Monotectic alloys show promising applications in wear-resistant automotive components, once these systems have remarkable self-lubricating properties that are of great interest for using in bearings. Much research has been devoted to better comprehend monotectic reactions. Some studies assume that the interphase spacing evolution in monotectic alloys follows the classical relationship used for eutectics or the dendritic growth relationship; however, some studies reported that the growth laws seem not to be valid for some cases. Because of that, obtaining single mathematical expressions that allow describing the development of solidification structures as a function of thermal parameters is very important. Based on the above, this chapter proposes a systematic analysis of the monotectic growth laws proposed in the literature and suggests exclusive growth laws as a function of solidification parameter for monotectic alloys solidified under different heat extracting configurations.

ResumoLigas monotéticas apresentam aplicações promissoras em componentes automotivos resistentes ao desgaste. Muitos estudos têm sido realizados a fim de melhor compreender a reação monotética. Algumas pesquisas assumem que a evolução do espaçamento interfásico (λ) nas ligas monotéticas obedece à clássica relação utilizada para eutéticos: . . v G C λ = , ou ainda a relação de crescimento dendrítico , em que v é a velocidade de solidificação e C uma constante para ambos os casos, G é o gradiente de temperatura e a e b são constantes, entretanto, para alguns casos, as leis apresentadas não se mostraram válidas. No presente trabalho foram analisados os resultados desses experimentos de solidificação unidirecional em regime não estacionário, com as ligas hipomonotéticas Al-0,9%Pb e Al-5,5%In, com a liga monotética Al-1,2%Pb e com as ligas hipermonotéticas Al-5,0%Bi, Al-7,0%Bi e Al-2,1%Pb em configurações de extração de calor ascendente e descendente, a fim de propor nova lei de crescimento unicamente para sistemas monotéticos. Pôde-se estabelecer uma lei para crescimento de monotéticos em função da posição a partir da interface metal/molde, λ = k. (P) Monotectic alloys show promising applications in wear-resistant automotive components. Much research has been devoted in order to better comprehend monotectic reactions. Some researches assume that the interphase spacing evolution in monotectic alloys follows the classical relationship used for eutectics: λ2v = C, or the dendritic growth relationship , where v is the solidification velocity and C a constant value for both cases, G is the thermal gradient and a and b are constants. However, some studies reported that the aforementioned growth laws seem not to be valid for some cases. In the present study, the results of directional unsteady-state solidification experiments with hypomonotectic Al-0.9wt%Pb and Al-5.5wt%In, monotectic Al-1.2wt%Pb and hypermonotectic Al-5.0wt%Bi, Al-7.0wt%Bi and Al-2.1wt%Pb alloys, under different heat extracting configurations ( upward and downward) were taken into account to propose a new and exclusive growth law for monotectic systems. It was possible to establish a single monotectic growth law as a function of position from the metal/mold interface, λ = k.(P) 0,5.