Search

The temporal evolution of microstructural features in metals and ceramics has been the subject of intense investigation over many years because deviations from normal grain growth behavior are ubiquitous and strongly dictate observed mechanical and magnetic properties. To distinguish among different grain growth scenarios, we examine the time evolution of the information content of both synthetic and experimental coarsening microstructures as quantified by both a computable information density (CID) and a spectral entropy along with selected metrics and measures of shared information and interaction strength. In these approaches, microstructural evolution is described in terms of two time series representations, namely: (1) strings and their compressed counterparts that reflect the information contained in the configuration of a system over time, and (2) the spectra of graph Laplacians that embody the information contained in a coarsening grain network. These approaches permit one to characterize dynamically evolving microstructures and to identify correlation times associated with different coarsening scenarios. Moreover, as the information content of a system is a proxy for the entropy, a thermodynamic description of grain growth is also described. [ABSTRACT FROM AUTHOR]

Abstract Electron beam melting (EBM) has been applied to fabricate a high Nb-TiAl alloy with a fully dense microstructure and good tensile properties at both room and high temperatures. The effects of preheating and melting parameters on melting, solidification, phase transformation and resulting microstructure formation in as-EBM high Nb-TiAl alloy were investigated by performing a design-of-experiments. Results show that the limited EBM processing window can be broadened to produce different characteristic microstructures ranging from nearly fully lamellar γ/α 2 to equiaxed γ grains. Such a broadened processing window has been achieved by using stronger preheating beam current. A numerical simulation was performed to understand temperature evolution at a fixed point of interest where electron beam passed several times with a certain line offset within one build layer. Both the preheating and melting stages were considered in the model. Modelling results show that a higher preheating beam current resulted in a longer hold time within the temperature range between 1300 and 1380 °C (i.e. single α-phase region). This helped to produce fine lamellar microstructure in the high Nb-TiAl alloy. Fundamental principles are thus proposed in terms of controlling microstructure formation and fabricating fully dense high Nb-TiAl alloy in as-EBM condition. Graphical abstract Unlabelled Image Highlights • A fundamental principle is proposed to control the microstructure of Nb-TiAl alloy in EBM with competitive tensile properties. [ABSTRACT FROM AUTHOR]

Oxygen and nitrogen have been both known to have a strong hardening effect on Ti and its alloys, while also imposing a serious embrittlement effect. In the present work, Ti samples with non-uniformly dispersed oxygen and nitrogen solid solutions were produced using high purity Ti via powder metallurgy (PM) methods. The experimental results suggested that, when the solutes are non-uniformly distributed, the high solute content region can serve as strengthening particles as that in metal matrix composites. In light of this, we propose a design of novel structure in high oxygen/nitrogen Ti materials to achieve both improved strengths and ductility. The highlight of the structure is a design of strain gradient at the matrix-particle interface, which can mitigate the strain compatibility that commonly reported in general MMCs as the crack initiator. Instead of using ceramics as reinforcements, here we propose to use the matrix phase itself that hardened by high oxygen/nitrogen solutes as reinforcing particles. [ABSTRACT FROM AUTHOR]

In this paper, we report that a selective laser melted (SLM) AlSi10Mg alloy has unique hierarchical microstructures. There are micro-sized Al grains and transgranular ultrafine cellular structures around primary Al, and the cell boundary is made up of alternate eutectic Si and eutectic Al phases. The SLM AlSi10Mg alloy has both high tensile strength and high strain-hardening capability, which are superior to Al-Si alloys fabricated by conventional powder metallurgy and cast methods. Post-tensile high-resolution microscopy analyses provide further evidence supporting Orowan looping as a strengthening mechanism of the SLM Al-Si alloy. [ABSTRACT FROM AUTHOR]

In the present work, we studied the effect of the aspect ratio of carbon nanotubes (CNTs) on strengthening aluminum metal matrix composites (Al MMCs). To this end, Al samples reinforced with CNTs of various aspect ratios were produced via three different powder metallurgy methods. Microstructural examination revealed that the CNTs were uniformly dispersed in the materials with a range of aspect ratios from 6.5 to 55. The tensile results showed that the CNTs exhibited a strong strengthening effect in the composites regardless of their aspect ratios. However, the post-loading examination and quantitative analysis indicated that there was a strengthening mechanism transition for CNTs, which was closely associated with the aspect ratio or length of CNTs. The origin of such transition was explored from the viewpoint of dislocation-CNTs interaction under loading. The findings may provide a new insight in understanding the strengthening behaviors of CNT-reinforced MMCs. [ABSTRACT FROM AUTHOR]

Dynamic recrystallization, grain refinement and strengthening mechanism were investigated in the ultrastrong and ductile α Ti-xSn alloy processed by spark plasma sintering (SPS) and hot extrusion. Compared with pure Ti, the yielding and ultimate tensile strength of Ti-xSn alloy were greatly increased by 140% (993.88 MPa) and 92% (1086.76 MPa). The alloyed solutes dragged nucleation and grains growth of the recrystallization process. The bimodal microstructure was occurred and the average grain size was refined with increasing the alloyed contents. The fraction of deformed strips was increased but the fraction of the recrystallized grains was decreased. Brittle Ti 3 Sn compound (∼100 μm) was formed in the high Sn content samples. The quantitative analysis of the relationship between the fraction of recrystallized grain, low angle grain boundary fraction, activation energy for grain growth and solid solute atoms indicated either a linear or parabolic relationship. Quantitative analysis of strengthening effects pointed out that solid-solution strengthening effect, strain hardening and boundary strengthening were the main contributors to the great strength enhancement. The toughening mechanism was discussed by the compatible uniform strain and postponed necking. Rapid cracks initiation and propagation after uniform strain led to gradual ductility sacrifice. The present work may provide a new understanding on the relationship among the mechanical properties, microstructure and processing of Ti alloy. [ABSTRACT FROM AUTHOR]

In the present work, we report a novel bimodal and multi-layered grain structure in pure titanium produced via powder metallurgy. It was found that the hot-extruded pure Ti consists of multiple grain layers, which exhibited substantially different mean grain sizes. The microstructural development during hot extrusion was then investigated for the pure Ti via an interrupted extrusion experiment. The influence of this unique structure on the mechanical properties of the material was also studied under uniaxial quasi-static tension. The experimental results showed that the samples with different arrangement of the grain layers exhibited very different mechanical behavior. Namely, with combining a small part of fine grain layers, the material showed significantly increased yield strength and slightly decreased uniform plastic strain. Yet, the elongation-to-failure was decreased markedly for the multilayered material. Postmortem examinations indicated that this may attribute to the absence of deformation twins in the fine grains that leads to formation of microvoids, which finally develop into large cracks. [ABSTRACT FROM AUTHOR]

Many studies have shown that carbon nanotubes (CNTs) have excellent strengthening effect as a reinforcement in pure aluminum (Al). However, it is unknown that whether such merit can be also achieved in strong Al alloys for achieving higher-strength Al matrix composites. In this study, CNTs were incorporated into pure Al and a high-strength Al alloy (AA5083) via the same powder metallurgy route. Results showed that during the dispersion stage, the high energy ball milling process caused different amounts of deformation to pure Al and AA5083, which led to a better dispersion state of CNTs in powders and composites of pure Al. Although the two composites had the same tensile strength coincidentally, the reinforcing effect of CNTs in pure Al composite was more than five folds larger than that in AA5083, suggesting a strong matrix effect on strengthening behavior of CNTs in Al matrix composites. The present finding may show significant guidance for the optimization of fabrication processes and development of high-performance CNTs/Al composites. [Display omitted] • Strengthening behavior of CNTs/pure Al and CNTs/AA5083 composites were compared. • The dispersion states of CNTs in the CNTs/pure Al and CNTs/AA5083 composites were compared especially. • The reinforcing efficiency of CNTs under poor dispersion state and fine dispersion state were discussed. [ABSTRACT FROM AUTHOR]

Zinc oxide aerogels possess significantly potential applications in gas sensors, photocatalysis, and photodetector. In this regard, monolithic zinc oxide aerogel was prepared successfully by using the dispersed inorganic sol-gel method (DIS method) combined with a furnace calcining in mixed atmosphere of 500°C. With subsequent thermal treatment in selected atmospheres and designed heating program, the aerogel is featured with high porosity, large specific area (177 m2 g−1) and narrow particle sizes distribution. The photoluminescence spectrum (PL) with no temperature dependent shifts of the maximum of the spectral PL intensity concerning the zinc oxide aerogel being investigated suggests that it is relative to the structural and optical properties. In summary, the attractive properties of the zinc oxide aerogel expound the potentially optical and optoelectronic applications of ZnO nanostructures. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectroscopy and accelerated immersion testing results indicate that a lower quench rate leads to lower exfoliation corrosion resistance in 7055 aluminium alloy. The mechanism was discussed based on the change in grain boundaries microstructure and microchemistry due to slow quenching. Because of the increase of Zn and Mg content, grain boundary particles in the slowly-quenched specimens are more electrochemically active and tend to accelerate corrosion despite their large size and spacing; moreover the wide precipitates free zones depleted of solutes near grain boundaries tend to be more active as well and accelerate corrosion along grain boundaries. [ABSTRACT FROM AUTHOR]

We utilize total-internal reflection to isolate the two-dimensional surface foam formed at the planar boundary of a three-dimensional sample. The resulting images of surface Plateau borders are consistent with Plateau's laws for a truly two-dimensional foam. Samples are allowed to coarsen into a self-similar scaling state where statistical distributions appear independent of time, except for an overall scale factor. There we find that statistical measures of side number distributions, size-topology correlations, and bubble shapes are all very similar to those for two-dimensional foams. However, the size number distribution is slightly broader, and the shapes are slightly more elongated. A more obvious difference is that T2 processes now include the creation of surface bubbles, due to rearrangement in the bulk, and von Neumann's law is dramatically violated for individual bubbles. But nevertheless, our most striking finding is that von Neumann's law appears to holds on average, namely, the average rate of area change for surface bubbles appears to be proportional to the number of sides minus six, but with individual bubbles showing a wide distribution of deviations from this average behavior. [ABSTRACT FROM AUTHOR]

Scanning electron microscopy was used to observe the microstructures of a cork wood. It showed that the wood consists of countless rectangular and honeycomb wood cells. The wall of each wood cell connects with adjacent wood cells at the middle of the cell wall. More careful observation showed that the walls of the wood cells are a kind of fibre reinforced biocomposite consisting of crystalline cellulose fibre layers and hydrocarbonated polymer matrix. The crystalline cellulose fibres in different fibre layers possess different directions, which compose a kind of fibre helicoidal microstructure. In the microstructure, the helicoidal angle is very large. The maximum pullout force of the fibre helicoidal microstructure, which is closely related to the fracture toughness of the wood, was theoretically and experimentally investigated and compared with that of the fibre parallel microstructure. It showed that the maximum pullout force of the fibre helicoidal microstructure is markedly greater than that of the fibre parallel microstructure and that the larger the helicoidal angle, the more the maximum pullout force will increase compared with that of the parallel microstructure. [ABSTRACT FROM AUTHOR]

Bone possesses excellent mechanical properties, which are closely related to its favorable microstructures optimized by nature through millions of years. In this work, a scanning electron microscope (SEM) was used to observe the microstructures of a shankbone. It showed that the bone is a kind of bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. The hydroxyapatite layers are further composed of long and thin hydroxyapatite sheets. The hydroxyapatite sheets in different hydroxyapatite layers distribute along different orientations, which composes a kind of intersectant microstructure. The maximum pullout force of the intersectant microstructure was investigated and compared with that of 0° microstructure with their representative models. The result indicated that the maximum pullout force of the intersectant microstructure is markedly larger than that of the 0° microstructure, which was experimentally verified. [ABSTRACT FROM AUTHOR]

Abstract: Scanning electron microscope (SEM) observation shows that Chamidae shell is a kind of bioceramic composite consisting of inorganic aragonite and organic protein materials. The inorganic aragonite distributes in the shell in the form of layers parallel with the surface of the shell. The observation also shows that the aragonite layers consist of numerous aragonite sheets. These aragonite sheets are of long and thin shape and perpendicular to the layers where they are located. More careful observation shows that the aragonite sheets in different aragonite layers possess different orientations, which compose a kind of the interlaced structure of the aragonite sheets. The maximum pullout force of the interlaced structure is investigated and compared with that of the parallel structure of the aragonite sheets based on their microstructural models. The result shows that the maximum pullout force of the interlaced structure is markedly larger than that of the parallel structure. A comparative experiment for the maximum pullout force of both the interlaced and the parallel structures is also conducted, which gives identical conclusion. [Copyright &y& Elsevier]

Abstract: The effect of 0.7at% boron on the phase transformation of Ti–46.5Al–8Nb during a range of different continuous cooling rates from the alpha single phase region has been investigated. In addition the microstructure of Ti–46.5Al–8Nb and Ti–46.5Al–8Nb–0.7B during water quenching at a range of different temperatures near the alpha transus temperature (T α) has been examined. It has been found that the trend of the variation of microstructures with different cooling rates is the same in the two alloys varying from massive gamma (γm) to lamellar, but boron addition increases the cooling rate to obtain these microstructures. During water quenching at different temperatures (T 1 ≅ T α, T 2 < T α, and T 3 ≪ T α) boron addition has a very strong effect on the trend of the variation of microstructures. [Copyright &y& Elsevier]

Abstract: The elegant microstructures of insect cuticle obtained through long-time evolution endow the cuticle with excellent mechanical properties. Scanning electron microscope (SEM) observation shows that the cuticle of Tumblebug (an insect) has a basic characteristic of laminated structure consisting of highly oriented chitin fibers and sclerotized protein matrixes. Compared with manmade advanced composites, it contains more detailed heterogeneous microstructures. The observation also shows that there are many tiny holes in the cuticle and fibers distribute continuously round the holes forming a kind of circumcolumnar layup. With the observed results, a kind of special composite laminate specimen with the circumcolumnar layup is designed and fabricated. Its rupture strength is tested and compared with that of the conventional one with the holes drilled. The comparison shows that the rupture strength of the former is obviously higher than that of the latter. The larger the hole, the larger increase in the rupture strength can be achieved. The experimental result is verified with the representative models of the circumcolumnar and drilling-hole layups. [Copyright &y& Elsevier]

Abstract: Insect cuticles as a natural biocomposite include many favorable microstructures which have been refined over centuries and endow the cuticles excellent mechanical and physical properties, such as light weight, high strength and toughness, etc. The various microstructures of a Scarabaei cuticle are investigated with a scanning electronic microscope and reported in this paper. It is found that the cuticle is a kind of fiber-reinforced biocomposite composed of chitin-fiber layers and sclerous protein matrixes. Different chitin-fiber layers have different orientations, composed of crossed and helicoidal structures at different location. In the helicoidal structure, each fiber layer rotates with an almost fixed angle against its neighboring layer. The maximum pullout energy of the helicoidal structure is analyzed based on the representative model of the structure. The result shows that the pullout energy of the helicoidal structure is markedly larger than that of the conventional 0°-structure. A biomimetic composite with the observed helicoidal structure is designed and fabricated. A comparative test shows that the fracture toughness of the biomimetic composite is markedly larger than that of the 0°-layer composite. [Copyright &y& Elsevier]

Most structural materials existing in nature take the form of a composite. After centuries of evolution, these materials have gained highly optimized microstructures and performance. In this work, a natural biocomposite, chafer cuticle, was observed with SEM, and it was found that the insect cuticle has a laminated structure with chitin fiber and protein matrix. Special helicoidal layups of chitin fibers were found with the chitin fiber being of nanometer scale. The relationship between the nanometer scale of the chitin fiber and the fracture strength of the cuticle was analyzed. The results show that the nanometer scale of the chitin fiber is profitable to maintain and improve the fracture strength of the biocomposite. [ABSTRACT FROM AUTHOR]

In this study, the microstructures of Rutelidae cuticle, a natural biocomposite, were observed with scanning electronic microscope (SEM). It was found that the insect cuticle has a laminated microstructure consisting of chitin fiber and protein matrix. There are particular spiry layups in the cuticle. The maximal pull-out force of the spiry layup is analyzed and compared with that of conventional 0°-layup based on their representative models. The result shows that the pull-out force of the spiry layup is markedly larger than that of the conventional 0°-layup. The corresponding experiment on the maximal pull-out forces of both spiry layup and the 0°-layup is conducted, and it shows that the maximal pull-out force of the spiry layup is markedly larger than that of the 0°-layup, which verifies and demonstrates the validity of the presented model. [Copyright &y& Elsevier]

Insect cuticle as a natural biocomposite includes many favored microstructures which have been refined over centuries and endow the cuticle eminent mechanical properties. This paper first studies the microstructures of chafer cuticle through SEM observations. Several peculiar fiber configurations and fiber-ply arrangements such as branched fiber, acanth-fiber and helicoid plies are observed. These microstructures are useful for man-made fiber-reinforced composites to improve their mechanical properties. Then, a special configuration of the branched fiber found in chafer cuticle is in details analyzed through a mechanical model and experimental verification. The pullout force of fibers as an index is firstly studied through parameter study. The factors, which can improve the pullout forces, are identified. Finally, the maximal pullout force of the branched fiber is experimentally tested and compared with that of plain straight fiber. It is proved that the maximal pullout force of branched fibers is obviously greater than that of the plain straight fibers. [Copyright &y& Elsevier]

The molluscan shell is a natural ceramic composite with excellent fracture strength and fracture toughness, which are attributed to their unique microstructures. SEM observation on Bivalva shell showed that the shell consists of laminated aragonites and organic layers. There are different shapes and arrangements of aragonites. The higher fracture roughness of this laminated microstructure is analyzed. The laminated microstructure of the shell is used for the biomimetic designs of the ceramic/polymer and ceramic/polymer/fiber composite. Comparison of test of the biomimetic ceramic composite with the original ceramic material shows that the fracture toughness of the biomimetically designed ceramic composite increases markedly than that of the original ceramic material. [Copyright &y& Elsevier]

The insect cuticle is a typical natural composite with excellent strength, stiffness, and fracture toughness. Scanning electron microscope observation of the microstructure of Hydrophilidae (an insect) cuticle showed several unique plies and structural characteristics, which may provide available information to the design of advanced composites. The microstructure found in the vicinity of pore canals in the insect cuticle was used for the design of the composite laminate with a hole. Compared with the composite laminate with a normally drilled hole, it was found that the strength of the specially designed composite laminate increases markedly, which is of important significance to the design of high-performance composites. [Copyright &y& Elsevier]

To better understand the structure-mechanical properties relation of additively manufactured Ti-6Al-4V (Ti64) alloys, a comparison study was performed on Ti64 alloys fabricated by powder-based selective laser melting (SLM) and sintering methods. It is found that the SLM Ti64 alloy has prior β grains filled with (lath α + needle α′) structure. While Ti64 alloys sintered over and below β → α transformation temperature have widmanstatten α + β and lamellar α + β structure, respectively. The SLM Ti64 alloy has higher strength and hardness than sintered alloys, but possesses similar Young's modulus to the spark plasma sintered alloy. The mechanisms leading to the different mechanical properties are discussed based on phase compositions and contents. The results suggest that SLM Ti64 alloys potentially have better mechanical performance compared with those fabricated by conventional sintering methods. Unlabelled Image • Ti64 alloys fabricated by selective laser melting exhibit lath α and needle α′. • Ti64 sintered above and below β transformation temperature have widmanstatten and lamellar-(α+β) structure, respectively. • SLM Ti64 alloys have higher strength and hardness but similar Young's modulus compared with SPS alloys. • High tensile strength in SLM Ti64 alloys is mainly contributed by needle α′. [ABSTRACT FROM AUTHOR]

The grain morphology and texture control in electron beam melted (EBM) Ti-47Al-8Nb γ-TiAl alloy is considered. The EBM process window to obtain a columnar lamellar colony (CLC) grain structure was defined following a critical assessment of thermal gradient and liquid-solid interface velocity by using numerical simulation. Experimentally, an epitaxial grain growth during solidification of Ti-47Al-8Nb has been realised by using the optimum EBM parameter sets. The length of the CLC grain structure reached up to ∼600 μm (compared to the powder layer thickness of 70 μm). The texture analysis and phase identification performed using electron backscatter diffraction (EBSD) provided important insights in understanding the solidification and phase transformation processes during the EBM fabrication. It was found that the solidification path for EBM high Nb-TiAl alloy involves the high-temperature α-phase field (i.e. L+β→α and α→α 2 +γ phase transformation processes). The epitaxial growth of prior β grains and the anchoring effect of residual B2-phase are very likely to be responsible for the formation of CLC microstructure. Image 1 • We provide a new method to overcome the difficulty of lamellar orientation control caused by the uncertain orientations of α phase generated from β→α solid phase transformation between adjacent layers during EBM. • With the tight control of both thermal gradient and velocity of solidification front, EBM of high Nb-TiAl alloy produced a highly columnar prior β grain structure within which the presence of γ/B2 lamellae and extended lamellar colonies along the Z-direction was found. • The length of the columnar lamellar colony structure reached up to ∼600 μm (compared to the powder layer thickness of 70 μm). [ABSTRACT FROM AUTHOR]

In this paper, MoS2 ultrathin nanosheets with high purity were successfully synthesized via a facile hydrothermal method. The microstructure and morphology of as-prepared MoS2 were characterized by High solution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), and Raman spectrum (RS). When evaluated as a lubricating additive for polyimide composites, the results of friction and wear test showed that PI-MoS2 composites exhibited outstanding friction-reducing and anti-wear properties. In particular, when the MoS2 content was 7wt.%., the friction coefficient and wear rate of corresponding composite decreased 29% and 88%, respectively. More importantly, the PI-7wt.%MoS2 composite still possessed low friction coefficient and wear rate under high load or sliding rate. This implied that MoS2 ultrathin nanosheets owned excellent self-lubricating property, and was a promising lubricating additive to enhance the tribological properties of polymer. [ABSTRACT FROM AUTHOR]

Ultrafine-grained Al-Mg-Si alloys with four different Mg/Si ratios (=0.75, 1.10, 1.48, and 1.94) were prepared by using extrusion and cold-drawing. The microstructural evolution during aging treatment was examined by using transmission electron microscopy. Hardness and electrical conductivity of the alloys were, respectively, measured before and after aging treatment. Experimental results showed that $$ \beta^{\prime\prime} $$ precipitates were dispersed within the grain interior in all the four aged alloys. Although the precipitate size was insensitive to the Mg/Si ratio, the precipitate number density as well as the inter-precipitate spacing was greatly dependent on the Mg/Si ratio. The optimized Mg/Si ratio within present work was 1.48, which led to the densest precipitation, and resulted in the highest hardness and simultaneously greatest conductivity. These findings are rationalized by considering the precipitation behaviors in the ultrafine-grained length scale and their effect on the hardness-conductivity relationship. A strengthening model was proposed for the ultrafine-grained Al-Mg-Si alloys, which accounted for the multiple contributions from grain size, dislocations, solid solution atoms, and precipitates to the hardness. The calculations were in good agreement with the experimental results. Similarly, the effect of multiple microstructural features on the electrical conductivity was also quantitatively described by adopting a model. The contribution of precipitation to both the hardness and conductivity is well demonstrated for the ultrafine-grained Al-Mg-Si alloys, which will be helpful for material design of advanced ultrafine-grained Al alloys with enhanced performance. [ABSTRACT FROM AUTHOR]

Transient liquid phase (TLP) diffusion bonding of a Ti 3 Al-based alloy and TiAl intermetallics was firstly conducted with Ti–15Cu–15Ni (wt%) interlayer. Ti 2 Al layer, α 2 -Ti 3 Al band, Ti-rich phase, Ti 2 Ni and Ti 2 Cu compounds were formed within the joint and the joint showed a low shear strength of 74–79 MPa. For the newly designed Ti–Zr–Cu–Ni–Co system filler alloy, the bonded joint mainly consisted of Ti-rich phase, Ti 2 Al layer, (Ti, Zr) 2 Al phase and (Ti, Zr) 3 Al dissolved with Cu, Ni and Co. The joints bonded at 1253 K for 600 s with a pressure of 2 MPa presented the maximum shear strength of 435 MPa at room temperature, and the strength of 234 MPa was maintained at 873 K. CuZr and Zr 2 Ni phases rather than Ti 2 Ni and Ti 2 Cu compounds were formed within the latter joint. The formation of the CuZr and Zr 2 Ni phases as well as the plastic α-Ti phase increased the joint ductility to a great extent. [ABSTRACT FROM AUTHOR]

A traditional Ti 13Zr 21Cu 9Ni (wt.%) filler metal was used to join Ti 3 Al-based alloy and TiAl intermetallics, and the joints brazed at 1213–1233 K for 600 s presented a shear strength of 113–149 MPa at room temperature. For the improvement of the joint strength a Ti Zr Cu Ni Co filler metal was designed. The shear strength of the joints brazed with the Ti Zr Cu Ni Co filler at 1283 K for 300 s reached 278 MPa, increased about 86.6% compared with the Ti Zr Cu Ni system filler. The overall hardness in the joint brazed with the Ti Zr Cu Ni Co filler was uniformly lower than the joint brazed with Ti Zr Cu Ni filler. The Ti 3 Al/TiAl joint brazed with Ti–Zr Cu Ni mainly consisted of Ti 2 Al, α 2 -Ti 3 Al and the residual filler metal of Ti(Cu, Al) 2 + CuZr. The phase sequence within the Ti 3 Al/TiAl joint brazed with Ti Zr Cu Ni Co filler from TiAl side to Ti 3 Al side can be described as the follows: TiAl substrate/Ti 2 Al +α 2 -Ti 3 Al/α 2 -Ti 3 Al + Ti-rich phase/residual filler metal/Ti-rich phase/Ti-rich phase + O-Ti 2 AlNb/Ti 3 Al substrate, and the fracture surface of the corresponding joint was characterized by Ti-rich phase, indicating that compared with the traditional Ti Zr Cu Ni filler the joint ductility was increased to a great extent. [ABSTRACT FROM AUTHOR]

7050 aluminium alloy metal matrix composites reinforced with different weight fractions of Al3Ti particles were fabricated using an in situ synthesis method and subsequent rolling, solution and aging treatment. The effects of Al3Ti particle content and particle size on the microstructures and mechanical properties of the composites were investigated by means of hardness measurements, optical microscopy and electron probe. We concluded that the grain size of the composites was smaller than that of the matrix alloy, and with an increase in the plastic deformation, the dispersion of particles was more uniform and fine. It was also found that the hardness of the composites increases with increasing weight fraction and decreasing particle size. By increasing the plastic deformation, the hardness of both the composites increased first and then decreased with the following deformation. In addition, the heat treatment contributed to the hardness. [ABSTRACT FROM AUTHOR]

Abstract: A Graceful Fig shell’ microstructures are observed with a scanning electronic microscope (SEM). It shows that the shell is a kind of natural hierarchical bioceramic composite. The shell is composed of parallel aragonite-layers and each aragonite layer consists of thin aragonite sheets. Furthermore, each thin aragonite sheet is composed of lesser nano-aragonite fibers. It is also found that the aragonite fibers in arbitrary two adjacent aragonite-layers compose a kind of intersectional microstructure. The maximum pullout energy of the intersectional microstructure is investigated and compared to that of conventional parallel microstructure. It shows that the maximum pullout energy of the intersectional microstructure is markedly larger than that of the parallel microstructure. The larger the intersectional angle of the intersectional microstructure is, the more the maximum pullout energy of the intersectional microstructure will increase, compared to that of the parallel microstructure, which is experimentally validated. [ABSTRACT FROM AUTHOR]

Abstract: Insect cuticle is a kind of natural biocomposite. There are many eximious microstructures in the cuticle which come through biologic evolution over many centuries and endow the cuticle with excellent mechanical properties. In this work, the microstructures of a Tumblebug cuticle are observed through a scanning electronic microscope (SEM). Several kinds of different fiber distributions and fiber shapes are found at the different locations of the cuticle, which may provide beneficial information to the design of high-performance synthetic composites. The maximum pullout energy of a kind of particular dendritic fibers found in the cuticle is investigated and compared with that of conventional straight fibers based on their pullout models. It indicates that the maximum pullout energy of the dendritic fiber is markedly larger than that of the conventional straight fiber, and that the more the branches of the dendritic fiber is, the more the maximum pullout energy of the dendritic fiber will increase compared to that of the conventional straight fiber, which is experimentally validated. [ABSTRACT FROM AUTHOR]

Abstract: Scanning electron microscope (SEM) observation shows that a shank bone is a kind of bioceramic composite consisting of inorganic hydroxyapatite and organic collagen protein. The hydroxyapatite possesses laminated microstructure and the each hydroxyapatite layer is composed of numerous long and thin hydroxyapatite sheets. The hydroxyapatite sheets in an arbitrary hydroxyapatite layer make an almost fixed angle with the hydroxyapatite sheets in their adjacent hydroxyapatite layers which compose a kind of particular screwy microstructure. The maximum pullout energy of the screwy microstructure, which is closely related to the fracture toughness of the bone, is theoretically investigated and compared with that of the parallel microstructure of the sheets. It shows that the maximum pullout energy of the screwy microstructure is markedly larger than that of the parallel microstructure, which is experimentally verified. [Copyright &y& Elsevier]

Aluminum composites reinforced with carbon-based nano-particles or fibers have been widely studied. Yet, the rate dependence of their properties has been barely reported. In the present study, CNTs-reinforced Al composites with CNTs of two aspect ratios were produced by different powder metallurgy methods, followed by spark plasma sintering and hot extrusion. The mechanical properties and the underlying mechanisms of CNTs-reinforced Al composites at various loading rates were studied, with the aim of exploring the role of CNTs on strengthening, esp. on rate-dependent properties. The mechanical experiments revealed that the addition of CNTs not only increased the strength but also the strain rate sensitivity in comparison with pure Al. It was found that, under dynamic loading, the materials showed an increased strength and elongation-to-failure simultaneously, due to improved strain hardening rates. A careful analysis suggested that the long-range back stress produced at the CNTs-Al interfaces and the geometrically necessary dislocations accumulated due to strain gradient along the interface, mainly contributed to the strain hardening of CNTs/Al composites. A novel microstructure-based model using microscopically non-uniform dispersion of CNTs was proposed to account for the mechanical properties with better prediction than the traditional models. The results might shed some light on understanding metal matrix composites reinforced with nano-particles or fibers. [ABSTRACT FROM AUTHOR]

We report the characterisation of microstructures and high-cycle-fatigue (HCF) properties of Type 304 stainless steel joints processed by brazing. Pure copper was applied as the filler metal for brazing at 1120 °C. A two-phase microstructure was obtained within the joint region: the star-shaped precipitates and copper matrix. The precipitates with an average size of 0.43 μm were rich in iron and chromium. A fixed orientation relationship was found between the precipitates and copper matrix. The joint exhibited much higher tensile strength and HCF life when compared to pure copper. The strength enhancement can be attributed to the presence of precipitates. Furthermore, the effect of joint interface roughness as well as defects was critically investigated. The joint interface roughness showed little influence on the HCF lives. Post-examinations revealed that fatigue crack initiation and propagation occurred entirely within the joint region, hence being consistent with the similar HCF lives regardless of the pre-defined interface roughness conditions. In addition, it was found that the HCF lives decreased exponentially with the increase of initial defect area. Fractography analysis revealed that fatigue striation spacings near the crack initiation zone increased with the increase of defect area, suggesting that the larger defects result in higher crack growth rate, hence shorten the overall fatigue life. [ABSTRACT FROM AUTHOR]

The elastic mechanical parameters of initial and pre-twisted copper wires were investigated with the aid of a self-developed micro-torsion tester. It was found that the apparent elastic shear modulus and the apparent Young tensile modulus of the copper wires decrease by 13.3 and 8.4% after pre-twist deformation, respectively. In addition, the indentation modulus also decreases as the deformation is increased. When the deformation is more than 30%, the indentation modulus of pre-twisted copper wires is smaller than that of initial copper wires. Microstructural analyses show that the elastic modulus decreases with the proportion of faults. [ABSTRACT FROM AUTHOR]

Abstract It is generally recognised that electron beam melted (EBM) Ti-6Al-4V alloys exhibit a microstructural gradient along the build direction, but there have been some inconsistent experimental observations and debate as to the origin and magnitude of this effect. Here we present an unambiguous evaluation of this microstructural gradient and associated mechanical property along the EBM build direction on purpose-built round bar RB samples with build height of 380 mm and rectangular plate RP samples with build height of 120 mm. Columnar prior β grain width was found to increase (from 86 ± 38 to 154 ± 56 µm in RB and from 79 ± 34 to 122 ± 56 µm in RP samples) with the build height and the similar increase was also observed for α lath width (from 0.58 ± 24 to 0.87 ± 33 µm in RB and from 1.50 ± 45 to 1.80 ± 49 µm in RP samples). These observations can be attributed to the thermal gradient in the powder bed that produced a cooling rate gradient along the build height. The measured α lath width variation along the build height followed a log-normal distribution. The graded microstructure resulted in a decrease in micro-hardness which correlated very well with the mean α lath width by following a Hall-Petch relation. [ABSTRACT FROM AUTHOR]

Abstract The influences of EBM processing and post-processing on microstructure, mechanical properties and cracking behaviour in a γ′ precipitation-strengthened nickel-base superalloy DZ125 are critically assessed. Results show that a solution treating and ageing (STA) is required to obtain γ′ precipitates with a cuboidal shape. The columnar grain width was found to gradually increase from the bottom to the top of the as-EBM sample having a total build height of 80 mm, whereas there was little gradient in γ′ size. The presence of EBM induced intergranular cracks can be closed by hot isostatic pressing (HIP), however reappearance of intergranular cracks with a much wider crack opening width was observed after STA treatment. EBM induced cracks are classified as liquid-state cracking, as the classic dendritic morphology were found on the cracked surfaces. The post-processing induced cracks can be attributed to the effect of γ′ dissolution and re-precipitation of fine γ′ during the cooling stage of solution treatment. The results suggest that HIP is not an effective approach in healing liquid-state cracks in EBM fabricated γ′ precipitation-strengthened superalloys. Graphical abstract Unlabelled Image Highlights • γ′ precipitation-strengthened Ni-base superalloys are gaining increasing attention for electron beam melting (EBM). • This work represents the first study to reveal the crack reappearance in hot-isostatic-pressing (HIP) post-processed EBM Ni-base superalloy. • EBM induced cracks are classified as liquid-state cracking. • The reappearance of such cracks after post-processing suggests that HIP is not an effective approach in healing liquid-state cracks. [ABSTRACT FROM AUTHOR]

Discusses the single-phase alpha-SiAION with elongated grains from Si3N4 powder for a broad range of compositions of practical interest. Concept of nucleation and growth for microstructure control; Slow transformation reaction; Correlation of fracture toughness with microstructure.

The effects of nickel (Ni) content on the mechanical properties and microstructure evolution in the weld metals of commercial K65 oil and gas pipeline steel were studied. Increase Ni content could significantly improve the strength and low temperature impact toughness (−40 °C and −60 °C) of the weld metal. The above influences of Ni were attributed to the formation of predominant acicular ferrite (AF), at the expense of grain boundary ferrite (GBF), ferrite side plates (FSP) and martensite/austenite (M/A) constituent in weld metal. EBSD results indicated that GBF keeps K-S or N-W relations only with the prior austensite grain that belongs to one side of the grain boundary and the variants belong to the same bain group which always forms low angle boundary. Moreover, the retained austenite as one part of M/A constituent was mainly found in the weld metal with lower Ni content. It indicated that the transformation process could be promoted more completely by the increase of Ni content. The mechanism of the toughness improvement brought by Ni increasing was ascribed to the relatively uniform transformation to final microstructure, which reduces the appearance of GBF and M/A constituents. [ABSTRACT FROM AUTHOR]

The microstructure control and refinement in length scale are pursued in the development of next generations of Pb-free solder alloys with high reliability in harsh environments. In the present work, the influences of nucleation undercooling, as brought by solder ball size, over the microstructure evolution and nanomechanical behavior in Sn-3.0Ag-0.5Cu (wt%) Pb-free solder alloys, have been quantitively investigated using Differential Scanning Calorimeter (DSC), Scanning Electron Microscopy (SEM) and nanoindentation. The results reveal that undercooling increases with the decrease of solder ball size. The frequency of interlaced grain microstructure was significantly increased in 200 μm balls, with a further increase of undercooling by ∼10 K. The volume fraction of primary β-Sn increased with larger undercooling, leading to microstructure refinement with a finer spacing of both β-Sn dendrite and eutectic Ag 3 Sn. The length scale of refinement is on the order of ∼2, as the solder ball size reduced from 650 μm to 200 μm. Nano-hardness and creep resistance increase with smaller ball size and larger undercooling. Nano-hardness values are relatively higher as more eutectic regions being measured due to the strengthening effect of finer and denser eutectic Ag 3 Sn, and also the refinement of interlaced β-Sn grains. The creep exponent is insensitive to the loading force or solder ball size. The variation of nanomechanical deformation behavior was reduced in the 200 μm balls, due to the substantial microstructure refinement, while the dominant creep mechanism stays as the dislocation climb for various solder ball sizes. • Sn3.0Ag0.5Cu ball solidification is nucleation controlled with size independency. • More hypo-eutectic and refined microstructure formed with larger undercooling. • Interlaced microstructure becomes more frequent via a deeper undercooling by 10 K. • The fine eutectic Ag 3 Sn enhances the nano-hardness and creep properties of solder. • Nanomechanical data variation was reduced with refined homogeneous microstructure. [ABSTRACT FROM AUTHOR]

Effect of coherent L1 2 nanoprecipitates on the tensile behavior of a novel-designed Al 0.2 CrFeCoNi 2 Cu 0.2 high-entropy alloy is investigated in this study. Different heat treatments after cold rolling were used to achieve the alloys with two different microstructures. One is composed of a fcc matrix and coherent L1 2 (Ni,Cu) 3 Al nanoprecipitates after annealing at 700 ° C for 20 h; the other owns a fcc single-phase structure after annealing at 800 °C for 1 h as reference. Furthermore, the two alloys have nearly identical average grain sizes (~4.5 µm), and thus the exclusive effect of L1 2 nanoprecipitates could be identified by directly comparing their tensile behaviors. It is shown that the presence of L1 2 nanoprecipitates results in increases of 259 MPa and 316 MPa in the yield strength and ultimate tensile strength, respectively, accompanied by the maintenance of a high elongation (30.4%). This excellent strengthening effect is explained by the interaction between dislocations and L1 2 nanoprecipitates during the tensile straining process. Dislocation shearing of the L1 2 nanoprecipitates, which is evidently observed and also verified by the yield strength increment calculation, leads to predominant planar dislocation glide and the formation of crystallographically aligned slip bands as the main deformation mechanism, eventually resulting in a considerable work-hardening capacity enhancement with almost none harm to the elongation. [ABSTRACT FROM AUTHOR]

Strengthening-toughening mechanism of powder metallurgy Ti-Si alloy was investigated by interrupted in-situ tensile tests. The fabricated Ti-Si alloy was strong and ductile. Slip band was blocked mainly by solutes and grain boundaries. Narrow deformed strips, aligned low angle grain boundaries and twin boundaries also played a positive role in this blockage. Cross-slip in the strain hardening stage lowered the difference value of ultimate tensile and yielding strength. Two-stage toughening mechanism was studied (necking onset was demarcation point). In the homogeneous deformation period before necking, strain compatibility was improved by the intergranular rotation (rotation axis along [0001], [-1100] and [-1102]), high-angle intragranular rotation, intergranular sliding and minor twinning deformation. In the heterogeneous deformation period after necking, microcracks initiation/coalescence was dragged by uniform stress distribution. Cracks propagation was also suppressed by dense grain boundaries and front plastic grains. The present comprehensive analysis of strength and toughness provided an in-depth understanding about the relationship among the processing, mechanical properties and microstructure of Ti alloy. [ABSTRACT FROM AUTHOR]

Powder metallurgy magnesium (Mg) composites reinforced with multi-walled carbon nanotubes (MWCNTs) were developed by an effective three-step process. CNTs were uniformly dispersed on the Mg powders surface without damaged structure. A large amount of twins appeared in the as-extruded CNT/Mg composites, and the basal texture was weakened comparing to as-extruded pure Mg, which played a positive role in the ambient tensile deformation. The elongation to failure of Mg composite with 0.08 wt% CNTs has increased greatly by 32%. [ABSTRACT FROM AUTHOR]

[Display omitted] • 450 °C very-high-cycle fatigue of Ti60 and effect of cyclic pre-strain. • S-N curve with duality characteristic. • Surface cracking mechanism competes with the subsurface one in the life regime of 107. • Local grain texture is important for the subsurface cracking at low stress. • Cyclic pre-strain increases the fatigue strength of ∼100 MPa, despite duality remains. High-cycle and very-high-cycle fatigue at 450 °C in near-α titanium with bi-modal microstructure are investigated. Stress-life duality appears with one data group spanning from 105 to 107 and the other from 107 to 109 cycles, characterized by surface and subsurface cracking, respectively. Misfit strain induced by the high misorientation of a particular primary α-grain relative to its surroundings, termed as local texture, promotes the subsurface fatigue-crack initiation. Fatigue strength increases up to 100 MPa owing to cyclic pre-strain at 450 °C, but the duality remains. Strain hardening by activation of prismatic slip is responsible for the improved fatigue strength. [ABSTRACT FROM AUTHOR]

• As-built samples have shown increased α-lath width along the build direction. • HIPing helped to remove the graded microstructure and increased α-lath width by 50%. • Graded microstructure in as-built samples led to graded cyclic softening behaviour. • As built samples from the bottom showed 38% lower plastic strain range than the top. • Application of HIPing reduced the graded cyclic deformation behaviour. Cyclic deformation and damage mechanisms in electron-beam-melted Ti-6Al-4V are investigated. As-built samples exhibit a graded microstructure over the height of 120 mm, with samples from the top having larger α-laths and higher plastic strain. After HIPing, the α-lath width is greater, with reduced grain misorientation, and lower microstructural and property gradients. In both conditions, the observed cyclic softening is dominated by a monotonic reduction in the friction stress and an increase in grain misorientation, suggesting the lath structure progressively fragments into smaller grains. As-built samples show typically lower fatigue life due to crack initiation from gas pores and lack-of-fusion defects. [ABSTRACT FROM AUTHOR]

Nanometer-sized grains (around 50–100 nm) were generated in the surface layer (0–30 μm) of an Mg–3Gd alloy by means of surface mechanical attrition treatment (SMAT) at room temperature. The deformation process and the formation mechanism of nano grains were investigated by using transmission electron microscopy. The results show that twinning dominates the initial stage of the plastic deformation when the dislocation slips are obstructed. And till all the coarse grains are divided into substructures by twin–twin interactions and twin-dislocation arrays intersections, dislocation slips and stacking faults begin to play an important role in impelling subgrains to nanograins by lattice rotating through dislocation arrays slipping. Dynamic rotation recrystallization is the primarily formation mechanism of the nanocrystalline of Mg–3Gd alloy by SMAT, which is distinct from the migration recrystallization normally observed in severe plastic deformation process. [ABSTRACT FROM AUTHOR]

Abstract: Gaomiaozi (GMZ) Bent has been recognized as the potential buffer/backfill material for construction of Chinese deep geological repository for disposal of high-level radioactive waste (HLW). For investigation of pressure and suction effects on the thermal volumetric behavior of the highly compacted GMZ01 Bent, a new suction-temperature controlled oedometer was developed. Several suction and pressure controlled cyclic heating and cooling tests have been performed on highly compacted GMZ01 Bent. Suctions ranging from 4 to 110MPa, temperatures from 25 to 80°C and vertical loads from 0.1 to 5MPa were applied. Results show that heating at constant suction and pressure induces either swelling or contraction. At high pressure and low suction, heating tends to induce contraction, while at low pressure and high suction, heating induces expansion. Thermal volumetric strain of GMZ01 Bent tested strongly depends on the overconsolidation ratio (OCR). Two opposite mechanisms are considered to explain the observed phenomena, that is, the volume increase induced by the thermal expansion of the mineralogical components and the adsorbed water and the double-layer thickness at the microstructure level, as well as the volume reduction caused by the macrostructural rearrangements. [Copyright &y& Elsevier]

Abstract: GMZ bentonite has been considered as a possible material for engineered barrier in the Chinese program of nuclear waste disposal at great depth. In the present work, the hydraulic conductivity of this bentonite was determined by simultaneous profile method. A specific infiltration cell equipped with five resistive relative humidity probes was designed for this purpose. The water retention properties were studied under both confined and unconfined conditions; the results show that at high suctions (>4 MPa) the water retention capacity is independent of the confining condition, and by contrast, at low suctions (<4 MPa) the confined condition resulted in significant low water retention. Furthermore, the microstructure was investigated at mercury intrusion porosimetry (MIP) and Environmental Scanning Electron Microscope (ESEM) in different states: on oven-dried powder, bentonite slurry, as-compacted and wetted samples. It has been observed that the soil powder is constituted of aggregates of various sizes; these aggregates are destroyed by full saturation at a water content equal to the liquid limit; compaction at the initial water content of 11–12% and a dry density of 1.7–1.75 Mg/m3 led to a microstructure characterized by a dense assembly of relatively well preserved aggregates; saturation of the compacted sample under constant volume condition defined a non-homogeneous microstructure with the presence of well preserved aggregates. This non-homogeneous microstructure would be due to the non uniform distribution of the generated swelling pressure within the soil sample upon wetting. The hydraulic conductivity determined has been found decreasing first and then increasing with suction decrease from the initial value of about 80 MPa to zero; the decrease can be attributed to the large pore clogging due to soft gel creation by exfoliation process, as observed at ESEM. [Copyright &y& Elsevier]

• The ambient texture was determined by the parent austenite texture and variant selection. • The major prior austenite texture were B {0 1 1}[2 1 1] and {0 1 1}[2 2 3]. • The ambient textures were promoted by strong Bain group and variant selection. • The austenite texture of Cu, Goss and S orientations were not found. The ambient textures and their evolutions in an 800 MPa grade hot rolled low carbon micro-alloyed complex steel were analyzed. The prior austenite were firstly reconstructed and subsequently, determined the prior austenite texture unambiguously and calculated the corresponding variant fractions. It was found that the ambient texture was concurrently determined by the parent austenite texture and variant selection during the following phase transformation. The major prior austenite texture were B {0 1 1}〈2 1 1〉 and {0 1 1}〈5 3 3〉. They primarily give rise to the ambient transformation γ texture of {1 1 1}〈 2 3 - 1 〉, {1 1 1}〈2 5 - 3〉 and {1 1 1}〈 1 - 2 - 3 〉 by the selection of B1 or B2 group and α texture of {0 0 1}[1 1 0] by the selection of B3 group. The austenite textures of {2 1 0}〈3 6 1〉, {6 3 1}〈3 5 3〉, {6 1 8}〈1 2 1〉, also contribute to the overall transformation texture by strong variant selection. However, the austenite texture of Cu {1 1 2}〈1 1 1〉, Goss {1 1 0}〈0 0 1〉, S {1 2 3}〈6 3 4〉 orientations that were commonly transformed in the previous researches were not found in this steel. [ABSTRACT FROM AUTHOR]

This article focuses on the influence of iron ion irradiation on the aqueous corrosion resistance of zircaloy-4. Materials irradiated with energetic particles respond by undergoing changes in the internal microstructures, phase distributions, dimensions, mechanical and corrosion properties. Heavy ions in the MeV energy range impart energy to the atoms of the target materials and produce a displacement cascade consisting of highly localized interstitials and vacancies. There is a growing interest in the effect of irradiation on the structure and the corrosion property of zirconium alloys in recent years.