In situ deposition behavior of silica-based layers and its effect on thermal degradation of IN713 turbine blades during operation of a micro-gas turbine

This study examined the in situ deposition behavior of silica-based layers on IN713 turbine blades during the operation of a 13 kgf-class gas turbine at a rotation speed of 20,000/min as well as its effect on the degradation of the metallic substrate. Tetraethylorthosilicate (TEOS) was mixed with the fuel (liquid petroleum gas, LPG) and burned to generate silica-based coating precursors for deposition from the flame. Two deposition conditions were adopted. For condition 1 (C1), the silicon-to-carbon ratio in the mixed fuel was set at 0.1 mol% for the first 5 min and at zero mol% for the final 95 min in a 100-min operation. For condition 2 (C2), the ratio was set at 0.005 mol% during the entire 100 min operation. The total TEOS feed was the same under both conditions. C1 resulted in a rather uniform and thicker (5-10 μm on the pressure side) porous silica-based coating on the blade than C2. The in situ deposited layer of C1 was well preserved on the blade and protected the underlying metallic substrate from oxidation during the entire 100 min operation. The layer on the C2 blades was ∼5 μm thick at the region near to root, but was too thin in the other areas on the blade to be protective. The early build-up of a porous layer to an effective thickness on the blades produced a thermal barrier toward the substrate as well as a diffusion barrier toward the oxidizing elements during operation.     

钇,铈对低铪镍基K444返回合金组织与力学性能的影响

研究了Y,Ce对含铪(Hf)镍基铸造高温合金K444返回料(添加50%返回料)合金的力学性能和组织的影响.研究结果表明:适量Y,Ce(Y<0.03%,Ce<0.015%(质量分数))添加到返回料合金后,一方面,Y,Ce具有去除N,O等有害杂质的作用,使O含量由15×10~(-6)降低到8×10~(-6),N含量由35×10~(-6)降低到18×10~(-6),从而使返回料合金得到净化.另一方面,Y,Ce细化了枝晶组织,减少了共晶和大块状碳化物数量,并且强化了晶界.和未加Y,Ce的返回料合金相比.添加Y,Ce使返回料合金室温拉伸强度提高约100 MPa,塑性提高近一倍;使900℃的高温瞬时拉伸性能波动较为平稳,塑性提高近一倍.添加Y,Ce还可以提高返回合金900℃/274 MPa条件下的持久性能,达到新料水平;可以明显延长K444返回合金900℃/274 MPa条件下的蠕变第二阶段,提高蠕变寿命.     

轻质化MA/ODS镍基高温合金高温氧化行为

采用机械合金化(MA)和真空烧结工艺制备了Y2O3质量分数为2%～20%的氧化物弥散强化(ODS)镍基高温合金,在1 000℃空气中对合金试样进行100h的静态氧化实验,研究了Y2O3含量对合金高温氧化性能的影响与作用机制.结果表明:适量稀土氧化物Y2O3的加入(质量分数≤5%)可促进完整Cr2O3氧化膜的形成,提高氧化膜与合金基体的附着力,改善氧化膜的抗剥落性,减缓合金在1 000℃的氧化速度,从而有效提高合金的抗高温氧化性能.但过量添加则会使其抗氧化性能迅速下降.     

GH220合金中晶界针状碳化物的成因

研究了镍基高温合金在1123K,392MPa下周期持久断裂过程中晶界针状碳化物的析出过程。分析了它的形成原因,实验采用二种热处理工艺,得到二种不同的晶界状态:直晶和弯晶。透射电镜分析结果表明,无论何种晶界状态,晶界碳化物都有一个由颗粒状碳化物向针状碳化物转化的过程。而弯晶处理的合金,首先发生由弯晶向平直晶界的转变,即尺寸较大且不规则状的晶界碳化物逐渐断裂成颗粒状排列的晶界碳化物,该过程所需时间较长,这就解释了弯晶合金比如直晶合金针状碳化物量少的原因。提出了一个由颗粒状碳化物向针状碳化物转化的模型。     

高温合金涡轮盘材料的裂纹扩展速率

用直流电位研究了高温合金涡轮盘材料的裂纹扩展速率，结果表明：高温合金涡轮盘材料的裂纺展速率快慢，不完全取决于材料强度，更主要地取决于持久塑性，在考察高温合金涡轮盘材料的裂纹扩展时，不能认速率值ｄａ／ｄＮ的绝对值来衡量，还应看裂纹扩展速率曲线的斜率是否锐减或曲线出现明显的拐点，以及曲线所对应的应力强度因子△Ｋ的范围。     

Effect of H impurity on misfit dislocation in Ni-based single-crystal superalloy： molecular dynamic simulations

The effect of H impurity on the misfit dislocation in Ni-based single-crystal superalloy is investigated using the molecular dynamic simulation.It includes the site preferences of H impurity in single crystals Ni and Ni 3 Al,the interaction between H impurity and the misfit dislocation and the effect of H impurity on the moving misfit dislocation.The calculated energies and simulation results show that the misfit dislocation attracts H impurity which is located at the γ/γˊinterface and Ni₃ Al and H impurity on the glide plane can obstruct the glide of misfit dislocation,which is beneficial to improving the mechanical properties of Ni based superalloys.     

Role of Mg on Structure and Mechanical Properties in Alloy 718

The role of Mg in alloy/718 has been systematically investigated. Mg raises not only high temperature tensile and stress-rupture ductilities but also increases considerably smooth and notch stress-rupture life. Mg containing alloy 718M is free of stress-rupture notch sensitivity. Mg improves creep and fatigue interaction properties (LCF or cyclic stress rupture) at any grain size. The basic role of Mg is equilibrium segregation at grain boundaries which helps to change continuous grain beundary (5-Ni3Nb morphology to discrete globular form which has a retardation effect on intergranular fracture. Mg promotes the change from intergranular to transgranular fracture mode.     

Influence of γ' precipitate on deformation and fracture during creep in PM nickel-based superalloy

FGH96 is a powder metallurgy nickel based superally used for turbine disk of aero-engines. In the present study FGH96 alloy with four different γ' precipitate microstructures were produced via solution heat-treatment with different cooling rates, and the maximum cooling rate reached 400°C/min which was a super cooling rate for Nickel-based superalloy. The creep tests were conducted for PM FGH96 alloy under the testing condition of 704°C and 690 MPa. The relationship between the creep properties and the distribution of γ' precipitate was established. The creep mechanism was analyzed by using TEM and ACTEM, and the dislocation movement was studied at the atomic scale. The creep strain rate was calculated through a physically based crystal slip model established based on crystal plasticity. The calculated results were consistent with the test ones, illustrating the validity of the model. The fracture mechanism was also investigated, and the results showed that the creep cracks generated on the surface due to the oxidation. It was observed that the cracks propagated in different ways depending on the different average diameters of γ' precipitate. With the decrease of the average γ' precipitate size,the critical shearing stress increased and the resistance of the dislocation slipping increased. The fracture mechanism for the primary stage transformed from intragranular to intergranular due to the change of dislocation slipping.