Materials Science Forum Vols. 636-637

Abstract: In this study, corrosion behaviour of Al–12Si-20Mg-XTi alloys (Ti content varied between 0 and 4 wt.%) was investigated. Characterizations of the alloys were carried out by microstructural examinations and corrosion tests. Microstructural results showed that precipitation of the Mg2Si phases was observed in Al-12Si-20Mg-XTi alloy matrix as two different morphologies; i.e. as a polyhedral primary particle and as a chinese script. Upon addition of Ti, Al3Ti intermetallic precipitated in the alloy. Corrosion tests were carried out by immersing the alloys in “30 g/l NaCl+10 ml/l HCl” solution. Evaluation of corrosion was determined by measuring weight loss for 24 hours and by potentiodynamic polarization tests. Corrosion resistance of the alloy was approximately constant with 1 wt % Ti addition whereas at higher additions, the corrosion rate increased.

Abstract: In the present study we examine the crystallographic structure of the , ’’ and  phases present in nickel base 718 alloy. The chemical ordering of Nb atoms and possible planar faults that may be observed in ’’ precipitates are detailed. High resolution transmission electron microscopy (HRTEM) observations of various faults are reported. The decomposition of a matrix dislocation to form a locked V shaped configuration is shown. The observation along [110] type direction allows to identify the type of defect, which is observed as a pure geometric stacking fault.

Abstract: The influence of post-inoculation and of cerium and antimony additions on the solidification process and on the formation of chunky graphite in ductile iron heavy-section parts have been studied previously in the case of near-eutectic alloys. It appeared of interest to complement these works by analysing the effect of carbon equivalent on graphite degeneracy. In the present work, hypo-, hyper- and near-eutectic melts have been cast in large blocks and standard cups. Analysis of the corresponding cooling curves recorded during solidification as well as microstructure observations on these casts have been carried out. A clear effect of carbon equivalent as promoter of chunky graphite formation is observed. The results have been added to the set of data already available and various correlations are discussed.

Abstract: Twenty brass Chinese cash coins with complex compositions were studied for a better understanding of the metallurgical cash production in China, during the 17th, 18th and 19th centuries. Elemental composition was obtained through energy-dispersive micro X-ray fluorescence spectrometry of small cleaned areas on the coins rims. Results showed that these brass alloys (Cu-Zn) frequently contain up to 3% Sn, have highly variable Pb content (from n.d. up to 14%) and Fe, Sb, and As as minor elements. Microstructures were assessed by optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and preliminary micro X-ray diffraction analysis. All the coins present typical as-cast microstructures although very fine-grained, which are supported by binary (Cu-Zn) and ternary (Cu-Zn-Sn) equilibrium phase diagrams, that explain microstructural differences due to the presence of Sn in these brasses.

Abstract: Asymmetrical rolling, in which the circumferential velocities of the working rolls are different, is a method to impose shear deformation in addition to the thickness reduction. As a consequence, the deformation texture can be modified as compared to the classical rolling. In this work, the asymmetrical rolling of invar (Fe-36%Ni) and the influence of the deformation route are studied. The Invar® alloy has been deformed by asymmetrical rolling with a 83% thickness reduction. The texture of the deformed alloy was measured by X-ray diffraction at different levels through the thickness: upper side- middle- down side. With asymmetrical rolling, the deformed texture is a copper type texture but the components were rotated about 5-7° around the Transverse Direction (TD) axis as compared to the ideal position of these components in the pole figure representation. The rotation of the pole figure is an indicator of the amount of shear really introduced in the material during asymmetrical rolling. Finally, a simple model was developed in order to establish the condition to obtain either shear texture or grain refinement.

Abstract: In the present study, equiatomic powder blends of Ni and Ti were mechanically activated for a short period of time in a planetary ball mill using different levels of energy input. The characterization of the mechanically activated materials was achieved by scanning electron microscopy, X-ray diffraction, differential thermal analysis and chemical analysis (oxygen and nitrogen measurements). During mechanical activation no phase transformation was induced and the high temperature reaction between Ni and Ti elemental powders was shifted to lower temperatures. Moreover, the temperature and the intensity of the exothermic reaction, i.e. the reactivity observed in the powder blends, decreased with the increase in the level of milling energy input. A maximum oxygen content of 0.39 wt% was measured after mechanical activation.

Abstract: This paper presents a research concerning the equilibrium of ferrite and secondary cementite and Widmanstätten structure formation, resulting in precise conditions. If all researchers agree with the mechanisms of ferrite and massive cementite formation in steels, the Widmanstätten structure formation is rather disputable and new data in the area of massive transformation might account for the formation of Widmanstätten structures in the low carbon steels. For the massive phase and Widmanstätten structures, the mathematic relations regarding the rate of growth are presented.

Abstract: The paper presents the results of theoretical and experimental research regarding the establishing of some chemical positions of the bearing alloy and of cladding technology. The final properties of the materials depend on the kinetics and thermodynamics of the interface processes. In the paper the diffusion zone developed between the two bimetal materials is revealed and characterized under the aspect of chemical composition and structure. An application for this research that could lead to increasing the endurance of the steel products cladded through welding is the case of boring bits with three cones, which work under short oiling conditions and variations of the contact pressure.

Abstract: Upward directional transient solidification experiments have been carried out with an Al-1.0wt%Fe alloy. Tensile tests were carried out with samples collected along the casting length and these results have been correlated with measured cell spacings, since cellular growth has prevailed along the directionally solidified casting. The resulting mechanical properties include ultimate tensile strength, yield tensile strength and elongation. The used casting assembly was designed in such a way that the heat was extracted only through the water-cooled system at bottom of the casting. During non-equilibrium solidification, typical of DC (direct chill) castings, different cooling rates occur from the casting cooled surface up to the top of the casting, causing the formation of metastable intermetallic phases (AlmFe, Al6Fe, etc) in addition to the stable Al3Fe phase. The extensive presence of plate-like Al3Fe phase in the as-cast structure adversely influences the mechanical properties of Al-Fe alloys, since this morphology is more likely to induce microcracks than the fibrous Al6Fe phase. In order to permit an appropriate characterization of these intermetallic phases, they were extracted from the aluminum-rich matrix by using a dissolution technique. These phases were then investigated by optical microscopy and SEM techniques. It was found that the ultimate tensile strength, the yield strength and the elongation increase with decreasing cell spacing and experimental laws correlating cell spacing and these mechanical properties have been established.

Abstract: This paper reports preliminary studies regarding a new fabrication process for aluminium alloy matrix particulate reinforced composites, which uses ceramic preforms with alumina and tailored amounts of reactive copper oxide, CuO. An Al2O3-CuO mixture with 75 mol% CuO was selected, aiming at a 10-40vol% reinforcement phase fraction in the final composite, after aluminium infiltration. Molten aluminium infiltration progress was studied as a function of ceramic’s composition, doping, and infiltration time. The resulting microstructures were investigated by OM, SEM, FESEM and EDS in order to establish the liquid aluminium infiltration profile at the metal/ceramic interface. Infiltration experiments showed that the 3CuO (s) + 2Al (l) → 3Cu (l) + Al2O3 (s) redox reaction is triggered at the experimental conditions used, but the infiltration process is slow and does not go to completion. The use of NaOH as a doping agent promotes effective infiltration of molten aluminium upon the ceramic green mixture.