restrepoarango: I've merged your recent post with this other one of your, from 5 years ago. I'm sorry you haven't had much of a response as yet, but you topic is a little obscure. You can wait for an expert to weigh in, or you can try some literature searches. You'll get the best results if you give us as much of your application as you can:
How would you suggest to make an alloy of Bismuth and Antimony under vacuum?
Do those metals form an alloy? In what proportions do you need this alloy? Does it have to be under a vacuum? Why not melt together and pour?
Would it be appropriate to use a heavy wall Schlenk flask and hard vacuum conditions?
Will a sizable quantity of these two metals deform enough? What pressure differential do you mean for "hard vacuum? Only the vendor can tell you if the "Schlenk flask" can handle that pressure without imploding. Just because its thick walled, and meant to vacuum filter a liquid, doesn't mean it won't implode under very strong vacuum. Warning: I have never seen a vacuum flask implode, so if it were to, the damage risk is likely very serious.