JOURNAL OF MATERIALS SCIENCE 24 (1989) 2891-2897 Permanent deformation of (Co, Ni)Zr intermetallic compounds through phase transformation MORIHIKO NAKAMURA National Research Institute for Metals, Tsukuba Laboratories, Sengen, Tsukuba, Ibaraki 305, Japan YOSHIO SAKKA National Research Institute for Metals, Nakameguro, Meguro-ku, Tokyo 153, Japan (Co, Ni)Zr intermetallic compounds, which have Bf structure at room temperature and B2 structure at elevated temperatures, were heated and cooled repeatedly in the temperature range between room temperature and 1 223 K. This process produced the large permanent deformation in Co30Ni20Zrs0 . Permanent elongation by as much as 0.2 to 0.3% per cycle was observed for the specimen parallel to the columnar structure, which grew from the bottom to the top of the button ingot, and permanent shrinkage by as much as 0.2% per cycle was observed for the specimen perpendicular to the columnar structure. For example, permanent elongation of about 30% was obtained after 93 cycles of the heating and cooling process in the former specimen, but no permanent elongation nor shrinkage was observed in the specimen parallel and perpendicular to the columnar structure for Co36Ni14Zr~0. The latter alloy had a different preferred orientation of the columnar structure from the former. These facts show that the crystal orientation influenced the permanent deformation caused by this transformation. 1. Introduction CoZr is an intermetallic compound with B2(CsC1) structure and exhibits no phase transformation even at temperatures as low as liquid nitrogen temperature [1]. On the other hand, NiZr is an intermetallic com- pound with Bf(CrB) structure. Both compounds have been reported to have no composition range of zir- conium [2]. The substitution of nickel for cobalt is therefore expected to cause phase transformation from B2 to Bf structure. Co40NiloZrso showed phase transformation as the temperature decreased to liquid nitrogen temperature, and the reverse transformation at about 373 K as the temperature increased from liquid nitrogen temperature [3]. (Co, Ni)Zr is an intermetallic compound which is composed of groups VIII and IVa elements in the Periodic Table, and NiTi, which is a famous shape- memory alloy, consists of elements of the same groups as (Co, Ni)Zr. The shape-memory effect of NiTi results from the martensitic transformation as the temperature falls, and the reverse transformation as it rises. Thus, it is interesting to examine the phase trans- formation behaviour of (Co, Ni)Zr intermetallic com- pounds. In this work, (Co, Ni)Zr, which showed phase transformation above room temperature, was examined macroscopically using a thermal exten- someter and large permanent deformation was found when Co30Ni20Zrs0was heated and cooled cyclically in the temperature range from room temperature to 1123K. 2. Experimental procedure The materials used for melting were electrolytic cobalt flakes (99.90wt %), electrolytic nickel (Ni + Co > 99.95 wt %) which was induction melted in vacuum, and non-consumable arc-melted sponge-zirconium. Co30Ni20Zrs0 and Co34Ni16Zrs0 were non-consumable arc-melted and button ingots of 100 g were obtained; 100g Fe-15 wt % Ni was also arc melted to compare with (Co, Ni)Zr. The weight loss of an ingot was less than 0.03 wt % and therefore chemical analysis was not carried out. (Co, Ni)Zr ingots were annealed at 1173 K for 180 k sec in vacuum followed by machining to specimens with a height of 9 mm and a cross-sectional area of 2.3 × 2.3 mm 2 for thermal expansion measure- ment. Both the annealed and the as-melted ingots had grains elongated from the bottom to the top of the button ingots. Then, the height direction of the specimen was chosen to be parallel or perpendicular to the elon- gated direction of the grains. As-melted Fe-Ni alloy was machined to specimens with the same geometry. Thermal expansion was measured using a Formaster (Fuji Denpa Co.) in which a specimen was heated and cooled in vacuum with induction heating. The heating rate of the specimen was 950 K/3 rain to 950 K/24 rain, and the specimen was cooled naturally from 1223 K to room temperature or at cooling rates of 950 K/3 rain to 950 K/24 rain. Both the heating and cooling rates of 950 K/6 min were mainly used when heating and cooling were cyclically repeated in the temperature range from room temperature to 1223 K. 0022-2461/89 $03.00 + .12 © 1989 Chapman and Hall Ltd. 2891