Application of Nonlinear Ultrasonic Measurement for Quality Assurance of Diffusion Bonds of Gamma Titanium Aluminum Alloy and Steel

A new nonlinear C-scan acoustic microscope (NCAM) has been developed and applied to inspect diffusion bonds of gamma titanium aluminum alloy–chromium molybdenum steel (γ TiAl–steel). The large mismatch of acoustic impedance gives strong ultrasonic reflection and masks a small signal from imperfections at the interface. However, NCAM detects indications of minute cracks or gaps, which are rarely observed by a conventional pulse–echo inspection method. Application of high-power ultrasound, with amplitude ten times greater than the conventional method, results in generation of second harmonic signals. All A-scope signals were stored in a computer, and frequency components were analyzed by fast Fourier transformation (FFT). As a result, no indication of fundamental frequency component was observed on a C-scan image, whereas clear indications of the second harmonic components were observed on the C-scan image. The minute cracks or gaps were confirmed at the indicated area by micrographic analysis following the inspection. Moreover, a quality assurance process for the γ TiAl–steel bond with a combination of linear and nonlinear ultrasonic responses is proposed.     

INFLUENCE OF COMPOSITION AND DISPERSOID ON FATIGUE FRACTURE BEHAVIOUR OF Al-Mg-Si ALLOYS

A study was made of the fatigue fracture behaviour under different aging conditions of twoAl-Mg-Si alloys with different chemical compositions and dispersoid contents.Thedispersoid phase can alter the mode of the deformation uniformity of alloys.The dispersoid it-self may decohere from the dispersoid/matrix interface under cyclic stress to form smalldimples.     

制备Y_2O_3弥散铁素体合金粉末方法的研究

为了开发作为快增殖堆及聚变堆结构候选材料的ODS铁素体合金,采用氮气雾化方法制备Fe-Cr-Ti-W-V合金粉末.采用溶胶-凝胶法、沉淀法和化学浸润等方法向合金中添加Y2O3颗粒,对各种添加方法得到合金粉中的Y2O3的形貌、粒度、密度分布进行了分析与对比,结果表明:上述3种方法都可以成功地将Y2O3添加到铁素体基合金粉体中;采用溶胶-凝胶法弥散分布Y2O3,可获得Y2O3颗粒分布均匀、直径在50nm以下的颗粒约占总数的50%、颗粒的平均圆度为1.25的基本圆形的粉体.     

Reliability of composite solder bumps produced by an in-situ process

In an attempt to develop a thermally stable solder system, an in-situ Pb-Sn solder composite reinforced with Cu₆Sn₅ dispersoids was investigated for its thermal stability. The stability was evaluated mainly by measuring the growth rate of intermetallics at in-situ composite solder/BLM interface as a function of the number of reflow soldering cycles and aging time. The rates were compared with those of the eutectic Pb-Sn and Sn-Ag solders. After the thermal treatments, the solder joints were tested for their shear strengths. The results indicated that the in-situ composite solder has a higher shear strength and better thermal stability than the eutectic Pb-Sn solder. Jointly appointed by CAAM at POSTECH     

Influence of TiB2 nanoparticles on elevated-temperature properties of Al-Mn-Mg 3004 alloy

Two contents (1.5% and 3%) of TiB₂ nanoparticles were introduced in Al-Mn-Mg 3004 alloy to study their effects on the elevated-temperature properties. Results show that TiB₂ nanoparticles were mainly distributed at the interdendritic grain boundaries with a size range of 20–80 nm, which is confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Therefore, the volume fraction of the dispersoid free zones is greatly reduced and the motion of grain boundaries and dislocations is inhibited more effectively at elevated temperature. After peak precipitation heat treatment, the yield strengths in the alloy with 3% TiB₂ addition at room temperature and 300 °C were increased by 20% and 13% respectively, while the minimum creep rate at 300 °C was reduced to only 1/5 of the base alloy free of TiB₂, exhibiting a considerable improvement of elevated-temperature properties in Al-Mn-Mg alloys.     

Microstructural characterization of INCOLOY alloy MA 956

Oxide dispersion strengthened (ODS) ferritic materials obtained by mechanical alloying (MA) display particular microstructure and texture. In this paper a microstructural characterization of an INCOLOY MA 956 alloy in the recrystallized (zone annealed) condition is presented. The alloy exhibits a highly anisotropic microstructure, consisting of elongated grains with a high grain aspect ratio (GAR). The alloy also exhibited strong crystallographic texture. The crystallographic direction <111> was approximately parallel to the extrusion direction of the material. The yttria particles, added to the starting powders, react with aluminum and oxygen present in the system during thermomechanical processing and form mixed (Y,Al) oxides. The analysis of extracted particles showed that the majority of yttrium‐aluminum oxides were tetragonal (Y₃Al₅O₁₂) and orthorhombic (AlYO₃). Quantitative analysis using TEM micrographs showed two classes of dispersoid sizes.     

Ce和Zr对新型Al-Cu-Li合金力学性能与组织的影响

本文通过微观观察和拉伸测试的手段,对比研究了在一种高Cu/Li比的新型Al–5.8wt%Cu–1.3wt%Li合金中分别加入Ce, Zr或者两者共同添加对其合金的微观组织与力学性能的影响。微观观察表明：当Ce和Zr共同添加合金与单一添加Ce或者Zr的合金比较,金属间化物弥散体由粗大的多边形颗粒转变成无规则的细小粒子,相应的拉伸断口断裂模式由脆性的沿晶断裂向塑性穿晶断裂转变。进一步微观分析表明：Ce的添加促进了Al-Cu-Li合金中主要强化相T₁的析出。Ce和Zr共同添加合金与单一添加Ce合金相比,由于相对较少的Cu被束缚在尺寸较小的AlCuCe弥散体中,该合金基体中的Cu过饱和度在固溶淬火后相对更高。因此,Al-Cu-Li-Ce-Zr合金与Al-Cu-Li-Ce合金相比较其析出相种类向T₁转变,尺寸变得更小,晶粒更加细化导致了该合金在峰时效时抗拉强度,屈服强度分别相对提高了19.6%和16.1%并具有与之相当的延伸率。     

Effect of Ca addition on microstructure of twin-roll cast AZ31 Mg alloy

A twin-roll cast (TRC) AZ31-0.7Ca alloy sheet has been subjected to thermo-mechanical treatment (TMT) followed by annealing and its microstructure was evaluated. The as-cast microstructure of TRC AZ31-0.7Ca alloy is essentially similar to that of TRC AZ31 alloy, except for the presence of Al₂Ca dispersoid particles. The presence of Al₂Ca particles imparts significant changes to the microstructure of TMT-ed TRC alloy such as the refinement of grain size and evolution of textures different from those of ingot cast and TRC AZ31 alloys.     

粉末气溶胶红外消光作用的试验与理论分析

从气溶胶光电干扰的角度出发简单叙述了气溶胶的形成过程 (分散法和凝聚法 )和试验研制的气溶胶的基本特征 ,并对气溶胶抑制红外辐射的机理 (散射和吸收 )作了简单分析 ,测试研究了试验用粉末气溶胶两个厚度下的衰减效果 ,理论上尝试了两种分析气溶胶遮蔽效果的计算方法 (瑞利散射和 Mie散射 )。最后应用瑞利散射理论 ,尝试计算了粉末气溶胶的遮蔽效果 ,在一定范围内 ,计算值与试验值能够极好的相符合     

化工材料pH值例行分析及应用

pH值是指原材料水溶液的pH值,所以pH值测定都依赖于水,测定过程总是将材料转变为水溶液、水萃取液或水分散体,然后进行测定.由此可见,必须首先进行水的pH值研究,然后才能谈及材料的pH值问题.对pH值的测定方法依材料的性质不同而不同,很有必要研究一套较通用的测定方法.从研究水的pH值开始,其后在对各种非金属材料的pH值例行分析进行初探.