Materials Science and Engineering A 527 (2010) 3310–3316 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Neutron diffraction study of the stress distribution in steel matrix around active NiTi inserts V. Davydov a,c,∗ , P. Lukᡠs a , M. Vrána a , B. Malard b , J. Pilch b , V. Maximov a , P. ˇ Sittner b a Nuclear Physics Institute, 250 68 ˇ Reˇ z, Czech Republic b Institute of Physics, Na Slovance 2, 182 21 Praha, Czech Republic c Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Bˇ rehová 7, 115 19 Prague, Czech Republic article info Article history: Received 7 April 2009 Received in revised form 13 December 2009 Accepted 13 February 2010 Keywords: In-situ neutron diffraction Shape memory alloys Residual stresses abstract The present work deals with a non-conventional application of multifunctional materials such as shape memory alloy in engineering components. The concept of active inserts has been adopted in order to redistribute compressive stresses emerged in cutting disc during its operation. According to the present design, the small pre-strained elliptical NiTi elements were placed into openings of steel cutting disc in places with expected maximum stress concentration. To study the stress interaction of the NiTi inserts with steel matrix in detail, the in-situ method of neutron diffraction was employed for residual stress mapping. The diffraction experiments were focused substantially on scan of internal stresses around inserts and their evolution with increased temperature. The performed studies confirm the potential ability of NiTi insert to induce the compressive stress within steel matrix with applied temperature. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Much attention has been drawn towards shape memory alloy (SMA) materials during the few last decades, because of the enhanced properties that they offer. Their functional characteris- tics are of especial concern, namely the ‘memory’ of its original, cold, forged shape, and ability to return to that shape after being deformed by applying heat. Shape memory alloy materials from the point of functionality are occurred in two basic phases; martensite and austenite [1]. Austenitic phase exists upon high temperatures at one allotropic form with high lattice symmetry. Martensitic phase emerges by cooling of austenitic phase down to the certain temperature, or the same austenite–martensite transformation can be induced by the increase of applied external mechanical stress. If an SMA ele- ment is in a martenistic phase at defined temperature and under external mechanical stress, then under elevation of temperature the martensitic phase transforms back into austenitic phase, which is the most stable at high temperatures. If martensitic phase has been pseudo-plastically deformed, in the range even up to 7%, then during temperature increase it returns back to the primary shape of material in the austenitic phase. In case this reverse transfor- mation is impeded by external mechanical force, the mechanical ∗ Corresponding author at: Nuclear Physics Institute, Neutron Physics Laboratory, 250 68 ˇ Reˇ z, Czech Republic. Tel.: +420 266172034; fax: +420 220941130. E-mail address: davydov@ujf.cas.cz (V. Davydov). stress reaches the value of 1.5 GPa; the stress is growing till the reverse transformation of martensite into austenite is completed, or till the moment when martensite starts to deform plastically. This effect was employed at the concept of active redistribution of residual stress in cutting discs, where the SMA elements (mixture of austenite and reoriented martensite) were embedded into the steel matrix at places with possible concentration of critical val- ues of residual stress. This necessary oriented SMA element upon increasing temperature exerts pressure at the place of contact with steel matrix and redistributes residual stress by the way dependent on its design. The transformation mechanisms of NiTi alloys were experimen- tally studied by diffraction methods in tensile and compressive modes [2–7]. However, there are only limited published literatures about the application of NiTi-based shape memory alloys [8–11]. The idea exploited in present work has not been published yet. Therefore the results presented in present paper have a tentative character and serve to verification of assembling technology of specimens. To perform residual stress studies, the in-situ neutron diffraction method was chosen as a suitable technique for determination of stresses non-destructively from the inner volume of components, mainly due to the high penetrability of neutrons [12,13]. Measure- ments have been made under increased temperature to simulate operating conditions of cutting tool, without an application of an external load. Obtained stress values were considered regarding to the redistribution efficiency of compressive stress fields induced by SMA insert in the steel matrix. 0921-5093/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2010.02.044