Study of the governing mechanisms during the synthesis of (La,Ce,Nd,Pr)(Cu,Ni)5 by low energy mechanical alloying

P. LACOURT; M.R. ESQUIVEL; G. MEYER

Ciudad de Buenos Aires

Congreso; ISMANAM 2008-XV International symposium on Metastable, Amorphous and Nanostructured Materials; 2008

Fernando Audebert-Laura Damonde-Facultad de Ingenieria-UBA

The processing of metals to synthesize alloys by low energy mechanical alloying (LEMA) presents the advantage that the temporal evolution is slow and the successive stages occurring can be studied in detail [1,2]. The features of these steps are correlated to the governing mechanisms of fracture and cold welding which can be studied by the combined analysis of the morphology, crystallite size, strain induced, particles size distribution and chemical composition of samples withdrawn at different integrated milling times (mt). In this work, a (La,Ce,Nd,Pr)(Cu,Ni)5 intermetallic was synthesized from a mixture of chunks of an alloy of mischmetal (La,Ce,Nd,Pr) and powder (Ni,Cu) metals according to the following route:  (La,Ce,Nd,Pr) + 5 (Ni,Cu)                                             (La,Ce,Nd,Pr)(Cu,Ni)5 Samples were withdrawn at different mt´s and analyzed by different techniques: X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and Energy Dispersive Spectroscopy (EDS). Cell parameter values, crystallite sizes and strain, particles morphology and size distribution during milling were obtained. Phases were quantified by Rietveld analysis. Four stages were observed during the synthesis process: Initial, Intermediate, Final and Completion. Initial stage, governed by fracture of (La,Ce,Nd,Pr) was detected up to mt of 15 h. Most important morphological changes were observed in these particles. Intermediate stage was observed up to 70 h. This stage is also influenced by cold welding as observed in the ball like shape of particles and initial formation of AB5 is detected. Final stage is observed between mt of 70 h and  120 h. Shared control of cold welding and fracture is observed in the cracked surface of ball like shape particles. At longer mt, the completion stage is reached. Refinement of the structure is observed and no further chemical composition changes are detected. Final microstructure features are discussed according to evolution observed during LEMA.  References: [1]  M.R. Esquivel, G. Meyer, Mat. Sc. Forum, 570,  2008, 72-77. [2] M.R. Esquivel, G. Meyer, J. Alloys Compd, 446-447, 2007, 212-217.