There's essentially one train that features throughout the series - the one in
Tintin in America and
The Broken Ear, for example. There might be some variations, I haven't got the books to hand. Curiously, I read about that just the other day, but I'm not sure where. Apparently the design is based on an actual locomotive, of which only nine were built (I'm doing this from memory, if I find the source I'll cite it). Hergé had a technical plan of the train and therefore used it often. If anyone wants to try and find it, please be my guest. I thought it was in
Hergé, ou le secret de l'image by Pierre Fresnault-Deruelle, but I've looked through it just now and can't seem to find it.
Incidently, that book draws a parallel between the train sequence in
Tintin in America and AM Cassandre's 1927 poster design
Étoile du Nord (personally, I can see a greater similarity with
Nord Express). Cassandre's work may be of interest to Tintin fans, since not only were he and Hergé contemporaries, but their poster design work was similar, and Cassandre's travel posters evoke the same sense of movement and adventure that Tintin embodies. Good stuff, but perhaps a bit off-topic, so I won't go too far down that road (or railway line).
The carriages in
Prisoners of the Sun seem to be very much like the actual ones still in use on Peruvian railways, except the actual ones are red. There's a photograph
here or you can see a full-page image in the book
Tintin, Grand Voyageur du Siècle. I don't know what kind of couplings are used, but I think I saw a photograph once of a steam locomotive that looks very much like the one in the Incan story.