Experimental study of the phase equilibria in the Fe-Mn-Al system
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I.
INTRODUCTION
THE phase equilibria of the Fe-Mn-AI ternary system have practical importance for the development of cryogenic alloys, heat-resistant steels, and magnetic materials,t1,21 Since K6ster's research work in 1933, the phase equilibria of this system have been studied several times, t3-lu The research results were first complied by Rivlin[12] and, more recently, were summarized by Qingsheng. [131 K6ster and Tonn et al. [3] presented the a/y phase equilibrium of the isothermal section at 1200 ~ and the liquidus projection of the Fe comer in the Fe-Mn-Al system and pointed out that the compositions of stable y phase can extend up to 20 wt pct A1 and 50 wt pct Mn and predicted that the y -+ fl-Mn phase transformation may occur when the compositions of Mn and A1 are increased to certain values. In 1939, Degischer determined the liquidus projection of the A1 comer and the partial isothermal section at 600 ~ using X-ray diffraction.t4] The 760 ~ isothermal section proposed by SchmatztSl showed the main feature of the Fe-Mn-A1 system, in which the three-phase (a + y + r) region is found between the compositions of 44 and 50 at. pct Fe. In 1977, Chakrabarti[6] determined the integrated isothermal section at 1000 ~ using X-ray diffraction and the metallographic method; however, bcc phase, limited only in the range of above 20 at. pct Fe, does not appear in the Mn-A1 side in his result, which is in contradiction with the Mn-A1 binary phase diagram proposed by Murray.t14] In order to clarify this question, the present authors have studied the phase equilibria of the Fe-Mn-A1 temary and Mn-A1 binary systems at 1000 ~ and 1100 oC,[8'9'10] and the research results were in agreement with Murray's. In addition, Liu and Hao calculated the phase equilibria above 750 ~ using the subregular solution model;t9] the calculated results provide some important information for XING JUN LIU, Associate Professor, and SHI MING HAO, Professor, are with the Department of Materials Science and Engineering, Northeastern University, Shenyang 110006, People's Republic of China. LE YING XU, Professor, and YANG FENG GUO, Senior Engineer, are with the Institute of Metal Research, Academia, Sinica, Shenyang 110015, People's Republic of China. HUI CHEN, formerly Graduate Student, Department of Materials Science and Engineering, Northeastern University, is Senior Engineer, Shenyang Institute of Technology, Shenyang 110045, People's Republic of China. Manuscript submitted March 3, 1994. METALLURGICAL AND MATERIALSTRANSACTIONS A
the experimental study of the phase equilibria in this system. In order to obtain overall phase equilibria of the FeMn-A1 system over a wide range of temperature, this article will determine four isothermal sections at 800 ~ 900 ~ 1200 ~ and 1300 ~ using the metallographic method and diffusion couple technique and two vertical sections of 4 wt pct A1 and 8 wt pct A1 using differential thermal analysis (DTA).
II.
EXPERIMENTAL PROCEDURE
A. Preparation of Alloys and Diffusion Couples The raw materials of binary Fe-AI and
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