Fracture and mechanical properties of steel fibre reinforced Zn–5Al (Zamak 5) alloy

Abstract

Steel fibre reinforced Zn–5Al alloy (Zamak 5) metal matrix composite beams with different volume fractions of steel fibres were produced with varying notch to depth ratios. The fracture and mechanical properties of the specimens were investigated for their mode I fracture behaviour using three point bending tests under static loading at room temperature. Steel fibres with contents of 1, 2 and 3% of the total volume of Zn–5Al alloy were used as matrix materials. The critical stress intensity factor was determined using the initial notch depth method.     

Formation of sulphide 'patches' on inclusions in C – Mn steel weld metal

Abstract

Following earlier observations indicating that sulphide coatings can form on inclusion surfaces in a C – Mn steel weld metal when cooled from high temperature, experiments have been carried out to examine the effects of cooling rate on the nature of sulphide precipitation on inclusions when cooled through the austenite range. It is found that fast cooling rates give thin films whereas slow rates produce thick films or 'patches'. The increase in film thickness is assessed in terms of the S/Mn ratio as measured by EDX.     

Densification and microstructural evaluation during laser sintering of M2 high speed steel powder

Abstract

In the present work, the densification and microstructure of M2 high speed steel powder processed by direct laser sintering method was studied. Test specimens were produced using a 200 W continuous wave CO₂ laser beam at different scan rates ranging from 50 to 175 mm s^?1. The building process was performed under argon and nitrogen atmospheres in order to evaluate the role of sintering atmosphere. It was found that the sintered density strongly depends on the laser scan rate and thus on the duration time of the laser beam on the surface of the powder particles. Generally, with a decrease in the scan rate higher densification was obtained. However, formation of large cracks and delamination of the sintered layers is feasible at low scan rates. The results also demonstrated that sintering under argon atmosphere yields better densification compared to a nitrogen atmosphere, in particular at higher scan rates. The microstructure of laser sintered parts consisted of large and elongated pores parallel to the building direction. The metal matrix structure was found to be heterogeneous, i.e. carbon rich austenite was formed due to carbon segregation. This structure consisted of fine cellulars or dendrites of martensite and retained austenite. This article describes the influence of manufacturing parameters on the densification of laser sintered M2 high speed steel powder. The microstructural features of the processed parts are also addressed.     

Young's modulus and adhesion coefficient of amorphous Ni–P coatings on a metal substrate

In the present paper the Young's modulus and adhesion coefficient of amorphous Ni–P coatings obtained from aqueous solutions were determined. The measurements were carried out using a vibrating reed apparatus. In the temperature range 550–590 K, crystallization of Ni and formation of nickel phosphide Ni₃P were observed. The Young's modulus of Ni–P amorphous layers on stainless steel at room temperature was found to be about 112 GPa. The adhesion coefficient γ of the examined layers depends on the layer thickness a _f and strongly decreases for a _f > 8 μm. This dependence corresponds to the change of the relative adhesion coefficient of about 40% for 8 μm < a _f < 15 μm. It was also shown that the adhesion coefficient does not depend on the temperature, at least in the range 300–550 K.     

Effect of pulsed current on reactively synthesised TiB2 consolidated by plasma pressure compaction

Abstract

The effect of pulsed current on TiB₂ formed by reactive consolidation between titanium and boron is reported in this paper. This consolidation was performed using the plasma pressure compaction (P²C) technique. A comparison between the pulsed and control samples reveals that pulsed current reduces grain growth (pulsed samples had an average grain size of 2·79 μm compared to 5·99 μm) while increasing sintering rates (pulsed samples were on average 15·5% more dense). The reduced grain growth and increased densification is due to the removal of adsorbed oxygen from the surface of the powder.     

Adhesion of nylon-6 to triazine trithiol-treated metals during injection molding

Abstract —An examination was made of the adhesion of nylon-6 resin to treated metals such as phosphor bronze, brass plates, and electronickel platings during injection molding. No adhesion to any of these metals was noted to occur under ordinary injection molding conditions and an aqueous solution of 1,3,5-triazine-2,4,6-trithiol mononatrium (TTN) was thus used to induce adhesion. Following treatment with aqueous TTN solution under optimal conditions, nylon-6 adhered tightly to all the above metals under ordinary injection molding conditions. The TTN treatment led to the formation of surface films containing metal salts of 1,3,5-triazine-2,4,6-trithiol (TT). Conditions were made optimal with regard to time, temperature and TTN concentration. Adherent films were generally formed when bronze and brass were treated for short periods, at low temperature, and at low TTN concentration, although this was not the case with nickel plating. There was no adhesion to nickel plating even for a prolonged treatment time, high temperature, and high TTN concentration. Adherent and non-adherent films did not differ in the chemical structures of the metal salts of TT but they did differ in morphology. Good adhesion was noted in the case of TT-metal salts present at low density on the metal surface. Some films readily reacted with amino compounds under conditions similar to those generally used for the injection molding of nylon. The adhesion was concluded to be due to the formation of interfacial bonds during injection molding.     

Modelling of electromagnetic processes in system 'welding arc–evaporating anode' Part 2 – model of arc column and anode metal

Abstract

A mathematical model of electromagnetic processes occurring in the 'arc column–anode region–evaporating anode' system is suggested. Electric charge transfer processes in the multicomponent plasma of the electric arc and in the bulk of the metallic anode are described using the Ohm's law and charge conservation law generalised for a case of discontinuity of the electric field potential at the boundary between the arc plasma and the anode surface. A procedure was developed for finding the numerical solution of the stated problem by the shock capturing method, allowing modelling of the electromagnetic processes in the 'welding arc–evaporating anode' system in the presence of a reverse potential jump in the anode region (negative anode drop). Results of modelling of the said processes for gas metal arc and plasma transferred arc welding of steel in an inert gas (Ar) atmosphere are given.     

Hot chamber diecasting with Si3N4 ceramic injection system: application to aluminium alloy components

Abstract

Although hot chamber diecasting is an appropriate technology for producing high quality cast components, there are material limitations; at the process temperature, aluminium alloy erodes the immersed steel shot sleeve and plunger. Attempts have been made to employ a Si₃N₄ ceramic in place of steel. High quality Al hot chamber diecast components can be manufactured in this manner, but long production runs are not possible because failures occur in the ceramic sleeve even after, for example, a few thousand shots. The fracture in the ceramic sleeve is caused by high stresses arising from the plunger galling the sleeve surface owing to penetration of the Al alloy into the gap between the sleeve and plunger. The infiltrated Al alloy has been found to react chemically with the ceramics; silicon in the ceramic reacts with iron particles present as inclusions in the Al alloy. Hence, the purity of the molten Al alloy in the crucible is a significant factor in the production of high quality diecast components. To prevent penetration of the Al alloy, the injection system is cleaned periodically using hydrochloric acid, which dissolves the infiltrated Al alloy. Since etching by HCl can reduce the strength of the ceramic parts, this cleaning process must also be reconsidered. Recommendations to improve the quality of hot chamber diecast Al components are proposed.     

A New Concept for Adhesion Promotion in Metal–Polymer Systems by Introduction of Covalently Bonded Spacers at the Interface

A new concept for molecular interface design in metal–polymer systems is presented. The main features of this concept are the replacement of weak physical interactions by strong covalent bonds, the flexibilization of the interface for compensating different thermal expansions of materials by using long-chain flexible and covalently bonded spacers between the metal and the polymer as well as its design as a moisture-repellent structure for hindering diffusion of water molecules into the interface and hydrolysis of chemical bonds. For this purpose, the main task was to develop plasmachemical and chemical techniques for equipping polymer surfaces with monotype functional groups of adjustable concentration. The establishing of monotype functional groups allows grafting the functional groups by spacer molecules by applying usual wet-chemical reactions. Four processes were favoured for production of monotype functional groups by highly selective reactions: the plasma bromination, the plasma deposition of plasma polymers, the post-plasma chemical reduction of O-functionalities to OH-groups, and the chemical replacement of bromine groups by NH₂-groups. The grafting of flexible organic molecules as spacers between the metal layer and polymer improved the peel strength of the metal. To obtain maximal peel strength of aluminium coatings to polypropylene films and occurrence of cohesive failure in the polypropylene substrate, about 27 OH groups per 100 C-atoms or 6 COOH groups per 100 C-atoms were needed. Introducing C_6–11-aliphatic spacers 1 OH or COOH group per 100 C-atoms contributed about 60% of the maximal peel strength of the Al–PP system, i.e. 2 or 3 spacer molecules per 100 C-atoms were sufficient for maximal peel strength.     

Research on slag modifying agents for CaO–Mg based hot metal desulphurisation

Abstract

To improve the slag/iron separation problems in CaO–Mg based hot metal desulphurisation, experiments were carried out to generate a more fluid slag and to reduce the amount of hot iron entrapped within the desulphurising slag. The optimised slag modifying agent effectively decreased the melting temperature and viscosity of CaO–Mg based desulphurising slag. The optimised modifying agent has been successfully applied to industrial production. Industrial tests show that the average desulphurisation exceeded 82% when using the 80CaO–15Mg–5CaF₂ desulphurising agent at 3·5–4·0 kg t^–1, and with an average final S of 0·005%. The skimming time decreased from nearly 12 min to ～6·5 min. The heat loss during desulphurisation decreased to ～19°C which is favourable to the subsequent steelmaking process. Average total Fe content in post-desulphurisation slag is 34% with 0·7–0·8 kg t^–1 modifying agent, a decrease of ～30% in iron loss compared with current status.