Microstructure Of As-extruded Research Articles

Microstructure evolution and mechanical properties of a novel ultrastrong and ductile PM Ti6Al4V composite

Novel in-situ polycarbosilane (PCS)-derived TiC particles reinforced Ti6Al4V composites with ultrahigh strength and good ductility were fabricated by powder extrusion. The grain microstructure, dynamic recrystallization (DRX), texture orientation, mechanical properties and strengthening mechanisms were systematically investigated. The pyrolysis of PCS and in-situ reaction with Ti6Al4V matrix promote the formation of TiC particles and Si atoms solid-solution. TiC particles provide many heterogeneous nucleation sites for DRX and restrict grain growth by pinning effect, forming many fine equiaxed α grains. The average grain size of α-Ti is refined from 50.17 μm in as-sintered Ti6Al4V alloy to 3.17 μm in as-extruded Ti6Al4V-3PCS composite. The basal texture with {0001}<11 2‾ 0> orientation is dominant in the as-extruded microstructures, originating from the deformed α grains during β single-phase extrusion. The incorporation of PCS activates the occurrence of DRX and weakens the {0001}<11 2‾ 0> basal texture. Benefiting from the in situ formed TiC particles, solid solution Si atoms and low interstitial oxygen (O) contamination, the as-extruded Ti6Al4V-3PCS composite achieves the best combination of room-temperature strength and ductility, with 1307 ± 18 MPa in ultimate tensile strength (UTS), 1178 ± 25 MPa in yield strength (YS) and 10.0 ± 0.8% in elongation (EL), much higher than those of wrought Ti6Al4V alloy (ASTM B381). This work offers a feasible route for fabricating novel ultrastrong and ductile Ti6Al4V composites.

Achieving high strength-ductility synergy in Mg-6Sn-3Zn-0.3Zr (wt.%) alloy via a combination of casting, pre-treatment and hot extrusion

Achieving the strength-ductility synergy in Mg alloys is a gigantic challenge, especially in rare-earth-free Mg alloys. In this study, a new Mg-Sn-Zn-Zr alloy with high ultimate tensile strength (∼284–326 MPa) without sacrificing elongation-to-failure (∼22.1–27.6%) was developed by utilizing casting, pre-treatment and hot extrusion. Strong random rather than basal texture is observed both in as-cast and pre-treatment samples. Subsequently, the strong texture is effectively weakened via hot extrusion whilst remaining random. More importantly, after hot extrusion, the grain sizes of as-cast and pre-treatment samples were significantly refined down to about 10 µm. Examination of as-extruded microstructures of the alloy reveals that the grain refinement is highly associated with the particle stimulated nucleation (PSN) and continuous/discontinuous dynamic recrystallization (C/DDRX) mechanisms. Moreover, the results suggest that the combination of pre-treatment and hot extrusion not only promotes multiplication of geometrically-necessary dislocations (GNDs) but enhances dynamic precipitation, which boosts the formation of fine and homogenous precipitates. Based on the results of X-ray diffraction (XRD), transmission electron microscope (TEM) and selected area electron diffraction (SAED), the precipitates are Mg2Sn phases. Furthermore, the main orientation relationship identified by high resolution TEM (HRTEM) between Mg2Sn phases and α-Mg matrix could be described as (111)Mg2Sn or (220)Mg2Sn ∥ (0001)Mg with a coherent interface. The refined grains size, ultra-fine precipitates and high density of GNDs would substantially contribute to the enhancement of the strength and the corresponding contributions are calculated to be ∼183–185 MPa, ∼30.9–38 MPa and ∼14.2–31.7 MPa, respectively. Besides, texture weakening or randomizing, grain refinement and coherent interfaces are mainly responsible for the high ductility. The current study can provide beneficial insights into the development of high-performance rare-earth-free Mg alloys with favorable microstructure via a combination of casting, pre-treatment and hot extrusion processing.

The temperature effect on the plastic deformation of the Mg88Zn7Y5 alloy with LPSO phase studied by in-situ synchrotron radiation diffraction

The temperature dependence of the compressive deformation behavior of the Mg88Zn7Y5 alloy with a high volume fraction (~85%) of the long-period stacking-ordered (LPSO) phase was studied by in-situ synchrotron radiation diffraction. The as-extruded microstructure exhibits a fully recrystallized α-Mg phase with a nearly random texture. The LPSO phase, identified as the 18R polytype, is represented by wavy lamellae elongated along the extrusion direction and has an intensive basal texture. The alloy compressed along the extrusion direction at room temperature shows a superior yield strength of 480 MPa. With increasing deformation temperature, the yield strength is reduced by 15% at 200 °C and by 46% at 300 °C, respectively. At all tested temperatures, the basal slip is activated in the α-Mg matrix far below the yield strength. The macroscopic yielding of the alloy is controlled by the activation of deformation kinking in the LPSO phase. The synchrotron radiation diffraction data indicate the stress localization at kinks with respect to the grains having the same orientation.

Effects of Ga content on the microstructure and mechanical properties of as-extruded Mg-xGa alloys

Microstructures and mechanical properties of the as-extruded Mg-xGa (x = 1, 3, 5, 7 wt%) alloys were investigated in the present work. Examination of as-extruded microstructures revealed that the grains were gradually refined from an average size of 45 µm (Mg-1Ga) to 15.7 µm (Mg-7Ga). Meanwhile, the volume fractions of Mg5Ga2 precipitates and dynamic recrystallization grains were significantly increased with increasing Ga content, and the texture was continuously weakened. The grain refinement and texture weakening were mainly ascribed to the increasing dynamic recrystallization stimulated by increasing Mg5Ga2 precipitates. The tensile test showed the as-extruded Mg-xGa alloys possessed both high strength and ductility that can meet the mechanical properties required by orthopedic implants. The tensile properties of as-extruded Mg-xGa alloys were gradually increased with increasing Ga content, reaching the highest yield strength of 166 MPa, ultimate tensile strength of 268 MPa, and elongation of 22.2% (Mg-7Ga). The enhanced tensile properties were benefited from a combination of grain refinement strengthening, solid solution strengthening and precipitation strengthening.

Microstructure and Mechanical Properties of Pure Magnesium Subjected to Hot Extrusion

The as-cast pure magnesium (Mg), with a purity of 99.99%, was hot-extruded at 300 °C to prepare a Mg bar with a diameter of 8 mm. The microstructure and mechanical properties of the sample before and after extrusion were investigated. The results show that the as-extruded microstructure is obviously refined with a large number of subgrains rather than equiaxed grains. A great number of (102) tensile twins can be observed significantly in the microstructure at the temperature. Mechanical properties including yield strength (YS) and ultimate tensile strength (UTS) increase greatly but uniform elongation (UE) decreases slightly as a result of work hardening.

Investigation into the Extrudability of a New Mg-Al-Zn-RE Alloy with Large Amounts of Alloying Elements

The present study was aimed at determining the extrudability of a newly developed Mg-Al-Zn-RE magnesium alloy with large amounts of alloying elements. The experimental and numerical investigation clearly showed that the extrudate temperature was a crucial factor in deciding if a critical temperature between 754 K and 768 K (481 °C and 495 °C) was reached during extrusion, above which hot shortness occurred. Under the extrusion conditions applied, dynamic recrystallization (DRX) occurred, leading to grain refinement from a mean grain size of 165 μm in the as-solid-solution-treated billet to 8.0 to 10.9 μm in the extruded rods. Second-phase particles, such as Mg17Al12 and Al11La3, were found to distribute on grain boundaries and aid in grain refinement. The mechanical properties of the extrudate were greatly influenced by the as-extruded microstructure and extrusion condition. As the initial billet temperature decreased, the ultimate tensile strength (UTS) and elongation of the alloy increased, while yield strength (YS) remained almost unchanged. At an initial billet temperature of 523 K (250 °C), a stem speed of 3.93 mm/s, and a reduction ratio of 29.8, the extruded magnesium alloy had a mean grain size of 8 μm. Its YS, UTS, and elongation reached 217 ± 3 MPa, 397 ± 7 MPa, and 20 ± 1.3 pct, respectively.

Microstructural evaluation of a Fe-12Cr nanostructured ferritic alloy designed for impurity sequestration

Fast reactor fuel cladding candidate materials require proficiency in extreme environments consisting of high temperatures and irradiation doses in excess of 150 displacements per atom (dpa). Nanostructured oxide dispersion strengthened (ODS) alloys have been developed extensively for this purpose due to their notable high temperature strength, creep resistance, and irradiation resistance. However, their properties can deteriorate if interstitial impurities such as C and N are not well controlled during the fabrication process. A new Fe-12Cr nanostructured ODS alloy OFRAC (Oak Ridge Fast Reactor Advanced Fuel Cladding) with solute additions of Mo, Ti, and Nb has been developed to provide the desired properties mentioned above while simultaneously sequestering impurities within the matrix. After extrusion at 850 °C, the as-extruded microstructure consists of an average 490 nm grain size and a high number density (6.8 × 1023 m-3) of 2.2 nm diameter (Y,Ti,O) nanoclusters distributed homogeneously in the matrix. Atom probe tomography investigations suggest non-stochiometric compositions for the smallest nanoclusters. In addition, a second population of nanometer scale (Nb,Ti) rich carbonitrides is also present in the microstructure that captures the potentially detrimental C and N impurity atoms present in the matrix. Atom probe tomography results indicate elemental segregation of Cr, Mo, and Nb to grain boundaries in the as-extruded material, consistent with previous investigations of solid solution strengthening by solute additions. The ability of OFRAC to sequester impurities introduced from the powder metallurgical approach to nanostructured ferritic alloy development, compounded with its beneficial mechanical properties, makes this alloy a competitive candidate for fast reactor applications.This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Microstructure and mechanical properties of PM Ti600 alloy after hot extrusion and subsequent annealing treatment

In this paper, Ti600 alloy was successfully prepared by elemental powder metallurgy method followed by subsequent hot extrusion (950 °C, extrusion ratio of 9:1) and vacuum annealing. The microstructure and mechanical properties were systematically investigated. The as-sintered alloy presented Widmanstatten microstructure and large amount of pores. After extrusion, the pores had been closed, and the as-extruded microstructure consisted of both DRX grains and elongated grains. In addition, the as-extruded Ti600 alloy exhibited (0002)αTi//ED fiber texture and two types of ultrafine precipitates Y2O3 and (TiZr)6Si3 were observed within the grains. In comparison with the as-sintered sample, the mechanical properties of the specimen after extrusion were significantly improved, and the maximum yield strength of 1450 MPa was achieved. After annealing below the β transition temperature, the microstructure mainly contained equiaxed grains. The corresponding yield strength and hardness gradually reduced but the failure strain increased, and the maximum compressive failure strain of 38% was obtained after annealing at 950 °C. After annealing at 1050 °C in the β single-phase region, the bi-model structure was obtained. As the annealing temperature increased to 1100 °C, the alloy completely changed to Widmanstatten structure. The corresponding yield strength and hardness increased but the failure strain reduced.

Development of low-alloyed and rare-earth-free magnesium alloys having ultra-high strength

Developing ultra-high strength in rare-earth-free Mg alloys using conventional extrusion process is a great challenge. What is even more difficult is to achieve such a goal at a lower processing cost. In this work, we report a novel low-alloyed Mg-2Sn-2Ca alloy (in wt. %) that exhibits tunable ultra-high tensile yield strength (360–440 MPa) depending on extrusion parameters. More importantly, there is little drop in mechanical properties of this alloy even when it is extruded at a speed several times higher than those used in the reported high strength Mg alloys. Examination of as-extruded microstructures of this Ca-containing Mg alloy reveals that the ultra-high strength is mainly associated with the presence of surprisingly submicron matrix grains (down to ∼0.32 μm). The results suggest that the Ca addition promotes accumulations of the pyramidal dislocations, which eventually transform into the low angular grain boundaries (LAGBs). The high number density of LAGBs separate the α-Mg matrix via either discontinuous dynamic recrystallization (DDRX) mechanism in the early stage or the continuous dynamic recrystallization (CDRX) mechanism in the later stage of extrusion, which effectively enhances the nucleation rates of the DRXed grains. More importantly, large amount of Ca segregation along LAGBs, accompanied with dynamically precipitated Mg2Ca nano-phases, are detected in the present non-severely deformed samples. It is the combination of solute segregations and numerous Mg2Ca nano-precipitates that contributes to the formation of the ultra-fine grains via pinning mechanism. The ultrafine grains size, Ca enrichment in most LAGBs, and residual Mg2Ca nano-precipitates would in turn contribute significantly to the enhancement of the yield strength of the as-extruded Mg-2Sn-2Ca (wt.%) alloy. The low content of alloying elements and the fast one-step extrusion process render the present alloys low-cost and thus have great potential in large-scale industry applications.

Microstructure evolution and mechanical properties of P/M Ti-22Al-25Nb alloy during hot extrusion

In this paper, Ti-22Al-25Nb alloy bars were successfully prepared by elemental powder metallurgy and subsequent hot extrusion (1200°C, extrusion ratio of 10.56:1). The microstructure characterization, texture and mechanical property have been systematically investigated. Results showed that DRX occurred prior near grain boundary and further refined the B2 grains during the hot extrusion process. Besides, the as-extruded microstructure consists of both DRX grains and elongated grains, in addition, the as-extruded Ti-22Al-25Nb alloy exhibited strong (110)B2//ED. Meanwhile, {001}<111> and {111}<13-1> fiber textures were also introduced due to dynamic recrystallization. The good combination of tensile strength (1122.7MPa) and elongation (7.9%) have been obtained in the as-extruded Ti-22Al-25Nb alloys at room temperature. Besides, the as-extruded alloy also exhibited super-high tensile strength at elevated temperatures (close to 916.5MPa at 650°C and 613.1MPa at 800°C). The enhanced properties can be attributed to the comprehensive effects including deformation textures, grain refinement and dissolution of bulks α2 phase.

Microstructures and Mechanical Properties of Direct-Extruded Novel Mg Alloys

Abstract Non-flammability and high production rate are prerequisite for extending application of Mg extrusion products. In this respect, the present study focuses on microstructure development and mechanical behavior of two novel Mg alloys as compared with a commercial Mg alloy. As a reference, Mg-8Al-0.4Zn (AZ80 bal. wt.%) is extrudable at low speed of 0.5-2.5 m/min. This is due to hot shortness during extrusion, which results from low melting point of secondary phases like Mg 17 Al 12 . Furthermore, Mg alloys are reactive in molten state and rapidly ignited as contacting with oxygen in air. Hence, a non-flammable Mg alloy was developed by a trace addition of 0.3%Ca and 0.2%Y, which form protective oxide layer on Mg grains (AZ80+0.3%Ca+0.2%Y denoted as SEN8). In other way, Mg-5Sn-4Al-1Zn (TAZ541) was developed for high-speed extrusion. Hereby Mg 2 Sn precipitate makes Mg matrix thermally stable due to its high melting point. Three Mg alloys were extruded in the form of 50 mm x 4 mm plate with extrusion ratio of 25:1 at 350 °C with 1.1 m/min. As-extruded microstructures exhibited fully recrystallized structure with equiaxed grains as well as partially elongated grains along the extrusion direction. There was no big difference in grain size with 17.7~19.6 µm. SEN8 showed the weakest texture owing to the effect of Ca and Y. This made yield strength of SEN8 lower and uniform strain higher than AZ80. Mg 2 Sn particles led to higher work hardening of TAZ541 than AZ80 and SEN8. Moreover, SEN8 and TAZ541 had higher hardening capacity due to lower yield strength and higher work hardening rate than AZ80. That is, their relatively weak textures resulted in superior hardening ability. This presented that texture has a more dominant effect on mechanical properties rather than grain size in extruded Mg alloys. Regarding the effects of Ca, Y and Sn, it enables development of next generation Mg alloys with high strength and non-flammability for high-speed extrusion.

High tensile ductility and strength in the Ti-42Al-6V-1Cr alloy

With the aim of developing a new TiAl alloy with excellent tensile properties, a novel Ti-42Al-6V-1Cr (at. %) alloy was manufactured through casting and hot extrusion in the (α + β) phase region. The microstructure and tensile properties of the as-extruded alloy were investigated. The as-extruded microstructure consisted of fine lamellar colonies and mixtures of γ and B2 grains around the lamellar colony boundaries. The lamellar colony size and spacing of the as-cast alloy were significantly refined by hot extrusion. At room temperature, the tensile strength of the as-extruded alloy was 1113 MPa and the tensile ductility was 2.4%, demonstrating a good combination of high strength and ductility. The as-extruded alloy maintained high tensile strength over 860 MPa up to 800 °C. It was considered that the high lamellar fraction, fine lamellar colony size and fine lamellar spacing in the as-extruded alloy may be responsible for the high strength and improved ductility. A large number of dislocations were observed in the B2 grains. The Burgers vectors of dislocations in B2 grains were determined using the g·b analysis and <110> type dislocations were observed in specimens that had been deformed at room temperature. The {111}<110> slip systems satisfy the von Mises criterion of five independent slip systems that are necessary for a polycrystal to undergo a general homogeneous strain. It is noteworthy that the dislocation emission in the B2 grain occurs at the intersection between the γ twins and the boundary of the γ and B2 grains. This allowed the stress concentration at grain boundaries to be released. The B2 phase is shown to be beneficial to the room-temperature ductility of the present alloy.

Microstructure and mechanical properties of extruded Mg–1Ca–1Zn–0.6Zr alloy

The microstructure and tensile property of extruded Mg–1Ca–1Zn–0.6Zr alloy have been examined by means of electron backscattered diffraction, scanning and transmission electron microscopy. A fine microstructure and a typical basal texture are obtained in the extruded alloy which exhibits a yield strength as high as 306MPa along with a moderate elongation ~11%. The refined as-extruded microstructure is a result of the combination of dynamic recrystallisation and the Zener pinning effect induced by the fine precipitates. Both discontinuous and continuous dynamic recrystallisation are found to be operative in this study. Under tensile stress, cracks nucleate and propagate in the large Mg2Ca(Zn) particles which are formed during the solidification of casting and retained after extrusion.

Micromechanisms of grain refinement during extrusion of Mg–0.3 at.% Al at low homologous temperature

Coarse grained Mg–0.3at.% Al (0.33 in wt.%) alloy was processed by direct extrusion with a reduction ratio of 25:1 at a temperature of ~433K. The extrusion remainder was removed from the die and analysed in three distinct zones: the cast billet, the conical zone of extrusion die, and the as-extruded rod. The zones were characterized by electron backscatter diffraction (EBSD) and light microscopy techniques to identify the processes responsible for grain refinement. Complex networks of {10–12} twins in practically all grains produced a noticeable microstructural fragmentation even before the material reached the conical zone of the die. Deformation twinning extended up to the entrance zone of the conical die where it was followed by a continuous dynamic recrystallization (CDRX) that gradually changed low angle boundaries to high angle boundaries. It is apparent that geometrically necessary dislocations play a crucial role in the formation of new grain boundaries. CDRX results in a bimodal structure with grain diameters ~3 and ~30μm. As a material flows through the conical zone, the ratio of large to small grains is progressively decreased by CDRX in favour of fine grains. The as-extruded microstructure (a rod 8mm in diameter), with an average grain diameter of ~2.1μm, shows a strong texture where the vast majority of grains (99.99%) have the c-axis oriented at least 30° from the extrusion direction.

Microstructural and mechanical characterisation of 7075 aluminium alloy consolidated from a premixed powder by cold compaction and hot extrusion

The present work concerns the processing of 7075 Al alloy by cold compaction and hot extrusion of a premixed powder. To this end, a premixed Al–Zn–Mg–Cu powder, Alumix 431D, was uniaxially cold pressed at 600MPa into cylindrical compacts 25mm in diameter and 15mm thick. Subsequently, selected green compacts were subjected to either a delubrication or presintering heat treatment. Extrusion of the powder compacts was performed at 425°C using an extrusion ratio of 25:1. No porosity was present in the microstructures of the extruded alloys. Heat treatment prior to extrusion had a great effect on the degree of alloy development in powder compacts and, as a direct consequence, remarkably affected the extrusion process and the as-extruded microstructures and mechanical properties of the processed materials. Hot extrusion caused banded structures for the alloys consolidated from the green and delubricated powder compacts. The alloy extruded from the presintered powder compact showed a fine, recrystallized microstructure which resulted in a superior combination of mechanical properties for the consolidated material.

Fabrication and compressive properties of porous TiAl-Mn intermetallics by powder metallurgical route

We investigated the effects of process parameters on the microstructure and compressive properties of reactive-sintered porous TiAl-based intermetallics. Different extrusion ratios were selected in order to change the as-extruded microstructure and thus obtain various types of porous structures (unidirectional and spherical pores) after reactive sintering. In addition, different environmental conditions, such as vacuum and air, were used during the reactive sintering stage. It was revealed that the compressive strength is influenced by the unidirectionalty of the pores. High unidirectionalty led to higher yield strength at room temparature and at 1073 K. The compressive properties of the porous TiAl intermetallics were also influenced by the environment where reactive sintering is carried out.

Thermal Flow Deformation Behavior and Mechanism of As-Cast and As-Extruded Burn Resistant Titanium Alloy

Hot compressive deformation tests of burn resistant titanium alloy (Ti-35V-15Cr-Si-C) with initially as-cast and as-extruded microstructure were performed at deformation temperature between 900°C to 1200°C for as-cast and 900°C to 1150°C for as-extruded alloy, and strain rates between 10-3s-1to 1s-1. The compressive true stress vs. true strain curves were measured, the deformation activation energy was calculated and the microstructures after deformation were studied. The results show that dynamic reversion is the primary soften mechanism of the burn resistant titanium alloy during hot deformation. At the higher strain rate ( =1s-1), the ‘Necklace’ Dynamic Recrystallization will occur for as-cast alloy, and a Continuous Recrystallization will occur for as-extruded alloy. At the lower strain rates, both as-cast and as-extruded burn resistant titanium alloy display the continuous recrystallization. The extruded alloy presents larger dynamic recrystallization regions than that of the as-cast alloy.

Influence of Degree of Deformation on Anisotropy in Mechanical Properties in Wrought Magnesium Alloy ZK60

A direct-chill (DC) cast magnesium alloys ZK60 has been forward-extruded at 300 °C in a single pass at two extrusion ratios (ER) 12 and 44, which correspond to a total degree of deformation (φ) of 2.5 and 3.8, respectively. The as-extruded microstructure in both cases consists of two colonies of grain sizes, i.e. about 15 µm and &lt;5 µm, and highly deformed original grains which have not recrystallized. The crystallographic texture at both extrusion ratios consists of a predominant component accompanied by a relatively weaker component in the extrusion direction. Although, the qualitative crystallographic texture at both extrusion ratios remains fairly similar, a higher extrusion ratio gives a relatively weaker basal texture. A relatively higher degree of DRX and much lesser volume fraction of coarse grains (&gt;25 µm) at higher extrusion ratios give significantly weaker strength differential effect (difference in tensile yield stress and compressive yield stress).

Effect of extrusion on microstructure and properties of a submicron crystalline Cu–5 wt.%Cr alloy

The submicron crystalline Cu–5 wt.%Cr alloy, prepared by mechanical alloying and hot press sintering, was extruded at various temperatures from 100 °C to 900 °C, and the effects of extrusion ratio and temperature on microstructure and properties have been investigated. The results show that, by extrusion, the Cu grains of alloy can be further refined, and the higher the extrusion ratio, the finer and more homogeneous the as-extruded microstructure. Though the Cr particles in the alloy can be hardly deformed or refined during extrusion, they can prevent the dynamically recrystallized Cu grains from overgrowth. The extrusion temperature has significant effect on the microstructure feature of the Cu matrix. Different extrusion temperatures lead to different deformation types and corresponding microstructure features. The optimal extrusion temperature of the alloy is 600 °C. By extrusion at 600 °C, the finest dynamically recrystallized grains of about 200 nm can be obtained, and the alloy presents both high strength and good ductility.

α- and β-Mn precipitates in the spinodal Fe30Ni20Mn25Al25 alloy

Precipitates in the spinodal alloy Fe30Ni20Mn25Al25, produced by drop-casting followed by hot extrusion, have been investigated using transmission electron microscopy. The as-extruded microstructure consisted of alternating, coherent body-centred cubic and B2 (ordered body-centred cubic) rods aligned along ⟨100⟩ directions with a wavelength of ∼60 nm. Upon annealing at 550°C, precipitates were formed having two distinct morphologies: relatively spherical precipitates with the α-Mn crystal structure and more elongated precipitates with the β-Mn crystal structure. Both precipitates existed simultaneously after annealing at this temperature for up to at least 99 h. The compositions of the precipitates and the orientation relationships between the precipitates and the spinodal matrix were determined.