Search

Eleven k inds of pure i r o n specimens dopted with a s m a l l amount of r a r e e a r t h elements were used i n present research. Int e r n a l f r i c t i o n s were measured with a t o r s i o n pendulum. Experimental r e s u l t s sh~wed that the n i t rogen Snoek peak becomes broadened and the optimum i n t e r n a l f r i c t i o n s h i f t s t o a higher temperature. When the r a r e e a r t h elements a r e increased the n i t rogen peak tends t o separa te i n t o two pa r t s . I n genera l , the he ight of ni trogen Snoek peak decreases with the inc rease of rase e a r t h contents . On the b a s i s of the experimental r e s u l t s i t i s suggested t h a t the r a r e e a r t h elements i n t he i n t e r i o r o f pure i r o n g r a i n s is i n a s t a t e of s o l i d so lu t ion . The high temperature i n t e r n a l f r i c t i o n s were measured i n two pure i r o n specimens conta in ing d i f f e r e n t content of Lanthanum. Two i n t e r n a l f r i c t i o n peaks were obtained i n each specimen. One i n t e r n a l f r i c t i o n peak around 550'C i s the g r a i n boundary peak of pure i ron , while the o the r i n t e r n a l f r i c t i o n peak around 700°C is a new one. Af t e r t r e a t i n g one of the above two specimens i n t o very l a r g e g r a i n s i n specimen both the i n t e r n a l f r i c t i o n peaks of pure i r o n and new one were a l lodisappeared . Only the pure i r o n g r a i n boundary peak around 500 C w a s observed i n the pure i r o n specimen containing no r a r e e a r t h elements. Therefore, the new i n t e r n a l f r i c t i o n peak may be assoc ia ted with the g r a i n boundary which adsorbed a small amount of r a r e e a r t h elements. Based on the r e s u l t s presented as above, i t may be concluded t h a t the r a r e e a r t h elements i n pure i r o n d i s t r i b u t e not only i n the i n t e r i o r of g ra ins i n a s t a t e of s o l i d so lu t ion , but a l s o segregate s l i g h t l y at the g r a i n boundary a r e a i n a s t a t e of adsorpt ion .

Three types of specimens of Fe-Cr-Al alloys containing a small amount of rare earth elements were used in this work. Several internal friction peaks were observed at high temperature in each specimen. (1) For specimen 1, Cr13Al6Mo2 (with 0.05 wt% Ce) internal friction peaks occurred at temperatures around 450°C, 624°C and 690°C with frequencies of vibration of 0.67Hz, 0.59Hz and 0.55Hz respectively. The activation energies of the last two peaks were found to be about 3.3ev and 4.0ev. (2) For specimen 2, Cr27Al7Mo2 (with 0.056 wt% Ce) still three internal friction peaks occurred at temperatures around 523°C, 663°C and 713°C with frequencies of vibration of 0.61Hz, 0.56Hz and 0.52Hz respectively. The activation energies of the last two peaks were found to be about 3.6ev, 4.0ev. (3) For specimen 4, Cr23Al6 (with 0.065 wt% Y) three internal friction peaks were also observed at temperatures around 529°C, 632°C and 690°C respectively. 3.1ev and 3.9ev are the activation energies related to the last two peaks. It is suggested that the first peak is Zener relaxation peak to be associated with the stress induced reorientation of Fe-Cr atomic pairs. The other two peaks are the solute grain boundary peaks of Fe-Cr and Fe-Re. Based on the results mentioned above, the mechanism of improvement of the high temperature properties of Fe-Cr-Al alloys by the addition of a small amount of rare earth elements was discussed.