Interfacial microstructure and mechanical behaviour in laser clad TiCp/Ni alloy coatings

Abstract

Coatings of TiC_p reinforced composite have been produced by laser cladding. Two kinds of coating with different TiC_p origins were investigated, i.e. undissolved TiC_p and in situ TiC_p. For undissolved TiC_p, epitaxial growth of TiC, precipitation of CrB, and a chemical reaction occur at phase interfaces, and nanoindentation loading curves show pop in marks caused by the plastic deformation associated with crack formation or debonding of TiC_p from the matrix. As for in situ TiC_p, no pop in mark appears. Meanwhile, in situ TiC_p produces hardness and elastic modulus values that are higher than those produced by the coating that contains undissolved TiC_p.     

New processes or old: complex shape processing of advanced ceramics

Abstract

Demand for advanced ceramics with more complex shapes continues to grow. This in combination with the need for more reliable components has forced manufacturers to look for improvements in their current processing techniques and to adopt new processes which may be better suited to fulfil market demand. New processing concepts have emerged over the past decade on two fronts, improved casting technologies, and rapid manufacturing routes that do not require moulds. In the present paper, examples of both routes are given. Possible advantages of combining conventional and emerging methods are discussed.     

Electrodeposition of Cu from acidic sulphate solutions in presence of Bis-(3-sulphopropyl)-disulphide (SPS)

Abstract

This paper deals with the behaviour of bis-(3-sulphopropyl)-disulphide Na salt (SPS) during Cu electrodeposition from an acidic sulphate solution. This investigation was carried out by cyclic voltammetry and in situ Raman spectroelectrochemistry. Parameters describing nucleation, charge transfer kinetics, mass transport effects and anodic stripping behaviour were derived by quantitative analysis of the cyclic voltammograms. SPS effects have been found on nucleation rate, exchange current density and cathodic Tafel slopes. Voltammetry highlighted the cathodic reactivity of SPS. In situ surface enhanced Raman spectroscopy spectra can be measured only at low cathodic polarisations and for limited electrodeposition times. In situ solution Raman spectroscopy was carried out separately on the catholyte, anolyte and undivided cell. Progressive decrease in the S–S vibration could be followed both in the catholyte and in the anolyte. Cathodic formation and further reaction of thiol and the formation of Cu containing complexes in the undivided cell was assessed.     

UV Laser Micromachining of Polymers for Microfluidic Applications

We have recently begun to explore the use of UV laser ablation micromachining to construct microfluidic devices in polymers. This technique can create microchannels rapidly and modify the resulting polymer surface in a single step. By ablating under different atmospheres, it is possible to alter both the surface chemistries and physical surface morphologies of the microchannels. We have employed electroosmotic flow measurements, chemical mapping, and optical microscopy to characterize the microfluidic devices. In addition, we have studied the parameters affecting the ablation, such as the laser wavelength, laser fluence, laser firing repetition rate, and the material being ablated.     

Processing and damping behaviour of porous copper

Abstract

The well distributed open cellular porous copper was fabricated by present powder metallurgy technique based on space holder method, Depending on the volume fraction and size of the space holding particle, the porosity can be varied in the wide range of 30–85% and pore size from micron to millimetre in magnitude of order respectively. The damping behaviour and related relative dynamic modulus of the porous copper were investigated by a multifunction internal friction apparatus as a function of temperature from room temperature to 600°C. The results of investigation disclose that the porous copper can obtain a higher damping capacity than that of bulk one. In addition to this, an internal friction peak was found in the spectra of internal friction against temperature for the porous copper, it was proposed that the viscous sliding of the grain boundaries should be responsible for the appearance of the peak, and the dependence of the peak on porosity can be understood in terms of the anelastic relaxation mode of grain boundary.     

PRESSURE FORCE CONTROL FOR FABRICATION OF PLASTIC MICROFLUIDIC CHIPS WITH HOT EMBOSSING METHOD

A pressure force control system for hot embossing of microfluidic chips is designed with a moment motor and a ball bearing lead screw. Based on the numeric PID technique, the algorithm of pulsant integral accelerated PID control is presented and the negative effects of nonlinearity from friction, clearance and saturation are eliminated. In order to improve the quick-response characteristic, independent thread technique is adopted. The method of pressure force control based on pulsant integral accelerated PID control and independent thread technique is applied with satisfactory control performance.     

A review of laser fabrication of metallic engineering components and of materials

Abstract

The state of the art and directions for the future development of two laser based technologies, direct laser fabrication in which powder is fed into the focal point of a laser, and a laser powder bed technology are outlined in this review. The areas in which these technologies have made significant contributions are: the manufacture, directly from powder, of alloys and of functionally graded materials which enables a range of compositions to be assessed rapidly and the manufacture of net shape and the repair of engineering components. It is suggested that rapid assessment of structure/property relationships in a range of compositions will continue to be a useful application of laser fabrication. It is further concluded that the two approaches, direct laser fabrication and laser powder bed will continue to be developed since each has its own advantages and disadvantages; direct laser fabrication is the preferred technique for alloy development work and for component repair but laser bed technology is currently the preferred technology for the manufacture of small components which require a good surface finish. Improvements in surface finish, in dimensional accuracy, in microstructural control and in process control with real time feedback to control properties are nevertheless required if these technologies are to increase their impact in the area of the manufacture of net shape components.     

Guest Editorial: Personal perspective on microstructure of steels: 25th anniversary of MST and collection of papers in honour of Sir Robert Honeycombe

Abstract

The shape memory properties and microstructure associated with γ(fcc) → ?(hcp) martensitic transformation in an Fe–14Ru alloy have been investigated. The degree of shape recovery was measured via a bending test, and the microstructure was examined using X-ray diffractometry, optical microscopy, and transmission electron microscopy. The Fe–14Ru alloy showed shape recovery to some extent, but to a lower degree than in Fe–Mn–Si based shape memory alloys. The lower strength of the matrix, the presence of ? and α′ martensites at room temperature, and the higher stacking fault energy in the Fe–14Ru alloy are thought to be responsible for the weaker shape memory effect.