短时氧化对定向凝固高温合金不同取向腐蚀性能的影响

为了研究定向凝固高温合金不同取向氧化前后的常温腐蚀性能,选择镍基高温合金DZ125和钴基高温合金DZ40M在1050℃下进行不同时间的短时氧化,研究合金不同取向的氧化行为;对氧化前后合金在3.5%NaCl溶液中进行电化学实验,研究氧化对定向凝固高温合金不同取向常温腐蚀性能的影响。结果表明:定向凝固高温合金晶界或亚晶界附近容易发生局部腐蚀,纵截面晶界和亚晶界面积分数小,因此耐蚀性优于横截面;与合金横截面相比,纵截面晶界结构不利于扩散,故其氧化速率小于横截面;短时氧化后在合金表面生成分层结构的氧化物,对合金起到保护作用,一定程度上提高耐蚀性。     

真空热处理对激光近净成形In625和C-276合金性能的影响EI北大核心CSCD

对激光近净成形两种镍基高温合金Inconel 625和Hastelloy C-276分别进行热处理实验,然后分析热处理工艺参数对合金室温拉伸性能的影响。结果分析表明:在800,900℃去应力热处理后,Inconel 625合金抗拉强度提升不明显,而在1000℃以上进行固溶处理后,合金抗拉强度得到提高。1100℃热处理后,Inconel 625合金的抗拉强度与沉积态相比得到明显提高。在800,900℃去应力热处理后,Hastelloy C-276合金强度也未明显提高,而在1000℃以上进行热处理,随着热处理温度提高,合金抗拉强度逐渐升高。1150℃进行热处理后,Hastelloy C-276合金的抗拉强度与沉积态相比得到明显提高。激光近净成形工艺制备的两种镍基高温合金室温拉伸断裂方式为韧性断裂。     

镍基单晶高温合金涡轮叶片缘板杂晶的研究进展

镍基单晶高温合金涡轮叶片缘板杂晶的出现严重影响叶片的力学性能,导致叶片报废。综述了关于缘板杂晶的形成本质的研究,总结了不同影响因素对缘板杂晶形成的影响及原因并概况了几种不同杂晶的控制方法,指出了以往研究中存在的问题,展望了未来研究的方向。     

冷拉减面率对C形环用Inconel X-750丝材组织性能的影响

文章通过冷拉拔加工制备减面率为0%、30%、60%的Inconel X-750丝材,分别在650℃、730℃、810℃下时效处理16h,研究冷拉减面率对X-750合金组织性能的影响,特别是减面率对γ′相形状、分布、数量及尺寸的影响。经定量分析,增大冷拉减面率除了有细化晶粒的作用外,还能一定程度地增加γ′相析出的颗粒数量及体积分数,减小γ′相尺寸,进一步加强沉淀强化的作用。时效温度对X-750丝材的晶粒尺寸没有明显影响,对γ′相的数量、尺寸及形状影响较大。采用730℃时效处理16h的标准工艺制备的X-750丝材,经加工为弹簧后制造成金属C形密封环,其回弹量及泄漏率均满足要求,实验条件下密封性能良好。     

镍基单晶合金中温疲劳性能应力集中敏感性

疲劳是涡轮叶片的一种主要失效模式.本文开展了DD11单晶合金在650℃中温条件下2种应力集中系数(K_t=1(光滑状态)、K_t=3(缺口状态))的旋转弯曲疲劳性能研究,对比了2种应力集中系数下的疲劳强度,并开展了相关断口分析.结果表明:应力集中系数由K_t=1增大到K_t=3时,疲劳极限由446 MPa降低为311 MPa,说明DD11单晶合金疲劳性能存在应力集中敏感性;疲劳寿命由10~5提高到10~7时,光滑状态由600 MPa降低为420 MPa,疲劳强度降低幅度为180 MPa,而缺口状态由370 MPa降低为290 MPa,降低幅度为80 MPa,说明应力集中条件下DD11单晶合金的疲劳寿命对于外载变化较敏感.断口分析表明,光滑试样断口(应力500 MPa/疲劳寿命9.7×10~5)由几个相交的光滑晶体学平面组成,疲劳源萌生在距表面100μm左右的铸造孔洞;缺口试样断口(应力340 MPa/疲劳寿命8.1×10~5试样)呈平面状,与应力轴垂直,为多源疲劳模式,疲劳源观察到小刻面,在加工刀痕不连续位置萌生.     

Characteristic study of N07718 superalloy surface prepared by cold spray

For better performance in erosive–corrosive, wear and other extreme environmental conditions surface properties of metals and alloys are usually altered by different techniques. Amongst the various surface coating techniques cold spraying is a relatively new and less reported method. Coating formation at energy lower than the melting stage of materials brings novelty to this process. In this study surface of UNS No. - N07718 alloy is altered by cold spraying chromium-carbide (nickel-chromium) layer. The microstructure properties of this cold sprayed surface are observed by various characterization techniques and the results are used to study mechanism of coating layer formation by cold spray process. This newly developed cold sprayed surface is found to be eligible for further testing in wear and erosive-corrosive environmental conditions.     

Stress dependence of the creep behaviors and mechanisms of a third-generation Ni-based single crystal superalloy

Elevated temperature creep behaviors at 1100℃ over a wide stress regime of 120–174 MPa of a thirdgeneration Ni-based single crystal superalloy were studied. With a reduced stress from 174 to 120 MPa,the creep life increased by a factor of 10.5, from 87 h to 907 h, presenting a strong stress dependence.A splitting phenomenon of the close-(about 100 nm) and sparse-(above 120 nm) spaced dislocation networks became more obvious with increasing stress. Simultaneously, a_0010 superdislocations with low mobilities were frequently observed under a lower stress to pass through γ'precipitates by a combined slip and climb of two a_0110 superpartials or pure climb. However, a_0110 superdislocations with higher mobility were widely found under a higher stress, which directly sheared into γ'precipitates.Based on the calculated critical resolved shear stresses for various creep mechanisms, the favorable creep mechanism was systematically analyzed. Furthermore, combined with the microstructural evolutions during different creep stages, the dominant creep mechanism changed from the dislocation climbing to Orowan looping and precipitates shearing under a stress regime of 137–174 MPa, while the dislocation climbing mechanism was operative throughout the whole creep stage under a stress of 120 MPa, resulting a superior creep performance.     

Characterization of centrifugally atomized Al-12Si-5Fe-3Cu-1Mg(wt%) alloy powder and extruded rod

The Al-12Si-5Fe-3Cu-1Mg(wt%) alloy was rapidly solidified by centrifugal atomization. The microstructural characteristics of rapidly solidified powder and the microstructure changes with heat treatment were investigated in terms and related to powder size. The microstructures of the powder consisted of dendritic -Al, eutectic phase, Cu-rich phase, and needle-like intermetallic compounds. These phases were much finer than that of ingot cast structure and the size decreased with increasing cooling rate. The X-ray diffraction of the atomized powders revealed the presence of non-equilibrium 3-(AlFeSi) intermetallic phase. This phase appeared to transform to an equilibrium -(AlFeSi) phase by heating at temperatures above 470°C. The extruded rod which was hot extruded at 360°C with an extrusion ratio of 40:1 also revealed the presence of the -(AIFeSi) intermetallic phase. Using DSC, the exothermic peak due to precipitation from the supersaturated -Al matrix was observed in the range of 200–250°C during continuous heating of atomized powder, and the size of the peaks increased with decreasing powder size.     

Oxidation behaviors of Ni-Cr-Al superalloy foams at 1 000 ℃ in air

The oxidation behaviors of Ni-16Cr-xAl （x=4.5%, 9.0%, mass fraction） superalloy foams in air at 1000℃ were investigated. The effects of AI content on the resistance to high temperature oxidation were examined. The oxidation mechanisms of the foams were discussed. The results show that the resistance to the oxidation of the Ni-16Cr-xA1 based alloy at 1 000 ℃ increases with the content of A1 increasing from 4.5% to 9.0%. Complex oxide products are formed on the surface of the superalloy foams after the oxidation. Cr203 and A1203 are the predominant oxides for the scales of the foams with 4.5% A1 and 9% A1, respectively. Excellent high temperature oxidation resistance and superior pore conformation stability for the Ni-16Cr-xA1 based superalloy foam with 9% A1 can be mainly attributed to the formation of relatively continuous and protective A1203 oxides on the surface of the foam.     

A modern and robust methodology for modeling anisotropic creep characteristics of Ni-based DS and SC superalloys

According to more recent work,the Wilshire equations have shown good prediction accuracy in a wide range of materials and stress-temperature conditions,particularly in extrapolation of short term results to long term predictions.In the current paper,this methodology was further developed for modeling anisotropic creep characteristics(i.e.minimum creep strain εmin ,stress rupture life tf and time to a specified strain tε)of four typical Ni-based directionally solidified(DS)and single crystal(SC)superalloys,where a simple orientation factor related to the ultimate tensile strength(UTS)was introduced.The application of these simplistic approaches showed that the anisotropic creep characteristics in a wide range of stress-temperature conditions can be accurately simulated.Meanwhile,during the application of the modified Wilshire equations,break points occurring at the specified stress levels agree well with the transition of creep deformation mechanisms occurring in different stress regions,which provides confidence for using this method.