How to display subcategory articles in the category view?

This is a matter of your template.
To display the subcategories in a list view as well you would have to customize the template. I do not know what kind of template you use and how the file is named which displays the subcategories, but you could change it so that it displays the articles of the current category. Therefore you will have to take a look at the wp loop.

Another option would be to look for a theme that does so.

And there are plugins to display Articles on posts, but therefore you would have to implement the category pages manually.