Fabrication of thick, crack-free quasicrystalline Al–Cu–Fe coatings by electron-beam deposition

• Published in: Surface & coatings technology Vol. 291; pp. 406 - 412
• Main Authors: Polishchuk, S., Ustinov, A., Telychko, V., Merstallinger, A., Mozdzen, G., Melnichenko, T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2016
• Subjects: Channels; COATINGS; CRACKING; Cracking (fracturing); Critical thickness; DEPOSITION; FABRICATION; Fracture mechanics; PVD thick coatings; Quasicrystal; RESIDUAL STRESS; Substrates; Thermal expansion; THERMAL EXPANSION COEFFICIENT; PVD thick coatings; Cracking; Critical thickness; Quasicrystal; Residual stress
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2016.03.002

Quasicrystalline Al-Cu-Fe coatings have been fabricated using electron-beam physical vapour deposition (EBPVD) at substrate temperatures in the 570–890K range. The structure of some coatings deposited in that way contains defects, like channel cracks. It is shown that residual stresses developed during coatings cooling to room temperature may lead to the channel cracking in the coatings. X-ray diffraction analysis has demonstrated that residual stresses in the crack-free Al-Cu-Fe coatings increase linearly with deposition temperature, which is caused by the rise of thermal stresses due to the difference in thermal expansion coefficients of the coating and substrate material. The analysis of the residual stresses dependence on the deposition temperature has enabled the thermal expansion coefficient of the coating material to be determined at αc=(17.1±1.3)∗10−6K−1.The fracture toughness of the coating material in terms of the stress intensity factor has been estimated at K1C=1.68±0.11MPam. These characteristics of the Al-Cu-Fe coatings obtained have been used for the calculation of a critical thickness, below which the crack-free structure of the coatings is retained. The obtained values of the critical thickness were compared with the results of experimental study of surfaces of the Al-Cu-Fe coatings deposited onto different substrates at various temperatures. We observed that the channel cracking was inhibited if the coating was thinner than the corresponding critical thickness. •Residual stresses in thick PVD quasicrystalline Al-Cu-Fe coatings were measured.•The main mechanism of the stress relaxation in the coatings is a channel cracking.•Thermal expansion of the coating material is estimated to be (17.1±1.3)∗10−6K−1.•The coating material fracture toughness is estimated at K1С=1.68±0.11MPa∗m1/2.•The critical coating thickness, above which the cracking becomes probable, is found.