High-Rate Sputter-Deposited Tantalum Coatings on a Steel Liner for Wear and Erosion Mitigation

摘要

A prototype, rifled steel liner of 20-min inside diameter was coated with -50 to 125 micronmeter tantalum at -22.6 micronmeter/hour in krypton gas using a triode-sputter system. It was test fired with l5OO rounds for the mitigation of high-temperature and pressure wear and erosion. Growth surface analysis showed predominately alpha-phase and minimal beta-phase surface tantalum. Area detector images showed near random, slight preferred (211) crystalline orientation. X-ray diffraction revealed a thin layer of surface zinc oxide and copper firing debris on the coating surface. Compressive surface residual stress peaked near the center of the tube. Photomicrograph metallurgical examination showed general good adhesion in major parts of the bulk coatings, along with a thin layer of beta-phase nucleation, and alpha-phase or mixed alpha- and beta-phase grain growth. There was excellent behavior in soft and ductile a-tantalum areas, but cracking and disbonding occurred in beta- tantalum areas. Coating liftoff and coating loss occurred most frequently in land/groove transition and land areas, less in groove areas. Near the breech end where no coating was sputtered, the steel substrate suffered extensive cracking and environmentally-assisted heat damages.