PVD coating and substrate pretreatment concepts for corrosion and wear protection of magnesium alloys

Composite titanium nitride layers produced on the AZ91D magnesium alloy by a hybrid method including hydrothermal modification of the layer

“…The effect of layers' hydrothermal tightening on the corrosion resistance was significantly more effective than thermal oxidation or oxynitriding in glow discharge conditions (430 • C/8-16 h) [13]. It is appropriate at this point to refer the results of the present study to the results obtained by other authors working with titanium nitrides surface layers on magnesium alloys [5,[14][15][16][17]. The results reported in the reference [14,15] indicate that TiN type titanium nitride layers resulted in a relatively low increase of corrosion resistance, with the corrosion potential shift almost an order of magnitude smaller than for the composite TiN-Ti-Al type titanium nitride layers that we developed.…”

“…One should notice, however, that this type of solution does not make the coatings tight, unlike the hydrothermal tightening process that we have developed. Polarisation corrosion tests demonstrate good effectiveness of the nitride layers alloyed with magnesium in a relatively weak corrosive environment (0.05 M NaCl) [16]. The TiN-Ti-Al layers developed in the course of our investigations prove effective in a much more aggressive environment (0.5 M NaCl), but it should be noted that they do not exhibit passive range.…”

“…They also fail to eliminate the risk of galvanic corrosion, related to their cathodic character, resulting in limited application prospects. It is only the most recent works carried out in this area by Hoche et al [5,16,17], that demonstrate significant potential of a solution based on producing titanium nitride coatings alloyed with magnesium (Ti-Mg-N and Ti-Mg-Al-N type layers), leading to a reduced difference in the chemical activity between the coatings and the magnesium substrate and, consequently, a reduced risk of galvanic corrosion. One should notice, however, that this type of solution does not make the coatings tight, unlike the hydrothermal tightening process that we have developed.…”

“…Unlike the TiN-Ti-Al layers however, these layers are characterised by limited tribological resistance, especially in terms of load bearing capacity. All this seems to make our hydrothermally tightened TiN-Ti-Al type titanium nitride layers competitive compared with the TiN-Ti-Mg type layers [5,16,17], especially in terms of achieving at the same time high corrosion and mechanical resistance, essential for high reliability of the layers. The added advantage is the simplicity and the low cost of the hydrothermal tightening method.…”

In Situ Aluminum Alloy Coating on Magnesium by Hot Pressing

“…Hoche et al [25] and Li et al [26] studied the coating of magnesium by PVD coating, and the results showed that several PVD coating concepts were tested for the Mg alloys. Unfortunately, no promising PVD coating has been found related to corrosion and residual stress yet.…”