X70管线钢在役焊接局部脆化区的组织及精细结构

采用焊接热模拟试验研究了X70管线钢在役焊接粗晶区和临界粗晶区的显微组织及其精细结构,并和常规焊接进行了对比.结果表明,X70管线钢在役焊接粗晶区和临界粗晶区的组织在类别上与常规焊接相差不大,主要都是粒状贝氏体和贝氏体铁素体,不同的只是数量的多少和尺寸的大小.透射电镜下,在役焊接和常规焊接的粗晶区与临界粗晶区的主要形貌都是铁素体板条和分布在板条之间或板条基体上的岛状物,铁素体板条的亚结构都是高密度位错.在役焊接粗晶区和临界粗晶区的铁素体板条宽度都比常规焊接的要小,位错密度都比常规焊接的要高.     

射流电沉积镍工艺研究

通过射流电沉积瓦特镍电解液研究了电压、电解液温度、射流速度、主盐浓度、阳极喷嘴口径对沉积电流、沉积速率、电流效率的影响.结果表明:在电压为45V,温度为50℃,阴阳极间距离为17mm,NiSO4·6H2O浓度为280g/L时,从沉积电流、沉积速率、电流效率来看,效果最好.电压的增大使得沉积电流、沉积速率、电流效率增大,当电压增大到45V后,电流效率不再增大,而是趋于平稳,到55V后,沉积层烧焦.试验还发现,电解液流速和阳极喷嘴口径越大,沉积速率、电流效率也越大.     

Microstructure and tensile behavior of (BN/SiC)n coated SiC fibers and SiC/SiC minicomposites

Interphase plays an important role in the mechanical behavior of SiC/SiC ceramic-matrix composites (CMCs). In this paper, the microstructure and tensile behavior of multilayered (BN/SiC)_n coated SiC fiber and SiC/SiC minicomposites were investigated. The surface roughness of the original SiC fiber and SiC fiber deposited with multilayered (BN/SiC), (BN/SiC)₂, and (BN/SiC)₄ (BN/SiC)₈ interphase was analyzed through the scanning electronic microscope (SEM) and atomic force microscope (AFM) and X-ray diffraction (XRD) analysis. Monotonic tensile experiments were conducted for original SiC fiber, SiC fiber with different multilayered (BN/SiC)_n interfaces, and SiC/SiC minicomposites. Considering multiple damage mechanisms, e.g., matrix cracking, interface debonding, and fibers failure, a damage-based micromechanical constitutive model was developed to predict the tensile stress-strain response curves. Multiple damage parameters (e.g., matrix cracking stress, saturation matrix crack stress, tensile strength and failure strain, and composite’s tangent modulus) were used to characterize the tensile damage behavior in SiC/SiC minicomposites. Effects of multilayered interphase on the interface shear stress, fiber characteristic strength, tensile damage and fracture behavior, and strength distribution in SiC/SiC minicomposites were analyzed. The deposited multilayered (BN/SiC)_n interphase protected the SiC fiber and increased the interface shear stress, fiber characteristic strength, leading to the higher matrix cracking stress, saturation matrix cracking stress, tensile strength and fracture strain.     

固溶时效对热等静压制得的TC4钛合金组织与性能的影响

采用热等静压工艺对Ti-6Al-4V雾化预合金粉的粉末冶金技术进行了研究，采用不同的固溶温度、时效温度以及时效时间，研究了热处理工艺对TC4钛合金组织和性能的影响。结果表明，采用预合金粉工艺制备的Ti-6Al-4V粉末钛合金材料性能良好，于965℃固溶并采用水冷，然后在470℃时效，试样的强度较好。     

覆膜砂用酚醛树脂/MMT纳米复合材料制备与性能研究

利用己内酰胺同时作为热塑性酚醛树脂内增韧和蒙脱石（MMT）有机改性剂，通过一步原位插层法制备了改性酚醛树脂／MMT纳米复合材料。结果表明，酚醛树脂能较好地插层至4MMT的片层，用于覆膜砂时，由于树脂强韧性和耐热性的综合改善，覆膜砂的综合性能得到明显提高，特别是当MMT加入量为4％左右时，覆膜砂冷态抗拉、抗弯强度分别提高了25％和30％以上。     

基于SYSWELD的运行管道在役焊接热循环数值模拟

采用焊接过程数值模拟软件SYSWELD建立模型,以水为运行介质,对X70管道在役焊接粗晶区的热循环进行了数值模拟,探讨了介质流速、管道壁厚和焊接热输入等因素对在役焊接热循环的影响规律,并对数值模拟结果进行了验证.结果表明,在役焊接粗晶区t8/5值随着水流速度的增大而减小,但减小的幅度不大;当流速小于0.5 m/s时,t8/3和t8/1随流速的增大而大幅减小,当流速大于0.5 m/s时,t8/3和t8/1随流速增大而缓慢减小.t8/5和t8/3均随着管道壁厚的增加而先增大后减小,在壁厚为8 mm时达到最大值;t8/1随着壁厚的增加而逐渐增大.随着焊接热输入的增加,t8/5,t8/3和t8/1均增大.焊接热循环计算结果和实测结果吻合较好,相对误差小于8%.     

Phase and microstructural evolution during the heat treatment of Sm–Ca–α-sialon ceramics

The phase and microstructural evolution of multi-cation Sm–Ca–α-sialon ceramics was investigated. Six samples were prepared, ranging from a pure Sm-sialon to a pure Ca-sialon, with calcium replacing samarium in 20 eq% increments, thus maintaining an equivalent design composition in all samples. After pressureless sintering at 1820 °C for 2 h, all samples were subsequently heat treated up to 192 h at 1450 and 1300 °C. The amount of grain boundary glass in the samples after sintering was observed to decrease with increasing calcium levels. A M′_ss or M′_ss-gehlenite solid solution was observed to form during the 1450 °C heat treatment of all Sm-containing samples, and this phase forms in clusters in the high-Sm samples. The thermal stability of the α-sialon phase was improved in the multi-cation systems. Heat treatment at 1300 °C produces SmAlO₃ in the high-Sm samples, a M′_ss-gehlenite solid solution in the high-Ca samples, and a Sm–Ca–apatite phase in some intermediate samples.     

Enhanced out-of-plane thermal conductivity of polyimide composite films by adding hollow cube-like boron nitride

Boron nitride nanosheet (BNNS) is widely used in electronic thermal management due to its excellent planar thermal conductivity and insulating properties. However, it is challenging to improve the out-of-plane thermal conductivity of BNNS-doped composites due to the anisotropy of the thermal conductivity of BNNS. Therefore, the BNNS in the matrix must be oriented to obtain composites with high out-of-plane thermal conductivity. In this study, BNNS powders with directional structures were synthesized directly using sodium chloride templates. The as-obtained BNNS powders have a unique hollow cube-like structure with an ultra-low density of 2.67 × 10⁻² g/cm³ and nearly 8 times the volume of the same mass of two-dimensional (2D) BNNS, making it easy to form the out-of-plane thermal conductivity paths in the polymer matrix. In addition, the high out-of-plane thermal conductivity of 4.93 W m⁻¹ K⁻¹ at 23.3 wt% loadings was obtained by doping it into a polyimide (PI) matrix. This value is 9.7 times higher than that of 2D BNNS-doped PI at the same loadings, 17.6 times higher than pure PI, and 6.1 times higher than the thermally conductive PI film sold by DuPont. Therefore, the prepared composite film has great potential for application in electronic thermal management.     

Analysis of fracture failure of fir-tree serrations of stage II turbine disks

This paper presents an analysis of fracture failure of fir-tree serrations in stage II turbine disks in a certain type of engine. On the basis of statistical analysis, basic fracture features and fracture mechanisms of stage II turbine disk serrations have been summarized. The reasons for the serration fracture failure are: (a) the first order bending resonance k=5 in the turbine blade occurring at the speed of 9700 rpm; (b) the unreasonable design of the five-serration structure, which causes each serration to bear non-uniform stresses; (c) the disk being made of the alloy GH2036 having a low fatigue resistance; (d) the high intergranular corrosion sensitivity of GH2036. Finally, measures, i.e. the change of the five-serration structure into a three-serration structure and the replacement of GH2036 with GH2132, have been given to prevent the fracture failures, and the application has indicated that these measures are effective.