PM 2 Tec 2003: PM industry turning the corner

Abstract

MPIF's 2003 International Conference on Powder Metallurgy and Particulate Materials in Las Vegas attracted 1100 delegates from more than 30 countries. JOSEPH M. CAPUS reviews the event, while JOHN DUNKLEY assesses developments pointing the way to higher density, higher performance PM components.     

Warm powder compaction substitutes conventionally double pressed and double sintered synchroniser hubs

Abstract

Within a project supported by the European Union a consortium consisting of the companies Fraunhofer Institute for Structural Durability LBF, AMES, Miba, GKN, Federal Mogul, Höganäs, RWTH Aachen, Peugeot/Citroën and Fiat worked on the realisation of heavyduty gearbox components by warm powder compaction technology. In this paper, part of this work will be reported, namely the manufacturing of synchroniser hubs by this new technology. Until now these hubs were manufactured by the double pressing and double sintering route.

Based on service load measurements in a gearbox of a Peugeot 506, vehicle fatigue tests were carried out with conventionally and warm pressed hubs. The results of fatigue tests with hubs as well as the durability tests carried out in the gearboxes of Peugeot/Fiat revealed the same performance for both technologies. As a consequence, the hubs produced by warm powder compaction can substitute for the ones produced conventionally. Further, the new technology reveals economic advantages with regard to the powder price as well as production costs.     

Volume changes of binary mixtures during solid state sintering

Abstract

The influence of the mixture concentration on densification of Fe-Cr, Fe-Mo, and Ti-Cu compacts during solid state sintering were investigated. The hypothesis was put forward before that only S and V shaped curves for concentration dependencies of densification exist as a result of solid phase sintering of mixtures. It was shown, in this paper, that the above idea on the existence only two types of the plots was correct. These curve shapes can be explained on the basis of diffusion interaction of metals, applying the multiparticle model of a two component compact.     

Tensile and fatigue properties of cold and warm compacted Alumix 431 alloy

Abstract

In this experimental study, tensile and fatigue properties of the Alumix 431 alloy (Al, Zn, Mg and Cu alloys) produced using the conventional press and sinter processes in different pressures and temperatures are investigated. The results clearly showed that the warm compacted specimens can reach the mechanical properties of the cold compacted ones under less pressure. In the fatigue tests it was observed that fracture started from large pores as shown in all scanning electron microscope (SEM) examinations and ductile fracture occurred. 85% of the 180 MPa/80°C and 77% of the 230 MPa/RT specimens fractured at the machined surface. Tensile and fatigue properties of warm compacted (180 MPa/80°C) and cold (230 MPa/RT) compacted specimens are almost equal at these same densities. This result indicates the economic benefit of warm compaction by the much lower applied compaction pressure.     

Low viscosity feedstocks for powder injection moulding

Abstract

Powder injection moulding (PIM) carried out with the use of low viscosity feedstocks offers numerous benefits for manufacturing small complex shape parts. Unlike typical high pressure metal injection moulding (HPIM) viscous feedstocks, soft tooling can be employed for prototyping and small volume manufacturing. Compared to HPIM, there are very few studies on the rheology of low viscosity feedstocks. The objective of this paper is to clearly determine, using a statistical method, optimal models which define viscosity as a function of three parameters: shear rate, temperature and solid loading for low viscosity feedstocks. With the statistical method employed, it was found that the models of Herschel–Bulkley, Arrhenius, and Maron and Pierce can be used respectively to effectively model each of the three parameters stated previously. Moreover, the combination of these three models in one global model is proposed to predict the combined effect of the three parameters on low viscosity PIM feedstocks.     

A way to reduce environmental impact of ladle furnace slag

Abstract

In the last decades the European steel industry has made continuous efforts to reduce residues and byproducts and to increase recycling in order to reduce its environmental impact. While some steelmaking slags have been widely characterised and, to a certain extent reused, ladle furnace (LF) slag is used in different applications because of its specific properties. The main purpose of the case study presented in this paper concerns the reduction of potential LF slag environmental impacts, because of its intrinsic physicochemical properties. During the handling and cooling of LF slag, it disintegrates into a powder due to instability of the dicalcium silicate, causing an increase in dust emissions to the environment. The approach presented in this paper aims to reduce this phenomenon in order to achieve a more sustainable solution in term of reduction of powder dispersion in the environment, of costs saving and of nuisance reduction in the surroundings areas.     

Modelling and characterisation of Mo2C precipitation and cementite dissolution during tempering of Fe–C–Mo martensitic steel

Abstract

The precipitation and Ostwald ripening behaviour of needle shaped Mo₂C particles during the tempering of a ternary Fe-C-Mo martensitic steel have been characterised and modelled, taking account of local equilibrium, the capillarity effect, and the simultaneous enrichment and dissolution of cementite. Particles of Mo₂C are represented as paraboloids of revolution, with the tip radius chosen to yield the maximum lengthening rate. Transmission electron microscopy has been used to validate the theory; measurements of the average length, volume fraction, and number density of particles showed good agreement with experimental observations.     

Fatigue crack growth in some PM low alloy steels consolidated by rotary forging and sintering

Abstract

Fatigue crack propagation rates under plane strain conditions have been investigated for three PM low alloy steels consolidated to high densities by rotary compaction followed by sintering and heat treatment. It is shown that the densities and properties are intermediate between those of pressed and sintered materials and of powder forged materials. Threshold stress intensities compare satisfactorily with those for wrought counterparts, but resistances to crack growth are inferior to those of wrought steels. Possible reasons for the properties of the rotary compacted materials are considered in the light of their microstructures and the behaviour of other PM materials.     

New viscoplastic model to simulate hot isostatic pressing

Abstract

Most of the numerical simulation software on the hot isostatic pressing (hipping) process is based on viscoplastic modelling of densification, such as the well known Abouaf's model. These constitutive equations are generally obtained from a viscoplastic potential depending on Green's equivalent stress. An implicit coupling between isotropic and deviator parts is therefore only defined by an equivalent stress. A new viscoplastic formulation proposed by Stutz introduces an explicit coupling between isotropic and deviator parts of the stress state, allowing then more flexibility to take into account the experimental results achieved from isotropic, die compaction, and creep tests. This paper deals with the presentation of this new formulation which has been implemented in the finite elements software PreCAD, and the subsequent changes observed in numerical simulations. These simulations achieved with PreCAD software, are compared with an experiment on a complex part manufactured by CEA Grenoble.     

Inferences on plastic properties and coefficient of friction during simultaneous compression deformation of dissimilar sintered powder metallurgical preforms

Abstract

Plastic working of powder metallurgical (PM) material necessitates the development of fundamental data such as flow stress, densification behaviour, coefficient of friction, apparent strength coefficient, apparent strain hardening exponent, plastic Poisson's ratio, etc. In the present work compression and standard ring compression tests have been carried out to generate the fundamental data for simultaneous deformation of sintered steel and copper powder metallurgical preforms. The results reveal that the behaviour of individual materials during simultaneous deformation is strongly influenced by local micromechanical interactions at the metal - metal interface. In addition to this, the test conditions (iso-stress and iso-strain) strongly influence the severity of interaction. The interfacial friction coefficients are less than that of the same material when tested between hard tools. The optimal process parameters with higher interfacial friction, which can enhance the solid state joining of dissimilar materials, have been identified. The flow stress of the composite (steel - copper combination) during simultaneous deformation can be estimated if the flow stress of the individual materials comprising the combination/composite are known. With these studies, it should be possible to extend the inferences to the major deformation processes.