Material science is interested in how to optimize the properties of materials for a particular application. Hardness, tensile strength, elasticity, creep, conductivity. Crystal structure and grain boundaries
You will find them altering the recipe for metal alloys, plastics, composites and in semiconductors manufacture.

Its a bit more specialized and so tends to pay more. The caveat being there are less positions to fill.

Less about the contraption more about the material.
Machine design is in the domain of the Mechanical Engineer.