기계적 합금화에 의한 비고용 Cu-Nb계 비평형 합금의 제조
Fabrication of nonequilibrium alloy powders in immiscible Cu-Nb system by mechanical alloying
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본 연구에서는 순 Cu 및 Nb 혼합분말에 대하여 Ar 분위기 중 고에너지 볼밀처리를 실시하여 기계적 합금화(MA) 효과를 조사하였다. CuxNb100 - x(x = 5-50) 조성의 혼합분말을 각각 120시간까지 MA 처리한 결과, Cu의 bcc-Nb 과포화 고용체가 30 at% Cu까지 넓어짐을 X선 회절분석, DSC 열분석 및 저온비열 측정을 통한 초전도 천이온도 변화로부터 알 수 있었다. 120시간 MA 처리한 Cu30Nb70 조성합금의 열분석 결과 broad한 발열반응만이 관찰되었으며, 볼밀처리에 의하여 계에 축적되는 에너지는 볼밀시간에 따라 증가하여 7.5 kJ/mol 에 포화됨을 알 수 있었다. Miedema et al.의 계산에 의하면 Cu30Nb70 혼합분말과 과포화 고용체의 자유에너지 차가 7 kJ/mol이며, 본 연구에서 MA에 의하여 계에 축적된 에너지 값과 거의 같은 사실로부터 이 계에서 열역학적으로 과포화 고용체가 충분히 얻어질 수 있음을 나타내는 것으로 판단된다.
Abstract
Mechanical alloying (MA) by high energy ball mill of pure copper and niobium powders was carried out underthe Ar gas atmosphere. The supersaturated solid solution can be produced in the range up to CuxNb100 x (x = 5-30) by MAsuperconducting transition in the low-temperature specific heat. The Cu30Nb70 samples ball-milled for 120 hrs exhibit only abroad exothermic heat release. The total energy, Ht accumulated during MA for the mixture of Cu30Nb70 powders increasedwith milling time and approached the saturation value of 7.5 kJ/mol after 120 h of miling. It can be seen that the freenergy diference between the supersaturated solid solution and the mixture of Cu30Nb70 powders is estimated to be 7 kJ/mol by Miedema et al. Hence it is thermodynamicaly posible to assume the formation of a supersaturated solid solutionKey words Mechanical alloying, Immiscible Cu-Nb system, Supersaturated solid solution, Total enthalpy, Superconductingtransition... .... .. ... Cu-Nb. ... ... .....†..... ...... , .. , 534-729(2006. 9. 20. .. )(2006. 10. 2. .... ). . . ..... . Cu . Nb ..... ... Ar ... . .... ..... .... ... ...(MA) ... ..... . CuxNb100 x(x = 5-50) ... ..... .. 120.... MA ... .. , Cu. bcc-Nb ....... 30 at% Cu.. .... X. .... , DSC ... . .... ... .. ... .... ..... .. ... . 120.. MA ... Cu30Nb70 ..... ... .. broad. ...... ...... , ..... ...
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