High-Temperature Behavior of Metals

The design of new alloys as well as the optimization of processes involving whichever form of high-temperature deformation cannot disregard the characterization and/or modelling of the high-temperature structural response of the material [...

Improving the thermal response flexibility of 2- and 3-phase composite phase change materials by metallic triply periodic minimal surface structures

The percolation of organic Phase Change Materials (PCMs) into metallic skeletons produces Composite PCMs (C-PCMs). This paper explores Al-Si-Mg alloy Sheet-based Primitive-Schwarz (PS) Triply Periodic Minimal Surface (TPMS) C-PCMs filled by paraffines, comparing them with C-PCMs built with inverse Body-Centred Cubic (BCC) structures. The aim is to derive guidelines for improving the thermal response flexibility of these systems. The lattice geometrical features and C-PCM properties are calculated and modelled as a function of porosity (e), proportional to storable energy. For e > 0.8, the Effective Thermal Conductivity (lambda(eff)) of PS-based C-PCMs is higher than that of BCC-based, reaching 68 % of the maximum theoretical value. Design considerations are used to define a set of feasible C-PCMs whose thermal response is numerically simulated. The PS favours shorter transients than BCC (6.3 % less for e =0.8). The e increase, and, consequently, lambda(eff) reduction, in PS-based C-PCMs raises both storage potential and storage times (542 s vs 694 s for e = 0.8 vs 0.9). Minor changes in the storage times can be obtained by lattice size variation at constant e. The peculiarity of sheet-based TPMSs of splitting the volume into non-interconnected subdomains is exploited to design 3-phase C-PCMs, employing two PCMs having different melting temperatures

Role of microstructure in the exploitation of self-healing potential in form-stable composite phase change materials based on immiscible alloys

Metallic Phase Change Materials (PCMs), based on solid-liquid transitions, represents one of the most promising technologies for efficient Thermal Energy Storage (TES), due to their superior thermal conductivity and energy storability per unit volume, but suffer of limited solutions for their handling at the molten state. The use of Miscibility Gap Alloys (MGAs) allows to manage PCM volume expansion and keep it confined when molten, preventing interaction with the environment. A relevant example is provided by the Al-Sn system, where Al covers the role of the high-temperature stable and highly thermal-conductive passive matrix and Sn the active PCM. The alloy can thus be considered a Composite PCM (C-PCM). The response fastness of these systems depends on their thermal diffusivity, subjected to abrupt variations under the presence of discontinuities and damages. In this sense, the authors investigated the possibility to employ molten Sn mobility in a potentially damaged C-PCM for self-healing purposes, aimed to restore, at least partially, the material continuity and thus its thermal diffusivity. Exudation heat treatments above the melting temperature of Sn were performed on sets of Al-40%wt. Sn metallic composites, produced either with powder metallurgy or liquid metal routes, in order to quantify and assess the mobility of the Sn under simulated operating conditions. Exudation tests assess Simple Mixed powders and liquid metal routes sample as the ones with the highest healing potential. Al dissolution and re-deposition was established by EDS analyses as one of the principal Sn mobility mechanisms. Laser Flash Analysis tests, as well as microstructural investigations, were performed on the samples before and after both healing-focused and simulated service heat treatments to evaluate the changes of thermal diffusivity. Healing-focused treatment at 250°C for 1 hour generally displayed a moderate thermal diffusivity recovery and simulated service by shorter cycles between 170°C and 270°C slightly reduce it. The beneficial role of healing focused heat treatments at 250°C for 1 hour suggests that the presence of fully molten Sn phase during service for relatively long time could be beneficial for functional healing. The requirements of suitable Al-Sn microstructures for self-healing purposes, granting at the same time the C-PCM functionalities, i.e., thermal energy storage and form-stability, were set

Biological activity of enantiomeric complexes [PtCl2L2](L2 is aromatic bisphosphanes and aromatic diamines)

Enantiomeric complexes of formula [PtCl(2)L(2)] [L(2) is (R)-(+)-BINAP and (S)-(-)-BINAP, where BINAP is 2,2'-bis(diphenylphosphane)-1,1'-binaphthyl, and (R)-(+)-DABN and (S)-(-)-DABN, where DABN is 1,1'-binaphthyl-2,2'-diamine], were tested for their cytotoxic activity against three cancer cell lines and for their ability to bind to the human telomeric sequence folded in the G-quadruplex structure. Similar experiments were carried out on prototypal complexes cisplatin and cis-[PtCl(2)(PPh(3))(2)] for comparison. Platinum complexes containing phosphanes proved less cytotoxic to cancer cell lines and less likely to interact with the nucleobases of the G-quadruplex than those containing amines; in both cases the S-(-) isomer was more active than the R-(+) counterpart. More specifically, whereas all the platinum complexes were able to platinate the G-quadruplex structure from the human telomeric repeat, the extent and sites of platination depended on the nature of the ligands. Complexes containing (bulky) phosphanes interacted only with the adenines of the loops, whereas those containing the less sterically demanding amines interacted with adenines and some guanines of the G-quartet

High-Temperature Behavior of High-Pressure Diecast Alloys Based on the Al-Si-Cu System: The Role Played by Chemical Composition

Al-Si-Cu foundry alloys are widely applied in the form of high-pressure diecast components. They feature hypo- or nearly eutectic compositions, such as AlSi9Cu3(Fe), AlSi11Cu2(Fe), and AlSi12Cu1(Fe) alloys, which are used in the present study. Diecast specimens, with a thickness of 3 mm, were used for tension tests. The short-term mechanical behavior was characterized at temperatures from 25 up to 450 C. At temperatures above 200 C, the tensile strength properties (YS and UTS) of the investigated alloys were severely affected by temperature, and less by chemical differences. Material hardness and ductility indexes better highlighted the differences in the mechanical behavior of these age-hardenable alloys and allowed us to relate them to the microstructure and its changes that took place at test temperatures. Thermodynamic calculations were found to be useful tools to predict phases formed during solidification, as well as those related to precipitation strengthening. By means of the performed comprehensive material characterization, deeper knowledge of the microstructural changes of Al-Si-Cu foundry alloys during short-term mechanical behavior was obtained. The gained knowledge can be used as input data for constitutive modeling of the investigated alloys

A phase mixture model for anisotropic creep of forged Al-Cu-Mg-Si alloy

Aluminium wrought alloys are frequently applied to manufacture structural components of complex shape and used in a temperature range where creep phenomena take place.The aim of this paper is to analyze creep behavior of forged AA2014 alloy and to develop a constitutive model to describe inelastic response undermulti-axial stress state. Experimental data show that creep rates depend essentially on the loading direction within the power law creep regime,while in the power law breakdown range creep anisotropy is not essential and can be neglected.Microstructural observation suggest that the anisotropy of creep is primarily caused by elongated grains and grain boundaries as are suit of material processing. Assuming the inhomogeneous deformation indifferent microstructural zones including interiors of elongated grains and grain boundary regions,a phase mixture model of inelastic deformation is developed.The model include constitutive equations for individual phases and an interaction rule to capture the direction dependent creep.Additional state variables including the normalized dislocation density and the normalized particle size as well as corresponding evolution equations are introduced to describe hardening/recovery and over aging processes.Through a change of variables the modelis reduced to a set of kinetic equations such that the material parameters can be identified from families of creep curves for two loading directions.Results of identification are presented for the temperature of 1501C and several stress levels

High-Temperature Behavior of Metals

The design of new alloys as well as the optimization of processes involving whichever form of high-temperature deformation cannot disregard the characterization and/or modelling of the high-temperature structural response of the material [...