加热炉用钴合金Co-20耐热垫块改进试验

基于钴基合金Co-20的主要成分，采用双真空冶炼和熔模铸造，试制了铸坯加热炉用钴合金耐热垫块。检测结果表明，试制合金的硬度、耐磨性和高温抗氧化性均优于Co-20。试制垫块在武汉钢铁(集团)公司第一热轧厂3#加热炉试用，情况良好。     

Insight of the dendrite deformation in Ni-based superalloys for increased misorientation along convergent boundaries

The dendrite growth and the associated misorientation evolution on the platform base of a single crystal investment casting were investigated. It was found that the long secondary dendrite arm(LSDA) grew through the whole platform, and a convergent boundary of dendrite arms(CBDA) formed simultaneously between the corresponding branched arms and the extended secondary arms from the blade zone. The corresponding orientation measurement confirmed that the misorientation of dendrite arms between the two sides of the CBDA monotonically increased from 5.9° at one platform edge to 33.5° at the other platform edge. Additionally, the LSDA dendrite deformation was also identified by the accumulated misorientation within the LSDA dendrite core. Furthermore, it was deduced that the increased misorientation along the CBDA was caused by the LSDA dendrite deformation, and the reason of LSDA dendrite deformation was further discussed based on the associated strain distribution around the LSDA. Because of a 33.5° misorientation along the CBDA, it was indicated that the dendrite deformation might be the formation mechanism of high angle boundary.     

硬质合金刀具铣削镍基单晶高温合金DD5磨损试验

为探究在干切削和水基微量润滑(WMQL)条件下刀具磨损对DD5铣削表面质量的影响规律,采用四刃PVD-TiAlN涂层硬质合金刀具以及超景深显微镜和扫描电镜等设备,以刀具副后刀面磨损宽度为主要评价指标,对硬质合金刀具副后刀面磨损形态、磨损机理进行分析和研究,并采用三维轮廓仪对零件表面粗糙度进行测量.研究结果表明,与干切削相比,采用水基微量润滑冷却技术,能够延长刀具寿命并改善材料的铣削加工性;硬质合金刀具的主要磨损机理为粘结磨损、磨粒磨损、氧化磨损和扩散磨损.     

A crystallographic model for the orientation dependence of low cyclic fatigue property of a nickel-base single crystal superalloy

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Meso approaches for the creep damage behavior of nickel-base directionally solidified superalloys

IntroductionNickel-basehightemperatureresistancesuperalloysarsewidelyusedingasturbinesandjetengines.DireetionallysolidificationwasintroducedtoenhancecreepsbengthbyelindnahnggrainboundariesnormaltotheappliedstresswherevoidsarelikelytOoccurundercreepload.Inpractice,however,theappliedstressmaynotbeuniaxialnordirectedparalleltOthegrainboundaries.Singlecrystalswerethusdeveloped.CongregationoflowtempefAnremeltingelementsongrainboundaries,grainboundaryoxidation)etc.,areadditionalfactorsthatwoulddeg…     

Research on the processing experiments of laser metal deposition shaping

Laser additive direct deposition of metals is a new rapid manufacturing technology, which combines with computer-aided design (CAD), laser cladding and rapid prototyping. The advanced technology can build fully dense metal components directly from CAD files with neither mould nor tool. Based on the theory of this technology, a promising rapid manufacturing system called “Laser Metal Deposition Shaping (LMDS)” has been constructed and developed successfully by Chinese Academy of Sciences, Shenyang Institute of Automation. Through the LMDS system, comprehensive experiments are carried out with nickel-based superalloy to systematically investigate the influences of the processing parameters on forming characteristics. By adjusting to the optimal processing parameters, fully dense and near-net-shaped metallic parts can be directly obtained through melting coaxially fed powder with a laser. Moreover, the microstructure and mechanical properties of as-formed samples are tested and analyzed synthetically. As a result, significant processing flexibility with the LMDS system over conventional processing capabilities is recognized, with potentially lower production cost, higher quality components, and shorter lead-time.     

Molecular dynamics study of mosaic structure in the Ni-based single-crystal superalloy

The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed three-dimensional misfit dislocation network, with index of $\langle 011\rangle${\{}100{\}} and the side length of the mesh 89.6\,{\AA}, is formed around a cuboidal $\gamma '$ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the $\gamma $ and $\gamma '$ phases as well as the $\gamma $/$\gamma '$ interface direction, but is independent of the size and number of the cuboidal $\gamma '$ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal $\gamma '$ precipitate, i.e.~the amount of the dislocation is proportional to the total area of the $\gamma $/$\gamma '$ interface, which may be used to explain the relation between the amount of the fine $\gamma '$ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.     

Very-High-Cycle-Fatigue of in-service air-engine blades, compressor and turbine

In-service Very-High-Cycle-Fatigue(VHCF)regime of compressor vane and turbine rotor blades of the Al-based alloy VD-17and superalloy GS6K,respectively,was considered.Surface crack origination occurred at the lifetime more than 1500 hours for vanes and after 550 hours for turbine blades.Performed fractographic investigations have shown that subsurface crack origination in vanes took place inspite of corrosion pittings on the blade surface.This material behavior reflected lifetime limit that was reached by the criterion VHCF.In superalloy GS6K subsurface fatigue cracking took place with the appearance of flat facet.This phenomenon was discussed and compared with specimens cracking of the same superalloy but prepared by the powder technology.In turbine blades VHCF regime appeared because of resonance of blades under the influenced gas stream.Both cases of compressor-vanes and turbine blades in-service cracking were discussed with crack growth period and stress equivalent estimations.Recommendations to continue aircrafts airworthiness were made for in-service blades.     

High temperature tensile properties and fracture behavior of cast nickel-base K445 superalloy

The tensile properties and fracture behavior of a cast nickel-base superalloy K445 in the temperature range of 25-1 000℃were investigated.The microstructure and fracture surfaces of the alloy were investigated by OM,SEM and TEM.The results revealed that an anomalous yield strength phenomenon exists in the alloy at medium high temperature.The yield strength decreases gradually with the increase of temperature,reaches the minimum value at 650℃,and then increases again to obtain 940 MPa,which is almost the ...     

Effect of cyclic recovery heat treatment on surface recrystallization of a directionally solidified superalloy

Microstructural evolution and micro-har dness of a directionally solidified Ni-bas e superalloy subjected to shot-peening during cyclic recovery heat treatment was studied. It was found that γ′ dissolved and dislocation annih ilation occurred during heating, while γ′ re-precipitated when temperature dropped. Due to the formation of a stable dislocation network at γ/ γ′ interface, full recovery and therefore complete elimination of the surface recrystallization are difficult by the present cyclic recovery heat treatment .