C.S. Kiminami

Severe Plastic Deformation of Mg-Fe Powders to Produce Bulk Hydrides

We describe in the present work the production of bulk Mg hydrides by hydrogenation treatment of samples processed by severe plastic deformation. The compact bulk samples of Mg-Fe have been obtained by high pressure torsion. The ternary complex Mg2FeH6 and the binary MgH2hydrides have been synthesized by hydrogenation treatment at 350°C, at 3 MPa during 24 h. The average grain refinement after HPT was modest as estimated by XRD. A comparison between the XRD patterns of the powders and of the HPT samples showed the formation, as expected, of a preferred orientation in the latter. The XRD of the hydride HPT samples (H-HPT) showed the presence of Mg, Fe, MgH2 and Mg2FeH6. The first de-hydrating reaction of the alloys (after H-HPT) was studied by differential scanning calorimetry (DSC). These results showed a reduction in the hydrogen dessorption temperature in comparison with commercial MgH2, indicating thermodynamic destabilization of the hydrides as a result of the high density of dislocations in the H-HPT samples.

Microstructure Characterization and Kinetics of Crystallization Behavior of Tubular Spray Formed Fe43.2Co28.8B19.2Si4.8Nb4 Bulk Metallic Glass

Abstract In this study the Fe43.2Co28.8B19.2Si4.8Nb4 (at.%) alloy was processed by spray forming in an industrial facility with the aim of investigating the formation of amorphous phases. The thicker layers (5–15 mm) presented partial/fully crystalline microstructure with onset of crystallization of the amorphous phase at Tx = 595 °C. On the other hand, thinner layers (below 2.5 mm) presented fully amorphous structure, and glassy behaviour with glass transition (Tg) at 555 °C. The thermal stability and the crystallization kinetics of the alloy were studied using the isothermal DSC curves, measured at different heating rates and temperatures. Despite its good glass-forming ability (GFA) and high stability against crystallizations, its incubation time for crystallization is almost zero. In order to rule-out the complete crystallization mechanism, in situ temperature resolved studies using TEM were done. In addition, the amorphous part of the deposit was heat treated at various temperatures/times and the results were compared with the in situ crystallization behavior observed by TEM.

Effect of the addition of Mn on the tensile properties of a spray-formed and extruded Al-9Si-4Cu-1Fe alloy

The microstructure and the tensile properties of a spray-formed and extruded Al-9Si-4Cu-1Fe alloy were investigated. Manganese (0.3, 1, 2 in wt%) was added to the alloy to avoid the formation of the needle-like β-AlFeSi intermetallic phases that are highly detrimental to the alloys ductility. The deposits were extruded at 623K with a n area reduction of 5 to 1. Small faceted dispersoids surrounding the equiaxial α-Al matrix, mainly in the form of silicon particles, were identified by SEM-EDS, as well as the Mn-containing α-Al15(Fe,Mn)3Si2 phase. The presence of the needle-like β-Al(Fe,Mn)Si was scanty, even with the lowest Mn content. The room temperature tensile tests of all the extruded alloys showed a significant increase in elongation to fracture when compared with the values observed fo r the as-spray formed deposits.This result can be ascribed to the elimination of porosity promoted by the extrusion process and to the smaller grain size of the extruded samples.