Welcome Danny
There are some questions that need to be addressed to give you better answers. Others gave you choices on solid metals and kits. All well and good. But the question I have for you is what quality kits are you using. There are plenty of kits today that that are coated. Some are coated with an acrylic and some are just better quality kits. If you are using kits with 24K gold and lesser platings than you will always have problems. Plating such as Rhodium, Titanium, Platinum and chrome have great wear resistant characteristics. Here is some reading info from Craft Supply which is a well known vendor of good quality kits.
Pens and Platings - Craft Supplies USA
Now to address your other problem about cracking. This is a topic that can take pages and pages to hit all the possibilities. I am sure you will get some more responses but I will give some highlights.
If you are getting cracks in acrylics your technique needs work so will not touch that but can be lumped in at the bottom of wood blanks as I will explain.
Wood blanks---- Some woods are just prone to crack no matter what you do such as the dreaded Snakewood blanks and there are more. Some times woods are not completly dry when worked and that is something you can correct easily by letting to dry or slowly drying in a toaster oven on low heat cycling on and off. There are plenty of threads on this stuff here and you need to do some searching unless people want to spell it all out for you then they can.
Then there is drilling these blanks and also acrylic blanks, heat is your enemy in any phase of pen turning. Sharp tools and drill bits are a must. Good turning techniques is a must. Learn to use the tools and present them to the material properly. All materials are not the same and are not turned the same. Again too much for me to go into.
Then there is the assembly of the components. Care is needed to make sure the inside of the tubes are clean from stray glue or resins if cast. The ends must be reamed. This is a step many newbies forget. If a component is hard to press on then the tube will probably need filing which can be done with small round files or reamers. You should never have to force the parts on. They must be centered as they slide on. Any amount of cocking and they will distort the tube and cause cracks.
Now cracks in finishes is another topic that has pages of info. The type of finish, the amount of finish, the age of the finish, the final sanding and buffing and remember heat is your enemy. So are you seeing cracks in the finish or the entire blank and if so what is the blank material.
But do have fun. It is a fun hobby.