Creep behavior of AZ31 magnesium alloy in low temperature range between 423 K and 473 K

The deformation behavior of coarse-grained AZ31 magnesium alloy was examined in creep at low temperatures below 0.5 T _m and low strain rates below 5 × 10⁻⁴ s⁻¹. The creep test was conducted in the temperature range between 423 and 473 K (0.46–0.51 T _m) under various constant stresses covering the strain rate range 5 × 10⁻⁸ s⁻¹–5 × 10⁻⁴ s⁻¹. All of the creep curves exhibited two types depending on stress level. At low stress (σ/G < 4 × 10³), the creep curve was typical of class I behavior. However, at high stresses (σ/G > 4 × 10³), the creep curve was typical of class II. At the low stress level, deformation could be well described by solute drag creep whereas at the high stress level, deformation could be well described by dislocation climb creep associated with pipe diffusion or lattice diffusion. The transition of deformation mechanism from solute drag creep to dislocation climb creep, on the other hand, could be explained in terms of solute-atmosphere-breakaway concept.     

Experimental and numerical investigation on ductile-brittle fracture transition in a magnesium alloy

Tensile test on smooth and circumferentially notched specimens, systematic observation of fracture surfaces and large deformation finite element analysis were conducted to understand the deformation and failure behavior of a magnesium alloy (AM60). The plastic deformation is considered to be dominated by twining mediated slip. The tensile properties were not sensitive to the strain rates applied (3.3 × 10⁻⁴∼0.1). Corresponding to the same loading level, higher stress triaxiality but lower plastic strain was observed in the specimens with a smaller notch profile radius. Deformation and failure of the magnesium alloy were sensitive to the constraint level and ductile-brittle fracture transition occurred with decreasing the notch profile radius.     

Synthesis and electrochemical application of carbon nanotubes obtained from hexachloroethane

Carbon nanotubes (CNTs) with the average inner (outer) diameter of 10–20 nm (20–40 nm) and length up to 100s of nanometers were synthesized via Wurtz reaction at 400 °C for 12 h, using C₂Cl₆ and Na as reactants. These CNTs, having more defects because of the sp³ bonding raw material of C₂Cl₆, were used as electrode material to detect dopamine (DA) via cyclic voltammetry. The results show that there exists linear relation between peak currents and DA concentration in the range of 2 × 10⁻⁷∼2.8 × 10⁻⁴ mol L⁻¹.The linear regression equation is expressed as Ip (μA) = 0.089 + 0.134c (μmol L⁻¹). This CNTs-modified electrode showed high sensitivity with detection limit of 1 × 10⁻⁷ mol L⁻¹.     

High-rate deformation and spall fracture of hadfield steel under action of high-current nanosecond relativistic electron beam

Features of the plastic deformation and dynamic spall fracture of Hadfield steel under conditions of shock wave loading at a straining rate of ∼10⁶ s⁻¹ have been studied. The shock load (∼30 GPa, ∼0.2 μs) was produced by pulses of a SINUS-7 electron accelerator, which generated relativistic electron bunches with an electron energy of up to 1.35 MeV, a duration of 45 ns, and a peak power on the target of 3.4 × 10¹⁰ W/cm². It is established that the spalling proceeds via mixed viscous-brittle intergranular fracture, unlike the cases of quasi-static tensile and impact loading, where viscous transgranular fracture is typical. It is shown that the intergranular character of the spall fracture is caused by the localization of plastic deformation at grain boundaries containing precipitated carbide inclusions.     

Small angle magnetization rotation of amorphous ribbons under tensile and compressive stress

Small angle magnetization rotation of Metglas 2826MB, 2605SC and 2605CO and Vitrovac 4040 ribbons under both tensile and compressive stress is investigated. It appears that there is no significant difference between the saturation magnetostriction of a ribbon when measured in tension or compression. Values determined forλ _s are 2826MB: 12.5±0.7×10⁻⁶; 2605SC: 30±2×10⁻⁶; 2605CO: 37±2×10⁻⁶ and 4040: 10.4±0.7×10⁻⁶.     

Compressive deformation behavior of ternary compound Cr<Subscript>2</Subscript>AlC

The compressive properties of ternary compound Cr₂AlC at different temperatures and strain rates were studied. When tested at a strain rate of 5.6 × 10⁻⁴ s⁻¹, the compressive strength decreases continuously from 997 ± 29 MPa at room temperature to 523 ± 7 MPa at 900 °C. The ductile-to-brittle transition temperature is measured to be in the range of 700 to 800 °C. When tested in the strain rate range of 5.6 × 10⁻⁵ to 5.6 × 10⁻³ s⁻¹, Cr₂AlC fails in a brittle mode at room temperature, whereas the deformation mode changes from a brittle to a ductile as the strain rate is lower than 5.6 × 10⁻⁴ s⁻¹ when compressed at 800 °C. The compressive strength increases slightly with increasing strain rate at room temperature and it is less dependent on strain rate when tested at 800 °C. The plastic deformation mechanism of Cr₂AlC was discussed in terms of dislocation-related activities, such as kink band formation, delamination, decohesion of grain boundary, and microcrack formation.     

Effect of transient change in strain rate on plastic flow behaviour of low carbon steel

Plastic flow behaviour of low carbon steel has been studied at room temperature during tensile deformation by varying the initial strain rate of 3·3 × 10⁻⁴s⁻¹ to a final strain rate ranging from 1·33 × 10⁻³s⁻¹ to 2 × 10⁻³s⁻¹ at a fixed engineering strain of 12%. Haasen plot revealed that the mobile dislocation density remained almost invariant at the juncture where there was a sudden increase in stress with a change in strain rate and the plastic flow was solely dependent on the velocity of mobile dislocations. In that critical regime, the variation of stress with time was fitted with a Boltzmann type Sigmoid function. The increase in stress was found to increase with final strain rate and the time elapsed in attaining these stress values showed a decreasing trend. Both of these parameters saturated asymptotically at a higher final strain rate.     

Internal friction,crack length of fracture origin and fracture surface energy in alumina-zirconia composites

Two series of alumina-zirconia composites, i.e. alumina-unstabilized zirconia and alumina-partially stabilized zirconia with 3 mol % Y₂O₃, with different zirconia content were slip casted and fired at 1550°C for 3 h. Elastic constant, bending strength and fracture toughness were measured. Internal friction was determined to follow the formation of cracks, nondestructively, which could be one of the fracture origins. The crack length of the fracture origin and the fracture surface energy were calculated by applying Griffith's fracture theory. Microstructures of the fracture surfaces were observed using a scanning electron microscope. For the unstabilized zirconia system, the increase in the internal friction of the order from 10⁻⁴ to 10⁻³ was a guide to find the formation of cracks which lead to the fracture. The increase in the cracks becoming a fracture origin lead to the increase inK _lc and also to the apparent increase in the fracture surface energy. For the partially stabilized zirconia system, the increase in the fracture surface energy with an increase in zirconia content, keeping low internal frictions of the order of 10⁻⁴, indicates the intrinsic strengthening of the grain boundaries in comparison to the unstabilized zirconia system. Internal friction is the most suitable nondestructive physical quantity to find the microcracks which leads to the fracture.     

Mechanical behaviour of partially crystallized amorphous alloys

Deformation and fracture of partially crystallized Ni₅₅Pd₃₅P₁₀ amorphous alloys have been investigated. The samples with a few percent crystallization show a fracture stress (175 kg mm⁻²) and apparent Young's modulus (19.5×10³kg mm⁻²) greater than those completely amorphous or partially crystallized 50%. On the other hand, the fracture strain of the former are lower than those of the two latter. A simulated model with mixtures of carborundum powder with grease, shows accord with morphological and mechanical aspects of the partially crystallized alloys. As expected, microcrystals embedded in an amorphous material act as obstacles to plastic flow.     

Mechanical and fracture behavior of powder metalurgy processed Ti3Al-based alloys

This work considers structural and compression mechanical properties of three Ti₃Al-based alloys processed by powder metallurgy. Mechanically alloyed powders were compacted by hot-pressing to non-porous homogenous compacts. Prior to compression tests, all compacts were homogenized by a solution treatment at 1050°C (α + β region) for 1h, followed by water quenching. The compression tests were performed from room temperature to 500°C in vacuum at a strain rate of 2.4 × 10⁻³ s⁻¹. Detailed microstructural characterization has been evaluated by scanning electron microscopy (SEM), followed by electron dispersive spectroscopy (EDS) and X-ray diffraction analysis. Fracture topography was examined by SEM. The Ti₃Al-Nb alloy exhibits the highest ductility in the whole temperature range, whereas addition of Mo to Ti₃Al-Nb alloy yields the highest ultimate compression strength. A correlation between ductility and the fracture mode exists for all materials.     

The fracture energy of some epoxy resin materials

The double cantilever beam technique has been used to measure the fracture energy of a series of cured epoxy resins. A range of materials was produced by varying the proportion of resin to hardener agent (Araldite CT200 and hardener HT901 — phthalic anhydride, CIBA Ltd) and by adding silica flour or aluminium powder as a filler. The fracture energy for crack initiation in the cured epoxy resins ranged from approximately 10³ to 10⁵ erg cm⁻², and in the “filled resins” from 10⁴ to 5×10⁵ erg cm⁻², as the proportion of hardener increased. The fracture energy for crack arrest was somewhat lower at the higher hardener contents and particularly for the Al-filled material.     

Synthesis and electrical properties of Gd<Subscript>2</Subscript>MO<Subscript>5</Subscript> (M = Zr,Hf)

Polycrystalline Gd₂ZrO and Gd₂HfO₅ have been prepared by heat-treating coprecipitated oxide mixtures, and their order-disorder phase transitions have been studied in the range 20–1600°C. The materials have been shown to consist of nanostructured grains with a nanodomain size of ∼40 nm. Their electrical conductivity has been determined by impedance spectroscopy in air between 300 and 1000°C. The 1000°C conductivities of Gd₂ZrO₅ and Gd₂HfO₅ are 3.7 × 10⁻³ and 1.8 × 10⁻³ S/cm, and the respective effective activation energies are 1.37 and 1.56 eV.     

Quasi-static and dynamic compressive behaviour of poly(methyl methacrylate) and polystyrene at temperatures from 293 K to 363 K

Flow stress, Young’s Modulus, energy and strain of fracture of poly(methyl methacrylate) (PMMA) and polystyrene (PS) were studied under compressive loading at strain rates of 10⁻⁴–10 s⁻¹ and temperatures from 293 K to temperatures ∼20 K below T _g. It was found that the energy of fracture shows an increase in the quasi-static strain rate (10⁻⁴–10⁻³ s⁻¹) region and becomes constant in the low strain rate (10⁻²–10 s⁻¹) region, while the strain of fracture shows a slow decrease with rate over the strain rate range tested. The activation energies and volumes of PMMA and PS at yield stress, 20% and 30% strain were evaluated using Eyring’s theory of viscous flow. ΔG was found to be constant for all strain rates and strains for both PMMA and PS. The activation volume for both materials increased as a function of strain.     

Influence of temperature and strain rate on cohesive properties of a structural epoxy adhesive

Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive are studied experimentally. Two parameters of the cohesive laws are given special attention: the fracture energy and the peak stress. Temperature experiments are performed in peel mode using the double cantilever beam specimen. The temperature varies from −40 to + 80°C. The temperature experiments show monotonically decreasing peak stress with increasing temperature from about 50 MPa at −40°C to about 10 MPa at + 80°C. The fracture energy is shown to be relatively insensitive to the variation in temperature. Strain rate experiments are performed in peel mode using the double cantilever beam specimen and in shear mode, using the end notch flexure specimen. The strain rates vary; for peel loading from about 10⁻⁴ to 10 s⁻¹ and for shear loading from 10⁻³ to 1 s⁻¹. In the peel mode, the fracture energy increases slightly with increasing strain rate; in shear mode, the fracture energy decreases. The peak stresses in the peel and shear mode both increase with increasing strain rate. In peel mode, only minor effects of plasticity are expected while in shear mode, the adhesive experiences large dissipation through plasticity. Rate dependent plasticity, may explain the differences in influence of strain rate on fracture energy between the peel mode and the shear mode.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

The strain rate and temperature dependence of microstructural evolution of Ti–15Mo–5Zr–3Al alloy

A compressive split-Hopkinson pressure bar apparatus and transmission electron microscopy (TEM) are used to investigate the deformation behaviour and microstructural evolution of Ti–15Mo–5Zr–3Al alloy deformed at strain rates ranging from 8 × 10² s⁻¹ to 8 × 10³ s⁻¹ and temperatures between 25 °C and 900 °C. In general, it is observed that the flow stress increases with increasing strain rate, but decreases with increasing temperature. The microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result, primarily, of dislocations and the formation of α phase. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. The amount of α phase increases with increasing temperature below the β transus temperature. The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current loading conditions.     

Sorption-atomic-absorption determination of platinum,palladium, and rhodium in dead autocatalysts

The conditions for determination and group concentration of platinum metals (PMs) in the presence of matrix components using new S,N-containing complex-forming sorbents in solutions obtained after decomposition of decontaminated autocatalysts are proposed. The technique of atomic-absorption determination of PMs from a solution (n × 10⁻⁴−n × 10⁻²; s _r = 0.15–0.07) and a solid phase (n × 10⁻⁵−n × 10⁻⁴; s _r = 0.20–0.12) is developed.     

Electrical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CaO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses exhibiting majority charge carrier reversal

The thermoelectric power and d.c electrical conductivity of x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses were measured. The Seebeck coefficient (Q) varied from +88 μ V K⁻¹ to −93 μV K⁻¹ as a function of V₂O₅ mol%. Glasses with 10 and 15 mol% V₂O₅ exhibited p-type conduction and glasses with 25 and 30 mol% V₂O₅ exhibited n-type conduction. The majority charge carrier reversal occurred at x = 20 mol% V₂O₅. The variation of Q was interpreted in terms of the variation in vanadium ion ratio (V^{5 +}/V^{4 +}). d.c electrical conduction in x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses was studied in the temperature range of 150 to 480 K. All the glass compositions exhibited a cross over from small polaron hopping (SPH) to variable range hopping (VRH) conduction mechanism. Mott parameter analysis of the low temperature data gave values for the density of states at Fermi level N (E_F) between 1.7 × 10²⁶ and 3.9 × 10²⁶ m⁻³ eV⁻¹ at 230 K and hopping distance for VRH (R_VRH) between 3.8 × 10⁻⁹m to 3.4 × 10⁻⁹ m. The disorder energy was found to vary between 0.02 and 0.03 eV. N (E_F) and R_VRH exhibit an interesting composition dependence.     

Preparation and characterization of indium oxide (In2O3) films by activated reactive evaporation

The electrical and optical properties of In₂O₃ films prepared at room temperature by activated reactive evaporation have been studied. Hall effect measurements at room temperature show that the films have a relatively high mobility 15 cm²v⁻¹s⁻¹, high carrier concentration 2·97 × 10²⁰/cm³, with a low resistivityρ = 1·35 × 10⁻³ ohm cm. As-prepared film is polycrystalline. It shows both direct and indirect allowed transitions with band gaps of 3·52eV and 2·94eV respectively.     

Elevated temperature sliding wear behavior of WCP-reinforced ferrous matrix composites

WC_P-reinforced ferrous matrix composites were processed by direct addition of WC_P (100–150 μm) and the melt of the matrix alloy to a rotating mold at 1000 rpm. Dry sliding wear behaviors of the composites containing about 80 vol.% of WC_P and high-speed steel counterpart were investigated at room temperature and 400 °C against a rotating die steel ring. And wear experiments were performed under loads of 50, 100, and 150 N and a fixed sliding velocity of 30 m/s. Results show that at room temperature, both materials exhibited a marked increase in wear rate with load applied. Wear rates of the composites and high-speed steel under loads of 50, 100, and 150 N at room temperature achieved 1.61 × 10⁻⁶, 2.14 × 10⁻⁶, 3.56 × 10⁻⁶, and 3.11 × 10⁻⁶, 23.08 × 10⁻⁶, 57.39 × 10⁻⁶ g/m, respectively. At a testing temperature of 400 °C, the composites exhibited a marked increase in wear rates and high-speed steel exhibited mild wear (characterized by extremely low wear rates) over the range of loads considered in these experiments. Wear rates of both the composites and high-speed steel at 400 °C achieved 2.42 × 10⁻⁶, 5.19 × 10⁻⁶, 6.64 × 10⁻⁶, and 4.1 × 10⁻⁶, 8.92 × 10⁻⁶, 26.02 × 10⁻⁶ g/m, respectively, under different loads. Finally, the wear-mechanism was discussed in this article.