C. García Oca

An analysis of strengthening mechanisms in a mechanically alloyed, oxide dispersion strengthened iron aluminide intermetallic

Abstract An iron aluminide alloy of base composition Fe-40Al has been prepared by mechanical alloying and processed using a variety of powder consolidation methods and heat treatments to produce a range of grain sizes and oxide dispersoid sizes. The strengths of these materials have been determined at room temperature and related to the various aspects of microstructure. Fine dispersoid particles may pin grain boundaries and help determine the fine grain size and contribute very significantly to the material strength. Grain size strengthening is shown to be a rather small component of the material strength, with the matrix strength being rather high for this intermetallic. The influence of other factors such as texture and the direction of application of stress (tension or compression) are also briefly discussed.

Microstructure and room temperature strength of Fe-40Al containing nanocrystalline oxide particles

Abstract The microstructure and room temperature strength of a mechanically alloyed ODS FeAl alloy are examined in a large number of differently processed and heat-treated materials and the strengthening contributions due to nanocrystalline oxide particles, to fine grain size, and to matrix effects are analysed. Submicron grain materials with small oxide particles show significant hardening due to the fine particles and a similar, significant hardening due to the fine grain size. The texture created during processing influences strengthening by determining the barrier efficiency of the lower-angle or higher-angle grain boundaries present, and thus modifies the Hall–Petch slope describing grain-size strengthening.

Mechanical behaviour of dilute Al-Mg alloy processed by equal channel angular pressing

Abstract Heavy deformation by ECAP of Al–3Mg leads to a high level of strengthening due to the fine microstructure, with perhaps additional dislocation hardening. Analysis of grain boundary hardening is difficult due to the different numbers of dislocations and the various types of grain boundaries present.

High temperature structural coarsening of an ODS FeAl intermetallic

Abstract The coarsening of oxide particles and grains in an ODS FeAl intermetallic has been examined during annealing at high temperatures under conditions where recrystallization does not yet occur. Coarsening of the yttria particles is shown to be controlled by the diffusion of the metallic species through the intermetallic matrix, while the increases of grain size by grain growth are determined by the pinning action of the large number of yttria particles. Hardness falls during the annealing and is seen to depend on both particle size increases and grain size increases.

Obtaining good ductility in an FeAl intermetallic

Abstract Deformation and fracture mechanisms leading to tensile failure have been examined in a mechanically-alloyed and a recrystallized Fe–40Al intermetallic. It is shown that tensile failure begins by the initiation of a small crack near the sample surface at a given level of strain, and crack propagation occurs rather quickly thereafter such that the total strain at failure is only slightly larger than the crack initiation strain. Crack propagation is initially slow, and affected by the test environment, and later it is faster and unaffected by test environment. Deformation localizes into slip bands and crack nucleation takes place easily, at a small strain, in the recrystallized material of large grain size. In the as-extruded material, deformation remains homogeneous under the influence of the small distributed particles, and crack initiation over a scale of many grain dimensions is slow. Possibilities for further ductility improvements by microstructure control are discussed.

Possibilities for improving the corrosion resistance of Fe–40Al intermetallic strip by prior oxide protection

Abstract Iron aluminides do not generally show good aqueous corrosion resistance. The present study attempts to improve their corrosion resistance by prior surface oxidation. While good corrosion resistance can indeed be obtained, it is found to be difficult to ensure that the oxide layer is continuous and defect free.

Influence of machining conditions on tensile stress and ductility of a mechanically alloyed Fe-40Al intermetallic

Abstract The influence of a variety of machining conditions on the tensile behaviour of a mechanically alloyed FeAl intermetallic has been examined. Yield behaviour is hardly affected by machining conditions, and ductility is only weakly sensitive to machining speed or cutting depth. This behaviour seems to be related more with the extent of subsurface damage or work hardening than with the roughness of the machined samples.