Sliding wear characteristics of Zr-based bulk metallic glass fabricated through laser powder bed fusion
Zr-based bulk metallic glasses (BMG) possess a unique combination of high strength, high elastic limit, and excellent corrosion resistance, making them promising materials for highly stressed structural applications. However, high cooling rates are crucial in achieving the demanded amorphous microstructure, leading to major geometrical restrictions in established casting routes. Laser powder bed fusion (LPBF) of metals recently emerged as a promising technique for the fabrication of BMGs. In particular, the subsequent layer-wise energy-input and the rapid solidification of the melt have been proven to be suitable to overcome current limitations in size and complexity. Additionally, the technique allows generating components with differences in microstructure between the bulk and the surface. Considering possible applications for Zr-based BMGs as structural materials such as gears, the tribological characteristics are of great interest. While the wear properties of cast BMGs have been widely investigated, the impact of the cyclic reheating and increased oxygen content in additively manufactured BMGs is rarely reported yet.
In the present contribution, Zr59.3Cu28.8Al10.4Nb1.5 BMG with varying crystalline fractions was manufactured by means of LPBF. Wear volumes and mechanisms were investigated using reciprocating ball-on-plane sliding wear tests. Counterbody was a bearing steel ball. Silicon oil, which prevents only oxidation, and synthetic gear oil with anti-wear additives were used for lubrication. Wear was analyzed by scanning electron microscopy on the wear track and the subsurface material, and white light confocal microscopy together with thermophysical characterization through differential scanning calorimetry and x-ray diffraction.
While severe abrasive wear occurs under silicon oil, the technical gear oil shows its wear-reducing effect on the BMG. Nevertheless, wear is higher than that of martensitic steels previously studied. First results show that the crystalline fraction of the material close to the surface of the BMG component strongly influences its wear resistance. Therefore, it is indicated that the selectively adjustable energy-input through LPBF can be utilized for tailoring wear behavior.