Effect of Strain Ratio on Fatigue Model of Ultra-fine Grained Pure Titanium

The ultra-fine grained(UFG)pure titanium was prepared by equal channel angular pressing(ECAP)and rotary swaging(RS).The strain controlled low cycle fatigue(LCF)test was carried out at room temperature.The fatigue life prediction model and mean stress relaxation model under asymmetrical stress load were discussed.The results show that the strain ratio has a significant effect on the low cycle fatigue performance of the UFG pure titanium,and the traditional Manson-coffin model can not accurately predict the fatigue life under asymmetric stress load.Therefore,the SWT mean stress correction model and three-parameter power curve model are proposed,and the test results are verified.The final research shows that the threeparameter power surface model has better representation.By studying the mean stress relaxation phenomenon under the condition of R≠-1,it is revealed that the stress ratio and the strain amplitude are the factors that significantly afiect the mean stress relaxation rate,and the mean stress relaxation model with the two variables is calculated to describe the mean stress relaxation phenomenon of the UFG pure titanium under different strain ratios.The fracture morphology of the samples was observed by SEM,and it was concluded that the final fracture zone of the fatigue fracture of the UFG pure titanium was a mixture of ductile fracture and quasi cleavage fracture.The toughness of the material increases with the increase of strain ratio at the same strain amplitude.

Characterization of microarc oxidation coatings on pure titanium

Key Laboratory for Beam Technology and Materials Modification, Institute ofLow Energy Nuclear Physics, Beijing Normal UniversityThe morphology, composition, and phase structure of the oxide coatings produced on the surface ofpure titanium by alternating-current microarc discharge in aluminate solution were investigated byX-ray diffraction and scanning electron microscopy. The profiles of the hardness H and the elasticmodulus E in the coatings were determined using a nanoindentation method. The concentrationdistributions of Ti, Al, and O in the coating show that this coating over 30 mu m thick contains twolayers: an outer layer and an inner layer. The oxide coating is mainly composed of TiO_2 rutile andAl_2TiO_5 compounds. During oxidation, the temperature in the microarc discharge channel was veryhigh to make the local coating molten. From the surface to the interior of the coating, H and Eincrease gradually, and then reach maximum values of 9.78 GPa and 176 GPa respectively at a distanceof 7 mu m from the coating/titanium interface. They are also rather high near the interface.

Surface nanocrystallization of commercial pure titanium by shot peening

The surface nanostructures of commercial pure titanium was realized by the modified shot peening equipment commonly used in industry through the special treatment process. The results show that high-energy-shot-peening(HESP) commonly used to prepare nanostructured surface layers can be achieved by the increase of pill size, pill speed, and treatment time in the commercial shot peening equipment. XRD, SEM and TEM were used to characterize the surface layer microstructure of treated specimens. The analytic results show that the main deformation mode of commercial pure Ti is twinning. At the beginning of deformation, the dislocations are formed and twins occur within or on plane, then twins in intersection plane appear, and at last the twin characteristics disappear in the surface layer after longer treatment time. The deformation layer depth increases with treatment time in a certain period when the pill size and speed are unchanged. And in the severe plastic deformation (SPD) layer in which the twins are not identified easily by using SEM, the nanocrystalline microstructures are found under TEM. The finest grain size in the surface layer is about 40 nm, and the depth of nanostructured layers is over 60 μm. The microhardness of the nanostructured surface layers is enhanced significantly after shot peening compared with that of the initial simple.

Plasma Niobium Surface Alloying of Pure Titanium and its Oxidation at 900 ℃

A niobium-modified layer on pure titanium surface was obtained by means of double glow plasma surface alloying technique. The modified layer was uniform, continuous, compact and well adhered to the substrate. The niobium composition in the modified layer decreased gradually from the surface to the substrate. The oxidation behavior of the niobium-modified layer was investigated and com- pared with the untreated surface at 900 ~C for 100 h. Characterization of the layers was performed using X-ray diffraction and scanning electron microscope, respectively. The test results show that the oxidation behavior of pure titanium was improved by niobium alloying process. Niobium has a positive influence on the oxidation resistance.

Anisotropy of Mechanical Behavior in Commercially Pure Titanium Sheets

Commercially pure titanium( CP Ti) sheets show typical planar anisotropy due to inherently crystallographic texture and rolling process. To characterize the initial,planar,plastic anisotropy of CP Ti sheets in forming process,uniaxial tensile tests of cold-rolled TA1 sheets at 0°,45° and 90° to the rolling direction were performed at room temperature,corresponding stress-strain curves and Lankford coefficient( r value) were obtained. Based on Hill'48 and Barlat'89 yield criteria,the anisotropic behavior of TA1 sheets was investigated. In order to verify the accuracy of two models,the experimental values of yield stress and r were compared with predicted ones. It revealed that Barlat '89 criterion with M = 6 is the best agreement with experimental data,and the obtained model can be used in the simulation of forming process.

Effect of electropulsing on anisotropy behaviour of cold-rolled commercially pure titanium sheet

The specimens cut from the cold-rolled pure titanium sheet at 0°,45°and 90°to the rolling direction were treated by high density electropulsing(maximum current density J=(7.22-7.96)×10^(3)A/mm^(2),pulse period t_(p)=110μs).The mechanical properties and microstructures of the cold-rolled,electropulsed and conventional annealed commercially pure titanium sheet were examined by using uniaxial tension test machine and optical microscope(OM),respectively.The results show that the deformation behavior of the electropulsed pure titanium sheet is significantly different from that of conventional annealed pure titanium sheet.The difference of the mechanical properties between the 0°,45°and 90°direction specimens is almost diminished.It is mainly due to the increase in dislocation mobility and formation of lamellar microstructure after the electropulsing.

Mechanical Property Prediction of Commercially Pure Titanium Welds with Artificial Neural Network

Factors that affect weld mechanical properties of commercially pure titanium have been investigated using artificial neural networks. Input data were obtained from mechanical testing of single-pass, autogenous welds, and neural network models were used to predict the ultimate tensile strength, yield strength, elongation, reduction of area, Vickers hardness and Rockwell B hardness. The results show that both oxygen and nitrogen have the most significant effects on the strength while hydrogen has the least effect over the range investigated. Predictions of the mechanical properties are shown and agree well with those obtained using the 'oxygen equivalent' (OE) equations.

Planar anisotropy of commercially pure titanium sheets

Commercially pure titanium （CP Ti） sheets show typical planar anisotropy due to the inherently crys- tallographic texture and manufacturing process. To char- acterize the planar anisotropic behaviors of CP Ti sheets in the forming process, uniaxial tensile tests of TA0 sheets were performed along rolling, transverse, and diagonal directions at room temperature; corresponding stress-strain curves and Lankford coefficients were obtained. Based on Hi11＇48 and Barlat＇89 yield functions, the planar anisotropy of TA0 sheets was investigated. In order to verify the accuracy of two models, we compared the experimental and predicted values of yield stress and Lankford coeffi- cients. It reveals that Barlat＇89 criterion with M = 10 is good agreement with experimental data, and the obtained function can be used in simulation of forming process.

Transformation mechanism and mechanical properties of commercially pure titanium

In order to establish the rolling process parameters of grade-2 commercially pure titanium(CP-Ti),it is necessary to understand the transformation mechanism and mechanical properties of this material.The β→α transformation kinetics of the grade-2 CP-Ti during continuous cooling was measured and its hot compression behavior was investigated using Gleeble-1500 thermal mechanical simulator.Dynamic CCT diagram confirms that cooling rate has an obvious effect on the start and finishing transformation and microstructures at room temperature.The critical cooling rate for β-phase transforms to α phase is about 15 °C/s.When the cooling rate is higher than 15 °C/s,some β phases with fine granular shape remain residually into plate-like structure.The plate-like α phase forms at cooling rate lower than 2 °C/s,serrate α phase forms at medium cooling rates,about 5-15 °C/s.The flow stress behavior of grade-2 CP-Ti was investigated in a temperature range of 700-900 °C and strain rate of 3.6-40 mm/min.The results show that dynamic recrystallization,dynamic recovery and work-hardening obviously occur during hot deformation.Constitutive equation of grade-2 CP-Ti was established by analyzing the relationship of the deformation temperature,strain rate,deformation degree and deformation resistance.

Head Curvature of Pure Titanium Sheet Influenced by Process Parameters and Controlling in Hot Rolling Process

We investigated the influences of process parameters on the head curvature of pure titanium sheet in hot rolling process and proposed the controlling means. First, the thermal simulation experiments for pure titanium TA1 were carried out to investigate the hot deformation behaviors of pure titanium in the temperature range of 700-800 ℃ with strain rate range of 1-20 S-1, and the processing map was established to determine optimized deformation parameters. Then, the finite element model has been constructed and used to analyze the effect of process parameters on the direction and severity of head curvature of pure titanium sheet. The process parameters considered in the present study include workpiece temperature, work roll diameter, pass reduction, oxide scale thickness of workpiece surface, and interface friction coefficient. The simulation results show that the workpiece temperature and the interface friction coefficient are the two main factors. The proposed controlling means was carried out on a hot rolling production line and solved the head curvature problem effectively. The rolling practices indicate that the rolling yield is improved greatly.

Effect of plane surface and wrinkly surface of pure Titanium on corrosion resistance and bacterium accumulation: an in vivo study

Objective: To study the effect of surface configuration on the corrosion resistance and bacterium accumulation of pure Titanium(Ti) when used in oral environment. Methods: Six edentulous volunteers with healthy oral mucosa participated in an in vivo study. Two kinds of pure Ti testing pieces with plane and wrinkly surface were fixed in the polished surface of upper complete dentures. After 6-month wearing, dynamic polarization curves were traced with electrochemical method and the amount and species of bacterium adhered on pure Ti were examined. Results: ① Ep and Ip of specimen in oral cavity was higher than that left in air, which meant corrosion resistance falling. Compared to plane one, Ecorr of wrinkly specimen was more positive and Ep and Ip were more higher, so its corrosion resistance reduced. ② Individual difference put a significant influence on amount of bacterium adhered on pure Titanium, but had no relation to species of bacterium. To the same patient, wrinkly samples collected more bacterium than plane ones, and exhibited G - coccus beside G + coccus. Conclusion: From the perspective of corrosion behavior and benefit to periodontal tissue, wrinkly surface should not be adopted when pure Ti prosthesis is made,especially on connector part of denture.

The surface treatment on oxide film of pure titanium Part 1. The effect of Anodic oxidation

目的：研究阳极氧化对纯钛种植材料氧化膜的影响。方法：5片直径9mm厚2mm的纯钛在升压速度为7～8v／min、电流密度≤10mA／cm。的条件下分别进行阳极氧化处理，（A）10v10min，（B）24v10min，（C）40v10min，（D）24v40min，（E）24v2h。用potentiostat仪检测以上样品在生理盐水和人造海水中的电化学行为。结果：以上样品的颜色呈：A蓝色，B淡黄色，C粉红色，D金黄色，E深黄色。随着电压的升高和作用时间的延长，2．55峰渐渐强化，2．34峰弱化。在生理盐水中，阳极氧化膜的开路电势稳定于0mV，而自然氧化膜则很快从一50上升到～40mV，极化电流比自然氧化膜的低100倍。在人造海水中，阳极氧化膜的开路电势稳定在-90mV，自然氧化膜则从-480mV快速上升到-310mV，且活化电流明显高于阳极氧化膜。结论：阳极氧化膜的颜色可能和膜的厚度有关，而颜色对种植体上的修复体有影响，因此，金黄色被选为理想的颜色。2．55和2．34峰的变化规律尚无法解释。阳极氧化膜的稳定性和耐腐蚀性远远高于自然氧化膜。因此，阳极氧化法是一种提高纯钛氧化膜耐腐蚀性的好方法。

Cell Attachment of Periodontal Ligament Cells on Commercially Pure Titanium at the Early Stage

Summary: In order to study the character of periodontal ligament cells (PDLCs) attaching on commercially pure titanium (cpTi) by morphology and metrology on the early stage (24 h), 1×105/ml PDLCs in 2 ml culture medium were seeded on cpTi discs fixed in 24-well culture plates. Morphology of cell attachment was observed by contrast phase microscope, scanning electron microscope (SEM) and fluroscence microscopy. Cell adhesion was analyzed by MTT at 0.5, 1, 2, 4 h respectively. PDLCs could attach and spread on cpTi discs. SEM showed that PDLCs had pseudopod-like protuberance. PDLCs showed different attaching phases and reached saturation in cell number at 2 h. It was concluded that PDLCs had good biocompatibility with cpTi, and showed a regular and dynamic pattern in the process of attaching to cpTi.

Diffusive healing of internal fatigue micro-cracks in pure titanium

The internal micro cracks with the critical length about 30?μm and thickness less than 1?μm were introduced into the pure titanium samples by uniaxial tension compression low cycle fatigue method. The experimental results indicate that the internal fatigue micro crack clearly evolves from the original penny shaped crack into a string of spherical voids in the longitudinal section plane of the fatigue sample after the vacuum diffusive healing at the high temperature. The quantitative relationship between the radius and the spacing of spherical voids depends on the crack position (within grains, on grain boundaries or transgranular sites) and its orientations within the grain. The diffusive healing, the related thermodynamics and mechanism, and the effect of the surface tension anisotropy on the relationship between void diameter and void spacing are also discussed.

Calculation of the Surface Energy of Pure Titanium

Anodic oxidation on pure titanium(α-Ti) surface causes the formation ofinterferential films with different colours,mainly golden,pink and blue.The col-our changes with the thickness of the ox-ide film.One of the factors,which influ-ences the growth rate of the film,may bethe grain surface energy.at least at the

Effects of surface roughness on corrosion resistance of pure Titanium:An in vivo observation

Objective: To study the effect of surface configuration and roughness on the corrosion resistance of pure Titanium (Ti) after used in oral environment for half a year.Methods:Three edentulous volunteers with healthy oral mucosa participated in an in vivo study.Four kinds of pure Ti testing pieces with different surface roughness were fixed in the polished surface of upper complete dentures and the other in the tissue surface of the dentures.After 6-month wearing the denture,dynamic polarization curves were traced with electrochemical method.Results:Ep and Ip of specimen used in oral cavity was higher than that left in air,which meant corrosion resistance falling.Compared to plane one,Ecorr of wrinkly specimen was more positive,and Ep and Ip were more higher,so its corrosion resistance reduced.With the increase of surface roughness,Ep and Ip increased from 0.937 V and 1.810 μA (GroupⅡ) to 1.701 V and 2.252 μA(GroupⅣ)respectively,there was even no passivation in GroupⅢ(which was the most coarse),so proneness to corrosion enhanced.For specimen with the same surface roughness,Ep and Ip of GroupⅣ(1.701 V and 2.252 μA respectively),which was placed on polished surface of denture base,was higher than that on tissue surface(GroupⅤ,1.304 V,1.946 μA).Conclusion:From the perspective of corrosion behavior,wrinkly surface should not be adopted when pure Ti prosthesis is used,and surface roughness on the polishing surface of pure Ti prosthesis should be paid more attention,especially on clasps and connectors,where there is often more force to be exerted.

Effect of Surface Modification on Corrosion Resistance of Pure Titanium.An in Vivo Observation

Objective: The aim of this experiment is to study the effect of three methods of surface modification on the corrosion resistance of commercial pure Titanium when used in oral environment for half a year.Method:48 specimens of pure titanium were made and divided into four groups randomly, one group was selected randomly as Group I (control group), the other three groups were treated by three methods of surface modification individually, GroupⅡ:heating oxidation in air(400℃,30min.), GroupⅢ:anodization (45 volts, 10 min.),GroupⅣ:TiN coating(firing temperature 200℃ , total coating time 62min.). Six edentulous volunteers with healthy oral mucosa participated in the in vivo study. One testing piece from each group was selected and fixed in the polished surface of upper complete dentures. Dynamic polarization curves were traced with electrochemical method after the specimens were placed either in oral cavity or in air for 6 months. Results: After all specimens were used, Ecorr altered in every group , Ecorr from high to low were in turn: TiN coating group>heating oxidation group> anodization group>control group, no obvious passive potential Ep and Ip was found in control group. Heating oxidation in air exhibited similar Ep to anodization, but Ip was remarkably lower than that of anodization; TiN coating showed obviously different polarization curves compared with heating-oxidation group and anodization group, Ecorr was positive, and no Ep and Ip was found. Conclusion: Under present experimental condition, all the three treatment methods could enhance corrosion resistance of pure titanium in oral environment, heating oxidation in air exhibited better resistance to corrode than anodization, TiN coating possessed the most excellent corrosion resistance, even after exposed in oral condition for 6 months, there was little change of corrosion resistance. Therefore TiN coating could be adopted to improve corrosion resistance of pure titanium in oral environment.

波纹辊轧制TA1钛板退火处理后的织构演变

采用波纹辊+平辊轧制(CFR)和平辊+平辊轧制(FFR)在400℃下制备了TA1纯钛板材。利用SEM和EBSD技术分析TA1纯钛板在650℃保温1h退火处理后的微观组织和织构演变特征。结果表明,板材经过波纹辊轧制后,在RD方向上呈现周期性显微组织变化,在ND方向上表现出渐进式显微组织梯度。二道次平轧后,将试样进行650℃保温1h退火处理,CFR钛板晶粒等轴化程度低于FFR钛板。对两种工艺的极图分析后发现,两种轧制工艺制备的钛板织构都为典型的基面双峰TD织构,CFR钛板厚度方向的中间区域织构有一定弱化,并且沿TD轴方向的极密度强区多且分散。此外,两种轧制工艺制备的钛板的织构类型相近。

两种不同材料种植体修复牙列缺损的力学性能及美学效果观察

目的:观察钛合金种植体与纯钛种植体修复牙列缺损的力学性能及美学效果。方法:回顾性分析2020年1月-2022年9月笔者医院收治的160例牙列缺损患者的临床资料,按种植体不同修复方式分为观察组79例(108颗牙,采用钛合金种植体)和对照组81例(112颗牙,采用纯钛种植体)。比较两组的种植有效率、咀嚼效率、牙齿总咬合力、牙周健康指数、并发症发生率及美学评分差异。结果:两组种植总有效率比较,差异无统计学意义(P>0.05),但观察组显效率显著高于对照组(P<0.05);两组咀嚼效率治疗后均显著升高,且观察组咀嚼效率显著高于对照组(P<0.05);两组牙齿总咬合力随时间延长逐渐升高,且观察组各时间段内总咬合力显著高于对照组(P<0.05);两组菌斑指数、牙龈指数及龈沟出血指数均较术前降低,且观察组显著低于对照组(P<0.05);观察组种植体周围炎发生率显著低于对照组(P<0.05);观察组红白美学指数评分显著高于对照组(P<0.05)。结论:相比于纯钛种植体,钛合金种植体用于修复牙列缺损患者具有更强力学性能,可改善患者咀嚼和咬合能力,降低种植体周围炎的发生率,提高美学效果。

力学性能可调的高氧钛原位电弧增材制造

通过电弧增材制造原位制备高氧钛,并对高氧钛的成分偏析、显微组织和力学性能进行研究。结果表明,高氧钛试样的显微组织主要呈现为针状α相集束。随着氧含量的增加,试样针状α相逐渐变宽,集束尺寸变大。受氧的强化作用以及晶粒尺寸效应共同影响,试样的强度先提高后下降,伸长率显著下降,断裂形式由塑性断裂向解理断裂过渡。当氧含量达到0.37%(质量分数)时,伸长率约为7%,试样抗拉强度超过730 MPa,约为商业纯钛的2倍。