Premartensitic anelasticity in indium-thallium alloys
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ANELASTIC studies have yielded much insight into metallurgical reactions.~ All investigations on the elastic and anelastic properties of the high temperature (austenitic) phase prior to the martensitic transformation revealed almost complete or partial elastic softening as well as a pronounced increase of the damping in a wide temperature range as the transformation is approached from above. 2'3'4 The observed damping increases seem clearly related to the unusual pretransformation properties of the high temperature phase. However, a complete mechanistic understanding of this damping and how it is specifically related to the transformation mechanism is lacking at this time. This paper reports on the low frequency anelasticity of an In-24 at. pct TI alloy in the range of temperature T, M, < T < Ms + 80 °C (Mr = martensitic start temperature). The experimental results are consistent with what is presently known about the incommensurate premartensitic state. This study was conducted using vibrating single crystalline reeds and previously described experimental apparatus. 5 Almost complete computer control of the apparatus permitted on-line measurements and data analysis. The single crystals were grown by the Bridgman technique and were subsequently homogenized 20 °C below the melting temperature for seven days. Wet chemical analysis of the ingots indicated that the composition gradient was less than 0.5 at. pct T1 over the long dimension of the reed. The resonance frequency of the reeds broke sharply at the published martensite start temperature of - 8 °C, further substantiating a satisfactory overall compositional homogeneity of the samples. Typical raw data of the study are presented in Figures 1 and 2, which show small amplitude and amplitude dependent resonance curves, respectively. It can be seen from Figure 1 that a pronounced damping maximum occurs at 39 °C at a frequency of 108.6 Hz. Figure 2 shows that the resonance frequency of the In-T! crystal decreases as the maximum amplitude of vibration increases, i.e., indicates the nonlinear softening of the sample. The results of the analyses of the raw data are shown in Figures 3 through 5. Figure 3, the Arrhenius plot of the relaxation times r obtained from the Condition for a dampMANFRED WUTTIG, formerly with the Department of Metallurgy, University of Missouri Rolla, Rolla, MO 65401, is with the Department of Chemical Engineering, University of Maryland, College Park, MD 20742 C. Y. LEI, formerly with the Department of Metallurgy, University of Missouri-Rolla. MO 65401. is with the Department of Materials Science, University of Illinois, Urbana, IL 61801. TETSURO SUZUKI is with the Institute of Applied Physics, University of Tsukuba, Sakura, lbaraki, 305 Japan. This paper is based on a presentation made in the symposium "Pretransformation Behavior Related to Displacive Transformations in Alloys" presented at the 1986 annual AIME meeting in New Orleans, March 2 6, 1986. under the auspices of the ASM-MSD Structures Committee. METALLURGICALTRANSACTIONS A
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