Materials Science and Engineering A 527 (2010) 3595–3601 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea The role of residual stress in the tension and compression response of WC–Ni A.D. Krawitz a,∗ , E.F. Drake b , B. Clausen c a University of Missouri, Columbia, MO 65211, USA b NOV Reed Hycalog, Conroe, TX 77303, USA c Los Alamos National Laboratory, NM 87545, USA article info Article history: Received 18 January 2010 Received in revised form 12 February 2010 Accepted 15 February 2010 Keywords: Neutron scattering Strain measurement Residual stresses abstract The interaction of uniaxial applied stress with the thermal residual stress state in a WC–10 wt.% Ni cemented carbide composite was studied. A previously proposed model, based on results for uniaxial compressive loading, explains the observed asymmetric relaxation of the pre-existing thermal residual stress. This model predicts that the sense of the asymmetry would reverse in the case of tensile loading. The main purpose of the present work was to test this prediction. The reversal of signs was observed. The addition of tensile data has enabled the role of thermal residual stress on stress–strain response to be further elucidated. More complex behavior is observed with respect to the response of the variance in residual stresses, as measured by changes in diffraction peak breadths. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Cemented carbide composites have high toughness for materi- als of such high hardness, and this is the basis for their use in severe service environments such as drilling hard rock [1,2]. They are par- ticulate composites with high volume fractions f of small, angular particulate carbides, most commonly tungsten carbide, WC. In the present case f = 0.84, the particle size is about 1 m, and the hard- ness is 89 HRA. Commercial grades most often contain cobalt (Co) as the binder metal. They also possess stress–strain responses that are continuously curved [3] and have very large thermal residual stresses (trs) as a result of the liquid phase sintering process and the large difference in coefficients of thermal expansion of the binder metals and WC [4–7]. Prior work suggests that, in addition to the materials and microstructures of these systems, the residual stress state and its interaction with applied stresses may also play a role in the unusually high toughness of these materials [8]. This study is concerned with the role of thermal residual stresses in the mechanical response of this class of composite materials, that is, the interaction of the pre-existing trs with applied stress. The trs is, on average, tensile in the Ni and compressive in the WC, as expected from the coefficients of thermal expansion (CTE) of the two materials; see Table 1. The point-to-point stress states in both phases are complex [4]. This is due to the fine scale of the microstructure, in which the Ni binder phase surrounds the WC particles, and the angularity of the WC. This leads to constraint of ∗ Corresponding author. Fax: +1 5738845090. E-mail address: krawitza@missouri.edu (A.D. Krawitz). the Ni as it tries to shrink more than the WC during cooling from the sintering temperature, at which the Ni is liquid. The degree of constraint is related to the WC particle size; it increases as the WC particle size decreases. In a study of WC–20 vol.% Co, the WC trs ranged from -755 MPa for 0.6 m WC particles to -383 MPa for 5.1 m WC particles [5]. The counterbalancing Co stresses are +1712 and +869 MPa for the 0.6 and 5.1 m WC, respectively. Thus, the mean stresses double as the WC particle size decreases an order of magnitude. The stress state has a high hydrostatic component due to the constraint of the surrounding WC particles, which is how the Ni (or Co) supports stresses an order of magnitude greater than its flow stress. The trs values for the WC–10 wt.% Ni composite studied here are about -400 and +2000 MPa for the WC and Ni, respectively; see Table 1. Studies of WC and Ni diffraction peak breadths support, and provided the original insight for, the idea that the stresses vary significantly from point to point in a WC particle or Ni binder region. Peak breadth effects have been observed due to changes in both temperature and applied load. For temperature, peak breadth changes from 20 to 700 K were observed and found to be essentially reversible [7]. Lowering the temperature increased both the mag- nitude and variance of the trs. A finite element study has addressed the issue of stress distribution and found that the range of stresses in both the angular WC particles and the binder regions is large [4]. In fact, even though the average WC stress is compressive, there are regions with tensile stress, at one end of the distribution, and regions with very high magnitudes of compressive stress at the other. The converse is true for the binder phase. Thus, the thermal stresses in cemented carbide composites are high in magnitude and are distributed over a wide range of values due to the WC particle shape and the microstructure. 0921-5093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2010.02.046