Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： The effect of alloying element V on the microstructure and high temperature creep properties of a diretional solidified nickel-base superalloy was researched by varying the amount of V addition. The alloy composition was set in a controlled fixedness except for element V, and then the effect of V can be assessed. The alloys were directionally solidified by utilizing Bridgeman casting process and followed by appropriate post heat treatment. The microstructure and high temperature creep properties of the prepared alloys were then characterized. The results shown that, with lower amount of V addition, the alloying V existed mainly in acicular type carbides rather than in blocky type carbides; while for the higher addition of V, the shape of vanadium carbides in the alloys transition from acicular type to blocky type. When the V content reaches 1.04 % in the alloy, the shape of carbides has been transformed into blocky type completely. After solid solution treatment, the carbides in the alloy were dissolved partly, and the acicular carbides in the alloy with lower V content dissolved much more than the blocky carbides in high V content alloy. Under the condition of 980℃/216 MPa and 760℃/725 MPa, the stress rupture life is shorter for the alloy with lower V content, but loger for that with higher V content. The amount of M23C6 type carbide precipitated at grain boundaries in the alloy with higher V content is less than that with lower V content during creep test and aging heat treatment. During creep test, cracks initiate and grow mainly at the MC type carbide within grains or the M23C6 type carbides precipitated at the grain boundaries. Therefore, the increase of V content is of benefit for the improvement of creep life of the alloy.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Single crystal nickel-based superalloys mainly consisting of g and g ' phases are widely used in turbine blades for their excellent mechanical performances, in particular creep resistance at high temperatures. The creep properties of single crystal superalloys are inherently anisotropic. Although commercial single crystal superalloys are all along <001> orientation, it is difficult to ensure the exact orientation during production, and in service the applied centrifugal force on blades unavoidably deviates from <001> orientation, so the study on non-<001> oriented single crystal superalloys is significant on improving the creep theory of superalloys. Compared with the <001> oriented single crystal superalloys, the <011> oriented ones generally display poor creep resistance. Through pre-rafting treatment of g ' phase in <001> oriented single crystal superalloys, the creep resistance of the alloys are expected to be enhanced by changing the deformation mechanism, especially by hindering dislocation movements, but the effect of the treatment on <011> oriented alloys is still not clear. For this reason, by means of pre-compression, creep tests and microstructure observation, the effect of the pre-rafting of g ' phase on creep behavior of a [011] oriented single crystal nickel-based superalloy at 1040 ℃, 137 MPa is studied. Results show that after pre-compression at 1040 ℃, 180 MPa along [100] orientation for 38 h, the g ' phase in the [011] oriented alloy has transformed into P-type rafted structure parallel to the compressive stress axis. Different strain energy density distribution and lattice strain on crystal planes during pre-compression are the main reasons for the rafting behavior of g ' phase. Dislocations slipping in g matrix channels is the main deformation mechanism of the [011] oriented alloy with and without pre-compression. Thereinto, many dislocations-climbing movements occur in the pre-compressed one. The lateral pre-compression remarkably improves the creep strength of the alloy at 1040 ℃, 137 MPa. The elimination of gable channels, relatively narrow roof channels during steady-state creep stage, the formation of micro-bottleneck-like channels and labyrinth-like microstructures due to the lateral growth of g ' rafts, and the more effectively activated slip systems of dislocations are beneficial to impeding dislocation movements and responsible for the better creep resistance of the pre-compressed alloy.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Due to its excellent ductility and moderate strength, QT400-18L ferrite ductile iron has been widely used in producing core components of wind power equipment such as the hub of a wind turbine. Most of the researches have focused on the exploration of mechanical properties at low temperature, but none of them give the explanation on microcosmic mechanism of ductile iron during low temperature impact and the mechanism of crack nucleation and propagation of ferrite ductile iron during impact fracture has not been analyzed. In this work, the impact toughness of QT400-18L ferrite ductile iron was measured by V-notch Charpy impact test at different temperatures, the influence of low temperature impact toughness and the fracture behavior of ferrite ductile iron were discussed. The results show that the cleavage fracture resistance of QT400-18L ferrite ductile iron is reduced with the decrease of impact temperatures. Above ductile-brittle transition temperature (DBTT), most of the total fracture energies are expended during the crack propagation process. Below DBTT, both crack initiation energy and crack propagation energy decrease obviously. By using in situ fracture metallographic observation method, crack initiation and propagation of QT400-18L ferrite ductile iron under different temperatures were analyzed. Above DBTT, graphite nodules play the role of crack blunting and reducing crack propagation rate; in DBTT range, the fracture morphology shows mixed fracture with cleavage and dimples, which are related to graphite nodules; below DBTT, deformation twins lead to the nucleation of microcrack and result in cleavage fracture, the deformation twinning could possibly play a significant role in the ductile to brittle transition of QT400-18L ferrite ductile iron.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni-based single crystal (SC) superalloys have been widely used to produce turbine blades of aeroengines, but under the action of centrifugal force, creep damage is still the main failure mode. In service, the blades experience multiple cycles of various conditions of high temperatures, low stresses and intermediate temperatures, high stresses, and due to effective and efficient means of cooling and insulating the blades during operation, the actual temperature the blades bear can be smaller than the working temperature at the hot ends of aeroengines, so the systematical study on the creep behavior of SC superalloys at intermediate temperatures, high stresses is significant. It is generally considered that dislocations cutting g′ phase is the main deformation mechanism of SC alloys at intermediate temperatures, high stresses, and dislocations cutting into g′ phase can be decomposed into different configurations for different alloy systems, even under similar conditions. Moreover, large amount of dislocations cutting into g′ phase means the degradation of creep performance of the alloys, so it is significant to study the cutting modes of dislocations. In this work, by means of creep tests, TEM observations and diffraction contrast analysis of dislocations, the deformation mechanisms of a Ni-based SC superalloy during steady-state creep at intermediate temperatures, high stresses are studied. Results show that, under the conditions of 760 ℃, 760 MPa and 800 ℃, 650 MPa, dislocations cutting into g′ phase are decomposed to form partial dislocations plus superlattice intrinsic stacking faults (SISF). Thereinto, the leading a/3<112> super Shockley partial dislocations cut into g′ precipitates, while the dragging a/6<112> Shockley partial dislocations remain at g′/g interfaces, and between them there exists SISF. Additionally, super dislocations shearing into g′ phase can cross slip from {111} to {100} crystal planes to form Kear-Wilsdorf (K-W) locks with non-plane dislocation core structure, which can inhibit the slip and cross slip of dislocations to enhance the creep strength of the alloy. At 850 ℃, 500 MPa, stacking faults disappear in the alloy, and some a<110> super dislocations cutting into g′ rafts can be decomposed to form the configuration of two partial dislocations with Burgers vector of a/2<110> plus antiphase boundary (APB), and K-W locks are released for high-temperature thermal activation results in the cross slip of dislocations from cubic slip systems to octahedral ones.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： TiN-Cu nanocomposite films were deposited on high speed steel by arc ion plating with an axisymmetric coil magnetic field at the back of the target. The influence of the coil magnetic field intensity on the moving rate of cathode spot and arc column shape on the target surface, as well as on the surface morphology, deposition rate, nanoindentation hardness and elastic modulus of the deposits was investigated. It is shown that the emitting probability of the melt metal drops on the target decreases, and the size and quantity of the macroparticles in the deposited films reduces with the increasing coil magnetic field intensity. The deposited films consists merely of TiN phase without metal Cu phase or Cu compound and possess an obvious preferred orientation along (111) plane. The deposition rate, indentation hardness and elastic modulus of the films increase rapidly to a maximum value and then decrease slightly with the increasing coil magnetic field intensity. The maximum values of hardness and elastic modulus are 35.46 GPa and 487.61 GPa, respectively.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Magnetic characteristics of the as-quenched fully and partially amorphous Al85Ni5Y4Fe2Co2 alloy were measured by VSM (vibrating sample magnetometer). The results show that the magnetization curves of the two alloys pass the origin of coordinates and extend through the first and the third quadrants, no remanence and coercivity were observed. The magnetism of the fully and partially amorphous alloys is all a combination of paramagnetism and diamagnetism. The magnetic susceptibility of the fully amorphous alloy is 2.41×10- 4 and that of the partially amorphous alloy is 2.73×10- 4. The magnetisms of the alloys annealed at 330℃and 390℃ were also tested respectively. The magnetic susceptibility of the linear portion of the magnetization curve increases from 2.53×10-4 to 2.81×10-4 as the annealing temperature rises from 330℃ to 390℃. The hybrid microstructures of the alloys may account for the evolution of the corresponding magnetisms.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：采用粉末靶射频磁控溅射方法，制备非晶Al2O3薄膜，分析了溅射工艺参数对Al2O3薄膜微观结构、表面形貌、光学性能的影响规律及机理，并探究其抗菌特性。研究结果表明：增加氧通量、降低溅射功率和缩短溅射时间均会减小非晶Al2O3薄膜颗粒度与粗糙度，同时也降低薄膜的沉积速率；并且，氧通量的增加和溅射时间的缩短均会使非晶Al2O3薄膜禁带宽度变宽（最大值可达4.2eV）、透光率增大（超过90%）；光照条件下非晶Al2O3薄膜24h抗菌率最高可达98.6%，体现出了较好的光催化抗菌性。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：为了确定稀土元素Sc对T6态铸造Al-9.0%Si-4.0%Cu-0.4%Mg合金的低周疲劳行为的影响规律，针对T6态铸造Al-9.0%Si-4.0%Cu-0.4%Mg合金和Al-9.0%Si-4.0%Cu-0.4%Mg-0.3%Sc合金的低周疲劳行为进行了对比研究. 结果表明，在低的外加总应变幅下，Al-9.0%Si-4.0%Cu-0.4%Mg合金在整个疲劳变形期间均表现为循环应变硬化，Al-9.0%Si- 4.0%Cu-0.4%Mg-0.3%Sc合金在疲劳变形初期表现为循环应变硬化，在疲劳变形后期则表现为循环稳定；而当外加总应变幅较高时，Al-9.0%Si-4.0%Cu-0.4%Mg(-0.3%Sc) 合金均呈现循环应变硬化. 稀土元素Sc的加入可以有效地提高T6态Al-9.0%Si-4.0%Cu-0.4%Mg合金的循环变形抗力和低周疲劳寿命. 在较低的外加总应变幅下，T6态Al-9.0%Si- 4.0%Cu-0.4%Mg(-0.3%Sc) 合金的循环变形机制为平面滑移，而当外加总应变幅较高时则为波状滑移机制.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：研究了Inconel 625镍基合金焊接接头在 25 ℃和 760 ℃温度条件下的低周疲劳行为。分析了在上述两个温度下的循环应变—疲劳寿命数据和应力—应变数据，进而给出了Inconel 625合金在此温度范围的疲劳参数。结果表明：合金在不同温度条件下进行低周疲劳后的弹性应变幅和塑性应变幅与载荷反向周次的关系可分别用Basquin和Coffin-Manson公式来描述；在25 ℃时合金的循环应力响应行为主要为循环软化；而在760 ℃时，主要呈现为循环硬化。上述行为归因于循环形变过程中位错—位错，位错—孪晶界以及位错—析出相间的相互作用。
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