A compreensão dos efeitos provocados pela adição de 'AL' na fase metaestável A1 do sistema 'ND'-'FE' está vinculada com o entendimento dos mecanismos de coercividade dos imãs 'ND'-'FE'-b. Para isso foram estudadas ligas ternárias 'ND'-'FE'-'AL' ricas em 'ND' de composições: 'ND'- (20-x)%'FE'-x%'AL' com x=1,2,3,4,5,7 e 10%at. Nas amostras brutas de fusão foi encontrada uma fase metaestável cuja T diminuiu conforme o aumento do teor de 'AL': de 245'GRAUS'c (x=0) ate 160'GRAUS'c (para x=10). O 'H IND.C' destas amostras brutas de fusão foi encontrada uma fase metaestável cuja 'T IND.C' diminuiu conforme o aumento do teor de 'AL': de 245'GRAUS'c (x=0) até 160'GRAUS'c (para x=10). O 'H IND.C' destas amostras diminuiu de 5 koe para 3.2 roe (na mesma faixa de composições). A microestrutura eutetica destas ligas sofreu um engrossamento das lâmelas conforme o aumento do teor de 'AL'. Após o tratamento térmico a 600'GRAUS'c por 2 horas, amostras com x variando de 1 a 4%'AL' ainda apresentaram uma fase ferromagnética cuja 'TC' e ligeiramente maior que a amostra bruta de fusão. A microestrutura sofreu uma mudança importante, apresentando esta fase ferromagnética não mais na forma de autetico fibroso mas na de agulha. Para 10'> OU ='x'> OU ='s, as amostras tratadas termicamente não apresentaram nenhuma fase ferromagnética.

An understanding of the effect of Al addition on the metastasble A1 phase of the binary Nd-Fe system is related to a comprehension of coercivity mechanisms in Nd-Fe-B magnets. For this reason, Nd-rich ternary Nd-Fe-Al alloys were studied : Nd-(20-x)Fe-xAl with x = 1, 2, 3, 4, 5, 7, and 10at%. In the as-cast samples a metastable phase was encountered whose Tc diminished as the Al contente increased: from 245°C (x = 0) to 160°C (for x = 10). H for these samples decreased from 5 kOe to 3.2 kOe over the same composition range. The eutectic microstructure of the alloys coarsened as the Al contente increased. After annealing at 600°C for 2 hours, samples with x varying from 1 to 4at% Al still presented a ferromagnetic phase whose Tc is slightly higher than that of the as-cast samples. The microstructure underwent an important change with the ferromagnetic phase appearing in the form of needles instead of the fibrous eutectic. For 5-10 at% Al, the annealed samples did not presente a ferromagnetic phase. To identify the phases presente in these materials, the ferromagnetic µ and paramagnetic phases were studied. Samples corresponding to these phases were studied by magnetic measurements, metallography, Mössbauer spectroscopy and x-ray diffraction. The results obtained led to the identification of the phase presente in annealed samples with x = 4 as the µ phase. The ferromagnetic metastable phase (A1) in as-cast samples also presentes the structure of µ. For x 5, the annealed samples contain the phase. The kinetics were studied for the transformation of the metastable A1 phase, presente in as-cast samples (with x = 5,7, and 10), into the paramagnetic phase. The fraction of the remaining A1 phase was determined after annealing at temperatures between 400°C and 600°C for 15 min anda t 450°C for times between 0 na 2 h. The exponentes of the Johnson and Mehl equation were determined for these curves.