Using differential scanning calorimetry as an analytical tool for ultrafine-grained metals processed by severe plastic deformation

Differential Scanning Calorimetry (DSC) is a thermal analysis technique that measures the energy absorbed or released by a sample as a function of temperature or time. Analysis by DSC has wide applications for examining solid-state reactions and solid-liquid reactions in many different materials. Quantitative analyses of the kinetics of reactions may be assessed by reviewing the interrelation between activation energy analysis methods. In recent years, DSC has been applied in the examination and analysis of bulk ultrafine-grained materials processed through the application of Severe Plastic Deformation (SPD). This overview examines these recent reports with reference to materials processed using the procedures of Equal-Channel Angular Pressing (ECAP), High-Pressure Torsion (HPT) and Accumulative Roll-Bonding (ARB). In addition, some critical issues related to DSC analysis are also discussed

Grain structure and texture development during ECAP of two heat-treatable Al-based alloys

The microstructures of a spray-cast Al-7034 (Al-Zn-Mg-Cu) alloy and an Al-2024 (Al-Cu-Mg) alloy were studied using electron back-scatter diffraction (EBSD) after processing through equal-channel angular pressing (ECAP). The EBSD results demonstrate there is a relatively rapid increase in the fraction of low-angle boundaries during the initial ECAP passes and a subsequent more gradual increase in the fraction of high-angle grain boundaries in subsequent passes. The crystallographic textures and their rotations during ECAP were analysed through EBSD

Evolution of microstructure and precipitation in heat-treatable aluminium alloys during ECA pressing and subsequent heat treatment

The precipitation and evolution of microstructure in a spray-cast Al-7034 alloy and a commercial wrought Al-2024 alloy were studied after equal-channel angular pressing (ECAP) using transmission electron microscopy and differential scanning calorimetry (DSC). Microstructural examination showed the grain sizes of both alloys were reduced to the range of ~0.3–0.5 µm through ECAP. The DSC analysis identified the occurrence of thermal effects involving the formation, coarsening, dissolution and melting of the precipitate phases and concurrent recrystallization. The heating and ageing response of the alloys processed by ECAP was identified by micro-hardness testing of the samples after interrupted heating and ageing treatments

Hardness homogeneity on longitudinal and transverse sections of an aluminum alloy processed by ECAP

Billets of a commercial-purity aluminum Al-1050 alloy were processed by equal-channel angular pressing (ECAP) at room temperature for up to six passes and microhardness measurements were recorded on the longitudinal and cross-sectional planes of each billet. Large numbers of datum points were recorded in order to minimize the errors in the results. The measurements show the hardness increases significantly after the first pass and then increases by very small amounts in subsequent passes. There are regions of lower hardness running in bands near the top and bottom surfaces of each billet. With increasing numbers of passes, the lower hardness region near the top surface disappears and the region near the lower surface remains in place but becomes less extensive. Neglecting the very small region of lower hardness near the bottom surface, the results show there is a potential for achieving excellent three-dimensional homogeneity after six passes of ECAP.<br/

The evolution of homogeneity during processing aluminium alloys by HPT

Disks of a commercial purity aluminium Al-1050 alloy and Al-1%Mg alloy were processed by high-pressure torsion (HPT) at room temperature for up to a maximum of 5 turns under a pressure of 6 GPa. Following processing, hardness measurements were recorded across the surfaces of the disks. These measurements showed low values of hardness at the center and high values near the edges of the disks and the hardness increased in both alloys with increasing numbers of turns. The evolution of homogeneity in hardness was rapid in Al-1050 compared to the Al-1%Mg alloy. After 5 turns of HPT under a pressure of 6 GPa, the hardness was fully homogeneous across the total surface of the Al-1050 disk whereas there was a region of lower hardness around the center of the Al-1%Mg disk. The results reveal the significant difference between both alloys where the higher rate of recovery in the Al-1050 alloy leads to a rapid evolution of the hardness homogeneity

Influence of strain rate on the characteristics of a magnesium alloy processed by high-pressure torsion

A commercial magnesium AZ31 alloy was processed by high-pressure torsion (HPT) through 5 turns at 453 K using three different rotation rates. The results show that HPT introduces significant grain refinement to an average grain size of 0.5 ?m. The processed structures were heterogeneous in the centers of the disks and homogeneous at distances at and above 1 mm from the disk centers. The measured values of the microhardness were also reasonably homogeneous after HPT except only near the disk centers. The hardness values and the average grain sizes were correlated with the local strain rates by using the imposed rotation rates and estimates of the strains within the disks. The results demonstrate the hardness and the average grain size both exhibit a small dependence on the local strain rate.<br/

Adsorption capacity of activated carbon for n-alkane VOCs

The volatile organic compounds (VOCs) in the indoor air come from many sources including building materials, furnishings, occupant activities and in some cases, the ventilation air. Granular activated carbons (GAC) have been increasingly used to remove these contaminants, particularly for small commercial buildings and those located in urban centers or near industrial plants where the quality of outdoor air may be worse than that of the indoor air. Tests were conducted to determine the efficiency of GAC in removing VOCs from the indoor air. Seven n-alkanes VOCs covering a wide range of molecular sizes were selected for these tests. They were pentane, hexane, heptane, octane, nonane, decane, and undecane. The breakthrough time and VOC mass adsorbed on GAC for these individual VOCs were obtained. It was found that the adsorption capacity of GAC decreases as the initial VOC concentration, C0, decreases.Les compos\ue9s organiques volatiles (COV) pr\ue9sents dans l'air int\ue9rieur proviennent de nombreuses sources, dont les mat\ue9riaux de construction, l'ameublement, les activit\ue9s des occupants et, dans certains cas, l'air de ventilation. Les charbons actifs granulaires (CAG) sont de plus en plus utilis\ue9s pour \ue9liminer ces contaminants, particuli\ue8rement dans les petits b\ue2timents commerciaux et ceux qui sont situ\ue9s dans les centres urbains ou pr\ue8s des usines industrielles o\uf9 la qualit\ue9 de l'air ext\ue9rieur peut \ueatre pire que celle de l'air int\ue9rieur. Des tests ont \ue9t\ue9 effectu\ue9s afin de d\ue9terminer l'efficacit\ue9 des CAG pour \ue9liminer les COV de l'air int\ue9rieur. Sept COV n-alkanes couvrant un large \ue9ventail de tailles mol\ue9culaires ont \ue9t\ue9 retenus pour ces tests : pentane, hexane, heptane, octane, nonane, d\ue9cande et und\ue9cane. On a mesur\ue9 le d\ue9lai de p\ue9n\ue9tration et la masse de COV adsorb\ue9e par les CAG pour ces COV individuels. On a observ\ue9 que la capacit\ue9 d'adsorption diminuait \ue0 mesure que la concentration initiale (C0) des COV diminuait.Was published in Engineering Solutions to Indoor Air Quality Problems Conference Proceedings, 2000, pp. 241-253Peer reviewed: YesNRC publication: Ye

Wear resistance of SPD-processed alloys

Various different severe plastic deformation processes(SPD) have been developed to produce ultra-fine grained (UFG) materials during the last two decades. One very important material property that the UFG materials should have for structural materials application is good wear resistance. This review paper presents some recent work related to the wear resistance of materials processed by SPD, in particular for alloys processed by using equal-channel angular pressing (ECAP) and accumulative roll-bonding (ARB)