Vietnam Journal of Science and Technology 56 (3B) (2018) 50-42 INVESTIGATION OF THE CONDITION TO SYNTHESIZE HAp/CNTs COATINGS ON 316LSS Nguyen Thi Thom 1, 2, * , Pham Thi Nam 1 , Nguyen Thu Phuong 1 , Dinh Thi Mai Thanh 2, 3 1 Institute for Tropical Technology, VAST, 18 Hoang Quoc Viet, Cau Giay District, Ha Noi 2 Graduate University of Science and Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, District, Ha Noi 3 University of Science and Technology of Hanoi, VAST, 18 Hoang Quoc Viet, Cau Gia, Ha Noi * Email: ntthom@itt.vast.vn Received: 16 July 2018; Accepted for publication: 9 September 2018 ABSTRACT Hydroxyapatite/carbon nanotubes (HAp/CNTs) nanocomposite was successfully synthesized as a coating on 316L stainless steel (316L SS) by electrodeposition technique. Effects of some factors such as: scanning potential range, scan rate, scan number, and synthesis temperature on the characteristic of the coatings were investigated. The characteristics of materials were determined by FT-IR, XRD, SEM, and mechanical test. Optimal conditions to synthesize HAp/CNTs/316L SS coatings are 0 ÷ -1.65 V/SCE of potential range, 5 mV/s, 5 scans at 45 o C. At the condition, obtained nanocomposite coatings are composed of HAp and CNTs with 6.9 μm of the coating thickness. The presence of 6.95 % of CNTs in the nanocomposite, the solubility of HAp/CNTs coatings is lower than pure HAp coating. In addition, the hardness of the HAp/CNTs coatings reaches 5.6 GPa, which was higher nearly 25 % in comparision with pure HAp. Keywords: hydoxyapatite (HAp), HAp/CNTs nanocomposite, electrodeposition, 316L SS. 1. INTRODUCTION Nowadays, the demand for high quality biomedical materials is increasing due to the growth of injuries number. The most used biocompatible medical materials for surgery and orthopedics in hospitals are: 316L SS, CoNiCrMo, Ti and Ti6Al4V. Generally, the materials have excellent mechanical properties but in some cases they can be corroded in the biological environment after body implementation [1]. Therefore, new research to improve the quality of the biomedical materials based on metals and alloys are attracting scientists. Hydroxyapatite (HAp) is a main component of bone tissue, has osteoconductive, biocompatible and excellent bioactive properties [2]. HAp can be used as bioactive coatings on the metals or alloys. However, high solubility in biological environments as well as poor