Investigation of microstructure and mechanical properties of steel fibre–cast iron composites

Abstract

The aim of the present experimental study was to investigate improvement of the toughness and strength of grey cast iron by reinforcing with steel fibres. The carbon content of the steel fibres was chosen to be sufficiently low that graphite flakes behaving as cracks were removed by carbon diffusion from the cast iron to the steel fibres during the solidification and cooling stages. To produce a graphite free matrix, steel fibres with optimum carbon content were used and the reinforced composite structure was cast under controlled casting conditions and fibre orientation. Three point bend test specimens were manufactured from steel fibre reinforced and unreinforced flake graphite cast iron and then normalising heat treatments were applied to the specimens at temperatures of 800 and 850°C. The fracture toughness and strength properties of the steel fibre reinforced material were found to be much better than those of unreinforced cast iron. The microstructures of the composite at the fibre–matrix transition zone were examined.     

Calcium silicate based high efficiency thermal insulation

Abstract

The preparation by hydrothermal synthesis of a high efficiency, calcium silicate based thermal insulation is described using raw material mixes of silica, bentonite, and magnesium acetate or acetic acid. The materials were reacted in a high pressure autoclave at 200–250°C resulting in a product consisting of cenospheres of needle-like xonotlite crystals and some tobermorite. Properties including density, strength, microstructure, thermal stability, and water absorption and water repellence are presented.     

Numerical simulation of metal powder die compaction with special consideration of cracking

Abstract

Powder die compaction is modelled using the finite element method and a phenomenological material model. The Drucker–Prager cap model is modified with the goal to describe the formation of cracks during powder transfer, compaction, unloading, and ejection of the parts from the die. This is achieved by considering the cohesive strength and the cohesion slope, which characterise the current strength of the powder compact in the Drucker–Prager model, as state dependent variables. Evolution equations are formulated for these variables, so that the strength increases by densification and decreases by forced shear deformation. Some of the parameters appearing in the evolution equations are determined from measured green strength values. An iron based powder (Distaloy AE) is used for the experiments. Examples are shown to demonstrate that the density distribution can be calculated accurately as compared with an experiment, that cracking can be modelled at least qualitatively correctly, and that the compaction of complex 3D parts can be simulated.     

Behaviour of metal powders during cold and warm compaction

Abstract

An instrumented die was used to investigate the behaviour of metal powders during cold (ambienttemperature) and warm (up to 140^°C) compaction. This instrument enables simultaneousmeasurement of density, die wall friction coefficient, the triaxial stresses acting on the powderduring the course of compaction and ejection pressure. Commercial iron, titanium, aluminium,316L stainless steel (SS) and aluminium–silicon powders were employed for investigation. Theresults demonstrated the advantages of powder preheating on the compaction behaviour of metalpowders concerning green density, dimensional changes, frictional behaviour, ejectioncharacteristics and compactibility. However, the outlines also determined that the response ofthe non-ferrous powders to powder preheating is somehow different from those of the ferrouspowders. In this context, the behaviour of prealloy aluminium–silicon powders during compactionwas found of particular interest, as their compactibility is strongly affected by powder preheating,whereas the dimensional changes after ejection decrease considerably. This article presents theeffect of cold and warm compaction on the consolidation and ejection characteristics of ferrousand non-ferrous metal powders. The influence of compaction condition (pressure andtemperature) with considering of the powder characteristics and densification mechanisms areunderlined.     

Rheology Feature of Simple Metal Melt

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Surface Modification of Polymer Films for Improved Adhesion of Deposited Metal Layers

Plasma treatment and vacuum Al deposition on films from biaxially oriented polypropylene is a multistep large scale industrial process, mainly ending up in packaging film laminates. As atmospheric plasma treatment processes suffer from lack of reproducibility, low pressure plasma treatment processes that can be operated in-line with the metal deposition are being developed. Process development is difficult, because the final packaging film laminate has to deliver optimum properties of adhesion as well as of the barrier against oxygen and water vapor permeation. As a typical production run involves tens of thousands to up to one hundred thousand square meters of film, experiments on an industrial scale are expensive, so smaller scale experimental processes are needed, which so far do not match well enough with industrial process characteristics. Moreover, bonding mechanisms between the treated substrate film and the deposited Al layer are not sufficiently understood. This paper describes the sequence in development and optimization of substrate films and plasma treatment that has been performed on an experimental as well as on an industrial scale. A sufficient correlation between experimental and industrial scales was achieved, which helps to perform development and optimization on a small scale before scaling up to industrial processes. However, improvement is still needed both in fundamental understanding of the aluminum–polypropylene interface as well as in experimental equipment and methodology.     

Multilayer Metal Film Plating on Glass

It has been shown that an under-layer of SiO₂ · nH₂O on a silicate glass surface, promotes the adsorption of Sn(II) hydroxycompounds, resulting in the formation of Sn–O–Si chemical bonds. It also: contributes to the formation of monodispersed Sn(II) compound nanoparticles; levels the glass surface micro-relief; ensures the deposition of fine-grained metal films; increases the rate of Ni–P and Cu electroless plating; and increases the rate of the adhesion interaction between the surface of the silicate glass and metal films. It opens up the possibility of electroless and electrochemical plating of 5–10 μm thick multilayer metal and alloy films.     

Material and processing behaviour of thermoplastics filled with low melting metals

Abstract

Polymer blends filled with solid fillers such as metal fibres or carbon black can no longer fulfil the increasing demands on electrical and thermal conductivity. High levels of hard fillers increase the melt viscosity unacceptably, causing a minimised process window, high mechanical stresses on the polymer as well as an increased abrasion on both mould and machinery. The high electrical conductivity required for connectors, moulded interconnect devices or sensors can be achieved by a novel material developed by IKV, Aachen, and Siemens AG, Erlangen/Germany. It combines fibre filled polymer blends with low melting metal alloys. These alloys have the advantage of being already molten during processing and of not solidifying before the cooling phase. The result is a free flowing material that allows the injection moulding of complex geometries. A passage conductivity of the moulded parts in the range of pure metals can be achieved.     

Highly porous metals and ceramics

Abstract

Cellular solids are a class of highly porous materials that covers a wide range of structures, such as foamed materials, replicated porous or additive manufactured structures, honeycombs, lattice structures, interconnected fibres or hollow spheres and syntactic foams. The pores can be more or less closed or completely open. Depending on their morphology and composition, these materials possess unique properties and are used as components in special and advanced engineering applications. These include filtering liquids and particles in gas streams, porous burners, biomedical devices, lightweight stiff structures, impact absorbers, sound damping modules, thermal management components, etc. The present paper gives an overview on the main fabrication methods and the resulting architectures, in relation to applications of metals and ceramics with >50 vol.-% porosity.     

Aluminium powder particles produced by SAMD technique: typical characteristics and correlations between processing conditions and powder size

Abstract

The present paper consists of two parts. In the first part the principles of a new method of metal powder production, termed 'solid assisted melt disintegration (SAMD)' are discussed and the typical characteristics of the produced powder are outlined. In the second part the effects of some processing parameters on the size distribution and mean diameter of the powder are reported. The SAMD method involves mixing solid particles (i.e. alumina) with the liquid aluminium alloy aided by mechanical agitation. The shear force induced by the impeller is transferred to the metal via the non-wetting solid medium and results in melt disintegration. The resulting mixture of aluminium droplets and alumina particles are subsequently cooled in air and screened through 300 μm sieve to separate alumina from solidified aluminium powder particles. The SAMD technique has demonstrated the capability to produce a wide particle size distribution. The small sized particles (i.e. <53 μm) exhibited irregular shapes, but larger ones were mostly spherical. These powder particles were dense (pore free) without attached satellite particles and exhibited a relatively coarse microstructure. The processing parameters investigated include the size of Al₂O₃ particles, Al₂O₃/Al weight ratio, stirring speed and stirring time. It was concluded that there exists an optimum value for each of the aforementioned parameters corresponding to a minimum in the mean particle size.