چكيده به لاتين
Abstract:
In the present research by using the Copper capacity to improve the physical properties, and its nanometric structure to improve mechanical properties, and also using Tantalum as the secondary element to increase the mechanical properties and thermal stability, we tried to produce the Nanocrystalline Copper-Tantalum alloys with an adequate conductivity and hardness, and a high thermal stability. For this purpose the effect of the Process Control Agent, amount of Tantalum and size of balls on milling of powders were investigated, then the effect of atmosphere, temperature and method of sintering were investigated to produce tablets to achieve an even better conductivity and hardness. In this regard, the Mechanical Alloying process was used to produce Nanocrystalline powders using planetary ball mill. After powder production process, the morphology and particle size of powders were examined by means of SEM, as well as microstructure and crystallites size by XRD and TEM. DSC test was taken for the sample milled with the mix balls, containing 5 atomic % tantalum. According to the DSC graph, temperatures of 550, 700 and 850℃ were selected for sintering. Sintering was performed in the atmospheres of Nitrogen, Argon and Vacuum for all samples at the temperature of 550℃, according to the measurement of electrical and microhardness properties for all samples it was observed that Vacuum condition indicates better properties for all samples, therefore sintering was done at the temperatures of 700 and 850℃ in the Vacuum. Sintering at the temperature of 850℃ showed better properties than other two temperatures for all samples, therefore this temperature was chosen for Spark Plasma Sintering. Analysis of XRD pattern showed that production of nanocrystalline samples, milled with mixed balls, containing 5% atomic tantalum, has the smallest crystallite size among all the samples (12 nm), In addition Spark Plasma Sintering method at the temperature of 850℃ was used for this sample showing the highest electrical (35.5 % IACS) and thermal (139.05 W/mK) conductivity, as well as the most microhardness (220.9 HV) in comparison to other Copper-Tantalum samples and also milled pure Copper, Meanwhile the crystallite size of this sample remained in the nanometeric scale (41 nm) despite the Sintering at the temperature of 850℃, which represents the high thermal stability of the aforementioned sample.
Keywords: Nanocrystalline Copper-Tantalum alloys, Mechanical Alloying, Spark Plasma Sintering, Thermal Stability
