Nanostructures in Ti processed by severe plastic deformation

Metals and alloys processed by severe plastic deformation (SPD) can demonstrate superior mechanical properties, which are rendered by their unique defect structures. In this investigation, transmission electron microscopy and x-ray analysis were used to systematically study the defect structures, including grain and subgrain structures, dislocation cells, dislocation distributions, grain boundaries, and the hierarchy of these structural features, in nanostructured Ti produced by a two-step SPD procedure-warm equal channel angular pressing followed by cold rolling. The effects of these defect structures on the mechanical behaviors of nanostructured Ti are discussed

Previous heat treatment inducing different plasma nitriding behaviors in martensitic stainless steel

In this work we report a study of the induced changes in structure and corrosion behavior of martensitic stainless steels nitrided by plasma immersion ion implantation (PI3) at different previous heat treatments. The samples were characterized by x-ray diffraction and glancing angle x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and potentiodynamic measurements. Depending on the proportion of retained austenite in the unimplanted material, different phase transformations are obtained at lower and intermediate temperatures of nitrogen implantation. At higher temperatures, the great mobility of the chromium yields CrN segregations like spots in random distribution, and the alpha'-martensite is degraded to alpha-Fe (ferrite). The nitrided layer thickness follows a fairly linear relationship with the temperature and a parabolic law with the process time. The corrosion resistance depends strongly on chromium segregation from the martensitic matrix, as a result of the formation of CrN during the nitrogen implantation process and the formation of CrxC during the heat treatment process. Briefly speaking, the best results are obtained using low tempering temperature and low implantation temperature (below 375 degrees) due to the increment of the corrosion resistance and nitrogen dissolution in the structure with not too high diffusion depths (about 5-10 mu m). (c) 2006 American Vacuum Society

Surface preparation of powder metallurgical tool steels by means of wire electrical discharge machining

The surface of two types of powder metallurgical (PM) tool steels (i.e., with and without nitrogen) was prepared using wire electrical discharge machining (WEDM). From each grade of tool steel, seven surfaces corresponding to one to seven passes of WEDM were prepared. The WEDM process was carried out using a brass wire as electrode and deionized water as dielectric. After eachWEDM pass the surface of the tool steels was thoroughly examined. Surface residual stresses were measured by the X-ray diffraction (XRD) technique. The measured stresses were found to be of tensile nature. The surface roughness of the WEDM specimens was measured using interference microscopy. The surface roughness as well as the residual stress measurements indicated an insignificant improvement of these parameters after four passes of WEDM. In addition, the formed recast layer was characterized by means of scanning electron microscopy (SEM), XRD, and X-ray photoelectron spectroscopy (XPS). The characterization investigation clearly shows diffusion of copper and zinc from the wire electrode into the work material, even after the final WEDM step. Finally, the importance of eliminating excessive WEDM steps is thoroughly discussed

Effect of Weld Schedule on the Residual Stress Distribution of Boron Steel Spot Welds

Press-hardened boron steel has been utilized in anti-intrusion systems in automobiles, providing high strength and weight-saving potential through gage reduction. Boron steel spot welds exhibit a soft heat-affected zone which is surrounded by a hard nugget and outlying base material. This soft zone reduces the strength of the weld and makes it susceptible to failure. Additionally, different welding regimes lead to significantly different hardness distributions, making failure prediction difficult. Boron steel sheets, welded with fixed and adaptive schedules, were characterized. These are the first experimentally determined residual stress distributions for boron steel resistance spot welds which have been reported. Residual strains were measured using neutron diffraction, and the hardness distributions were measured on the same welds. Additionally, similar measurements were performed on spot welded DP600 steel as a reference material. A correspondence between residual stress and hardness profiles was observed for all welds. A significant difference in material properties was observed between the fixed schedule and adaptively welded boron steel samples, which could potentially lead to a difference in failure loads between the two boron steel welds

The influence of thermal cycles on the microstructure of grade 92 steel

The microstructure in the heat-affected zone (HAZ) of welds made from the 9 wt pct chromium martensitic Grade 92 steel is complex and has not yet been completely understood. There is a lack of systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds as a function of the welding process. In this study, the microstructure in the HAZ of an as-fabricated single-pass bead-on-plate weld on a parent metal of Grade 92 steel was systematically investigated by using an extensive range of electron and ion-microscopy-based techniques. A dilatometer was used to apply controlled thermal cycles to simulate the microstructures in the different regions of the HAZ. A wide range of microstructural properties in the simulated materials were then characterized and compared with the experimental observations from the weld HAZ. It was found that the microstructure in the HAZ of a single-pass Grade 92 steel weld can be categorized as a function of a decreasing peak temperature reached as (1) the completely transformed (CT) region, in which the original matrix is completely reaustenitized with complete dissolution of the pre-existing secondary precipitate particles; (2) the partially transformed (PT) region, where the original matrix is partially reaustenitized along with a partial dissolution of the secondary precipitate particles from the original matrix; and (3) the overtempered (OT) region, where the pre-xisting precipitate particles coarsen. The PT region is considered to be the susceptible area for damage in the commonly reported HAZ failures in weldments constructed from these types of steels

Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

[EN] This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25-60°C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest iG values at 60°C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H3PO4 media from a corrosion point of view for all the temperatures analysedThe authors would like to express their gratitude to the Spanish MAEC (PCI Mediterráneo C/8196/07, C/018046/08, D/023608/09) and to Asuncion Jaime for her translation assistance.Sánchez Tovar, R.; Montañés Sanjuan, MT.; García Antón, J.; Guenbour, A.; Ben Bachir, A. (2011). Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures. Corrosion Science. 53(4):1237-1246. https://doi.org/10.1016/j.corsci.2010.12.017S1237124653

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

For the class of steels collectively known as high strength low alloy (HSLA), an acicular ferrite (AF) microstructure produces an excellent combination of strength and toughness. The conditions for the occurrence of the AF transformation are, however, still unclear, especially the effects of austenite deformation and continuous cooling. In this research, a commercial HSLA steel was used and subjected to deformation via plane strain compression with strains ranging from 0 to 0.5 and continuous cooling at rates between 5 and 50 °C s −1 . Based on the results obtained from optical microscopy, scanning electron microscopy and electron backscattering diffraction mapping, the introduction of intragranular nucleation sites and the suppression of bainitic ferrite (BF) laths lengthening were identified as the two key requirements for the occurrence of AF transformation. Austenite deformation is critical to meet these two conditions as it introduces a high density of dislocations that act as intragranular nucleation sites and deformation substructures, which suppress the lengthening of BF laths through the mechanism of mechanical stabilisation of austenite. However, the suppression effect of austenite deformation is only observed under relatively slow cooling rates or high transformation temperatures, i.e., conditions where the driving force for advancing the transformation interface is not sufficient to overcome the austenite deformation substructures

Microstructure and Fabric Transitions in Calcite Tectonites from the Sierra Alhamilla

A suite of marble specimens from the Sierra Alhamilla (Spain), deformed to large strains under natural conditions at about 300° C shows distinct variations in microstructure and fabrics. It can be demonstrated that the development of crystallographic preferred orientations and grain shape fabrics are strongly dependent on recrystallized grain size. This is interpreted to reflect the relative importance of various deformational mechanisms. Superplasticity seems to have a sharp upper grain size limit at 10–15 /smm. Within the power law creep regime, deformation in fine grained aggregates is probably dominated by diffusional, in coarser ones by dislocation mechanisms. The transition is a gradual one, and may span a grain size range of 30 /sm

Garotas de loja, história social e teoria social [Shop Girls, Social History and Social Theory]

Shop workers, most of them women, have made up a significant proportion of Britain’s labour force since the 1850s but we still know relatively little about their history. This article argues that there has been a systematic neglect of one of the largest sectors of female employment by historians and investigates why this might be. It suggests that this neglect is connected to framings of work that have overlooked the service sector as a whole as well as to a continuing unease with the consumer society’s transformation of social life. One element of that transformation was the rise of new forms of aesthetic, emotional and sexualised labour. Certain kinds of ‘shop girls’ embodied these in spectacular fashion. As a result, they became enduring icons of mass consumption, simultaneously dismissed as passive cultural dupes or punished as powerful agents of cultural destruction. This article interweaves the social history of everyday shop workers with shifting representations of the ‘shop girl’, from Victorian music hall parodies, through modernist social theory, to the bizarre bombing of the Biba boutique in London by the Angry Brigade on May Day 1971. It concludes that progressive historians have much to gain by reclaiming these workers and the service economy that they helped create