Recrystallization behavior of a heavily cold-rolled Ni 3 Al(B,Zr) alloy
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THE compound Ni3Al is an excellent structural intermetallic material suitable for high-temperature application. It is the main strengthening phase in Ni-based superalloys. The unique property of Ni3Al is that its flow stress increases with temperature up to around 600 °C. A major drawback of polycrystalline Ni3Al is its poor ductility and brittle intergranular fracture. However, a trace amount of boron addition to hypostoichiometric Ni3Al drastically improves its cold ductility and makes the material suitable for thermomechanical processing. A number of multiphase Ni3Al-based alloys have been developed, in order to combine strength and ductility in Ni3Al-based alloys. Simultaneously, ternary alloying additions are expected to enhance the mechanical properties. The present study was carried out with one such type of material, which is commercially known as IC50. The composition of this alloy is Ni-21.8Al-0.34Zr-0.1B (in at. pct), and this is a two-phase material, with Ni3Al intermetallic phase (␥⬘) combined with a Ni-base phase (␥). The importance of this material is that it is used as a master alloy to develop the other multiphase compositions. A systematic study was carried out, for looking into the deformation and recrystallization behaviors of this material. In a previous communication,[1] the changes in order and crystallographic texture during annealing of heavily cold-worked Ni3Al(B, Zr) alloy were reported. The detailed studies on various changes during cold deformation are available in two other communications.[2,3] The annealing study was carried out with 73 pct cold-rolled sample. The present article reports the changes in microstructure during the recrystallization anneal and the kinetics of recrystallization.
B. BHATTACHARYA, formerly Postdoctoral Student, Materials and Metallurgical Engineering Department, Indian Institute of Technology, Kanpur–208016, India, is Manager, Flat Products Technology, Tata Steel, Jamshedpur–931001, India. R.K. RAY, Professor, is with the Materials and Metallurgical Engineering Department, Indian Institute of Technology. Contact e-mail: [email protected] Manuscript submitted May 2, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
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EXPERIMENTAL
The material was obtained in the form of a continuously cast sheet of ⬃1-mm thickness. After initial homogenization treatment, a two-phase microstructure with an average primary grain size (of ␥⬘) of 40 to 45 m was obtained. A second phase (␥), comprising about 25 pct by volume fraction, was dispersed as small islands within the ␥⬘ grains. It was further determined that the ␥ islands were not of pure ␥, but contained small particles of ␥⬘ phase inside them. The details of the initial preparation of the material and the cold rolling process are given in two previous communications.[2,3] The alloy, cold rolled by an amount of 73 pct, was selected for the annealing study. The cold-rolled plate was cut into small pieces, each of which was subsequently sealed into a quartz capsule in high vacuum (⬃10⫺4 Pa). These encapsulated specime
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