Degassing Behavior of Nanostructured Al and Its Composites

The synthesis of bulk ultrafine-grained (UFG) and nanostructured Al via cryomilling can frequently require a degassing step prior to consolidation, partly due to the large surface area of the as-milled powders. The objective of this study is to investigate the effects associated with cryomilling with stearic acid additions (as a process-control agent) on the degassing behavior of Al powders. This objective was accomplished by completing select experiments with Al-7.5Mg, Al-6.4 wt pct Al85Ni10La5, and Al-14.3 wt pct B4C. The interaction between Al and stearic acid was determined using thermal analysis combined with Fourier transform infrared spectroscopy (FTIR). The degassing experiments were carried out under high vacuum (10−4 to ~10−6 torr) in a range from room temperature to 400 °C, with the pressure of the released gases monitored using a digital vacuum gage. The results showed that the liberation of chemisorbed water was suppressed in cryomilled Al powders and both the chemisorbed water and stearic acid were primarily released in the form of hydrogen. It was also demonstrated that under certain conditions, a nanostructure (grain size ~100 nm) can be retained following the hot vacuum degassing of cryomilled Al

Ultrafine eutectic coatings from Fe-Nb-B powder using laser cladding

In this paper, a laser cladding process was proposed to obtain ultrafine eutectic Fe-Nb-B alloy coatings on AISI 1020 steel substrate in which the power and scanning speed were defined. The laser cladding process can be used as a rapid solidification processing route to produce single laser tracks and coatings (overlapped tracks) with pre-placed powders deposited onto a mild steel substrate in order to obtain a minimal dilution between the coating/substrate. This research aims to produce a coating of Fe74.25Nb8.25B17.5 (at.%) alloy over the AISI 1020 steel substrate by laser cladding using a pre-placed powder method to investigate the parameters on coating production, dilution, microstructure, and properties. The final goal is to find an appropriate processing parameter range to obtain coatings with high hardness and possibly good wear resistance. The microstructure and behavior of powder, cladding layers and coatings were examined by X-ray Diffractometry, Differential Scanning Calorimetry, Scanning Electron Microscopy and Transmission Electron Microscopy of selected samples prepared with a Dual Beam microscope using a Focused Ion Beam. For the processing conditions used, the coatings showed larger exothermic crystallization peaks. The results of microhardness from coatings showed values of hardness over 700 HV160COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2013/05987-8; 2015/19978-

Cryomilling for the fabrication of a particulate B4C reinforced Al nanocomposite: Part II. Mechanisms for microstructural evolution

Cryomilling was successfully employed to fabricate particulate B4C-reinforced Al matrix nanocomposite powders. In order to investigate the microstructural evolution during cryomilling, composite powders were milled for different times. These powders were collected from the milling chamber and the microstructures were characterized to reveal the formation mechanism for this nanocomposite. The microstructural evolution, including the morphology and size of the milled composite powders, the size and distribution of the B4C, and the dimension of the Al grains, is discussed on the basis of the experimental results.close151