Effect of shot peening on scuffing resistance of Cu-Ni austempered ductile iron

Significance Statement

Wear of materials is a complicated process that depends on material properties and running conditions. Lubrication is the widely-used method known to reduce wear in mechanical components like gears. The lubricant works to lessen the severity of the superficial shear stress by reducing wear and friction by dissipating heat between any contacting surfaces. Under normal tribological conditions, a thin, compressed elastohydrodynamic oil film separates the contacting surfaces.

However, at times the surfaces operate too close that some surface asperities are in contact and boundary lubrication prevails. When the oil film breaks down, the entire load is assumed to be supported by the asperities leading to mechanical contact. This results in accelerated wear. Scuffing occurs in the start-ups, before full hydrodynamic lubrication occurs, or when the lubricant temperature exceeds a certain value leading to a significant drop in the lubricant viscosity.

Several studies on tribological attributes of austempered ductile iron (ADI) are not certain whether shot peening improves scuffing resistance of austempered ductile iron or not. Therefore, in a collaboration between University of Malta and Clausthal University of Technology in Germany, researchers proposed a method to compare the scuffing resistance of shot peened copper-nickel austempered ductile iron to the as-austempered specimens. The authors evaluated scuffing resistance by testing specimens under boundary lubrication conditions. Their work is published in the journal, Surface & Coatings Technology.

Experimental data of the scuffing of austempered ductile iron, before and after shot peening, was obtained. A cantilever loaded flat ended ADI pin was made to slide on a rotating steel disk. The pin was attached to one end, and to other were attached force transducers. The tribometer was fixed to an on-site computer that tracked and recorded wear and temperature of the pin and disk as well as frictional force.

The authors conducted their experiments under starved lubrication using synthetic base gear oil at ambient temperature. They used a constant loading approach instead of progressive loading, so as  to avoid the pin’s behavior from being affected by its speed and loading history. Two conditions, ground as-austempered and shot peened ADI, were tested in this study.

The as-austempered test pieces endured 0.2×104 cycles before failure. The low endurance limit can be pinned to plastic flow of the ausferritic structure and micro-facture of the asperities of the sliding surfaces. However, shot peening lead to a higher scuffing resistance and endured 2.1 x104 cycles before failure. The authors found that, the indentations formed by shot peening served as lubrication pockets. Therefore, the lubricant results in a load-bearing hydrodynamic pressure that supports the load and also results in a low coefficient of friction between the two surfaces. Additionally, the higher hardness and compressive stresses present at the surface of shot peened components contributed to the higher scuffing resistance.

About the author

Ann Zammit graduated in Mechanical Engineering at the University of Malta in 2003, after which she started working in the semiconductor industry at ST Microelectronics Malta Ltd. She later joined the University of Malta in 2005 as a research engineer. In 2008 she was employed as an Assistant Lecturer and in 2014 as a Lecturer within the Department of Metallurgy and Materials Engineering (DMME) at the University of Malta.

Ann was awarded a PhD degree in 2014 for her work dealing with tribological and mechanical characteristics of surface modified austempered ductile iron as a gear material. Her main research interests are in the areas of material heat treatment, surface engineering, shot peening, laser surface treatments, mechanical testing and tribology.

Since February 2015, Dr Zammit has been coordinating the academic and industrial activities within the DMME laboratories. She is also a peer reviewer for a number of international journals and is on the editorial board of the International Journal of Peening Science and Technology.

About the author

Dr Ing. Stephen Abela following six years of technical Industrial experience, Stephen Abela decided to further his studies at University. He received his B.Eng (Hons) degree in Engineering from the University of Malta in 1998. The same year, Stephen Abela joined the the Department of Metallurgy and Materials Engineering (DMME) with the University of Malta as a Research assistant. In this capacity, Stephen helped the department in the setting up of the heat treatment facility and establishing itself as the heat treatment and surface engineering service supplier in Malta. He joined the academic compliment of DMME in 2000.

In 2007, Stephen Abela received a PhD degree from the University of Malta, for his work related to the develop Ion Beam Assisted Deposition technology for magnesium alloys. He was subsequently promoted to lecturer where he now lectures various courses at both under and postgraduate level while he continues his research particularly focusing on surface engineering of light alloys and water treatment technologies using renewable energy.

About the author

Lothar Wagner studied Mechanical Engineering with specialisation in Materials Technology at the Ruhr-University Bochum. After receiving his Dr.-Ing. degree he went for two years as Research Associate and AvH-Fellow to the University of Rochester in Rochester, NY, USA. After returning to Germany, he worked as Senior Research Associate at the TU Hamburg-Harburg where he became Lecturer of Materials Science and Forming Technology.

Lothar served as Full Professor of Materials Technology and Physical Metallurgy at the newly found TU Cottbus where he also became a Member of the Directorium of the Research Center of Light Alloys Panta Rhei. Thereafter, he became Full Professor and after only three more years Director of the Institute of Materials Science and Engineering at TU Clausthal. In addition, Lothar had various appointments, e.g., as Adjunct Professor at Clemson University, SC, USA, as Guest Professor at the Xinxiang University, Henan, P. R. China and as Guest Professor at NPU of Xi’an University, Shaanxi, P. R. China.

Lothar was the Chairperson of the 8th International Conference on Shot Peening in Garmisch-Partenkirchen and also of the 12th International Conference on Shot Peening in Goslar.

He has authored or co-authored more than 350 publications.

About the author

Mansour Mhaede received a Bachelor’s Degree (1996) and a Master’s Degree (2001) in Chemical Engineering from Minia University, Egypt. In 2008, he obtained the Dr. –Ing. degree from TU Clausthal (Germany). From 2004 he is working as a research associate at the Institute of Materials Science and Engineering of TU Clausthal.

His research activities address the characterisation, and evaluation of mechanical properties, fatigue & corrosion fatigue performance and corrosion behaviour of metallic materials in correlation with mechanical surface treatments and coatings. In addition, he serves as an Editorial Board member and potential peer reviewer of several international journals.”

About the author

Rui Wan graduated in Materials Science and Engineering at TU Clausthal (Germany) in 2010. Following this, betwen 2011 and 2013 he worked as a Scientific Assistant in the Institute of Materials Science and Materials Engineering also at TU Clausthal. In 2013, he started working in industry as a Materials Engineer at Muhr und Bender KG.

About the author

Prof. Maurice Grech studied at the University of Malta and Birmingham, UK. During his distinguished career he worked at TeleMalta Corporation and Malta Development Corporation, now Malta Enterprise. He is now a full professor and has for the last thirty years occupied various positions at the University of Malta including that of Head of the Department of Metallurgy and Materials Engineering, for over 15 years, and Dean of the Faculty of Engineering.

Prof Grech has over 40 publications in fields like ‘Austempered Ductile Iron’, ‘Heat Treatment’, ‘Surface Engineering, and others. Whist at the University, he has acquired funds for several capital intensive projects that lead to the installation of state of the art heat treatment, surface engineering, testing and analytical facilities. He led numerous research projects including those with EU funding. Between 2007-2012 he was Principal of the Malta College of Arts Science and Technology (MCAST), Malta’s Vocational College with over 6000 full time students and 4000 evening learners. His major contribution during this period included the introduction of degree programmes and the acquisition of parity of esteem between vocational and traditional qualifications. His contributions in the field of education have been acknowledged both nationally through the Lifetime Excellence Award bestowed by the Malta Chamber of Professional Engineers and internationally through a number of awards including the FCGI Fellowship. Whilst at MCAST Prof Grech attracted circa €50 million worth of ESF and ERDF projects.

Reference

A. Zammit1, S. Abela1, L. Wagner2, M. Mhaede2, R. Wan2, and M. Grech1. The effect of shot peening on the scuffing resistance of Cu-Ni austempered ductile iron. Surface & Coatings Technology, volume 308 (2016), pages 213-219.

Show Affiliations
  1. Department of Metallurgy and Materials Engineering, Faculty of Engineering, University of Malta, Malta
  2. Institute of Materials Science and Engineering, Clausthal University of Technology, Germany

 

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