Investigation On Magnetocaloric Properties And Solid Solution Strengthening Of Gd-based Solid Solution Alloy

Magnetic refrigeration has outstanding advantages in energy saving and environment protection in comparison with traditional vapor-compression refrigeration. A magnetic refrigerating material also as a refrigerant-filling case requires possessing enough strength. At present, it's only metal Gd that could be used as the refrigerant-filling case. Metal Gd must be strengthened because of its lower strength. In this thesis, we investigated the binary and ternary Gd-based solid solution alloys by adding light rare-earth elements( La,Ce,Pr,Nd), heavy weight rare-earth elements (Dy,Y)and C element. Some results are as the followings. The curie temperatures, adiabatic temperature and magnetic entropy changes of the Gd-based alloys decrease and the microhardnesses of the alloys increase with addition of rare-earth elements, La, Ce, Pr, Nd, Dy and Y among thoes adding elements, Dy has the least damage on magnetic entropy change of Gd. Gd can be strengthened remarkably by addition of C atom. The curie temperature of C-containing Gd has no change in comparison with pure Gd. The adiabatic temperature and magnetic entropy changes of Gd have a small decline with addition of C element. Gd1-xCx alloy will react with moist air and become a white powder when x over 0.1. selected Gd0.98C0.02 alloy is the best for the refrigerant-filling case making. Its microhardness and tensile strength are 54% and 23% respectively higher than that of pure Gd while the adiabatic temperature and magnetic entropy changes decline in a small degree. X-ray and metallographic examinations indicate that Gd0.98C0.02 alloy is a single phase solid-solution with a hexagonal lattice structure as same as Gd'. The ternary Gd0.98-xDyxC0.02 (x=0.2) alloys were made on the basis of above binary Gd-based solid solution. Its curie temperature can be tuneable with a experiential formula,Tc=295-112x (x=0.2). The adiabatic temperature changes of the as-cast alloys with different curie temperatures have no much change in a magnetic field change of 0-1T. The curie temperatures of as-cast alloys can be elevated by heat treatment,which is because Dy atoms have a tendency to congregate into the crystal interface from interior during annealling. A small second phase forms in the alloy ingots and can increase by annealing treatment.