HVOF Application of Nickel and Nickel Alloy to Tungsten Heavy Alloy for Jacketed Penetrators

Report No. ARL-TR-3095
Authors: John V. Kelley and Russell Kilbane
Date/Pages: November 2003; 20 pages
Abstract: In recent years, there has been an increased desire to replace depleted uranium (DU) anti-armor penetrators with tungsten heavy alloy (WHA) penetrators. However, the ballistic performance of WHA does not compare with that of DU. Many methods of improving the ballistic properties of tungsten have been explored. One recent method includes jacketing a long thin core of WHA with a more ductile metal. This report examines the use of thermal-sprayed, high-velocity oxy-fuel coatings to apply the jacket material. However, applying thermal-sprayed coatings onto a tungsten substrate is a challenge. The differences in the coefficients of thermal expansion (CTE) make it difficult to achieve adequate adhesion of most coatings to tungsten. Further compounding the problem are residual stresses inherent in thermally sprayed coatings. The thicker the coating desired, the more likely disbonding will occur upon cooling of the substrate. Early attempts to apply an Ni coating (0.010-0.020 in thick) to a tungsten substrate yielded immediate disbonding and/or cracking of the coatings. The work presented is an investigation focusing on modifications to spray parameters and the use of multiple thin layers to minimize heat transfer and achieve better adhesion. The use of a material with a CTE nearer to that of tungsten as a bond coat and grading of coating materials was also examined as a method for increasing the overall adhesion of the coating system.
Distribution: Approved for public release
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Last Update / Reviewed: November 1, 2003