Design and strengthening behaviour of Ti2AlC/TiAl composite by low-temperature hot-pressing process

In situ Ti₂AlC/TiAl composite was first fabricated by reactive hot-pressing technique at low temperature of 1150°C for 2?h using Ti₃AlC₂ and Ti–Al alloy powders. The composite with fine-grained structure consisted of TiAl, Ti₃Al and Ti₂AlC phases. The Vickers hardness, flexural strength and fracture toughness of the Ti₂AlC/TiAl composite reached 5.2?GPa, 937.7?MPa and 7.7?MPa?m^1/2, respectively. The action mechanism for the composite was mainly attributed to the grain refinement, the uniform distribution of the dispersed Ti₂AlC particles, transgranular cracking, crack deflection, crack bridging and pull-out of Ti₂AlC.     

A Nanoindenter Based Investigation of Gold–Ruthenium Alloy Microcontact Behavior under Cyclic Condition

Abstract

A nanoindenter based experimental setup was used to characterize gold–ruthenium (Au5%Ru) microcontact behavior under cycling and hot-switching conditions where a cantilever beam with a contact bump was cycled in and out of physical contact with a flat plate to simulate the action of MEMS ohmic contact switches. Cantilever beam and flat plate were fabricated from silicon, and then sputter coated with 300 nm of Au5%Ru as the contact material. All contacts failed in adhesion with either shorter fatigue life (about 1–2 million cycles) or longer life (about 6 million cycles). The smoother contact surface had shorter fatigue life. The Au5%Ru contact material had longer life and higher resistance than gold. Further, contact resistance was constant during cycling up to failure. Different contact parameters: adhesion force, threshold force, strain hardening/softening and plastic deformation were monitored during cycling. Adhesion force in Au5%Ru microcontact was smaller than in gold. Threshold force was larger in Au5%Ru than in gold. Time-dependent and plastic deformations as well as cyclic softening were observed in Au5%Ru. Thus, elastic-viscoplastic material model(s) with strain softening capability are needed for the analysis of Au5%Ru microcontact behavior.     

Mechanics of the indentation test and its use to assess the adhesion of polymeric coatings

The indentation test provides a simple means by which the adhesion of coatings can be qualitatively assessed. On the way to establishing a quantitative measurement of the adhesion strength of coatings and films, it is important that the mechanics of this test are clearly understood. To investigate the influence of factors such as the coating thickness, the indenter radius, and friction during the test, numerical simulations of the indentation of a typical polymeric coating, polymethylmethacrylate (PMMA), bonded to a rigid substrate were conducted by using the finite element method. The stress generated during the indentation test were obtained by employing an accurate constitutive model of the elastic-viscoplastic behaviour of the polymeric coating under consideration. The results of this analysis illustrate the effects of the factors mentioned above on the deformation of the coating during indentation, its confinement, and interfacial shear, and the normal, shear, and hoop stress distributions occurring during indentation. These results provide insight into the possible failure mechanisms operative during the indentation of thin coatings and the important effects of the coating thickness during such tests.     

Effects of the functional groups of polystyrene on its adhesion improvement and corrosion resistance

Novel functionalized polystyrenes having groups such as epichlorohydrin, epoxy, acetyl, C=C double bond, and carboxyl were synthesized by the reaction of polystyrene with epichlorohydrin, unsaturated hydrocarbons, and organic anhydrides in the presence of Lewis acid catalysts. The adhesion capability and corrosion resistance of the new synthesized functionalized polystyrenes to metals under various conditions were investigated. A very good relationship was observed between the quantity of functional groups bonded to the aromatic rings of the polystyrenes and the adhesion and corrosion resistance properties of the polyfunctionalized polystyrenes. It was also observed that the new polyfunctionalized polystyrenes obtained by chemical modification with maleic anhydride, acetic anhydride, isoprene, butadiene, and epichlorohydrin in the presence of cationic catalysts resulted in high adhesion and anti-corrosion properties.     

HYBRID NEURAL MODELLING OF FLUIDISED BED DRYING PROCESS

The aim of this study was to investigate the applicability of hybrid neural models in modelling of drying process. A study aimed at extending a neural network mapping was also carried out. In this approach dimensionless numbers (Re, Ar, H/d) were used as inputs to predict the heat transfer coefficient in a fluidised bed drying process. To produce a data set necessary to train the networks, trials of drying different materials in a fluidised bed were carried out. On the basis of this network, a hybrid model describing the process of drying in a fluidised bed dryer was built. Results obtained were compared not only with available experimental data but also with results obtained using other types of models: a pseudo-dynamic neural model and a classical mathematical model. The analysis of results leads to a conclusion that hybrid models constitute a solid alternative method of process modelling.     

EFFECT OF ADDITION OF VARIOUS ACRYLATES ON THE PERFORMANCE OF ETHYL CYANOACRYLATE ADHESIVE

Polyalkyl 2-cyanoacrylates begin to retropolymerize and deteriorate dramatically at temperatures above 80°C. They bond rapidly to the metal surfaces and readily lose strength even at ambient temperatures. These two drawbacks of the cyanoacrylates have made this class of adhesives unpopular as structural adhesives. Several attempts have been made to increase the thermal stability and the stability of the bond between the metal surfaces by adding chemicals like cyclopentadienoates and anhydrides to the cyanoacrylates. Cyclopentadienoates are not available commercially, and, therefore, in this study, we have selected various acrylates and methacrylates in the cyanoacrylate formulation and these were tested to various temperatures. Interesting results have been obtained and reported.     

Thermal and ablative properties of binary carbon nanotube and nanodiamond reinforced carbon fibre epoxy matrix composites

The thermal and ablative properties of carbon nanotube (CNT) and nanodiamond (ND) reinforced carbon fibre epoxy matrix composites were investigated by simulating shear forces and high temperatures using oxyacetylene torch apparatus. Three types of composite specimens—(i) carbon fibre epoxy matrix composite (CF/Epoxy), (ii) carbon fibre epoxy matrix composite containing 0.1 wt-% CNTs and 0.1 wt-% NDs, and (iii) carbon fibre epoxy matrix composite containing 0.2 wt-% CNTs and 0.2 wt-% NDs—were explored. The ablative response of composites was studied through pre- and post-burnt SEM analysis and further related with thermogravimetric analysis, weight loss profile and thermal conductivity measurements. The novel nanofiller composites showed marked improvement in their thermal and ablative properties. A 22% and 30% increase in thermal conductivity was observed for composites containing 0.1 wt-% CNTs/0.1 wt-% NDs and 0.2 wt-% CNTs/0.2 wt-% NDs respectively. These nanofillers also improved the thermal stability of thermosetting epoxy matrix, and an increase of 13% and 20% was recorded in the erosion rate of composites containing 0.1 wt-% CNTs/0.1 wt-% NDs and 0.2 wt-% CNTs/0.2 wt-% NDs respectively. This improvement is due to the increased char yield produced by the increase in the loading of nanofillers, i.e. CNTs and NDs. Insulation index and insulation to density performance have also been improved due to increased thermal conductivity and char yield.     

机械镀铜及铜合金工艺及其耐蚀性研究

在机械镀锌和机械镀铝-锌工艺的基础上,通过调整活化剂和促进剂的种类及用量,研制开发了机械镀铜及铜合金工艺.利用该工艺在钢基表面上得到了铜以及铜-锌、铜-锌-铝、铜-镍等合金镀层.这些铜及铜合金镀层的耐蚀性能皆好于机械镀锌层,尤以铜-镍合金镀层的耐蚀性能最高,提高15倍左右;在铜-锌中加入2%～3%的铝可以进一步将铜-锌合金镀层的耐蚀性能提高2～3倍.     

化学复合镀的研究现状及镀层的应用

化学复合镀层因复合粒子的性能特点而广泛应用本文就国内外化学复合镀的研究现状和发展趋势进行了综述具体从硬度、耐磨性、自润滑性方面对各种Ni-P基、Ni-B基化学复合镀的工艺研究及镀层结构与性能特点进行了阐述,并认为目前关于化学复合镀的研究仍然集中在耐磨和自润滑镀层方面对不同化学复合镀层的应用做了总结,并对其提出了展望。     

Zn-Ni合金镀层的黑色钝化工艺研究

在含M为10％～14％的Zn-Ni合金镀层上先钝化再进行封闭处理,可获得色泽均匀、结晶细致的转化膜、讨论了钝化工艺条件及封闭剂、pH值对转化膜耐蚀性的影响：经过正交实验和单因素实验,确定了最佳钝化配方为：40g/L铬酐、40mL／L醋酸、10g/L成膜促进剂、0．45h/L硝酸、温度20℃、时间30～40s。研究了封闭条件,确定的封闭剂的组成为：120～220g/L硅酸钠,1～3g/L氟化钠,0．1～0．3g/L硫酸锂,最佳pH值为10．5硫酸铜点滴实验、中性盐水浸泡实验、扫描电镜以及交流阻抗测试表明：Zn-Ni合金镀层先经钝化再经封闭处理后耐蚀性能明显提高：该钝化工艺操作简单,具有应用价值．