Volume Fraction Of Dispersoids Research Articles

Effects of Zr, Al, and Al+Zr Addition on Phase Evolution Characteristics and Strengthening Mechanisms of Fe‐42Ni‐2Y2O3 Oxide Dispersion Strengthening Steels Developed by Mechanical Alloying and Spark Plasma Sintering

In the present study, Fe‐42 wt% Ni‐2 wt% Y2O3 super‐invar‐based steels have been explored to study the effects of Zr, Al, and Zr+Al addition on phase evolution, strengthening mechanisms, and mechanical behavior. Three different compositions, such as Fe‐42Ni‐2Y2O3‐2Zr (2YZr), Fe‐42Ni‐2Y2O3‐2Al (2YAl), and Fe‐42Ni‐2Y2O3‐2Zr‐2Al (2YAlZr), are developed by mechanical alloying (MA) followed by spark plasma sintering (SPS) at 1100 °C with an applied pressure of 60 MPa. The 2YZr alloy after SPS shows the evolution of a uniform grain size of ≈1.7 μm, whereas 2YAl reveals the formation of bimodal grain structure sintered under the same condition. Conversely, the combined effect of Al and Zr addition results in the evolution of ultrafine grained structure (≈380 nm) after SPS at the same condition (i.e., at 1100 °C). The superior mechanical strength of the 2YAlZr alloy (5.3 GPa/1415 MPa) is attributed to the evolution of uniformly dispersed extremely fine (60 nm) high‐density Al‐ and Zr‐rich oxide complexes in the ultrafine grained matrix. The analysis of strengthening contributions to the yield strength is found to be correlated well with the experimental results and attributed to the morphology of microstructural constituents, their stability, and volume fraction of dispersoids in the matrix.

Improving the elevated-temperature mechanical properties of AA3004 hot-rolled sheets by microalloying with Mo and optimizing the process route

The present work investigated the influence of Mo addition and thermomechanical process routes on microstructural evolution and elevated-temperature mechanical properties of Al–Mn–Mg 3004 alloys. Various combinations of heat treatment and hot rolling were applied to fabricate hot-rolled sheets. The results revealed that microalloying with Mo and two-step heat treatment increased the number density and volume fraction of dispersoids and decreased the volume fractions of dispersoid-free zones. The different processing routes had important impacts on microstructural evolution. The alloys processed with heat treatment followed by hot rolling had finer and better distributions of dispersoids than those subjected to hot rolling prior to heat treatment. The former resulted in higher tensile strengths at room and elevated temperatures. Among all conditions, the Mo-containing alloy subjected to two-step heat treatment followed by hot rolling exhibited the highest elevated-temperature properties and reached a yield strength of 93 MPa at 300 °C. Both the base and Mo-containing alloys subjected to two-step heat treatment followed by hot rolling showed excellent thermal stabilities up to 350 °C and almost no significant change in yield strengths after thermal exposure at 300–350 °C for 100 h.

Effect of homogenization on second phases and mechanical properties of AA 5052 aluminum alloy tube billets fabricated by HCCM vertical continuous casting

AA 5052 aluminum alloy tube billets were prepared by HCCM vertical continuous casting to study the effect of homogenization temperature and time on the second phases and mechanical properties. The volume fraction of constituent, length of constituent colonies, number density and volume fraction of dispersoids were examined in different homogenization conditions. Optimized homogenization can be obtained at 560 °C for 20 h, and the elongation of the HCCM continuous casting billet increases from 25.5% (as-cast) to 35.5%, while that of the semicontinuous casting billets only increases from 21.5% (as-cast) to 23.5%. In particular, fine and interlaced Mg2Si and Al6(Fe,Mn) phases are obtained after HCCM continuous casting, which is different from the separated distribution phases after traditional semicontinuous casting and improves the effectiveness of homogenization treatment.

Synergistic strengthening by nano-sized α-Al(Mn,Fe)Si and Al3Zr dispersoids in a heat-resistant Al–Mn–Fe–Si–Zr alloy

Strengthening by dispersoids in Al alloys has been limited by either low number density or low volume fraction of dispersoids. In the present work, the influence of an addition of 0.28 wt% Zr on precipitation hardening behavior of AA3003 alloy subjected to different heat treatments has been investigated. A superior microstructure simultaneously consisting of nano-sized α-Al(Mn,Fe)Si and Al3Zr dispersoids at peak-aged state was achieved by two different heat treatment regimes, ramp heating with a speed of 50 °C/h and isothermal aging at 400 °C. As a result, a substantial increase in yield strength of 30 MPa (43%) was achieved in comparison to AA3003 alloy. Meanwhile, the AA3003-Zr alloy exhibits excellent heat-resistance with a stable yield strength from 12h (106 MPa) up to 250h (107 MPa) during isothermal aging at 400 °C. This remarkable thermal stability was ascribed to the continuously hardening from Al3Zr precipitation, which compensates the strength loss from α-dispersoid coarsening. Besides, TEM study shows that the precipitation kinetics of Al3Zr is significantly enhanced compared with the reference binary Al–Zr alloy, which is attributed to the Si content in the alloy. This work proposes an effective method to design a low-cost heat-resistant Al alloy in mass production.

The effect of Mn on the high temperature flow stress of Al–Mg–Si alloys

The demand for Al–Mg–Si extrusion alloys in the transportation sector is increasing rapidly. An important aspect of the process is high temperature extrusion and in particular, the breakthrough force for the extrusion press. The breakthrough force varies as a function of the extrusion ratio, extrusion speed and temperature, the complexity of the profile and the flow stress of the alloy. Further, Mn and Cr are often added to the alloy which form dispersoids during homogenization which precipitation strengthen the alloy at high temperature. This work presents a new approach to calculate the volume fraction of dispersoids using electron microprobe analysis, electrical resistivity measurements and transmission electron microscopy (TEM). The new method substantially increases the accuracy of the volume fraction determination compared with traditional image analysis or TEM since the volume of material sampled is much larger avoiding effects of local segregation. Using the volume fraction and dispersoid size measurements, a high temperature flow stress model based on dislocation theory has been developed. It is shown to describe the high temperature flow stress measurements to within 5% in 95% of the cases. The model was validated by independent experimentation where it predicted the flow stress within 5% accuracy. The flow stress model can be used independently based on experimental quantification of the dispersoids or as part of a through process model which includes a KWN based precipitation model for dispersoids and then implemented as constitutive equation for a FEM based model of the extrusion process.

Post-FSW Cold-Rolling Simulation of ECAP Shear Deformation and Its Microstructure Role Combined to Annealing in a FSWed AA5754 Plate Joint.

Friction stir welds are considered reliable joints for their lack of voids, cracks and distortions. When compared to the base material, friction stir welding (FSW) joints typically exhibit finer grain structured (especially at the nugget zone, NZ). Similarly, refined grain structure can also be obtained by severe plastic deformation (SPD) techniques, such as equal channel angular pressing (ECAP). In fact, the fine grain structures produced within the NZ of FSW or friction stir processed (FSP) materials are usually coarser than the ones achieved by ECAP. The former is characterized by lower dislocation density, higher high-angle boundary fraction and different mechanical strength, compared to what can be obtained by ECAP. In this study, a dedicated cold-rolling (CR) set-up, specifically designed to simulate an ECAP-equivalent shear deformation, was used to further refine the grain structure of FSW AA5754 sheets. The effect of ECAP-equivalent deformation induced by CR in a 2 mm-thick AA5754-H111 FSW joint was investigated. FSW was carried out at two different rotational (ω) and translational (v) welding speeds, 600 rpm, 200 mm/min and 1800 rpm, 75 mm/min, respectively. FSW sheets were then CR to obtain an equivalent shear strain of ε ~ 1.08, that is equivalent to 1-ECAP pass carried out with an internal die channels intersecting at an angle φ = 90° with a curvature extending over an angle Ψ = 20°. By CR, the sheet thickness reduced only by ~20%. The role of annealing on the FSW and CR plastically deformed AA5754 was also investigated. This was applied either prior or after FSW, and it resulted that whenever it follows the FSW, the mean volume fraction of dispersoids and Mg-rich particles is higher than the case of annealing preceding the FSW process. On the contrary, it was found that the annealing treatment had a minimal role on the dispersoids and particles mean size. The here reported post-FSW ECAP-simulated deformation, obtained by a customized CR process, showed sheet integrity and a significant concurrent grain size refinement.

Microstructure, elevated-temperature mechanical properties and creep resistance of dispersoid-strengthened Al-Mn-Mg 3xxx alloys with varying Mg and Si contents

In the present work, the effects of magnesium and silicon addition on microstructure, elevated-temperature yield strength and creep resistance of Al-Mn-Mg 3xxx alloys were investigated. The microstructure evolution under as-cast and heat-treated conditions was quantitatively evaluated by optical and electron microscopy. Results revealed that both magnesium and silicon had an important influence on the distribution and volume fraction of precipitated dispersoids in 3xxx alloys. Without Mg or Si addition, dispersoids could hardly form during the precipitation heat treatment; hence, the alloys free of Mg or Si possessed low yield strength and creep resistance at elevated temperature. A significant improvement in elevated-temperature yield strength and creep resistance was obtained over a wide range of Mg (0.5–1.5wt%) and Si (0.25–1wt%) content studied due to the precipitation of a large number of dispersoids. The best combination of yield strength and creep resistance at 300 ℃ was obtained by the alloy containing 1.0wt% Mg and 0.25wt% Si with the maximum volume fraction of dispersoids and the minimum volume fraction of dispersoid free zone. The effects of dispersoid strengthening, solid solution strengthening and grain size on yield strength and creep resistance were discussed based on experimental results.

Evolution of microstructure and elevated-temperature properties with Mn addition in Al–Mn–Mg alloys

Abstract

Influence of heat treatment and its sequence on elevated-temperature properties of Al-Mn-Mg 3004 alloy

Various heat treatments with different sequences between the peak precipitation treatment (375°C/48h, referred to as “P”) and the high temperature treatment (450–600°C, referred to as “H”) were performed in Al-Mn-Mg 3004 alloys to simulate their thermal treatments during thermomechanical fabrication processes in the present work. Their influences on the dispersoid precipitation and elevated-temperature properties (yield strength and creep resistance at 300°C) were investigated. The results indicate that the size of dispersoids increased while the volume fraction of dispersoids decreased with increasing “H” temperature when “P” was performed either prior to or after “H” (denoted as “PH” and “HP”, respectively), which results in the reduction of the elevated-temperature properties. However, the yield strength and creep resistance after “PH” treatments were always higher than those after “HP” treatments at the same “H” temperature. When the “H” temperature during “PH” treatments is controlled below 500°C, the materials can still maintain the appropriate yield strength and creep resistance, providing the possibility for Al-Mn-Mg 3004 alloy to adapt to the conventional fabrication processes but still maintain high elevated-temperature properties.

Effect of magnesium on dispersoid strengthening of Al—Mn—Mg—Si (3xxx) alloys

The effects of magnesium addition on the dispersoid precipitation as well as mechanical properties of 3xxx alloys were investigated. The microstructures in as-cast and heat-treated conditions were evaluated by optical microscopy and transmission electron microscopy. The results reveal that Mg has a strong influence on the distribution and volume fraction of dispersoids during precipitation heat treatment. The microhardness and yield strength at ambient temperature increase with increasing Mg content. The solid solution and dispersoid strengthening mechanisms of materials after heat treatment are quantitatively analyzed. Dispersoid strengthening for the alloys is the predominant strengthening mechanism after precipitation heat treatment. An analytical model is introduced to predict the evolution of ambient-temperature yield strength.

Enhanced elevated-temperature properties via Mo addition in Al-Mn-Mg 3004 alloy

The present work investigates the influence of adding Mo to an Al-Mn-Mg 3004 alloy on elevated-temperature properties as well as their thermal stability during long-term thermal holding at 350 °C and 400 °C. In as-cast and heat-treated conditions, both microhardness and yield strength increase with increasing Mo contents and reach peak values at 0.3 wt. % followed by a plateau. With an optimized Mo content (0.3 wt. %), the volume fraction of dispersoids is increased while the volume percentage of the dispersoid-free zone is greatly reduced compared to the base alloy free of Mo, resulting in the remarkable increases in elevated-temperature strength and creep resistance. The results of the long-term thermal holding show that compared with the rapid drop of elevated-temperature strength and creep resistance in the base alloy, the Al-Mn-Mg alloy with 0.3% Mo is thermally stable up to 350 °C, exhibiting a slight decrease of stability at 400 °C. The combination of high elevated-temperature properties and their excellent thermal stability at 350–400 °C with Mo addition makes Al-Mn-Mg 3xxx alloys the promising candidates for elevated-temperature applications.

Evolution of Intermetallics, Dispersoids, and Elevated Temperature Properties at Various Fe Contents in Al-Mn-Mg 3004 Alloys

Nowadays, great interests are rising on aluminum alloys for the applications at elevated temperature, driven by the automotive and aerospace industries requiring high strength, light weight, and low-cost engineering materials. As one of the most promising candidates, Al-Mn-Mg 3004 alloys have been found to possess considerably high mechanical properties and creep resistance at elevated temperature resulted from the precipitation of a large number of thermally stable dispersoids during heat treatment. In present work, the effect of Fe contents on the evolution of microstructure as well as high-temperature properties of 3004 alloys has been investigated. Results show that the dominant intermetallic changes from α-Al(MnFe)Si at 0.1 wt pct Fe to Al6(MnFe) at both 0.3 and 0.6 wt pct Fe. In the Fe range of 0.1–0.6 wt pct studied, a significant improvement on mechanical properties at elevated temperature has been observed due to the precipitation of dispersoids, and the best combination of yield strength and creep resistance at 573 K (300 °C) is obtained in the 0.3 wt pct Fe alloy with the finest size and highest volume fraction of dispersoids. The superior properties obtained at 573 K (300 °C) make 3004 alloys more promising for high-temperature applications. The relationship between the Fe content and the dispersoid precipitation as well as the materials properties has been discussed.

Grains versus subgrains: How growth kinetics is affected by the presence of nanosized dispersoids

Abstract In this study, a Monte Carlo (MC) simulation framework is developed to predict and analyze subgrain growth in Al–4.5Zn–1Mg alloy influenced by dispersion of nanosized particles. The simulation is performed at a definite temperature and certain volume fraction of dispersoids. In order to convert Monte Carlo simulation time to real time, the activation energy and pre-exponential factor for determining the coefficient of diffusion of high angle grain boundaries are utilized. It was found that the outputs are not compatible with experimental results. Therefore, grain boundary diffusion coefficient ( D GB ) is best-fit into experimental results to improve the precision of the simulation and temperature dependent values for D GB are estimated. Kinetics of the subgrain growth in the presence of and without nanosized dispersoids is investigated using power law approach and values of growth exponent are predicted to be 2.8 and 2.2, respectively. The growth exponent is a constant in subgrain growth power law with a direct relation to the rate of subgrain growth. This reduction in growth rate exponent indicates the significance of the presence of second phase particles on diminishing subgrain growth rate.

Isothermal and Non-Isothermal Annealing of Cold-Rolled Al-Mn-Fe-Si Alloys with Different Microchemistry States

Investigation of the microstructural evolution of Al-Mn-Fe-Si alloys during annealing after cold rolling has been carried out. The effect of microchemistry state in terms of Mn in solid solution, constituents, size and volume fraction of dispersoids, introduced prior to cold rolling through different homogenization treatments, on microstructural evolution is compared during subsequent isothermal and non-isothermal heating experiments, with focus on the dependency of the amount solute (potential for concurrent precipitation) and pre-existing particles prior to deformation. It is clearly demonstrated that the actual kinetics and final microstructure are the result of a delicate balance between processing conditions and microchemistry state. In general, non-isothermal annealing treatments produce inhomogeneous microstructure, as compared to isothermal annealing. Moreover, more and finer particles (resulting from low-temperature homogenization) tend to hinder boundary motion, leading to even slower recrystallization kinetics and coarse non-equiaxed grains with a strong P texture component.

Modelling the Evolution in Microchemistry and its Effects on the Softening Behavior of Cold Rolled AlFeMnSi-Alloys during Annealing

A dedicated diffusion controlled precipitation model for AlMnFeSi-alloys, based on classical nucleation and growth theory, has been implemented and coupled to a phenomenological softening model accounting for the combined effect of recovery and recrystallization during annealing after cold rolling. The result is a fully coupled precipitation and softening model which in principle is capable of accounting for variations in solute levels and size and volume fraction of dispersoids and their interaction with the softening behavior during annealing.

A new approach to incorporating the effect of nano-sized dispersoids on recrystallization inhibition into Monte Carlo simulation

In this research, a new approach to incorporating the effect of nano-sized dispersoids on recrystallization was developed as a combination of physical modeling and Monte Carlo simulation. The energy stored during preceding deformation and the nucleation rate at the onset and during recrystallization were calculated using a physical model and were incorporated into the Monte Carlo simulation. The conventional approach to incorporating the Zener drag effect was also considered for comparison with the new approach. Predictions were validated by comparing the microstructures obtained from the simulations with those from experimental results. It was found that the general Monte Carlo approach to incorporating the effect of second-phase particles on recrystallization inhibition was not suitable for nano-sized dispersoids being significantly smaller than the lattice size of the simulation. The effect of dispersoids could be incorporated into the simulation using a combination of analytical modeling and Monte Carlo approach. By using this approach, it was possible to differentiate between small variations in the volume fraction of dispersoids.

Phase-field simulation of phase coarsening at ultrahigh volume fractions

In this paper, the dynamics of phase coarsening at ultrahigh volume fractions (0.9≤VV≤0.96) is first studied based on two-dimensional phase-field simulations by numerically solving the time-dependent Ginzburg–Landau and Cahn–Hilliard equations. It is shown that the cubic average radius of particles is approximately proportional to time that is in good agreement with one of experimental observations. The microstructural evolutions for different ultrahigh volume fractions are shown. The scaled particle size distribution as functions of the dispersoid volume fraction is presented. The interesting finding is that the particle size distribution derived from our simulations at ultrahigh volume fractions is close to Wagner’s particle size distribution due to interface-controlled ripening rather than Hillert’s grain size distribution in grain growth. The changes of shapes of particles are carefully studied with increase in volume fraction. It is found that some liquid-filled triple junctions are formed as a result of particle shape accommodation at ultrahigh volume fraction, VV≈0.96.

Simulating Phase Coarsening of Ultra-High Volume Fractions

The dynamics of phase coarsening at ultra-high volume fractions is studied based on two-dimensional phase-field simulations by numerically solving the time-dependent Ginzburg-Landau and Cahn-Hilliard equations. The kinetics of phase coarsening at ultra-high volume fractions is discovered. The microstructural evolutions for different ultra-high volume fractions are shown. The scaled particle size distribution as functions of the dispersoid volume fraction is presented. The particle size distribution derived from our simulation at ultra-high volume fractions is close to Wagner's particle size distribution due to interface-controlled ripening rather than Hillert's grain size distribution in grain growth. The changes of shapes of particles are carefully studied with increase of volume fraction. It is found that more liquid-filled triple junctions are formed as a result of particle shape accommodation with increase of volume fraction at the regime of ultra-high volume fraction.

The Stretch, Limit and Path Forward for Particle Reinforced Metal Matrix Composites of 7075 Al-Alloys

Al-based metal matrix composites [MMCs] have been the research interest of a wide spectrum of material scientists throughout the world for some over two decades now. The present paper has chosen one alloy system namely the 7xxx series and from an extensive literature review concluded that since the beginning of the new millennium nothing note worthy has been added to the knowledge already gained in the last quarter of the last century except confirm the earlier findings that MMCs if properly fabricated by choosing the processing route and with appropriate size and volume fraction of dispersoids can improve most of the mechanical, corrosion and wear resistant properties of the base alloy. The author’s own research activities using this alloy system for making MMCs that include attempts to improve upon the properties by making composites, ageing and also secondary processing have been included. An attempt has been made to establish the stretch to which improvement is possible in the alloy system by making composites and trying all other routes known for meaningful improvement in properties. Further, the way forward for such particulate composites has been drawn to realise the material scientists’ dream of seeing such MMCs as engineering components. For this, the areas which now need research include mass production of composites, focus on its machining, joining, processing as also reduction in the size of dispersoids are some of the areas that have been identified and discussed in the paper.

Modeling effects of constituents and dispersoids on tensile ductility of aluminum alloy

The modeling effects of constituents and dispersoids on the tensile ductility of aluminum alloy were studied. The results show that the tensile ductility decreases with the increase of the volume fraction and size of constituents. Thus, purification can improve the tensile ductility by decreasing the volume fraction of constituents (normally compositions of Fe and Si) and the first-class microcracks. The model also indicates that the tensile ductility decreases with the increase in the volume fraction of dispersoids. Decreasing the volume fraction of dispersoids along the grain boundaries by proper heat-treatment and improving the cohesion strength between dispersoids and matrix can also improve the tensile ductility by decreasing the volume fraction of the second-class microcracks.