金属材料大气环境静态腐蚀老化的疲劳特性

对ＬＣ４ＣＳＡｌ合金和３０ＣｒＭｎＳｉＮｉ２Ａ钢的疲劳件在大气环境预腐蚀其疲劳寿命性能。检验了疲劳寿命的分布特性。分析了材料在大气环境预腐蚀后疲劳寿命分布的数字特征,寿命分散系数,疲劳Ｓ－Ｎ曲线等的变化。以及冷挤压强化 疲劳增寿效应与大气环境腐蚀日历时间的关系。     

预应力腐蚀对2A12-T4铝合金疲劳寿命的影响

进行了两种温度三种应力水平下2A12-T4铝合金试样在EXCO溶液中不同浸泡时间的预应力腐蚀试验,而后进行疲劳试验至试件断裂。采用多元方差分析,确定了腐蚀温度、浸泡时间和应力水平是影响试件疲劳寿命的显著因素,三者的共同作用会加剧试样的腐蚀,降低试样的疲劳寿命。根据试验结果,采用回归算法,建立了以腐蚀温度、浸泡时间和应力水平三参数表征的剩余疲劳寿命计算模型,理论值与试验值对比,二者误差约为25%。通过扫描电镜观察,分析了腐蚀温度、浸泡时间和应力水平对试件微观损伤的机理。     

铝合金腐蚀损伤的形态学研究

在实验室中对LY12CZ铝合金试件进行预腐蚀,随后再对其疲劳寿命评诂.在预腐蚀实验中，设置了3组腐蚀时间和3种腐蚀溶液温度以模拟不同的环境.利用扫描电镜和光学显微镜对预腐蚀后试验件上的腐蚀损伤进行观测，从形态学角度分析了腐蚀时间和腐蚀溶液温度的不同给损伤形态造成的影响.最后提出腐蚀损伤的评价指标：腐蚀坑深度和表面腐蚀损伤度，并给出了不同深度、损伤度对应下的试验件疲劳寿命。     

预腐蚀疲劳寿命影响系数模型研究

针对腐蚀环境下飞机结构疲劳寿命评定问题,研究了恒幅应力水平下的地面停放预腐蚀影响系数C模型，根据统计分析推导出C曲线的关系式;疲劳试验数据分析结果建立了预腐蚀影响系数C模型.结果表明，随着腐蚀时间的增加,疲劳寿命影响系数C不断下降;同一时间下,应力水平S高,影响系数C大;应力水平S低,影响系数C小；在一定的腐蚀疲劳条件(时间、应力水平)下,可求出任一给定可靠度p时的Cp值和疲劳寿命预测值.     

变幅载荷下铝合金的腐蚀疲劳裂纹起始寿命

试验测定了铝合金切口件在变幅块谱下于３．５％ＮａＣｌ溶解中的腐蚀疲劳裂纹起始（ＣＦＣｌ）寿命,结果表明,变幅载荷谱中的大超载会显著延长ＣＦＣＩ寿命,并用超载方式和加载顺序具有明显的影响,根据反映大小载荷交互作用和腐蚀效应的超载ＣＦＣＩ寿命曲线,探讨了应用Ｍｉｎｅｒ累积损伤定则建立变幅载荷下切口件ＣＦＣＩ寿命估算模型的可行性,并应用平均秩对变幅块谱下ＣＦＣＩ寿命的分布进行了统计分析,讨论了变幅载荷谱     

预腐蚀温度对铝合金LY12CZ腐蚀损伤及疲劳性能的影响

    根据ASTMG34-1标准对铝合金LY12CZ实验件进行了剥蚀实验.研究了预腐蚀温度对铝合金试验件腐蚀损伤形貌的影响,并分析了预腐蚀温度对试验件疲劳寿命的影响.利用试验测量得到的表面腐蚀损伤度数据,建立了不同腐蚀温度下损伤度演化的概率模型,并对其演化过程的特征进行了讨论.最后推导出了温度影响下腐蚀损伤度的预测模型,模型预测结果和试验结果符合较好     

压气机叶片腐蚀条件下振动疲劳寿命分析

为了探究压气机叶片结构在腐蚀环境下振动疲劳寿命变化规律,依据实际工况特点,研究预腐蚀对叶片结构振动疲劳行为的影响。以试验结果为基础,建立基于腐蚀影响系数曲线（C-T曲线）的振动疲劳寿命关系式。结果表明:构建的腐蚀影响系数曲线能较准确地描述压气机叶片预腐蚀后疲劳寿命的变化规律,具有良好的适用性;采用幂函数式的腐蚀影响系数曲线计算结果精度相对较高,用其对15个当量日历年限下的压气机叶片进行对数疲劳寿命评估预测,其对数疲劳寿命降低约28%。     

过盈配合对沉头铆钉无载孔疲劳寿命的影响分析

针对飞机结构中过盈配合对无载孔疲劳寿命的影响开展了研究,通过试验对比分析了普通铆接试验件和过盈量1%铆接试验件。结合有限元分析,采用多轴疲劳理论对不同过盈量的铆接紧固孔在疲劳载荷下的损伤参量进行研究,确定过盈量对疲劳损伤的影响规律。实验结果表明:过盈量为1%铆接紧固件可提高紧固孔的疲劳寿命15%左右;通过有限元分析,适当的过盈量可降低紧固孔的应力幅和应变幅,进而降低疲劳损伤参量。     

加速预腐蚀与疲劳试验估算飞机结构日历寿命的新方法

提出估算日历寿命的一种新方法—线性累积破坏率准则法，其物理意义明确，简单明了.飞机机体的损伤模式描述为疲劳损伤和预腐蚀疲劳损伤，并将飞机结构的日历寿命定义为地面停放日历寿命和飞行日历寿命之和.选取破坏率为损伤参量，在环境腐蚀当量关系加速预腐蚀疲劳试验的基础上，通过疲劳寿命分布形式和概率密度函数求出破坏率来估算预腐蚀环境下的日历寿命.利用一组预腐蚀与疲劳试验数据对该方法进行了验证.     

30CrMnSiA合金钢当量加速腐蚀试验

基于某海域舰面停放环境谱,采用30CrMnSiA材料制备模拟件,在某海域采取悬挂方式开展自然暴露试验的同时在试验室环境下开展了加速腐蚀试验。对腐蚀后试样的失重和疲劳寿命进行了测试,结果表明,30CrMnSiA试验件在当量加速腐蚀试验时间和某海域自然老化时间匹配时,腐蚀失重和疲劳寿命在95%置信度下一致。     

Electrochemical conditions for environment-assisted cracking of 6061 Al alloy

We have investigated the influence of electrochemical conditions on environment-assisted cracking (EAC) of 6061 aluminum alloy in acidic chloride solutions. An EAC test was conducted by means of potential-controlled slow strain rate technique. In addition, thermal desorption spectroscopy (TDS) was employed to determine amount of hydrogen absorbed in the specimens under the same electrochemical conditions as those in the EAC tests. As a result, almost no EAC and very small amount of hydrogen absorption were found in a potential range lower than the film breakdown potential, while the higher potential induced severer EAC and much larger hydrogen absorption. The specimen pre-immersed in the chloride solution of pH 1, which derived voluntary breakdown of the oxide film, suffered preferential grain boundary attack. When the tensile test was conducted in air for the specimen with pre-immersion, the fracture strain became slightly smaller than that without pre-immersion. Moreover, the fracture strain drastically decreased and deep cracks was observed, namely the EAC occurred, when the pre-immersed specimen was examined by the EAC test under the cathodic condition which induced no EAC and very small hydrogen absorption for the specimen without pre-immersion.     

碳纤维-铝合金电磁铆接与准静态压铆对比

为了探究电磁铆接技术在碳纤维复合材料上的可行性,采用碳纤维-铝合金结构为研究对象。探究了碳纤维-铝合金电磁铆接接头的干涉量及剪切、拉脱性能,并与传统准静态压铆技术进行了对比。结果表明:无论是Φ4 mm铆钉,还是Φ6 mm铆钉,电磁铆接结构相对干涉量不仅均匀性更好,而且平均值更高,分别从4.96%提升到5.20%,6.85%提升到7.85%;电磁铆接接头剪切性能有较大提高,对于Φ4 mm铆钉和Φ6 mm铆钉,电磁铆接最大剪切力相比准静态压铆分别提高了19.7%和5.2%;电磁铆接接头拉脱性能有较小提高,对于Φ4 mm铆钉和Φ6 mm铆钉,电磁铆接最大拉脱力相比准静态压铆提高了3.9%和6.6%。结果说明电磁铆接技术更适合复合材料的连接。     

690合金在ETA和AVT水工况下的电化学特性

采用Tafel极化曲线法和电化学阻抗法研究了690合金在乙醇胺(ETA)和全挥发处理(AVT)两种水工况下的电化学行为,并着重考察了pH值、温度、Cl-和SO42-对690合金电化学性能的影响.结果表明,在两种不同水工况下,pH值升高会提高690合金的耐蚀性,而温度升高和Cl-,SO42-的加入则均会加速690合金的腐蚀.在相同条件下,690合金与ETA水工况有更好的兼容性,ETA的缓蚀性能优于NH3.     

Effect of CaCl_2 and NaHCO_3 in Physiological Saline Solution on the Corrosion Behavior of an As-Extruded Mg–Zn–Y–Nd alloy

In this study, the corrosion behaviors of an as-extruded Mg–4%Zn–2%Y–1.8%Nd(in wt.%) alloy in different physiological saline solutions were investigated and compared. The results indicated that the alloy in the 9 g/L NaCl had the higher corrosion resistance than that containing with CaCl_2 and NaHCO_3. Moreover, it demonstrated that the corrosion behaviors of the alloy in two types of solutions were all dependent on the pre-immersion time. In the 9 g/L NaCl solution, the corrosion current densities of the alloy decreased firstly with the pre-immersion time being 4 h and then increased with the pre-immersion time prolonging from 4 to 48 h. However, in the 9 g/L NaCl solution containing with CaCl_2 and NaHCO_3, the corrosion current density of the alloy exhibited the adverse trend with the prolonging the pre-immersion time. Failure analysis demonstrated that the changes of corrosion resistance in two solutions were mainly dominated by the constituents formed in surface films.     

EFFECTS OF HEAT TREATMENT AND ENVIRONMENT ON CRACK PROPAGATION RATE IN STEEL GC-4 UNDER CORROSION FATIGUE AND STRESS CORROSION

Comparative investigations were carried out of the effect of heat treatment regimes Jor steelGC-4(40CrMnSiMoVA)on its crack propagating rates,from corrosion fatigue,(da/dN)_(CF),or stress corrosion cracking,(da/dt)_(SCC),in media with various constituentsand pH values.Both(da/dN)_(CF) and(da/dt)_(SCC) accelerate with the increase of yield stressof the steel,yet the former is far less than the later.In comparison with media,the(da/dt)_(SCC) in distilled water is slightly greater than that in 3.5% NaCl solution,and the(da/dN)_(CF) in distilled water is far less than that in 3.5% NaCl solution.With the pH valueincreasing in 3.5% NaCl solution,the(da/dN)_(CF) lowers down and the(da/dt)_(SCC) speedsup.An explanation was also proposed with concept of the cyclic hardening and softening atcrack tip,as well as the crack closure and occluded cell effect.     

Determination of upper Boundary pitting resistance potential values for austenitic stainless steels under corrosion fatigue

In this study Mode IV-corrosion fatigue (CF) characterized by additional superposition of pitting corrosion was investigated. Corrosion fatigue and polarization experiments were carried out on three austenitic (17Cr–13Ni–5Mo–0.15N, 25Ni–20Cr–5Mo–1.5Cu and 18Cr–10Ni–2Mo–0.5Ti) stainless steels in 0.05 M sulphuric acid to which 20000 ppm Cl^? was added. The CF strength decreased drastically when Mode IV-conditions apply. The damaging effect of pitting corrosion in Mode IV was very pronounced. The relation between pitting, repassivation of the pits and Mode IV-CF was investigated and it was found that for rotaing beam CF the measured repassivation potential represents a conservative upper boundary value below which mode II-CF (i.e. CF under stable passivity) replaces Mode IV-CF, when operating below stress ranges of 75% of the fatigue strength measured in air.     

受剪载荷下C/SiC铆接接头应力数值模拟与实验验证

通过建立有限元模型研究C/SiC铆接接头剪切应力分布及接头剪切破坏形式,并采用实验的方法对模型的准确性进行验证。计算结果表明:按本研究方案尺寸设计的C/SiC铆接接头受剪切载荷时,应力分布合理,以铆钉被剪断的方式破坏。实验验证中所有接头以铆钉被剪断的形式破坏,断口出现在连接板内侧,与计算结果一致,说明本研究所建立的计算分析C/SiC铆接接头的破坏形式的模型是合理的。     

Pitting corrosion behavior of superferritic stainless steel in waters containing chloride

On a cost-performance basis, superferritic stainless steel (SFSS) grades can now be considered competitive choices for brackish and sea water cooling systems. The pitting corrosion of a SFSS (X2CrNiMoTi 25 3.6 3.5) was tested in a chloride/sulfate solution similar to sea water, as a function of temperature, pH, and salinity. Potentiodynamic polarization techniques and experimental stability diagrams were used to evaluate the pitting conditions. The critical pitting temperature (CPT) was found to be above 50°C, and the re-passivation tendency under critical temperatures was satisfactory even when the pH was less than the depassivation pH, a condition which simulates a propagating occluded cell. The SFSS behavior in the presence of chlorine was evaluated by means of potentiodynamic tests and by studying the cathodic reduction kinetics of Cl₂ and O₂ (air).     

Marmatite bioleaching with moderately thermoacidophilic bacterial strain and mineral analyses of solid residues

The bioleaching of a marmatite flotation concentrate with a moderately thermoacidophilic iron-oxidizing bacterial strain （MLY） is influenced significantly by temperature, pH, particle size, pulp density of ores and bacterial strains. Under such leaching conditions as the initial pH value of 1.5, temperature of 50℃, pulp density of 5%, particle size less than 35.5μm （over 90%） and inoculating the adapted strains of MLY, the leached Zn is over 95% after 10 d of bioleaching. SEM observations show the cell attachment and the surface features of solid residues under different leaching conditions. XRD and EDX analyses show that a mass of elemental sulfur form during the bioleaching process. The technological feasibility of a microbiological process using MLY for extracting zinc from the marmatite concentrate is demonstrated.     

制备条件对Au/AC催化分解臭氧性能的影响

研究了活性炭负载的金催化剂(Au/AC)对低浓度臭氧的催化分解性能,考察了前驱体溶液pH值、干燥方式、焙烧温度等制备条件对催化剂活性的影响,以及空速对臭氧分解率的影响。结果表明,在金前驱体溶液pH值为10、经微波辐射干燥、200℃氢气还原制备的催化剂,金颗粒在活性炭表面的分布更加均匀,尺寸更小,具有更高的催化活性。在室温、相对湿度45%和空速72000h-1时,对浓度为50mg/m3臭氧的分解率保持在90%以上(在2400min内)。N2吸附-脱附和XPS表征结果表明,活性炭载金催化剂在催化分解臭氧后,比表面积和孔体积略有下降;Au4f的XPS峰虽稍向高能方向移动,但仍保持催化活性;活性炭表面碳含量显著下降而氧含量大幅增加,说明活性炭上负载的Au在自身催化分解臭氧的同时,还起到了促进臭氧与单质碳反应的作用。