Microstructure and mechanical properties of metastable fcc phase wires in Mn-Al-C system manufactured by in-rotating-wat
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I.
INTRODUCTION
MANGANESE metal has four different crystal structures which change in the order of ~(A-2 type b c c ) ~ 3,(A-1 type fcc) ~/3(A-13 type cubic) ~ a(A-12 type bcc) with lowering temperature. 1 A stable phase at ambient temperature is the a-Mn with a very large lattice parameter of a = 0.89139 nm. The a-Mn alloy is extremely brittle and the reason appears to be due to a complex atomic configuration in the unit cell including 58 atoms. This embrittlement prevents a development as a practical material in spite of rather inexpensiveness as well as interesting engineering properties. It has been recently demonstrated that a meltquenching technique is very useful for the suppression of phase transformation in solid as is evidenced for the formation of metestable y phase in Fe-(Cr, Mo, W, or A1)-C alloys containing a ferrite-forming element as a solute element.2-5 Therefore, it was expected that the application of this technique to manganese-based alloys might suppress the transformation of y to a via fl phase and lead to a formation of the 3~-Mn alloy with an fcc structure which appears to be highly ductile. From this point of view, we examined the melt-quenched structure of manganese-carbon alloys containing various kinds of solute elements and found that the face-centered cubic (fcc) 3,-Mn solid solution formed even at room temperature in Mn-A1-C temary and Mn-A1-C-X (X -- Cr, Mo, Fe, Co, or Ni) quatemary systems containing aluminum solute element which leads to an extension of a- and 6-Mn phase fields. This paper deals with the composition range in which the metastable T phase forms in Mn-A1-C system and the microstructure and mechanical properties of the metastable ,/-Mn alloys.
A. INOUE, Research Associate, and T. MASUMOTO, Professor, are with The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai 980, Japan. H. TOMIOKA, Research Staff, is with Unitika Research and Development Center, Unitika Ltd., Uji 611, Japan. Manuscript submitted April 5, 1982.
METALLURGICALTRANSACTIONS A
II.
EXPERIMENTAL METHODS
The specimens used in the present work are Mn-AI-C ternary alloys. Mixtures of pure metals (manganese and aluminum) and graphite were prealloyed under an argon atmosphere in an induction furnace to prepare the master alloys. The melts were sucked up into quartz tubes of about 3 mm inner diameter and allowed to solidify. Since the difference between weighed and chemically analyzed compositions was less than 0.2 wt pct for aluminum and 0.1 wt pct for carbon, the compositions were determined by the weighed values in atomic percent. From these master alloys, long ribbons with a cross section of about 3 mm x 40 to 250/xm were prepared as the test samples for the structural observation by a modified single roller melt-spinning apparatus which enables the copper roller (20 cm in diameter) revolving at high speeds (2000 to 3000 rpm) to stop in a very short time (one to two seconds). The details of this apparatus are described in Reference 6. In addition, continuous wires of about
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