The Phase Transformation And Surface Bioactivation Research Of Ti-Zr Dental Alloys

In this paper, seven specimens of binary Ti-Zr alloys with zirconium contents ranging from 10 to 70 wt.% were prepared by arc melting with water-chilled copper hearths to study their phase transformation, influence of heat treatment and bioactive surface modification. X-ray diffraction(XRD), differential scanning calorimetry(DSC), metallographic observation and microhardness test were employed to analyze phase composition and phase transformation. Furthermore, hydrophily and surface morphology of the modified alloy surface were also analyzed by SEM and contact angle test. By experiment and analysis, the conclusions are as follows:The results show that apart from Ti-10 Zr and Ti-20 Zr, Ti-Zr alloys prepared by arc melting with water-chilled copper hearths formed supercooled β phase during cooling and a significant amount of supercooled β phase was observed in as prepared Ti-60 Zr alloy. In addition, α phase shows an acicular structure, with β phase an equiaxial structure in Ti-Zr alloys during metallographic observation. The α phase was obtained from the diffusion transformation of the high temperature β phase, and the β phase left to room temperature was called the supercooled β phase, which was related to the width of the α and β phase region in the equilibrium phase diagram. At the same cooling rates, the narrower the two-phase region was, the more easily the β phase formed. Microhardnesses of the alloys show a trend from ascendent to smooth, with Ti-50 Zr the highest, 330.9 HV3.Heat treatment processes were also studied to obtain single α phase in Ti-30 Zr, Ti-50 Zr, Ti-60 Zr and Ti-70 Zr. As to Ti-30 Zr, Ti-50 Zr, Ti-60 Zr and Ti-70 Zr after heated to 1000 ℃ at the rate of 10 ℃·min-1 and isothermal treatment for 2 h, single α phases could be obtained when they were cooled to room temperature at the rate of 2 ℃·min-1, 2 ℃·min-1, 5 ℃·min-1 and 5 ℃·min-1, respectively. Furthermore, Ti-30 Zr, Ti-50 Zr, Ti-60 Zr and Ti-70 Zr after heated to 600 ℃, 600 ℃, 400 ℃ and 600 ℃ at the rate of 10 ℃·min-1 separately and isothermal treatment for 2 h and then furnace cooling to room temperature, single α phases could also be obtained.Water contact angle tests and surface microstructure observation were performed after SLA(Sand-blasted, Large-grit, Acid-etched) surface treatment to Ti-Zr alloys. The results show that Ti-10 Zr and Ti-20 Zr have α type matrix compatible with SLA and can easily form 3D multihole microstructure, which is good for enhancing surface biological activity. The hidrophily of the SLA surface of high zirconium content α+β type titanium zirconium alloys(Ti-30 Zr, Ti-50 Zr, Ti-60 Zr and Ti-70Zr) after heat treatment to single α phase was improved; after heat above the critical temperature of α/β transformation(1000 ℃) soaking for 2 h, and then cooled to room temperature at very low cooling rates, the SLA surface appeared striated grooves. However, as to the SLA surface after isothermal heat treatment below the critical temperature, no groove appeared, the entire surface was relatively flat.