Fracture characteristic of a (Si–Al–O–N)–SiC composite studied by transmission electron microscopy

The microstructure and fracture characteristic of a pressureless-sintered (Si–Al–O–N)–6 wt% SiC composite have been investigated by a combination of transmission electron microscopy and microindentation fracture technique. SiC particles of nanometre size were dispersed in Si–Al–O–N grains and, at grain boundaries, were associated with strong strain fields. Si–Al–O–N grain boundaries were formed with an amorphous layer about 2 nm thick. However, interfaces between Si–Al–O–N and SiC embedded in the Si–Al–O–N grains were directly joined without any amorphous layer. The main fracture mode was an intergranular type, but some transgranular fracture by the dispersion of nanometre-sized SiC in the Si–Al–O–N grains are also observed at the crack wake zone. The fracture toughening mechanisms of crack deflection, bridging and microcracking were not observed in the (Si–Al–O–N)–6 wt% SiC nanocomposite system.     

The study of metal ion release and cytotoxicity in Co–Cr–Mo and Ti–Al–V alloy in total knee prosthesis – scanning electron microscopic observation

We surgically retrieved two cobalt(Co)–chromium(Cr)–molybdenum(Mo) and five titanium(Ti)–aluminum(Al)–vanadium(V) alloy knee prostheses from patients because of mechanical failure and pain. We examined the distribution of the small particles which were released from the Co–Cr–Mo and Ti–Al–V alloys using a backscattered scanning electron microscopy (SEM). In addition we analyzed the metals in the artificial knee joints and the tissues adjacent to them using energy dispersive X-ray spectroscopy (EDS). We demonstrated that a myriad of fine particles, produced by the abrasion of both Co–Cr–Mo and Ti–Al–V alloys, accumulated in the synovial cells. As Co–Cr–Mo alloys disintegrate easily in the cells, Co dissolves from the peripheral areas of them, although Cr remains within the cells. In contrast Ti–Al–V alloys are very stable in the synovial cells. From these findings we conclude that the Co–Cr–Mo alloys are hazardous to the body as the alloys release Co which enters the body. In contrast the Ti–Al–V alloys are very stable and are patently safer. Artificial joints, however, are still in considerable need of improvement.     

Internal stress and adhesion of amorphous Ni–Cu–P alloy on aluminum

This study investigated the effect of saccharin on the internal stress and the adhesion of amorphous Ni–Cu–P deposited on aluminum. An amorphous Ni–Cu–P deposit with slight compressive stress can be produced when one adds 8–10 g/l saccharin into the Ni–Cu–P deposition solution. The stress relief mechanism was investigated. The addition of saccharin restrains the coalescence of the islands within Ni–Cu–P nodules and reverses the internal stress of the electroless Ni–Cu–P deposit from tensile to compressive. The adhesion strength of the Si/Ti/Al/Ni–Cu–P multilayer specimen obtained with 10 g/l saccharin is around 35 to 45 MPa, and the fracture occurs at the silicon substrate after the pull test. The shear strength of the Ti/Al/Ni–Cu–P bump (100×100 μm) on Si is 132.9±12.7 g, and the fracture occurs at the Ni–Cu–P deposit after the shear test. Moreover, the inhibition of coalescence of the fine islands within Ni–Cu–P nodules increases the brightness and the hardness of the deposit.     

Condensation of Self–Trapped Charge–Transfer Excitations and Interplay between Quantum and Thermal Effects at the Neutral–to–Ionic Transition

The cooperativity between self–trapped electronic excitations is carried to extreme in the case of the neutral–to–ionic phase transition which is observed in some organic mixed–stack charge–transfer crystals. This electronic–structural phase transition manifests itself by a change of the degree of charge–transfer and a dimerization distorsion along the stacking axis in the ionic phase. Thermal charge–transfer excitations associated with the formation of structurally relaxed ionic strings along neutral chains are at the heart of mechanism of this uncommon phase transition. Symmetry and thermodynamics analysis of the neutral–to–ionic transition in the prototype compound, tetrathiafulvalene–p–chloranil, in particular the recent determination of the pressure–temperature phase diagram, make possible to present a consistent picture of this phase transition. Supported by a phenomenological approach, taking into account the quasi–one–dimensional nature of the system and the interplay between quantum and thermal effects, the experimental results show that the neutral–to–ionic transition results from the condensation and the ordering (crystallization) of charge–transfer excitations, following a phase diagram analogous to the solid–liquid–gas one.     

Corrosion behavior of Al–Si–Cu–(Sn, Zn) brazing filler metals

The corrosion behavior of Al–Si–Cu–(Sn, Zn) filler metals in a 3.5% NaCl aqueous solution were studied using electrochemical tests. The results showed that the addition of Sn or Zn to the Al–Si–Cu filler metal raised its corrosion current density sharply and caused its corrosion potential to become more active. Sn or Zn elements exert harmful effects on such low-melting-point brazing filler metals in that the corrosion resistance is degenerated, and damage is accelerated with an increase in the Sn or Zn content. Scanning electron microscopy (SEM) micrographs of the corroded surfaces of these Al–Si–Cu–(Sn, Zn) filler metals indicate that the Al-rich phase (i.e., Al–Si, Al–Si–Cu, and Al–Si–Cu–Sn eutectic phases) dissolves preferentially, while the Si particles and CuAl₂(θ) intermetallic compounds remain intact.     

Joining of zirconia to metal with Cu–Ga–Ti and Cu–Sn–Pb–Ti fillers

The method of brazing by capillary impregnation of Cu–Ga melt through a titanium powder layer situated between brazed details is elaborated. Samples of ZrO₂ ceramic/metal brazed joints using Cu–Ga–Ti filler and Cu–Sn–Pb–Ti filler were fabricated. The joints’ shear strength was 277±37 MPa for the Cu–Ga–Ti and 156±25 MPa for the Cu–Sn–Pb–Ti.     

Crystal chemistry and Calphad modeling of the σ phase

A systematic review of the crystal chemical properties of the σ phase is presented, with special emphasis on the atomic order, i.e. the distribution of the atoms on the different sites of the crystal structure. The data available in the literature have been systematically assessed, and are complemented by an experimental investigation in the following systems: Al–Nb, Al–Ta, Cr–Mn, Cr–Os, Cr–Re, Cr–Ru, Co–Mo, Fe–Mo, Fe–Re, Mn–Mo, Mn–Re, Mn–V, Mo–Re, Nb–Pt, Nb–Re, Ni–V, Pd–Ta, Re–V, Rh–Ta and Ru–W. The properties are analyzed as a function of composition and the nature and atomic size of the elements involved. The possibility of an order–disorder transition has also been reviewed and completed by diffraction experiments in two systems (Cr–Mn and Ni–V). First-principles calculations on the σ phase are reviewed in line with the Calphad approach. An analysis of the literature data concerning the Calphad modeling of systems involving the σ phase has been made. The different models used are presented and discussed. The conclusions of crystal structure data analysis are used to make some recommendations about the choice of a model in the frame of a Calphad assessment.     

Amorphization of eutectic alloys by shock compression

The eutectic alloys Au–Si, Au–Ge, Al–Si and Al–Ge, known to be highly brittle under normal compression, were subjected to high-speed shock compression in order to induce amorphization. Plastic deformation was easily achieved in Au–Si, Al–Si and Al–Ge, yielding thin foils of these alloys. However, an amorphous phase was confirmed only in the case of Au–Si. Furthermore, a superstructure was observed in various locations in the Au–Si thin foil. Au–Ge was pulverized upon shock compression.     

Bending property and phase transformation of Ti–Ni–Cu alloy dental castings for orthodontic application

Bending property of Ti–Ni–Cu alloy castings was investigated in a three-point bending test for orthodontic application in relation to the phase transformation. The compositions of the alloys were Ti–50.8Ni and Ti–40.8Ni–10.0Cu (mol %), and four cross-sectional shapes of the specimens were selected. Heat treatment was performed at 713, 753 or 793 K for 1.8 ks. The bending load changed by the cross-sectional size and shape mainly because of the difference in the moment of inertia of area, but the load–deflection relation did not differ proportionally in the unloading process. The difference between the load values in the loading and the unloading processes was relatively small for Ti–Ni–Cu alloy. With respect to the residual deflection, there was no significant difference between Ti–Ni and Ti–Ni–Cu alloys with the same treatment condition. The load values in the loading and the unloading processes decreased by each heat treatment for Ti–Ni alloy; however, the decrease in the load values for Ti–Ni–Cu alloy was not distinct. It is proved that Ti–Ni–Cu alloy castings produce effective orthodontic force as well as stable low residual deflection, which is likely to be caused by the high and sharp thermal peaks during phase transformation.     

Photo-stabilization properties of transparent inorganic UV-filter/epoxy nanocomposites

Transparent inorganic UV-filter/epoxy nanocomposites with high photo-stabilization properties were reported in this paper. First, inorganic UV-filter ZnO, core-shell structural silica–titania (S–T) and silica–titania–silica (S–T–S) nanoparticles were synthesized. Transparent inorganic UV-filter/epoxy (ZnO/epoxy, S–T/epoxy and S–T–S/epoxy) nanocomposites were subsequently prepared from the transparent epoxy and the as-prepared nanoparticles via in situ polymerization method. Optical properties of inorganic UV-filter/epoxy nanocomposites, namely visible light transparency and UV-light shielding efficiency, were studied using an UV–Vis spectrophotometer. The photo-stabilization properties of inorganic UV-filter/epoxy nanocomposites were examined by the light-emitting diode (LED) lifetime test. The results showed that the photo-stabilization effect of inorganic UV-filter on the lifetime of LED lamp obeys the following sequence: ZnO > S–T–S > S–T. Compared with the UV LED lamps encapsulated with pure epoxy, the lifetime of UV LED lamps encapsulated with ZnO/epoxy, S–T–S/epoxy and S–T/epoxy nanocomposites has been improved by 76%, 54% and 33%, respectively.     

Creep behavior of Ti3Al–Nb intermetallic alloys

It is well known that Ti₃Al–Nb alloys are potential materials for aerospace applications. The creep property is an important consideration when materials are used at high temperature. In this article, the effect of microstructure of Ti–25Al–10Nb alloy on the creep property was investigated, and the creep property of Ti–25Al–10Nb alloy modified by small addition of silicon (0.2 at.%) or carbon (0.1 at.%) was observed. The alloy with the addition of molybdenum to replace part of niobium (2 at.%) was also studied. The experimental results show that the furnace-cooled Ti–25Al–10Nb alloy has superior creep resistance to the air-cooled Ti–25Al–10Nb alloy at 200 MPa, but exhibits poor creep resistance at 250 MPa or above. Small addition of silicon to the Ti–25Al–10Nb alloy may increase creep resistance. Small addition of carbon to the Ti–25Al–10Nb alloy may reduce creep resistance but raise rupture strain. Molybdenum is the most effective alloying element to increase creep resistance for the Ti–25Al–10Nb alloy. The creep mechanism of Ti–25Al–10Nb alloy is governed by dislocation climb.     

Composition, Microstructure, and Superconducting and Ferroelectric Properties of Bi–Sr–Ca–Cu–O/Pb–Ti–Zr–O Heterostructures

Ferroelectric–superconductor heterostructures consisting of a ferroelectric Pb–Ti–Zr–O film on a superconducting Bi–Sr–Ca–Cu–O ceramic substrate or a superconducting Bi–Sr–Ca–Cu–O film on a ferroelectric Pb–Ti–Zr–O ceramic substrate with Ag, Au, Pd, and Pt barrier layers are prepared and investigated. Thin-film Bi₂Sr₂CaCu₂O_{8 + x} /ZrO₂/Pb(Ti_0.6Zr_0.4)O₃ (superconductor/barrier/ferroelectric) heterostructures on LaAlO₃ substrates are for the first time produced and characterized. The superconducting and ferroelectric transition temperatures in the heterostructures are 80 and 638 K, respectively.     

Viscosities of Multicomponent Silicate Melts at High Temperatures

In the present work; the viscosities in the quaternaries CaO–Fe _n O–MgO–SiO₂, Fe _n O-MgO–MnO–SiO₂, and CaO–MgO–MnO–SiO₂ and the quinary CaO–Fe _n O–MgO–MnO–SiO₂ were studied. The experimental technique employed was the well-established rotating cylinder method, using a Brookfield digital viscometer mounted over a specially designed graphite furnace. Generally, iron crucibles were used along with iron spindles. Periodic calibrations of the experimental setup were made using the standard reference slag recommended by the European Union. The measurement's were carried out up to a maximum temperature of 1773 K in all cases. The reliability of the measurements were checked at different rotation speeds as well as during thermal cycling, and excellent reproducibility of the results was noted. The experimental viscosity values were incorporated into a viscosity model. Equations based on the model for calculating the viscosities of the quarternary systems CaO–Fe _n O–MgO–SiO₂, Fe _n O–MgO–MnO–SiO₂, and CaO–MgO–MnO–SiO₂ and the quinary system CaO–Fe _n O–MgO–MnO–SiO₂ are provided.     

Creep-resistant porous structures based on stereo-complex forming triblock copolymers of 1,3-trimethylene carbonate and lactides

Stereo-complexes (poly(ST–TMC–ST)) of enantiomeric triblock copolymers based on 1,3-trimethylene carbonate (TMC) and L- or D-lactide (poly(LLA–TMC–LLA) and poly(DLA–TMC–DLA)) were prepared. Films of poly(ST–TMC–ST) could be prepared by solvent casting mixtures of equal amounts of poly(LLA–TMC–LLA) and poly(DLA–TMC–DLA) solutions and by compression moulding co-precipitates. Although compression moulding was performed at 191 °C, thermal degradation was not apparent and materials with good tensile properties could be obtained. For compression-moulded poly(ST–TMC–ST) specimens containing approximately 16 mol % lactide, the values for E-modulus, yield stress and elongation at break were respectively 17, 1.7 MPa and 90%. Also a very low long-term creep rate of 2.2×10^–7 s^–1 was determined when specimens were loaded to 20% of the yield stress. When compared with compression-moulded poly(TMC), poly(ST–TMC–ST) specimens deform at a rate that is one to two orders of magnitude lower. Furthermore, poly(ST–TMC–ST) specimens showed complete dimensional recovery within 24 h after loading to 20% and 40% of the yield stress for 40 and 5.5 h, respectively. Highly porous poly(TMC) and poly(ST–TMC–ST) structures with interconnected pores were prepared by a method combining co-precipitation, compression moulding and salt leaching. After prolonged compressive deformation, solid and porous poly(ST–TMC–ST) discs showed significantly better recovery behaviour than poly(TMC) discs.     

Hypervelocity impact damage to Ti–6Al–4V meshes reinforced Al–6Mg alloy matrix composites

An Al–6Mg alloy matrix composite reinforced with Ti–6Al–4V meshes was fabricated by pressure infiltration method; its damage behaviors impacted by hypervelocity aluminum projectiles were investigated. Results showed that the thin Ti_f/Al–6Mg composite target exhibits better protection efficiency and energy absorption ability than Al–6Mg alloy target. With projectile sizes increasing, bulge and spallation were observed on the back of the composite target. The Ti–6Al–4V meshes were tensed and deformed drastically in the spallation region, where micro-damages such as interfacial debonding and cracks were dominant. Shear localization was the primary failure characteristic for thin Al–6Mg alloy target. The adiabatic shear bands were observed near the crater of Al–6Mg alloy, not in Ti_f/Al–6Mg composite target. It was ascribed to the Ti–Al interfacial bonding strength and the high temperature strength for Ti–6Al–4V alloy.     

Long crack growth behavior of implant material Ti–5Al–2.5Fe in air and simulated body environment related to microstructure

The fatigue crack propagation behavior of Ti–5Al–2.5Fe with various microstructures for biomedical applications was investigated in air and in a simulated body environment, Ringer's solution, in comparison with that of Ti–6Al–4V ELI and that of SUS 316L stainless steel. The crack propagation rate, da/dN, of Ti–5Al–2.5Fe in the case of each microstructure is greater than that of the Widmanstätten structure in Ti–6Al–4V ELI in air whereas da/dN of Ti–5Al–2.5Fe is nearly equal to that of the equiaxed structure in Ti–6Al–4V ELI in air when da/dN is plotted versus the nominal cyclic stress intensity factor range, ΔK. da/dN of the equiaxed structure and that of the Widmanstätten structure in Ti–5Al–2.5Fe are nearly the same in air when da/dN is plotted versus ΔK. da/dN of Ti–5Al–2.5Fe is nearly equal to that of SUS 316L stainless steel in the Paris Law region, whereas da/dN of Ti–5Al–2.5Fe is greater than that of SUS 316L stainless steel in the threshold region in air, when da/dN is plotted versus ΔK. da/dN of Ti–5Al–2.5Fe or Ti–6Al–4V ELI is nearly the same in air and in Ringer's solution when da/dN is plotted versus the effective cyclic stress intensity factor range, ΔK_eff, whereas da/dN of Ti–5Al–2.5Fe or Ti–6Al–4V ELI is greater in Ringer's solution than in air when da/dN is plotted versus ΔK.     

Fatigue studies of high-palladium dental casting alloys: Part II. Transmission electron microscopic observations†

The microstructures of two representative high-palladium dental alloys, a Pd–Cu–Ga alloy and a Pd–Ga alloy, which had been subjected to cyclic fatigue in uniaxial tension were investigated by transmission electron microscopy (TEM). Two different mechanisms were found to dominate microplastic deformation during fatigue: twinning in the Pd–Cu–Ga alloy, and planar slip of dislocations in the Pd–Ga alloy. In addition, stress-induced precipitation occurred in the Pd–Ga alloy during cyclic loading. Heat treatment simulating the firing cycles for dental porcelain resulted in the formation of a previously unreported bcc phase in the Pd–Cu–Ga alloy, and in the elimination of the characteristic tweed structure found in the Pd–Ga alloy for the as-cast condition.     

Microstructure and mechanical property of laser melting deposition (LMD) Ti/TiAl structural gradient material

This article presents fabrication, microstructure and mechanical properties study of Ti/TiAl functional gradient material. Ti–47Al–2.5V–Cr/Ti–6Al–2Zr–Mo–V gradient material was successfully fabricated by the laser melting deposition (LMD) manufacturing process. Microstructure and chemical composition was characterized by OM, SEM, TEM and EPMA. The Vickers hardness and room-temperature tensile property was evaluated on longitudinal direction. Results showed that fully lamellar (FL) microstructure consisted of γ-TiAl and α₂-Ti₃Al was formed on the Ti–47Al–2.5V–Cr side, while coarse basket weave microstructure was formed on the Ti–6Al–2Zr–1Mo–1V side. No cracking was found in the gradient zone after aging at 800 °C for 48 h. The room-temperature tensile strength of the as-deposited specimen is up to approximately 1198.8 MPa in the longitudinal direction, while the tensile elongation is approximately 0.4%, indicating a typical brittle fracture.     

Amorphization Behavior and Nanocrystalline Structure of Fe–P–Si–V Alloys

It is found that Fe–P–Si–V alloys tend to be in an amorphous state on cooling at a rate of 10⁵to 10⁶K/s. As compared to Fe–P–Si alloys, the crystallization behavior of the Fe–P–Si–V alloys is more complex owing to the formation of both metastable and equilibrium silicides. The metastable phases are nanocrystalline, as evidenced by transmission electron microscopy, which ensures a noticeable strength gain.     

Plastic deformation and fracture behaviors of nitrogen-alloyed austenitic stainless steels

The plastic deformation and fracture behaviors of two nitrogen-alloyed austenitic stainless steels, 316LN and a high nitrogen steel (Fe–Cr–Mn–0.66% N), were investigated by tensile test and Charpy impact test in a temperature range from 77 to 293 K. The Fe–Cr–Mn–N steel showed ductile-to-brittle transition (DBT) behavior, but not for the 316LN steel. X-ray diffraction (XRD) confirmed that the strain-induced martensite occurred in the 316LN steel, but no such transformation in the Fe–Cr–Mn–N steel. Tensile tests showed that the temperature dependences of the yield strength for the two steels were almost the same. The ultimate tensile strength of the Fe–Cr–Mn–N steel displayed less significant temperature dependence than that of the 316LN steel. The strain-hardening exponent increased for the 316LN steel, but decreased for the Fe–Cr–Mn–N steel, with decreasing temperature. Based on the experimental results and the analyses, a modified scheme was proposed to explain the fracture behaviors of austenitic stainless steels.