Sintering behaviour and interfacial toughness of HAp/TCP coatings on HAp/Ti nanocomposite substrates

Abstract

Spark plasma sintering (SPS) is used in rapid compaction of materials in order to achieve higher compact density and in improving mechanical strength and toughness. However, implants produced by SPS do not have preferred positions for formation of a bone-like apatite layer on their surface due to their high density. Biphasic-calcium phosphate (BCP) ceramics consisting of stable hydroxyapatite (HAp) and soluble tri-calcium phosphate (TCP) are developed to achieve a controllable biodegradation rate and biological stability by adjusting the TCP/HAp ratio. The primary goal of this study is to improve mechanical properties and bioactivity of implants. HAp/20 wt% Ti nanocomposite powders were chosen for bulk, and also HAp/TCP nanocomposite powders were chosen for coatings with weight percentages of 75/25, 50/50 and 25/75, respectively. The samples were sintered for 5 min at a compaction pressure of 30 MPa and at different temperatures of 650 and $$750^{\circ }\hbox {C}$$ . The phase changes of the coatings are studied by X-ray diffraction. Mechanical properties such as interfacial toughness are investigated. The results show that amount of TCP increases with increasing sintering temperature in HAp/75 wt% TCP coating, however no significant change was observed in amount of TCP in HAp/25 wt% TCP coating. Also, the maximum value of interfacial toughness is equal to $$34\, \hbox {MPa mm}^{1/2}$$ , which was obtained for 75 wt% HAp–25 wt% TCP coating sintered at $$750^{\circ }\hbox {C}$$ .