G. Caruana

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.

Control of M23C6 carbides in 0.45C–13Cr martensitic stainless steel by means of three representative heat treatment parameters

Abstract Heat treatment parameters closely control the amount of carbides in steels. In this study, the influence of three parameters (heating temperature, heating rate and cooling rate) on the area percentage of M23C6-type carbides in the quenching microstructures of 0.45C–13Cr martensitic stainless steel has been studied. The experimental results obtained in this study demonstrate that the amount of carbides in the quenching microstructures of this steel can be severely modified through the heating and cooling conditions of the heat treatment.

Thermal stability of an AlNi3Al composite processed by powder metallurgy

Abstract The potential of Al Ni 3 Al composites for high-temperature applications, especially when friction is involved, is currently being explored. In this work, the thermal stability of an Al Ni 3 Al composite obtained by extrusion of Al and 5 vol% of spherical Ni3Al powder particles was investigated at temperatures up to 500 °C. The metal/intermetallic composite proved stable up to 300 °C. At higher temperatures, dissolution of Ni3Al particles occurred with formation of concentric layers of Al3Ni and Al3Ni2 phases. The amount of Ni aluminides for each annealing condition was determined by applying a specifically developed mathematical procedure. Dissolution of Ni3Al up to 500 °C was found to obey a parabolic-type law with an activation energy of 156 kJ mol−1. Activation energies for growth of Al3Ni2 and Al3Ni were 209 and 110 kJ mol−1, respectively, in agreement with the literature. The thermal stability shown by this composite makes it a good candidate for high-temperature applications up to 300 °C.

Microstructural characterization of P/M Ni3Al consolidated by HIP

Abstract Rapidly solidified powder of Ni 3 Al doped with boron was produced by inert gas atomization and consolidated by hot isostatic pressing (HIP). Morphology and microstructure of the powder were studied. From the particle morphology, it could be deduced that the solidification time was similar at least to the time necessary for complete fragmentation of the liquid. The powder showed a two-phase microstructure that was finer the smaller the particle size. The presence of dendrites of NiAl (β) phase was consistent with the diagram proposed by Schramm and not with the traditional diagram of Singleton et al. The microstructure of the material consolidated at 1100°C and 1200°C was studied. A monophasic structure was observed after HIP, and no relevant microstructural differences were seen between the two temperatures used.

Extrudability of PM 2124/SiCp aluminium matrix composite

Abstracts are not published in this journal

Aluminum/Ni3Al composites processed by powder metallurgy

Abstract The suitability of powder metallurgy for processing aluminium matrix composites reinforced with Ni 3 Al powder particles was evaluated. The composite exhibited a sound bond between the matrix and reinforcement, with no interfacial reaction during consolidation by extrusion or even after a heat treatment of 1000 h at 300 °C. These results show the advantages of powder metallurgy compared with ingot metallurgy.

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.

Microstructure and mechanical properties of a rapidly solidified Ni3Al–Cr alloy after thermal treatments

Abstract The effect of thermal treatments at 750, 900 and 1000°C on the microstructure and mechanical properties of a rapidly solidified Ni3Al–Cr alloy is reported. The microstructure of the ribbons in the as-rapidly solidified (RS) condition consisted of a partially ordered Ni3Al matrix and a fine Cr-rich second phase located at cell and grain boundaries. New and coarser α-Cr particles precipitated after annealing at 750°C. No significant changes in the microstructure were observed for longer times. The α-Cr precipitates tended to dissolve in the Ni3Al matrix after annealing at 900 and 1000°C. This dissolution seems to be controlled by the lattice Cr-diffusion in Ni3Al since the volume fraction of α-Cr particles decreased with increasing time and/or temperature of thermal treatments.The mechanical properties of the ribbons were influenced by the microstructural changes such as grain size, volume fraction and size of the α-Cr precipitates, that occurred during the annealing treatments. Thus, ribbons in the RS condition and after annealing at 750°C were brittle however, they exhibited ductile behaviour after thermal treatments at 900 and 1000°C.

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...

Rapidly solidified Al3CrX (Ni, Mo) ribbons: structure and decomposition behaviour

Abstract Melt-spun ribbons of Al-3at.%Cr, containing 1 at.% Ni and 0.3 at.% Mo respectively, were examined in the as-spun condition and after annealing. Al 13 Cr 2 and Al 3 Ni precipitates appear in the Al3Cr1Ni alloy, mainly with thermal treatments, the decomposition temperature being 430 °C. Meanwhile only Al 13 (Cr, Mo) 2 precipitation appears in the Al3Cr0.3Mo alloy and this decomposes at 420 °C.