某多级轴流压缩机双层穿孔板降噪方案设计及试验验证

为了提高轴流压缩机内流场气流品质,降低压缩机现场运行产生的噪声,本文提出了一种在压缩机出口下游管道壁面安装降噪结构的方案。根据轴流压缩机噪声特性,利用马大猷教授提出的穿孔板吸声理论,同时考虑切向流及高声强的影响,设计了一种双层穿孔板,采用流管法测试了样件的吸声性能,最后在压缩机现场运行过程中对降噪结构上、下游截面进行了噪声测量。结果表明:降噪结构穿孔板在设计的频率范围内具有良好的吸声性能,其下游截面的噪声明显降低。

某过程工业用离心压缩机模型级轴向推力测量研究

以某小流量系数离心压缩机模型级为研究对象,测量了模型级叶轮盖侧以及盘侧间隙的静压分布以及叶轮的轴向推力。测量结果表明:叶轮盘侧间隙与盖侧间隙静压分布沿半径增大的方向基本呈线性分布;叶轮轴向推力是静态力与动态力的合成,静态力是主要成分,动态力也占有较高比例;叶轮轴向推力基本上随着机器马赫数的增加而增大,主推力基本上随着流量的减小而增大,但到近喘振点时主推力会有所减小。

高压EIGA法制备Ti-6Al-4V合金粉末及其3D可打印性

采用电极感应熔炼气雾化(EIGA)设备制备Ti-6Al-4V合金粉末,研究高压(5.5~7.0 MPa)雾化压力对粉末特性和显微结构的影响,并分析激光打印(LMD)件的力学性能。结果表明:所制备的粉末粒径分布在1~400μm,随着雾化压力的增加,粉末的平均粒径逐渐减小。在气压6.0和6.5 MPa下制备的粒径分布在100~150μm范围内的粉末具有较好的流动性。粉末的氧含量随着压力的升高而增加,但均在0.06%~0.20%较低范围内。LMD制备的TC4试样主要由具有魏氏结构的α和β两相组成,其极限抗拉强度和屈服强度分别约为1100 MPa和1000 MPa。EIGA法制备的钛合金粉末具有良好的3D可打印性,LMD制备的TC4合金的力学性能超过铸造或锻造件的。

Evaluation of contrast-enhanced helical hydro-CT in staging gastric cancer

AIM: To discuss the helical computed tomography (CT) characteristics of gastric cancer and evaluate the diagnostic value of contrast-enhanced helical hydro-CT (HHCT) in staging gastric cancer.METHODS: A total of 50 patients with gastric cancer were included in this study. The CT findings in them were retrospectively analyzed and correlated with pathologic findings at surgery. All patients were preoperatively imaged by plain and contrast-enhanced helical CT after orally ingesting 1 000-1 500 mL water. Peristalsis was minimized by intra-venous administration of spasmolytics.RESULTS: The foci of gastric cancer became more prominent in all the 50 patients and showed strong enhancement in contrast-enhanced HHCT. The tumor was located at the gastric cardia in 14 cases, at the gastric fundus in 3 cases, at the gastric body in 8 cases, at the gastric antrum in 4 cases, at the gastric fundus and the body in 8 cases, at the gastric body and antrum in 11 cases, and at three segments of the stomach in 2 cases.The CT features of gastric cancer were focal or diffuse mural thickening, soft tissue mass, cancerous ulcer, stenosis of stomach, infiltration to adjacent tissues, lymph node and distant metastases. Strong contrast enhancement of the gastric wall was closely related to gastric cancer. The accuracy rate of contrast-enhanced HHCT in staging gastric cancer was 86% (43/50). The detection rate of lymph node metastases by CT was 60% (12/20).CONCLUSION: Contrast-enhanced HHCT is a reliable method to diagnose and stage gastric cancer.

Cavitation erosion behavior of WC coatings on CrNiMo stainless steel by laser alloying

The WC powder was precoated on the surface of CrNiMo stainless steel and then made into an alloying layer by using the laser alloying technique. Phases in the layers were investigated by X-ray diffraction （XRD） analysis and surface morphologies after cavitation erosion were observed with the help of scanning electron microscopy （SEM）. The cavitation erosion behavior of the CrNiMo stainless steel and WC laser alloying layer in distilled water was tested with the help of ultrasonic vibration cavitation erosion equipment. The results showed that the thickness of the laser alloying layer was about 0.13 mm. The layer had a dense microstructure, metallurgically bonded to the substrate, and no crack had been found. The cavitation erosion mass loss rate of the laser alloying layer was only 2/5 that of the CrNiMo stainless steel. The layer had better cavitation resistance properties because of its metallurgical combination and the strengthening effects of the precipitate phases.

Characterization of Fe_3Si-based coatings on low silicon steel by pulsed Nd:YAG laser cladding

The Fe3Si based coating was produced on the Fe-1 Si steel surface by a pulsed Nd：YAG （yttrium aluminum garnet） laser. Its phase constitution and microstructure were characterized by using X-ray diffraction （XRD）, optical microscope （OM）, and field emission scanning electron microscope （FESEM） with associated energy dispersive spectroscopy （EDS） and transmission electron microscopy （TEM）. The hyperfine structure of the coating was studied by Mrssbauer spectra （MS） and the magnetic property was also measured at room temperature by a vibrating sample magnetometer （VSM）. The obtained coating is pore and crack-free with dense microstructure and high Si content. The metallurgical bonding between the coating and the substrate was realized. The microstructure of the coating is typical fine dendrites. The major phase was confirmed by XRD and TEM to be the ordering D03 structured Fe3Si phase. In addition, there were smaller amounts of the Fe5Si3 phase and the γ-Fe phase in the coating. Compared with the substrate, the laser cladding coating has a lower saturation magnetization and a higher coercive force. The poor magnetic property might be because of rapid solidification microstructure and phase constitution in the coating.

Fabrication of wear-resistant layers with lamellar eutectic structure by laser surface alloying using the in situ reaction between Cr and B_4C

To improve the wear resistance of Cr5 steel, wear-resistant layers with lamellar eutectic microstructure were fabricated by laser surface alloying（LSA）, which is dependent on the in situ reaction between Cr and B_4C. Our results indicated that the hypoeutectic structures of the LSA layers were divided into interdendritic eutectic structures and dendrites. The area fraction of the eutectic structures increased with increasing laser scanning speed, which improved the hardness and wear resistance of the LSA layers. The average hardness of the LSA layer prepared at a scanning speed of 8 mm/s was HV_（0.2） 883.9, which was 1.8 times greater than that of the traditional quenched layer（approximately HV 480）. After sliding for 659.4 m, the specimen prepared at a scanning speed of 8 mm/s exhibited a volume loss of 0.0323 mm^3, which was only 29.5% of the volume loss of the traditional quenched specimen.

Retrogression characteristics of a novel Al-Cu-Li-X alloy

Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy （TEM）, and differential scanning calorimetry （DSC）. The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ＇ precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ＇ and θ＇ phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240°C causes the dissolution and coarsening of δ＇ and θ＇ precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T1, T2, δ＇, and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis.

Laser cladding of high-entropy alloy on H13 steel

High-entropy alloy layer up to 150 lm in thickness was formed on H13 substrate with a metallurgical bonding at the coating/substrate interface. Simple solid solution phases were formed in the coating layer with a typical microstructure composed of both dendrite and interdendrite. The microstructure at the top of the cladding zone consists of equiaxed grains while that at the bottom consists of columnar grains. The coating layer exhibits great enhancement in microhardness and wear resistance compared with the H13 substrate.

Effect of Temperature on Microstructure and Formability of Al-10 mass% Si Coatings

The type-1aluminized（Al-10mass% Si）coating on hot stamped steel is used in commercial applications.The effect of temperature on microstructure and formability of the Al-10mass% Si coating was investigated.Hot-dip aluminized 22MnB5 steel was heated at 870,900,930,and 1 050 ℃ for 5 min.After heat treatment at different temperatures,the microstructure of Al-10mass% Si was characterized by field-emission scanning electron microscopy and energy-dispersive spectroscopy.The results show that when the Al-10mass% Si coating was heated at 870℃for 5min,three types of intermetallic phases were formed：two ternary Fe-Si-Al phases（Fe2SiAl7＋Fe2Si2Al5and Fe2SiAl2＋Fe2Si2Al5）and one binary Fe-Al phase（FeAl3）.The phases in the coating became Fe2SiAl2＋Fe2Si2Al5and FeAl3,the binary Fe-Al phase near the interface became Fe2Al5 and the Si-rich layers were decreased with the increase of heating temperature.When the heat treatment was 1 050℃for 5min,the Si-rich layer disappeared,the coating consisted of FeAl and Fe3 Al,and the Kirkendall voids were formed.When the heating temperature was increased through 870,900,and 930℃,the coating hardness was reduced and cracks were formed in the coating after hot stamping.The formability of the coating with temperature change was confirmed by a hot stamping test.When heated at 1 050 ℃,the coating was formable but continuous Kirkendall voids were observed.

Laser Surface Alloying of Low Carbon Steel Using High-entropy Alloy Precursors

The Al0. 5CoCrCuFeNi high-entropy alloy powders with simple face-centered-cubic （FCC） solid solution structure were introduced into the surface layer of a low carbon steel during laser surface alloying. A high performance surface layer with extremely fine martensite as the dominant phase was obtained, resulting in a great improvement in microhardness, wear resistance, and corrosion resistance. The great enhancement of microhardness and wear resistance of the laser alloyed layer is mainly due to the formation of extremely fine martensite hard phase, the solid solution strengthening of the alloying e!.ements in supersaturated a-Fe solid solution, and the existence of size effect and strain effect under rapid solidification. The enhancement of corrosion resistance is due to the alloying of Al, Co, Ni, Cr and Cu in the laser alloyed layer.

Effect of MgO on Oxidation Process of Fe_3O_4 in Pellets

Induration process of oxidized pellets involves the oxidation of Fe3O4 and re-crystallization of Fe2O3.The oxidation process of Fe3O4 is significant for pellets to obtain better ambient strength.Thus,the effect of MgO on oxidation process of Fe3O4 was investigated.The unreacted core model was applied to analyze the oxidizing induration process of pellets.The experimental results show that MgO plays a negative role in the oxidation process of Fe3O4.The oxidation rate of Fe3O4 in MgO-fluxed pellets（95.0% Fe3O4 ＋5.0% MgO）is slower than that in standard acid pellets（100% Fe3O4）.The relation between oxidation ratio of Fe3O4 and time was calculated based on the unreacted core model for both MgO-fluxed pellets and standard acid pellets.According to verification experiments,the values calculated by model coincide well with the experimental values.Therefore,the unreacted core model could be applied to describe the oxidizing induration process of pellets.

Clinical factors associated with the number of gallbladder polyps

Gallbladder polyps(GBPs),which are defined as a pathological change protruding from the gallbladder mucosa,are one of the main causes of hospital admission for cholecystectomy.The incidence of GBPs is 4.2 to 9.5%in China.To date,the etiology of GBPs has not yet been clearly defined.According to previous studies,metabolic status is strongly associated with GBPs.⑵A single polyp is more likely to exhibit a malignant transformation,and large(diameter greater than 10 mm)single polyps should be resected together with the entire gallbladder.However,multiple polyps seem unlikely to transform.Thus,number of GBPs is an important factor that affects the treatment of GBPs.However,clinical factors associated w让h the number of GBPs are not completely understood;therefore,the aim of the current study is to investigate these factors.

Model Algorithm Research on Cooling Path Control of Hot-rolled Dual-phase Steel

With the development of advanced high strength steel,especially for dual-phase steel,the model algorithm for cooling control after hot rolling has to achieve the targeted coiling temperature control at the location of downcoiler whilst maintaining the cooling path control based on strip microstructure along the whole cooling section.A cooling path control algorithm was proposed for the laminar cooling process as a solution to practical difficulties associated with the realization of the thermal cycle during cooling process.The heat conduction equation coupled with the carbon diffusion equation with moving boundary was employed in order to simulate temperature change and phase transformation kinetics,making it possible to observe the temperature field and the phase fraction of the strip in real time.On this basis,an optimization method was utilized for valve settings to ensure the minimum deviations between the predicted and actual cooling path of the strip,taking into account the constraints of the cooling equipment′s specific capacity,cooling line length,etc.Results showed that the model algorithm was able to achieve the online cooling path control for dual-phase steel.