The Effect of Ion Implantation on the High Temperature Deformation of Molybdenum
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IONimplantation has now become an almost indispensable tool in the production of semiconductor devices but, although there has been metallurgical interest in the technique for many years, l it has been somewhat slower in finding metallurgical applications. Since the thickness of the implanted layer is limited to a few tens or hundreds of nanometers, depending on the ion species and energy, most research has been focussed upon surface-sensitive properties. Thus the potential usefulness of ion implantation has been demonstrated, for example, in corrosion and oxidation studies, 2 in the field of tribology 3 and in fatigue situations? Ion implantation is also of interest in nuclear technology since it offers the possibility of simulating radiation effects such as void formation, swelling and blistering, at dose rates which may be more than a thousand times higher than those in a typical fast reactor. Ion implanted molybdenum has been the subject of considerable 5-7 attention and the question arose as to how ion implantation might affect the structure and mechanical properties of this metal in thin sheet form. The results reported here comprise, therefore, a study of the high temperature deformation of ion implanted molybdenum. The experiments were directed towards investigating possible effects at the lower strain rates which are typical of creep conditions and around which most interest centers. EXPERIMENTAL PROCEDURES Since the initial impetus for this work arose primarily from an interest in creep properties the experiments were designed and performed as accelerated creep tests. Even though they are probably more accurately described as low strain rate tensile tests they show the typical features of creep tests and will be referred to using this terminology. In the absence of any previous experience with this type of test it was decided to investigate a range of ions,
I. W. HALL, formerly with the Department of Materials Engineering and Solid State Institute, Technion, Haifa, Israel, is currently Assistant Professor, Department of Mechanical and Aerospace Engineering,Universityof Delaware, Newark, DE 19711.
Manuscript submitted November 10, 1980.
initial stresses and temperatures. The tests were thus performed in several series, within each of which the test conditions were constant. All creep test specimens were prepared from 0.2 m m thick pure molybdenum sheet with a grain size of ~ 1/~m, containing 36 ppm O z, 7 ppm C, 5 ppm N 2, ~ 100 ppm W, 44 ppm Fe. The initial three series of tests were carried out using specimens 4 mm wide and 6 mm gage length. Each series was given a recrystallization anneal of 1 h at 1300, 1400 or 1450 ~ prior to implantation and testing. These preliminary tests gave an indication of the type of effects which occurred and subsequent tests were performed using rather larger specimens, 6 mm wide and 8 mm gage length, recrystallized for 1 h at 1400 ~ The larger specimens permitted the use of lower initial stresses a n d / o r higher temperatures, thus more closely approaching true creep c
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