ECAP对SLM纯钛组织演变和力学性能影响

等通道转角挤压（equal channel angular pressing,ECAP）成功对选择激光熔化（selective laser melting, SLM）制备的纯钛进行了改性处理。采用两通道夹角Φ=120°,ψ=20°的模具,在室温下对SLM制备的纯钛进行单道次变形改性处理,并对其显微组织和力学性能进行了评价。结果表明：SLM+ECAP纯钛试样组织细化,晶粒尺寸由13 μm减小到7 μm,位错密度增加。ECAP变形过程中,孪生和连续动态再结晶同时存在,拉伸与压缩孪晶的出现和位错密度的增加共同促使SLM+ECAP纯钛试样显微硬度增加了13%,屈服强度和极限抗拉强度分别提高了18%和20.4%,而延伸率略有减小。     

纯钛、纯锆在模拟口腔唾液中的腐蚀行为研究

采用正交实验法与电化学实验研究了纯钛、纯锆在模拟口腔唾液中的腐蚀行为。采用SEM分析了腐蚀表面的微观结构特点。结果表明:模拟口腔唾液中的氟离子浓度对实验结果影响最大,氟离子浓度越高,材料越不耐腐蚀;模拟口腔唾液中的pH值对材料的腐蚀影响小于氟离子浓度。经过复合超细化处理的超细晶材料耐腐蚀性能提高,并且纯钛的耐腐蚀性能优于纯锆的。     

ECAP制备超细晶生物医用钛及钛合金的研究进展

钛及钛合金由于质轻、弹性模量低、生物相容性佳和骨整合性优异,已成为应用最广泛的生物医学金属材料之一。然而,较低的塑性、耐腐蚀性能和耐磨损性能限制了其发展和应用。剧烈塑性变形被认为是对金属材料最有效的晶粒细化方法之一,其中,等通道转角挤压（ECAP）是制备块状超细晶（UFG）/纳米晶金属材料的常用技术。通过ECAP变形,可以制备具有优异综合性能的UFG钛及钛合金。本文综述了生物医用UFG钛及钛合金的ECAP制备方式,着重讨论了ECAP变形对钛及钛合金的组织、力学性能、耐腐蚀性能和耐磨损性能的影响,分析了钛及钛合金的ECAP变形机制和晶粒细化机制,提出了通过ECAP变形结合传统塑性加工和变形后热处理来进一步优化钛及钛合金综合性能的想法。     

CP-Ti和Ti-0.2Pd合金的显微组织对其耐蚀性的影响

采用动态电位极化和交流阻抗方法研究工业纯钛(CP-Ti Grade 2)和钛钯合金(Ti-0.2Pd Grade7)在模拟体液中的耐蚀性;研究热处理和等通道径角挤压(ECAP)处理获得的两种钛金属的显微组织对耐蚀性的影响;利用交流阻抗谱对各种处理方式得到的表层特征进行研究。结果表明:ECAP处理大幅度提高了两种金属的耐蚀性,马氏体组织的CP-Ti比魏氏组织的CP-Ti具有更高的耐蚀性,均匀等轴粗晶的空冷CP-Ti的腐蚀电流密度较低。ECAP处理的Ti-0.2Pd表面显示双层膜结构,其余处理方式的试样表面显示具有单层膜结构。     

工业纯钛TA2双钨极氩弧焊焊接接头腐蚀性能研究

钛及钛合金凭借其比强度高、密度小和良好的耐腐蚀性能,广泛应用于汽车、生物医疗、航空航天、石油化工、海洋工程等领域。双钨极氩弧焊相比较传统的钨极氩弧焊可以抑制焊接缺陷,提高焊接速度。本文研究了工业纯钛TA2双钨极氩弧焊焊接接头的耐腐蚀性能,研究表明,双钨极氩弧焊焊缝中心细小的枝晶几乎占据了整个焊缝界面的50%,靠近焊缝的热影响区为均匀分布的等轴晶,双钨极氩弧焊提高了工业纯钛的耐腐蚀性能,扩大了其在恶劣环境下的使用范围。     

原始晶粒尺寸对ECAP变形纯钛组织性能的影响

室温下,对923 及1023 K退火1 h所得的不同原始晶粒尺寸的工业纯钛进行ECAP变形。通过TEM、EBSD、室温拉伸和显微硬度测试研究原始晶粒尺寸对ECAP变形纯钛组织性能的影响。探讨纯钛ECAP变形孪生行为和变形机制。结果表明,退火温度越高,原始晶粒尺寸越大。1道次变形后,1023 K退火纯钛的晶粒细化效果更显著。4道次变形后,923 K退火纯钛的组织更细小均匀。随着变形道次的增加,屈服强度不断增大,1道次变形后增幅最大,约为100%,且原始晶粒尺寸越大,强度增幅越大。纯钛ECAP变形机制包括位错滑移和孪生,原始晶粒尺寸越大,孪晶数量越多。     

体外浸泡纯钛的表面腐蚀和ECAP的影响

采用在Ringer模拟体液静态体外浸泡的方法,研究工业纯钛试片经过一定时间的浸泡后的失重和表面形貌的变化。采用等通道径角挤压(ECAP)方法处理工业纯钛并与粗晶纯钛进行对比,对ECAP处理的TA9和粗晶TA9也做了对比。结果表明:纯钛在400℃ECAP处理后的微观组织形成具有明显方向性的板条状组织,ECAP纯钛表面沉积的Na Cl晶体数量大于粗晶Ti,TA9也表现出相似结果。纯钛的腐蚀机制是一种受到电偶腐蚀控制的均匀腐蚀,细晶组织导致电偶的数量增加。     

SPS烧结Ti-35Nb-7Zr-5Ta合金在Hank's模拟人工体液中的电化学腐蚀行为

利用放电等离子烧结技术制备了生物医用Ti-35Nb-7Zr-5Ta(Ti-Osteum)合金,采用开路电位、动电位极化曲线和电化学阻抗谱方法研究了该合金在Hank's模拟人工体液中的电化学腐蚀行为及其腐蚀机理,并与纯Ti(TA1)和Ti-6Al-4V(TC4)合金进行了对比研究。结果表明:与TA1和TC4合金相比,SPS烧结Ti-Osteum合金在模拟人工体液中具有最小的腐蚀电流与钝化电流密度、最大的极化电阻以及接近的腐蚀电位,从而显示了良好的耐腐蚀性能,3种材料耐腐蚀性能高低依次为:Ti-OsteumTC4TA1;SPS烧结Ti-Osteum合金在模拟人工体液中耐腐蚀性能优异的主要原因是具有高的致密度、单相β型组织以及表面容易形成稳定的复合氧化物钝化保护膜。     

密度可控钛纳米棒阵列的制备及其矿化性能研究

通过控制电解液中的草酸含量,在医用纯钛表面构建密度可控的钛纳米棒阵列。利用场发射扫描电镜(FE-SEM)和原子力显微镜(AFM)对钛表面纳米棒阵列形貌和密度进行了表征,并在模拟体液(2SBF)中对其矿化性能进行研究。结果表明:钛纳米棒阵列密度随着草酸含量的增加而增大,钛表面构建纳米棒阵列结构有利于类骨钙磷矿物的沉积,当纯钛表面纳米棒阵列密度为(1.79±0.04)×1010/cm2时,在模拟体液中矿化性能优异,可见这种结构有利于材料与骨组织形成骨性结合,提高临床疗效。     

Ti-Ta合金在硝酸中电化学腐蚀研究

以8 mol/L硝酸溶液为腐蚀介质,对Ti-6Ta和Ti-32Ta合金进行极化曲线和交流阻抗谱测试,并与TA2纯钛进行对比,研究不同Ta含量钛合金的电化学性能差异。结果表明,加入6%的Ta元素后,合金的腐蚀电流密度比TA2纯钛降低了近一半;加入了32%的Ta元素后,合金的自腐蚀电位提高,腐蚀电流密度比TA2纯钛降低了66%;Ti-6Ta和Ti-32Ta合金腐蚀后表面氧化膜均为单层结构;添加Ta元素可以极大地提高钛合金的电荷转移电阻,使相位角升高、变宽,增强耐腐蚀性能。     

纯镁切应力变形后的微观组织演变、力学性能、腐蚀行为

纯镁为密排六方结构,具有较少的独立滑移系导致其塑性较差。研究了纯镁变形后的微观组织演变、力学性能、腐蚀行为。结果表明,纯镁经过等径角挤压（ECAP）变形后晶粒明显细化以及基面织构发生了弱化,导致纯镁的塑性得到了显著地提高。等径角挤压变形后纯镁强度降低主要是因为基面织构弱化影响大于晶粒细化。此外,等径角挤压变形后纯镁自腐蚀电位和腐蚀电流密度明显增加,纯镁的抗腐蚀性能显著提高。纯镁的腐蚀机理可能从局部腐蚀向均匀腐蚀转变,从而减少了样品在标准模拟体液浸泡中的腐蚀脱落,确保了试样的完整性。     

Comparative effect of grain size and texture on the corrosion behaviour of commercially pure titanium processed by equal channel angular pressing

The effect of grain size and texture on the corrosion properties of commercially pure titanium was investigated. Equal channel angular pressing (ECAP) was used to produce different grain size and various crystallographic orientations. Electrochemical impedance spectroscopy was employed to measure the corresponding surfaces’ general corrosion resistance. Samples with the (0 0 0 2) planes parallel to the surface were found to offer the highest corrosion resistance, regardless of their grain size.     

Influence of regulated modification of nitride layer by oxygen on the electrochemical behavior of Ti–6Al–4V alloy in the Ringer's solution

The corrosion behavior of oxynitrided Ti–6Al–4V alloy was investigated in the Ringer's solution (simulated body fluid) at a temperature of 37°C. The oxynitriding of the alloy was carried out by leaking controlled oxygen‐containing medium into the reaction chamber at the final stage of the nitride formation. It was determined that oxynitriding improved corrosion resistance of Ti–6Al–4V alloy as it provided lower corrosion current density by 1.3–1.5 times and higher corrosion potential. In this paper, we analyzed that the resistance of the double layer had increased with the increase of the oxygen content in titanium oxynitride. Its value was higher compared with untreated alloy, indicating higher corrosion resistance of the oxynitrided one.     

激光选区熔化制备Ti−6Al−4V合金的显微组织及在人工模拟唾液中的电化学腐蚀行为

为了进一步提高植入体的耐腐蚀性,通过激光选区熔化制备Ti?6Al?4V合金.借助扫描电镜、电子背散射、透射电镜、电化学腐蚀试验和接触角试验对其显微组织和在人工模拟唾液中的电化学腐蚀行为进行研究.结果表明:激光选区熔化制备Ti?6Al?4V合金在堆积方向呈现典型的β柱状晶,在扫描方向呈近圆形棋盘状组织,而锻造和锻造+热处...     

Optimization of Oxidation Temperature for Commercially Pure Titanium to Achieve Improved Corrosion Resistance

Thermal oxidation of commercially pure titanium (cp-Ti) was carried out at different temperatures, ranging from 200 to 900 °C to achieve optimum corrosion resistance of the thermally treated surface in simulated body fluid. Scanning electron microscopy, x-ray diffraction, Raman spectroscopy and electrochemical impedance spectroscopy techniques were used to characterize the oxides and assess their protective properties exposed in the test electrolyte. Maximum resistance toward corrosion was observed for samples oxidized at 500 °C. This was attributed to the formation of a composite layer of oxides at this temperature comprising Ti₂O₃ (titanium sesquioxide), anatase and rutile phases of TiO₂ on the surface of cp-Ti. Formation of an intact and pore-free oxide-substrate interface also improved its corrosion resistance.     

等通道转角挤压对生物Mg-Zn-Ca合金显微组织与腐蚀行为的影响

旨在探讨等通道转角挤压(equal-channel-angular-pressed,ECAP)对生物医用Mg-3Zn-0.2Ca合金的显微组织以及腐蚀行为的影响。对铸态Mg-3Zn-0.2Ca合金进行了1,2,4道次的剪切挤压变形。采用光学显微组织观察、X射线反射法、电化学等手段研究了挤压道次对镁合金显微组织、织构以及腐蚀行为的影响,也特别关注了ECAP对试样的不同截面方向的显微组织演变以及模拟体液(simulatedbodyfluid,SBF)电化学腐蚀行为的影响。结果表明:ECAP变形后铸态Mg-3Zn-0.2Ca镁合金晶粒逐渐细化,变形后镁合金呈现出与挤压方向呈一定角度的002面剪切织构;随着挤压道次增加,合金的耐蚀性先增加后降低。等通道转角挤压对合金耐蚀性的影响是晶粒尺寸、晶体缺陷和织构变化的综合效果;ECAP变形后合金不同截面方向呈现不同的耐蚀性,垂直于挤压方向截面的耐蚀性优于另2个方向截面的耐蚀性。     

TA2纯钛H3PO4溶液阳极氧化着色膜的表征和电化学分析

利用恒压控制阳极氧化法在H3PO4溶液中于TA2纯钛表面制备了不同颜色的氧化膜,利用扫描电镜、X射线能谱仪、X射线衍射仪、X射线光电子能谱仪分析了着色膜的形貌、成分、物相和价态,使用电化学工作站在Hank’s模拟体液中研究了着色膜的Tafel极化曲线和电化学阻抗谱(EIS)。结果表明:SEM显示着色膜由一层表面多孔、内层致密的膜层构成;EMAX显示膜层由单一的Ti和O元素构成;XRD和XPS显示膜层主要由Ti4+和O2-组成,呈非晶态TiO2结构;Tafel极化曲线显示随着电压升高,着色膜腐蚀电位正移、腐蚀电流密度下降;EIS显示随着电压升高,着色膜容抗弧半径增大、阻抗值增加,耐腐蚀性提高。     

Influence of microstructural changes on corrosion behaviour of thermally aged Ti‐6Al‐7Nb alloy

Solution treatment and ageing (STA) is an effective strengthening method for α + β titanium alloys. This paper reports the effect of solution treatment and aging on the corrosion behaviour of Ti‐6Al‐7Nb alloy in a simulated body fluid (Ringer's solution). Ti‐6Al‐7Nb alloy is hot rolled in the α + β field and subjected to solution treatment above and below its beta transus temperature (1283 K). The solution treated specimens are water quenched (WQ), air‐cooled (AC), and furnace cooled (FC) at three different rates, and subsequently aged at 823 K for 4 h. Microstructural changes were examined using optical microscopy and phases developed were analyzed using XRD. The influence of microstructure on the corrosion performance of the alloys are discussed in detail based on the Open Circuit Potential (OCP), passive current density and area of repassivation loop values obtained from the cyclic polarization study in Ringer's solution. The passive current density was low (0.5 μA/cm²) for the specimen with duplex microstructure obtained for specimen solution treated at 1223 K, air‐cooled, and aged, in comparison with that for as‐rolled specimen (1.5 μA/cm²). The corrosion aspects resulting from various heat treatments are discussed in detail.     

Improving corrosion resistance of pure Al through ECAP

Abstract

Significant grain refinement and corrosion resistance improvement were achieved in industrial pure Al through equal channel angular pressing (ECAP). The effect of microstructure change on its corrosion resistance was investigated by optical/electron microscopy observation, constant immersion tests, polarisation tests and electrochemical impedance spectroscopy (EIS) in aqueous NaCl solution. The ultrafine grained (UFG) bulk pure Al (with grain sizes of 300–500 nm) has a higher pitting potential E_pit, a lower corrosion current density I_corr in polarisation tests and an increased polarisation resistance R_p from EIS plots, along with reduced corrosion damage in immersion tests, compared with the as cast material. It was found that the improved corrosion resistance resulted from the uniform distribution of fine Si containing impurities and the formation of a denser oxide film. The ECAPed samples with smaller Si containing impurities have lower microgalvanic currents and reduced susceptibilities of pitting corrosion, which is consistent with the classical ‘small cathode, large anode’ mechanism. The strain induced crystalline defects, for example, high angle grain boundaries and dislocations, appear to provide more nucleation sites for the formation of a denser and thicker oxide film, thus enhancing its corrosion resistance.     

Corrosion resistance in different environments and structural features of dental casting alloys for resin bonding

The influence of different electrolytes on the corrosion behaviour of three dental casting alloys for resin bonding with different nobility was investigated. The alloys were studied in the metallurgical state representing that in the oral cavity. Structural and morphological characterisation was performed by means of optical and electronic microscopy and EDS microanalysis. The corrosion resistance was evaluated by means of potentiodynamic anodic polarization curves recorded in three different aggressive environments: artificial saliva (pH = 6.7), Ringer's solution and 0.1 N NaCl solution added with lactic acid (pH = 2). The latter solution is recommended by UNI EN ISO 8891 for the static immersion corrosion test. For comparison purposes the electrochemical behaviour of the pure alloying metals in this solution was also investigated. Results showed a satisfactory corrosion resistance of the alloys examined. The synthetic saliva was the least aggressive electrolyte for all of them but it did not allow to distinguish the corrosion behaviour of these alloys although their differences in nobility and structure. The chloride‐containing solutions showed a better distinction in the corrosion behaviour, as matter of facts, as the chloride content increased, the higher (Cu + Ag) amount was in the alloy, the higher was its current density in the immunity region of the anodic polarisation curves. The environment recommended by the normative UNI EN ISO 8891 resulted the most sensitive and effective for the discrimination of the corrosion resistance of precious metal alloys for resin bonding with different nobility by means of the potentiodynamic test.