Effect of deformation on the damping capacity in an Fe-23 pct mn alloy
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Table I.
Chemical Composition and Transformation Temperatures of Fe-23 Pct Mn Alloy Chemical Composition (Wt Pct)
Transformation Temperature (K)
Alloy
Mn
C
Fe
Ms
As
Af
Fe-23 pct Mn
23.30
0.015
bal
387
435
487
JOONG-HWAN JUN and CHONG-SOOL CHOI Internal friction is defined as the specific capacity of a material to convert the mechanical energy of vibration into heat that is dissipated in the material,[1] and the increasing interest in this ability of a material has led to the development of new damping alloys such as Mn-Cu,[2] Ni-Ti,[3] Cu-Zn-Al,[4,5] and cast irons[6,7] for engineering applications. Recently, Fe-high Mn alloys undergoing nonthermoelastic g(fcc) → ε(hcp) martensitic transformation have received significant attention due to their low cost and pronounced damping characteristics.[8–13] In the previous studies,[14,15,16] we have reported that the damping capacity of an Fe-Mn alloy is dependent on the ε martensite volume percent, and proposed that boundaries of various types associated with ε martensite, such as stacking fault boundaries in ε martensite, ε martensite variant boundaries, and g/ε interfaces give rise to a high damping capacity. As is well known, ε martensite can be formed both by cooling (thermal ε martensite) and by deformation (stress-induced ε martensite). Most of the studies[13–19] on the damping capacity of Fe-Mn alloys up to now, however, have been focused solely on the relationship between thermal ε martensite and damping capacity, and few studies have been performed to clarify the influence of the ε martensite induced by deformation on the damping capacity of Fe-Mn alloys. Therefore, this work aims to report the damping capacity of an Fe-23 pct Mn alloy with respect to deformation at room temperature and to discuss it in relation to the microstructural evolution. The Fe-23 pct Mn alloy was prepared using a high frequency induction furnace in a vacuum atmosphere. The chemical composition of the alloy is listed in Table I. The ingot of 5 kg was homogenized at 1423 K for 24 hours and then hot-rolled into sheets with different thicknesses. All sheets were solution treated at 1323 K for 1 hour followed by a water quench and cold-rolled at room temperature in a range of 0 to 20 pct reduction in thickness. The final thickness of the sheets was 1.3 mm. From these sheets, various specimens for damping measurements, microstructural observations, and X-ray diffraction analyses were prepared by spark cutting. The volume fractions of constituent phases such as g austenite (fcc), ε martensite (hcp), and a' martensite (bcc) were measured by X-ray diffraction using the average of multiple peaks corresponding to each phase.[20,21,22] The martensitic transformation temperatures (Ms, As, and Af) were determined from dilatometry, and the values are also given in Table I. Thin foils for transmission electron microscopy (TEM) were jet polished in a solution of 10 pct perchloric acid (HClO4) and 90 pct acetic acid
JOONG-HWAN JUN, Researcher, Research Institute of Iron and Steel Technolo
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