Influence of microstructure on strength and fracture toughness ofβ-Sialon

-Sialon (Si_6–z Al _z O _z N_8–z ) withz = 0.5 was fabricated by hot-pressing of a spray dried mixture of –Si₃N₄ and aluminium-isopropoxide solution. Phase composition, flexural strength and microstructure of a sintered body were investigated. Phases identified by XRD were -Sialon and a small amount of O-Sialon. The flexural strength (three-point bending) was about 1500 MN m^–2. This value, about three times higher than that of -Sialon fabricated from -Si₃N₄ and -Al₂O₃ powder, was mainly due to the homogeneous microstructure without large defects such like clusters of large grains. -Sialon was heat treated at 2000 °C for 2 h in 4 M Pa N₂ to develop elongated -Sialon grains with high aspect ratio. Microstructure, flexural strength and fracture toughness (K _Ic) of it were investigated. Both strength andK _Ic were lower than those of hot-pressed sample, even though an elongated microstructure was achieved. This fact showed that the toughening of -Sialon with elongated grains could not be achieved without grain boundary phase which resulted in a crack deflection.     

Effect of annealing on the microstructure, room-temperature strength, and fracture toughness of Al2O3−ZrO2−TiN ceramics

The microstructure, phase composition, room-temperature flexural strength, and fracture toughness of Al₂O₃−ZrO₂−TiN (AZT) ceramics were studied on specimens annealed in air at 1000, 1200, and 1400°C. The strength of the ceramics decreased with annealing temperature. The degradation in strength was caused by defects formed on or near the surface of the ceramics during oxidation of TiN which started at 600–700°C. The surface defects after annealing are influenced by the formation of rutile (TiO₂) at 1000 and 1200°C, aluminum titanate (Al₂TiO₅), and titanium suboxide Ti₅O₉ at 1400°C as well as by diffusion processes associated with ZrO₂. If the annealing of smooth AZT specimens in air resulted in lower strength, specimens in the form of single-edge notched beam (SENB) exhibited a considerable increase in fracture toughness (K _Ic) with annealing temperature. Such behavior was caused by the formation of an oxide layer which hindered the propagation of the main crack from the notch base. Thermal treatment of the smooth AZT specimens and further edge notching and testing did not result in a change of K _Ic values. The Al₂O₃ and Al₂O₃−ZrO₂ ceramics were also tested for comparison. Translated from Problemy Prochnosti, No. 1, pp. 132–138, January–February, 1999.     

Influence of nano-ZrO2 additive on the bending strength and fracture toughness of fluoro-silicic mica glass–ceramics

Fluoro-silicic mica glass–ceramics were prepared by a sintering process and different proportions of nano-ZrO₂ particles (3Y-TZP) were integrated during the process. Bending strength and fracture toughness were evaluated using a three-point bending test and a Vickers indenter, respectively. The bending strength and fracture toughness improved in significantly with the increase in the quantity of nano-ZrO₂ additives. The highest bending strength of 324.3 ± 12.3 MPa and fracture toughness of 4.2 ± 0.11 MPa m^1/2 were obtained with 30% (wt.) nano-ZrO₂. Good results were also obtained in morphological observations. The glass–ceramic is homogenous and the ZrO₂ grains embed in the lamellar structures of the fluoro-silicic mica homogenously and completely and array well and compactly. On the fracture surface, both the transgranular fracture and the intergranular fracture can be observed clearly.     

Effects of high-temperature annealing on the microstructure and properties of C/SiC–ZrB2 composites

C/SiC–ZrB₂ composites prepared via precursor infiltration and pyrolysis (PIP) were treated at high temperatures ranging from 1200 °C to 1800 °C. The mass loss rate of the composites increased with increasing annealing temperature and the flexural properties of the composites increased initially and then decreased reversely. Out of the four samples, the flexural strength and the modulus of the specimen treated at 1400 °C are maximal at 216.9 MPa and 35.5 GPa, suggesting the optimal annealing temperature for mechanical properties is 1400 °C. The fiber microstructure evolution during high-temperature annealing would not cause the decrease of fiber strength, and moderate annealing temperature enhanced the thermal stress whereas weakened the interface bonding, thus boosting the mechanical properties. However, once the annealing temperature exceeded 1600 °C, element diffusion and carbothermal reduction between ZrO₂ impurity and carbon fibers led to fiber erosion and a strong interface, jeopardizing the mechanical properties of the composites. The mass loss rate and linear recession rate of composites treated at 1800 °C are merely 0.0141 g/s and 0.0161 mm/s, respectively.     

Influence of duty cycle on the microstructure and microhardness of pulse electrodeposited Ni–CeO2 nanocomposite coating

The Ni–CeO₂ nanocomposite coatings have been synthesized by pulse electrodeposition technique with different duty cycles (6, 9 and 17%) from a Watts-type electrolyte containing nano-sized CeO₂ particles. The XRD results show that the (2 0 0) orientation is dominant over (1 1 1) orientation in the Ni–CeO₂ nanocomposite coatings prepared with 6 and 17% duty cycles, while the opposite is true for the sample prepared with 9% duty cycle. The maximum amount of CeO₂ (10 wt%) incorporation in the coating occurs at 9% duty cycle. The crystallite size changes from micrometer to nanometer as the duty cycle changes from 6 to 9%. The hardness increases as the duty cycle increases from 6 to 17%. However, a coating with optimum smoothness and small number of microcracks is obtained at 9% duty cycle.     

Influence of the fiber volume fraction and the fiber Weibull modul on the behavior of 2D woven SiC/SiC — a finite element simulation

Summary The behavior of two-dimensional woven SiC/SiC ceramic matrix composite (CMC) is studied by numerical simulations based on the finite element method (FEM). Starting point of the investigations is a micromechanical model regarding a three-dimensional unit cell, which takes damage and fracture of the single components—fiber bundles and inter yarn matrix—into account. The scattering of the strength values which is characteristic for ceramic material is involved using Weibull distribution. In a first step the unit cell regarded within the simulations is cooled down to consider the residual thermal stresses resulting from the fabrication process. In a second step the unit cell is subjected to tensile loading and its behavior—especially the influence of the scattering of the strength values—is studied. To be able to estimate the influence of important parameters on the behavior of the composite a macrostructure is built up using the results obtained for a large number of unit cell. Thus an averaging effect is reached and the behavior obtained for the macrostructure should be characteristic for the composite. Doing so, the influence of the fiber volume fractionv _f and the fiber Weibull modulM _f on the composite behavior can be studied.Dedicated to Prof. Dr.-Ing. Dr.-Ing. E. h. mult. Oskar Mahrenholtz on the occasion of his 70th birthday     

Effect of strain rate on the fracture behaviour of epoxy–graphene nanocomposite

In this study, epoxy-based nanocomposite was fabricated by the addition of graphene nanosheet via a solution casting method. To investigate the effect of strain rate on tensile properties of epoxy, tensile tests were done on standard samples at different strain rates (0.05–1 min^?1). The role of strain rate and presence of graphene on fracture behaviour of epoxy were also studied by investigation of the fracture surfaces of some samples by scanning electron microscopy (SEM). Finally, Eyring’s model was performed to clarify the role of strain rate on activation volume and activation enthalpy of epoxy. The results of tensile tests showed a maximum strength of epoxy–graphene nanocomposite at the graphene wt% of 0.1%. Tensile strength of epoxy obviously improved with increasing strain rate, but tensile strength of epoxy/graphene nanocomposite sample was less sensitive. Fracture micrographs showed that the mirror zone of the fracture surface of epoxy diminished by increasing strain rate or addition of graphene; and final fracture zone also became rougher. Finally, by investigation of the activation enthalpies, it was showed that much higher enthalpy was needed to fracture the nanocomposite sample, as the activation enthalpy changed from 41.54 for neat epoxy to 67.34 kJ mol^?1 for EP–0.1% GNS sample.     

Influence of notch radius and microstructure on the fracture behavior of Al–Zn–Mg–Cu alloys of different purity

The influence of notch radius on the fracture behavior of two high-strength Al–Zn–Mg–Cu alloys with different Fe content in the T73 condition was investigated. The fracture toughness tests were performed on non-fatigue-precracked notched bending specimens with different notch radii ranged from 0.15 mm to 1.0 mm. The obtained data were interpreted using the concept of Notch Fracture Mechanics combined with finite-element method (FEM) calculations. It was found that both alloys are very sensitive to the notch radius. The fracture toughness increases with increasing notch radius. For a given notch radii, the increase in fracture toughness is more significant for the more pure alloy. The fracture behavior of investigated alloys with respect to microstructural features and their relation with the fracture micromechanisms were analyzed.     

Influence of processing on the microstructure of Cu–8Cr–4Nb

The particle-strengthened Cu–8 at.%Cr–4 at.%Nb alloy is processed by consolidation of atomized powders followed by extrusion to obtain bars and rolling to produce sheets. Comparison of copper matrix grain and second-phase particle structures in both extruded and rolled Cu–8Cr–4Nb was performed. Extruded material displayed locally banded arrangements of Cr₂Nb particles, while the distribution of particles was more uniform in rolled material. Mean Cr₂Nb particle sizes were found to be essentially the same for both processing methods. Non-spherical particles in the extruded alloy showed some preferred orientation, whereas the rolled material displayed a more uniform particle orientation distribution. Extruded material exhibited a dual grain size distribution with smaller grains in banded regions. The mean grain size of 1.36 μm in extruded material was larger than the 0.65 μm grain size of rolled material. A [101] texture was evident in extruded material, whereas the rolled material was only slightly textured along the [001] and [111] directions. The processing differences for the rolled and extruded forms give rise to different microstructures and hence higher creep strength for the extruded material in the temperature range of 773–923 K.

---

Influence of MgO addition on mechanical and ablation characteristics of ZrB2–SiC composites developed through microwave sintering

Journal of Materials Science - Zirconium diboride (ZrB2) is a credible candidate for hypersonic aerospace applications owing to magnificent characteristics such as higher melting point temperature,...     

Influence of Sc and Zr additions on microstructure and properties evolution of Al–Zn–Mg alloy

Journal of Materials Science - In this study, the effects of different Sc?+?Zr compound addition on the tensile properties, impact toughness, stress corrosion cracking (SCC) properties,...     

Effect of pulsed current on the microstructure evolution of Cu–Sn intermetallic compounds

The dissolution behaviour between Cu and Sn during spark plasma sintering (SPS) was investigated with emphasis on the intrinsic effect of the applied pulsed current. Metallographic analyses revealed that the phase formation of Cu–Sn intermetallics was significantly influenced by the applied pulsed current as a series of phase evolutions along the sintering temperature occurred: Cu₆Sn₅?+?Sn?→?Cu₆Sn₅?+?Cu₃Sn?→?Cu₃Sn. The evolution of Cu–Sn intermetallic compounds (IMCs) was analysed by considering the accelerated atomic diffusion and the increased flux of Cu into the IMCs with a pulsed current, which can provide new insights into the basic understanding of the SPS process and promote the development of rapid forming process of IMCs joints for applications at higher temperatures.     

Influence of material and process parameters on microstructure evolution during the fabrication of carbon–carbon composites: a review

Journal of Materials Science - Carbon–carbon composites (CCCs) are a unique form of carbon fiber-reinforced materials that exhibit excellent thermomechanical properties under extreme...     

Effect of ZrB2 and Polyvinyl Butyral Content on the Oxidation Resistance of ZrB2–SiC Coatings Produced by Slurry Brushing Method

ZrB₂–SiC coatings are prepared on the surface of graphite by slurry brushing method to improve the oxidation resistance. Effects of ZrB₂ content and polyvinyl butyral (PVB)–ethanol solution concentration on microstructure and static oxidation behavior of the ZrB₂–SiC coatings are investigated at 1200 °C in air. The results indicate that increasing ZrB₂ content improves the oxidation resistance of the coatings. When ZrB₂ content increases from 30 to 45 wt%, weight loss rates of the coated samples after oxidation at 1200 °C for 120 min decrease from −0.92% to −1.67%. Increasing binder solution concentration raises component content in the coatings. As PVB–ethanol binder concentration increases from 0.025 to 0.075 g mL⁻¹, weight loss rates of the coated samples after oxidation at 1200 °C for 120 min decrease from 0.32% to −0.38%. Excellent oxidation resistance of ZrB₂–SiC coating is attributed to self-sealing ability of B₂O₃ and borosilicate glass. The composite glass can inhibit oxygen diffusion by filling defects in the coating promptly. The borosilicate glass phase can enhance the fluidity of the composite glass. ZrO₂ and ZrSiO₄ particles restrict the growth of the microcrack, which improves the oxidation resistance of ZrB₂–SiC coating.     

Influence of Al2O3/SiO2 ratio on the microstructure and properties of low temperature co-fired CaO–Al2O3–SiO2 based ceramics

In this work, in order to obtain the materials for low temperature co-fired ceramics applications, CaO–Al₂O₃–SiO₂ (CAS) based ceramics were synthesized at a low sintering temperature of 900 °C. The influences of Al₂O₃/SiO₂ ratio on the microstructure, mechanical, electrical and thermal properties were studied. According to the X-ray diffractomer and scanning electron microscopy results, the addition of the Al₂O₃ is advantageous for the formation of the desired materials. Anorthite(CaAl₂Si₂O₈) is the major crystal phase of the ceramics, and the SiO₂ phase is identified as the secondary crystal phase. No new crystal phase appears in the ceramics with the increasing Al₂O₃ content. More or less Al₂O₃ addition would all worsen the sintering, mechanical and dielectric properties of CAS based ceramics. The ceramic specimen (Al₂O₃/SiO₂ = 20/18.5) sintered at 900 °C shows good properties: high bending strength = 145 MPa, low dielectric constant = 5.8, low dielectric loss = 1.3 × 10^?3 and low coefficient of thermal expansion value = 5.3 × 10^?6 K^?1. The results indicate that the prepared CAS based ceramic is one of the candidates for low temperature co-fired ceramic applications.     

Experimental research of carbon fiber filament＇s fracture toughness based on focus iron beam

以商用碳纤维T300和T800为研究对象,采用聚焦粒子束（FIB）技术精确刻蚀了碳纤维单丝的缺陷,分析了碳纤维单丝的断裂性能。通过单丝拉伸试验获得碳纤维拉伸强度,并利用扫描电镜观察试件的断裂截面,基于镜像方法和Griffith断裂理论获得拉伸强度与镜像半径之间的关系,进而对碳纤维单丝的断裂韧性KⅠC进行了估算。结果表明：采用FIB刻蚀缺陷的方法估算得到的T300碳纤维单丝的KⅠC为1.32MPa.m1/2,与采用试剂溶解方法得到的数据（1.25MPa.m1/2）相比较,两者相差小于10%。     

Prediction of the temperature dependence of fracture toughness of 12Cr–2Ni–Mo refractory steel

We study the influence of temperature and the size of the specimens on the characteristics of static crack resistance of 12Cr–2Ni–Mo refractory steel. It is shown that, in the temperature range 20–450°C, the increase in the thickness of specimens leads to an insignificant increase in fracture toughness obtained along a 5% secant line according to the standards of evaluation of the characteristics of crack resistance. The evaluation of the characteristics of crack resistance of 12Cr–2Ni–Mo steel with regard for the scale effect according to an earlier developed numerical-experimental model reveals the existence of satisfactory agreement with the experimental data in the entire investigated temperature range. Translated from Problemy Prochnosti, No. 4, pp. 78–88, July–August, 2009.     

Influence of embedded gap and overlap fiber placement defects on the microstructure and shear and compression properties of carbon–epoxy laminates

This paper presents results from an experimental study of the influence of embedded defects created during automated fiber tape placement, on the mechanical properties of carbon/epoxy composites. Two stacking sequences have been examined, [(−45°/+45°)₃/−45°] and [90°₄/0°₃/90°₄], in which gaps and overlaps have been introduced during fiber placement. These materials have been cured in an autoclave either with or without a caul plate, then analyzed by ultrasonic C-scan. The microstructures were characterized by scanning electron microscopy. In-plane shear tests were performed on the ±45° laminates and showed that the use of a caul plate does not affect mechanical behavior of plies in the embedded defect region. Compression tests were performed on 0°/90° laminates and in this case the presence of a caul plate is critical during polymerization as it prevents thickness variations and allows defects to heal.     

Influence of sulphur on the microstructure and properties of Ag–Cu–Zn brazing filler metal

Abstract

The effect of sulphur on the microstructure and properties of Ag45–Cu30–Zn25 brazing filler metal was investigated. Under the given experimental conditions, the sulphuration products mainly consisted of CuS, ZnS, Ag₂S, Cu₂S and Ag₃CuS₂. These sulphides not only distributed on the surface but also diffused into the interior of the filler metal and cut apart the matrix thereby significantly damaging the tensile strength of the filler metal from 658 to 283 MPa. The corresponding fracture characterisation turned from ductile fracture to brittle fracture. The sulphides existed as solid particles, which hinder the spreading of the liquid filler metal and the spreading area dramatically decreased from 317?09 to 18?55 mm², which indicates that the filler metal rarely wets the base metal.