Surface engineering alumina armour ceramics with laser shock peening

• Published in: Materials & design 2017-11, Vol.134, p.523-538
• Main Authors: Shukla, P., Robertson, S., Wu, H., Telang, A., Kattoura, M., Nath, S., Mannava, S.R., Vasudevan, V.K., Lawrence, J.
• Format: Article
• Language: English
• Subjects: Al2O3; Ceramics; Hardness; KIc, fracture toughness, residual stress; LSP; Microstructure
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2017.08.066

•Laser shock peening of Al2O3 armour ceramic was performed for the first-time.•29% and 6% increase in compressive stress was found at 0° and 90° direction using X-ray diffraction method.•Fluorescence method verified the above and showed −172MPa of maximum compressive stress.•Thus, a 10% increase in hardness and 12% enhancement in fracture toughness was measured.•LSP of Al2O3 armour ceramic rendered microstructural refinement and grain size reduction. [Display omitted] Laser shock peening (LSP) of Al2O3 armour ceramics is reported for the first-time. A 10J, 8ns, pulsed Nd:YAG laser with a 532nm wavelength was employed. The hardness, KIc, fracture morphology, topography, surface residual stresses and microstructures were investigated. The results showed an increase in the surface hardness by 10% which was confirmed by a reduction in Vickers indentations size by 5%. The respective flaw sizes of the Vickers indentations were also reduced (10.5%) and inherently increased the KIc (12%). Residual stress state by X-ray diffraction method showed an average stress of −64MPa after LSP, whilst the untreated surface stress measured +219MPa. Further verification with the fluorescence method revealed surface relaxation with a maximum compressive stress of −172MPa induced after LSP within the Al2O3 armour ceramic. These findings are attributed to a microstructural refinement, grain size reduction and an induction of compressive stress that was relaxing the top/near surface layer (post LSP) from the pre-existing tensile stresses. Further process refinement/optimization will provide better control of the surface properties and will act as a strengthening technique to improve the performance of armour ceramics to stop bullets for a longer period of time and protect the end-users.