Amorphous materials have been traditionally prepared by rapid solidi®cation, vapour phase deposition and solid state interdiffusion, etc. Over the last few years, a considerable amount of work has been performed on amorphization by high-energy ball milling. Two categories of amorphization by ball milling can be identi®ed: (i) mechanical alloying of elemental powders involving material transfer between the components and (ii) mechanical milling (MM) or mechanical grinding of a single composition material, such that no material transfer need occur [1]. Yermakov et al. [2] ®rst reported the formation of amorphous CoxY1yx alloys through the MM of crystalline intermetallics, such as Co3Y, Co2Y, Co5Y and Co17Y2. Since then, a number of amorphous alloys have been obtained by MM of the corresponding polycrystalline intermetallic compounds. In this case, defects introduced by deformation during milling must be responsible for raising the free energy of the crystalline compound above that of the amorphous phase, thus providing the necessary driving force for solid-state amorphization [3]. Recently, the crystalline-to-amorphous transformation has also been reported for pure elements, such as Si [4, 5] and Ge [6]. It is proposed that the pressure-induced amorphization and crystallite-re®nement-induced amorphization may apply to the amorphization of Si and Ge induced by MM [4, 7]. Moreover, Tsukushi et al. [8, 9] found that organic molecular crystals have been amorphized by MM using a vibrating mill. However, there are only a few reports on the amorphization of metal oxides, such as Na2O5 [10] and Ta2O5 [11], induced by MM. During the milling of Nb2O5 or Ta2O5, the amorphous phase is formed ®rst, and further milling results in recrystallization of the amorphous phase formed. However, the mechanism for amorphization of the oxide has not been well understood. To my knowledge, amorphization of metal carbide by MM has not so far been reported. In the present paper, high-energy ball milling is performed on Al4C3 in order to investigate the possibility of amorphization of Al4C3 as well as the mechanism responsible for the structural evolution of Al4C3. Al4C3 powders together with the steel balls (10 mm in diameter) were sealed in a stainless steel vial in an argon-®lled glove-box. The weigh ratio of the balls to the powder was 30:1. Dry milling was carried out in a QM-1SP planetary-type ball mill with a planetary rotation speed of 230 rev miny1. At selected times, a small amount of the sample powders were taken out for structure analysis. The as-milled powders were characterized by a Rigaku D=max-3B X-ray diffractometer with Cu Ka radiation and a Phillips EM420 transmission electron microscope. The powders for transmission electron microscopy (TEM) examination were suspended in anhydrous toluene, and then a few drops of the mixture were pipetted onto a carbon support ®lm. Fig. 1 shows the X-ray diffraction (XRD) patterns of the Al4C3 powders milled for various times. With prolonged milling time, the intensities of all the peaks decreased, and the peaks were broadened owing to reduction in grain size and accumulation of lattice strain. After milling for 20 h, several peaks disappeared. Assuming that contributions of the grain size and the strain to the integrated intensities of peaks follow Cauchy and Gaussian distributions, respectively, then the grain size and the internal strain can be estimated from the Cauchy and Gaussian integral breadth components of the Voigt function [12]. By applying this method to the sample milled for 20 h, the average grain size of Al4C3 was calculated to be about 8 nm and the strain was around 1.7%. After milling for 50 h, only a halo peak corresponding to an amorphous phase was observed in the XRD pattern (Fig. 1). To demonstrate the structural evolution of the powder, the samples milled for 20 and 50 h were