See the docs:
>>> Blog.objects.in_bulk([1])
{1: }
>>> Blog.objects.in_bulk([1, 2])
{1: , 2: }
>>> Blog.objects.in_bulk([])
{}
Note that this method only works for primary key lookups, but that seems to be what you're trying to do.
So what you want is:
Article.objects.in_bulk([1, 2, 3])