Deformation behavior of a Ni 3 Al(B,Zr) alloy during cold rolling: Part I. changes in order and structure
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I. INTRODUCTION
THE Ni3Al-base intermetallic alloys are well known for their excellent high-temperature properties. Among the other qualities, good mechanical strength, positive temperature coefficient of flow stress, oxidation and creep resistance, flexibility of alloy design, etc. have made this group of alloys a distinct category among the future generation materials. The problem of inherent brittleness of polycrystalline Ni3Al has been substantially solved by boron addition,[1,2] and this has led to the initiation of significant research in the field of material processing through cold deformation. Comprehensive investigations have been carried out with single-phase boron-doped hypostoichiometric Ni3Al on its cold rolling characteristics, in which the material has been successfully subjected to cold work up to 85 pct and above without any major problem. A number of multiphase Ni3Al-base compositions are being developed for several advanced applications. Oak Ridge National Laboratory (ORNL, Oak Ridge, TN) has developed a master alloy for the purpose of designing other advanced compositions, and this is designated as IC50. Very little work appears to have been carried out to date on the deformation characteristics of this and similar alloys. The present work undertakes a systematic study of the behavior of an IC50 composition during room-temperature rolling. The investigation basically aims at the evaluation of microstructural and textural changes with cold rolling. It also makes an attempt to study the strain-induced structural changes in the material, if any, as has recently been detected in the single-phase Ni3Al(B).[5] The entire work has been divided into two parts. Part I describes the changes in ordering and structure that take place during cold rolling. The microstructural and textural changes are described in part II. II. EXPERIMENTAL The alloy was obtained from ORNL in the form of a continuously cast sheet of 1-mm thickness. The nominal B. BHATTACHARYA, formerly Postdoctoral Student, Department of Materials and Metallurgical Engineering, Indian Institute of Technology, is Deputy Manager, CRM Complex, Tata Steel, Jamshedpur-831 001, India. R.K. RAY, Professor, is with the Department of Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur-208 016, India. Manuscript submitted February 9, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
composition of the hypostoichiometric alloy as determined by ORNL was Ni-21.8Al-0.1B-0.34Zr (in at. pct). The sheet was cut into small pieces of nearly 10-mm width and 50mm length, and subsequently sealed in quartz capsules in high vacuum (,1024 Pa). The encapsulated samples were then subjected to homogenization anneal at 1150 8C for 24 hours, which produced a two-phase microstructure with an average primary grain size of 40 to 45 mm. The volume fraction of the second phase was about 25 pct. The homogenized samples were subjected to cold rolling at room temperature in a two-high laboratory rolling mill. The diameter of the rolls was 150 mm and the
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