FUNCTIONALLY GRADED ALUMINUM METAL MATRIX COMPOSITE COLD SPRAY COATINGS ON ALUMINUM 7075 SUBSTRATE

Aluminum alloys have widespread use in the aerospace and maritime industries due to their high specific strength, good corrosion resistance, and low cost. Gas dynamic cold spray, cold spray for short, is a thermal spray technique that is used for in-field repair of metallic surfaces to include aluminum. To improve the wear resistance of aluminum, the metal must be reinforced with a filler. Additionally, to prevent delamination issues with cold sprayed coatings, a compositionally graded coating is required. To date, there has not been a study on the cold spray of compositionally graded, dual-reinforced aluminum metal matrix composites (Al-MMC). Al reinforced with aluminum oxide (Al2O3) and boron nitride nanotubes (BNNT) were cold-sprayed onto aircraft-grade aluminum (Al-7075) alloy. High energy ball milling was used to create coating compositions of 10, 20, and 30 vol.% Al2O3, 2 vol.% BNNTs, as well as 1 vol.% BNNT with 10 vol.% Al2O3. The different coating compositions were then graded over one another by means of cold spray and their subsequent properties of adhesion strength and wear resistance were studied. Results from these tests were also qualitatively evaluated using optical and scanning electron microscopy, as well as optical profilometry. All four graded coating compositions experienced equal or increased adhesion strength, while failing cohesively, leaving the base cold spray composition intact (i.e., still adhered to the substrate).
Office Of Naval Research, Young Investigator Program. Arlington, VA, 22217
Lieutenant Commander, United States Navy
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