1,721,004 research outputs found
Novel approach based on tensile strain hardening analysis to assess the integrity of an Al alloy produced through High-Pressure Die Casting
No full textThe analysis of the structural integrity of components in Al alloys produced by High Pressure Die Casting (HPDC) is paramount for identifying a correlation between process-microstructure-mechanical properties, a correlation that allows to classify the quality process parameters, and identify potential application areas. The tensile test represents the simplest method to pursue this aim, and the tensile strain hardening analysis seems to be capable of providing interesting correlations. In fact, an innovative method based on the analysis of strain hardening through the formalism of the constitutive equation of Voce has provided interesting results in other foundry materials, such as spheroidal cast irons. In this work, we report the results of the application of the innovative method to an Al alloy produced by HPDC in two components having two different geometries. One geometry is that of a round tensile specimen, adopted as a reference since it has an "ideal" microstructure according to the PD CEN/TR 16748:2014 standard, and a second one is a real U shape geometry. The innovative procedure has uniquely identified that the Al alloy with "ideal" microstructure has better microstructural integrity of the material from the U geometry casting, demonstrating that the innovative procedure can also be used successfully for Al alloys produced by HPDC
DSC analysis of strengthening precipitates in ultrafine Al-Mg-Si alloys
No full textEqual channel angular pressing (ECAP) was carried out on solution annealed samples of Al–Mg–Si–Zr and Al–Mg–Si–Zr–Sc alloys to achieve a substantial grain refinement of the materials. Post ECAP aging was then investigated on the ultrafine grained alloys by DSC and TEM analyses.
DSC scans were carried out with heating rates ranging from 5 to 30°C min–1. Peak identification was performed by the support
of literature information and TEM analyses. Precipitation kinetics revealed to be similar for both alloys but the Sc-free alloy showed
a recrystallization peak at temperatures ranging from 310 to 340°C, depending on the strain accumulated during ECAP. On the contrary, the Sc-containing alloy showed a greater grain stability. Analyses of peak positions and of activation energies as a function of ECAP passes experienced by the samples revealed large modifications of precipitation kinetics in the ultrafine-grained alloys with respect to the coarse-grained materials
Rapid solidification of silver-rich Ag-Cu-Zr-Al alloys
Full text linkIn this work amorphous/crystalline Ag–Cu–Zr–Al composites with 80 wt.% Ag were obtained by rapid
solidification exploiting the presence of a miscibility gap in the liquid. Undercooling favored the separation
of a silver-rich liquid, that solidifies as f.c.c.-Ag solid solution, and a remaining liquid that falls in the
glass forming compositional range of the Cu–Zr–Ag–Al system. Alloys with nominal composition (at.%)
Ag73.0Cu12.7Zr12.1Al2.2 (alloy A), Ag73.1Cu17.2Zr9.7 (alloy B0), Ag72.5Cu16.7Zr9.4Al1.4 (alloy B1), Ag71.8Cu16.2
Zr9.1Al2.8 (alloy B2) were studied. All the alloys have a silver content (80 wt.%) corresponding to the
one required for commercial precious alloys. The effect of the cooling rate and the composition on phase
selection and microstructures was evaluated by comparing slowly cooled master ingots and rapidly
quenched ribbons. In alloys B0, B1 and B2, the amorphous fraction progressively reduces when increasing
the Al content. For alloy A, amorphization of the silver poor liquid can be obtained only at high quenching
rate. A ductile fracture behavior of the as-spun ribbons is combined with high hardness values (260–
290 HV)
Welding of IN792 DS superalloy by high energy density techniques
No full textLaser (LBW) and Electron Beam (EBW) welding have been used to produce seams on 2 mm thick plates of directionally solidified (DS) IN792 superalloy. For each welding technique a grid of samples were prepared by varying the pass speed (v) and keeping constant the other process parameters. The experiments were carried out at room temperature and with pre-heating (PHT) at 200 °C and 300 °C to find the best process conditions. The microstructural changes in molten zone (MZ) and heat affected zone (HAZ) were investigated finding that EBW guarantee a better quality and efficiency of the process without any macro defects. About the microstructure, the amount of ordered γ’ phase in the MZ is similar (≈ 25 %) for both welding techniques and quite lower than the value (70 %) of the original alloy
Tensile Properties of a Cast Al-Si-Mg Alloy with Reduced Si Content and Cr Addition at High Temperature
No full textTensile properties of an Al-Si-Mg casting alloy with reduced Si content and Cr addition were investigated at room and high temperatures. It was found that the studied alloy exhibits a remarkable performance up to 200 degrees C, with comparable or slightly higher strength than typical values for Al-Si-Mg-Cu alloys, commonly used for high-temperature applications, and good elongation. This is due to the choice of proper heat treatment and to the formation of dispersoids containing Cr during heat treatment, which are stable at the considered temperatures, as demonstrated by scanning and transmission electron microscopy (STEM) analysis. Interestingly, exposure to 300 degrees C during tensile tests enhanced an additional formation of dispersoids. It is believed that heating the material in T6 condition led to such observed dispersoids formation since precursors were already present in the Al matrix. This is not sufficient to avoid material softening at 300 degrees C, but it represents an interesting point in order to develop alternative heat treatment routes for dispersion-strengthened Al alloys
Assessment of the austempering process evolution through tensile testing
No full textThe capability of a constituent equation based on physical parameters to relate the plastic behavior with the microstructure was investigated in Austempered Ductile cast Iron 1050 (ADI 1050) to assess the stability of the residual austenite produced during austempering to obtain the optimum ausferritic microstructure. The critical time-window to interrupt austempering is that when the austempering transformation has come to saturation and an austenitic fraction characterized by maximum stability is produced (Stage I of austempering), before the precipitation of detrimental carbides e' takes place (Stage II of austempering). The ADI 1050 was quenched after different times during austempering, and the quenched samples were deformed through tensile testing at room temperature. The trends of ultimate tensile strengths Rm and elongations to rupture eR were consistent with the observed microstructure, and for very long austempering times a significant reduction in ductility was found, which could be rationalized as the occurring of e' precipitation. However, the Rm and eR data trends showed a large dispersion, so that it was impossible to identify unambiguously the optimum timewindow of austempering. For this reason, tensile flow curves were modelled with a constituent equation based on physical parameters related to the microstructure of materials. These parameters showed a lower dispersion with smooth trends against the austempering times, so they allowed to determine the critical time-window to stop the austempering industrial process for the best ausferrite
Assessment of the microstructure evolution of an austempered ductile iron during austempering process through strain hardening analysis
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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