Metallurgical Analysis of Premature Failure of a Phosphor Bronze Worm Wheel
Tóm tắt
Worm drives are commonly used where large reduction in speed and greater transfer of torque are required within a small space. Phosphor bronze is normally used material for this application owing to its lower coefficient of friction and good wear and fatigue properties. This work presents a failure analysis of a worm wheel. Analysis revealed that around 40% of the teeth of worm wheel were broken. Failure mode was identified to be intergranular brittle fracture using scanning electron microscopy. A number of casting voids could be observed. In addition, network of intermetallic phases were present along the grain boundaries. These phases were identified to be Cu3Sn and Ni3P using elemental mapping through wavelength dispersive spectroscopy technique. These phases were found to have significantly higher hardness compared to the matrix and their precipitation along grain boundaries made the alloy susceptible to intergranular fracture even under small increase in service stress than nominal level.
Tài liệu tham khảo
P.R.N. Childs, Chapter 11: Worm Gears, Mechanical Design Engineering Handbook (Butterworth-Heinemann, Oxford, 2014), pp. 439–458
ISO/TR 14521 Gears—Calculation of load capacity of worm gear. https://www.iso.org/standard/51227.html (2010). Accessed 5 Aug 2018
B. Sadık, E. Atik, Evaluation of effect of alloy elements in copper based CuSn10 and CuZn30 bearings on tribological and mechanical properties. J. Alloy. Compd. 489, 262–268 (2010)
ASM International, ASM Handbook: Fractography, vol. 12 (ASM International, Materials Park, 1987)
H.R. Pritchard, Survey of literature on the effect of testing temperature on the properties of wrought copper-base alloys, US Department of Commerce, Report R-1435 (1958)
Specification for phosphor bronze ingots and castings, Bureau of Indian Standards, IS 28:1985
S. Fürtauer, D. Li, D. Cupid, H. Flandorfer, The Cu–Sn phase diagram, part I: new experimental results. Intermetallics 34, 142–147 (2013)
UNS C90700, Copper Development Association Inc. https://alloys.copper.org/alloy/C90700. Accessed 1 Aug 2018
H.S. Kim, On the rule of mixtures for the hardness of particle reinforced composites. Mater. Sci. Eng., A 289, 30–33 (2000)