Microstructure evolution and densification behaviour of powder metallurgy Al–Cu–Mg–Si alloy

ABSTRACT

An Al–Cu–Mg–Si alloy was prepared by conventional press-sintering powder metallurgy using elemental Al powder. The phase transformation process of Al–Mg, Al–Si alloy and Cu during the sintering process was investigated in details. It was found that a series of phase transitions take place in the alloy to disrupt the oxide film of Al particle and enhance the densification process. The relative density of the sintered samples reached 98%. A new Al–Mg–Cu–O compound was found at the grain boundaries except the MgAl₂O₄ phase, it is speculated that the disruption of the oxide film was also associated with the other alloy compositions except for Mg. Furthermore, no detectable AlN compound was found at the grain boundary region although sintering with flowing nitrogen atmosphere, which is benefit from the high density of the green compact and the excellent wettability between the liquid phase and the aluminium.     

Influence of quenching methods on martensitic transformation and mechanical properties of P/M processed Cu–Al–Ni–Ti shape memory alloys

The effect of quenching conditions on phase transformation characteristics and microstructural features of Cu–Al–Ni–Ti shape memory alloys (SMAs) have been studied. The alloys were synthesised via conventional powder metallurgy process using elemental metal powders. Four different quenching techniques, such as (a) two-step quenching, first to 100°C and then to 0°C; (b) two-step quenching, initially to 40°C and later to 0°C; (c) direct quenching to 40°C and (d) direct quenching to 0°C, were used. The microstructural features and phase transformations that the alloys had undergone were studied using FE-SEM and XRD techniques. The martensitic phase transformation analyses were carried out by differential scanning calorimeter while the mechanical properties were studied by microhardness and flexural bending tests. The results obtained clearly indicate that the quenching routes followed have a remarkable influence on the properties of Cu-based SMAs.     

High temperature properties of ductile CuAlNi shape memory alloys with boron additions

The use of polycrystalline CuAlNi alloys for high temperature applications is restricted to very small shape changes due to their brittle nature. Additions of alloying elements such as manganese and boron have been introduced to improve the ductility of the material. The behaviour of these alloys has been studied in terms of the influence of these elements on the stability of the microstructure after high temperature annealing or after room and high temperature deformation. The results show that the martensitic structure produced by quenching the alloy from the β-temperature has a lower degree of order than that obtained after further annealing at 300°C for up to an hour. Also, the alloys containing higher boron concentrations present a lower degree of order in all cases. Similarly, the ductility has been much influenced by the boron content. The ductility is greater, in particular at high temperatures, in the alloys with lower concentration of boron.     

Shape strains associated with thermally-induced and stress-induced martensite in a CuAlNi shape memory alloy

Accurate measurements have been made of the shape strain accompanying the formation of the 2H orthorhombic γ′₁ martensite during cooling and during compressive stressing of a Cu14%Al3.4%Ni shape memory alloy. In both transformations the displacement vectors have magnitude 0.087 and are near [1̄10]_B in the [010]_B-[1̄10]_B-[1̄11]_B stereographic triangle, the habit planes are near (3̄3̄1)_B on both sides of the (1̄10)_B symmetry plane and the dilatation parameter is unity.Crystallographic analysis using the geometrical theory indicates that the two shape strains, associated with the two kinds of habit plane, are approximately consistent with two different {121}_o twinning heterogeneities in the martensite. However, the discrepancies between the measurements and the theoretical calculations are sufficiently large to suggest that the complementary strain is more complex than a simple shear on the martensite twinning elements.     

Effects of Fe and Ni additions on emerging Al–4·5Cu–1·5Mg powder metallurgy alloy

Abstract

In recent laboratory studies, a method designed to modify an emerging Al–Cu–Mg powder metallurgy alloy with Fe and/or Ni additions was successfully developed. The objectives of this research were designed to expand upon this work with an emphasis on characterising the industrial processing behaviour and thermal stability of the alloy with and without additions of these transition metals. All powder compacts exhibited an industrial sintering response that mirrored prior laboratory findings thereby confirming commercial viability. Subsequently, tensile specimens were machined from industrially sintered bars, heat treated to the T6 temper and then subjected to various conditions of thermal exposure at temperatures up to 280°C. Differential scanning calorimetry (DSC) data confirmed that Fe/Ni additions reduced the precipitation kinetics of the S-type phases responsible for peak strengthening at temperatures <160°C and thereby enhanced the thermal stability of important tensile properties such as yield strength. At higher temperatures (>200°C), the Fe/Ni additions were less effective with both alloys exhibiting comparable levels of strength degradation.

Lors d’études récentes en laboratoire, on a développé avec succès une méthode conçue pour modifier un alliage émergeant de la métallurgie des poudres, Al–Cu–Mg, avec des additions de Fe et/ou de Ni. Cette recherche a pour but d’élargir ce travail avec une emphase sur la caractérisation du comportement du traitement industriel et de la stabilité thermique de l’alliage, avec ou sans additions de ces métaux de transition. Tous les compacts de poudre exhibaient une réponse industrielle de frittage qui reflétait les trouvailles antécédentes en laboratoire, confirmant ainsi la viabilité commerciale. Subséquemment, on a usiné des échantillons pour mesure de résistance à la traction à partir de barres frittées industriellement et on les a traités thermiquement à l’état T6. On a ensuite soumis les échantillons à des conditions variées d’exposition thermique à des températures allant jusqu’à 280°C. Les données de DSC ont confirmé que les additions de Fe/Ni réduisaient la cinétique de précipitation des phases de type S, responsables de l’endurcissement de pointe à des températures <160°C et augmentaient ainsi la stabilité thermique des propriétés importantes de résistance à la traction comme la limite d’élasticité. À des températures plus élevées (>200°C), les additions de Fe/Ni étaient moins efficaces, les deux alliages exhibant des niveaux comparables de dégradation de la résistance.     

Influence of hot isostatic pressing on the structure and properties of an innovative low-alloy high-strength aluminum cast alloy based on the Al–Zn–Mg–Cu–Ni–Fe system

Hot isostatic pressing (HIP) is applied for treatment of castings of innovative low-ally high-strength aluminum alloy, nikalin ATs6N0.5Zh based on the Al–Zn–Mg–Cu–Ni–Fe system. The influence of HIP on the structure and properties of castings is studied by means of three regimes of barometric treatment with different temperatures of isometric holding: t ₁ = 505 ± 2°C, p ₁ = 100 MPa, τ₁ = 3 h (HIP1); t ₂ = 525 ± 2°C, p ₂ = 100 MPa, τ₂ = 3 h (HIP2); and t ₃ = 545 ± 2°C, p ₃ = 100 MPa, τ₃ = 3 h (HIP3). It is established that high-temperature HIP leads to actually complete elimination of porosity and additional improvement of the morphology of second phases. Improved structure after HIP provides improvement properties, especially of plasticity. In particular, after heat treatment according of regime HIP2 + T4 (T4 is natural aging), the alloy plasticity is improved by about two times in comparison with the initial state (from ~6 to 12%). While applying regime HIP3 + T6 (T6 is artificial aging for reaching the maximum strength), the plasticity has improved by more than three times in comparison with the initial state, as after treatment according to regimes HIP1 + T6 and HIP2 + T6 (from ~1.2 to ~5.0%), which are characterized by a lower HIP temperature.     

Development and characterization of Nickel–Titanium–Zirconium shape memory alloy for engineering applications

Shape Memory Alloys (SMA) are unique class of alloys which possess various engineering applications. One such SMA is Nickel–Titanium (Nitinol) shape memory alloy. The problem, however with Nickel is that the metal may leach out in form of toxic Ni²⁺ ions. The latter may prove costly when used in various applications. To increase the corrosion resistant properties of Nitinol and to evaluate its shape memory properties, small amount of Zirconium i.e. 5 and 10 at % are added into the existing Nitinol system. Buttons of Nitinol and Nickel–Titanium with Zirconium additions are made using the button arc furnace. For the characterization of the alloys, various techniques including Energy Dispersive Spectroscopy (EDS), Back Scattering Electron (BSE) imaging, Differential Scanning Calorimetry (DSC) have been performed. The work conducted reveals that addition of Zirconium in Nitinol has marked influence on microstructure, shape memory properties, transformation temperature, hardness values, and corrosion properties of the alloy.     

The effects of Zr and Ti on the microstructure and tensile properties of Al–Cu–Mg aluminium alloy

The effects of Al–5Ti–1B and Al–15Zr master alloys on the structural characteristics and tensile properties of Al–4.5Cu–0.3Mg aluminium alloy were studied. Al–5Ti–1B was found to be more effective than Al–15Zr in grain refining of the alloy. It could be seen that average grain size reduces from 570 to 260?μm when 0.01?wt-% Ti addition; additionally, while different amounts of Ti and Zr were added to the alloy, the dendritic structure changes from long dendrite to rather rosette-like morphology. Furthermore, tensile testing of cast specimens revealed that ultimate tensile strength (UTS) of the cast alloy increases from 241 to 283 and 260?MPa after adding the optimum amount of Ti and Zr containing master alloys, respectively. Moreover, UTS values of T6 heat-treated specimens also showed 73 and 61% improvement after adding 0.05?wt-% Ti and 0.3?wt-% Zr to the alloy. Fracture surface examinations exhibited a transition from brittle fracture mode in as-cast to ductile fracture in refined and T6 heat-treated specimens.     

Properties of a 45Ti–45Ni–10Nb shape memory alloy in the as-cast and pressed states

The structural and functional properties of specimens cut from as-cast and pressed rods of a 45Ti–45Ni–10Nb (at %) alloy have been studied in as-delivered state. The homogeneity of the properties under study has been verified along the rod length and from rod to rod. The laws of formation of the alloy structure as a function of the technology of its manufacturing have been studied. The structure influences the mechanical behavior and the main functional properties of the alloy. The pressed state is shown to be preferable as compared to the as-cast state.     

Phase composition,texture, and anisotropy of the properties of Al–Cu–Li–Mg alloy sheets

The formation of the anisotropy of the mechanical properties, the texture, and the phase composition of thin-sheet Al–4.3Cu–1.4Li–0.4Mg and Al–1.8Li–1.8Cu–0.9 Mg alloys have been studied by X-ray diffraction and tensile tests. Various types of anisotropy of the strength properties of the alloys have been revealed: normal anisotropy (strength in the longitudinal direction is higher than that in the transverse direction) in the Al–4.3Cu–1.4Li–0.4Mg alloy and inverse anisotropy in the Al–1.8Li–1.8Cu–0.9Mg alloy. It is shown that the anisotropy of the strength properties is dependent not only on the texture of a solid solution, but also on the content and the texture of the δ' (Al₃Li) and T1 (Al₂CuLi) phases and their coherency and compatibility of deformation with the matrix.     

Effects of Fe and Ni additions on an emerging Al–4·4Cu–1·5Mg powder metallurgy alloy:

Abstract

The effects of Fe and Ni additions to an Al–Cu–Mg powder metallurgy alloy were studied. The transition elements were incorporated through two different approaches, admixed elemental powders and prealloying of the base Al powder. Prealloying proved to be the superior alloying technique as it did not invoke any negative effects on the general sintering behaviour of the baseline alloy. The microstructures of prealloyed materials also exhibited a refined distribution of the aluminide phases formed. These included Al₇Cu₂Fe, Al₇Cu₄Ni and Al₉FeNi as identified through a combination of SEM/EDS and XRD. The most promising alloy was identified as Al–4·4Cu–1·5Mg–1Fe–1Ni as it exhibited tensile properties that exceeded those of the baseline material. This advantage was also found to persevere after thermal exposure.

On a étudié les effets d’additions de Fe et de Ni sur un alliage d’Al–Cu–Mg obtenu par la métallurgie des poudres. On a incorporé les éléments de transition au moyen de deux approches différentes – poudres élémentaires ajoutées ou préalliage de la poudre d’Al de base. Le préalliage était supérieur comme technique d’alliage puisqu’il n’invoquait pas d’effets négatifs sur le comportement général de frittage de l’alliage de référence. La microstructure des matériaux de préalliage exhibait également une distribution raffinée des phases d’aluminures formées. Celles-ci incluaient Al₇Cu₂Fe, Al₇Cu₄Ni et Al₉FeNi, telles qu’identifiées au moyen d’une combinaison de SEM/EDS et de XRD. L’alliage le plus promettant était l’Al–4·4Cu–1·5Mg–1Fe–1Ni, puisqu’il exhibait des propriétés de traction qui excédaient celles du matériau de référence. On a également trouvé que cet avantage persistait après une exposition thermique.     

Preparation of Ti–Ni binary powder via electroless nickel plating of titanium powder

Abstract

In this study, Ti powder (average size: 45 μm) was plated/coated by electroless Ni with hydrazine hydrate as reductant. The Ni plating was carried out at 85°C and pH 9–10. The influence of process parameters such as plating period as well as reductant concentration was investigated. The Ni plated Ti powder was characterised by scanning electron microscopy, energy dispersive spectrometer analysis and X-ray fluorescence. It is found that a pure/uniform Ni layer may be deposited on the Ti powder particles. The deposited mass increases as plating period/reductant concentration increases.     

Physical simulation study of the dynamic recrystallization kinetics of an Ni–Cu–Al alloy

The influence of temperature and deformation on the dynamic recrystallization kinetics of an Ni–30Cu–3Al heat-resistant alloy has been studied on the basis of experiments using a torsion plastometer. The process is simulated and mathematical model is proposed for estimating the dynamically recrystallized grain sizes. Good agreement between the calculated and experimental data is achieved.     

On development of press and sinter Al–Ni–Mg powder metallurgy alloys

Abstract

The objective of this research was to initiate the development of powder metallurgy alloys based on the Al–Ni–Mg system. In doing so, binary (Al–Mg) and ternary (Al–Ni–Mg) blends were prepared, compacted and sintered using elemental and master alloy feedstock powders. Research began with fundamental studies on the sintering response of the base aluminium powder with additions of magnesium. This element proved essential to the development of a well sintered microstructure while promoting the formation of a small nodular phase that appeared to be AlN. In Al–Ni–Mg systems a well sintered structure comprised of α aluminium plus NiAl₃ was produced at the higher sintering temperatures investigated. Of these ternary alloys studied, Al–15Ni–1Mg exhibited mechanical properties that were comparable with existing commercial 'press and sinter' alloys. The processing, reaction sintering and tensile properties of this alloy were also found to be reproducible in an industrial production environment.     

Effect of annealing treatment on microstructure and mechanical properties of hot isostatic pressing compacts fabricated using Ti–6Al–4V powder

The effects of annealing temperature and annealing time on microstructure evolution and mechanical properties of Ti–6Al–4V titanium alloy prepared using powder hot isostatic pressing were investigated. The results showed that when annealing temperature was <?1173?K, the globularisation of primary α was observed, and the morphology of secondary α changed from acicular shapes to acicular and continuous lathy grains. Scanning electron microscopy fracture surface showed that the fracture mechanism changed from transcrystalline dimple type to a mixture of transcrystalline and intercrystalline dimple types with increasing annealing temperature. The tensile strength and elongation varied with the temperature in an opposite trend. However, they varied similarly with increasing annealing time. Microhardness was sensitive to the annealing time, resulting into a maximum microhardness of 396.95?HV at 1173?K for 3?h.