J. J. Cruz-Rivera

Analysis of Ostwald ripening in Ni-rich Ni-Ti alloys by diffusion couples

The coarsening kinetics of γ′ precipitates in Ni-rich Ni-Ti alloys are studied using a Ni-11.5 wt% Ti and pure Ni diffusion couple. The formed concentration gradient allowed to study the aging process at 1023 K (750 °C) in Ni-rich Ni-Ti alloys with Ti content from 8.62 to 11.15 wt% Ti. In general, during the coarsening of γ′ precipitates, the experimental coarsening kinetics do not fit well to the LSW or TIDC theoretical models and anomalous behaviour of coarsening rate constant (kr) associated with γ′ volume-fraction is confirmed at high values.

Comparative study of Oswald ripening and trans-interface diffusion-controlled theory models: Coarsening of γ′ precipitates affected by elastic strain along a concentration gradient

According to Lifshitz, Slyozov, and Wagner (LSW) and Trans-Interface Diffusion-Controlled (TICD) theoretical models, this paper reports the microstructure and its coarsening behavior of γ′ metastable-coherent precipitates in concentration gradient of Ni-13.75Ti (at%)/Ni generated by diffusion couple. The coarsening of precipitates was evaluated in two different Ti contents (R1-11.4Ti (at%) and R2-13Ti (at%)) generated along the concentration gradient and includes average size, size distributions and growth rate. The solvus and metastable-coherent bimodal lines as determined at 850 °C of 9.16 (at%) and 9.92Ti (at%) respectively by scanning electron microscopy. This paper suggests that elastic strains produced by the matrix/precipitate lattice mismatch caused significant deviations between the experimental results and those predicted by the LSW or TIDC theories. Activation energies for TIDC (Qi) and LSW (Qr) are Qr: 219.69 and 172.61 kJ mol-1 for R1 and R2 regions, respectively, and Qi: 218.46 and 164.56 kJmol-1 for R1 and R2 regions, respectively. A concentration gradient allows the study of various alloys with different concentration and volume-fraction in a single sample.

Morphological Evolution and Coalescence of γ’ Precipitates

Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes No. 120, 31136, Chihuahua, Chih., México. Universidad Autónoma de San Luis Potosí, Instituto de Metalurgia, Sierra leona 550, Col. Lomas 2 sección, C. P. 78210, S.L.P., México, Universidad Autónoma de Chihuahua (UACH), Facultad de Ingeniería, Circuito No. 1, Nuevo Campus Universitario, CP 31125 Chihuahua, Chih., México. Instituto Politécnico Nacional, ESIQIE-DIM, 118-556, D.F., México.

Study of precipitation along a concentration gradient

The present work is based on the microstructural characterization method proposed by T. Miyazaki [13], the so-called Macroscopic Composition Gradient (MCG) method. This technique allows the investigation of phase transformations in a single specimen and helps to evaluate the mechanical properties for different alloy compositions. It is based on the microstructural observation of a continuous concentration gradient, which can be generated by several methods, for instance, diffusion coupling, imperfect homogenization of coarse discontinuous precipitates, etc.