There is no known alloy called "Nitra" in the field of metallurgy. It's possible you're thinking of a different name or there's a misunderstanding.

Could you please clarify what you mean by "Nitra alloys"?

Perhaps you're thinking of:

* Nitinol, a nickel-titanium alloy known for its shape memory effect.

* Nitralloy, a trade name for a specific type of steel used for nitriding.

* A specific alloy with a different name.

Let me know if you can provide more details, and I'll do my best to help you find the information you're looking for!