Carl R. Ribaudo

Laser-Clad NiAICrHf alloys with improved alumina scale retention

A new mechanism for the improved retention of alumina scales formed on laser-clad NiAICrHf alloys has been observed. Laser cladding is the process where fine metal powders are rapidly melted and fused to a solid substrate using a CO2 laser. The effects of laser cladding upon scale retention on NiAICrHf alloys after cyclic and isothermal exposure to air were investigated using thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The calculated compressive stress in the scale due to constrained cooling exceeded the probable compressive strength of alumina. Additions of up to ≈ 2.5 wt pct Hf increasingly promote retention of scales grown at 1200 °C, with laser-clad samples of ≈ 2.5 wt pct Hf alloy retaining almost completely intact scales. The improvement in scale retention is due to improved toughness in scales containing hafnia polycrystallites, possiblyvia microcracking initiated by anisotropic thermal contraction of the hafnia. Laser cladding the 2.5 wt pct Hf alloy provides a large concentration of ~ 1 µm Hf-rich particles that are precursors of the hafnia in the scale as well as a finer dendrite spacing that reduces the mean free distance between particles.

Engineered surfaces for improved gear scuffing resistance

Scuffing is a severe form of adhesive wear that can occur on gear flanks operating at combinations of high sliding speed and contact stress in marginal lubrication. Engineered Surfaces (ES) refers to the selection, application, and use of certain topographical modification (TM) techniques and thin film coatings applied using advanced physical vapor deposition (PVD) to improve the tribological performance of mechanical components. In this study, the effects of ES technology upon the scuffing resistance of helical gears were empirically determined. Six different treatments of ES technology were tested along with a baseline treatment of uncoated ground surfaces. In the testing, the gear speed was kept constant while the input torque on the gears was incrementally increased until scuffing was observed. Three ES treatments produced statistically significant increases in the scuffing torque relative to the baseline. Increases in mean scuffing torque using ES technology were as high as 89%.Copyright