416 Materials Science and Engineering A 179/A 180 (1994) 416-421 Heat treatment of rapidly solidified Fe63Cr18Ti4B15 I. T.H. Chang, K. Ishii* and B. Cantor Oxford Centrefor Advanced Materials and Composites, Universityof Oxford, Parks Road, Oxford OX1 3PH (UK) Abstract The crystallization behaviour and microstructural development during the annealing of amorphous melt-spun Fe63Cr18Ti4B15 ribbons have been investigated by a combination of differential scanning calorimetry, transmission electron microscopy (TEM) and energy dispersive X-ray microanalysis. The crystallization onset, peak, and finish temperatures of the amorphous alloy are 571,589 and 600 °C respectively during continuous heating at 5 °C min- 1. The incubation time for the onset of crystallization obeys the Arrhenius law, with an activation energy of 1.5 eV. The crystalli- zation process obeys the Johnson-Mehl-Avrami law, with an Avrami exponent near to three, indicating near-spherical 3D growth on pre-existing nuclei, producing an equiaxed structure as observed by TEM. The activation energy for crystal growth is 1.8 eV. Isothermal annealing for 2 h at temperatures in the range 550-1000 °C produces microstructures consisting of a mixture of ferrite, faulted Cr-rich body centre tetragonal M2B boride particles and small Ti-rich primitive tetragonal M3B 2 boride particles depending on the annealing temperature. 1. Introduction In situ Fe-based particulate composites have attracted much attention recently because of their unique properties, such as high strength, excellent thermal stability and superior corrosion and oxidation resistance [1-7]. The composites consist of stable borides embedded in an Fe matrix and are manu- factured from Fe-TM-B alloys (TM = transition metal) by rapid solidification followed by hot consolidation [1-4]. The alloys are fully or partially amorphous after rapid solidification [3-5], and the final microstructures are controlled by amorphous/crystalline and crystal- line/crystalline transformations during subsequent annealing and consolidation. The present work concentrates on differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) studies of the heat treatment of a rapidly solidified Fe63CrlsTi4B15 quaternary alloy prepared by melt spinning. This paper describes the crystallization behaviour and microstructural evolution in melt-spun Fe63CrlsTi4B~5 alloy during heat treat- ment within the temperature range 500-10000 °C. 2. Experimental methods Amorphous ribbons of Fe61CrlsTi4Br15, 30-50/zm in thickness, were manufactured by chill block melt *Present address: Kawasaki Steel Corporation, 1 Kawasaki- cho, Chiba, Japan. spinning in air. Specimens of the amorphous ribbons were annealed for 2 h in sealed quartz tubes filled with Ar gas, at different temperatures in the range 550-1000 °C. Crystallization kinetics were monitored with a Dupont 2000 thermal analyzer/910 differential scanning calorimeter during continuous heating at 5 °C min-1 from 200-710 °C and isothermal heating in the range 400-655 °C. The microstructures and micro- compositions of the as-melt spun and annealed ribbons were examined by a combination of TEM and energy dispersive X-ray microprobe analysis (EDX). TEM specimens were prepared by mechanical polishing followed by twin-jet electro-polishing in 73 vol.% ethanol + 8 vol.% perchloric acid + 10 vol.% butylcel- losolve + 9 vol.% distilled water at - 10 °C to - 15 °C, and were then examined in a Philips CM20 transmis- sion electron microscope fitted with a LINK Systems energy dispersive X-ray analyzer. 3. Results and discussion 3.1. DSCstudy Figure 1 shows a typical DSC trace obtained during continuous heating to 710 °C at a rate of 5 °C min -~. The continuous heating DSC trace showed a small, broad exothermic peak over the temperature range 510-570 °C, and a large, sharper exothermic peak with onset, peak and finish temperatures of 571, 589 and 600 °C respectively, associated with crystallization of the amorphous alloy. The crystallization temperature of amorphous Fe63CrlsTi4B15 was higher than those of 0921-5093/94/$7.00 © 1994 - Elsevier Sequoia. All rights reserved SSDI 0921-5093(93)05803-B