Cavitation erosion behaviour of niobium

• Published in: Wear 2012-01, Vol.274-275, p.220-228
• Main Authors: Brunatto, S.F., Allenstein, A.N., Allenstein, C.L.M., Buschinelli, A.J.A.
• Format: Article
• Language: English
• Subjects: Acceleration; Annealing; Applied sciences; CA-6NM martensitic stainless steel; Cavitation; Cavitation erosion; Cold rolling; Erosion rate; Exact sciences and technology; Fatigue; Fatigue failure; Fracture mechanics (crack, fatigue, damage...); Friction, wear, lubrication; Fundamental areas of phenomenology (including applications); Machine components; Mechanical engineering. Machine design; Niobium; Physics; Power generation; Solid mechanics; Structural and continuum mechanics
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2011.09.001

► We studied the niobium cavitation erosion behaviour. ► Niobium samples in the cold-worked state have smaller cavitation–erosion resistance than the same material in the annealed condition. ► Cavitation–erosion failure mechanism in niobium occurs in a sequence of events comprising the fracture of debris allied to the effect of fatigue and microcracks formation. ► Annealed niobium presents similar incubation period but a worse behaviour in the maximum erosion rate stage, when confronted to the ASTM CA-6NM martensitic stainless steel results. Cavitation erosion behaviour of niobium was investigated by means of a 20kHz ultrasonic vibrator at peak-to-peak amplitude of 50μm, aiming to determine the niobium potential as a material for the manufacturing of hydraulic machine components. The study was emphasized for the three first cavitation stages of the cumulative erosion–time curve. The modification of the niobium surface morphology as a function of the testing time in the incubation, acceleration, and maximum erosion rate stages was verified by SEM analysis. Samples were prepared from 98.9% purity and 90% reduction cold-rolled niobium bar. The study was performed for niobium samples in both the cold-worked and annealed conditions. Samples of CA-6NM martensitic stainless steel, a typical material utilized for hydraulic turbines manufacturing, were also analysed for comparison purpose. Annealing treatment of niobium decreases its hardness and increases its ductility, leading to an increase of the incubation period when compared with the cold-worked niobium. Cavitation erosion failure mechanism in niobium occurs in a sequence of events comprising the work-hardening effect and the fracture of debris allied to the effect of fatigue and microcracks formation. Finally, annealed niobium presents similar incubation period but worse behaviour in the maximum erosion rate stage than CA-6NM steel.