高强度和低弹性模量Ti−Nb−Fe−Zr合金的显微组织和力学性能

将Zr添加到Ti−Nb−Fe合金中开发生物医用低模量、高强度β钛合金。采用电弧熔炼法制备Ti−12Nb−2Fe−(2,4,6,8,10)Zr(摩尔分数,%)铸锭,随后对其进行均匀化、冷轧和固溶处理。通过光学显微镜、X射线衍射和透射电子显微镜等技术分析合金的物相和显微组织。采用拉伸试验测定力学性能。结果表明,Zr和Fe在合金中具有显著的固溶强化效果,因此,所有合金的屈服强度和抗拉强度分别高于510 MPa和730 MPa。Zr对变形机制的影响较小,孪晶出现在所有变形合金中,且对强度和塑性有益。具有亚稳β相的Ti−12Nb−2Fe−(8,10)Zr合金表现出低弹性模量、高抗拉强度和良好的塑性,是生物医学植入物的合适候选材料。

New role of α phase in the fracture behavior and fracture toughness of a β-type bio-titanium alloy

The role of α precipitates formed during aging in the fracture toughness and fracture behavior of β-type bio-titanium alloy Ti–29Nb–13Ta–4.6Zr(TNTZ) was studied. Results showed that the fracture toughness of the TNTZ alloy aged at 723 K decreases to the minimum of 72.07–73.19 kJ·m^(-2)when the aging time is extended to 4–8 h and then gradually increases and reaches 144.89 kJ·m^(-2)after 72 h. The decrease in fracture toughness within the aging time of 4–8 h is caused by the large stress concentration at the tip of acicular α precipitates with a high aspect ratio and the preferential crack propagation along the inhomogeneous acicular α precipitates distributed in “V-shape” and “nearly perpendicular shape”. When the aging time is extended to 8–72 h, the precrack tip is uniformly blunted, and the crack is effectively deflected by α precipitates with multi long axis directions, more high homogeneity, low aspect ratio, and large number density. Analysis of the effect of αprecipitates on the fracture behavior suggested that the number of long axis directions of α precipitates is the key controlling factor for the fracture behavior and fracture toughness of the TNTZ alloy aged for different times.

Using Cavitation Peening to Improve the Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting

Although Electron Beam Melting (EBM) is an innovative technology, the fatigue properties of materials manufactured by EBM may be lower than those of casted and wrought materials due to defects and surface roughness. In order to enhance the fatigue life of components or structures manufactured by EBM, a mechanical surface treatment technology, e.g., peening, would be effective because peening introduces high compressive residual stress at the surface which can extend the fatigue life considerably. In the present study, specimens were manufactured by EBM using titanium alloy Ti-6Al-4V powder. Two types of specimens were prepared: as-built and as-machined specimens. Specimens of each type were treated by cavitation peening or shot peening. The fatigue lives of the specimens were evaluated by a plate bending fatigue tester. The residual stress and surface roughness were also evaluated. The results obtained showed that the fatigue strength of as-built specimens can be improved by 21% by cavitation peening or shot peening, and the fatigue life under particular applied stresses can also be extended by 178% by cavitation peening.

Influence of Alloy Elements on the Osteoconductivity of Anodized Ti-29Nb-13Ta-4.6Zr Alloy

Anodizing is expected to be an effective method to improve the osteoconductivity of the Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy because the bioactivity of anodized Ti is good. However, it is not known how the alloy elements influence the surface roughness, composition, hydrophilicity, and osteoconductivity of the anodized film on the Ti alloy. In this study, we investigated the effects of anodizing on the surface properties and the osteoconductivity of the anodized TNTZ alloy, focusing on the functions of the individual alloy elements. The anodized oxides of the Nb, Ta, and Zr metals were hydrophobic at all the voltages applied, in contrast to the anodized oxide of Ti. As well as pure Ti, a TiO2-based oxide film formed on TNTZ after anodizing. However, the oxide film also contained large amounts of Nb species and the molar Nb/Ti ratio in the TNTZ alloy was high, which makes the surface more hydrophobic than the anodized oxide on Ti. In vivo tests showed that the osteoconductivity of the TNTZ alloy was sensitive to both its surface roughness and hydrophilicity. When the TNTZ alloy was anodized, the process increased either the surface hydrophobicity or the surface roughness at the voltage used in this study. These changes in the surface properties did not improve its osteoconductivity.

Low-cost surface modification of a biomedical Zr-2.5Nb alloy fabricated by electron beam melting

The Zr-2.5Nb alloy with a fine microstructure consisting ofαlaths was successfully prepared by electron beam melting(EBM).The thermal oxidation behaviors and kinetics of the as-built,and the EBM-built and hot isostatically pressed(HIPed)Zr-2.5Nb materials in a temperature range of 450-600°C were in-vestigated and compared with those of the alloy prepared by conventional casting and forging.It was found that the oxidation kinetics of the as-built and the forged materials followed the parabolic rate law during isothermal oxidation at 550°C,but the HIPed materials exhibited a parabolic-to-linear kinetic transition,suggesting that the larger grain sizes enhanced the oxidation.The oxide layers of all materials were composed of a large fraction of monoclinic zirconia phase(m-ZrO_(2))and a small fraction of tetrago-nal zirconia phase(t-ZrO_(2)),and transformed from t-ZrO_(2)to m-ZrO_(2)with increasing oxidation time.The surface hardness of the as-built,the forged and the HIPed materials increased from 215,204,and 188 HV before oxidation to 902,1070,and 1137 HV after oxidation,respectively.The cross-sections of the materi-als showed the presence of micropores and microcracks inside the oxide layers with thicknesses ranging from 4 to 8μm.With the oxidation temperature of 600°C and oxidation time duration of 3 h,a dense black m-ZrO_(2)oxide layer with smooth surface and 902 HV hardness was obtained on the EBM as-built Zr-2.5Nb materials.

Corrosion Behavior of MgZnCa Bulk Amorphous Alloys Fabricated by Spark Plasma Sintering

Centimeter-sized Mg65Zn30Ca5 bulk amorphous alloys were fabricated by the spark plasma sintering process from the amorphous powders with a size smaller than 5 la m prepared by ball-milling. The sintered Mg65Zn30Ca5 samples were in an amorphous state when the spark plasma sintering was performed at a temperature of 383 K under a pressure of 600 MPa. The data of polarization curves presented that the sintered Mg65Zn30Ca5 bulk amorphous alloys exhibited higher corrosion resistance than pure Mg and AZ31B alloy owing to high content of Zn and homogeneous structure. A calcium phosphate compound layer was formed on the sintered Mg65Zn30Ca5 bulk amorphous sample after immersion in Hanks＇ solution, which is effective in improving corrosion resistance and bioactivity. The sintered MgZnCa bulk amorphous alloys with large dimensions broaden the potential application of bulk amorphous alloys in the biomedical fields.