T. Waitz et al. Acta Materialia 52(2004)137-14 to the amorphous rings weak(200)B2 reflections were observed. It should be mentioned that a volume fraction of about 5% corresponds to coarse spherical particles of the Ti2 Ni lattice that have survived the hpt in both cases S=6.7 and 7.3(cf. P in Fig. 1(a) 3. 2. Nanocrystallization after different heat treatments The onset of the crystallization was measured by DSC (cf. Fig 3). The analysis of the dSc curve of the HPT specimen with the lower strain(S= 6.7) yields that both the crystallization temperature and the crystall zation enthalpy are lower than in the case of s=7.3. Tx (Tp)are 352C(374C)and 362C(379C)in the case of S=6.7 and 7.3, respectively. The crystallization en- harpies△H67and△H73 are about-1.4and-1.7kJ mol corresponding to S=6.7 and 7.3, respectively Fig. 4 shows TEM bright field images of annealed specimens. Figs. 4(a) and(b)correspond to the defo mations S=6.7 ands=7.3, respectively; in addition the R pecimens were isothermally annealed at a temperature T=352°c 0,0 S=6.7 -0.5 374°C 00 Temperature['CI 0.5 T=362°c 0,0 0.5 Fig 4 Nanocrystalline phase formed after isothermal annealing of HPT deformed amorphous Ni-503at %Ti. TEM bright field images. T=379°c (a)S=6.7 after annealing at 340C for 5 h. Most of the grains are -1.0 smaller than about 50 nm containing both B2 and R-phase.(b 7.3 after annealing at 340C for 5 h. Frequently areas are Temperature[C] observed that contain mainly smaller grains (e.g. near S) and are adjacent to areas where larger gra dominating (e. g. near M Fig. 3. DSC curves of the crystallization of HPT deformed Ni- B2 phase and R-phase are found in the smaller grains near S. R 503at%Ti (heating rate 40C/min). (a)S=6.7. An exothermic peak marks a grain of the R-phase. Martensite occurs in the grains near occurs at Tp=374C; the crystallization temperature T=352C is M having a diameter of about 120 nm.(c)S=7.3 after annealing at indicated.(b)S=7.3. The crystallization occurs at a higher tempera- 450.C for I h. Almost all grains larger than about 150 nm contain ture(p=379°C,Tx=362°Cto the amorphous rings weak h200iB2 reflections were observed. It should be mentioned that a volume fraction of about 5% corresponds to coarse spherical particles of the Ti2Ni lattice that have survived the HPT in both cases S ¼ 6:7 and 7.3 (cf. P in Fig. 1(a)). 3.2. Nanocrystallization after different heat treatments The onset of the crystallization was measured by DSC (cf. Fig. 3). The analysis of the DSC curve of the HPT specimen with the lower strain (S ¼ 6:7) yields that both the crystallization temperature and the crystalli￾zation enthalpy are lower than in the case of S ¼ 7:3. Tx (Tp) are 352 C (374 C) and 362 C (379 C) in the case of S ¼ 6:7 and 7.3, respectively. The crystallization en￾thalpies DH6:7 and DH7:3 are about )1.4 and )1.7 kJ/ mol corresponding to S ¼ 6:7 and 7.3, respectively. Fig. 4 shows TEM bright field images of annealed specimens. Figs. 4(a) and (b) correspond to the defor￾mations S ¼ 6:7 and S ¼ 7:3, respectively; in addition the specimens were isothermally annealed at a temperature Fig. 3. DSC curves of the crystallization of HPT deformed Ni– 50.3at.%Ti. (heating rate 40 C/min). (a) S ¼ 6:7. An exothermic peak occurs at Tp ¼ 374 C; the crystallization temperature Tx ¼ 352 C is indicated. (b) S ¼ 7:3. The crystallization occurs at a higher tempera￾ture (Tp ¼ 379 C, Tx ¼ 362 C). Fig. 4. Nanocrystalline phase formed after isothermal annealing of HPT deformed amorphous Ni–50.3at.%Ti. TEM bright field images. (a) S ¼ 6:7 after annealing at 340 C for 5 h. Most of the grains are smaller than about 50 nm containing both B2 and R-phase. (b) S ¼ 7:3 after annealing at 340 C for 5 h. Frequently areas are observed that contain mainly smaller grains (e.g. near S) and are adjacent to areas where larger grains are dominating (e.g. near M). B2 phase and R-phase are found in the smaller grains near S. R marks a grain of the R-phase. Martensite occurs in the grains near M having a diameter of about 120 nm. (c) S ¼ 7:3 after annealing at 450 C for 1 h. Almost all grains larger than about 150 nm contain martensite. 140 T. Waitz et al. / Acta Materialia 52 (2004) 137–147