Neutron diffraction study of the formation of ordered antiphase domains in cubic titanium carbide TiC 0.60

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Neutron Diffraction Study of the Formation of Ordered Antiphase Domains in Cubic Titanium Carbide TiC0.60 I. Khidirov and A. S. Parpiev Institute of Nuclear Physics, Academy of Sciences of Uzbekistan, Tashkent, 100214 Uzbekistan email: [email protected] Received May 14, 2012

Abstract—A series of superstructural reflections (described within the sp. gr. Fd3m) are found to be split into three symmetric parts in the neutron powder diffraction pattern of titanium carbide TiC0.60 annealed at a tem perature of 600°C. No splitting of superstructural reflections is observed in the neutron diffraction pattern of TiC0.60 annealed at relatively high temperatures (780°C). This phenomenon can be explained by that fact that the ordering of carbon atoms at relatively high temperatures (780°C) is accompanied by the formation of ran domly oriented rather large antiphase domains (APDs) (450 Å). At relatively low temperatures (600°C), stacking faults arise in the arrangement of partially ordered carbon atoms. In this case, relatively small ordered APDs (290 Å) are formed, along with disordered ones. DOI: 10.1134/S1063774513030085

INTRODUCTION The formation of ordered antiphase domains (APDs) is a widespread and wellknown phenomenon in substitutional solid solutions [1]. The formation of ordered APDs in interstitial alloys was found for the first time in [2, 3] when studying titanium carbohy dride TiCхHу. It is of interest to find out if this phe nomenon occurs in other interstitial alloys. It is more logical to search for its manifestation in titanium car bide, which is widely used in technology, and isostruc tural carbohydride titanium; therefore, we analyzed the composition of titanium carbide TiC0.60 by neutron powder diffraction in order to reveal APD ordering. We chose this composition because it was investigated previously and exhibited a series of phase transitions [4, 5]. However, the formation of ordered APDs has not been observed yet. EXPERIMENTAL A TiC0.60 sample was prepared by selfpropagating hightemperature synthesis [6] from Ti powder of PTEM grade (99.76 wt % purity) and soot of high purity grade. The carbon content in the final product was determined by chemical analysis. To homogenize the synthesis product, it was annealed in the tempera ture range of 1100–1200°С for 24 h with the subse quent cooling of the sample simultaneously with the furnace. Homogenizing annealing was carried out in an SShVL0.6.2 vacuum furnace at a residual pressure no higher than 1.33 × 10–3 Pa. According to the Xray diffraction analysis, the sample after homogenizing annealing is singlephase; it has a homogeneous com position and NaCltype structure (sp. gr. Fm3m) with

the lattice parameter а0 = 4.322 ± 0.002 Å. Then the sample was heattreated in an evacuated and sealed quartz ampoule in a SNOL furnace. The temperature was measured with an error of ±3°С. The sample state after each annealing cycle was fixed by quenching in water. The neutron diffraction pattern of the powder sample (put into a thin van

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