It is to be expected that intermetallic compounds synthesized by aluminum or silicon with transition metals such as Ti, Ni, Fe and Nb are used as structural materials. Because of their properties such as light weight, ability to resist corrosion and excellent mechanical properties at elevated temperatures, Ti±Al system intermetallic compounds have been practically applied as structural materials [1, 2]. Unfortunately, it is dif®cult to develop intermetallic compounds: They are neither easy nor inexpensive to fabricate using the usual processes, such as the melting method, because intermetallic compound is brittle and dif®cult for machining and forming. Combustion synthesis, using a huge enthalpy during synthesis, is anticipated as a useful powder metallurgy process [3]. The synthesis conditions and reaction rate have been studied experimentally and analyzed using the thermodynamic method [3±8]. It has been observed that the maximum temperature during the combustion synthesis was over the melting point of Al, for example, reaching 1367 8C [5]. In analyzing the combustion synthesis, Al is usually considered to be in a liquid state [3, 5]. However, the combustion synthesis process is completed in a very short period (in a few seconds), so it is very dif®cult to control. Therefore, it is important to clarify thermal behavior during the combustion synthesis. In this study, thermal behavior during the combustion synthesis of the Ni±Al system was examined by differential thermal analysis (DTA). The effects of the composition and heating rate on the thermal behavior are discussed. Gas-atomized aluminum powder 99.5% pure and with a diameter under 100 im and nickel powder 99.8% pure and with a diameter under 7 im were used as source powders. To mix the powders thoroughly, the mixing was carried out using a ball mill for 7.2 ks to obtain the stoichiometric composition (atomic ratio) of Ni:Al with 1:1, 2:1 and 3:1. The powder mixtures were pressed into green compacts with a diameter of 20 mm at a compacting pressure of 800 MPa for 900 s after pre-pressing at 80 MPa for 300 s. Stearic acid was used as a diewall lubricant. Atomic ratio, the weight percentage of Al, density, calculated density and Vickers hardness for the green compacts are given in Table I. A sample component micrograph by scanning electron microscopy (SEM) of a green compact of (Ni±33 at %Al) is given in Fig. 1. The black and white phases are Al and Ni, respectively. The production conditions described above yielded green compacts with a high density (about 0.9 of the calculated density) and a microstructure with a good distribution. Thermal behavior during the combustion synthesis was analyzed with a differential thermal analysis processor (TG-DTA2000-s) produced by the Mac Science Company. To examine the effect of the heating rate on the thermal behavior, the heating rate was set at 5, 10 and 40 8C miny1. Samples of about 50 mg with a cylinder for DTA were cut from the green compacts. Al2O3 powder was used as the standard sample. To prevent oxidization, high-purity (99.9999%) Ar gas was owed into the processor at