It actually depends on how far your work is from what you’re intending to do.
Carbon fiber for aerospace applications and modeling plasma for space propulsion are not the same area, but they are both within physics and specifically applicable to aerospace engineering. The details would be different but the general methodologies and approaches and underlying foundations have commonalities.
Similarly, a developmental psychology professor will very often take someone who has done their research experience in experimental or social or clinical psychology. Again, the approaches, theoretical frameworks, and methodologies are similar (more similar than the physics/engineering example above). But someone who only had anthropology experience, even if they were working on the same topic areas, would be less competitive because the foundations are different.
My guess is that alloy chemistry and nanofiber is close enough to the kind of work you want to do that it’ll “count.” It’s still materials science broadly speaking, even if it’s not biomaterials specifically. Biomedical engineering/science/ biological materials sciences tend to be pretty interdisciplinary fields.