Influence of grit blasting treatment using steel slag balls on the subsurface microhardness, surface characteristics and chemical composition of medical grade 316L stainless steel B. Arifvianto ⁎, Suyitno, K.A. Wibisono, M. Mahardika Center for Innovation of Medical Equipments and Devices (CIMEDs), Department of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University, Jl. Grafika 2 Yogyakarta 55281, Indonesia abstract article info Article history: Received 31 July 2012 Accepted in revised form 10 September 2012 Available online 17 September 2012 Keywords: Steel slag balls Grit blasting treatment 316L stainless steel Surface and subsurface characteristics Slag is a residue from the steel making processes which is at present still considered as an industrial waste due to its low utility. In this paper, the spherical steel slag balls obtained from the slag atomization process are evaluated for use in grit blasting treatment of medical grade 316L stainless steel. The modification in sub- surface microhardness, surface characteristics (morphology, roughness, mass loss) and chemical composition of the stainless steel after the grit blasting treatment with these particles is examined. The blasting treatment was carried out for 5–20 min using steel slag balls with a size of 1–2 mm in diameter and 0.7 MPa com- pressed air flow in normal direction toward the surface of the specimen. The result shows the increasing sub- surface microhardness, surface irregularity and roughness of the stainless steel by this treatment. Surface material removal takes place as well during the blasting treatment as indicated by the mass loss of the spec- imen. The mechanisms of the subsurface microhardness modification as well as those for the surface rough- ness and mass loss evolution during the grit blasting treatment are elucidated in this paper. The blasting treatment with the steel slag balls also introduces some bioactive elements such as Ca, Si and Mg on the spec- imen surface. In conclusion, the grit blasting treatment using the steel slag balls has potential for improving mechanical properties and bioactivity of stainless steel based biomedical implants. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Grit blasting treatment has been used for many years in the process- ing of biomaterials and biomedical implants [1–13]. This treatment uti- lizes multiple impacts of blasting particles to enhance surface roughness as well as the biocompatibility of metallic materials [6,8,9]. The previous studies demonstrate better cell attachment, proliferation and development on such a rough blasted surface [1–5]. Besides the roughness, the appropriate surface chemistry is required to improve the implant integration with bone tissue (osseointegration) [5,14]. The use of blasting particles with bioactive chemical elements is there- fore introduced as well to produce a surface with the desired surface chemistry [5]. The grit blasting treatment also improves the mechanical properties of metallic components. The surface severe plastic deforma- tion (S 2 PD) that occurs by grit blasting treatment enhances the surface and subsurface hardness thanks to the formation of nanocrystallites, residual stress and martensites at these layers [6,8,10]. Hence, this treat- ment is often chosen for improving the load bearing performance of metallic components. The grit blasting treatment has been developed into many variations according to the type of blasting particles used in the process. Al 2 O 3 [2,3,5–8,11–13], ZrO 2 [8], TiO 2 [4], SiO 2 [10], silica [9,11] and bioceramic [5] particles are among those which have been utilized in the processing of metallic biomaterials. In principle, the blasting particles have to be easily entrained in a compressed gas flow for being blasted toward the work surface. The particles must be also sufficiently hard and con- tain non-toxic elements so that their impacts are able to induce plastic deformation without introducing harmful contaminants to the blasted surface. It is reported that the presence of alumina contaminant com- promises the biocompatibility of the Al 2 O 3 -blasted titanium [13]. In this paper, the spherical steel slag balls, which are often called as P.S. balls [15,16], are introduced as the blasting particles for surface treatment of metallic biomaterials. Slag is a residue from the steel mak- ing process which is still considered as an industrial waste due to its low utilization. The extensive use of this material will therefore give benefit to the environment. The steel slag balls are produced by transforming the molten slag into a spherical shape with a diameter until 4.5 mm through the atomization process and cooling in the air [15,16]. The steel slag is currently used in cement fabrication [17,18] and its particle shape is utilized in the waste treatment technology [15]. The previous studies indicate the physical properties of steel slag balls, e.g. the Surface & Coatings Technology 210 (2012) 176–182 ⁎ Corresponding author. Tel.: +62 878 393 19041; fax: +62 274 521 673. E-mail address: b.arifvianto@gmail.com (B. Arifvianto). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2012.09.014 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat