressed pure magnesium has provided moderate corrosion resistance, which has opened a new window for materials design, especially for biomedical.     

搅拌摩擦加工制备羟基磷灰石增强镁复合材料的微观组织和力学性能

通过搅拌摩擦加工（Friction stir processing,FSP）制备了羟基磷灰石增强镁（HA/WE43）复合材料,研究了主轴转速对HA分布的影响及FSP加工前后材料微观组织和力学性能的变化。使用光学显微镜、SEM、TEM对该复合材料的显微组织进行了表征,同时对其显微硬度和室温拉伸性能进行了测试。结果表明:制得的HA/WE43复合材料晶粒尺寸相比于母材发生了显著的细化,加工过程中,HA颗粒的存在增强了FSP的晶粒细化作用;主轴转速较低时,HA/WE43复合材料中的HA团聚较严重,随着主轴转速的增加,HA的分布更加均匀,团聚现象得到改善;尽管局部团聚的HA颗粒会成为复合材料在拉伸变形过程中的裂纹源,但HA/WE43复合材料的极限抗拉强度、屈服强度和伸长率相对于母材仍有明显提高。      

Microstructure and elastic properties of sintered hydroxyapatite

The paper focuses on the dependence of microstructure and elastic properties of sintered hydroxyapatite on the processing parameters. Several specimens were sintered in conventional furnace at various temperatures. Elastic moduli were measured ultrasonically and information about the microstructure was recovered from these data and then verified by analysis of microphotographs. It was obtained that the average shape of pores becomes more round as the sintering temperature increases. That leads, in particular, to higher fracture toughness of the material since the stress concentration near pores is reduced.     

Microstructure and mechanical properties of AZ31 alloy ring processed by hot forging

AZ31 alloy ring was successfully processed by hot forging. The effects of effective strain and temperature distributions on the microstructure and the relationship between microstructure and mechanical properties of the ring were investigated. The effective strain distribution at the centre region is relatively uniform, while the temperature in or near the flash region is higher than the other regions. A refined but inhomogeneous microstructure is obtained in the ring. It shows that the larger the accumulated strain and the lower the temperature are, the finer and more homogeneous the microstructure will be achieved. The mechanical responses of the ring from different tensile directions differ greatly. The radial direction sample shows the lowest yield strength and the largest fracture elongation.