低压等离子喷涂316L不锈钢涂层组织对性能的影响

目的研究涂层组织形貌对涂层性能的影响。方法采用低压等离子喷涂方法制备316L不锈钢涂层,通过改变喷涂条件以及热处理工艺分别得到颗粒堆积、层片状和等轴晶三种不同组织的涂层。利用金相显微镜、X射线衍射、显微硬度计和浸泡实验,分析其金相组织、相结构、显微硬度和耐腐蚀性,对比分析三种不同涂层的性能。结果等轴晶涂层只含奥氏体相,而颗粒状和层片状涂层除奥氏体相外,还有?铁素体相。层片状涂层显微硬度最高(为262 HV0.3),颗粒状涂层次之(为243 HV0.3),等轴晶涂层硬度最低(为118 HV0.3)。在浓盐酸中浸泡1、2、3 h,层片状涂层质量损失分别为0.0110、0.0262、0.0445 mg/cm~2,颗粒状涂层质量损失分别为0.0078、0.0128、0.0262 mg/cm~2,等轴晶涂层质量损失分别为0.0071、0.0100、0.0126mg/cm~2。结论层片状涂层有最高的显微硬度和最差的耐腐蚀性,等轴晶涂层则有最好的耐腐蚀性和最低的显微硬度,颗粒状涂层介于两者之间。     

Realising equal strength welding to parent metal in precipitation-hardened Al–Mg–Si alloy via low heat input friction stir welding

Two millimetres thick Al–Mg–Si (6061Al-T6) alloy plates were friction stir welded at various welding conditions. Under a low rotation rate of 400?rev?min^–1 with rapid water cooling, the softening zone in the joint disappeared and a nanostructure with an average grain size of 80?nm was obtained in the stir zone (SZ). Therefore, a weld with equal strength to the parent metal (PM) was successfully achieved with the fracture occurring in the PM. Further, the average microhardness and ultimate tensile strength (UTS) of the SZs increased with the decreasing rotation rate and increasing cooling speed. The average microhardness and UTS of the SZ with nanostructure reached up to 134?HV and 505?MPa, respectively; though the initial strengthened precipitates disappeared. This work provides an effective strategy of achieving high property joints and enhancing the mechanical properties of precipitation-hardened Al alloys.     

无模拉拔成形连续柱状晶BFe10-1-1合金管材的残余应力

在拉拔温度850℃、拉拔速度0.7mm/s、进料速度0.5mm/s的条件下,对连续柱状晶组织BFe10-1-1合金管材进行无模拉拔成形,采用X射线法测定管材的残余应力,采用TEM进行微观组织分析,探讨了残余应力产生的机理。结果表明,沿着拉拔方向,无模拉拔合金管材的变形区外表面残余应力分布呈先升高后降低的趋势;已变形区残余应力值较为均匀;各点残余应力均为压应力,最大值为135MPa。无模拉拔成形过程中,连续柱状晶组织BFe10-1-1合金管材的晶界变得曲折,晶界周围出现不同密度的位错塞积,变形区沿拉拔方向的位错密度呈先增大再减小的趋势,这一趋势是导致产生不同程度残余应力的根本原因。     

氧化铝-氧化铈核/壳复合磨粒的研究

制备出以α-Al2O3为内核,以含Ce3+的氧化铈为外壳的氧化铝-氧化铈核/壳复合磨粒.以硝酸铈为前驱物,经红外干燥后,在α-Al2O3内核上覆盖一层硝酸铈,通过煅烧成为含Ce3+的氧化铈外壳.通过电子显微镜照片分析和X衍射分析表明:在α-Al2O3上覆盖上了氧化铈,形成氧化铝-氧化铈核/壳结构.通过电子探针分析和光谱半定量分析证明:核/壳结构中氧化铈所占比例为小于2％,通过激光粒度分析仪对氧化铝-氧化铈核/壳复合磨粒进行分析,其粒度d50为2μm左右.     

Some Features of Coalescence Processes and Mechanisms in Systems of Nonmetallic Crystalline Particles

The influence of particle size, presence of soluble impurities, and the development of solid-state polytype transitions in systems of nonmetallic crystalline particles on coalescence mechanisms during sintering is considered. The following cases that have not been studied previously are discussed. Coalescence is activated by oxygen during sintering fine plasma chemical powders of AlN, TiC, and TiN. Its mechanism may be considered as alloy formation realized by movement of a boundary between areas differing in oxygen concentration. Development of this coalescence governs the formation of collective grain growth centers. Polytype transitions in self-bonded SiC give rise to the occurrence of Ostwald coalescence accomplished as recrystallization by the grain in grain type. Polytype transitions in SiC and AlN may cause the growth of fine monopolytype grains at the expense of coarse grains consisting of a collection of multilayer polytypes. On the example of silicon-bonded SiC it is shown that during liquid-phase sintering of ceramic materials with solubility of solid phase in the liquid phase three types of Ostwald coalescence may be realized differing in the mass-transfer mechanisms: reprecipitation through the liquid phase (solution of carbon in silicon); joining of two or more single original SiC particles by a single-crystal shell forming as a result of crystallization of the condensed phase from the melt-solution; combined reprecipitation through a liquid phase and recrystallization by migration of boundaries between particles.     

Fractals

An elementary introduction to the concept of fractals is given. Some examples of fractals drawn from nature are briefly discussed. It is suggested that fractal geometry may be useful in characterizing the grain size and shape distributions in polycrystalline solids.     

Characterization of corn stover, distiller grains and cattle manure for thermochemical conversion

Corn stover, distiller grains and cattle manure were characterized to evaluate their acceptability for thermochemical conversion. The energy densities of ground corn stover, distiller grains and cattle manure after totally drying were 3402, 11,813 and 10,374 MJ/m³, compared to 37,125 MJ/m³ for coal. The contents of volatiles in corn stover, distiller grains and cattle manure were 77.4, 82.6 and 82.8%, respectively, on a dry and ash-free basis compared to 43.6% for coal. About 90% of the volatiles in corn stover, distiller grains and cattle manure were released at pyrolysis temperatures of 497, 573 and 565 °C, respectively. The combustion of corn stover, distiller grains and cattle manure were completed at 620, 840 and 560 °C, respectively. The heat values of the biomass and air mixture for stoichiometric combustion were 2.64, 2.75 and 1.77 MJ/kg for dried corn stover, distiller grains and cattle manure, respectively, as compared to 2.69 MJ/kg for coal. Combustion of 1 kg of dry corn stover, distiller grains and cattle manure generated 5.33, 6.20 and 5.66 Nm³ of flue gas, respectively, compared to 8.34 Nm³ for coal. Simulation showed that gasification of 1 kg of dried corn stover, distiller grains and cattle manure at 850 °C and ER of 0.3 generated 2.02, 2.37 and 1.44 Nm³ dry syngas at a heating value of about 4.5 MJ/Nm³, compared to 3.52 Nm³ at 5.8 MJ/Nm³ for coal. The molecular ratio of H₂ to CO in the biomass-derived syngas was close to 1.0, compared to about 0.5 for the coal-derived syngas.     

稀土对BNbRE重轨钢组织及临界点的影响

研究了BNbRE钢中残留稀土元素对其相变临界点、退火后珠光体组织及热轧态奥氏体晶粒的影响.结果表明,钢中残留稀土元素使Ar1温度降低,Ms温度升高;奥氏体晶粒细化,铁素体量减少,珠光体量增多.     

Effect of low-frequency rotary electromagnetic-field on solidification structure of continuous casting austenitic stainless steel

To understand the solidification behavior of austenitic stainless steel in rotary electromagnetic-field, the influence of low-frequency rotary electromagnetic-field on solidification structure of austenitic stainless steel in horizontal continuous casting was investigated based on industrial experiments. The results show that the solidification structure of austenitic stainless steel can be remarkably refined, the central porosity and shrinkage cavity can be remarkably decreased, and the equiaxed grains zone are enlarged by means of application of appropriate low-frequency electromagnetic-field parameters. The industrial trials verify that the stirring intensity of austenitic stainless steel should be higher compared with that of plain carbon steel. Electromagnetic stirring affects the macrostructure even if the average magnetic flux density of the electromagnetic stirring reaches 90 mT (amplitude reaches 141 mT) with the frequency of 3–4 Hz. Due to a higher viscosity, rotating speed of molten stainless steel is 20%–30% lower than that of molten carbon steel in the same magnetic flux density. Foundation item: Project(CSTC2007BB4216) supported by the Natural Science Foundation of Chongqing, China     

65Mn钢的ECAP变形研究

等径弯曲通道变形(简称ECAP)能实现材料的强烈塑性变形，获得超细晶组织，从而改善材料的综合性能．成功实现了C方式650℃珠光体钢65Mn的ECAP变形，累积等效真应变～5．75．ECAP5道次后，片层状珠光体组织演变成超细的渗碳体颗粒均匀分布于铁索体基体的组织，铁索体基体平均晶粒尺寸约0．3μm，渗碳体球平均尺寸约0．19μm．实验中，渗碳体的球化可能以两种机制进行：破碎渗碳体片的非均匀长大和细小球状渗碳体颗粒的形核长大．