Static and Cyclic Oxidation of Ti–44Al and Ti–44Al–xNb Alloys

Binary, Ti–44Al, and ternary, Ti–44Al–xNb (x=4, 8, and 11) alloys were subjected to static and cyclic oxidation in air up to a period of 1 week at 850 and 950°C. The oxidation behavior is characterized by plotting a graph between weight gain as a function of time or number of cycles. The binary alloy undergoes the most severe oxidation while Nb provides resistance to oxidation, which increases with an increase in concentration. Oxides were examined by SEM and EDX was used to perform chemical analysis. Alternate oxide layers rich in alumina and titania were found along with an aluminum-depleted zone underneath the oxide scale. Different microstructures were observed for the alloys subjected to static- and cyclic-heating modes. Defects like twins and stacking faults were generated after a static mode of heating, while transformation products at the grain boundaries dominate the microstructures for samples subjected to cyclic heating.     

13CrMo44管道的冬季焊接

在新立－新木输油管道改造工程中,管线需要部分更新,管径为 φ２１９ ｍｍ ｘ７ｍｍ,更新长度为１． ８９ ｋｍ。原设计材料为２０号钢,现在用库存１３ＣｒＭｏ４４钢代用。此管线为冬季施工,由于１３ＣｒＭｏ４４管材的特点,脆性大,可焊性较差,易产生冷裂纹。为保证焊接质量,按以下的工艺措施进行施工,采用的工艺参数见下表。 （ｌ）焊前对焊条进行烘干,温度为３５０℃。保温时间为２ｈ,现场施工时用保温筒保温,随用随取。 （２）焊接前对管口两侧２００ｍｍ范围内均匀加热,施工现场用柴油喷灯加热,加热温度为２００℃,预…     

2016年中国技能大赛——第44届世界技能大赛全国选拔赛上海

8月13日,人力资源社会保障部在上海举行2016年中国技能大赛——第44届世界技能大赛全国选拔赛开幕式.人力资源社会保障部部长尹蔚民出席开幕式并讲话,上海市人民政府市长杨雄、世界技能组织首席执行官大卫·霍伊先生出席开幕式并致辞,人力资源社会保障部副部长汤涛主持了开幕式.上海市人民政府副市长时光辉、世界技能组织副主席兼竞赛委员会主任施泰芬·普拉绍尔先生也出席了开幕式.     

Isothermal oxidation behavior of cast Ni-base superalloy K44

The oxidation behavior of a cast Ni-base superalloy K44 in air at 850-1 000℃ for 100 h was studied. The scales on the surface were determined by SEM and EPMA equipped with an EDXS. The results show that oxidation kinetics obey the parabolic law fi＇om which the values of activation energy Qp1=221.1 kJ/mol and Qp2=247.6 kJ/mol are estimated. The oxidation scales are composed of loose outer layer of TiO2/TiO-Cr2O3 and a small amount of NiCr204 and NiAl2O4, compact intermediate layer Cr2O3, and precipitate of internal oxides Al2O3.     

铸造镍基合金K44的高温蠕变行为

研究了铸造镍基高温合金K44在850——900℃，225—380 MPa的高温拉伸蠕变行为，结果表明，实验合金蠕变曲线具有较短的初始阶段和较长的加速阶段，加速阶段较长是由于筏形化的γ粒子和位错相互作用促成的，加速蠕变为应变软化阶段时，可以由关系式ε=εmin(1 c△ε)exp(n△ε)来描述，蠕变断裂数据遵守Monkman-Grant规律，裂纹起源于晶界或枝晶界的空洞。     

Thermomechanical treatment of the elinvar alloy 44NKhMT using plain shear

Conclusions To increase the hardness of products with large cross sections (elastic sensitive elements, parts of measuring apparatus) made of alloy 44NKhMT, while at the same time reducing the temperature coefficient of the modulus of elasticity (to Y_E 9·10^-6 deg^-1), thermomechanical treatment using plain shear strain may be recommended.Physicotechnical Institute, Academy of Sciences of the BSSR; Bardin Central Research Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 30–33, October, 1982.     

新型抗热腐蚀镍基高温合金K44的高温低周疲劳行为

研究了K44合金900℃低周疲劳性能和断裂行为。研究结果表明,该合金在循环形变过程中,首先表现出起始循环硬化或软化,随后循环稳定及最终失稳断裂三阶段。高应变幅下位错切割γ′相形成层错,降低变形阻力,合金表现出循环软化行为;低应变幅下位错在γ′相前塞积造成位错可动性降低,合金表现出循环硬化行为。疲劳裂纹主要萌生于试样表面或近表面缺陷处,以穿晶方式扩展;合金基体中块状碳化物对裂纹扩展起阻滞作用。     

Microstructure observations in rare earth element Gd-modified Ti-44 at% Al

Rare earth element Gd (0.15 at%) was added to Ti-44 at% Al to refine the microstructure. Almost all of the Gd atoms were found to form an oxide phase which was tentatively identified as Gd₂TiO₅. In the as-cast ingot the oxide phase possessed a complicated “finger” shaped morphology and formed a networked structure between the primary crystals. This morphology was broken down in the subsequent heat treatment at 1350°C to become discrete particles in the form of particulate, platelets or rods, often with a faceted appearance, although clusters of the particles reminiscent of their as-cast morphology were common. The distribution of the particles was improved by hot pressing which appeared to reduce the particle size and de-cluster them. Although the particles were not actually pinning the grain boundaries, their distribution seemed to have a significant effect on lamellar grain sizes after heat treatment. The addition of Gd appeared also to promote the formation of lamellae during cooling.     

Defect band formation in high pressure die casting AE44 magnesium alloy

The characteristics of defect bands in the microstructure of high pressure die casting (HPDC) AE44 magnesium alloy were investigated. Special attention was paid to the effects of process parameters during the HPDC process and casting structure on the distribution of defect bands. Results show that the defect bands are solute segregation bands with the enrichment of Al, Ce and La elements, which are basically in the form of Al₁₁RE₃ phase. There is no obvious aggregation of porosities in the defect bands. The width of the inner defect band is 4–8 times larger than that of the outer one. The variation trends of the distribution of the inner and outer defect bands are not consistent under different process parameters and at different locations of castings. This is due to the discrepancy between the formation mechanisms of double defect bands. The filling and solidification behavior of the melt near the chilling layer is very complicated, which finally leads to a fluctuation of the width and location of the outer defect band. By affecting the content and aggregation degree of externally solidified crystals (ESCs) in the cross section of die castings, the process parameters and casting structure have a great influence on the distribution of the inner defect band.

     

参加ISO/TC44第28届全会的报告

2007年7月9～12日,ISO/TC44第28届全体会议及有关分技术委员会（SC3,SC7）会议在法国巴黎召开。笔者以中国代表的身份参加了这些会议,会议的有关情况报告如下。     

Validated numerical modelling of galvanic corrosion for couples: Magnesium alloy (AE44)-mild steel and AE44-aluminium alloy (AA6063) in brine solution

A numerical model is presented in this work that predicts the corrosion rate of a galvanic couple. The model is capable of tracking moving boundary of the corroding constituent of the couple. The corrosion rates obtained from the model are compared with those estimated from mixed potential theory and two experimental techniques, namely Scanning Vibrating Electrode Technique (SVET) and immersion technique. The corrosion rates predicted using the model are in good agreement with those estimated from the experimental techniques for magnesium alloy AE44-mild steel couple, however, the model under predicts the corrosion rate for AE44-aluminium alloy AA6063 couple.     

Effects of lanthanum on structures and grain sizes of Ti-44Al alloy

１　ＩＮＴＲＯＤＵＣＴＩＯＮＴｉＡｌｂａｓｅｄｉｎｔｅｒｍｅｔａｌｌｉｃａｌｌｏｙｓｈａｖｅｂｅｅｎｅｘｐｅｃｔｅｄａｓａｎｅｗｋｉｎｄｏｆａｉｒｃｒａｆｔａｎｄａｅｒｏｓｐａｃｅｍａｔｅｒｉａｌｔｏｓｕｂｓｔｉｔｕｔｅｆｏｒＮｉ３ＡｌａｎｄＦｅ３Ａｌａｌｌｏｙｓｏｗｉｎｇｔｏｔｈｅｉｒｈｉｇｈｔｏｕｇｈｎｅｓｓａｔｅｌｅｖａｔｅｄｔｅｍｐｅｒａｔｕｒｅａｎｄｌｏｗｄｅｎｓｉｔｙ［１～３］．Ａｇｒｅａｔｎｕｍｂｅｒｏｆｒｅｓｕｌｔｓｆｒｏｍｏｔｈｅｒｒｅｓｅａｒｃｈｅｒｓｓｈｏｗｔｈａｔｍｉ…     

NUMERICAL SIMULATION OF COLUMNAR TO EQUIAXED TRANSITION FOR DIRECTIONALLY SOLIDIFIED Ti-44Al ALLOY

Solute diffusion controlled solidification model was applied to simulate the columnar to equiaxed transition (CET) during directional solidification of Ti-44Al alloy. The simulation results show that the solutal interactions from growing equiaxed grains play an important role on CET. The effects of the applied thermal gradient and pulling velocity, the equiaxed seed spacing and nucleation undercooling on the CET are investigated in the present simulation. The simulated results indicated that the columnar branch spacing depends not only on the thermal gradient and the pulling velocity, but also on number of the seeds. A spacing adjustment can occur through initiation of seeds that develop into new columnar grains. The dependence of the CET on the thermal gradient and pulling velocity, qualitatively agrees with the analytical CET model of Hunt.