Publications by Andreas Mortensen

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Metals are known to exhibit mechanical behaviour at the nanoscale different to bulk samples. This transition typically initiates at the micrometre scale, yet existing techniques to produce micrometre-sized samples often introduce artefacts that can influen ...

Metal Matrix Composite (MMC) materials provide combinations of properties which are of interest in several applications within the transportation industries. Their use in this industrial sector is, however, highly dependent on the simultaneous satisfaction of stringent performance and cost requirements. This is why solidification processing, which provides one of the most versatile and economical production routes for these materials, is the dominant process class used today for the production of MMC materi

In this work we develop a methodology to probe the strength and toughness of microscopic brittle phases by combining focused ion beam (FIB) milling methods with microtesting techniques and finite element simulation. We present results from tests conducted on alumina fibres and compare data thus obtained with known macroscopic fibre properties derived from tensile tests conducted on long sections of the fibres. The developed methodology is to be transposed towards the microscopic mechanical testing of irregu

This paper provides a review of theoretical and experimental research to date on the constrained steady state solidification of dilute binary alloy matrix composites. Steady state solidification can be experimentally observed in composites which contain a cylindrical reinforcement aligned parallel to the growth direction of samples solidified in a Bridgman furnace. Such experiments have been performed by several authors, using metallic or succinonitrile-based matrices. It is found that plane front, cellular

Sessile drop experiments on metal/ceramic systems have shown that an important improvement in wetting may be produced by introduction of alloying elements which form, by reaction at the metal/ceramic interface, a continuous layer of solid that is better wetted by the metal than the original substrate. We present results from a finite-difference analysis of the kinetics of reactive wetting under conditions where the rate of spreading is controlled by the rate of diffusion of the reactive solute element.

Circumferentially notched cylindrical bars of high volume fraction Al2O3 particle reinforced aluminium are tested in tension to probe the role of tensile stress triaxiality on damage and failure of such materials. The transverse strain is monitored with a ...

Particle Reinforced Metal Matrix Composites (PRMMCs) are produced by high-pressure infiltration of ceramic particle beds. Matrix materials are either pure Al or Al-4,5%Cu, and the reinforcement is made either of angular or of polygonal alumina particles. The resulting composites feature a high volume fraction (40-60%) of uniformly distributed reinforcement. These materials accumulate damage during deformation, in the form of particle cracking or matrix voiding; localization of damage induces final failure.

The densification rate and microstructural evolution of powder compacts densifying by solution-reprecipitation in the presence of a liquid phase are predicted with the assumption that solid particles are equisized spheres randomly packed and pulled together by a liquid that wets perfectly both the solid and its grain boundaries. The influences of applied pressure, initial packing density and of the ''sphering force'' due to changes in solid particle shape are accounted for. The resulting sintering rate reta

Infiltration by a pure matrix in the presence of preform deformation and partial matrix solidification is analyzed using a bounding approach for the preform rheology where solid metal is present. It is found, using parameters for the infiltration of short alumina fiber preforms by aluminum, that the two bounds are close in comparison to other factors of uncertainty in the prediction of infiltration rate. Using this approach, preform compression is shown to exert a significant influence on the infiltration r

A simplified model is proposed to quantity the effect of damage in the form of particle cracking on the elastic and plastic behaviour of particle-reinforced metal matrix composites under uniaxial tensile loading: cracked particles are simply replaced, in a ...

Activation volumes characteristic of room temperature compressive plastic deformation in Au- 45.2 at.% Cu- 1.7 at.% Pt, a near-AuCu alloy that orders to a fully L1(0) structure, are measured using the repeated stress-relaxation method. Four different ordering treatments (540 and 10(5)s at either 250 or 400 degrees C) are conducted on samples prior to deformation, leading to a classical two-variant polytwin structure after ordering at 400 degrees C, or alternatively a three-variant highly twinned structure a

Preforms of nickel powder or nickel/alumina powder blends were infiltrated with molten aluminum to produce nickel aluminides. Application of a pressure of 3.6 and 6.9 MPa on the melt allowed infiltration of preforms with nickel powder particles between 5 and 15 mum in diameter, which could not be infiltrated under the sole action of capillary forces. By varying the initial preform temperature from 705-degrees-C to 280-degrees-C, the diameter of nickel powder particles from 15 to 150 mum, and the volume frac

Composite materials are often made by infiltration, that is, by injecting a liquid matrix between packed solid fibers or particles. We give here direct proof that molten copper, slowly infiltrated into a broad spectrum of preforms, displays in initial phases of the process universal scaling and fractal geometric features that are characteristic signatures of percolation-dominated flow. Implications are that the microstructure of infiltrated composite materials can develop over length scales that far exceed

Infiltrated particle reinforced composites combine a dense matrix with particles that are in mutual contact and can therefore transfer compressive stress directly from one particle to the next. As a result, these composites may combine characteristics of t ...

Monocrystalline microwires of silver are produced by means of a novel casting process that combines precise mold production by silicon microfabrication with molten metal pressure infiltration. The wires have a shape amenable to tensile testing and a diamet ...

A method is presented that extends the replication process for the manufacture of open-celled metallic foams to include foams with spherical cells. Such foams are produced to a wide range of relative densities, tested for mechanical behaviour and resistanc ...

We show that steel-magnesium alloy laminated metal composites (LMCs) can be produced by gas pressure infiltration of a liquid magnesium alloy between layers of stacked dimpled steel sheets. Resulting LMCs are amenable to subsequent warm rolling. The LMCs a ...

Microcellular aluminium can be produced by replication in porous material with pores across a wide range of sizes but with otherwise identical structures. Compressive tests reveal a plasticity size effect, with samples showing higher strengths and higher r ...

A replication process for producing fine open-celled ceramic foam from preceramic polymers is presented and analysed. In this process, a porous sodium chloride compact formed by sintering was first infiltrated with polycarbosilane. After dissolution of the salt, the resulting polymer foam was cured by oxidation in air and pyrolysed to form a silicon carbide foam. The curing stage is the most critical step, and was investigated using a series of controlled curing experiments and finite-difference modelling o

Andreas Mortensen

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Cast aluminium single crystals cross the threshold from bulk to size-dependent stochastic plasticity

Solidification-processed metal matrix composites for the transportation industries

Probing the microscopic strength of alumina reinforcements

Steady-State Solidification Of Reinforced Binary-Alloys

Modelling kinetics of diffusion controlled reactive wetting: the role of reaction behind the triple line

Fracture of high volume fraction ceramic particle reinforced aluminium under multiaxial stress

Damage and fracture of particle-reinforced metal matrix composites

Kinetics of densification by solution-reprecipitation

Infiltration of fibrous preforms by a pure metal: Part V. Influence of preform compressibility

Tensile flow stress of ceramic particle-reinforced metal in the presence of particle cracking

Thermally activated deformation of two- and three-variant nanotwinned L10 Au–Cu–Pt

Synthesis Of Bulk And Reinforced Nickel Aluminides By Reactive Infiltration

Percolation and Universal Scaling in Composite Infiltration Processing

Effect of hydrostatic pressure on flow and deformation in highly reinforced particulate composites

Particle fracture in high volume fraction ceramic reinforced metals: governing parameters and implications for composite failure

The effect of size, orientation and temperature on the deformation of microcast silver crystals

Spherical pore replicated Microcellular Aluminium

Laminated Metal Composites by Infiltration

The plasticity size effect in replicated microcellular aluminium

Processing Of Microcellular Sic Foams .2. Ceramic Foam Production