Formation behavior of aluminide layers during the fabrication of Nb/Nb-aluminide laminate materials from Nb and Al foil

Laminate materials of Nb/Nb-aluminide were in-situ fabricated with pure Nb and Al foils by hot pressing. A pressure of 15 MPa was applied at the final temperature of the four-step heat treatment cycle, and this process made t he multi-layered materials where Nb and Nb-aluminide layers were well bonde d. The major phase of the layer was identified to be NbAl3 phase by X-ray d iffraction and SEM-EDS, and Nb2Al phase was also formed in the interface of Nb and NbAl3 layer. Therefore, the aluminide layer was stacked in the orde r of Nb/Nb2Al/NbAl3. The formation process of these phases is considered as , Nb(solid phase) + Al(solid phase) --> Nb(solid phase) + Al(liquid phase) --> Nb (solid phase) + NbAl3(solid phase) --> Nb(solid phase) + NbAl3(solid phase) + Nb2Al(solid phase). Nucleation and growth of the NbAl3 phase in t he first stage of the formation process is due to the solid Nb/liquid Al re action, and the formation of the Nb2Al layer in the second stage is caused by the diffusion of Nb into the NbAl3 layer. The thickness of aluminide lay ers (NbAl3 and Nb2Al phase) well agreed with values calculated by the diffu sion contorolled parabolic growth law.