OP, my initial reaction on a read and re-read of your post is that you don't sound very tuned in to what's a perfectly normal 14 month old.
I'm sorry, I know that sounds harsh, but you yourself sound harsh using words like badly behaved, strong minded and brattish in relation to a baby (yes, he's basically still a baby).
I’ve tried raising my voice, ignoring, time out
Not one of these is appropriate for this age group. Raising your voice will just scare and upset him, ignoring is totally inappropriate when they're so little and need reassuring (which in turn teaches them to contain their frustration themselves), and spot-on that he's far too young for time outs.
It really might help to think of him more as a little person trying to express needs and feelings, rather than a rebellious force that needs to be contained and conquered (which is kind of how your post comes across). I'd really recommend reading something like the AHA parenting website for an alternative view (can't off the top of my head remember whether they have specific bits for younger kids, but they may well).
I hope this hasn't sounded too harsh, OP, but I was quite taken aback by your post. You may find the screaming is frustration at going on to some new developmental change, or just that you're both getting a bit tense...but if you can reassure him and not feel it's some big reflection on him or you, it'll feel easier. 