Stabilization Effect of Zr and Ti Additions on the Ageing Characteristics of Al-1 wt% Si Alloy Through a Creep Study

Al-1 wt% Si and Al-1 wt% Si-0.1 wt% Zr–0.1 wt% Ti alloys were used to trace the effect of Zr and Ti additions on the behaviour of the steady state creep. After solid solution treatment specimens of both alloys were aged at 623, 673, 723 and 773 K and creep tests were performed at room temperature by applying stresses of 60.0, 62.4, 64.7 and 67.1 MPa. The results showed a sound stabilization effect of Zr and Ti on the ageing characterstics of binary Al-1 wt% Si alloy. Values of the applied stress sensitivity parameter, m, obtained were in the range of (20–34) for Al Si alloy and (14–19) for Al Si Zr Ti alloy. Time to rupture was found to be strongly increased by Zr and Ti additions. The activation energies of the precipitation process involved were found to be 81.9 kJ/mole and 33.7 kJ/mole of the Al Si and Al Si Zr Ti alloys respectively.     

Effect of SnSb Particle Size on Creep Behaviour under Power Law Regime of Sn-10%Sb Alloy

Sn-10 %Sb alloy was casted from the liquid state, drawn into wires of 0.55 mm in diameter or rolled into sheet of 0.2 mm thick. The as received as well as the heat treated specimens were examined by metallurgical microscope. Room temperature creep tests at constant loads were also carried out. The results obtained show that increasing annealing temperature, T_a, affects the structure and properties of the alloy. The increase of T_a leads to smaller SnSb particle size, therefore results in increasing its mechanical strength as measured by the decrease in steady state creep rate of specimen. The stress exponent parameter (m) calculated from the equation ϵ_S= A s_m was found to have higher values than usual and to decrease by increasing annealing temperature which was related to the associated decrease of the SnSb particle size.     

On the Size Distribution of Guinier-Preston Zones Grown in an Al-4.5 at.% Zn Alloy at Room Temperature

The size distribution SD of the Guinier-Preston (GP) zones grown in an Al-4.5 at.% Zn alloy were determined by analysis of the intensities of the small-angle X-ray scattering (SAXS) curves. Four different methods frequently used in the literature were applied and the obtained results were compared. In addition the SD's obtained by the SAXS methods were compared with that found by high-resolution electron microscopic investigations. – From these comparisons conclusions were drawn.     

Information on the Operating Mode of Decomposition during the Cooling of an Al-10 at.% Zn Alloy to Various Tq

Information about the operating mode of decomposition during cooling to various T_q were gained by SAXS method. After reaching the T_q wanted the samples were quenched into water of RT and the SAXS intensity curves were measured at RT. Strong evidence was found that below about 175 °C the decomposition starts in this alloy with the nucleation and growth of Guinier-Preston zones. As proved by other authors, 175 °C is the upper limit temperature T_rhm for the onset of the rapid homogeneous nucleation of precipitates.     

Structure Changes in an Al-4.5 at.% Zn-2.0 at.% Mg Alloy during Continuous Heating in Dependence on the Starting Conditions

Die in einer AlZn(4.5 at.-%) Mg(2.0 at.-%)-Legierung beim kontinuierlichen Aufheizen vonstatten gehenden Strukturumwandlungen wurden mit Hilfe von DSC und RKWS in Abhängigkeit vom Startradius, r_S = (0.7 … 2.7) nm, der metastabilen Phasen (GP-Zonen und/oder η'-Phase), die bei T_pre = R.T. oder 100°C gewachsen waren, untersucht. Die Stabilität der bei T_pre gebildeten metastabilen Phasen nimmt mit deren Größe zu, während eine Veränderung von T_pre keinen merklichen Einfluß zeigt. Startet man mit Partikeln von r_S > 1.6 nm, so erscheinen die Minima, die durch die Bildung von η'-Phase aus den aufgelösten GP-Zonen (1. Minimum) bzw. aus überkritischen Zonen entstanden sind (2. Minimum), mit Zunahme von r_S immer undeutlicher.     

半固态处理对Al-50wt;Si合金初晶硅形貌的影响研究

提高初晶硅的收率是Al-Si合金法制备太阳能级多晶硅的研究热点之一.本文对成分为Al-50wt; Si合金在580℃进行半固态热处理,分析初晶硅的形貌以及Al元素含量的变化.结果表明:随半固态处理时间的增加,初晶硅的尺寸逐渐增大,其原因是在熟化机制的作用下,尺寸为0.15～0.7 mm的初晶硅的含量显著增加,这一结果导致初晶硅的收率高于理论收率.同时,经过半固态热处理,片状初晶硅之间的富Al层容易酸洗去除,降低了初晶硅中的Al含量.     

冷却速率对Al-30wt％Si合金初晶硅形貌和杂质的影响研究

合金法提纯是制备太阳能级多晶硅的工艺之一,在Al-Si合金提纯多晶硅工艺中,冷却速率对初晶硅的形貌和纯度都有重要的影响.本文对成分为Al-30wt;Si合金采用不同冷却速率进行处理,分析初晶硅的形貌以及杂质含量的变化.结果表明,随冷却速率的降低,初晶硅的长度和宽度逐渐增加,初晶硅收率逐渐增加,并且在较低冷却速率下,初晶硅晶粒的<111>择优生长更加明显.同时,冷却速率对初晶硅中的杂质含量产生了显著影响,在较低冷却速率下,杂质的去除率较高,并且有利于Ti和B杂质的去除.为了获得较高的收率和较好的杂质去除率,Al-30wt;Si合金杂凝固过程中的冷却速率应低于3℃/min.     

粉体粒径及烧结工艺对ZrB2陶瓷致密化行为与晶粒长大的影响

利用热压烧结(HP)和放电等离子烧结(SPS)制备了ZrB2陶瓷,研究了粉体粒径和烧结工艺对ZrB2陶瓷致密化行为和晶粒长大的影响.结果表明,相同工艺下以平均粒径为200 nm的ZrB2粉体为原料替代平均粒径为2μm的ZrB2粉体可以明显促进粉体的致密化烧结,采用SPS替代HP工艺可以显著降低粉体的致密化温度,采用平均粒径为200 nm的ZrB2粉体在1900℃进行SPS工艺烧结即可实现ZrB2陶瓷的致密化烧结.     

The Effect of Additions of Mn and Fe on the Structure of an Al-2 at.% Zn-1 at.% Mg Alloy

The structure of an Al-1.9 at.% Zn-1.3-at.% Mg mother alloy with additions of Mn and Fe, respectively, were investigated by TEM and microprobe analysis for two different heat treatments, namely direct quench from 490 °C to 160 °C and a two-step ageing treatment (preageing at RT for 7d before storing at 160 °C), to explain the differences in the course of the hardness obtained during the ageing at 160 °C. The differences of the structure observed are explained in terms of the tendency of the additives to form intermetallic phases, particularly in the grain boundaries.     

Dependence of photoluminescence properties on excitation power in ZnO and ZnCdO microrods

ZnO and ZnCdO microrods have been prepared through a chemical bath deposition method. The structure of microrods has been characterized using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence spectra were recorded for ZnO and ZnCdO microrods at different excitation powers. The intensity of UV emission is enhanced with increasing excitation power. The width of UV emission increases for spectra at higher excitation powers. In particular, the paper shows that the influence of excitation power on the shift of emission band for ZnCdO microrods is more remarkable than that of ZnO microrods with the increase of excitation power. The definite experimental evidence demonstrated that the temperature coefficient β of ZnCdO microrods is much larger than the temperature coefficient of ZnO microrods. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of La/Ce-doping on phase transformation and crystal growth in TiO2-15 wt% ZnO gels

Titania based ceramic is a good candidate for environmental sensing materials. Ion doping is an effective method to improve the properties by modifying their microstructure and phase composition. By using differential thermal analysis and X-ray diffraction methods, the transformation behaviors of La³⁺/Ce³⁺-doped TiO₂-15  wt% ZnO gels were studied so as to modify the phase transformation and decrease the granularity of crystals. Experimental results show that, anatase, rutile and ZnTiO₃ nanocrystals can be tailored by varying La³⁺/Ce³⁺ contents and sintering temperatures. La³⁺/Ce³⁺ doping decreases the transformation temperature of gel to anatase and the forming temperature of ZnTiO₃ phase, enhances the transformation temperature of anatase to rutile and results in appearance of Zn₂Ti₃O₈ interphase. With the increases of La³⁺/Ce³⁺ contents, the transformation rates of ZnTiO₃, gel to anatase and anatase to rutile, as well as the granularity of the crystals are reduced. Ultimately, the action mechanism of La³⁺/Ce³⁺ doping was discussed.     

On the influence of impurity additions and quenching temperature on the course of the microhardness (HV) during a two-step ageing treatment of an Al-2.0 at.%Zn-1.3 at.%Mg Alloy

A pure as well as the analogous technical alloy were directly quenched from T_q = 400 °C or 490 °C to T_a, preaged at T_a (ranging between 50 °C and 160 °C) various times (t_a), and subsequently postaged at R.T. up to t_post = 42 d. — Ageing the samples below the upper limit temperature of the homogeneous formation of G.P. zones (T_hn) no essential difference in the course of the HV-number attained after one- as well as two-step ageing in dependence on the addition of impurity atoms and T_q could be found. — Contrary to this behaviour after pre-ageing at T_a > T_hn and postageing at R.T. a variation of both T_q and the content of impurity atoms shows a considerable effect. The reason is the difference in the density of nucleation sites for heterogeneous formation of precipitates of the η′- and/or η-phase in dependence of T_q and impurity content.     

预制层中Zn和ZnS对CZTS薄膜太阳电池的影响

采用磁控溅射后硫化的方法制备Cu2 ZnSnS4 (CZTS)薄膜,分别用Zn和ZnS作为锌源,在镀钼的钠钙玻璃衬底上以Zn(或ZnS)/Sn/Cu的顺序制备出不同的CZTS薄膜预制层.首先对预制层进行低温合金,然后以硫粉作为硫源进行高温硫化,得到CZTS薄膜.通过X射线衍射仪(XRD)、扫描电镜(SEM)及能谱仪(EDS)分别对所制备薄膜的晶体结构、表面形貌和薄膜组分进行分析表征;并用拉曼光谱表征了CZTS相的纯度.最后用CZTS薄膜制备了太阳电池,发现在预制层中以ZnS作为锌源得到的太阳电池有较高的性能参数,其开路电压:V =651 mV,短路电流密度:Jsc=11.4 mA/cm2,光电转换效率达到2.8;.     

Dependence of the Electric Properties and the Positron Lifetimes on the Dopant Content in La-doped SrTiO3

The resistivity, the dielectric constant, and the positron lifetimes in La-doped SrTiO₃ have been measured for La content x of 0—10 at.%. It was found that with increasing x, the variations of the resistivity and the dielectric constant and the positron lifetime parameters are nonmonotonic. The positron experiments have shown that the La-doping induces mainly formation of Sr vacancies and variation of Sr vacancy configuration; the most probable configuration is the isolated Sr vacancies (V) as x < 0.5 at.%, the associated defects (La V) for 0.5 < x < 1 at.%, and the associated defects (2 La V) above x = 1 at.%. The results suggest that the variation of the resistivity can be regarded as variation of electron density, and the variation of the dielectric constant results mainly from variations of the space-charge polarizaion and Sr-vacancy concentration and configuration.     

Dependence of ortho-positronium pick-off annihilation lifetime on free volume in water-methanol mixtures,and positronium bubble formation

Sizes of free volume were quantitatively calculated for water-methanol mixtures by means of the Kincaid and Eyring method. The results were discussed in relation to the pick-off annihilation lifetime of ortho-positronium in these mixtures. The existence of two ranges of methanol METH concentration in water was observed, within which the dependences of lifetime of o-Ps annihilating by the pick-off process τ₂ on the calculated free volume size are quite different. The problem that the calculated free volume was too small for the existence of o-Ps could be eliminated by the equilibristic formation of a bubble around o-Ps. Correlation was shown between the free volume radii and bubble radii. The obtained results testify to the existence of the strong dependence of τ₂ on the free volume radii. The peculiar shape of this dependence confirms the existence of the clathrate structure in METH-H₂O mixture.     

Ti对Al-Ti合金与金刚石的润湿性和把持力的影响

本文首先研究了Ti对Al-Ti合金与金刚石润湿性的影响,然后以不同Ti含量的Al-Ti合金为基体,加入金刚石,利用热压烧结制备没有和有金刚石铝基节块.测量了节块的抗弯强度并计算了铝基结合剂对金刚石的把持力.结果表明:随着Ti含量的增加,Al-Ti合金对金刚石的润湿性有明显的改善,所以当Ti含量为5wt;时,没有和含有金刚石的Al-Ti节块的抗弯强度值最高,分别为135 MPa和102.1 MPa;把持力系数最大,达到75.6;.