J.F.R. de Castro

Materials selection as an interdisciplinary technical activity: basic methodology and case studies

The technical activity known as Materials Selection is reviewed in its concepts and methodologies. Objectives and strategies are briefly presented and two important features are introduced and discussed; (i) Merit Indices: a combination of materials properties, which maximises the objectives chosen by the designer and (ii) Materials Properties Maps: a bi-dimensional space whose coordinates are pairs of properties in which materials can be plotted and compared directly in terms of their merit indices. A general strategy for the deduction of these indices is explained and a formal methodology to establish a ranking of candidate materials when multiple constraints intervene is presented. Finally, two case studies are discussed in depth, one related to materials substitution in the context of mechanical design and a less conventional case linking material selection to physical comfort in the home furniture industry.

Mechanical and Reactive Milling of a TiCrV BCC Solid Solution

Nowadays, many efforts have been concentrated in research and development of hydrogen absorbing materials due to a possible application as electrode for rechargeable batteries, on board hydrogen storage systems, getters, catalysts, etc. Novel technologies for materials processing have been used to generate new alloys with metastable structures, such as amorphous and/or nanocrystalline alloys. In this context, mechanical milling or mechanical alloying is a very attractive way to produce this alloys, specially when carried out under hydrogen atmosphere (reactive milling). In this work, we have studied the structural evolution of a TiCrV bcc solid solution during mechanical and reactive milling. The process parameters analyzed were: milling atmosphere (argon and hydrogen), milling time and gas pressure into the vials (in the case of reactive milling). Structural evolution was investigated by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). Hydrogen contents of the reactive milled alloys were determined using a Leco analyzer. Differential scanning calorimetry (DSC) was used to determine the hydrogen desorption temperature and the stability of the alloys.

Two Routes to Process the Mg-5at.%Nb Nanocomposite

In this work, we report the processing of MgH2 + 5at.% Nb nanocomposite by two different routes. In the first one, MgH2 and Nb powders were milled under argon for 20h, using a shaker mill. In the second route, Mg chips and Nb powders were milled under hydrogen atmosphere for 48h, using a centrifugal mill. The phase transformations and microstructural changes were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Significant differences in the morphology and phase formation were observed between the two processing routes. The nanocomposite obtained under hydrogen atmosphere showed a slight improvement in the hydrogen desorption properties as compared with the nanocomposite obtained under inert atmosphere. Moreover, we have observed that the addition of Nb improves the kinetics of Mg hydriding.