When compared to doping, how is alloying different? What modifications to the structure are brought about by both of these?
Alloying may be defined as “the process of adding one or more elements or compounds to interact with a base metal in order to obtain beneficial changes in its mechanical, physical, or chemical properties or manufacturing/processing characteristics.”
The section goes on:
However, elements or compounds that lead to a preferential microstructure and subsequent improved properties are covered. Examples of these are grain refiners (grain refining results in better forming or higher strength), inoculants added to molten cast irons to produce changes in graphite distribution and improvements in mechanical properties, magnesium-containing nodulizing (or spheroidizing) additions in ductile irons for high strength and ductility (up to 18% elongation), and the addition of certain elements, such as calcium, sodium, strontium, and antimony, to refine the structure of aluminum-silicon casting alloys as well as improve their tensile properties and ductility. Also included are discussions of some powder metallurgy (P/M) materials that technically may fall outside the definition of alloying given above. An example is copper- base dispersion strengthened materials. Copper can be strengthened by using fine dispersed particles of aluminum oxide. Because this oxide is not immiscible in liquid copper (i.e., it does not “interact”), dispersion strengthened copper cannot be made by conventional ingot metallurgy and alloying techniques; P/M techniques must be used. Dispersion-strengthened superalloys made by “mechanical alloying” are also described.
This is a very broad definition, does not restrict alloying to altering (or not) the crystal structure or microstructure. Note that even dispersion hardening by separate phase particles is considered 'alloying'.
Doping is not so clearly defined by ASM. It is much more common for using trace amounts of an element to alter the electrical (think semiconductors) or optical (laser gain media) properties (at least in my experience).