盐水介质中Ti12Mo5Ta合金的电化学特性(英文)

比较了未再结晶和再结晶Ti12Mo5Ta合金、未再结晶Ti12Mo合金和工业用纯钛(cp-Ti)在0.9%生理盐水(pH 2.3)中37°C下的电化学行为。从阳极极化曲线中得到了极低的钝化电流密度(10-6 A/cm2),这表明所有样品在酸性0.9%NaCl溶液中具有高的耐蚀性能。采用扫描电子显微镜(SEM)观察样品的表面形貌,发现所有样品表面受到了相同的腐蚀,而且经阳极动电位极化测试后的样品表面没有出现点蚀、裂纹或其它缺陷。使用等效电路模拟电化学阻抗谱(EIS)数据,以表征样品表面且更好地理解Mo和Ta的添加对cp-Ti及再结晶的影响。EIS结果证实,在开路电位下,所有样品在0.9%NaCl溶液(pH 2.3)中产生钝化(极化电阻约为105Ω·cm2)。在37°C时,样品在0.9%NaCl溶液中(pH 2.3)的耐蚀性顺序为:再结晶Ti12Mo5Ta未再结晶Ti12Mo5Ta未再结晶Ti12Mocp-Ti。     

Effects of cold working and heat treatment on microstructure and wear behaviour of Cu–Be alloy C17200

The effects of cold work process between aging and solution heat treatment on the microstructure, hardness and the tribologic behaviour of a copper–beryllium (Cu–Be) alloy C17200 were investigated. The wear behaviour of the alloys was studied using ‘pin on disc’ method under dry conditions. The results show that the formation of fine grained structure and γ phase particles enhances the mechanical properties of the alloy; nonetheless, they do not reduce the wear rate. This is attributed to the capability of the softer specimens to maintain oxygen rich compounds during the dry sliding test.     

氩气处理对AZ91含气量及组织的影响

AZ系镁合金中的高含气量(含氢量)往往导致铸造组织疏松问题。本试验研究了AZ91镁合金氩气除气工艺,主要研究了氩气流量、处理时间及处理方式对AZ91镁合金含气量及组织的影响。结果表明,常规熔铸AZ91镁合金含气量在9.2~10.3μg/g左右,经氩气处理后,合金含气量可最低降至5.2μg/g。氩气除气率与氩气流量及处理时间密切相关,增大氩气流量和延长处理时间,除气率提高。分步除气处理的效率高于连续处理,同时氩气处理后铸造组织也有明显细化效果,这可能与氩气的搅拌作用促进熔体中异质形核心均匀分布促进形核率提高有关。当氩气流量为1.0 L/min,两步处理的时间分别为2和1 min时,除气率可达43.7%,铸造组织平均晶粒尺寸由未处理的300μm降低至230μm。     

微量硼元素添加对Ti6Al4V-xB组织及性能的影响

采用高真空非自耗熔炼及吸铸方法制备不同硼含量的Ti6Al4V-xB(x=0,0.05,0.1,0.5,质量分数,%)合金,将合金在900℃下进行2 h保温退火。研究了不同微量硼元素添加对Ti6Al4V-xB的铸造显微组织及力学性能的影响。结果表明,微量硼元素的添加影响了钛合金高温形核过程,在固-液前沿富集B元素阻碍初始β-Ti长大,有效细化钛合金晶粒,当硼含量超过0.1%时,则有TiB相的析出。Ti6Al4V-xB合金的强度极限随硼含量的增加单调上升,由893 MPa变为966 MPa,这是细晶强化和析出强化共同作用的结果;合金的塑性则是先升高后降低,Ti6Al4V-0.05B的塑性提高了15%,而Ti6Al4V-0.1B与Ti6Al4V-0.5B的塑性则降低了50%,是因为析出脆性的Ti B相,形成脆性断裂敏感带。     

硼含量对有序态(Fe,Co)3V合金环境氢脆的影响

通过在真空和氢气环境下的拉伸实验,研究了硼含量对有序态(Fe,Co)_3V合金力学性能和环境氢脆的影响。结果表明,当在有序态(Fe,Co)_3V合金中添加0.02%B(质量分数)时,相对于无硼合金,合金的晶粒尺寸减小了27.5%,合金在真空和氢气中的抗拉强度和延伸率均达到最大值;而当硼含量继续增加时,合金的晶粒尺寸、合金在真空和氢气中的力学性能均保持不变。无硼有序态(Fe,Co)_3V合金在氢气中呈现严重的环境氢脆,当在合金中添加0.02%B后,合金氢脆因子降低了34.4%,合金的断口形貌由完全沿晶断口转变为穿晶和沿晶的混合断口;当合金中的硼含量继续增加时,合金的氢脆因子不再降低,恒定在50%左右,即硼原子只能部分抑制有序态(Fe,Co)_3V合金在氢气中的环境氢脆。     

累积叠轧TC4合金制备超细晶组织的研究

通过累积叠轧技术进行TC4合金超细晶组织的制备,考察了TC4合金的热变形特点以及叠轧工艺窗口,研究了叠轧工艺参数和热处理制度对叠轧板材界面结合和微观组织的影响。结果表明：TC4合金的应力-应变曲线表现为动态回复特征,热模拟条件下在加热温度(≥700℃)和变形速率(≤0.1s-1)下能够实现强烈塑性变形。最终TC4合金进行叠轧界面的防氧化处理后,并在加热温度为720℃、轧制速度小于0.5m/s时,获得良好的界面结合和板材质量。累积叠轧变形过程是α/β协同变形和剪切变形综合作用的结果,组织中存在拉长的条带组织以及大量的剪切带。随着叠轧层数的增加,条带组织的间距逐渐变小同时剪切带组织逐渐增加,在叠轧16层(变形量为92.3%)后条带间距为200nm~500nm之间。热处理过程中随着加热温度的增加,溶质扩散和再结晶过程促进了界面结合并最终与基体保持一致,同时叠轧16层的TC4板材在加热温度700℃、保温时间60min的热处理过程中能够实现完全再结晶,获得晶粒尺寸为300nm~600nm的超细晶组织。     

Comparative study on corrosion behaviors of Mg-Al-Zn alloys

A comparative study on corrosion behaviors of various Mg-Al-Zn alloys (AZ21, AZ41, AZ61 and AZ91 series, cast under same cooling conditions and controlled alloying composition) was carried out. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used for microstructural examinations. The corrosion behaviors were evaluated by immersion tests and potentiodynamic polarization measurements in 3.5% NaCl solution. The results showed that the influence of Al addition on corrosion resistance was more pronounced up to 4% (i.e. AZ41) above which its influence was at less extent. The deterioration of the corrosion resistance of the alloys, at higher Al contents, was attributed to the amount and morphology of β-Mg₁₇Al₁₂ intermetallics and the interruption of continuity of the oxide film on the surface of the alloys owing to coarsened β intermetallics.     

Effect of heating time on bonding interface,atom diffusion and mechanical properties of dissimilar titanium joints produced by thermal self-compressing bonding

Solid-state bonding between pure titanium and Ti6Al4V (TC4) alloy was conducted by a new bonding method named as rigid restraint thermal self-compressing bonding. Effects of heating time on bonding interface, atom diffusion and mechanical properties of the joints were studied. Results show that atom diffusion between pure titanium and TC4 alloy significantly takes place during bonding. The diffusion depths of Al and V in pure titanium side are increased with increasing heating time. Due to the enhancement of atom diffusion, bond quality of the bonding interface is improved along with the increase of heating time. The heating time seems to have little effect on microhardness distribution across the joint. However, the tensile strength and ductility of the joint have close relation to heating time. Prolonging heating time can improve the tensile strength and ductility of the joint, especially the latter. When the heating time increases to 450 s, solid-state joint with good combination of strength and ductility is attained.     

Corrosion performance of high pressure die-cast Al-6Si-3Ni and Al-6Si-3Ni-2Cu alloys in aqueous NaCl solution

The corrosion performance of high pressure die-cast Al-6Si-3Ni (SN63) and Al-6Si-3Ni-2Cu (SNC632) alloys in 3.5% (mass fraction) NaCl solution was investigated. X-ray diffraction (XRD) and microstructural studies revealed the presence of single phase Si and binary Al₃Ni/Al₃Ni₂ phases along the grain boundary. Besides, the single Cu phase was also identified at the grain boundaries of the SNC632 alloy. Electrochemical corrosion results revealed that, the SNC632 alloy exhibited nobler shift in corrosion potential (?_corr), lower corrosion current density (J_corr) and higher corrosion resistance compared to the SN63 alloy. Equivalent circuit curve fitting analysis of electrochemical impedance spectroscopy (EIS) results revealed the existence of two interfaces between the electrolyte and substrate. The surface layer and charge transfer resistance (R_ct) of the SNC632 alloy was higher than that of the SN63 alloy. Immersion corrosion test results also confirmed the lower corrosion rate of the SNC632 alloy and substantiated the electrochemical corrosion results. Cu addition improved the corrosion resistance, which was mainly attributed to the absence of secondary Cu containing intermetallic phases in the SNC632 alloy and Cu presented as single phase.     

Thermal Characterization of Polyhydroxyalkanoates and Poly(lactic acid) Blends Obtained by Injection Molding

In this work we present the thermal characterization of the full scope of polyhydroxyalcanoate and poly(lactic acid) blends obtain by injection molding. Blends of polyhydroxyalcanoate and poly(lactic acid) (PHA/PLA) were prepared in different compositions ranging from 0–100% in steps of 10%. The blends were injection molded and then characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). The increment of PHA fraction increased the degree of crystallinity of the blend and the miscibility of the base polymers as verified by the Fox model. The WAXD analysis indicates that the presence of PHA hindered the PLA crystallization. The crystallization evolution trough PHA weight fraction (wf) shows a phase inversion around 50-60%. SEM analyses confirmed that the miscibility of PHA/PLA blends increased with the incorporation of PHA and became total for values of PHA higher that 50%.