Martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys

The martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys was studied using microhardness measurements, classical differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and in-situ high-temperature X-ray diffractometry (XRD). The results for the Cu-10%Al alloy indicated a process dominated by the martensite ordering assisted by migration of quenched-in vacancies and followed by the consumption of the α phase. For the Cu-10%Al-10%Ag alloy the dominant process is the consumption of the α phase associated with a decrease in the ordering degree of the martensitic phase.     

Effect of quenching temperature on the formation and magnetic properties of the ferromagnetic τ-phase in Mn---Al---C alloys

The phase transformation and the formation of the ferromagnetic τ-phase of carbon-doped Mn---Al alloys were studied by means of differential thermal analysis, observation of the microstructure and magnetic measurements. For 70.8wt.%Mn-29.2wt.%Al alloys, the ε-phase exists from 880 °C in carbon-free samples to 790 °C in samples containing 0.6 wt.% carbon. It is found that the martensitic transformation of the carbon-doped Mn---Al alloy shows both isothermal and athermal transformation behavior. The grain size of the carbon-doped Mn---Al magnet decreases as the quenching temperature is decreased, but the coercivity iHc increases.     

Formation of intermetallic phases on 55 wt.%Al–Zn–Si hot dip strip

A study has been conducted to probe the formation of intermetallic phases on steel substrates immersed in 55 wt.%Al–Zn–Si hot dip baths as a function of dipping time and bath silicon content. Two bath compositions containing 1.3 and 1.5 wt.% Si, respectively, combined with two immersion times of 3 and 9 s were studied. It was found that the reaction rate and intermetallic phase formation varied in response to silicon content. Optical microscopy revealed a quantifiable difference in the development of the reaction layer between the two bath compositions. SEM-EDS revealed that the reaction layer that evolved on samples dipped in the 1.5 wt.% silicon bath were comprised of two intermetallic species, -AlFeSi/Fe₂Al₅, whilst in the 1.3 wt.% bath there were three clearly identifiable intermetallic species -AlFeSi/FeAl₃/Fe₂Al_5. A fourth phase appeared to be present in samples immersed in the 1.3 wt.% Si bath that, due to its fine structure, could not be conclusively identified. Experimental results from the literature and from this study have been assessed with reference to the phase stability predicted by MTDATA, a thermodynamic modelling package.     

Effects of Minor Element Additions to the Nanocrystalline FeAl Intermetallic Alloy Obtained by Mechanical Alloying

Chemical, microstructural, and mechanical properties of nanocrystalline FeAl intermetallic alloys with Li, Ce, and Ni additions have been assessed. Mechanical alloying and sintering procedures were used to produce and consolidate the alloys. The sintering procedure was based on room temperature uniaxial pressing followed by annealing in air of the pressed specimens. The mechanically alloyed powders have a microstructure consisting of micrometer-size particles that contain FeAl intermetallic nanocrystals. The three minor additional elements form a solid solution with the B2 intermetallic structure of the FeAl alloy. Densification greater than 90% has been obtained. The hardness values are higher than those obtained from specimens produced with conventional casting procedures. High resolution transmission electron microscopy images showed clusters of less than 5 nm with well-defined structure corresponding to Fe₃Al.     

Characterization of mechanically alloyed ternary Fe–Ti–Al powders

The effects of Ti-substitution for Fe in the Fe₃Al system on the mechanical alloying process were investigated. For this purpose, blended elemental powders with the following nominal compositions (at.%): Fe₇₅Al₂₅, Fe₇₀Ti₅Al₂₅, Fe₆₅Ti₁₀Al₂₅, Fe₆₀Ti₁₅Al₂₅, were mechanically alloyed in a high energy attritor-type ball milling system for up to 100 h. The structural evolution in these powders was characterized by scanning electron microscopy, differential thermal analysis and X-ray diffraction techniques. It was found that elemental powders were progressively transformed into nanocrystalline solid solutions during mechanical alloying. The addition of Ti in the powders shortened the milling time for solid solution formation. With increasing Ti content, the grain size of the solid solutions decreased, but the lattice parameter increased. Upon heating, the milled powders were transformed into ordered (Fe,Ti)₃Al intermetallic compounds in an extended range of temperature (from 350 to 500°C). Ti addition enhanced the occurrence of DO₃ ordering in heated powders.     

Preliminary investigations about effects of Zr, Sc and Ce additions on as-cast microstructure and mechanical properties of Mg-3Sn-1Mn (wt.%) magnesium alloy

In this paper, the effects of Zr, Sc and Ce additions on the as-cast microstructure and mechanical properties of Mg-3Sn-1Mn (wt.%) magnesium alloy were preliminarily investigated and compared. The results indicate that adding 0.36 wt.% Sc and 0.87 wt.% Ce to the Mg-3Sn-1Mn alloy, respectively leads to the formation of the extra phases of Mg-Sn-Sc and Mg₁₂Ce while adding 0.43 wt.% Zr does not cause the formation of any new phases. At the same time, adding 0.43 wt.% Zr or 0.87 wt.% Ce can refine the grains while adding 0.36 wt.% Sc coarsens the grains. Among the Zr- and Ce-containing alloys, the grains of the latter are relatively finer than those of the former. In addition, adding 0.43 wt.% Zr, 0.36 wt.% Sc and 0.87 wt.% Ce to the Mg-3Sn-1Mn alloy can improve the tensile and/or creep properties of the alloy. However, the addition of 0.43 wt.% Zr is not beneficial to the creep properties. Among the Zr-, Sc- and Ce-containing alloys, the alloy with the addition of 0.87 wt.% Ce exhibits the optimal tensile and creep properties.     

A Comparative Study on Crystal Structure and Magnetic Properties of Fe-Mn-Si and Fe-Mn-Si-Cr Alloys

In this study, the crystal structure and magnetic properties of Fe-30Mn-6Si (wt.%) and Fe-30Mn-6Si-5Cr (wt.%) alloys were compared by using X-Ray Diffraction (XRD) and Physical Properties Measurement System (PPMS) measurements. Detailed analysis of diffractograms at room temperature demonstrates that the Cr-free sample contains austenite and martensite phases, but for Cr-added sample the martensite phase disappears. According to micro hardness measurements, the presence of chromium decreased the hardness of the alloy. The magnetic saturation values at room temperature were measured as 11.32 emu/g for Fe-30Mn-6Si (wt.%) alloy and 18.34 emu/g for Fe-30Mn-6Si-5Cr (wt.%) alloy. The addition of Cr increased the magnetic saturation value of FeMnSi alloy while for both systems the hysteresis loop was quite narrow. As a result, both alloys exhibited soft magnetic characteristic.     

Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Hydriding properties of the nanocomposite 85 wt.% Mg–15 wt.% Mg2Ni0.8Co0.2 obtained by ball milling

The hydrogen sorption properties of the nanocomposite 85 wt.% Mg–15 wt.% Mg₂Ni_0.8Co_0.2 obtained by mechanical alloying in inert atmosphere were investigated. Absorption measurements were performed under a hydrogen pressure P = 1 MPa at temperartures ranging from 373 to 573 K, while desorption studies proceeded at P = 0.15 MPa and temperatures of 573 and 553 K. The addition of the intermetallic compound Mg₂Ni_0.8Co0_0.2 was shown to improve the hydriding kinetics of magnesium. The composite exhibited a high hydrogen capacity which did not decrease even after a large number of absorption–desorption cycles. Comparison of the hydriding kinetics of the intermetallic compounds Mg₂Ni and Mg₂Ni_0.8Co_0.2 indicated facilitation of the process by the presence of cobalt in the alloy. Magnetic measurement data on Mg₂Ni_0.8Co_0.2 showed formation of superparamagnetic precipitations of nickel and cobalt playing the role of active centres for dissociative chemisorption of hydrogen. The behaviour of the composite was explained by the catalytic effect of the intermetallic Mg₂Ni_0.8Co0_0.2, the existence of Ni and Co clusters on the surface and the process of mechanical alloying.     

Effect of annealing temperature on the microstructure and mechanical properties of an as-rolled Mg-9wt.%Li-3wt.%Al-1wt.%Zn alloy sheet

This study investigated the effect of annealing temperature on the mechanical properties of an as-rolled Mg-9.26wt.%Li-3,03wt,%Al-1,10wt.%Zn （LAZ931） alloy sheet. The dual-phase （a ＋ 13） LAZ931 alloy plate of 3 mm in thickness were roiled （67% reduction） and then annealed at temperatures at 100℃-350℃. The alloy＇s ductility showed a sharp concave downward tendency as a function of annealing temperature, The elongation of the LAZ931 alloy sheet increased with annealing temperature up to 150℃, followed by a sharp decrease of the alloy＇s ductility as the annealing temperature higher than 150℃. The specimen exhibited an extremely low elongation （only -0,5%） at annealing temperature around 300℃. Formation of brittle AILi particles on boundary resulted in Li depletion zone near by grain boundary, transforming the Li depletion zone into a （hcp） layer. The combined effects including brittle AILi particles on boundary and the hcp α layer on boundary resulted in the brittlement of the high-temperature-annealing sample.     

Microstructure and strength of brazed joints of Ti3Al-base alloy with different filler metals

The interfacial microstructure and properties of brazed joints of a Ti₃Al-based alloy were investigated in this paper to meet the requirements of the use of Ti₃Al-based alloy in the aeronautic and space industries. The effects of different brazing fillers on the interfacial microstructure and shear strength were studied. The relationship between brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. The brazed joints were qualitatively and quantitatively analyzed by means of EPMA, SEM and XRD. The results showed that using a AgCuZn brazing filler, TiCu, Ti(Cu,Al)₂ and Ag[s,s] were formed, the shear strength of the joint was decreased because of the formation of TiCu and Ti(Cu,Al)₂; using a CuP brazing filler, Cu₃P, TiCu and Cu[s,s] were formed at the interface of the joint, the former two intermetallic compounds decreased the shear strength. The analysis also indicated that using the TiZrNiCu brazing filler, the optimum parameters were temperature T=1323 K, joining time t=5 min, and the maximum shear strength was 259.6 MPa. For the AgCuZn brazing filler, the optimum parameters were joining temperature T=1073 K, joining time t=5 min, and the maximum shear strength was 165.4 MPa. To the CuP brazing filler, the optimum parameters were joining temperature T=1223 K, joining time t=5 min, and the maximum shear strength is 98.6 MPa. Consulting the results of P. He, J.C. Feng and H. Zhou [Microstructure and strength of brazed joints of Ti₃Al-base alloy with NiCrSiB, Mater. Charact., 52(8) (2004) 309–318], relative to the other brazing fillers, TiZrNiCu is the optimum brazing filler for brazing Ti₃Al-based alloy.     

Fabrication of ultrafine grained FeCrAl-0.6 wt.% ZrC alloys with enhanced mechanical properties by spark plasma sintering

Low mechanical strength, especially at high temperatures, is the key problem that limit the application of FeCrAl alloys as the accident tolerance fuel (ATF) cladding materials. Dispersion strengthening by carbide nanoparticles is an effective way to improve mechanical properties at high temperatures. In this work, an ultrafine grained FeCrAl-0.6 wt.% ZrC alloys with excellent mechanical properties were fabricated successfully by mechanical milling and spark plasma sintering. The effect of milling speed on powder characteristics, microstructure and mechanical properties of FeCrAl alloys were investigated. The particle size of the powders increase significantly after milling at 400 rpm, while it has a lower oxygen content. Increasing the milling speed decreased the resultant grain size and improved relative density. Transmission electron microscope (TEM) demonstrated the nano ZrC particles uniformly distributed in the matrix at higher milling speed, which effectively promotes grain refinement and dispersion strengthening. The results of mechanical properties show that the tensile strength, percentage elongation and hardness of FeCrAl-0.6 wt.% ZrC alloys at room temperature (RT) reached up to 1.05 GPa, 349.86 HV and 12.1%, respectively, after milling at 400 rpm. It is worth noting that the FeCrAl-0.6 wt.% ZrC alloy also exhibited a good high-temperature strength more than 110 MPa at 800 ℃, which is about 55.4% and 24.7% higher than previously reported FeCrAl-0.5 wt.% ZrC and FeCrAl-1.0 wt.% ZrC alloys, but the plasticity is reduced. The results demonstrated that the excellent mechanical properties were not only attributed to the dispersion strengthen by nanosized ZrC, a good interface bonding between Fe matrix and nanosized ZrC, but also the ultra-fine grained structure induced by the milling process.     

Effects of Mo and Zr on Microstructure, Mechanical Properties and Wear Resistance of Fe-Al Based Alloys

In this work the microstructure, mechanical properties and wear resistance of Fe-Al based alloys with various alloying elements were studied. The microstructures were examined by optical and scanning electron microscopy （SEM） equipped with an energy dispersive X-ray spectroscope （EDS）. Two types of alloys were prepared by vacuum arc melting. One is Fe-28Al based alloys （D03 structured） with and without alloying elements such as Mo and Zr. The other one is Fe-35Al based alloys （B2 structured） produced with the same manner. For both types of alloys, Mo addition had found to exhibit an equiaxed microstructure, while dendritic structure was observed to show the effect of Zr addition. These microstructural features were more evinced with increasing content of alloying element. Concerning the mechanical properties and wear resistance, Fe-35Al based alloys were superior to Fe-28Al based alloys over the whole temperature range investigated.     

Effects of zirconium addition on as-cast microstructure and mechanical properties of Mg–3Sn–2Ca magnesium alloy

At present, the mechanical properties of the Mg–3Sn–2Ca magnesium alloy are not satisfying and further enhance needs to be considered via further alloying/microalloying additions. The effects of Zr addition on the as-cast microstructure and mechanical properties of the alloy were investigated by using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that adding 0.41, 0.76 or 1.18 wt.% Zr can refine the grains of the alloy, and the primary CaMgSn phases in the Zr-containing alloys are changed from coarse needle-like net to relatively fine short block and/or particle-like shapes. As a result, the tensile and/or creep properties of the Zr-containing alloys are improved. Among the Zr-containing alloys, the alloy with the addition of 0.76 wt.% Zr exhibits the relatively optimum mechanical properties.     

Influence of disorder on electronic structure and magnetic properties in Fe-rich Fe–Si alloys

We present the results of ab initio calculations of the spin-polarized electronic structure of disordered bcc and fcc Fe_1 − xSi_x alloys from dilute solid solutions of Si on iron up to FeSi intermetallic compound composition (x=0.01..0.5) and ordered intermetallic phases FeSi in B20 structure and Fe₃Si in DO₃ structure. The self-consistent calculations were performed with the coherent potential approximation within the Korringa–Kohn–Rostoker method (KKR–CPA) for disordered case and by using the tight-binding linear muffin–tin orbital (TB LMTO) method for intermetallic compounds. In the last case the supercell approach has been utilized in order to take into account the structural defects for this ordered phase. In particular, we have performed a series of calculations in the BCC Fe_1 − xSi_x alloys with x=0.01, 0.015, 0.1, 0.15, 0.25.     

Nickel-free austenitic steels for cryogenic applications: The Fe-23% Mn-5% Al-0.2% C alloys

A study has been made of the influence of carbon and aluminium additions on the mechanical properties under uniaxial tensile loading and by Charpy V notch impact tests at room temperature and ?196°C on the Fe-24 % Mn alloys. It is concluded that the Fe-24 % Mn-5 % Al-0.2 % C appears as a new nickel-free iron-based alloy which is particularly interesting for cryogenic applications. In these alloys, both additions of carbon and aluminium contribute to the stability of the austenitic phase by suppressing the γ → ? martensitic transformation of the binary Fe-24 % Mn and to the solution hardening of the manganese-rich austenitic alloy.     

Processing and Characterization of Fiber Reinforced Intermetallic Matrix Composites

A series of intermetallic matrix composites reinforced with Al₂O₃ based fibers were fabricated by pressure casting. The Al₂O₃ based fibers used were DuPont's 20 μm diameter Fiber FP and PRD-166 fiber, Mitsui's 10 μm diameter Almax fiber, and Saphikon's 125 μm diameter single crystal Al₂O₃ fiber. The intermetallic matrices employed were alloys based on Ni₃Al, NiAl, Fe₃Al, Ti₃Al+TiAl, and Nb₂Al+NbAl₃. Optical, scanning and transmission electron microscopy were used to investigate the microstructure of the composites and the fibers. Tensile testing was conducted to determine the Weibull mean strength of the fibers in the as-received and heat treated conditions. The effect of fiber gage length on the Weibull mean strength of the PRD-166 and Fiber FP was evaluated. Indentation tests were performed to determine the effect of alloying additions on the fiber/matrix bond strength in shear in Saphikon fiber reinforced Ni₃Al composites.     

The role of microstructure in the mechanical behaviour of Ti-1.6 wt.%Fe alloys containing O and N

The effects of small changes to the heat treatment temperature within the (α + β) phase field on the room temperature properties of a Ti-1.6 wt.%Fe-0.56 wt.%O-0.04 wt.%N alloy are described. To identify contributions from the individual alloying elements the binary Ti-1.6 wt.%Fe and ternary Ti-1.6 wt.%Fe-0.6 wt.%O and Ti-1.6 wt.%Fe-0.04 wt.%N alloys were also investigated. It was found that the interstitial elements affected the degree of disorder in the ω_ath phase, and that the magnitude of this disordering was not merely consistent with changes in Fe concentration. The strength and ductility of the alloys free of additional nitrogen were independent of annealing temperature, whereas the alloys containing nitrogen showed a marked dependency on the temperature. Alloys containing nitrogen displayed a prismatic rather than basal texture after processing.     

Cast magnesium alloys for elevated temperature applications

The alloy development, microstructure, properties and uses of cast magnesium alloys for elevated temperature applications are reviewed. The alloying principles and strengthening mechanisms of magnesium are discussed to identify the potential alloy systems for elevated temperature applications in automotive and aerospace industries. It is concluded that the Mg-Zr family of sand cast alloys exhibit adequate mechanical properties at both ambient and elevated temperatures for aerospace applications, and Ca-modified sand cast AS41 alloy might provide a cost-effective alternative for the Zr-containing alloys. For diecasting applications, no current alloy systems meets the requirements of good high temperature properties, acceptable castability and low cost for critical automotive components, future development is especially needed in this area. Development of dispersion strengthened magnesium alloys and improvement of current Mg-Al-RE and Mg-Al-Si systems are the potential routes to expand diecast magnesium alloys to elevated temperature applications.     

Effect of thermomechanical treatment on the properties of Fe-11Al and Fe-14Al alloys

Fe-Al alloys have the potential to be relatively inexpensive soft magnetic materials if their formability could be improved. An investigation has been made on the effect of thermomechanical treatment on the properties of Fe-11 wt%Al and Fe-14 wt%Al alloys (designated Fe-11Al and Fe-14Al respectively). For the former the room temperature mechanical properties were found to be determined principally by the recrystallised grain size. A good combination of properties for Fe-11Al, i.e. high strength and ductility, was obtained when the grain size was less than about 100 m. The small grain size was produced by warm rolling at 600°C followed by 1 hour annealing at 600–700°C. On the other hand hot rolling followed by annealing resulted in large grain size, hence rendered the alloy brittle. The cold formability also exhibited a grain size dependence, with the Fe-11Al alloy with a fine recrystallised grain size having good cold rollability. In contrast Fe-14Al was brittle irrespective of the treatment given; ductility of less than 1% was observed in all cases and the cold rollability was limited. Ordering was not seen to be a factor affecting the observed mechanical properties and rollability of either alloy as all the thermomechanical treatments, other than an ordering treatment of 500 hours at 400°C, resulted in a disordered structure. The stress required to work these alloys at elevated temperatures were estimated from compression tests and it is apparent that for Fe-11Al the stress is greatly reduced (50%) from the room temperature value at 600°C and that at 750°C both alloys required a similar stress which was about 15% of the room temperature value. The magnetic properties of Fe-11Al compared favourably with Fe-14Al; the former has a higher saturation induction, a similar coercive force but a lower permeability than Fe-14Al.