51 research outputs found
Ordering and the micromechanics of Ti-7Al
The evolution of intergranular lattice strain in the α titanium alloy Ti–7Al wt% was characterised using in situ time-of-flight (TOF) neutron diffraction during room temperature tensile loading. Samples were aged to promote ordering and the formation of nanometre-scale α2 (Ti3Al). On ageing, at 550°C and 625°C, dislocations were observed to travel in pairs, and in planar arrays, which has been attributed to the presence of ordering. A slight change in c/a was observed, from 1.6949 to 1.6945, and a slight increase in the macroscopic modulus. However, no changes were observed in the residual lattice strains, which are the grain-orientation average elastic strains produced by plasticity. Therefore it is inferred that the changes in deformation mechanisms caused by ordering that result in an enhanced vulnerability to dwell fatigue affect primarily the extent of slip localisation. The overall strain distributions between grains in different orientations are not changed
The effect of aluminium on twinning in binary alpha-titanium
The deformation mechanisms of binary Ti–Al model alloys (0–13.1 at.% Aluminium) have been investigated with respect to the twinning activity using in-situ loading in combination with neutron diffraction as well as detailed post mortem electron backscatter diffraction analysis. A consistent starting grain size and texture was generated for all alloys promoting tensile twinning during compression testing. Long-wavelength neutron diffraction and selected area diffraction transmission electron microscopy analysis were carried out to detect evidence of Aluminium ordering and Ti3Al formation.It was found that raising the Aluminium content in Titanium does first slightly enhance twinning, with {10View the MathML source2} tensile twinning being by far the dominant type, while the critical residual intergranular strains for twin initiation decreases. This suggests that either the lowering of stacking fault energy by Aluminium or its solute solution strengthening effect are important factors. At around 7 at.% Aluminium a turning point in twinning activity was noticed and a further increase in Aluminium did result in a dramatic loss of twinning activity particularly when the material had been exposed to an additional low temperature age. The dramatic decrease of twinning activity is strongly correlated with increasing evidence of short range ordering and also early signs of Ti3Al-formation in case of the highest Aluminium content. In addition, electron backscatter diffraction analysis revealed that the formation of Aluminium ordered zones do severely hinder growth of twin boundaries
Hydrogen adsorption at dislocations and cracks in Fe
Solute adsorption to dislocations and cracks is considered in both the Boltzmann and Fermi-Dirac models. Explicit sums are developed for the integral amount of solute adsorbed in the defect fields. Examples of the use of the method are presented for the case of hydrogen in iron and compared with earlier results. The similarity of the condensed atmosphere of hydrogen to hydride precipitation is noted and its relevancy to hydrogen embrittlement models is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22483/1/0000024.pd
Effect of thermal and mechanical treatments on corrosion of API X-52 grade line pipe steel in flowing 3.5% NaCl solution
611-614Commercial API X-52 grade line pipe steel
was studied for its corrosion resistance in 3.5% NaCl solution under static and
dynamic conditions. Heat treatments and cold rolling resulted in considerable variations
in mechanical properties and microstructure of the steel. These treatments
resulted in insignificant changes in static corrosion rate, whereas considerable
variations in corrosion rate were
observed under dynamic conditions. Quenched and tempered steel showed the
maximum corrosion resistance and annealed steel showed the minimum resistance under
dynamic conditions
Microbiologically influenced corrosion of mild steel of cultures of sulphate reducing bacteria
327-329<span style="font-size:11.0pt;line-height:115%;
font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "times="" new="" roman";mso-fareast-theme-font:minor-fareast;mso-hansi-theme-font:="" minor-latin;mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">Microbiologically
influenced corrosion (MIC) of mild steel samples were studied in two different
bacterial strains, Pseudomonas fiuorescens and Desulphovibrio
vulgaris, isolated from cutting oil emulsions by potentiostatic
polarization technique. The relationship between the corrosion behaviour and
presence of biofilm on mild steel samples were determined. Bacteria were mixed
with corrosion products hindering the formation of a protective layer. In both
media, anodic depolarization was observed in the presence of ferric iron
reducing bacteria. Anodic depolarization was achieved by the bacterial
reduction of ferric to ferrous compounds. In the absence of the bacteria, both
anode and cathode were polarized.</span
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