The Structure and Mechanical Properties of Cr4Mo4V Steel Treated by PIII Carbonitriding

The composition and structure of PIII(plasma immersion ion implantation)carbonitrided Cr4Mo4V steel were analyzed using X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),optical microscopy(OM)and SEM.The results indicate that the nitride and carbide are dispersion phase precipitation and except formation of compound other implantation atoms dissolve into martensite matrix.The total concentration of carbon and nitrogen is about 30 at%near the surface,and still keeps at about 20 at%even at the depth of 8μm.The effect of treatment temperature,implantation time and ratio of N2 to CH4 on the hardness and wear resistance of carbonitrided layer are investigated.It is found that the hardness of Cr4Mo4V steel increases after treatment.The highest hardness of samples is 22.3 GPa,which is about 1.8 times than initial steel.The dry-wear resistance of the samples is also improved after treatment,and the sample with higher hardness shows the better wear resistance.     

AZ31镁合金薄壁管分流挤压速度影响规律仿真研究

基于DEFORM-3D平台,以军用战地发射塔天线用AZ31镁合金薄壁管分流挤压工艺过程为研究对象,研究建立了精确、高效的AZ31镁合金薄壁管分流挤压有限元模型。模拟研究揭示了挤压速度对挤压力、焊合压力及模口坯料金属峰值温度的影响规律。基于所得规律,综合考虑挤压力、焊合质量及挤出管材表面质量要求,获得了该规格AZ31镁合金薄壁管在2000t挤压机上的合理挤压速度范围为3.5~7mm/s。     

Study on superprism effect in the multilayer optical thin film stack

1Introduction Superprismeffectisaspecialphenomenon existinginphotoniccrystals(PCs)[12].Nowa days,manyresearchesdemonstratethatPCs possessanomalousdispersionandanisotropy propertiesnearthebandgap,leadPCsachieve hugedispersion[34].For1Dmultilayerstacks,whichownpeculiarproperties,canactasPCs,moreandmorepeoplechoosethisstructureto investigatesuperprismeffect[56].Wehaveused thesimpleststacks periodichighreflectance coatingsarrangedbyonly20layerstoachieve22μmofspatialdispersionbefore.Weselected…     

Microstructure and Properties of SAE 2205 Stainless Steel After Salt Bath Nitrocarburizing at 450 °C

Nitrocarburizing of the type SAE 2205 duplex stainless steel was conducted at 450 °C, using a type of salt bath chemical surface treatment, and the microstructure and properties of the nitrided surface were systematically researched. Experimental results revealed that a modified layer transformed on the surface of samples with the thickness ranging from 3 to 28 μm changed with the treatment time. After 2205 duplex stainless steel was subjected to salt bath nitriding at 450 °C for time less than 8 h, the preexisting ferrite zone in the surface transformed into austenite by active nitrogen diffusion. The main phase of the nitrided layer was the expanded austenite. When the treatment time was extended to 16 h, the preexisting ferrite zone in the expanded austenite was decomposed and transformed partially into ε-nitride precipitate. When the treatment time extended to 40 h, the preexisting ferrite zone in the expanded austenite was transformed into ε-nitride and CrN precipitate. Further, a large amount of nitride precipitated from preexisting austenite zone. The nitrided layer depth thickness changed intensively with the increasing nitriding time. The growth of the nitride layer takes place mainly by nitrogen diffusion according to the expected parabolic rate law. The salt bath nitriding can effectively improve the surface hardness. The maximum values measured from the treated surface are observed to be approximately 1400 HV_0.1 after 8 h, which is about 3.5 times as hard as the untreated material (396 HV_0.1). Low-temperature nitriding can improve the erosion/corrosion resistance. After nitriding for 4 h, the sample has the best corrosion resistance.     

均匀化温度对K4169合金显微组织和持久性能的影响

研究了两种均匀化温度下的热处理对K4169合金显微组织、Nb偏析和持久性能的影响。结果表明,随着均匀化温度的提高,合金中Laves的体积分数逐渐降低。1120℃时,Nb元素仍强烈偏析于枝晶间;当温度升高至1160℃时,Nb元素的偏析程度得到显著改善。经固溶和时效处理后,δ相分别主要以魏氏组织和颗粒状析出,1160℃处理试样中γ′′相的体积分数较大。650℃/620 MPa持久性能测试结果表明,持久寿命随均匀化温度的提高显著增加,但延伸率有所降低。持久断裂类型由穿晶韧性断裂变为沿晶-穿晶复合脆性断裂。     

Ink-jet printing and camera flash sintering of silver tracks on different substrates

A camera flash-lamp, which makes use of the enhanced photothermal effect in silver nanoparticles, was used for sintering of ink-jet printed silver tracks on Polyimide (PI), Polyethylene Terephthalate (PET) and photographic paper at room temperature. After the camera flashing the nonconductive tracks was changed and became conductive. The resistivity of all tracks on different substrates was decreased after the first flashing and the second flashing, while it exhibited a slight increase after the third and forth flashing. Irrespective of the number of flashings, the silver track printed on the PET substrate had the lowest resistivity and it can reach 6.2 μΩ cm after the second flashing, while the track that was printed on the photographic paper had the highest measured resistivity due to defects in the substrate. The thermal conductivity of the substrate had an important effect on the microstructure of the silver tracks after the flashing. The nanoparticles within the tracks printed on the photographic paper exhibited significant melting after flashing sintering. This melting was due to very low thermal conductivity of the photographic paper and slow heat dissipation to the substrate and the surroundings. The nanoparticles on the PI substrate exhibited less appreciable melting due to greater thermal conductivity of the PI and fast heat dissipation to the substrate and the surroundings.     

780MPa级热轧铁素体/贝氏体双相钢的组织与扩孔性能

设计了两种低成本的铁素体/贝氏体双相钢,通过光学显微镜、扫描电镜和拉伸试验机研究了不同Si含量对试验钢组织与性能的影响,研究了试验钢在扩孔过程中的裂纹形成及扩展行为。结果表明,通过合理控轧控冷技术,能够获得780 MPa以上抗拉强度,伸长率大于17%,综合性能良好的试验钢;随着Si含量的增加,试验钢的屈服强度和抗拉强度显著提高,但是伸长率和扩孔性能有所下降;本试验钢的裂纹扩展机制为微孔聚集模式。     

硝盐浴淬火烈度的计算及分析

通过对20Cr Mn Mo钢试棒进行渗碳后在不同温度和含水量硝盐浴中的淬火试验,得到和端淬距离对应的心部硬度值,进而计算出硝盐浴的淬火烈度,分析了影响硝盐浴淬火烈度的因素以及淬火烈度对渗碳淬火工件临界碳含量的影响。结果表明,在盐浴温度为170~200℃范围内,硝盐浴温度越高,淬火烈度越低;在含水量为0.7%~0.9%范围内,含水量越高,淬火烈度越高;盐浴搅拌速度越快,淬火烈度越高。随着硝盐浴淬火烈度提高,20Cr Mn Mo钢渗碳淬火工件临界碳含量降低。     

Microstructure and mechanical properties of SiC platelet reinforced BaOAl2O32SiO2 (BAS) composites

BaOAl₂O₃2SiO₂ (BAS) glass–ceramic powders were prepared by sol–gel technique. SiC platelet reinforced BAS glass–ceramic matrix composites with high density and uniform microstructure were fabricated by hot-pressing. The effect of additional crystalline seeds on hexagonal to monoclinic phase transformation of Barium aluminosilicate was studied. The effects of SiC platelet content on the microstructure and mechanical properties of the composites were also investigated. The results showed that the flexural strength and fracture toughness of the BAS glass–ceramic matrix composites can be effectively improved by the addition of silicon carbide platelets. The main toughening mechanism was crack deflection, platelets' pull-out and bridging. The increased value of flexural strength is contributed to the load transition from the matrix to SiC platelets.     

Mechanistic study of partial oxidation of methane to synthesis gas over supported rhodium and ruthenium catalysts using in situ time-resolved FTIR spectroscopy

In situ time-resolved FTIR spectroscopy was used to study the reaction mechanism of partial oxidation of methane to synthesis gas and the interaction of CH₄/O₂/He (2/1/45) gas mixture with adsorbed CO species over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts at 500–600°C. It was found that CO is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over H₂ reduced and working state Rh/SiO₂ catalyst. Direct oxidation of methane is the main pathway of synthesis gas formation over Rh/SiO₂ catalyst. CO₂ is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts. The dominant reaction pathway of CO formation over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts is via the reforming reactions of CH₄ with CO₂ and H₂O. The effect of space velocity on the partial oxidation of methane over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts is consistent with the above mechanisms. It is also found that consecutive oxidation of surface CO species is an important pathway of CO₂ formation during the partial oxidation of methane to synthesis gas over Rh/SiO₂ and Ru/γ-Al₂O₃ catalysts.