Estimation of the stress relief induced in CrN thin films by buckling

Pacquaut

Comptes Rendus. Mécanique

et al. 2011

Self Cite

Under repeated impact loadings -shot peening process, surface mechanical attrition treatment, erosive wear -metallic surfaces undergo severe plastic deformation which leads sometimes to a local change of their microstructure. These mechanically attrited structures (MAS) exhibit very interesting physical properties: high hardness, better tribological properties, etc. Consequently it is of primary importance to understand the mechanism explaining how these MAS are created and grow under such loadings. In this article, this mechanism is investigated with the help of a coupled experimental and finite element approach. First, the MAS are generated on an AISI1045 steel with a micro-impact tester which allows to know the impact energy and the location of impacts with a very good accuracy. The evolution of the MAS shape as a function of the impact number is presented. Then, the finite element investigation is presented. It is shown that a macroscopic stabilized elastic regime is reached after one hundred impacts. It also appears that a close cycle of plastic strain is observed locally in the zone where material transformation should happen during this regime. The severe plastic deformation achieved after a given number of cycles may thus explain the material transformation. Based on these results, we propose a mechanism based on a plastic strain threshold to explain the growth of the MAS. The resulting MAS size and shape appear to be in very good agreement with the experimental results. Finally, we conclude on the influence of the mechanical parameters that are involved in the proposed mechanism.

Section: Experimental Results On An Aisi1045 Steelmentioning

confidence: 99%

Investigation of mechanically attrited structures induced by repeated impacts on an AISI1045 steel

Pacquaut

Comptes Rendus. Mécanique

et al. 2011

Self Cite

“…In this paper a new method based on multiple impacts in a same point is developed to extract the elastoplastic behavior of metals at strain rates close to those induced by shot peening processes. It is based on the use of a standard industrial micropercussion device, which allows to accurately control the locations of impacts and their kinetic energies [12,13]. It is to be noted that no specific additional instrumentation is required to use the method developed in this paper.…”

Section: Introductionmentioning

confidence: 99%

Local identification of the stress–strain curves of metals at a high strain rate using repeated micro-impact testing

Grange

Materials Science and Engineering: A

2013

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Understanding the effect of various mechanical processes such as shot peening requires the knowledge of metal behavior at a high strain rate. The identification of this behavior is often performed using Hopkinson's bar devices. However, the resulting stress-strain curves correspond to a bulk behavior of the material and thus do not take into account the modification induced by surface preparations or surface treatments. In this paper, we have proposed a method based on local micro-impact testing to identify the stress-strain curves of metals near their surface. More precisely, this method is based on the determination of the best stress-strain curve which allows to reproduce the growth of the residual imprint at each impact for a given impact energy. The advantage of the method developed in this paper lies in its simplicity and low cost. In the first part, the repeated impact set-up is presented. Then the FEM strategy is detailed and the identification method developed. In the last part of this paper, an application to AISI1045 and AISI316L steels highlights the great interest of this method to obtain better stress-strain curves than those classically used. It points out the need to identify appropriate surface stress-strain curves when the surface behavior is concerned. As a matter of fact it should also concern other manufacturing processes such as machining or finishing.

“…However, if the mechanical behaviour of a pre-delaminated film can be fully predicted [9][10][11][12][13] and local stress relief induced in films by buckling can be estimated [20], the specific conditions that lead to buckling under repeated impacts have to be clarified. In particular, the influence of the substrate hardness remains quite uncertain.…”

Section: Introductionmentioning

confidence: 99%

Damage phenomena of thin hard coatings submitted to repeated impacts: Influence of the substrate and film properties

Lamri

Materials Science and Engineering: A

2013

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International audienceTo evaluate the surface fatigue resistance of some thin nitride films obtained by Physical Vapour Deposition (PVD) techniques, repeated impact tests have been performed under controlled impact conditions. Short and long duration tests have revealed the occurrence of an original damage phenomenon likely linked to a mechanical blistering of the films. As these blisters appear to be the first damage step, their formation has to be understood in order to be avoided in industrial applications. In particular, the role of the mechanical properties of the substrate has to be clarified as thin protective coatings may be used on pieces prepared using various heat treatments. finite element method (FEM) analysis has been conducted in order to better understand the specific mechanical conditions in the substrate and at the film substrate interface that could lead to such blistering phenomena. Correlations with the experimental results have been evidenced. From the modelling results the substrate properties have been shown to be of significant influence on the blister formation. However as they do not fully explain the origin of this phenomenon, the influence of the substrate microstructure has also been studied and the presence of vanadium carbides appears to be of major effect. (C) 2012 Elsevier B.V. All rights reserved