Effect of NiCr and NiCrAl coatings on the creep resistance of a Ni alloy

The effect of plasma sprayed NiCr and NiCrAl coatings on the creep resistance of Nickel alloy 690 at temperature of 1033 K was investigated. Experimental results showed that the coatings had a beneficial effect on the improvement of the creep resistance of substrate. However, there was almost no difference in the creep lives between the NiCr and NiCrAl coated specimens at a given stress level. The relation between the applied stress and time to rupture of the coated specimens can be estimated by using Larson-Miller equation. For the coated specimens tested at low applied stress levels, the product of the minimum creep rate and the time to rupture was a constant value. The θ projection method can be used to accurately characterize the creep behavior of the coated specimens. The variation of the creep strain along with time predicted by using θ projection method agreed well with the experimental results.     

Evaluation of polymer fracture parameters by the boundary element method

The boundary element method (BEM) for two-dimensional linear viscoelasticity is applied to polymer fracture. The time-dependence of stress intensity factors is assessed for various viscoelastic models as well as loading and support conditions. Various representations of the energy release rate under isothermal conditions are adopted. Additional boundary integral equations for the displacement gradient in the domain are linked to algorithms for the evaluation of path-independent J-integrals. The consistency of BEM predictions and their good agreement with other analytical results confirms BEM as a valid modelling tool for viscoelastic fracture characterisation and failure assessment under complex geometric and loading conditions.     

Preparation of H-bar cross-sectional specimen for in situ TEM straining experiments: A FIB-based method applied to a nitrided Ti-6Al-4V alloy

The in situ tensile straining of cross-sectional specimens inside a TEM is intrinsically very difficult to perform despite its obvious interest to study interfaces of surface treated materials. We have combined a FIB-based method to produce H-bar specimens of a nitrided Ti-6Al-4V alloy and in situ TEM straining stage, to successfully study the plastic deformation mechanisms that are activated close to the nitrided surface in the Ti-based alloy.     

Microstructure and mechanical behaviour of (Fe88Si12)95Al5 alloy prepared by aluminothermics

Abstract

The (Fe₈₈Si₁₂)₉₅Al₅ alloy was prepared by an aluminothermics. The (Fe₈₈Si₁₂)₉₅Al₅ alloy is composed of spheroidic α-Fe(Si,Al) precipitate with size of 20–50 nm and γ-Fe(Si,Al) matrix. The yield strength and fracture strain in compression of the (Fe₈₈Si₁₂)₉₅Al₅ alloy are 1500 MPa and 23% respectively. The shear bands propagating in the compressive deformation are arrested by the precipitation particles that resulted in large ductility and high strength simultaneously.     

Determination of the critical conditions for the initiation of dynamic recrystallization in boron microalloyed steels

From the present research, the critical conditions associated with the onset of dynamic recrystallization (DRX) of hot deformed boron microalloyed steels were precisely determined based on changes in the strain hardening rate (θ) as a function of the flow stress. For this purpose, a low carbon steel microalloyed with four different amounts of boron (29, 49, 62 and 105 ppm) was deformed by uniaxial hot-compression tests at high temperature (950, 1000, 1050 and 1100 °C) and constant true strain rate (10⁻³, 10⁻² and 10⁻¹ s⁻¹). Results indicate that the critical conditions for the initiation of dynamic recrystallization depend on the temperature and strain rate. In addition, both critical stress σ_c, and critical strain ?_c, were noticed to decrease as boron content increased. Such a behavior is attributed to a solute drag effect by boron atoms on the austenitic grain boundaries and also to a solid solution softening effect. The critical ratios σ_c/σ_p and ?_c/?_p for all boron microalloyed steels remain fairly constant (≈0.82 and ≈0.53, respectively), such values are in agreement with those commonly reported for Al-killed, C-Mn, Nb, Nb-Ti, high carbon and stainless steels.     

Synthesis and characterization of poly (o-phenylenediamine) hollow multi-angular microrods by interfacial method

Poly (o-phenylenediamine) (PoPD) hollow multi-angular microrods have been synthesized at 10 °C via an interfacial process using ferric chloride and o-phenylenediamine (oPD) as starting materials. The chemical structure of the one dimensional (1D) superstructure is proved to be phenazine-like, and contains the benzenoid and quinoid imine units doped partly with Cl. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations indicate that the resulting superstructure of PoPD is built from hollow nanofibers aligned parallel to the fiber axis by van der Waals' force. The possible formation mechanism of the structure has been proposed.     

Synthesis and characterization of WO3 nanostructures prepared by an aged-hydrothermal method

Nanostructures of tungsten trioxide (WO₃) have been successfully synthesized by using an aged route at low temperature (60 °C) followed by a hydrothermal method at 200 °C for 48 h under well controlled conditions. The material was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Specific Surface Area (S_BET) were measured by using the BET method. The lengths of the WO₃ nanostructures obtained are between 30 and 200 nm and their diameters are from 20 to 70 nm. The growth direction of the tungsten oxide nanostructures was determined along [010] axis with an inter-planar distance of 0.38 nm.     

Dynamic strength and failure behavior of titanium alloy Ti-6Al-4V for a variation of heat treatments

In our study, samples of Ti-6Al-4V were subjected to modifications of an aging treatment where temperatures for solution annealing and final aging as well as the cooling rate were varied. The titanium alloy was annealed above and below the β-transus temperature followed by cooling in a vacuum furnace or by water quenching. Additionally, the final annealing temperature was varied. Compression tests under quasistatic and dynamic loading rates were performed to determine the flow stress and strain hardening behavior. Furthermore, instrumented Charpy impact tests on U-notch specimen were performed at room temperature to monitor the load-time response of deformation and fracturing. The obtained high rate mechanical properties are discussed and correlated with the present microstructure. Our results reveal a very strong effect of the microstructure on the material behavior and will assist to choose the appropriate heat treatment technology, especially if impact loaded or safety structures have to be considered.     

Syntheses and characterization of CdCO3 and CdO nanoparticles by using a sonochemical method

Nanoparticles of CdCO₃ were synthesized by the reaction of Cd(CH₃COO)₂ and tetramethylammonium hydroxide (TMAH) by a sonochemical method. The CdO nanoparticles were obtained by heating of CdCO₃ nanoparticles at 400 °C. The CdCO₃ and CdO nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction (XRD), TGA, DTA and FT-IR spectroscopy.     

J-Resistance curve testing of HY80 steel using SE(B) specimens and normalization method

The normalization method is adopted for standard and nonstandard specimens in this paper to develop J-R curves for HY80 steel directly from load versus load-line displacement records without use of automatic crack length measurement. The standard specimens usually contain high crack-tip constraints, while the nonstandard specimens involve low crack-tip constraints. To obtain J-R curves with different constraints, a series of single edge notched bend (SE(B)) specimens with different crack lengths for an HY80 steel are tested in accordance with ASTM standard E1820. The normalization method is then used for determining crack extension and J-R curves for these SE(B) specimens.To validate the normalization method, the J-R curves determined using the normalization method are compared with those obtained by the elastic unloading compliance method for the SE(B) specimens. The comparison shows that good agreements exist between the two methods, and the normalization method is a viable tool to be used to determine J-R curves of the HY80 steel for the standard as well as nonstandard SE(B) specimens. In the J-integral calculations, the resistance curve test method, the basic test method and the modified basic test method specified in ASTM E1820 are evaluated. The results indicate that the modified basic method can be equivalent to the resistance curve method.