Characterization by XRD of intermetallics formed in multilayers Ni/Al bonds

A. URRUTIA; S. TUMMINELLO; D. G. LAMAS; S. SOMMADOSSI

Salvador de Bahia

Workshop; 3rd. IIW European-South-American School of Welding and Correlated Processes, SENAI CIMATEC. 07-09.10.2013, Salvador, BRASIL.; 2013

IIW - SENAI - CIMATEC

Characterization by XRD of intermetallics formed in multilayers Ni/Al bonds A. Urrutia (1), S. Tumminello (1,2), D. G. Lamas(1,3), S. Sommadossi(1,2)* (1) Lab. de Caracterización de Materiales, Fac. de Ingeniería, Univ. Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén, Argentina. (2) Materiales, IDEPA, CCT-Comahue-CONICET, Buenos Aires 1400, 8300 Neuquén, Argentina. (3) CCT-Comahue-CONICET, Buenos Aires 1400, 8300 Neuquén, Argentina. * silvana.sommadossi@fain.uncoma.edu.ar Keywords: Intermetallic phases, XRD, diffusion-reaction couples, Al-Ni Al-Ni system intermetallic phases are well known because of their attractive properties and the wide range of technological applications they satisfy; therefore a thorough comprehension of the system behavior is suggested. In particular, kinetic studies indicate the simultaneous development of intermetallic phases as a multilayer (Ci) bond generated by diffusion-reaction couples. The present work contributes to the morphological (SEM), chemical (EDS) and microhardness (HV) characterization of the intermetallic layers by means of preliminary conventional X-ray diffraction (XRD) analyses of Ni/Al diffusion-reaction couples between 800 and 1170°C. The intermetallic layers (Ci) were analyzed in bulk and powder form in order to establish correlation with important technological features. It has been found correspondence for 3 of 5 layers developed in the diffusion reaction couples with the predicted phases in the equilibrium phase diagram: C1: Al3Ni (Pnma), C2: Al3Ni2 (P3m1), C3: AlNi (Pm3m) compatible con Al1,1Ni0,9. According to the XRD analyses, the C4 do not present the NiAl, expected by the equilibrium phase diagram and the crystallographic pattern accepted in literature and therefore it was not identified yet. The C4 could be associated with the NiAl(Ni-rich) phase according to the well known thermodynamic behavior of NiAl, which shows an apparent phase duality. However from the technological point of view this phase duality for the single phase NiAl involves a well defined interface/discontinuity offering different characteristics (e.g. hardness, grain size). In addition, a martensitic transformation with layer morphology was found close to C4/C5(Ni3Al) interface, which can be controlled by thermal treatment.