单颗团聚CBN磨粒磨削TC4钛合金表面创成机制

目的 提出一种兼具耐磨性好、自锐性能优异的新型团聚CBN磨粒研制方法,解决单晶CBN磨粒因其力学特性各向异性而极易出现沿解理面大块破碎的问题,进而提升加工效率和磨削性能。方法 利用模压成形和高温液相烧结技术,制备了综合性能优异的新型团聚CBN磨粒,探究磨粒结合界面形成机制,并通过单颗磨粒磨削TC4钛合金试验,综合对比团聚CBN磨粒与单晶CBN磨粒的磨损状态和磨痕形貌,探明团聚CBN磨粒的磨削性能优势。结果 团聚CBN磨粒烧结界面新生成了TiB2、TiB和TiN;优选的烧结工艺参数为800 ℃,保温时间为10 min;相比于单晶CBN磨粒,团聚CBN磨粒的耐磨性和锋利度显著提升,磨削加工效率和质量明显改善。结论 由于团聚CBN磨粒内部微晶颗粒间金属结合剂的存在,提高了磨粒的断裂韧性,降低了因磨粒内部裂纹扩展而引起的宏观裂纹损伤深度,有效提升了磨粒的加工性能;磨削过程中随着磨粒的不断磨损,未出露的CBN晶粒逐渐参与磨削,确保了磨粒工作面有效磨粒数的动态平衡,有助于提升磨粒整体自锐能力。     

Oxidation resistance of SiCf/SiC composites with three-layer environmental barrier coatings up to 1360 °C in air atmosphere

Atmospheric plasma spraying (APS) was used to prepare three-layer environmental barrier coatings (EBCs) Si/Yb₂SiO₅/LaMgAl₁₁O₁₉ (LMA) on a SiC_f/SiC substrate. Isothermal aging test of the specimens were performed between 1000 and 1360 °C for 500 h. The flexural strength of the specimens after isothermal aging was investigated. Microcracks and holes were observed in the as-sprayed EBCs because of the shock cooling during the APS process, but reduced after isothermal aging, and the EBCs became denser. At least 80.07% of the flexural strength of the SiC_f/SiC substrate with EBCs was maintained after isothermal aging, but only 35.91% strength was maintained without EBCs. In particular, the retention ratio of flexural strength was 90.72% after isothermal aging at 1360 °C, despite a reaction between the layers of the EBCs. All the specimens with EBCs showed “pseudo-plastic” fracture, compared with the brittle fracture of specimens without EBCs.     

固溶温度对GH4720Li合金显微组织和力学性能的影响

通过光学显微镜、场发射电镜和力学性能测试,研究了固溶温度对GH4720Li合金显微组织(晶粒、γ′相)及力学性能的影响。结果表明:随着固溶温度的升高,一次γ′相含量减少,三次γ′相尺寸增大,晶粒长大的趋势也变得明显。当固溶温度超过1120 ℃后,一次γ′相回溶迅速,晶粒长大迅速,晶粒尺寸分布不均匀性增加。固溶温度与强度呈抛物线性关系,在1130 ℃强度出现峰值;固溶温度的升高,合金塑性下降,固溶温度超过1100 ℃时塑性下降得更快。680 ℃/830 MPa持久拉伸试验表明,随着固溶温度的提高,持久时间增加,当固溶温度超过1100 ℃持久时间增加明显,但超过1130 ℃持久时间基本不变;随着固溶温度的提高,持久塑性下降,但在1110 ℃之前下降缓慢,超过该温度塑性降低很快,甚至不达标。并讨论了固溶温度-组织-力学性能之间的关联性,该结果为GH4720Li合金盘件的固溶热处理工艺的选择提供了理论参考。     

某型航空发动机轴承环下润滑结构试验

以某型航空发动机轴承环下润滑结构为基础开展了轴承环下润滑结构的试验。通过对试验轴圆心位置在轴向集油环端面内侧和外侧2种方案试验对比发现,在内侧时改进润滑油入射点位置和集油腔空间后,试验过程中轴承温度和箱体振动变化平稳,试验后轴承未出现由于润滑不良而失效的情况。     

Preparation of submicron CdSxSe1-x@ZrSiO4 inclusion pigment and its application in ink-jet printing

A zircon-based inclusion pigment (CdS_xSe_1-x@ZrSiO₄) for ink-jet printing was successfully synthesized by calcining the precursor formed by coprecipitation of Si⁴⁺ and Zr⁴⁺ on the SiO₂ shell of CdS_xSe_1-x@SiO₂ with PAAS as a surfactant. The pigment with cubic or spheroidal morphologies was fully encapsulated within an intact and dense ZrSiO₄ shell, and the particle size was concentrated between 500 nm and 800 nm. The intact inclusion structure of the pigment particles was not easily damaged in the grinding stage of ink. The inclusion pigment, which was prepared in the optimum condition of pH value of 7.2 ± 0.2 for coprecipitation, calcination temperature of 900–950 ℃ and soaking time of 30 min, has a high quality of red hue, achieving the chromaticity values of L* = 62.03, a* = 27.35 and b* = 19.64, respectively. The red ink made from this pigment has a good thermal stability and color effect in glazes after calcination at 1210 ℃ for 30 min.     

Damage analysis of a SiCf/SiC ceramic matrix composite under stepwise fatigue loading with acoustic emission

Continuous fiber-reinforced ceramic matrix composites (CMCs) exhibit different damage mechanisms at multiple scales under cyclic loading. In this paper, the tension-tension fatigue behavior of a plain woven SiC_f/SiC CMC was investigated, and damage accumulation and evolution process were studied in detail via acoustic emission (AE) method. With the increase of cycles, the material exhibits obvious hysteresis behavior affected by interfacial slip and wear mechanisms. Most of the fibers with radial fracture characteristic have relatively high strength, showing excellent toughening property. In the stepwise cyclic loading process, the Kaiser effect of AE determines the initiation of AE activities at each initial loading moment, which shows obvious nonlinear damage accumulation behavior of the material. High-energy events are related to significant matrix cracking and fiber fracture, and the evolution process of material damage initiation and propagation is monitored in real time.     

Hot corrosion behavior of Yb2Si2O7 ceramic under NaVO3 salt attack

Hot corrosion behavior of Yb₂Si₂O₇ bulk exposed to NaVO₃ molten salt was investigated at 1000–1500 °C for 2 h. Results showed that YbVO₄ was produced on the bulk surface at 1000–1200 °C because of the acidity of the corrosion medium. The corrosion product of Yb₂SiO₅ was yielded at 1300–1500 °C due to the transformation of the corrosion medium from acidity to alkalinity. The content of YbVO₄ in the products decreased as the temperature increased, while that of Yb₂SiO₅ increased with an increase in temperature. In this paper, various hot corrosion mechanisms of Yb₂Si₂O₇ bulk exposed to NaVO₃ molten salt are discussed based on the formation of YbVO₄ and Yb₂SiO₅.     

航空发动机燃烧室帽罩变压边热成形技术

目的 提出帽罩零件真空环境变压边热成形新技术,解决航空发动机燃烧室帽罩零件冷成形回弹大、精度低、内部应力大,以及热成形壁厚不均、氧化严重等问题。方法 利用有限元仿真和工艺试验相结合的方法,选用GH3625高温合金板材研究变压边热成形过程中压边力加载路径对帽罩成形质量的影响,分析热成形模具热膨胀与回弹变形对帽罩尺寸精度的影响,建立考虑热成形、变压边力加载及模具补偿的成形方案。结果 在900 ℃条件下,帽罩热成形力相比室温下降低约70%,内外径回弹量分别降低约67%和59%。基于几何特征优化的压边力加载路径有助于减小零件型面的回弹。结合回弹变形和热膨胀变形补偿,确定模具总补偿量为内径?0.49 mm,外径?0.62 mm。工艺试验结果表明,采用模拟所确立的成形方案成形的帽罩质量较好,尺寸精度达到IT9级,型面精度在0.2 mm以内,切边后回弹量为0.1 mm,与有限元仿真结果吻合较好。结论 建立的有限元模型和变形补偿方案可以有效地优化帽罩的工艺成形过程,所提出的变压边热成形技术能够显著降低高温合金变形抗力和回弹,可以解决高精度帽罩零件成形制造难题。     

Microstructure and mechanical properties of a low activation cast WTaHfTiZr refractory high-entropy alloy

China Foundry - In the face of the requirement that nuclear fusion reactor materials exhibit more excellent thermal, mechanical and physical properties, a novel refractory high-entropy alloy,...