Role of atmosphere in the crystallization of amorphous plasma-sprayed Sm-Co deposits

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Abstract
Thick, machinable, and amorphous 1Sm‐5Co plasma‐sprayed deposits show a high resistance to magnetization and demagnetization at room temperature. This behavior is believed to be related to large internal stresses and variations in chemical composition present in the as‐sprayed material. Thermal treatments of these deposits, in argon, at temperatures substantially lower than those required for crystallization, produce little change in their magnetic behavior. Similar treatments in hydrogen, however, result in an easy approach to saturation and very low coercivity values. This different response of the material to hydrogen has been attributed to an increased mobility of the atoms in hydrogen, which permits sufficient rearrangement of the atoms so that high magnetization and low coercivity are achieved in the amorphous state. Use of a hydrogen atmosphere also results in a considerable increase in the temperature required for crystallization. Whereas crystallization occurs at about 500 °C in argon, temperatures of about 700 °C are needed to produce similar effects in hydrogen. The suppression of the crystallization processes in hydrogen has been attributed to a deposit‐hydrogen chemical interaction at the low temperatures. The results of this study indicate that amorphous 1Sm‐5Co is probably more suited for use as a means for storing hydrogen than is crystalline SmCo5 material.