No, in the context of the lliturgical days, they are not interchangeable. The terms refer to the different ranks or level of solemnity of the celebrations.
Memorials are the lowest celebrations of saints and are either Optional or Obligatory. Optional Memorials may be celebrated. Obligatory Memorials must be celebrated. But the level of solemnity for the all Memorials are the same. On Memorials, the Divine Office is mostly the office of the day, with the Collect, Second Reading, and often the antiphons for the Benedictus and Magnificat taken from the Proper. Some special memorials have special Proper texts (e.g. St. Martin of Tours), but the level of solemnity is the same. At the Daytime Hours, the saint is not commemorated. At Mass, the Collect is of the Saint, but everything else may be of the weekday.
Feasts are higher in rank, and take on greater solemnity. All texts for the Divine Office are Proper and what is missing from the Proper, are taken from the Commons. The Te Deum is said. At Mass, the Gloria is said, but not the Credo. There is no Evening Prayer I unless it is a Feast of the Lord that falls on a Sunday (e.g. Transfiguration, August 6).
Solemnities are the highest and begin with Evening Prayer I the evening before. At the Divine Office all texts are Proper, and anything not Proper are taken from the Commons. The Te Deum is said. Night Prayer is always said using the Sunday formulary rather than the weekday. At Mass, the Gloria and Credo are said. Holydays of obligation are always solemnities. No texts are taken from the weekday. Also, on a Solemnity, if it falls on a Friday, then the obligation to perform penance does not bind.