Studies on Helium Ion Irradiated NiAl Alloy

Abstract

IntroductionThe behaviour of helium in metals is of importance both from basic and technological points of view. In fusion reactors, helium will be implanted on the different components like first wall etc. Due to its low solid solubility in metals, it gets seggregated and forms bubbles affecting their properties [l]; exfoliations and blisters are also formed on the surface [2 to 41. Nickel is one of the important constituents of materials like steel which are proposed to be used in fusion reactors as first wall. The defects will be created in this material and their study is important.Defects in nickel and its alloys have earlier been studied [5 to 91. But the defects created by helium ions and their interaction with helium needs further work. Recently some work [lo, 111 on helium ion irradiation in nickel has been reported. In the present study isochronal annealings of 30 MeV a-ion irradiated nickel and nickel-aluminium alloy have been carried out using the resistivity technique.Experimental Nickel-0.5 wt% A1 and Ni-1.0 wt% A1 were made from nickel of 99.99% and aluminium of 99.99% purity. These alloys were melted in an arc furnace under inert atmosphere for a couple of times for better homogenisation. The buttons of nickel and Ni-A1 alloys were rolled down to a thickness of 0.05 cm in stages. Samples of size 1.0 x 0.5 cm2 were cut out and annealed at 1073 K and irradiated by helium ions of 30 MeV to various doses in a variable energy cyclotron. The temperature of the sample during irradiation was ~3 5 0 K. Nickel and Ni-0.5% A1 samples were irradiated to a dose of 6 x 10l6 ions/cm2 and Ni-1.0% A1 samples were irradiated to doses of 6 x 1 O I 6 ions/cm2 and 1 x l O I 7 ions/cm2. The helium concentration was estimated to be 95 appm in case of lower dose and z 120 appm for higher dose.The isochronal annealing of the samples was carried out from 353 to 1173 K and the resistivity was measured at liquid nitrogen temperature. The results show that there is a recovery peak at z 483 K in case of Ni-1.0% Al. There is no recovery after this temperature till 873 K from where there is an increase in resistivity till 1123 K and thereafter the resistivity decreases. Fig. 1 shows the isochronal annealing curve of 30 MeV a-ion irradiated pure nickel and Ni-0.5% A1 and Fig. 2 shows the curve for Ni-1.0% Al. It is seen that in these curves, the resistivity starts decreasing nearly up to x523 K with a recovery peak at ~4 8 3 K in case of Ni-1.0% A1 as shown in Fig. 3. After this temperature, the resistivity is practically constant up to a temperature of 873 K from where it shows a negative recovery, i.e. the resistivity increases. The increase in resistivity continues till 1123 K. This temperature is different for Ni, Ni-0.5% Al, and Ni-1.0% Al. After this the resistivity Results and discussion') Bombay 400085, India.