Water damage, shows apple logo then goes blank?

So I bought an iPhone 6 64gig off a friend who said he dropped it into the pool and it only stayed in the water for maybe a couple seconds at most. He put it in a bag of rice and dried it all out and then plugged it into the charger and only the apple logo would show, then the screen goes blank. You can see the backlight is still lit but the actual phone and software wont boot. I then took the phone apart and looked for any signs of corrosion but couldn't find any except for on a small screw below the battery, I used a dry tooth brush and rubbed most of it off and then re assembled the phone and yet it still does the same thing. I tried a hard reset and its only still showing the apple logo for maybe 5 seconds then just a blank screen with the backlight still on. Is this a battery issue? do I need to try to clean the entire inside of the phone with alcohol? is there anymore drying techniques I can try on it? The phone has been like this for about 3 weeks now and I'm worried the longer I take to fix it the worse things can get inside the phone please help me!!! TIA!!! Also all of the water stickers are still solid white on each of the 4 stickers I saw, even the one on the logic board and in the charging port. The phone is less than a year old and I'm also wondering if maybe since the stickers are still white that I might be able to get it covered under the warranty?