Suitable material for gears in gear pump

It would be of help to send some picture of the worn gears in order to see where and how they wear. Do you have any knowledge about the pressure ?

I may be wrong but I don't think helical gears will work in a pump.

Helical gears are commonly used in external gear pumps. Some of the benefits are reduced noise, reduced loading on the teeth, reduced pulsation, etc. The downside compared to spur gears is that they produce axial loading, and there can be some sliding friction on the teeth. There are also double helical gears, aka herringbone or v-shape, which eliminate the axial loading, but are much more difficult to manufacture. I could be wrong, but I don't think helical gears are any more efficient at producing pressure.

Maag (Textron), Witte and Zenith are three of the top manufacturers of polymer gear pumps. Between them they use spur, helical and herringbone gears. The gear material is commonly tool steel or other special heat-treated, nitrided or hard-coated steels. I am not familiar enough with this process, these pumps or these materials to give advice on material selection. It might be best to contact one of the above, or another manufacturer of polymer gear pumps for advice.