Microstructure, martensitic transformation and superelasticity of Ti49.6Ni45.1Cu5Cr0.3 shape memory alloy

The aim of this study is to investigate the microstructure, martensitic transformation behavior, shape memory effect and superelastic property of Ti_49.6Ni_45.1Cu₅Cr_0.3 alloy, with Cu and Cr substituting for Ni. After annealing, the alloy showed single step A-M/M-A transformations within the whole annealing temperature range of 623 K to 1273 K even in the presence and Ti₂(Ni, Cu) precipitates. With the increase of the annealing temperature, the transformation temperatures exhibited three stages: increasing from 623 K to 873 K, decreasing from 873 K to 1023 K and unchanging from 1023 K to 1273 K. Meanwhile, the critical stress for stress induced martensitic (SIM) transformation decreased to a minimum value and increased after that, exhibiting a V shape curve. The alloy annealed at 623, 773 and 923 K exhibited shape recovery ratio more than 90% when the deformation strain was below 20%.     

Vickers indentation tests in a Zr62.55Cu17.55Ni9.9Al10 bulk amorphous alloy

Vickers indentation tests were conducted on a Zr_62.55Cu_17.55Ni_9.9Al₁₀ bulk amorphous alloy to investigate the evolution of shear bands and its plastic deformation dimension via a bonded interface technique. Under all indentation loads, the plastic deformation is accommodated through semi-circular and radial shear bands. The plastic deformation dimension increases with increasing the indentation loads. A simplified λ = C(P)^0.5 model was put forward to predict and estimate the plastic deformation dimension characterized by shear bands in the subsurface. For the Zr_62.55Cu_17.55Ni_9.9Al₁₀ amorphous alloy, C is about 15.314 µm/N^0.5. The normalized shear band zone is independent to the indentation load.     

Preparation and characterization of Al18B4O33 + BaPbO3/Al hybrid composite

In this paper, the aluminum borate whisker (ABOw) and BaPbO₃ particles (BPOp)/Al hybrid composite with radiation protection function was fabricated by squeeze casting technique. The microstructure and properties of the hybrid composite were investigated. The test results show that BPOp and aluminum matrix have a reaction, and this reaction forms a coating on the surface of ABOw. The introduction of BPOp increases radiation protection function of the matrix evidently, at the same time, the hybrid composite has better mechanical properties compared with the aluminum matrix and ABOw/Al composite.     

Effects of surface modification of β-CaSiO3 on electrospun poly(butylene succinate)/β-CaSiO3 composite fibers

In this experiment, pure PBSU fibers, PBSU/12.5% β-CaSiO₃, and PBSU/25% β-CaSiO₃ composite fibers were fabricated by electrospinning. In order to investigate the effects of surface modification of β-CaSiO₃ on composite fibers, β-CaSiO₃ nanowires were surface esterified using dodecyl alcohol. SEM micrographs showed that composite materials with modified β-CaSiO₃ have homogeneous fibrous structures similar as that of pure PBSU fibers, while the fibers containing unmodified β-CaSiO₃ were inhomogeneous and much larger in diameter, and also junctions where β-CaSiO₃ agglomerated could be found. Mechanical testing showed that with the addition of unmodified β-CaSiO₃ into PBSU matrix, the tensile strength of fibrous materials decreased obviously, and the decrease degree increased with increased β-CaSiO₃ content. However, the tensile stresses of composite materials after surface modification of β-CaSiO₃ turned back and increased about 40% compared to those containing unmodified β-CaSiO₃. All of these results suggested surface modification of β-CaSiO₃ was an effective approach to obtain composite fibrous materials with better morphologies and enhanced mechanical properties, and this method is supposed to be feasible in other fibrous material systems.     

Whiskers of Al2O3 as reinforcement of a powder metallurgical 6061 aluminium matrix composite

An Al-Mg-Si alloy matrix composite reinforced with 10 vol.% of alumina whiskers (Al₂O₃w) has been processed by powder metallurgy and investigated. The Al₂O₃w were produced as single crystal c-axis alpha-alumina fibres at pre-pilot scale via vapour-liquid-solid (VLS) deposition in a cold-wall air-tight furnace with alumina linings. As far as we know, this is the first report of the utilization of whiskers of Al₂O₃ as reinforcing elements for Al alloys. Tensile tests have been performed on the composite at room and high temperatures. Results show that the AA6061 alloy reinforced with the as-produced Al₂O₃ whiskers has remarkably high mechanical properties at room temperature. This is attributed to the high quality of the Al₂O₃ single crystals and to the strong bonding attained between them and the 6061 alloy matrix.     

In situ Al3Ti and Al2O3 nanoparticles reinforced Al composites produced by friction stir processing in an Al-TiO2 system

Al and TiO₂ powders were selected to fabricate in situ Al composites via multiple pass friction stir processing (FSP) based on the thermodynamic analysis. The microstructural investigations indicated FSP would induce reaction between Al and TiO₂. Al₃Ti and Al₂O₃ particles were formed after 4 pass FSP with 100% overlapping. The in situ particles were about 80 nm in size at various FSP conditions, and ultrafine matrix grains 602 nm in size were obtained when water cooling was applied during FSP. Tensile tests indicated that the in situ nanocomposites exhibited pronounced work hardening behavior and a good combination of strength and ductility.     

Microstructure and mechanical properties of pulsed electric current sintered B4C-TiB2 composites

Monolithic B₄C, TiB₂ and B₄C-TiB₂ particulate composites were consolidated without sintering additives by means of pulsed electric current sintering in vacuum. Sintering studies on B₄C-TiB₂ composites were carried out to reveal the influence of the pressure loading cycle during pulsed electrical current sintering (PECS) on the removal of oxide impurities, i.e. boron oxide and titanium oxide, hereby influencing the densification behavior as well as microstructure evolvement. The critical temperature to evaporate the boron oxide impurities was determined to be 2000 °C. Fully dense B₄C-TiB₂ composites were achieved by PECS for 4 min at 2000 °C when applying the maximum external pressure of 60 MPa after volatilization of the oxide impurities, whereas a relative density of 95-97% was obtained when applying the external pressure below 2000 °C. Microstructural analysis showed that B₄C and TiB₂ grain growth was substantially suppressed due to the pinning effect of the secondary phase and the rapid sintering cycle, resulting in micrometer sized and homogeneous microstructures. Excellent properties were obtained for the 60 vol% TiB₂ composite, combining a Vickers hardness of 29 GPa, a fracture toughness of 4.5 MPa m^1/2 and a flexural strength of 867 MPa, as well as electrical conductivity of 3.39E+6 S/m.     

A novel method to control agglomeration of ultrafine YAl2 particles in YAl2p/MgLiAl composite

A MgLiAl matrix composite reinforced with modified ultrafine YAl₂ particles was developed by stirring casting, in which YAl₂ particles were modified by milling YAl₂ and Mg particles. The effects of milling on the microstructures of YAl₂ particles and the dispersity of YAl₂ particles in YAl₂-Mg mixture were investigated. The microstructures and mechanical properties of the composite were presented. The results show that, after mix milling, elemental magnesium exists around YAl₂ particles and YAl₂ particles distribute homogeneously in YAl₂-Mg mixture. YAl₂-Mg mix milling is greatly beneficial to control agglomeration of ultrafine YAl₂ reinforcement in matrix, and the reinforcement is uniformly distributed in the matrix. The tensile strength of the 5 vol.% YAl_2p/MgLiAl composite increases by 90% as compared to the matrix alloy, while the elongation is keep at 7%.     

Processing of Al/B4C composites by cross-roll accumulative roll bonding

In the present study, Al/B₄C composites were successfully produced in the form of sheets, through accumulative roll bonding (ARB) and cross-roll accumulative roll bonding (CRARB) processes. The CRARB process was performed in two steps. In the first step, the strips were roll-bonded with a draft percentage of 66% reduction, while in the second step the strips were roll-bonded with a draft percentage of 50%. The results indicated that the dispersion of the B₄C particles in the CRARB process is more homogeneous than the ARB process. In addition, the tensile strength of the CRARBed composite is higher than that of the ARBed composite.     

High-frequency induction soldering of magnesium alloy AZ31B using a Zn−Al filler metal

Magnesium alloy AZ31B plates were soldered by means of high-frequency induction soldering using a Zn−Al filler metal in argon gas shield condition. The interfacial microstructure and phase constitution of the soldered joint were investigated. The experimental results show that α-Mg solid solution and α-Mg + MgZn eutectoid structure were formed in soldering region. Moreover, the zinc solid solution and the aluminum solid solution in the original filler metal disappeared completely after the soldering process. Test results indicate that the shear strength of the soldered joint is 19 MPa. The fracture morphology of the soldered joint exhibits intergranular fracture mode and the crack originates from α-Mg + MgZn eutectoid structure.     

Effect of microstructure on cleavage resistance of high-strength quenched and tempered steels

The relationship between microstructure and cleavage resistance in quenched and tempered high-strength bainitic and martensitic steels is investigated by means of Charpy-V tests, uniaxial tensile test on unnotched specimens and electron back scattered diffraction (EBSD). Steels under investigation are low/medium carbon (C = 0.10-0.40%) steels with yield strength in the range YS = 500-1000 MPa.Results show that the tensile strength and the cleavage resistance of quenched and tempered (Q&T) steels appear to be controlled by different structural parameters and not, as in the case of polygonal ferritic steels, by the same structural unit. In particular, yield strength is controlled by the mean subgrain size, whereas the structural unit controlling the critical cleavage stress is the covariant (bainitic or martensitic) packet, whose size is slightly lower than the average unit crack path (UCP). The critical stage in the fracture process appears to be the propagation of a Griffith crack from one packet to another, and the resistance offered by high-angle boundaries is approximately the same as that of low-C steels with bainitic or polygonal ferrite microstructure.     

Al/SiC composite coatings of steels by thermal spraying

Thermal spraying has been used to coat carbon steels (F112) and austenitic stainless steels (AISI 304) with aluminium matrix composites. Mixtures of aluminium powder and SiC particles were used as spraying material. A sol-gel silica coating was laid on SiC particles to reduce the porosity of the composite coatings and to inhibit the formation of aluminium carbide. The sol-gel silica coating acts as an active barrier enhancing the wettability of the reinforcement by molten aluminium. Coatings with a reinforcement volume fraction up to 30 vol.% were obtained with porosities of about 1.0 vol.%. The incorporation of sol-gel silica coated SiC particles reduces the coefficient of thermal expansion of the composite coating and enhances its adhesion to the substrates more than when uncoated SiC particles were used.     

Tensile property and cold formability of a Mg96Zn2Y2 alloy sheet with a long-period ordered phase

The tensile property and cold formability of a Mg₉₆Zn₂Y₂ alloy sheet containing Mg-, long-period ordered (LPO)-, and Mg₃Zn₃Y₂-phases were investigated. The Mg₉₆Zn₂Y₂ alloy sheet exhibited a high yield stress of 320 MPa and elongations of 11% at room temperature and could be prepared by hot-rolling. After, annealing at 773 K for 0.6 ks, although the yield stress decreased to 200 MPa, elongation increased to 20%. Texture randomization due to re-crystallization of the Mg phase that occurred in the annealed Mg₉₆Zn₂Y₂ alloy sheet was confirmed by EBSD analysis. The formability of a Mg₉₆Zn₂Y₂ alloy sheet and an AZ31-O sheet was evaluated via a 90° V-bending test at room temperature. The annealed Mg₉₆Zn₂Y₂ alloy sheet could be bent without cracking with a minimum bending radius per thickness of R/t = 3.3, which is less than that of the as-rolled Mg₉₆Zn₂Y₂ alloy sheet and the AZ31-O sheet. This improvement in the cold formability of the Mg₉₆Zn₂Y₂ alloy sheet is considered due to an increase in randomness of the Mg phase that results from re-crystallization of the Mg phase.     

Formation of reactive layers in brazed Ti and Cu using a melt-spun Zr41.2Ti13.8Ni10.0Cu12.5Be22.5 alloy

Investigations on the microstructure of brazed Ti and Cu when using a Zr_41.2Ti_13.8Ni_10.0Cu_12.5Be_22.5 alloy revealed that mainly Ti-rich compounds were formed at the brazed joint after brazing at 790 °C for 10 min. However, detailed microstructural investigations revealed that the interfacial areas close to the Cu consisted of orthorhombic Cu₄Ti, orthorhombic Cu₃Ti, hexagonal Cu₂TiZr and tetragonal CuTi compounds. The formation of a Cu₂TiZr Laves phase at the interfacial areas close to the Cu possibly suppresses a diffusion of Cu into the central areas of the brazed joint due to its characteristics of a high solubility and high melting temperature.     

Co2SnO4/activated carbon composite electrode for supercapacitor

A new kind of Co₂SnO₄-based electrode materials for supercapacitor was synthesized by co-precipitation method. The microstructure and surface morphology of Co₂SnO₄ were characterized by X-ray diffraction and scanning electron microscopy, respectively. Cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy were employed for the determination of specific capacitance and the equivalent series resistance of Co₂SnO₄/activated carbon composite electrode in KCl solution. It was shown that the composite electrode with 25 wt% Co₂SnO₄ had excellent specific capacitance up to 285.3 F g⁻¹ at the current density of 5 mA cm⁻². In addition, the composite electrode exhibited excellent long-term stability and, after 1000 cycles, 70.6% of initial capacitance was retained. Regarding the low cost, easy preparation, steady performance and environment friendliness, Co₂SnO₄/activated carbon composite electrode could have potentially promising application for supercapacitor.     

Enhanced piezoelectric and mechanical properties of ZnO whiskers and Sb2O3 co-modified lead zirconate titanate composites

ZnO whiskers and Sb₂O₃ co-modified lead zirconate titanate (denoted as PZT/ZnO_w/Sb₂O₃) piezoelectric composites were fabricated using a solid state sintering technique. The characteristic diffraction peaks of the PZT perovskite and ZnO phases were identified from all the composites, suggesting the retention of these individual phases. The grain size of PZT was found to be reduced with Sb₂O₃ addition. A high relative density of 96.5%-99.1% was achieved in PZT co-doped with ZnO_w and Sb₂O₃. Both the piezoelectric and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites showed significant improvement over the monolithic PZT. The intrinsic effects of ZnO_w and Sb₂O₃ on the electrical and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites were discussed.     

Improving the strength and biocompatibility of porous titanium scaffolds by creating elongated pores coated with a bioactive, nanoporous TiO2 layer

This paper reports a novel way of improving the mechanical properties and biocompatibility of porous Ti scaffolds using a combination of the modified sponge replication method and anodization process. The use of a stretched polymeric sponge as a novel template allowed the creation of elongated pores in a porous Ti scaffold, which, accordingly, led to a high compressive strength of 24.2 ± 2.08 MPa at a porosity of approximately 70 vol%. Furthermore, the surfaces of the Ti walls were coated successfully with a bioactive nanoporous TiO₂ layer using the anodization process, which enhanced the biocompatibility remarkably, as assessed by the attachment of MC3T3-E1 cells.     

Ge2Sb2Te5 and PbZr0.30Ti0.70O3 composite films for application in phase change random access memory

The improvement in the phase change characteristics of Ge₂Sb₂Te₅ (GST) films for phase change random access memory (PCM) applications was investigated by doping the GST films with PbZr_0.30Ti_0.70O₃ (PZT) using cosputtering at room temperature. The doped films showed a retarded crystallization to a higher temperature and higher resistivity in the crystalline state compared to pure GST films. Phase separation has been observed in annealed GST-PZT films and the segregated domains exhibited relatively uniform size. The reduced reset voltage of GST-PZT based cell was due to the reduced programming volume by incorporating PZT into GST. This work clearly reveals the highly promising potential of GST-PZT composite films for application in PCM.     

Size controllable synthesis of ultrafine silver particles through a one-step reaction

A simple one-step reduction method was explored to synthesize silver particles of different size. During synthesis, Polyvinylpyrrolidone (PVP) and CH₂O were used as the protective agent and the reducing agent, respectively. It is found that the reaction parameters including the concentration of PVP and AgNO₃, the amount of ammonia and the reaction temperature has great influence on the size and uniformity of silver particles. By careful tuning the reaction parameters, mono-disperse silver particles with the size of 40-2000 nm can be obtained controllably. It is considered that there were two growth modes: diffusional growth and aggregation.     

Preparation process and properties of LiCoO2/PANI/dodecylbenzenesulfonate composite electrode materials

Composite materials that combine the lithium exchanging material LiCoO₂ and the conductive polymer poly(aniline) (PANI) have been investigated regarding their possible application to electrode materials of lithium batteries. Such composite materials have been prepared by means of polymerization of aniline in acidic suspensions of LiCoO₂ particles. PANI was synthesized by oxidative polymerization of aniline by ammonium persulfate in the presence of sodium dodecylbenzenesulfonate (SDBS) as a micellar template and dopant. The composite material consisted in LiCoO₂ particles dispersed in a continuous matrix of PANI. The ribbon-like morphology of the powdered material was distinctly different of the morphologies of the parent materials. The conductive material had conductivity close to that of PANI because the LiCoO₂ content of the composite material was low. The presence of the poorly conductive inorganic phase caused a significant loss of conductivity, showing that LiCoO₂ blocked electronic transfers between PANI crystallites. Ammonium persulfate caused the loss of lithium from LiCoO₂ when it was used at high concentration in the polymerization recipe. In this case a new phase made of Co₃O₄ formed by chemical decomposition of Li_xCoO₂. Thin films prepared from stable suspensions of composite materials in water show comparable electrical performance to that measured for bulk materials.