D. Spinelli

Surface characterisation of plasma-nitrided iron by X-ray photoelectron spectroscopy

Abstract The nitriding by plasma has the potential to improve the tribological and mechanical properties on a number of substrates, and offers various advantages as compared with other methods used in the modification of surfaces. We prepared four samples by nitriding the iron substrates in a gas mixture (80% H 2 and 20% N 2 ) under a pressure of 9.0 mbar, discharge frequency of 10 kHz and temperature of 773 K, for periods of 1, 2, 4 and 6 h. We characterised the samples by scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness techniques, and detected the presence of Fe 4 N and Fe 2–3 N phases. We employed X-ray photoelectron spectroscopy (XPS) to obtain chemical-state and quantitative information of the plasma-nitrided iron surfaces. In situ cleaning was carried out by argon ion bombardment. The Fe 2p 3/2 photoelectron peaks for all samples presented three components, associated with Fe 0 , Fe 2+ and Fe 3+ , while the N 1s lines showed two components, the main one due to iron nitride and the other is connected with oxidised nitrogen.

Experimental Evaluation of

This work presents an investigation of the ductile tearing properties for an API 5L X60 pipeline steel using experimentally measured crack growth resistance curves (J-R curves). Use of these materials are motivated by the increasing demand in the number of applications for manufacturing high strength pipes for the Brazilian oil and gas industry including marine applications and steel catenary risers. Testing of the pipeline steels employed side-grooved SE(T) specimen with varying crack size to determine the J-R curves based upon the unloading compliance method using a single specimen technique. Recent developed compliance functions and eta-factors applicable for SE(T) fracture specimens are introduced to determine crack growth resistance data from laboratory measurements of load-displacement records. This experimental characterization provides additional toughness data which serve to evaluate crack growth resistance properties of pipeline steels using SE(T) specimens with varying geometries.Copyright

Fatigue and monotonic properties of an interstitial free steel sheet (FMPIF)

Abstract In the present work, the monotonic and low cycle fatigue properties of a thin sheet produced from an interstitial free steel containing titanium additions were investigated. A special grip alignment fixture permitted the fatigue tests be conducted under deformation control and completely reversed cyclic strain. The material presented different fatigue behavior for the transverse and longitudinal directions, related to the rolling direction. A comparison between the monotonic and cyclic stress—strain curves in the transverse direction showed that the material exhibits cyclic hardening at all tested strain amplitudes. The strain—life relationship was obtained for the transverse direction; buckling of longitudinal specimens made it impossible to obtain such a relationship.

Thermal, Mechanical, and Hygroscopic Behavior of Sisal Fiber/Polyurethane Resin-based Composites

This work reports hygroscopic, thermal, and mechanical properties of biomass composites comprising sisal fiber reinforcing castor oil PU resin. The effects of reinforcement geometry and alkaline treatment of fibers were evaluated. In general, alkaline treatment improved quasi-static tensile properties of composites with short randomly oriented and long aligned sisal fibers, respectively. On the other hand, an adverse effect of alkaline treatment was observed in the mechanical behavior of the composite with bidirectional fabric architecture. The outstanding influence of moisture on thermo-mechanical properties of biomass composites was confirmed through thermogravimetric and differential scanning calorimetry techniques. Dynamical-mechanical thermal analysis showed increased storage modulus (i.e., stiffness) and decreased damping properties of biomass composites as compared to neat PU matrix. Dynamical-mechanical testing also detected unexpected decrease on glass transition temperature of composites in regard to the neat polymer resin; resin plasticization due to moisturized fibers and/or alkaline treatment residues was identified as probably the culprit.

Nitriding of H-12 tool steel by direct-current and pulsed plasmas

Abstract Direct-current (DC) and pulsed plasmas were used to nitride samples of AISI H-12 tool steel with treatment time varying from 1 h to 6 h. X-ray diffraction (glancing-angle and θ –2 θ geometry), conversion electron Mossbauer spectroscopy, conversion X-ray Mossbauer spectroscopy and Vickers microhardness were used as analytical techniques. The near-surface compound layer consists of a mixture of γ′-Fe 4 N and e-Fe x (N,C), while the near-diffusion zone compound layer consists of a mixture of γ′-Fe 4 N, e-Fe x (N,C), α″-Fe 16 N 2 and γ-austenite. For a DC plasma the dependence of compound layer thickness on nitriding time obeys a parabolic law, but for a pulsed plasma this dependence does not follow a parabolic law.

Near-surface composition and microhardness profile of plasma nitrided H-12 tool steel

Samples of AISI H-12 tool steel were plasma nitrided at 500°C in a mixture of H2-20% N2 under a total pressure of 6 mbar, by using DC and pulsed glow discharges. The treatment time varied from 1 to 6 h. X-ray diffraction (glancing angle and u-2u geometry), conversion electron Mossbauer spectroscopy, conversion X-ray Mossbauer spectroscopy, electron probe microanalysis, optical micrograph and Vickers microhardness were used as analytical techniques. The obtained results suggest that, under the present experimental conditions: (i) The near-surface compound layer consists of a mixture of g%-Fe4N and o-Fex(N, C); (ii) the near-diffusion zone compound layer consists of a mixture of g%-Fe4N, o-Fex(N, C), aƒ-Fe16N2 and g-austenite; (iii) the dependence of compound layer thickness on nitriding time violates the parabolic behavior and emphasizes effects from cathode sputtering and radiation-enhanced diffusion.

Mechanical performance of carbon-epoxy laminates Part I: quasi-static and impact bending properties

In Part I of this study, quasi-static and impact bending properties of four aeronautical grade carbon-epoxy laminates have been determined and compared. Materials tested were unidirectional cross-ply (tape) and bidirectional woven textile (fabric) carbon fiber lay-up architectures, impregnated with standard and rubber-toughened resins, respectively, giving rise to 1.5 mm-thick laminates. Quasi-static mechanical properties assessed in transversal mode loading were modulus of elasticity, flexural strength and tenacity at the maximum load, whereas the net absorbed energy was determined under translaminar impact conditions. Two-dimensional woven carbon fiber reinforcements embedded in a rubber-toughened matrix presented the best mechanical performance under static loading. Under dynamic loading conditions, woven fiber fabric pre-forms were favorably sensitive to increasing impact energies regardless the nature of the employed epoxy resin. However, it was concluded that great care should be taken with this material within the low energy impact regimen.

Effect of surface rolling on fatigue behavior of a pearlitic ductile cast iron

Surface rolling is a mechanical treatment usually used in parts fabricated with steel and ductile cast iron, specifically in stress concentration regions, to improve fatigue properties. This process hardens and introduces compressive residual stresses to the surface of the material through the application of controlled strains, thus provoking a reduction of resulting tensile stress at its surface under cyclic loading. This work deals with the effect of surface rolling on high cycle fatigue behavior of a pearlitic ductile cast iron used in crankshafts by the automotive industry. Rotating bending fatigue tests were performed in both smooth and notched specimens, the latter either with or without a surface rolling treatment. Compressive residual stresses and heavy plastic deformation imposed on the surface grains due to cold work made difficult the nucleation and propagation of the crack at the rolled surface of the notch. As a consequence, surface-rolled notch testpieces presented a higher endurance limit (478 MPa) than both smooth (299 MPa) and notched (166 MPa) testpieces did. The surface rolling apparatus developed for this work proved to be very efficient and simple, providing good control of parameters involved in the process (i.e., rolling load, frequency, and number of revolutions).

Microstructural and Fractographic Characterization of a Thermally Embrittled Nuclear Grade Steel: Part I - Annealing

A nuclear reactor pressure vessel steel was submitted to different annealing heat treatments aimed at simulating neutron irradiation damage. The obtained microstructures were mechanically tested with subsequent metallographic and fractographic characterization. The relevant microstructural and fractographic aspects were employed in the interpretation of the mechanical behavior of the microstructures in both quasi-static (J-R curve) and dynamic (Charpy impact) loading regimes. A well defined relationship was determined between the elastic-plastic fracture toughness parameter J-integral and the Charpy impact energy for very most of the microstructures.

Microstructural and Fractographic Characterization of a Thermally Embrittled Nuclear Grade Steel: Part II - Quenching and Tempering

A nuclear reactor pressure vessel steel was submitted to different quenching and tempering heat treatments aimed at simulating neutron irradiation damage. The obtained microstructures were mechanically tested and submitted to metallographic and fractographic survey. The relevant microstructural and fractographic aspects were employed in the interpretation of the mechanical performance of the thermally embrittled microstructures. A well defined correlation was determined between the elastic-plastic fracture toughness parameter J-integral and the Charpy impact energy, which was achieved for some of the Q&T microstructures.