tea leaf vs black tea

tea leaf and black tea both are nouns.

Word	Noun	Adjective	Verb	Adverb
tea leaf	Yes	No	No	No
black tea	Yes	No	No	No

As nouns, black tea is a hyponym of tea leaf; that is, black tea is a word with a more specific, narrower meaning than tea leaf:

Other hyponyms of tea leaf include tea bag, green tea, oolong.

tea leaf (noun)	black tea (noun)
dried leaves of the tea shrub; used to make tea	fermented tea leaves