Partially yttria-stabilized zirconia coatings produced under plasma-assisted EBPVD with bipolar pulsed bias and under electron bombardment-assisted positive bias conditions

Previous research using radio frequency (rf) plasma-assisted electron beam (EB) PVD to deposit partially yttria-stabilized zirconia (PYSZ) thermal barrier coatings has shown the benefits of this method in terms of structure control, giving improved strain tolerance. New results are reported showing that pulsed direct current (dc) power supplies can give these benefits without the power-matching problems of rf supplies. However, for optimal coatings additional substrate heating is needed. Here a new method for EBPVD of PYSZ is reported, in which the substrates are held at a positive potential and are heated by energetic electron bombardment both before and during deposition. The resulting coatings are smoother than the plasma-assisted ones and have a dense fibrous structure. These coatings, and the pulsed power plasma-assisted ones, are compared in terms of structure, phase composition, adhesion and resistance to impact conditions; also, comparisons are made with a conventional EBPVD deposit. These comparisons confirm the improved toughness and adhesion, under bend tests, of the electron-bombarded coatings and highlight their potential for further development.