F. Fouquet

Precipitation effects on thermopower in Al-Cu alloys

Abstract The precipitation influence on the thermoelectric power (TEP) of Al-Cu alloys (with from 2 up to 5 wt% Cu) has been observed. It has been shown that incoherent θ precipitates have no influence on TEP, in agreement with previous observations in various metallic alloys where similar precipitates form. On the opposite metastable plate-like precipitates (GP zones, θ″, θ′) induce a contribution to TEP, which is the larger the higher the measuring temperature; furthermore a correlation between the sign of this contribution and the nature of the stresses induced by the particles is observed.

Laser surface melting of a pearlitic grey cast iron

Abstract Laser surface melt hardening of a pearlitic grey iron was carried out using a 1 kW continuous wave CO 2 laser, without preheating of the specimens and without prior graphite coating of the surface. It was shown that, with suitable laser processing conditions, it is possible to obtain melt areas without cracks in either single- or multiple-track melting experiments. In the case of single-track melting, the microstructure of the melted zone was composed of dendritic austenite and interdendritic ledeburite with a hardness of about 700 HV. For multiple-track melting, the austenite is partially transformed into cementite and martensite in overlapping regions, leading to an increase in the hardness.

Experimental and theoretical determinations of the yield stress of an alloy containing plate-like precipitates: θ′ phase in an Al-4wt.%Cu alloy

Abstract The evolution of the yield stress of an Al-4wt.%Cu alloy was studied during the stage in which the precipitates became coarser. The correlation between the yield stress and the thickness of precipitates allows us, in spite of the existence of three different orientations of precipitates in the matrix, to represent the precipitate configuration by a parallel-plate model. Using this model, good agreement is found between the experimental and theoretical values of the yield stress.

A study of the kinetics of crystallization of an amorphous metallic glass Fe83B14Si1.5C1.5 using thermoelectric power measurements

Abstract The kinetics of crystallization of the metallic glass Fe 83 B 14 Si 1.5 C 1.5 in the temperature range 448–723 K were studied using thermoelectric power (TEP) measurements at room temperature. The dependence of the TEP on the logarithm of the annealing time can be divided into three stages. In the first decreasing stage, two different processes occur in the glassy matrix; these two processes exert opposite effects on the heterogeneity of electron density, and they can be attributed to topological short-range order and chemical short-range order. In the second stage the TEP increases as a result of the primary crystallization of α-Fe. In the third stage the TEP decreases significantly again and the amorphous matrix crystallizes to Fe 3 B. The activation energies for these two different crystallization processes were found to be 46 kcal mol −1 and 81 kcal mol −1 respectively. When annealing is prolonged, Fe 3 B decomposes to α-Fe plus Fe 2 B.

Consolidation d'un alliage d'aluminium à 4% en poids de cuivre à l'Etat θ′. Relation entre limite elastique et dureté

Different ageing treatments have been used to produce θ′ precipitates in an AlCu 4 wt.% alloy. The tensile stress-strain curves which were obtained from the various states can be described by the equation σ = RE + Aϵm, where A and m are constants, the rate of work hardening being independent of the size and distribution of θ′ precipitates. Furthermore, a linear correlation between the conventional flow-stress RE and the Vickers hardness HV can be established. The same type of relation is also observed for the intrinsic contribution of θ′ precipitates to these two values.

Validity of a Lamellar Model for Yield Stress Variation of Alloy Containing Plate-like Precipitates

ABSTRACT The variation of yield stress of an Al-4 wt % Cu alloy during coalescence of θ′ plates is studied together with the geometrical parameters of precipitation. Different models of repartition for θ′ precipitates are investigated to explain these variations. The correlation between the evolution of yield stress and the thickness of 0′ plates leads to consider lamellar models.