Dynamic effects during sinter forging of axi-symmetric hollow disc preforms

The present paper reports an investigation on the dynamic effects during sinter forging of axi-symmetric hollow disc preforms at room temperature. The preforms have been prepared by compacting the copper metal powder within the closed-cavity circular compaction dies and experiments have been conducted on computer-controlled hydraulic press to investigate the effect of die velocity, i.e. dynamic effects on various deformation characteristics, e.g. flow of material, densification during dry and lubricated interfacial friction conditions, bulging and strains at preform-free surfaces and die loads. The theoretical analysis for die pressure distribution, average die load and bulged profile by ‘upper bound’ approach has been presented. The identification of critical sinter-forging characteristics and their interrelationships are the cornerstones of present study. The effect of die velocity along with other deformation characteristics on die load and inertia energy dissipation has been investigated critically using ‘design of experiment’ technique and the important interactions have been displayed graphically using ‘response surface methodology’ technique. The study on dynamic effects revealed that die velocity is the most critical factor during sinter-forging operations, especially at higher die speeds and hence, inertia energy must be considered during its analysis. The experimental and theoretical results have been found in close agreement with each other and it is expected that the work will be highly useful for the assessment of various deformation characteristics during processing of sintered materials.     

Crystal structures and phase transformation of deuterated lithium imide, Li2ND

Half-Heusler compounds of Sn-doped TiCoSb “TiCoSn_xSb_1−x (x = 0.0, 0.01, and 0.05)” were prepared and their thermoelectric properties were measured above room temperature. From the EDX analysis, all the samples have three phases: the TiCoSn_xSb_1−x, Co-rich, and Ti-rich phases. The values of the thermoelectric power increase with Sn doping, and a positive thermoelectric power is obtained in the sample of TiCoSn_0.05Sb_0.95. The thermal conductivity decreases both with increasing temperature and with Sn content. The maximum value of ZT for p-type material is 0.030 at 988 K in the sample of TiCoSn_0.05Sb_0.95.     

Corrosion of Three Commercial Steels Under ZnCl2 –KCl Deposits in a Reducing Atmosphere Containing HCl and H2S at 400–500°C

The corrosion of three commercial steels in a reducing atmosphere containing HCl plus H₂S in the presence of ZnCl₂–KCl deposits has been investigated at 400–500°C and compared with the corrosion of the same materials in a similar gas mixture free from H₂S. The presence of H₂S in the gas accelerated the corrosion of the three commercial steels beneath ZnCl₂–KCl deposits. All materials suffered from severe corrosion with partial detachment and spalling of the external scales. Degradation of the steels resulted from the penetration of chlorine-containing species through the scale formed initially down to the metal matrix, because chorine-rich species were detected close to the alloy/scale interface. Although the corrosion resistance generally increased with increasing Cr content, even the high-Cr stainless steel SS304 is still unable to provide good corrosion resistance against the ZnCl₂–KCl deposits in the presence of H₂S due to the bad adherence of the scales to the alloy. The mechanisms of attack are discussed on the basis of thermodynamic considerations and of the active-oxidation model.     

WE54镁合金中析出相的特点

WE54(Mg-5.4Y-2.3Nd-1.6Gd-0.5Zr)镁合金试样在铸态、T4和T6状态下,呈现出不同的显微组织形貌特征和微区化学成分,而且力学性能也随着处理工艺的不同而发生变化。采用金相显微镜、大功率X射线衍射仪、高分辨场发射扫描电镜及能谱仪分析研究了WE54合金的微观组织形貌、析出相以及微区化学成分的变化。结果表明,WE54合金在铸造状态下,Mg12Nd和Mg24Y5两种新相沿着晶界析出,呈现出网状结构,稀土Gd完全固溶在基体之中,在晶内和晶界析出物的微区化学成分分析中没有发现Gd;经过固溶处理后,铸态时沿晶界分布的大块析出物几乎全部固溶于基体Mg之中,力学性能有所提高;经过人工时效后,晶内析出大量细小的新相。经过对比试样沿横向和纵向析出相的特点,确定该析出相为片状结构。析出相沿3个方向排列分布,而且3个方向之间夹角互成120°,呈现出严格的位向关系,合金的强度进一步得到提高,但伸长率有所降低。     

双层晶粒硬质合金的试制

介绍双层晶粒硬质合金的制做方法，双层晶粒结构的合金与双重晶粒合金的区分在于晶粒层次分明，属于均匀晶粒结构范畴，这种结构的硬质合会有良好的综合性能，能够满足某些产品的特珠要求，实用性比较广。     

碘化钛的电子束熔炼提纯效果分析

通过对碘化钛电子束熔炼提纯效果分析，提出合理、经济的高纯钛制取工艺路线。     

Effect of pulse rise time on charging effects in plasma immersion ion implantation with dielectric substrates with planar and cylindrical geometries

Using a one-dimensional self-consistent fluid model, the effect of pulse rise time on charging effects at dielectric surfaces is investigated during plasma immersion ion implantation (PIII) with planar and cylindrical geometries. The numerical results demonstrate that the pulse rise time plays an important role in PIII process with dielectric substrates. It is found that the charge dose accumulated on the dielectric surface is significant as decreasing pulse rise time, and the surface potential decreases at the later stage of the pulse, which results in the lower ion impact energy. On the other hand, the longer pulse rise time would lead to the lower charge dose accumulated on the dielectric surface and higher ion impact energy at the later stage of the pulse, which would elevate the effective implanted dose and introduce the ions to the depth deep enough for surface modification.     

Effect of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece

Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerical simulation of vacuum hot bulge forming process of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC Marc. The effects of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece were analyzed by numerical simulation. The simulated results show that the Y-direction displacement and the equivalent plastic strain of the workpiece increase with increasing bulge temperature. The residual stress decreases with increasing bulge temperature. The optimal temperature range of BT20 titanium alloy during vacuum hot bulge forming is 750-850 ℃. The corresponding experiments were carried out. The simulated results agreed well with the experimental results.     

Ti-22Al-25Nb合金ISM熔炼过程中的成分控制

采用X荧光光谱(XRF)分析水冷铜坩埚真空感应炉熔炼(ISM)加入和不加入稀土Y的Ti-22Al-25Nb合金铸锭成分,分析结果表明,在保证获得成分均匀的合金铸锭的情况下,Al的挥发烧损在28.94%～33.88%之间;加入at为0.5%～1%Y,Y的挥发烧损在w为17.20%～34.26%;采取提高熔化温度降低保温时间的措施可以降低Al的挥发烧损.     

Group identification as a mediator of the effect of players’ anonymity on cheating in online games

This study aims to add to the discussion about the applicability of the classical deindividuation theory and social identity model of deindividuation effects (SIDE) in explaining online behaviours. It explores the effect of anonymity in facilitating social influence of group identity in online game cheating. A nationally representative survey was conducted face to face. Results from the survey administered in Singapore confirm predictions derived from the SIDE and challenge the classical deindividuation theory. Specifically, it was concluded that the frequency of gaming with online strangers (anonymous gaming) significantly predicted the frequency of cheating in online games. The effect of anonymity on game cheating was found to be significantly mediated by the group identification with online gaming communities/groups. Gender differences were found. Male gamers cheated more frequently than female gamers. Female gamers are more likely to cheat as a consequence of group identification than male gamers. Implications and future research are discussed.