夹杂对氢鼓泡形成的影响

通过粘接低熔点合金后拉伸,可使纯铁表面氢鼓泡被剖开,露出内部断口形貌.扫描电镜观察和能谱分析表明,氢鼓泡是含H2的空腔,大多数(88%)鼓泡核附近存在夹杂.这表明含H2空腔择优在夹杂界面处形成.当鼓泡中氢压产生的应力超过原子键合力(有可能被氢降低)时,裂纹从鼓泡核壁形成,产生断裂花样,氢进入已开裂的鼓泡就使它通过裂纹扩展而不断长大,直至鼓泡破裂,内部氢压释放.     

灰铸铁气体渗氮表面鼓泡和脆化爆裂成因探讨

对灰铸铁件经气体渗氮而出现的表面鼓泡及泡壳脆化爆裂的成因，作者观察分析表明：鼓泡壳下是原石墨，石墨尖端裂纹呈放射状，并与邻近石墨片相互贯穿呈网络状孔洞，这些缺陷主要由氢蚀和氢脆所致。     

低碳钢焊接接头氢渗透与氢损伤行为分析

对退火态低碳钢焊接接头进行了电解充氢,得到了接头不同位置产生氢损伤的微观组织,用电化学方法测量了焊后接头不同位置的氢渗透曲线,计算了接头不同位置的扩散系数、稳态平均氢浓度和扩散氢含量,解释了低碳钢焊接接头的不同位置充氢产生氢气泡、氢鼓泡及氢致裂纹数目差异的机理.结果表明,母材处表征扩散系数远小于焊缝处,平均氢浓度远大于焊缝处,导致母材处的氢渗透与损伤行为较明显,表面溢出氢气泡和近表面产生的氢鼓泡数目远多于焊缝处,然而焊缝处由于塑韧性较母材差,焊接残余应力较大,产生较多氢致裂纹,多位于氢浓度较大的近表面,内部由于拘束较大而产生少数细长裂纹.     

合金元素偏聚夹杂对针状铁素体管线钢焊接热影响区氢鼓泡的影响

L360MCS针状铁素体管线钢焊接接头经HIC试验后热影响区产生大量的氢鼓泡.剥开氢鼓泡的上半部分,露出氢鼓泡的断口形貌.用扫描电镜和EDS分析氢鼓泡的上下两部分.结果表明,在绝大多数氢鼓泡的形核区存在偏聚的颗粒状Ca,Al元素夹杂物.分析认为H原子进入基体后,夹杂物周围的内应力和空位浓度升高是形成氢鼓泡裂纹形核空腔的主要原因,活性H原子在空腔内复合成H2分子导致空腔中活性H原子浓度低于基体中氢原子浓度是氢高压形成的重要原因.     

应力和夹杂对车轮钢中氢鼓泡的影响

车轮钢在恒应力下充氢表面出现氢鼓泡的临界电流和无应力试样相同,恒应力下临界可扩散氢浓度C_σ~*落在无应力试样的分散带内,t检验表明应力对C_0~*没有影响．恒应力下发生氢致滞后断裂的门槛电流密度和门槛可扩散氢浓度分别为i_(th)=3 mA/cm~2和C_(th)=0．52×10~(-6),远小于出现氢鼓泡的相应值i_c=5 mA/cm~2和C_0~*=1．18×10~(-6)．无应力时,氢鼓泡并不择优沿夹杂产生;但在恒应力下,氢鼓泡择优沿长条状夹杂形核,其临界可扩散氢浓度从1．18×10~(-6)降为0．56×10~(-6)．     

Zr基块状非晶的氢损伤与氢致滞后断裂

研究了Zr41.2Ti13.8Ni10Cu12.5Be22.5块状非晶在充氢过程中氢致滞后断裂规律以及氢鼓泡的形核、长大及破裂过程.结果表明,当充氢电流i<20 mA/cm2时,不出现氢损伤(鼓泡及微裂纹),但在恒载荷条件下能发生氢致滞后断裂,其归一化门槛应力强度因子为KIH/KIC=0.63.当i>20 mA/cm2后,无载荷下充氢会产生氢损伤,恒载荷下发生滞后断裂时KIH/KIC从0.63降为0.26.氢鼓泡(直径约为30 nm)形核时的内压pi≈3.6 GPa.随氢的进入,鼓泡不断长大;内压增大至pC≈3.9 GPa时,鼓泡就会解理扩展变成裂纹;但扩展20-30 μm后,内压下降从而止裂.当一定量原子氢进入氢鼓泡后,它又能解理扩展,从而在鼓泡边缘局部解理断口上可以观察到止裂线.     

ZL102铸造铝合金炊具防粘涂层鼓泡原因的研究

本文用金相显微镜和电子探针研究了ＺＬ１０２铸造铝合金炊具防粘涂层部分产品在使用过程中逐渐产生鼓泡的原因。结果表明：产生鼓泡的产品是由于浇注前精炼、变质处理不充分，残留在合金缺陷（如气孔、疏松等）中的杂质，在高温使用过程中，逐渐扩散到产品表面，在防粘涂层下面产生一定的压力而引起的。     

Cu-0．1Fe-0．03P合金板材缺陷研究

采用扫描电镜及能谱分析、XRD分析和TEM分析等手段,对Cu-0.1Fe-0.03P合金热轧板鼓泡和冷轧薄板掉渣缺陷试样进行研究.结果表明,Cu-Fe-P合金中,P的脱氧作用增加了铜熔体的吸氢倾向,氢在合金中的弥散分布形成的气孔在热轧条件下聚集长大,是热轧板鼓泡的直接原因.鼓泡内表面的结晶状物质为Cu2O.后续的冷轧过程中,Cu2O相在应力的作用下破碎或小量的变形,其低塑性和与基体的低结合力是Cu-Fe-P冷轧薄板起皮掉渣的原因.     

高强度双头螺柱断裂失效分析

通过对双头螺柱化学成分、力学性能和金相组织进行分析,以及对其断口进行宏观形貌和微观形貌观察,最终确定双头螺柱断裂失效是由于表面螺纹沟槽处的大量氢鼓泡受到拉应力的作用在沟槽表面形成微裂纹造成的。     

油套管和管线管抗硫化氢腐蚀性能与夹杂物的关系

研究了油套管和管线管抗硫化氢腐蚀性能与夹杂物的关系。结果表明:大型B类夹杂物作为裂纹源可引起硫化物应力腐蚀(SSC)A法试验试样早期断裂,表面和内部夹杂物形成的"鱼眼"白点均可能成为裂纹源;夹杂物在D法双悬臂梁(DCB)试验断口上形成"鱼眼",降低了临界应力强度因子KISSC;无应力渗氢后拉伸断口上可见夹杂物形成的"鱼眼"。氢致开裂试验中,A、B、D类夹杂物均可形成氢鼓泡,氢鼓泡大小与夹杂的大小和聚集程度有关。     

On the relation between damage rate and stress level evolution in α-Cr2O3 thin films growing on Ni–33at%Cr

The blistering phenomenon has been studied in chromia films formed between 700 and 900 °C on Ni–33at%Cr. The experimental conditions of the blister occurrence and the damaged surface by blisters and spalls have been determined. From the comparison between the growth stress evolution in the oxide film – which has been related to the oxide microstructure development – and the damage rate the stress relaxation by creep is shown to prevent the formation of blisters and spalls.     

Mathematical modelling of exfoliation corrosion in high strength aluminium alloys

A mathematical model was developed for the formation of surface blisters during the exfoliation corrosion of wrought high strength aluminium alloys. The internal pressure of the blisters was calculated together with the dimensions that define the extent and the severity of the degradation. The effects of the elongated grain shape and of the heat treatment condition on exfoliation corrosion were investigated theoretically and found to compare favourably with experimental observations.     

Cathodic disbonding of an unpigmented epoxy coating on mild steel under semi- and full-immersion conditions

Cathodic disbonding of an unpigmented epoxy coating around a defect was studied with samples fully- and semi-immersed in 3.5 wt.% NaCl solution. Disbonding and the growth of blisters were monitored by scanning acoustic microscopy, which showed growth of blisters within the disbond for both type of samples. Scanning Kelvin probe potential maps suggest that blisters first form at local anodes. For semi-immersed samples, disbonding of the immersed part and the non-immersed part propagate with parabolic kinetics at identical rates, similar to fully-immersed samples. This implies that ion transport is along the coating–metal interface in both cases.     

不锈钢基体上化学镀铜工艺研究

不锈钢基体上化学镀铜易造成镀层鼓泡,这不仅影响了镀层与基体的结合力,而且直接影响到外观质量.为此,将镀前酸处理过的不锈钢片放在烘箱中加热,以除去酸洗时渗入到基体的氢.确定了热处理温度和时间,采用此方法解决了镀层起泡问题,得到所需要的镀层.     

Blistering phenomena on lacquered mild steel

Concentrically divided mild steel panels were used as substrates underneath artificial paint blisters, and electrical current flow was measured between the concentric regions during immersion in sea water, using a zero resistance ammeter. It was demonstrated that currents do flow between different regions of a steel substrate underneath a paint film, whilst it is corroding. Contamination of the blisters with sodium chloride was found to promote the corrosion processes and the current flow. Different types of corrosion processes were observed in the contaminated blisters, often with frequent movement of anodic and cathodic regions. In one instance, one of the contaminated artificial blisters grew to resemble a standard dome-shaped natural blister, and this was found to have a central anodic region surrounded by an outer cathodic region.     

真空液态挤压铸造工艺

分析了挤压铸造铸件中的气孔形成,提出了真空间接式液态挤压铸造工艺解决铸件气孔的有效方法,叙述了工 艺过程及其特点,实现工艺需注意的问题,以及有关实际应用情况。     

Localized coating failure of epoxy-coated aluminium alloy 2024-T3 in 0.5 M NaCl solutions: Correlation between coating degradation, blister formation and local chemistry within blisters

The role of pH on the nature and rate of the degradation of epoxy coatings on AA2024-T3 panels and subsequent corrosion of the substrate during immersion in NaCl solutions was investigated. In acidic solutions both blister formation and growth are rapid. Blisters become very large (≈1 cm) and new blisters appear to form for a certain time after exposure. Often very small (∼0.1 mm) clear blisters surround these large blisters. Enhanced blister formation is due to irreversibly increased permeability of the coating for chloride ions and protons, the formation of more defect sites within the coating, and the weakening/dissolution of the oxide layer in low pH environments. In neutral pH solutions, coatings fail by forming one, or at most two, active blisters (red in color) within a few days of immersion with the time-to-failure dependent upon coating quality and thickness. Blister growth is a very slow process, and blister diameters rarely exceed a few millimeters even after several weeks. The accumulation of corrosion product within the blister slows down the corrosion rate and blister growth. The chloride concentration in the occluded solutions within the blister is significantly increased over the bulk concentration, and the pH is often in the acidic range. From electrochemical measurements it can be concluded that the anodic and cathodic reactions are confined to the blister and its immediate surroundings, rather than involving more of the surface over which the coating is intact. Based on corrosion morphology it is concluded that replated copper contributes to the overall cathodic reaction.     

Use of acoustic emission technique for the early detection of aluminum alloys exfoliation corrosion

Exfoliation corrosion of aluminum alloys is a form of localized corrosion which affects many industries, specially aeronautics. The study of this corrosion mode using only electrochemical techniques is not fully efficient for the detection and control on line of this phenomenon. Therefore, we developed a non-destructive testing technique based on the acoustic emission recordings in order to follow-up this form of corrosion on aluminum alloys. Indeed, recent works have shown the interest of the acoustic emission for the detection, the monitoring and the localization of pitting corrosion on aluminum alloys. This pitting corrosion phenomenon is currently well understood and the experimental methodology acquired during that study is transposed to the study of exfoliation corrosion of aluminum alloys.The present study is conducted on two aluminum alloys: (Al 2024 T3, and Al 7449 T6 and T7). Samples are immersed 4 days in the modified ASTM STP 1134 saline solution. Observations of the structures after tests show that the exfoliation corrosion sensitivity of alloy 7449 T6 is more important than for alloy 7449 T7 which exhibits only the presence of small and non-occluded pits. Very severe exfoliation corrosion was also observed on Al 2024 T3, but after a longer immersion time or in a more acid solution.The recording of the acoustic emission activity shows evident links between this activity and the exfoliation corrosion rate. The analysis of the signal's characteristics reveals a population corresponding to the release of hydrogen bubbles. A few more energetic signals have also been observed. Their source can be either, the cracking resulting from the separation of sheets of metal, or the development and evolution of hydrogen bubbles formed inside blisters during exfoliation corrosion.     

Simulation eines Korrosionselementes bestehend aus einer beschichteten Stahlelektrode mit einer Verletzung

Simulation of a corrosion element consisting of a coated steel electrode with a damage Cathodic blisters are generated on samples with an anodic electrocoating bearing no conversion layer to simulate the corrosion element coated steel electrode/bar steel. Therefore potentiostatic polarisation experiments were carried out in 3 wt.% sodium chloride solution. The coating pigmented with titanium dioxide consists of oil-free polyester, melamin resin and polyalcohol. In our investigations we varied the polarisation potential, the time of corrosion loading and in a restricted manner the coating thickness of the coating. The polarisation potential ranged between the limiting values of the free corrosion potential of a coated electrode and that of a bar steel electrode. The galvanic current and the delaminated area consisting of the number of blisters as well as the growth-rate of blisters are measured. There exists a constant current density at the delaminated areas, because for the galvanic current and the delamination has been found the same time behaviour. The current density depends on the polarisation potentials in a non linear way. This shows that the ohmic resistance of the coating does not determine the rate of the electrochemical reactions at the phase boundary exclusively. Blister generation and blister growth-rate increase linearly with time of corrosion loading, but only the blister growth-rate is influenced by the polarisation potential.