Marcelino Torralba

Microstructure and high temperature mechanical properties of tin

Abstract The mechanical properties of tin have been studied by tensile tests in the temperature range 293–463 K. Tensile tests were performed for cylindrical samples at a constant strain rate and varying strain rates during deformation. In-situ-tensile tests also were conducted in ribbon-form samples. At the strain rates studied, deformation takes place preferentially by slip, although some scattered twins also were observed at lower temperatures. Strong grain growth occurs at the higher temperatures. Microstructural observations of deformed samples show that dynamic recrystallization is not important in the temperature range investigated. The fracture surface of the cylindrical samples changes from a chisel type of fracture at the lower temperatures to a simple shear type of fracture at the higher temperatures. Both the tensile strength and ductility decrease with increasing temperature. An explanation is given for the loss of ductility at high temperatures. The activation energy for creep, obtained from strain-rate-change tests is 35 kJ mol−1 and the stress exponent is about 6. These values are related to a slip mechanism controlled by pipe diffusion.

Texture of magnesium alloy films growth by physical vapour deposition (PVD)

Abstract The texture developed by four physical vapor deposited Mg alloys grown at two collector temperatures and their correlation with the microstructure have been studied. The alloys Mg–2.3Zr, Mg–10.6Zr and Mg–12Ti (wt%) deposited at around 150°C exhibited elongated grains growing in the normal direction to the deposit surface, but tilted with respect to the Z axis, with pores and cracks at the boundaries. A strong fibre texture of the ( 0001 ) basal plane component forming the fibre axis and the normal to the substrate plane an angle of 24, 18 or 12° depending on alloying element concentration has been found. The Mg–14Ti–1Al–0.9Mn (wt%) alloy, deposited at higher temperature, consisted of a region of columnar grains growing from the collector side followed by a thin region of equiaxed grains. Furthermore, a fibre texture with two components, the ( 0002 ) basal plane and the ( 1120 ) and the ( 1010 ) components in the collector and free surfaces, respectively, were present. Differences found in this alloy with respect to the alloys deposited at lower temperature were related to the surface diffusion phenomenon of adatoms caused by a higher collector temperature. The change in the second texture component from the collector to the free surface can explained by the decrease in the deposit strain energy.

Extrudability of PM 2124/SiCp aluminium matrix composite

Abstracts are not published in this journal

The lead-rich corner of the PbCaSn phase diagram

Abstract A study was carried out to determine the nature of the lead-rich corner of the PbCaSn phase diagram. 42 high purity ternary alloys were prepared with calcium contents up to 0.2wt.% and tin contents up to 3.0 wt.%. The liquidus and solidus temperatures of all the alloys were determined by differential thermal analysis. Isothermal solid sections were determined by X-ray diffraction measurements at several temperatures from the study of the lattice parameter versus composition curves. The equilibrium phases at room temperature were studied by means of the electron microprobe in slowly cooled samples and it is proposed that the α phase is the solid solution, that the β phase is CaPb 3 and that the γ phase is crystallographically similar to the CaPb 3 phase but contains tin. Some aspects of the binary PbCa system are also discussed.

Flow stress of rapidly solidified Al-5Cr-2Zr alloy as a function of processing variables

In a previous work, Lieblich et al. determined that room temperature hardness and tensile strength of as-extruded Al-5Cr-2Zr (wt.%) alloys obtained by gas atomization increased with decreasing powder particle size and extrusion temperature, and depended only very little on extrusion ratio and ram speed. The aim of the present study was to determine the influence of powder particle diameter and extrusion temperature on the flow stress of Al-5Cr-2Zr at temperatures ranging from 373 to 773 K. The contribution to the flow stress of different strengthening mechanisms is evaluated and related to the processing parameters.

Elevated temperature creep behavior of three rapidly solidified Al-Fe-Si materials containing Cr, Mn, or Mo

Abstract Research on the high temperature creep behavior of three rapidly solidified Al-Fe-X-Si (where X = Cr, Mn or Mo) dispersion strengthened materials with three different alloying compositions has been conducted. Firstly, microstructural examinations have been carried out on the as-received, thermally treated and tested samples. The microstructure consists of a fine Al matrix embedding small round-shaped Al 12 (Fe,X) 3 Si and Al 13 (Fe,X) 4 dispersoids. Grain sizes ranging from 0.85 to 1.45 μm and dispersoid sizes ranging from 45 to 54 nm were observed. Secondly, tensile tests were performed at high temperature from 573 to 823 K at strain rates ranging from 2.5×10 −6 to 10 −2 s −1 . The experimental data exhibited high apparent stress exponent, n ap , and high activation energy, Q ap . The rnicrostructure remained stable and fine after testing. The results are analyzed by means of various models used in the literature.

Characteristics of Al-Cr-Zr alloy powders made by confined nozzle atomisation

AbstractThe effects of superheat and powder particle size fraction on the characteristics of Al–5Cr–2Zr (wt-%) alloy confined nozzle atomised powder particulate has been investigated. The median powder particle size decreased from 62 to 38 μm with increase in superheat from 140 to 300 K for the atomising conditions studied, with a broadening of the size distribution and the increasing presence of large irregular powder particles at the lowest superheats. Essentially featureless α-Al based microstructures in splat caps and small sized powder particles were replaced by cellular α-Al with increasing amounts and sizes of primary L12Al3Zr and Al13Cr2 inclusions with increasing powder particle size. Refinement of the α-Al cell and intermetallic inclusion sizes in a fine compared with a coarse powder size fraction was consistent with the expected powder relationship between these variables. The decreased microhardness for coarser powder particle size fractions was attributed to the formation of increasingly coar...

Fracture of Al-4% Cu-0.1% Fe single crystals

The fracture behaviour of heat-treated Al-4% Cu-0.1% Fe single crystals was studied in tension at room temperature. Three heat-treatment conditions were examined: quenced, fully hardened and overaged. Slip lines, shear bands and fracture surfaces were studied to yield information on the plastic deformation processes occurring prior to fracture. The presence of stable Al7Cu2Fe particles was found to be an important factor in fracture formation. In the as-quenced condition two fracture planes of different topography were formed. Large shear zones together with scattered shallow dimples were observed in both planes due to stable particles. In the fully hardened condition fracture occurred without necking and usually by shearing along the conjugate slip system. The presence of shear zones and dimples of different sizes was observed. Finally, in the overaged condition fracture took place by void coalescence after strong necking, as in polycrystalline samples. No shear zones were observed on the fracture surface of these samples.

The threshold stress in a rapidly solidified Al–5Cr–2Zr alloy

Abstract In this paper, a new insight into the origin of the threshold stress is presented for a rapidly solidified Al–5Cr–2Zr (wt.%) alloy obtained by hot extrusion of powder particles of three different size fractions. The creep behaviour of this alloy at low temperature ( σ 0 . The value of σ 0 clearly diminishes as temperature increases. The magnitude of σ 0 is also strongly affected by the powder particle diameter, directly associated with the grain size: the larger the grain size, the lower the threshold stress. It is concluded that the threshold stress is related to the grain size through a Hall–Petch-type mechanism and that its temperature dependence is similar to the temperature dependence of the Hall–Petch coefficient.

Creep behaviour of a rapidly solidified Al-5Cr-2Zr alloy between room temperature and 823 K

Rapidly solidified (RS) Al-Cr-Zr alloys are established contenders for applications in the aircraft industry where lower cost, lightweight substitutes for titanium alloys are being sought for use in the temperature range of 473 to 723 K. Creep resistance is one of the critical properties of any material intended for high temperature applications. Therefore, a precise knowledge of creep behavior and a clear understanding of the mechanisms controlling creep in these materials are of great importance. The good thermal stability exhibited by the RS Al-5Cr-2Zr (wt.%) alloy makes it a good candidate for applications where high creep resistance is needed. This paper presents the results of creep behavior over a wide range of temperatures (0.32 to 0.88 Tm, where Tm = 933 K is the melt temperature of pure aluminum) of an Al-5Cr-2Zr alloy processed by gas atomization and extrusion and includes a brief discussion on the creep mechanisms that may be involved.