Fabiana Cristina Nascimento

Structural and magnetic study of the MnAs magnetocaloric compound

The temperature induced phase transition in MnAs is analyzed in this work using X ray Rietveld refinement. The results show the presence of the hexagonal phase (P63/mmc) at room temperature and the first-order structural-magnetic transition to the orthorhombic phase (Pnma) around 318 K was followed in detail. The MnAs magnetic characterization allowed to obtain the transition temperature and a maximum value of 47 J/(kg.K) for the measured magnetocaloric effect for a magnetic field variation of 5 T.

Estudo do efeito de memória de forma em ligas inoxidáveis usando ensaio de compressão

The shape recovery properties of an Fe-Mn-Si-Cr-Ni-Co based alloy were studied using compression tests. Analyzed were the elastic recovery (Er), shape recovery (Sr) and total shape recovery (TSR = Er + Sr) measurements as a function of training cycles. The results indicated that 3.3 was the best ratio between height (ho = 20 mm) and diameter (φo = 6 mm) to obtain a homogeneous deformation and defined loading curves. A major contribution of TSR was attributed to shape recovery. In the last training cycle, a TSR = 90 % was obtained, where 25% was attributed to Er.

Determinação das propriedades mecânicas da martensita-ε por indentação instrumentada em ligas inoxidáveis com memória de forma

ABSTRACT This work presents a hardness study and elastic modulus for the e-martensite and γ-austenite phases of an iron based shape memory alloy. Using instrumented indentation, it was possible to determine the hardness and elasticity modulus of these phases separately. The martensitic phase presented a hardness of 7.0 GPa and the austenitic phase presented a hardness of 3.0 GPa. The elastic modulus values were 202 and 137 GPa for the martensitic and austenitic phases, respectively.