熔体过热对Sn—Bi40合金熔体结构转变及凝固组织的影响

以Sn－40wt％Bi合金为研究对象,探索了其在不同温度下恒温过程熔体电阻率随时间的变化规律,以及不同熔体状态与凝固行为及组织的关系．结果显示：在一定的临界温度以上,熔体保温相应时间后电阻率发生异常变化,提示熔体发生了结构变化;且随过热温度的提高,熔体结构转变所需“孕育期”愈短,转变速度愈快．凝固实验表明,一定过热度及相应保温时间所引起的熔体结构状态不同,导致凝固过冷度增大、晶粒明显细化且形态也发生改变．进一步的探索还表明,对应特定保温时间,凝固过冷度在一定的熔体过热温度下出现最大值．对上述现象的作用机理进行了简要的分析讨论．     

热压烧结ZrB2／B4C陶瓷材料的组织与性能

以B4C、C、ZrO2为主要原料,采用反应热压法制备ZrB2／B4C陶瓷材料。通过对ZrB2／B4C陶瓷材料的显微组织及力学性能的综合分析,发现第二相ZrB2含量为20wt％时,材料具有较好的综合力学性能,相对密度为99．3％,维氏硬度为36．1GPa,抗弯强度为533．3MPa,断裂韧性为6．95MPa·m^1/2,比纯B4C陶瓷材料的性能均有所提高。材料为穿晶和沿晶断裂的混合断裂模式。     

Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties,electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated.The results indicated that with elevating the aging temperature from 100°C to 160°C,the aging response rate was greatly accelerated,and the UTS at peak aging condition decreased,while the corresponding TYS increased.However,the electrical conductivity of the alloy became higher.After aging for 24 h at 120°C,the peak UTS and TYS values were achieved as 591 MPa and 541 MPa,respectively;but the alloy achieved a lower conductivity,20.4 MS/m.When T6 temper was performed at 140°C for 14 h,the UTS decreased only by 1%of the former,whereas the TYS and the electrical conductivity increased obviously,which were up to 559 MPa and 22.6 MS/m,respectively.The major strengthening precipitates of the peak-aged alloy were GP zones andη′phase.The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature.There were obvious PFZs along the grain boundary both in T6 conditions aged at 140°C and 160°C.     

HC冷轧机带钢表面振纹分析及抑制研究

针对某 HC冷连轧机发生的带钢表面振纹问题,通过现场连续跟踪测试,并对采集到的振动信号进行分析与比较,及对轧机振动系统的固有特性仿真分析,发现带钢表面振纹主要由第七阶固有频率振动引起.最后,结合振纹间距与振动频率的关系,通过对冷轧带钢表面振纹成因及振纹影响因素的分析与研究,找到了引起轧机振动的原因,提出相应的振纹抑制措施应用于生产,并取得了良好的振纹抑制效果     

Effects of temperature and pressure on the structural and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on fused silica via pulsed laser deposition (PLD) at substrate temperatures from 300°C to 800°C and ambient oxygen pressures ranging from 10?2 mTorr to 240 mTorr. X-ray diffraction (XRD) and Raman spectra indicated that wurtzite ZnO was obtained in all cases. The highly c-oriented ZnO films were obtained for oxygen pressures above 11 mTorr. The room-temperature photoluminescence (PL) spectra demonstrated that all the films exhibited strong near-band-edge (NBE) emission, while d...     

前列腺素E2受体生化性质及功能的研究进展

前列腺素E2受体(EP)是一类G蛋白偶联受体,主要与前列腺素E2(PGE2)结合,在多种疾病的发生中发挥作用.研究发现EP在机体几乎所有系统,如心血管系统、呼吸系统、生殖系统、神经系统等的病理反应中发挥重要作用,甚至与肿瘤的发生也有关联.研究并掌握EP相关性质对于临床疾病的治疗有着重要的意义,在国际上已成为研究和报道的热点.本文简要综述了关于EP前沿的研究成果,以期为广大研究者提供借鉴,为进一步阐释EP作用机制以及相关研究乃至临床治疗提供新的思路.     

重庆四面山根系及土壤特性对优先路径分布的影响

通过分析不同土地利用状况(林地,灌草地和农地)下优先路径分布特征、土壤特性、及根系状况,探讨根系和土壤特性时优先路径的影响.采用染色法分析了三种不同土地利用状况下6块样地的优先路径分布,并分析了优先路径与根长密度、根孔和根面积之间的关系.结果表明,所有土地利用状况下0～10 cm土壤染色面积超过50％,在20 cm以下...