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Abstract The fragmentation and interfacial stress transfer of Cu 75 Zr 25 amorphous films with varying film thickness (h) on polyimide substrates were systematically investigated by using uniaxial tensile testing, in combination with in situ optical microscope and atomic force microscope characterizations. It is revealed that the interfacial stress transfer length increases monotonically as h increases. The interfacial stress transfer mechanism changes from elastic-plastic to approximately linear elastic at a critical point of h = 250 nm. This is related to h -dependent deformation-induced devitrification (DID) near the interfaces that the thinner Cu-Zr amorphous films display more DID. This study elucidates for the first time the effect of DID on the interfacial stress transfer, which will be helpful to design the interface with desired property for nanotechnological applications. Highlights • Fragmentation and interfacial stress transfer of Cu-Zr amorphous films were studied. • Interfacial stress transfer length increases as film thickness increases. • Thinner Cu-Zr amorphous films display more deformation-induced devitrification. • A crystallization gradient is induced by deformation along the film growth direction. • Interfacial stress transfer changes from elastic-plastic to linear elastic. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium matrix composite reinforced by graphite particles was fabricated using stir casting with graphite particle size of 50μm and graphite particle volume fraction of 10%. The as-cast composite was extruded at 250°C, 300°C and 350°C with an extrusion ratio of 12:1. The experimental results reveal that the extrusion temperature plays an important role on the microstructures and damping capacities. The aspect ratio of graphite particles increases as the extrusion temperature rises. Extrusion at 300°C leads to the highest damping values in low strain region at room temperature. It also demonstrates the highest damping values at elevated temperatures when the strain is 4×10−5. In addition, there are two definite damping peaks in the damping-temperature curves which occur at about 150°C and 350°C, respectively. [Copyright &y& Elsevier]

Abstract: In the present study, AZ91 magnesium matrix composites reinforced with six volume fractions (0.5, 1, 1.5, 2, 3 and 5vol.%) of submicron-SiC particulates (0.2μm) were fabricated by stir casting. The as-cast ingots were forged at 420°C with 50% reduction, and then extruded at 370°C with the ratio of 16 at a constant ram speed of 15mm/s. The microstructure of the composites was investigated by optical microscopy, scanning electron microscope and X-ray diffractometer. Microstructure characterization of the composites showed relative uniform reinforcement distribution, significant grain refinement and presence of minimal porosity. The X-ray diffractometer analysis showed that a strong basal plane texture was formed in both AZ91 alloy and SiCp/AZ91 composites during extrusion and the addition of submicron-SiC particulates could weaken the basal plane texture. The presence of submicron-SiC particulates assisted in improving the thermal stability, micro-hardness, elastic modulus and 0.2% yield strength. Both of the 0.2% yield strength and ultimate tensile strength increased with the increasing of submicron-SiC particulate content, however, decreased as the SiC particulate content overrun 2vol.%. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) reinforced magnesium matrix composite prepared by an improved process was extruded at 350°C with an extrusion ratio of 20:1. Most CNTs were individually and uniformly dispersed in the as-cast and the as-extruded composites. Moreover, good interfacial bonding was achieved, and Raman spectroscopy showed that the damage to CNTs was insignificant. The addition of CNTs could weaken basal plane texture. Meanwhile, the CNTs evidently improved the ultimate tensile strength, yield strength and Young's modulus of the as-extruded composite. Pulling-out CNTs proved that the length of the CNTs was not large enough to be compatible with the high strength of the CNTs. Grain refinement, load transfer mechanism and Orowan strengthening mechanism play important roles on the increase of the yield strength. The composites fabricated by our process showed high strengthening efficiency of CNTs. [ABSTRACT FROM AUTHOR]

Highlights: [•] A special γ′ morphological instability in a new Ni–Cr–Co-based P/M superalloy was studied. [•] Three heat treatments were applied to the alloy and microstructures were observed. [•] Microstructure of the alloy was homogenized by sub-solvus solution heat treatment. [•] Sub-solvus solution heat treatment influences morphology of γ′ fan-type structures. [•] Sub-solvus solution heat treatment makes γ′ fan-type structures regular and stable. [ABSTRACT FROM AUTHOR]

Abstract: Ageing treatment at 200°C and 225°C for various periods of time was introduced to the Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt.%) alloy, the age-hardening behaviour and phase transformation were analysed systematically. The alloy aged at 225°C exhibits accelerated ageing progress compared with that aged at 200°C. The precipitation sequences of the alloy aged at both 200°C and 225°C are supersaturated solid solution (SSSS)→β′′ (D019)→β′ (bco). Stacking faults and 14H LPSO phase formed in the alloy over-aged at 200°C and 225°C, respectively. The equilibrium β phase precipitated at the grain boundaries with the formation of precipitate free zone (PFZ) at the peak-aged stage, after further ageing treatment, the β phase got coarsened, which was accompanied with the widening of the PFZ. [Copyright &y& Elsevier]

Abstract: Particulate reinforced magnesium matrix nanocomposites were fabricated by semisolid stirring assisted ultrasonic vibration. Compared with the as-cast AZ91 alloy, the grain size of matrix alloy in the SiCp/AZ91 nanocomposite stirring for 5min was significantly decreased due to the addition of SiC nanoparticles. SiC nanoparticles within the grains exhibited homogeneous distribution although some SiC clusters still existed along the grain boundaries in the SiCp/AZ91 nanocomposite stirring for 5min. With increasing the stirring time, agglomerates of SiC nanoparticles located along the grain boundaries increased. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite stirring for 5min were simultaneously improved compared with the as-cast AZ91 alloy. However, the ultimate tensile strength and elongation to fracture of the SiCp/AZ91 nanocomposite decreased with increasing the stirring time. [Copyright &y& Elsevier]

Abstract In this paper we investigated the viscosity and density of melts Fe 73.5 Cu 1 M 3 Si 13,5 B 9 where M = Nb, Mo, V, Cr. It is shown that the lowest viscosity and activation energy of viscous flow has a melt with Nb, whose atomic radius is the largest. It is shown that the free volume of the melt is higher during cooling compared to heating, and it indicates irreversible structural changes in the melt. The critical temperature T k = 1770 K is found, above which the activation energy of the viscous flow changes. Highlights • Relationship of melt viscosity with the size of embedded atoms. • The critical temperature of change in the activation energy of the viscous flow. • Temperature dependence of free volume during heating and cooling of the melt. [ABSTRACT FROM AUTHOR]

The (micron[m]+submicron[s]+nano[n]) SiC particles (SiCp) reinforced AZ31B magnesium matrix composites (AZ31B/SiCp/m + s + n composites) were fabricated by stirring casting technology followed by hot extrusion. This method has successfully solved the homodisperse problem of SiCp/m + s + n in the magnesium matrix composites. The influence of SiCp/m + s + n on the dynamic recrystallization (DRX) behavior of the magnesium matrix was investigated by researching the TEM microstructures of composites. The results indicated that the addition of SiCp/m + s + n was helpful to increase the ratio of DRXed nucleation and reduce the average grain size of matrix. The particle deformation zone (PDZ) can be formed in the vicinity of micron SiCp, while the region with high dislocation density can be created around submicron SiCp owing to pin dislocation and deformation mismatch between matrix and particles. These regions are ideal sites for the formation of recrystallization nucleus. Meanwhile, the addition of fine SiCp(nano and submicron) may delay or hinder the growth of matrix grain through the pinning effect on the grain boundaries during hot extrusion. The tensile test indicates that the strength of the AZ31B/SiCp/m + s + n composites has a significant improvement. Compared with the single sized or bimodal sized particles reinforced magnesium matrix composites, the tensile strength of the AZ31B/SiCp/m + s + n composites were highlighted. [ABSTRACT FROM AUTHOR]

The effect of fly ash cenospheres (FACs) on the electromagnetic interference (EMI) shielding effectiveness (SE) of the magnesium matrix was investigated. Raw FACs and FACs modified by Ca(OH) 2 were employed as reinforcements. The two kinds of FACs dispersed uniformly in the matrix. Most unmodified FACs were severely broken in the composites, but the majority of FACs kept complete integrated in the composites reinforced by modified FACs. In the range of the testing frequency, raw FACs did not evidently improve the EMI SE of matrix. However, the modified FACs with better ball structure improved the EMI SE of matrix to 75–90 dB. This improvement is attributed to the reflection loss occurred at the outer face (R), absorption at interior place (A) of the composites as well as multiple reflection (B) between different modified FACs. [ABSTRACT FROM AUTHOR]

A particulate reinforced magnesium matrix nanocomposite was subjected to multidirectional forging (MDF). The results showed that the microstructure of the nanocomposite mainly consisted of some large initial grains and fine recrystallized grains along initial grain boundaries after 1 MDF pass. With increasing the MDF passes, the degree of dynamic recrystallization increased and ultrafine grains with average size of about 20 nm were observed in the nanocomposites after 6 MDF passes. The distribution of SiC nanoparticles in the nanocomposite was homogeneous outside some SiC nanoparticle dense zones after different MDF passes. Compared with typical basal texture obtained for 1 MDF pass, the basal pole intensity decreased firstly for 3 MDF pass and then increased for 6 MDF passes. Both ultimate tensile strength and elongation to fracture of the nanocomposite were enhanced with increasing the MDF passes, while yield strength decreased after 3 MDF passes and then increased slightly after 6 MDF passes. [ABSTRACT FROM AUTHOR]

The present study dealt with the AZ91 alloy subjected to multidirectional forging (MDF) under decreasing temperature conditions with emphasizing on relationship between microstructures and mechanical properties generated by MDF. The obtained results showed that grains of the alloy were gradually refined while the amount of the second phase precipitated along the grain boundaries was increased with increasing the MDF passes and decreasing the MDF temperature. Compared with the as-cast alloy, yield strength, ultimate tensile strength and elongation of the AZ91 alloy after MDF under decreasing temperature conditions were simultaneously increased. As the numbers of MDF passes were gradually increased and the MDF temperature was gradually decreased, the yield strength was gradually decreased, suggesting that texture softening may overwhelm the strengthening due to the grain refinement as well as the homogeneous distribution of precipitates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Friction stir processing (FSP) was applied to Mg–Gd–Y–Zn–Zr casting. [•] The grain boundary Mg3RE and LPSO phases in the casting dissolved after FSP. [•] Fine grains with LPSO phase distributed only within the grains was achieved. [•] High mechanical properties were obtained in FSP Mg–Gd–Y–Zn–Zr. [ABSTRACT FROM AUTHOR]

Abstract: Fine-grained commercial pure Mg was prepared by equal channel angular pressing. Heat treatments were carried out on ECAP processed samples to modify the microstructures, such as the density of dislocation, grain size and grain boundary, and their effects on internal friction at room and elevated temperatures have been studied in detail by dynamic mechanical analyzer (DMA). The ECAP processed pure Mg shows a high value of strain independence of internal friction, which is reduced after heat treatment due to the decrease of mobile dislocations, while the strain dependent part obviously increases owing to the larger grain size. Three internal friction peaks are observed during the measurements of temperature dependence of internal friction. The low temperature peak around 100–200°C is considered to be caused by thermally activated grain boundary relaxation, and it is obviously broadened compared with a Debye peak for a single relaxation time. The changes of activation energy and relaxation time distribution of this peak with an increase in grain size were also studied. The other two peaks at the temperature range of 200–350°C are frequency independent and associated with some irreversible structural transformation, they are considered to be related to the recrystallization. [Copyright &y& Elsevier]

Abstract: SiCp/Mg–Zn–Ca composite fabricated by stir casting was extruded at three different temperatures. Firstly, hot extrusion significantly improved particle distribution and refined the grains of the matrix. Even, nano-grains were observed in the composite extruded at 250°C. Secondly, extrusion evidently refined the size of the second phases, but also changed the distribution of the second phases. Extrusion temperatures obviously affected the size and distribution of the second phases. Thirdly, the interface between SiCp and matrix was also modified by hot extrusion. Finally, all as-extruded composites possessed good mechanical properties. Below 150°C, the UTS was very high in the extruded composites, but their strengths decreased sharply above 150°C. [Copyright &y& Elsevier]

Abstract: Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr alloy sheets containing long period stacking ordered (LPSO) phase were prepared by hot rolling at 400°C with total reduction of 96%. Microstructure evolution of the sheets during hot rolling was investigated, and its influence on mechanical properties was discussed. Twinning occurred during the early stage of hot rolling, and disappeared after total reduction higher than 89%. Average grain size was gradually refined, microstructure became much more homogeneous and volume fraction of LPSO phase decreased with increasing rolling reduction. Furthermore, the type of LPSO phases far from and near the block shaped phases were identified to be different. Basal texture was obtained during rolling process, but the intensity declined with the further rolling, which is mainly due to the dynamic recrystallization and the addition of RE elements. The as-rolled sheet with 96% reduction shows excellent mechanical properties: yield strength of 318MPa, ultimate tensile strength of 403MPa and elongation to failure of 13.7% at ambient temperature along the rolling direction. [Copyright &y& Elsevier]

Abstract: Particulate reinforced magnesium matrix nanocomposite prepared with semisolid stirring assisted ultrasonic vibration was subjected to extrusion at 350°C with an extrusion ratio of 12:1. Extrusion of the SiCp/AZ91 nanocomposite induced large scale dynamic recrystallization resulting in a fine matrix microstructure. There were two kinds of zones in the extruded nanocomposite: SiC nanoparticle bands parallel to the extrusion direction and refined-grain zones between the SiC nanoparticle bands. In the SiC nanoparticle bands, there were SiC nanoparticles along the boundaries of refined grains. The distribution of SiC nanoparticles was uniform although some agglomerates of SiC nanoparticles still existed in the SiC nanoparticle bands. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite were simultaneously improved by extrusion. Results from the extruded SiCp/AZ91 nanocomposite tensile testing at different temperatures (75, 125, 175 and 225°C) revealed an increase of the tensile strength and ductility values compared with the unreinforced and extruded AZ91 alloy. [Copyright &y& Elsevier]

Abstract: Microstructure and texture development of the equal channel angular pressed (ECAP) pure Mg with different rotation routes of A, Bc and C were investigated and related to the tensile mechanical property. Results showed that grain size was greatly decreased after 1 pass but varied with processing routes after the following ECAP. Due to a relatively high processing temperature, the refinement degree was limited via these three routes processing. Different preferred orientations of the basal plane were formed with three routes processing and there existed a rotation angle in (0002) pole figure from normal direction to transverse direction. Negative slope of the yield stress versus d−1/2 was obtained with routes Bc processing, which was attributed to the texture modification. Texture strengthening greatly increased the 0.2% yield strength, but decreased the ductility. [Copyright &y& Elsevier]