重载齿轮齿面疲劳损坏及预防

点蚀和剥落是重载齿轮齿面疲劳损坏最普遍的形式.根据齿轮失效分析实例,对齿面初始点蚀、破坏性点蚀和齿面剥落等三种主要疲劳损坏的特征、发生部位及破损危害程度进行了分析研究,较系统地论述了齿轮接触疲劳破坏机理,影响因素及其产生原因,并对有关的齿面破坏提出了相应的预防措施.     

Corrosion Behavior of 316LN and 316 Stainless Steels During Long-term Exposure to Aerated 0.5 M NaCl Using Electrochemical Noise Technique

In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m³) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl. Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R _N) as well as the spectral noise resistance at zero frequency (R _SN^o) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths, extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM). The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the unstable pits in 316LN after 7 days exposure. It was observed that R _N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period. Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days of exposure, an observation that corroborates well with the stable R _N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas the unstable pits initiated in 316LN get passivated in the simulated coastal environment.     

Corrosion fatigue short crack growth behaviour in a high strength steel

The influence of an aggressive environment (0.6 M, aerated NaCl solution) on short fatigue crack initiation and growth behaviour has been studied. The study involved three major test series, namely: air fatigue, corrosion fatigue, and intermittent air fatigue/corrosion fatigue. The above tests carried out under fully reversed torsional loading conditions at a frequency of 5 Hz, showed that it was the non-metallic inclusions which took part in crack initiation resulting from debonding at metal matrix/inclusion interface and pitting of inclusions in both air and corrosove environments, respectively. Short fatigue crack growth results in these two environments obtained by using plastic replication technique, indicated a large effect of microstructure i.e. prior austenite grain boundaries. The stage/stages at which the environmental contribution was dominant has been discussed by considering the results achieved from intermittent tests. However, the mechanisms involved in corrosion fatigue short crack growth have also been described in the light of results obtained from futher investigations carried out by conducting corrosion fatigue tests under applied cathodic potential conditions and tests on hydrogen pre-charged specimens under air fatigue and uniaxial tension conditions.     

环境因素对碳钢点蚀临界电势的影响

采用动电势扫描法测定了不同体系中碳钢发生点蚀的临界电势Eb。结果表明 :当Cl- 浓度 <0 .0 1mol/L时 ,随Cl- 浓度增加 ,临界电势负移并与Cl- 浓度成线性关系 ;pH值在 7～ 11之间 ,随pH值增加 ,临界电势正移并与pH值成线性关系 ;随温度增加 ,临界电势负移并与温度成线性关系。     

The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91

The influence of NaCl and CO₂ on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0°C and the concentration of CO₂ was < 1 ppm or 350 ppm. Different amounts of sodium chloride (0–70 μg/cm²) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X‐ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCl is very corrosive towards AZ91. However, the NaCl‐induced corrosion is inhibited by ambient concentrations of CO₂. Exposure in the absence of CO₂ gives rise to heavy pitting, with brucite, Mg(OH)₂, being the dominant corrosion product. In the presence of CO₂ a layer of hydrated magnesium hydroxy carbonate, Mg₅(CO₃)₄(OH)₂ · 5 H₂O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments.     

Pitting corrosion of Cr–Mn–N steel in sulphuric acid media

The resistance to pitting corrosion of austenitic stainless steel Cr18Mn12N has been studied in model solutions of sulphuric acid (0.5 m) containing chloride ions (0.5 m). The cyclic potentiodynamic method has been employed to investigate the effects of chloride ions and agitation rate on the pitting and repassivation potentials. Electron and optical microscopy, electron diffraction spectroscopy and atomic absorption spectrometry have been used to detect the surface sites for pit formation and the growth of pit nuclei. The results obtained with chromium–manganese–nitrogen steel have been compared with those of austenitic Cr18Ni9 stainless steel. A similarity in pit initiation is established, while steel composition exhibits no significant effect. Cr18Mn12N steel is less prone to repassivation as compared with Cr18Ni9 steel.     

Failure analysis and wear mechanism study of a heavily loaded gear

Failure analysis and a study of the wear mechanism were performed on a heavily loaded carburized gear with some unusual features. The analysis showed that the different failure forms on the tooth surface of the gear were dependent on the sub-surface shearing stress, the lubrication conditions and the surface roughness. Delaminations formed on the addendum surface were the main reason for the gear failure. A suggestion for improvement has been tried, and a desirable result has been obtained.     

The generation of surface roughness during slurry erosion-corrosion and its effect on the pitting potential

Results of experiments performed to isolate the effect of surface roughness generated during slurry erosion-corrosion of 304L stainless steel are presented. Surfaces prepared by grinding to different finishes show that increasing the roughness lowers the pitting potential in chloride solution. Subsequent erosion by an aqueous sand slurry then alters this pitting potential (E_p), as measured in the solution phase alone, in a manner dependent on the initial surface roughness. Surfaces which were initially rougher show a pronounced rise in _p after erosion, while those with an initially smoother finish show a fall in E_p after erosion. Measurement of E_p during erosion-corrosion does not fit either process, with values of _Ep lower than those predicted from the surface roughness alone.     

MnS夹杂物诱发钢材点蚀综述

MnS夹杂物诱发钢材点蚀,对钢材服役寿命、工作生产安全和社会经济发展产生巨大危害。首先,分析了MnS夹杂物诱发钢材点蚀的机理,包括电偶腐蚀机理、S和Cl-协同作用机理、封闭区域加速点蚀机理、贫铬区机理和微缝隙机理;其次,汇总了MnS夹杂物大小、形貌、分布,Cl-浓度、温度和应力对MnS夹杂物诱发钢材点蚀的影响;然后,总结了钢材防腐蚀的常用措施;最后,展望了防止MnS夹杂物诱发钢材点蚀的未来研究方向。