喷射成形M3高速钢偏析成因及凝固机理

采用喷射成形工艺制备直径250 mm大截面M3型高速钢，利用电火花直读光谱仪、金属原位分析仪、XRD、OM、SEM等手段，研究样坯特殊偏析形貌位置处合金元素分布和微观组织特征。结果表明，腐蚀后样坯低倍组织中存在2种偏析形貌：锭型偏析与环状偏析。锭型偏析区域内富集C及溶质元素；环状偏析区域主要富集C及Mo元素，较锭型偏析程度轻。由样坯边部至心部，碳化物形貌由条状向块状、鱼骨状转变；宏观偏析区域内碳化物偏析严重。基于实验结果，讨论了喷射成形工艺糊状区的组织变化及锭型偏析和环状偏析的形成，认为沉积阶段缓慢的冷却速率是出现上述结果的根本原因。因此，在利用喷射成形工艺制备大截面材料时，不应简单考虑为一种快速凝固技术。     

连铸坯中心偏析检测

对连铸坯进行了一些常规的检测,包括原位分析、高倍观察、能谱扫描和枝晶腐蚀。检测结果说明Q345连铸坯的中心偏析主要是C元素的偏析。发现元素偏析点总与疏松等缺陷重合及负偏析谷常存在于正偏析峰两侧,佐证了疏松孔洞的负压抽吸作用引发中心偏析的观点。同时,检测结果还指出中心偏析由多种驱动因素,需要进一步研究枝晶生长和未凝固钢液的流动。     

Fe含量对CuNi10FeMn1合金组织与性能的影响

研究Fe含量(1.05%~2.44%,质量分数)对CuNi10FeMn1合金组织、微观偏析、耐海水冲刷腐蚀性能和力学性能的影响,采用SEM、能谱和XPS等手段分析合金的腐蚀产物膜。结果表明:CuNi10FeMn1合金中Ni、Fe元素易于富集在枝晶干,Mn元素易于富集在枝晶间;随着Fe含量的增加,合金组织明显细化,α固溶体中的Fe含量增加;当Fe含量从1.05%增大至1.80%时,Ni、Fe元素的偏析比分别由0.49和0.45增大到0.77和0.61,偏析程度下降;当Fe含量继续增大时,Ni、Fe元素的偏析比则下降为0.62~0.65和0.49~0.51,偏析程度也随之增加。随着Fe含量的增加,合金的腐蚀速率呈先减小后增大的趋势,当Fe含量为1.80%时,合金腐蚀速率最小,表面形成致密的、缺陷较少的富Fe、Ni的腐蚀产物膜,对基体的保护作用增强,是其具有良好耐海水冲刷腐蚀性能的主要原因。随着Fe含量的增加,CuNi10FeMn1合金的抗拉强度和屈服强度由Fe含量为1.05%时的245和90MPa分别增大到Fe含量为2.44%时的303和151MPa,而断后伸长率由39.2%下降到32.8%。     

核用304不锈钢辐照促进应力腐蚀开裂研究

采用2 MeV质子束在360℃对国产核用304不锈钢试样进行了辐照实验,利用高温高压水环境的慢应变速率拉伸实验(SSRT)和SEM、EBSD、TEM等研究了核用304不锈钢辐照促进应力腐蚀开裂(IASCC)机理。结果表明,慢应变速率拉伸过程中辐照促进材料晶界和表面滑移台阶处形成应变集中,且其程度随辐照剂量增加而增加。滑移台阶穿过或终止于晶界,终止于晶界的台阶造成晶界处产生不连续滑移,易将位错传输到晶界,在晶界区域形成位错塞积和残余应变集中。而台阶不连续滑移的形成则受毗邻晶粒的Schmidt因子对的类型影响。另一方面,辐照促进晶界发生贫Cr富Ni元素偏析,其偏析程度随辐照剂量增加而增加。SSRT实验后辐照试样表面发生明显的沿晶应力腐蚀开裂,且裂纹数量随辐照剂量和外加应变增加而增加。同时,裂纹尖端区域发生明显晶界腐蚀,且氧化物宽度和长度随辐照剂量增加而增加。分析认为,辐照致晶界应变集中和元素偏析的协同作用造成材料变形行为和晶界腐蚀行为变化是IASCC发生的关键因素。     

VAR熔炼中搅拌磁场对元素宏观偏析的影响

在利用真空自耗电弧炉(VAR)熔炼钛及钛合金铸锭时,因VAR熔炼本身特点,铸锭规格大型化后会出现合金元素控制困难、宏观偏析等问题,对产品质量造成严重影响。通过对成品直径为1040 mm的TA2铸锭中Fe元素、TA10铸锭中Ni元素成分进行分析,设计实验探究搅拌磁场对元素宏观偏析的影响。实验通过改变熔炼时的电磁搅拌方式,探究搅拌磁场对Fe、Ni元素宏观偏析的影响。结果表明两次熔炼都使用交流搅拌磁场的铸锭其偏析程度远远小于一次直流搅拌、二次交流搅拌的铸锭,头底Fe元素偏析率降低到6.25%。头底Ni元素偏析率降低到6.41%。经过分析,主要原因是因为搅拌磁场会影响熔池深度及金属凝固时的结晶,减弱Fe、Ni元素在钛熔液里凝固时因溶质再分配造成的结晶浓度偏差。     

过热度和轻压下量对高强IF钢中心偏析的影响

通过热酸侵蚀、化学分析等方法,对不同浇注过热度、不同凝固末端轻压下量条件下生产的高强IF钢铸坯中心偏析情况进行研究,分析浇注过热度及轻压下量对铸坯中心偏析的影响。结果表明:试验条件下轻压下量为2.9 mm或3.9 mm对铸坯中心偏析没有影响,而浇注过热度为33℃或29℃对铸坯中心偏析影响较大,过热度越高,铸坯中心偏析越严重。浇注过热度为33℃时,P元素中心偏析度在0.95~1.08之间,S元素中心偏析度在0.91~1.12之间;浇注过热度为29℃时,P元素中心偏析度控制在0.95~1.03之间,S元素中心偏析度控制在0.93~1.07之间。在浇注条件允许的情况下,应该尽量降低浇注过热度。     

模拟偏析相Al2Zn在3%NaCl溶液中的电化学行为

根据Al-Zn-In合金中偏析相Al2Zn的元素组成熔炼出模拟偏析相合金,测试了模拟偏析相合金和Al-Zn-In合金的自腐蚀电位、极化曲线和交流阻抗谱.结果表明:相对于Al-Zn-In合金,模拟偏析相Al2Zn自腐蚀速率小,自腐蚀电位负,呈现阳极性;Al-Zn-In合金中的偏析相Al2Zn与合金基体构成微区电偶腐蚀,受到阳极极化优先溶解,引起阳极电流效率的损失.     

高酸性气田集输系统元素硫存在条件下腐蚀影响因素

针对地面集输系统的实际工况,研究了H2S、CO2以及Cl-共存条件下元素硫对材料应力腐蚀开裂和失重腐蚀的影响,结果表明元素硫对材料应力腐蚀开裂的影响有限,主要是影响材料的失重腐蚀;同时采用SEM(扫描电镜)、XRD(X射线衍射仪)对材料的断口和腐蚀产物进行了分析,最后总结、分析元素硫腐蚀机理。     

铸钢锭在轻压环境下的凝固组织及中心偏析问题研究

通过化学分析、热酸腐蚀的方法对铸坯进行分析,对厚度方向上的铸坯元素分布情况及不同凝固结构组织的偏析样貌进行定量、定性分析。结果表明,轻压环境下,钢坯的中心柱状晶结构组织及等轴晶结构组织都能得到较小的偏析度。钢坯为中心柱状晶结构组织时,对钢水过热度及压下量进行适当的调整可使得到的偏析度较低及其评级较好。     

微量锑和锡对铝基牺牲阳极材料性能的影响

熔炼了添加合金元素Sb和Sn的5种Al-Zn-In系牺牲阳极材料,采用恒电流方法测试了其电化学性能,采用金相显微镜、扫描电镜和能谱分析分别观察和分析了阳极材料的显微组织和组成.结果表明:Sb具有细化晶粒的作用,但晶界存在较多偏析相,电流效率偏低;与Sb相比较,Sn也具有细化晶粒的作用,电流效率有所提高,晶界偏析相较少,但阳极的表面腐蚀溶解不均匀;Sn和Sb的协同作用在于能有效地抑制Si的偏析,显著提高阳极的电流效率,使得阳极表面具有良好的腐蚀溶解性.     

END GRAIN ATTACK OF LD10CS PLATES DURING CHEMICAL MILLING

The end grain attack of LDIOCS aluminium alloy plates during chemical milling in hotaqueous solution of sodium hydroxide has been studied.The results show that themicrosegregation of some components,i.e.Cu,Si etc.,is the main reason of the end grain at-tack,and it is affected by the conditions of heat treatment as well.The end grain attacksignificantly diminishes while some technical measures which are beneficial to the reduce ofsegregation were taken during melting and casting.     

Corrosion of Aluminium—Literature Review 1965–1967

Abstract

Lewis and others report that stress-corrosion cracking and intercrystalline corrosion are the main problems associated with the aluminium alloys used in the aircraft industry. Stress-corrosion cracking occurs principally in the joints of integrally machined sections, and in forgings, as a result of the combination of stresses such as residual heat treatment stresses, airborne versus ground stresses and assembly stresses together with any corrosive environment combined with inadequate protection; in some susceptible alloys the stress corrosion takes the form of end grain attack at the radii of integrally machined sections. Intercrystaliine corrosion has also been a major problem both in the aircraft industry as well as industry in general. In the latter case the corrosion is sometimes attributed to misapplication and lack of care during handling or pretreatment.     

Klärung der Einzelmechanismen bei der Schädigung von Kupfer unter Kavitationsbeanspruchung in wäßrigen Medien

Study of the individual mechanisms giving rise to the destruction of copper under cavitation in aqueous media An experimental method developed by the authors enables the overall destruction mechanism during cacitation corrosion to be subdivided into the two main components “mechanical destruction” and “corrosion”. With the aid of impressed current it is then possible in a defined way largely to control the ratio of the two components of attack. Mechanical sollicitation due to the successive formation and collapse of bubbles in the liquid corresponds to the pattern found in corrosion fatigue; the authors have indeed found the phenomenological pattern of corrosion fatigue in some systems (grain boundary attack by electrochemical action, glide line attack by mechanical sollicitation).     

Corrosion of AA2024-T3 Part III: Propagation

Optical and electron microscopies and EBSD were used to study the early stages of corrosion propagation during stable pit formation on AA2024-T3. Polished AA2024-T3 developed large scale rings of corrosion product, typically a few hundred microns in diameter, within 2 h of exposure to 0.1 M NaCl at room temperature. These features were sectioned using diamond ultramicrotomy and substantial subsurface attack, in the form of intergranular corrosion was observed beneath these sites with virtually no grain etchout. A model is proposed for the mechanism of stable pit progression which involves extensive grain boundary attack, followed by grain etchout leading to open pit formation.     

Mechanism of intergranular attack in Zn–Al–Cd sacrificial anodes at elevated temperatures

Abstract

The premature failure of a Zn–0·3 Al–0·03Cd anode at 70°C in sea bed mud has been simulated in laboratory sea water using galvanostatic polarisation. The exposed surface of the anode suffered intense intergranular attack and some dissolution. Within the bulk of the material intergranular attack was observed, but no dissolution. Unpolarised alloys in a variety of environments exhibited the same type of attack; however, it could not be produced on pure zinc. No evidence could be found of segregation or precipitation of aluminium at grain boundaries. Moreover, specimens that had been solution treated to ensure a single phase microstructure suffered from intergranular attack in short term simulation tests. It is concluded that a previously proposed mechanism consisting of grain boundary precipitation of aluminium followed by its preferential dissolution is incorrect. It is proposed from analysis of the fracture morphology and the effect of test conditions that the failure is caused by hydrogen penetration.     

Upper nose temper embrittlement of a Ni-Cr steel

Temper embrittlement of a Ni-Cr steel was investigated both isothermally and with temperature changes. Embrittlement was most rapid in two temperature ranges: 490° to 550°C and just below the Ae₁, near 675°C. Embrittlement in the lower range was accompanied by rapid grain boundary attack by ethereal picric acid and fracture along austenite grain boundaries. Embrittlement in the upper range was accompanied by slow attack by ethereal picric acid and fracture mostly along ferrite grain boundaries. No increase in ferrite grain size was observed, but carbide particles grew during treatments in the upper temperature range. Embrittlement during slow cooling from 675°C appeared to be associated with the lower range.     

Analysis of intergranular corrosion attack on stainless steels by means of atomic force microscopy and optical microscopy. Part 1: Influence of heat treatment

The aim of this study is to quantify intergranular corrosion attack of heat treated low carbon austenitic stainless steel caused by segregation processes of P (0.2 at% P) by different methods. After nitric acid chromate test the intensity of intergranular corrosion attack was investigated by weight loss measurements as well as determination of depths of grooves by both the optical microscopy and AFM measurements. Generally, the largest attack of corrosion is noticed on samples heat treated at 550 °C. Results of weight loss include the corrosion of matrix, inhomogenities and grain boundaries. The depths of corrosion attack were determined by optical microscope on cross sections. This method can not distinguish between attacks at grain boundaries and attack of inhomogenities. Whereas, measurements of depths by line profiling of AFM‐surface images is related to grain boundary attack directly. The weight loss measurements as well as the optical microscopy and AFM‐measurements were compared for tested heat treatment conditions. It is concluded that the use of the AFM offers an advantageous method for quantifying intergranular attack.     

Corrosion of ultra-fine grained copper fabricated by equal-channel angular pressing

Corrosion of ultra-fine grain (UFG) copper fabricated by equal-channel angular pressing (ECAP) has been investigated in comparison with that in recrystallized coarse grain (CG) copper. Corrosion current was estimated by a Tafel extrapolation method to examine the kinetics of corrosion in a modified Livingstone etchant, which is sensitive to dislocations and grain boundaries. UFG copper exhibited a lower corrosion current in comparison with that in its recrystallized coarse grain (CG) counterpart despite the fact that the dislocation density and total fraction of grain boundaries are much greater in UFG copper than in CG copper. Corrosion damage on the surface of UFG copper is macroscopically rather uniform whereas obvious attack at grain boundaries and selective corrosion of some grain interiors were observed in CG copper.     

金属成形过程再结晶与晶体长大演化数值模拟

在金属成形过程中考虑再结晶和晶粒长大,构造热力——组织耦合的有限元程序并嵌入到商业化软件Deform中。模拟了自由镦粗中再结晶和晶粒长大演化过程并分析润滑情况对锻件晶粒度的影响。结果显示,良好的润滑可以改善锻件的变形均匀情况,获得精细均匀的晶粒度。     

Effect of Long-Term 1093 K Exposure to Air or Vacuum on the Structure of Several Wrought Superalloys

Long-term 1093 K heat treatments of three commercial superalloy sheet materials were undertaken in air and vacuum. With either exposure, significant precipitation of second phases occurred in the Co-base Haynes® Alloy 188 (HA 188) and the Ni-base Haynes® Alloy 230 (HA 230); however, much less precipitation was found in the exposed Ni-base alloy Inconel® 617 (IN 617). Although some grain growth occurred in HA 188, no changes in the grain size of either HA 230 or IN 617 were observed after 22,500 h at temperature. Oxidation during air heat treatments led to weight gain due to the formation of chromia + spinel scales and surface-connected grain boundary pits/oxides in all three superalloys. Both the weight gain and depth of intergranular attack were dependent on the square root of time, which is indicative of diffusion-controlled phenomena. Because many alloy samples had neighbors in close proximity, dmost vacuum heat treated specimens did not suffer significant loss of volatile elements. However, some exposed samples were subjected to unrestricted vacuum heat treatments, allowing estimates of volatilization to be made. Based on the data for HA 188, the weight loss during 1093 K vacuum exposure was diffusion controlled once the inhibiting effects of surface films on the as-received alloys were broken down.