without special external support, it's not truly possible (as far as I know) to morph one mesh directly into another, seperate, different mesh. The best way to achieve such a thing is with blend shape, which morphs between two models that have identical vertex order (ie. the 2 models are from the same object, just look different).

So, with 2 different objects, the only way to do it is to "fake" it, with effects or whatnot.