Part of the phase diagram for platinum-ruthenium (after Hutchinson (3))

On cooling hot alloy the first crystals to form will be Ru rich, at b, leaving the liquid Pt rich. Then, on further cooling, more solid forms, tracking down the solidus, bd. The Pt-rich liquid tracks down ac. As the solidification range is narrow (compared to Pt-5%Cu) and the cooling rate is faster, due to the larger temperature difference between alloy and investment, there is less opportunity for segregation or dendritic growth to occur